yi Gttin badtht quien ale San oe alia arias taht 01 ist cant saath oe $5 Shae ue rt Sper 5 dirssissttrersserss The Pacific Northwest Coast Living with the Shore Series editors, Orrin H. Pilkey and William J. Neal The Beaches Are Moving: The Drowning of America’s Shoreline New edition Wallace Kaufman and Orrin H. Pilkey Living by the Rules of the Sea David M. Bush, Orrin H. Pilkey, and William J. Neal Living with the Coast of Alaska Owen Mason, William J. Neal, and Orrin H. Pilkey Living with the Alabama-Mississippi Shore Wayne F. Canis et al. Living with the California Coast Gary Griggs and Lauret Savoy et al. Living with the Chesapeake Bay and Virginia’s Ocean Shores Larry G. Ward et al. A Moveable Shore: The Fate of the Connecticut Coast Peter C. Patton and James M. Kent Living with the East Florida Shore Orrin H. Pilkey et al. Living with the West Florida Shore Larry J. Doyle et al. Living with the Georgia Shore Tonya D. Clayton et al. Living with the Lake Erie Shore Charles H. Carter et al. Living with Long Island’s South Shore Larry McCormick et al. Living with the Louisiana Shore Joseph T. Kelley et al. Living with the Coast of Maine Joseph T. Kelley et al. Living with the New Jersey Shore Karl F. Nordstrom et al. From Currituck to Calabash: Living with North Carolina’s Barrier Islands Second edition Orrin H. Pilkey et al. The Pacific Northwest Coast: Living with the Shores of Oregon and Washington Paul D. Komar Living with the Puerto Rico Shore David M. Bush et al. Living with the Shore of Puget Sound and the Georgia Strait Thomas A. Terich Living with the South Carolina Shore Gered Lennon et al. Living with the Texas Shore Robert A. Morton et al. The Pacific Northwest Coast Living with the Shores of Oregon and Washington Paul D. Komar The Living with the Shore series is funded by the Federal Emergency Management Agency Duke University Press Durham and London 1997 © 1998 Duke University Press All rights reserved Printed in the United States of America on acid-free paper ce Typeset in Minion. Library of Congress Cataloging-in- Publication Data appear on the last printed page of this book. In memory of William Wick, who as Director of the Sea Grant College Program at Oregon State University valued the coast and saw the need for research that would help in its preservation Digitized by the Internet Archive in 2021 with funding from Duke University Libraries https://archive.org/details/pacificnorthwest01koma Contents List of Figures ix Preface xiv | A Northwest Coast Perspective 1! 2 Geological Evolution of the Northwest Coast 7 Plate Tectonics and Continental Growth 7 Sea Level and Its Imprint on the Northwest Coast 14 The Evolution of the Northwest Coast since the Ice Ages 24 Formation of the Northwest Estuaries 30 Dune Fields of the Northwest Coast 32 Summary 36 3 The Dynamic Northwest Coast 37 Seasons and the Coastal Climate 37 Ocean Wave Generation 38 Beach Cycles on the Northwest Coast 44 Nearshore Currents and the Movement of Beach Sand 48 Tides along the Northwest Coast 52 Water Level Fluctuations 54 Wave Run-up and Sneaker Waves 56 Tsunami: The Extreme Coastal Hazard 57 Summary 61 4 The Arrival of Man—Erosion Becomes a Problem 63 5 The Development and Destruction of Bayocean Spit 73 The Development of Bayocean Park 73 Construction of the North Jetty 78 The Erosion of Bayocean Spit 80 Patterns of Erosion Due to Jetties 86 Summary 91 6 Natural Processes of Erosion 93 The Development and Erosion of Siletz Spit 93 Development and Erosion Problems 93 Processes of Erosion 98 Beach Mining 102 Past Erosion on Siletz Spit 104 Bay-Side Erosion 106 The Erosion and Breaching of Nestucca Spit 109 The Erosion of Cape Shoalwater, Washington 113 Summary 116 7 The 1982-1983 El Ninho—An Extraordinary Erosion Event 117 E] Nifo as an Atmospheric and Oceanic Phenomenon 117 Responses of Oregon Beaches to El Nino 123 Alsea Spit Erosion 123 The Erosion of Netarts Spit 128 El Nino and Previous Erosion 132 Summary 133 8 Sea Cliff Erosion and Landsliding along the Northwest Coast 135 Processes of Sea Cliff Erosion 135 Landslides and Property Losses 145 Alongshore Variations in Sea Cliff Erosion 147 Rates of Sea Cliff Recession 155 Structures that Prevent Cliff Erosion 156 Summary 159 9 The Jump-Off Joe Fiasco 161 History of Erosion at Jump-Off Joe 161 The Development of Jump-Off Joe 166 10 The Northwest Coast—A Heritage to Be Preserved 175 References 185 Index 193 Vill Figures 1.1 1A 1.3 Deal DP 23 2.4 D5, 2.6 D/ 2.8 2.9 2.10 2.11 DAD, Ail} 2.14 2.15 2.16 Dj 2.18 2.19 2.20 2.21 Geography of the Northwest coast 2 Scenery along the Northwest coast 3-5 The northern half of the Oregon coast 6 Formation and subduction of the ocean crust 8 The Juan de Fuca and Gorda plates 10 Cape Lookout, Oregon 13 The maximum advance of glaciers into Washington 15 The marine terrace at Otter Rock, Oregon 17 Coastal uplift around a pivot line 18 Elevation changes along the Oregon coast 19 Elevations of the youngest marine terrace near Cape Blanco, Oregon 20 Changing sea levels over the past 40,000 years 21 The rise in sea level over the past 8,000 years 22 Yearly changes in sea level determined from coastal tide gauges 23 Approximate shoreline positions during low stands of sea level 25 The principal suppliers of sand to the Northwest coast 26 The degree of rounding of the beach sands on opposite sides of Tillamook Head, Oregon 28 Chart based on 1868-77 surveys of the Northwest coast 29 The Alsea Bay estuary 30 Sediment patterns within Yaquina Bay 31 The Coos Bay dune sheet 32 The precipitation ridge at the landward edge of the Coos Bay dunes 33 Two views of the Clatsop Plains 34 The Coos Bay dune field after the introduction of European beach grass 35 Large waves breaking against the rocks of Cape Disappointment, Washington 38 Seasonal variations in temperature and rainfall measured at Tillamook, Oregon 39 3.3 3-4 355 3.6 3.7 3.9 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 3.20 4.1 4.2 4.3 4.4 4-5 4.6 5.1 5.2 5.3 5-4 55 5:6 5-7 5.8 The transfer of energy from wind to waves to shore 39 Morphology of simple ocean waves 40 The seismometer at the Mark Hatfield Marine Science Center in Newport, Oregon 41 , Daily variations in wave conditions on the Oregon coast 42 Monthly variations of wave breaker heights on Northwest beaches 43 Seasonal changes in the beach profile in response to seasonal variations in wave energy 44 Beach profiles from Gleneden Beach and Devil’s Punchbowl Beach, Oregon 45 Seasonal profiles of Gleneden Beach, Oregon 46 Beach profile surveying technique employing an amphibious vehicle 47 Beach profiles from Solando, Washington 48 The nearshore cell circulation 49 The beach at Nestucca Spit, Oregon 50 The threat posed by rip current embayments 50 The patterns of sand accumulation around jetties 51 Daily tidal elevations measured in Yaquina Bay 53 Monthly variations in mean sea levels at Newport, Oregon 55 Heights of tsunami waves measured within bays and estuaries along the Northwest coast on March 28,1964 58 Map of Yaquina Bay showing the path followed by the tsunami surge generated by a subduction earthquake about 300 years ago 60 Log cabin of early settlers on the Northwest coast 68 The initial settlement of Newport along the shores of Yaquina Bay 69 Turn-of-the-century summer tent city at Nye Beach 70 Summer visitors at Nye Beach 70 The Burton expedition, July 1912 71 Early erosion on the coast 72 Bayocean Spit and Tillamook Bay today 74 The Bayocean Hotel as planned, and the completed structure 75 The natatorium at Bayocean 76 A group of houses atop a hill on Bayocean Spit early this century 77 The inlet to Tillamook Bay before and after construction of the north jetty in1914-17__ 80 Sand accumulation and shoreline changes at Tillamook Bay between 1914and1971 82 The natatorium on Bayocean Spit was destroyed by erosion during the 1930s 83 The once elegant Bayocean Hotel succumbs to erosion 84 5-9 5.10 5.12 5.13 5.14 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 6.10 6.11 6n2) 6.13 6.14 6.15 6.16 6.17 6.18 6.19 6.20 Sequence of aerial photographs of Bayocean Spit taken by the U.S. Army Corps of Engineers 85 Shoreline changes at the mouth of the Siuslaw River caused by jetty construction early in this century 87 Patterns of erosion and sand deposition after construction of the north jetty at the Tillamook Bay inlet 89 Entrance to Tillamook Bay on May 22,1947 89 Bayocean Spit on September 5, 1974, after construction of the south jetty 90 The remains of Bayocean resort 91 Siletz Spitin1971 94 A general view of the homes on Siletz Spit in1971 94 House under construction on Siletz Spit lost during the 1972-73 erosion 96 Houses on Siletz Spit threatened by erosion during the winter of 1972-73 97 Erosion on unprotected adjacent lots left this house on a promontory of rip-rap extending into the surf 98 Rip-rap placed on Siletz Spit during March 1976 to protect homes from erosion 99 Rip current embayments on Siletz Spit during the winter of 1972-73 100 Budget of beach sands for the littoral cell containing Siletz Spit 103 Aerial photos of Siletz Spit taken during February 1976 showing rip current embayments 104 Drift logs filling eroded rip current embayments on Siletz Spit 105 Sawed drift logs exposed within the eroding foredunes on Siletz Spit 106 Water flow patterns within Siletz Bay 107 House located on the narrowest portion of Siletz Spit threatened by both ocean-side and bay-side erosion 107 Analysis of the decreasing width of Siletz Spit due to erosion on its bay side 108 The breach that developed on Nestucca Spit in a February 1978 storm that struck during exceptionally high tides 110 Waves and tide conditions during the February 1978 storm that breached Nestucca Spit 111 Rip-rap placed to protect homes on Nestucca Spit during the February 1978 erosion 112 The breach on Nestucca Spit in February 1978 113 Coast and Geodetic Survey charts of Willapa Bay from 1911 and1912 114 Changing shorelines along Cape Shoalwater 115 6.21 7.1 WEP? 73 7.4 75 7.6 7-7 7.8 7-9 7.10 Filit Fa) 7-13 7.14 8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8 8.9 8.10 8.11 8.12 Cross sections of the inlet to Willapa Bay 116 The equatorial Pacific currents and westward trade winds 118 The sea level “wave” during the 1982-83 El Nifo measured at a sequence of equatorial islands and on the coast of Peru 119. Monthly sea levels measured with the tide gauge in Yaquina Bay 120 Wave breaker heights derived at Newport, Oregon, during the 1982-83 El Nino 121 Beach erosion and sand accumulation along the central Oregon coast resulting from the northward transport of sand during the 1982-83 El Nimo 122 Sand level changes north and south of Yaquina Head 124 Aerial view of Alsea Spit in 1978 showing the normal configuration of the inlet 125 The deflection of the channel leading into Alsea Bay in response to storm waves generated during the 1982-83 El Nino 125 House on Alsea Spit in the area most eroded during the early stages of the 1982-83 El Nino 126 Erosion on Alsea Spit after the 1982-83 El Nino shifting progressively toward the inlet 127 Netarts Spit 128 Oblique aerial photo of Netarts Spit and the inlet to Netarts Bay 129 The log seawall fronting the park on Netarts Spit prior to the 1982-83 El Nino 130 Progressive erosion of Cape Lookout State Park on Netarts Spit following the 1982-83 El Nifo 131 Examples of sea cliff erosion along the Oregon coast 136 Summary of the many processes and factors involved in the erosion of sea cliffs 137 Rapid cliff retreat in Gleneden Beach 138 Cliff erosion in Taft, Oregon 139 Examples of sea cliffs 141 Talus at the base of the sea cliff at Gleneden Beach State Park before and after major erosion 142 A heavily vegetated sea cliff 143 Graffiti carved into the sea cliff at Lincoln City 144 A wave surge channel on Cape Perpetua following a northwest- oriented fracture 145 A sea cliff in the Jump-Off Joe area of Newport 146 The classic form of aslump 147 Tilted trees and inclined ground demonstrate the disruption produced by the Jump-Off Joe landslide 148 8.13 8.14 8.15 8.16 8.17 8.18 8.19 8.20 8.21 8.22 9.1 9.2 9.3 9.4 9.5 9.6 9.7 9.8 9.9 9.10 9.11 10.1 10.2 10.3 10.4 10.5 10.6 10.7 10.8 A street and sewers in Stratford Estates destroyed by a slow-moving landslide 149 Number of landslides versus monthly precipitation amounts 149 The massive landslide on Cascade Head, Oregon, that occurred in 1934 150 Landslides in Ecola State Park on Tillamook Head 150 Littoral cells on the northern half of the Oregon coast form beach embayments between major rocky headlands 151 Sea cliffs on the Oregon coast 152 Sand grain diameters on the beaches of the Lincoln City littoral cell 155 The Taft area of Lincoln City in the 1920s and recently 157 A low line of rip-rap protects accumulated talus from wave attack during storms 158 Response to erosion at Gleneden Beach 159 The picturesque Jump-Off Joe sea arch 162 Cliff retreat at Nye Beach, Newport, 1868-1976 163 Photographs of Jump-Off Joe taken by tourists in 1880, 1915, and1978 164 Photos taken February 3, 1943, showing some of the damage caused by the 1942-43 landslide at Jump-Off Joe 165 Aerial view of the 1942—43 landslide areain 1961 166 Grading on the 1942-43 Jump-Off Joe slump block in December 1980 167 Construction of condominiums on the terrace remnant at Jump-Off Joe 170 The almost-completed condominiums 171 Lawn signs erected in the Jump-Off Joe area to discourage buyers 171 The building’s foundation failed during renewed slumping in1985 172 The final demolition of the condominiums in October 1985 172 The beaches were once major routes for north-south travel along the Northwest coast 176 Visitors enjoying a Northwest coast beach 176 Log barricade placed on the beach in front of the Surfsand Motel in Cannon Beach 177 Construction of a road across the beach at Neskowin 178 Annual construction of shore-protection structures in the Siletz littoral cell and their cumulative length 180 Massive rip-rap revetment on the beach in the Siletz littoral cell 181 This creosote-covered seawall is an unnecessary eyesore 182 An unnecessary seawall on the coast south of Cannon Beach 183 Preface When most people think of the Northwest coast, high waves crashing against rocks or surging across wide, sandy beaches come to mind. Much of the attraction of the ocean shores of Oregon and Washington lies in the great variety of the scenery: high, rocky headlands descending precipitously into the sea, sandy beaches fronting sea cliffs, and large expanses of blowing dune sand, all backed by the tree-covered slopes of the Coast Range and the Olympic Mountains. For some, the main attraction of the ocean shores of the Northwest is their seclusion; one can be alone there and in harmony with the forces of nature. Oregon and Washington are among the fastest growing states in the na- tion, and their ocean shores are the sites of much of the associated develop- ment. More and more sea cliffs and migrating dune fields are occupied by houses, condominiums, motels, and restaurants. Such development im- poses a need for permanence on an otherwise dynamic coast. Each winter, storm waves combine with nearshore currents to cut back beaches and cliffs, often resulting in significant damage to coastal properties, both pri- vate and public. The response has been to erect shore protection structures, and more and more beaches are backed by massive seawalls and mounds of rock rip-rap. Too often these structures are built with little regard for the dynamic nature of the coast and the processes of ocean waves and currents that continue to reshape the shore. This book is intended to provide the general public with information about the Northwest coast—its geological setting and the nature of the waves, currents, tides, and other ocean processes that affect it. We will ex- amine the natural responses of beaches and sea cliffs to ocean processes, particularly at spots where these have led to the erosion of coastal proper- ties. Erosion problems are discussed in a general sense and then docu- mented with specific examples: the erosion of Siletz and Nestucca Spits on the Oregon coast during the extreme storms of 1972 and 1978; the unusual processes that existed during the 1982-83 El Nifio, which caused erosion along much of the Northwest coast; and the shoreline retreat that has oc- curred along Cape Shoalwater on the Washington coast, the most massive erosion on any U.S. coast. Over the years I have presented much of this ma- terial as luncheon and dinner talks to the general public. The level of the presentation here is much the same—geared toward the general public and illustrated mostly by my own photographs. It would be easy to become despondent in the face of the rapidly expand- ing development on the Northwest coast and the proliferation of shore pro- tection structures. Yet, measures that will lead to the preservation of the re- maining natural areas are still possible. These will require basic changes in our attitudes toward development and shoreline management policies that incorporate our present understanding of erosion processes; most of all, they will require the support of the public. It is my hope that this book will be of assistance in achieving those goals. While undertaking research along the Northwest coast during the past 25 years, it has been my pleasure to work with several colleagues at Oregon State University; foremost among them are Professors William G. McDougal, James Good, Robert A. Holman, and Reggie Beach. I wish to take this opportunity to acknowledge the help they have given me over the years. In addition I owe a considerable debt of gratitude to the many stu- dents who have worked with me—much of the material in this book comes from their thesis research projects. Much of chapter 5 is based on the Ph.D. dissertation of Dr. Thomas Terich (Terich 1973). A full account of the devel- opment of Jump-Off Joe, described in chapter 9, is presented in Sayre and Komar 1988. The at oA are avy wee An The Pacific Northwest Coast | A Northwest Coast Perspective Early explorers of the Northwest coast were impressed by the tremendous variety of its scenery. Today, visitors can still appreciate those qualities. The low, rolling mountains of the Coast Range serve as a backdrop along most of the ocean shores of Washington and Oregon. In the north the tall Olym- pic Mountains extend right to the shore, as do the Klamath Mountains in southern Oregon and northern California (fig. 1.1). The coast that fronts the mountains is characterized by high cliffs exposed to ocean waves that are slowly cutting away the land (fig. 1.2). The most resistant rocks persist as sea stacks scattered in the surf. Sand and gravel accumulate only in shel- tered areas, where they form small pocket beaches on the otherwise rocky landscape. The longest stretches of beach are found in the lower-lying parts of the coast away from the high mountains of the extreme north and south. The Long Beach Peninsula, which forms a major portion of the Washington coast, extends northward from near the mouth of the Columbia River as a tongue of land that separates the ocean shores from Willapa Bay. It is the largest sand spit in the Northwest. In Oregon, the longest continuous beach extends about 60 miles from Coos Bay northward to Heceta Head near Flo- rence. This beach is backed by the impressive Oregon Dunes, the largest complex of coastal dunes in the United States. Along the northern half of the Oregon coast there is an interplay be- tween sandy beaches and rocky shores (fig. 1.3). Massive headlands jut out into deep water, their black volcanic rocks resisting the onslaught of even the largest storm waves. Between these headlands are stretches of sandy shore. Portions of these beaches form the ocean shores of sand spits such as Siletz, Netarts, Nehalem, and Bayocean. Landward from most of the spits are estuaries of the rivers that drain the Coast Range. Within each estuary, the fresh water of the river mixes with seawater before passing into the open Y, 2 °7 Cope Flattery Cape Elizabeth Grays Horbor Willapa Bay Long Beach Tillamook Head Tillamook Bay OCEAN Heceta Head G Ww G NX Q Coos Bay #& Cape Blanco 126° 124° Figure !.!1 Geography of the Northwest coast, the seaward edge of Washington and Oregon. PUGET’ soUND RANGE Figure |.2a The variety of scenery found along the Northwest coast: top, the rocky shores of northern Washington (photo by T. Terich); bottom, the flat, sandy beach of the Long Beach Peninsula (photo by T. Terich). ocean through the narrow inlet at the tip of the spit. Other bodies of water, such as Netarts Bay and the extensive Willapa Bay in Washington, are in- land intrusions of the sea that receive little freshwater flow from rivers. The first Western explorers and settlers were attracted to the Northwest coast by the richness of its natural resources. Earliest to arrive were the traders, who obtained pelts of sea otter and beaver from the Indians. Later came prospectors, who first sought gold in the beach sands and coastal mountains but often were content to settle down and “mine” the fertile farmlands along the river margins. Others turned to fishing, supporting themselves by harvesting the abundant Dungeness crabs, salmon, and other fish in the coastal waters. Also important to the early economy of the A Northwest Coast Perspective 3 Figure |.2b Top, Netarts Sand Spit in northern Oregon; bottom, Cape Perpetua on the mid-Oregon coast. coast—and today’s economy, too—were the vast tracts of cedar and Sitka spruce. Today, however, the most important “commodity” for the North- west coast economy is the vacation visitor. Vacationers arrive in thousands during the summer months, but it is still possible to leave Highway 101 and find a secluded beach or a quiet forest trail. There is cause for concern that the very qualities that have made the Northwest coast so attractive to people are being destroyed by human ac- tivities. Like most coastal areas, the Northwest is experiencing the pressures of development. Homes and condominiums are being constructed imme- diately behind the beaches, within dunes and atop cliffs overlooking the ocean. Everyone wants a view of the waves, the passing whales, and the evening sunset, as well as easy access to a beach. These desires are not always compatible with nature, however, and more and more homes are threat- ened by and sometimes lost to beach erosion and cliff landsliding. Problems can usually be avoided if people will only recognize that the coastal zone is fundamentally different from inland areas and act accord- Figure 1.2c Top, the massive dunes of the central Oregon coast; bottom, the rocky coast typical of southern Oregon. A Northwest Coast Perspective 5 Tillamook Head Cape Falcon Cape Meares Cape Lookout Cape Kiwanda Cascade Head Figure 1.3 The northern half of the Oregon coast, with large, rocky headlands separated by stretches of Cape Foulweather sandy beach. ingly. This requires some knowledge of ocean waves and currents and how they shape beaches and attack coastal properties. It also requires an under- standing that some parts of the shore are unstable, subject to erosion and sudden landslides. Familiarity with the processes and types of problems ex- perienced in the past can be helpful in selecting a safe homesite. It can also enhance your enjoyment of the coast and lead to an appreciation of the WASHINGTON Columbia River Necanicum River Nehalem Fiver Trask River Tillamook River Nestucca River Salmon River Siletz River qualities of the Northwest coast that can be and must be preserved. 2 Geological Evolution of the Northwest Coast The Northwest coast has been shaped by the interplay between geologic, cli- matic, and oceanographic processes. Tectonic activity deep within the earth accounts for the wide variety of rocks found along the shores of Oregon and Washington—mudstones and sandstones that originated in the sea as well as hard, black rocks that formed in volcanoes. Their differing degrees of re- sistance to erosion are responsible for the coast’s morphology. Sand and gravel eroded from the rocks have been shaped by waves into beaches and blown inland to form large tracts of dunes. Also important to the develop- ment of the present-day coast was the rise and fall of the sea level during the ice ages. Those sea level cycles, superimposed on a progressive long-term rise of the land resulting from continued tectonic activity, account for many of the landscape details visible today on the Northwest coast. Plate Tectonics and Continental Growth The geological setting of the Northwest has had much to do with the devel- opment of the physical features of Oregon and Washington. Indeed, the very existence of the land mass forming those states can be credited to the extraordinary geological processes of plate tectonics. Beginning in the 1960s, scientists began to develop a fuller appreciation of the impermanence and mobility of the earth’s surface. The science of plate tectonics arose primarily from discoveries within the ocean basins. Oceanographers found large mountains in the depths that form essentially continuous ridges and rises around the earth—a gigantic, globe-encircling system that is some 60,000 miles long. Sampling dredges bring up fresh vol- canic rocks from the crests of these ridges, and there is virtually no sedi- ment cover, indicating that the ridge system is very young in geological terms. The ridge crest is cut along its length by a steep-walled, symmetrical Spreading Ridge Submarine Trench Volcanoes lithosphere magma aesthenosphere subduction melting Figure 2.1 The formation of ocean crust at a spreading ridge and its subduction where the oceanic plate collides with a continental mass. Stars denote earthquakes formed by the plates scraping together. The melting of the subducted plate gives rise to volcanoes. canyon thousands of feet deep. Abnormally large amounts of heat flow from the earth’s interior in this area, which is a zone of frequent earth- quakes. These features are all associated with the formation of new ocean crust at the ridges. The earthquakes occur when the crust fractures as it is pulled apart, and the heat is associated with molten lava rising from deep within the earth to form the new crust. Such evidence from the ocean basins led to the concept of seafloor spreading, the notion that new ocean crust is formed at the submarine ridges by fracturing along the crest, with molten rock rising to fill in the gap. Once the new crust solidifies, it splits roughly in half and then spreads away from the ridge, the two halves moving down opposite flanks into deeper water. Figure 2.1 illustrates the process. The conditions depicted on the figure are those of the seafloor west of South America, but they are simi- lar to those found off the Northwest coast. The new crust formed at the spreading ridge moves slowly away from the ridge (shown by the arrows in the figure) as it is displaced by still newer crust. The formation of new crust at ocean ridges might seem to imply that the earth is expanding and slowly increasing its surface area. This would be the case if it were not for the fact that older crust is simultaneously destroyed in a process called subduction (fig. 2.1). The downbuckling of the ocean crust forms a submarine trench at the continental margin, and the site where this slab of descending ocean crust scrapes against the overlying continental mass is another earthquake zone. The subducting crust eventually gets deep enough within the earth to be remelted, and this molten rock supplies the lava that emerges in the nu- merous volcanoes of the Andes Mountains of South America and the Cas- cades of the Northwest. This basic pattern occurs around the entire margin of the Pacific Ocean, which has come to be known as the “Ring of Fire” as a result. In some areas the spreading ocean crust is subducted beneath another segment of ocean crust. In that case, a trench forms and the volcanoes develop into an island chain with an arcuate shape (arcuate because it lies on a spherical earth); examples of such island arcs are the Aleutian Islands of Alaska and the Mariana Islands of the western Pacific. The concept of seafloor spreading, forming and then destroying ocean crust, has been firmly established by many lines of evidence. Its ultimate cause is believed to be the slow movement of rock within the interior of the earth, rock that is sufficiently hot to make it soft and plastic but not fully molten. The ocean crust and the continents are rafted along by the flow, which apparently is part of a system of convection currents heated at still greater depths within the earth. Being less dense but thicker than the ocean crust, the continents float higher and extend down deeper, much as an ice- berg floats on water. The picture of the earth that emerges is of a mobile surface with impermanent continents and oceans. Nothing seems to be fixed. The crustal plates move about, colliding to form mountains or being subducted into the earth’s interior. These processes of global tectonics account for the principal features of the Northwest (Drake 1982; Orr et al. 1992). Mount Rainier, Mount Saint Helens, Mount Hood, and the other large peaks of the Cascades are volca- noes formed from oceanic rocks that melted during subduction and de- scended into the interior of the earth. The submarine trench off the North- west coast is not nearly as well developed as the one off the coast of South America shown in figure 2.1, and it is so filled with ocean sediments that it is not apparent in the bathymetry of the seabed. The spreading ridges off the Northwest coast—the Juan de Fuca and Gorda Ridges (fig. 2.2)—are offset by the Blanco Fracture Zone, a giant fault in the seabed that has been the source of a number of earthquakes felt along our coast. The two segments of the ridge formed by the fracture zone often act as crustal plates—respectively, the Juan de Fuca plate and the Gorda plate. New ocean crust is being formed at the Juan de Fuca and Gorda Ridges, and its general movement is eastward toward the continent, which sits atop the North American plate. The spread of the Juan de Fuca Ridge and the consequent movement of ocean crust toward the continent is estimated to occur at a rate of 2.3 inches per year (T. Atwater 1970). How- ever, that is not the rate at which this ocean crust collides with North America, because the latter mass is also moving. The actual convergence be- tween the ocean crust and the land mass is only about 1 inch per year and is at an oblique angle rather than being head-on. Subduction of the ocean plate beneath South America has produced catastrophic earthquakes in Peru and Chile (fig. 2.1). Until recently, scien- Geological Evolution 9 A wo oe _ iB) 2 AS bas iS Juan de au —~ (= a 2 i C= Fuca Plate < Go =) ” oO vv CA sae oO aa ° ne oa — SS c= o o © a oO A Ee oO = A q Oo dy oO A ‘a 4 ‘es ro) Gorda mee a Plate = A brs < % % Figure 2.2 The Juan de Fuca and Gorda plates beneath the sea west of Oregon and Washington move toward the coast as new crust is formed at the ocean ridges. The subduction zone is offshore, seaward of the continental shelf. tists were puzzled by the absence of such subduction earthquakes in the Northwest. Now, however, there is strong evidence that such earthquakes have occurred, but at intervals of hundreds to thousands of years. None has taken place within the last two or three centuries, since Europeans came to the Northwest, although myths and archaeological evidence indicate that the native inhabitants witnessed past catastrophic events (Hall and Ra- dosevich 1995). The principal evidence for major prehistoric earthquakes associated with subduction comes from investigations of estuarine marsh sediments buried by sand layers. These deposits suggest that portions of the coast sub- sided abruptly and were then overwashed by extreme tsunamis, or “tidal 10 waves, that swept over the area and deposited the sand (B. FE. Atwater 1987; Darienzo and Peterson 1990; B. F. Atwater and Yamaguchi 1991; Darienzo et al. 1994; Peterson and Priest 1995). The number of these layers found in Willapa Bay and Netarts Bay and carbon-14 dating of the sediments indicate that catastrophic earthquakes have occurred along the Northwest coast at least six times in the past 7,000 years, at intervals ranging from 300 to 600 years, with the last having occurred about 300 years ago. Given this esti- mated frequency of occurrence, there is a strong possibility that another major subduction earthquake and tsunami will occur during the next 100 years. The lack of subduction earthquakes within historic times suggests that the ocean plates and the North American plate are temporarily locked to- gether. If so, they must be accumulating energy, much as a compressed spring does. This is an ominous situation. Ideally, small earthquakes peri- odically release the tension generated when two plates come together, allow- ing the plates to slide by one another. The longer the plates remain locked together, the greater the amount of energy stored, and the more cata- strophic the resulting earthquake when the plates finally do break apart along the subduction zone. Scientists are still debating the magnitudes of past subduction earth- quakes in the Northwest, and hence the magnitude of an earthquake that could be expected in the future. The subduction process has caused consid- erable deformation and fracturing of the upper continental plate, and some scientists have suggested that this deformation releases part of the accumu- lating strain, thus reducing the magnitude of subduction earthquakes (Goldfinger et al. 1992; McCaffrey and Goldfinger 1995). Even so, they esti- mate that a future earthquake could be on the order of magnitude 8, com- parable to the earthquake that destroyed San Francisco in 1906. Estimates of the magnitudes of past earthquakes, based on the alongshore lengths of ruptures in the subduction zone inferred from the simultaneous subsidence of marshes and accumulations of tsunami sands within several estuaries (Darienzo and Peterson 1995), indicate that at least some had magnitudes greater than 8, possibly greater than 9. Perhaps the most definitive evidence for subduction earthquakes and tsunamis on the coast of Oregon and Washington has come, surprisingly, from Japan (Satake et al. 1996). In addition to devastating our coast, large tsunami waves generated off the Northwest coast would also travel across the Pacific Ocean and eventually reach the shores of Japan, though they would have weakened by then. The Japanese have kept detailed records on damage-causing tsunamis for nearly 400 years. These records reveal that damage occurred at a number of sites along the coast of Japan in January 1700, resulting from a tsunami that could only have come from the north- western United States. Considering that it would have taken about 10 hours Geological Evolution 11 for the tsunami waves to travel across the Pacific, the Japanese estimated that the subduction earthquake must have occurred at about 9:00 P.M. on January 26, 1700, a time that is consistent with Native American legends, which say the quake occurred on a winter night. The evidence is conclusive: major subduction earthquakes have oc- curred in the Northwest, causing large portions of the coast to drop imme- diately by several feet and generating huge tsunamis that washed over our coast and traveled in the other direction as far as Japan. Sediments begin to accumulate on ocean plates as soon as the plates are formed, the thickness increasing with time. The Juan de Fuca and Gorda plates have unusually thick accumulations of sediments due to their close proximity to the continent. (Rivers and coastal erosion deliver large amounts of mud and sand to the ocean.) Much of the accumulated sedi- ment is scraped off during subduction and is added to the continental mass, leading to long-term growth. Subduction also causes the progressive uplift of the land mass and carries deepwater sediments and the fossils they contain up into relatively shallow water. Remains of organisms that once lived at depths of 2,000-3,000 feet have been found in sediments on the Or- egon continental shelf and slope at depths less than 600 feet (Byrne et al. 1966; Kulm and Fowler 1974), clear evidence that significant uplift of the Northwest margin has taken place. Nearly all of Oregon and Washington was created by the accretion to the continent of ocean sediments and a series of volcanic island arcs similar to the present-day Aleutian Islands. The Blue Mountains of easternmost Or- egon are thought to be portions of ancient ocean crust and island arcs that were added to the continent during the late Triassic and Cretaceous geo- logic periods (Brooks 1979)—the age of dinosaurs—150—250 million years ago. Before that, what we now think of as the Northwest was part of a deep ocean basin. The oldest rocks found in the Coast Range of western Washington and Oregon date back to the Paleocene and Eocene epochs, about 40-60 million years ago. These old rocks are ocean basalts much like those being formed today by volcanic activity at spreading ridges. Apparently, a ridge similar to the present-day Juan de Fuca Ridge was situated to the west. The Klamath Mountains were present to the south, but otherwise there was an em- bayment in the coast with deep ocean water over the areas that are now the Coast Range, the Willamette Valley of Oregon, and the Puget Lowland of Washington. A center of unusually strong volcanic activity on the ridge crest formed a chain of islands that accreted to the continent and are now present as a north-south series of peaks in the Coast Range. In the Oligocene epoch, some 30 million years ago, thick layers of melted rock intruded into the older ocean crust rocks that now form the base of the Coast Range. These intruded volcanic rocks were extremely resistant to ero- 12 sion and today form the higher peaks of the Coast Range; Marys Peak west of Corvallis, the highest of the Coast Range mountains (elevation 4,097 feet), is an example. During the Miocene, 30-35 million years ago, volcanic activity generated the immense flows of the Columbia River basalts (Orr et al. 1992). Volcanic activity recurred to the west at the same time. This activity was somehow connected with the generation of the Columbia River basalts because the rocks are almost exactly the same. These Miocene volcanic rocks are par- ticularly important to the morphology of the modern coast because they are resistant to wave attack and form many of the major headlands along the Oregon coast; Yaquina Head, Cape Foulweather, and Cape Lookout are ex- amples (fig. 2.3). Figure 2.3 Cape Lookout on the north Oregon coast is composed of ancient volca- nic rocks highly resistant to wave attack. From the Oregon Highway Department. Geological Evolution 13 The ocean embayment into western Oregon and Washington persisted for many millions of years, accumulating seafloor sediments all the while. A major river entered the embayment from the southeast, carrying large loads of sediment that built out a delta (Chan and Dott 1983). Masses of this sedi- ment periodically slumped off the delta and flowed into the deep water of the embayment, settling out of suspension to form sand layers that are graded with the coarsest sand particles at the base and finest at the top (Heller and Dickinson 1985). These layers of deep-sea sands were eventually uplifted onto the land and are now visible in road cuts of highways crossing the Coast Range. Swamps developed along the margins of the ocean em- bayment, and the slow accumulation of dead marsh plants produced the coal beds found in the Coos Bay area. The embayment persisted until the Pliocene epoch, about 5 million years ago, at which time the Coast Range began to emerge from the sea and west- ern Oregon and Washington came into being. In terms of geologic time, the Northwest is thus very young. With the land’s emergence from the sea, rain, rivers, and ocean waves went to work to erode what formerly had been deep-sea crustal rocks and volcanoes, and ocean sediments hardened into rock. These processes have etched out the land, cutting away the weaker rocks and leaving behind the more resistant ones to form the peaks of the Coast Range and the headlands along the coast. The modern morphology of the coast is the product of this erosion over the last 5 million years. Sea Level and Its Imprint on the Northwest Coast The most recent epoch of the earth’s history, roughly the last two million years, has seen the repeated advance and retreat of glaciers over the conti- nents. At their maxima, the glaciers moved down across Canada and into the northern portions of the United States. The water that formed the ice came from the oceans, and each build-up and advance of the glaciers low- ered the sea level, causing the shoreline to migrate out to what is now rela- tively deep water. Because the water was alternately locked up in glaciers and released, the level of the sea went through cycles of highs and lows, and this, too, has had a major impact on the morphology of the Northwest coast. The continental glaciers moving down from the north only just reached the edge of the Northwest coast. The ice advanced as a tongue into the Puget Lowland, reaching south of the present-day site of Olympia, Wash- ington (fig. 2.4). Glaciers covered all the hills of the Puget Lowland and the San Juan Islands and lay high against the flanks of the Olympic and Cascade Mountains. Another tongue flowed seaward and carved out the trough that is now the Juan de Fuca Strait (fig. 2.4). Isolated glaciers formed in the Olympic and Cascade Mountains, and small remnants still remain there as evidence of the ice ages. Glaciers advanced into the Puget Lowland at least four times at intervals of hundreds of thousands of years. During the last advance the glacier acted as a dam at the north end of the Puget Lowland, trapping water to form a large lake. This lake filled the entire lowland, bounded by the ice wall on the north and by mountains on the other three sides. The water level rose until it spilled over the lowest pass of the Coast Range and then flowed down what is today the Chehalis River, which drains into Grays Harbor. This ex- plains why the modern Chehalis River, which is relatively small, occupies such a large valley. When the Chehalis drained the glacial lake of the Puget Lowland, its discharge of water was probably several times greater than that of the modern Columbia River (McKee 1972). The Columbia River also saw floods of immense proportions during the ice ages, and its discharge was also considerably greater than at present (Bretz 1969; Baker 1973; Allen et al. 1986). The Columbia floods also origi- nated in an ice-dammed lake, this one located in the area of Missoula, Mon- Figure 2.4 The maximum advance of glaciers into Washington formed a lobe in the Puget Lowland and another that flowed seaward and cut the Juan de Fuca Strait. After McKee 1972. Vancouver Island Bellingham 7S orice Baker O77, Orr OLYMPIC MOUNTAINS chehas,. e e Olympia Mount Rainier kilometers & Geological Evolution 15 tana. But this lake’s water was released suddenly when the ice dam failed, producing catastrophic floods. The released water flowed out across eastern Washington, carving large channels into even the most resistant rocks. The floodwaters funneled into the Columbia River, but its channel could not hold such large volumes of water, and part of it spilled up into the Wil- lamette Valley, forming a temporary lake. Since the glaciers did not actually reach most of the Northwest coast, their main impact on the coastal morphology has been indirect and is mostly the result of the changes in the level of the sea produced by the alter- nating growth and melting of the ice sheets. During high stands of the sea hundreds of thousands of years ago, the waves eroded the rocks and beveled them flat to form nearly level terraces. Those ancient terraces were carried upward by tectonic activity and can now be found miles inland and at high elevations in the Coast Range. Most apparent of the uplifted marine terraces is the youngest that backs the present-day shoreline along many miles of the coast (fig. 2.5). This ter- race is young enough to give the appearance of having recently emerged from the sea. Cliffs cut into the terrace by waves reveal that its lower por- tions consist of ancient mudstones eroded flat by waves thousands of years ago. A uniform layer of light-colored sand occurs in the sea cliff above the gray mudstone. Close study of the sand reveals that much of it was depos- ited on ancient beaches—its layering and other features are identical with those found in modern beaches. Dune sands and old soil horizons are also evident in the terrace deposits, further illustrating that the environment of that ancient coast was substantially the same as today’s. The lowermost uplifted terrace is the youngest of a series of marine ter- races that in places form stairways up the flanks of the Coast Range. The highest and oldest terrace in the series reaches elevations up to 1,600 feet in southern Oregon (Baldwin 1945). The older the terrace, the more degraded it has become through erosion, and also the more warped by tectonic activ- ity, so that old terraces are no longer level platforms (Kelsey 1990). The beach and dune sands of these old terraces are weathered and cemented by rusty iron oxide. However, the sand in even the oldest terraces is still identi- fiable as having originated in beaches and dunes. Some terrace sands have accumulations of valuable black sands like those found on the modern beach. These ancient black sands have been mined for gold, and excavations within the deposits have exposed drift logs that were deposited on beaches more than 100,000 years ago. The presence of marine terraces high up on the western slopes of the Coast Range does not mean that sea levels were formerly that much higher than at present. They are there because the coastal margin of the Northwest has been tectonically rising for hundreds of thousands of years. This pro- gressive rise of the land, together with the global oscillations in the absolute 16 Figure 2.5 Top, the marine terrace at Otter Rock, Oregon, showing the gray Ter- tiary mudstones dipping seaward beneath the lighter-colored Pleistocene sand; bot- tom, close-up of the Pleistocene sand showing layers typical of beach deposits and an 80,000-year-old drift log. level of the sea due to glacial advances and retreats, created the stairways of terraces. Each terrace does record a high stand of sea level, but not necessar- ily a level higher than at present. All the high stands are probably not re- corded because some terraces may have been eroded away, just as the sea is presently eroding the youngest uplifted terrace. Our knowledge of the ages of the various marine terraces is limited by the scarcity of fossils that can be used to date them. Fossil shells and corals found in the lowermost terrace in southern Oregon lived about 80,000 Geological Evolution 17 years ago (Kelsey 1990; Muhs et al. 1990), which is fairly conclusive evidence that the lowest terrace correlates with the high stand of sea level that reached a maximum 80,000 years ago. Based on that date plus the known ages of still earlier high stands of sea levels and an estimated rate of uplift for the Northwest coast, the ages of the next two higher terraces have been placed at about 105,000 and 125,000 years before the present (Adams 1984; Kelsey 1990; Muhs et al. 1990). This points to the considerable antiquity of the oldest terraces that have been lifted high up onto the slopes of the Coast Range. The tectonic rise of the marine terraces, and of the Northwest coast in general, has not been solely vertical. The uplift has also been part of a rota- tion about an inland pivot line located somewhere within the central low- lands of Puget Sound and the Willamette Valley (fig. 2.6; Reilinger and Adams 1982; Adams 1984; Kelsey 1990). The farther west from that pivot line (i.e., the closer to the coast), the more rapid the local vertical uplift. The ro- tational uplift of the coast has altered the slopes of the marine terraces, and the older the terrace, the more it has been affected. Some terraces now actu- ally slope landward rather than seaward (Adams 1984). The uplift rotation is not uniform north and south along the coast because some areas are ro- tating upward faster than others. Surveys along a north-south line extend- ing the full length of the Oregon coast (fig. 2.7) demonstrate that the small- est rates of uplift are occurring on the central coast between Newport and Tillamook, with progressively higher rates to the south toward the Califor- nia border and to the north toward Astoria (Vincent 1989; Komar and Shih 1993; Mitchell et al. 1994). According to the survey results shown in figure 2.7, the southern half of the Oregon coast is rising faster than the global rate of sea level rise, and most of the northern half is being submerged by the rising sea. The submer- gence rates of the north Oregon coast are on the order of 1-2 millimeters per year (4-8 inches per century), which is much smaller than the 4-6 milli- meters per year (16—24 inches per century) common along the east and Gulf Figure 2.6 The uplift of the coast due to the rotation of the land about a pivot point or line located in the central valley of the Puget Lowland and Willamette Val- ley. Marine Terraces Coast Range Central Valley es eas SS pivot line 4 i or ~ [S) > © x 25 3-8, g § 3 E 8 3 a a= a c @ i= aS aE so De a 9 3 pS os oO 7) a 8 L = me 1 (0) e me ° + Fbco o_ 0 ee? bd 3. Es : ots gas =o -2 nel7,) Land is rising faster than Land is being submerged ‘ = 2 -3 eustatic sea level rise by rising sea level I -4 42 43 44 45 46 Latitude Figure 2.7 Elevation changes along the length of the Oregon coast from Crescent City in northern California north to Astoria on the Columbia River, derived from P. Vincent’s analyses of geodetic surveys (Vincent 1989). Elevation changes relative to the varying sea level, with positive values representing a rise in the land relative to the global rise in sea level, and negative values the progressive submergence of the land by the sea (1 inch = 25 millimeters). coasts of the United States. The uplift of the Northwest coast measured during historic times (the last 100 years) is interpreted as being the result of accumulated strain from subduction of the oceanic Juan de Fuca plate be- neath the continent and has probably been under way since the last sub- duction earthquake occurred in 1700. The heights of the marine terraces along the coast must reflect the long- term difference between the uplift that occurs during periods between earthquakes and the abrupt lowering that occurs during the earthquakes. For example, the marine terrace at Bandon on the southern Oregon coast formed 80,000 years ago. Its uplift rate during historic times has been about 2 millimeters per year (8 inches per century), so one might expect the terrace to have risen more than 500 feet since its initial formation. In fact, its elevation is only about 100 feet. The discrepancy is likely accounted for by subsidence accompanying seismic events. If the subsidence averages 20-40 inches during each event, then the recurrence intervals would have to be on the order of 300-600 years (Komar et al. 1991), a figure in agree- ment with the time intervals determined by dating marsh deposits. Coastal subsidence during an earthquake is probably very uneven; there is considerable local folding and faulting, and this affects the elevations of the terraces. Figure 2.8 shows elevations of the youngest terrace in southern Oregon. The terrace is highest in the Cape Blanco area, which therefore Geological Evolution 19 must have the greatest rate of net uplift over the long term (Baldwin 1945; Kelsey 1990; Goldfinger et al. 1992). The height of the terrace decreases markedly toward the north, reaching a low point north of Coos Bay. This points to the significance of the uplift rate in controlling the present-day coastal morphology; the high, wave-cut cliffs of Cape Blanco are in marked contrast to the low area between Coos Bay and Heceta Head, where the sands of the Oregon Dunes have accumulated. Any records that remain of low stands in sea levels are beneath the sea on the continental shelf. This makes it difficult to learn much about what the Northwest coast must have been like during them. Drowned beaches and wave-eroded terraces have been identified on many continental shelves, some of them at water depths greater than 300 feet. Dredges have brought up the teeth of mastodons from these depths, evidence of the life that must have flourished long ago when sea levels were lower. However, more impor- tant than mastodon teeth has been the dredging up of intertidal organisms and marsh peat, material that when living had a close relationship with the level of the sea. By dating that material we can reconstruct former water lev- els and determine how much and how rapidly the sea has risen since its most recent low 20,000 years ago (fig. 2.9). At the time of the last glacial Figure 2.8 Elevations of the youngest marine ter- race near Cape Blanco on the Oregon coast. After Baldwin 1945. top of terrace wave-cut platform— 20 THOUSANDS OF YEARS BEFORE PRESENT 0 35 30 25 20 15 10 5 10) 100 200 300 DEPTH (feet) 400 Figure 2.9 Changing sea levels over the past 40,000 years due to the growth and melting of continental glaciers. After Curray 1965. maximum, the sea was nearly 400 feet lower than it is now. As the glaciers melted, the sea rose rapidly until about 6,000 years ago, when the rate slowed. The dashed line in figure 2.9 is an estimation of the sea level prior to 20,000 years ago, during the cycle associated with the previous glacial advance and retreat. Glacial fluctuations and sea level cycles have been oc- curring for more than a million years, with numerous high stands and low stands. The sea has repeatedly passed across the continental shelf, and the shelf itself is largely the product of the resulting erosion. Unfortunately, the shelf sediments record only the most recent cycle, that cycle having dis- rupted or covered most of the deposits laid down by previous cycles of wa- ter level change. The sea continued to rise until about 2,000 years ago (fig. 2.10), when it reached approximately its present level. However, analyses of tide gauge records indicate that the sea is still rising. Tide gauges record the hourly changes in the level of the sea during regular tidal cycles. If we take the measurements recorded on a tide gauge during one day and average them, we obtain the mean water level for that day. If those daily averages are in turn averaged over an entire year, we have a measure of the mean sea level at that tide gauge. When such analyses are repeated year after year, we can monitor the progressive change in sea level that might be caused by the continued melting of glaciers. Data from nearly all the tide gauges that have been in operation sufficiently long to reveal net changes in sea levels have been similarly analyzed (Gornitz et al. 1982; Hicks et al. 1983; Barnett 1984). Figure 2.11 shows 80-year records for four locations. Each location experi- enced considerable fluctuations in the level of the sea from year to year, with many small ups and downs. The sea level in any given year is affected by many oceanic and atmo- spheric processes (see chapter 3), which produce the small fluctuations. In Geological Evolution 21 spite of such irregularities, most tide gauge records reveal a long-term rise in the sea that can in part be attributed to glacial melting. The record from New York City (fig. 2.11), which shows a long-term average rise of 3.0 milli- meters per year (12 inches per century), is typical. The record from Galveston, Texas, also shows a rise in sea level, but the average rate is much higher, 6.0 millimeters per year (24 inches per century). Of course the ac- tual level of the sea is not rising faster at Galveston than at New York City. The difference is the result of changes occurring on land. The Galveston area is subsiding as a result of the pumping of oil and groundwater, and the higher rate in water level rise registered on that tide gauge represents the combined effects of the local land subsidence and the actual rise in sea level. In contrast, Juneau, Alaska, is rising faster than the global sea level, and its tide gauge record therefore indicates a net fall in the water level relative to the land (fig. 2.11). The record from the tide gauge at Astoria, Oregon, in- dicates that the level of the sea there has remained relatively constant with respect to the land. During at least the last half century, Astoria has been rising at just about the same rate as the sea. In fact, a careful analysis of the data from the Astoria gauge shows that the land is actually rising slightly faster than the water, the net rate being relatively small; it would amount to only 10-20 millimeters (less than an inch) if it continued for 100 years. The rate derived from the Astoria tide gauge is in agreement with the geodetic survey data analyzed in figure 2.7, which provides a more complete picture of the relative rise of the sea level along the Northwest coast. Obviously, with different areas of the land moving up and down at dif- ferent rates, it is difficult to determine how much of the change is actually due to the long-term global rise in sea level associated with glacial melting. Figure 2.10 The rise in sea level over the past 8,000 years. After Shepard and Curray 1967. THOUSANDS OF YEARS BEFORE PRESENT 8 i 6 5 4 3 2 I O DEPTH (feet) after Shepard and Curray (1967) 22 1900 1930 1970 M4 \ Pall | NEW YORK, D> NEW YORK [77° | h ny Arye yf ' i J Pav . GALVESTON, TEXAS A | Figure 2.11 The yearly changes in sea level deter- mined from coastal tide ASTORIA, : N gauges. The change at a OREGON specific station is the sum of the variations in the ac- tual worldwide sea level and the changing level of TaNEaU. A the land at that site, and ALASKA ; therefore differs from one Scale (inches) Scale (cm) station to the next (1 inch = 2.54 centimeters). After Hicks 1972. The best that can be done is to eliminate the records from areas that are un- dergoing obvious local subsidence or emergence and then combine the re- maining records to obtain a worldwide average. The results indicate that sea level is rising between 1 and 2 millimeters per year (Hicks 1978; Barnett 1984). This may not seem like much—it amounts to only about 4-8 inches in a century—but even that small rise can have a significant impact on low- lying coasts. When areas are also subsiding, it is the net local change that is important to beach erosion and the movement of the sea over the land. A rise of 4 mil- limeters per year is common on the east coast of the United States, and this rate represents a rise in water level relative to land of 16 inches in a century. We are fortunate in the Northwest because the level of the sea is pres- ently dropping with respect to the land or is only slightly higher than the tectonic rise (fig. 2.7). The erosion along our coast is much less than it would be if the sea were moving up over the land at the rates found on the Geological Evolution 23 East and Gulf Coasts. However, this advantageous situation may change in the future. A global warming trend has been under way since the 1960s, per- haps a “greenhouse effect” caused by the carbon dioxide and other gases hu- man activities have pumped into the atmosphere. If this warming contin- ues, sea levels are expected to rise faster than at present and could reach levels 2-10 feet higher by the year 2100 (Hoffman et al. 1983; National Re- search Council 1985). However, the significance of greenhouse warming is still being debated by scientists, and predictions of an associated major sea level rise are uncertain. If there is an accelerated rise in sea level, the greatest impacts would be in low-lying coastal areas of the eastern United States. The effect on the Northwest coast would be smaller and would come later, but we cannot ignore this potential hazard. The Evolution of the Northwest Coast since the Ice Ages Twenty thousand years ago, during the last advance of the glaciers, the shoreline of the Northwest was some 20-30 miles west of its present posi- tion (fig. 2.12). The beaches were close to the edge of the continent, and a wide, nearly level plain separated the mountains from the ocean. Rivers flowing out of the Coast Range crossed this flat coastal plain at a slow, me- andering rate. Today that plain is under water and forms the continental shelf. Portions of the old channel of the Columbia River found on the sea- floor indicate that its sediments were delivered to Astoria Canyon, which notches the edge of the continental shelf and slope (fig. 2.12). The river sed- iments dumped into Astoria Canyon then slumped into the deep ocean basin. During the lowest stand of sea level, the coastline was probably irregular (fig. 2.12) because the shoreline was close to the shelf edge, which is also ir- regular. There may have been only pocket beaches, and these probably were of limited extent because of the tendency for the sand to move offshore over the steep bottom slopes. As the glaciers began to melt and the sea level be- gan to rise, the shoreline migrated back across the coastal plain (the present continental shelf). The beaches were relatively continuous, with few if any stretches of rocky shore. No headlands were present on the shores of Or- egon and Washington then, and waves transported sand north and south along the ancient beaches, a transport that is not possible today because of the numerous headlands. Analyses of the minerals in sands from the former coastal plain beaches, which now lie underwater on the continental shelf, indicate that the net movement of sand along those ancient shorelines was to the north (Scheidegger et al. 1971). Most of the beach sand on the Northwest coast consists of grains of quartz and feldspar. Particles of these minerals are transparent or light tan, and this is the color of most of our beaches. How- 24 Bellingham MAXIMUM ADVANCE OF GLACIERS \ data 7. \ ympia / Aberdeen ~~ _— a Astoria Canyon e Portland IS PRESENT - DAY , IL 1 SHORELINE City Salem GLACIAL- PERIOD Newport » SHORELINE Corvallis 20,000 yrs BP 40,000 yrs BP e Eugene Figure 2.12 Ap- proximate shoreline Coquille Ont : HoleTE positions during Cape Blanto low stands of sea level when glaciers 100 miles reached their maxi- 100 km mum development. ever, the sands also contain small fractions of heavier minerals that are black, pink, various shades of green, and other colors. These grains are readily visible as specks in a handful of quartz-and-feldspar beach sand, al- though sometimes they are concentrated by the waves into black sand de- posits on the beaches. These heavy particles can often be traced to specific sources (Clemens and Komar 1988a, 1988b). Most distinctive are the miner- als derived from the ancient Klamath Mountains of southern Oregon and northern California (fig. 2.13). Klamath sands contain minerals such as glaucophane, staurolite, epidote, zircon, hornblende, hypersthene, and the distinctive pink garnet, which is often concentrated in pockets on the beach. In contrast, the rivers that drain the Coast Range transport sand that contains almost exclusively two minerals: dark green augite and a small amount of brown hornblende (fig. 2.13). Augite comes from volcanic rocks and is contributed to the rivers by erosion of the ancient seafloor rocks and intruded lavas high in the Coast Range. The Columbia River drains a vast Geological Evolution 25 hypersthene (45%) augite (19 %o) green hornblende (14 %) brown hornblende (9%) enstitite (4 %/o) zircon (2%) clear garnet (2%) Figure 2.13 The principal augite brown hornblende ; suppliers of sand to the Northwest coast are the Co- lumbia River, the Coast glaucophane pink garnet Range, and the Klamath Si seninOn betes Mountains. Each source sup- brown hornblende hypersthene plies different heavy minerals augite to the beach and estuarine epidote i 3 zircon sands, and this makes it pos- diopside sible to assess their respective staurolite olivine contributions. From Clemens and Komar 1988a. area that contains many types of rocks, and this is reflected in the diversity of the heavy minerals in its sand (fig. 2.13). The net northward movement of beach sand during lower sea levels (Scheidegger et al. 1971) is particularly indicated by the distribution of min- erals derived from the Klamath Mountains. Sand from the rivers draining the Klamaths moved northward along the beaches under waves arriving from the southwest, and the minerals from that southerly source can be found in shelf sand nearly as far north as the Columbia River. As the Kla- math-derived sand moved north, it combined with sand contributed to the beaches by rivers draining the Coast Range, so there is progressively more augite in the sand and a lower proportion of Klamath Mountain minerals. The Columbia River was a large source of sediment, but most of that sand moved to the north and so dominates the mineralogy of ancient beach sands found on the Washington continental shelf. Some Columbia River sand did move south along the Oregon beaches during times of low sea lev- els, mixing with the sand from the Klamath Mountains and Coast Range. To summarize, the absence of headlands during lowered sea levels per- mitted sands derived from the Klamath Mountains, the Coast Range volca- nic rocks, and the Columbia River to move north and south along the coast. Depending on their location along the former shoreline of the Northwest coast, beaches consisted of various proportions of mineral grains from 26 these sources. Although some of the beach sand was left behind when the shoreline moved inland during the rapid rise in sea level and now rests on the continental shelf, much of it moved landward along with the migrating shoreline. The beaches would have been low in relief at that time, and storm waves would have washed over them, transporting sand from the ocean shores to the landward sides of the beaches, thereby producing the beach migration. Additional sand was contributed by rivers and by the coastal plain as it was eroded by the advancing sea. About 5,000-7,000 years ago, the rate of sea level rise decreased as the water approached its present level (fig. 2.10). Also at about that time head- lands segmented the Oregon coast into pocket beaches or littoral cells. At some stage several thousand years ago, the headlands extended into suffi- ciently deep water to hinder further alongshore transport of the beach sand (Clemens and Komar 1988a, 1988b). The pattern of along-coast mixing of sand from various sources established during lowered sea levels is still partly preserved, however, in the series of littoral cells that lie between the headlands. Minerals derived from the Klamath Mountains are still present in virtually all of the beaches along the Oregon coast, even though the sand can no longer pass around the many headlands that separate those beaches from the Klamaths. At several locations on the Oregon coast there are distinct changes in beach sand mineralogies on opposite sides of headlands; that is, within ad- jacent but isolated littoral cells (Clemens and Komar 1988a, 1988b). The most dramatic change occurs at Tillamook Head south of Seaside, Oregon (fig. 2.14; Clemens and Komar 1988a, 1988b). The beach sand north of this headland is derived almost entirely from the Columbia River, and the abun- dant supply of sand has built out the shoreline significantly within historic times. The beach sand south of the headland contains abundant augite, in- dicating a Coast Range source from local rivers or cliff erosion. This beach sand also contains small amounts of Klamath Mountain minerals, the far- thest north the relict pattern of along-coast mixing during lowered sea lev- els can be found preserved in the modern beaches. There is also some Co- lumbia River sand in the beach south of Tillamook Head, but it got there by mixing southward with sand from the other sources during lowered sea lev- els and then migrating onshore. The Columbia River sand has been on the southern beach for thousands of years, but the beach sand north of the headland came from the Columbia River only within the last century or two. The different histories of the beach sands are substantiated by the de- gree of rounding of the individual grains. North of the headland the grains are fresh looking and angular, much like crushed glass, attesting to their re- cent arrival from the Columbia; the pounding surf has not had sufficient time to abrade and round the grains. South of the headland the grains are Geological Evolution 27 1e) VA ASASRR WR Bee lene Figure 2.14 Changes in the degree of rounding of the beach sands on oppo- site sides of Tillamook Head. The grains to the north are more angular TILLAMOOK because they arrived PIB le from the Columbia River | | more recently. Key: VA = very angular, A = angu- mous. AUGITE = jar, sa= subangular, SR | ROUNDING = = subrounded, R = beach Be a rounded, and WR = well m L—____4 rounded (1 kilometer ~ 0.6 mile). From Clemens CAPE FALCON and Komar 1988. much rounder, their sharp edges worn away during thousands of years of movement by wave swash on the beach (fig. 2.14). The beach north of Tillamook Head is part of the Clatsop Plains (fig. 2.15), which formed after the sea reached its present level (Cooper 1958; Rankin 1983). The Clatsop Plains consists of beaches that have grown sea- ward together with a series of large dune ridges and associated interdune lows, many of which are occupied by elongated lakes. Backing the sandy plains is a wave-cut sea cliff that is now much degraded; it must have formed soon after the sea level rose but before the Columbia River could supply sufficient quantities of sand to develop a fronting beach. Dated peat deposits from within the plains indicate that the prehistoric shoreline fronting the eroded cliff formed about 3,500 years ago (Rankin 1983). The beaches built out rapidly until about 1,400 years ago, and then accumulated at a slower rate up to the present. The Clatsop Plains is the only extensive stretch of shoreline on the Or- egon coast that has naturally accumulated volumes of sand sufficient for the beach to advance seaward. This, of course, is due to the presence of the 28 Columbia River. The rest of the Oregon coast has more limited sources of sand, and those beaches have continued to erode. Most of the sand from the Columbia River moves north along the Washington coast, and as a result most of the Washington beaches have built seaward. The Long Beach Penin- sula (fig. 2.15) is composed of Columbia River sand, and its northward ex- tension is likely in response to a net longshore transport of sand in that di- rection (Ballard 1964; Komar and Li 1991). At the south end of the peninsula, where it attaches to the mainland, there is a small stretch of old sea cliff, which indicates that this sand spit built seaward just as did the Clatsop Plains. This seaward growth is even more evident farther north in the area of Grayland, where there is an old cliff along many miles of the coast separated from the present shore by a coastal plain 1-1.5 miles wide. For the most part, the Washington beaches are continuing to advance sea- ward by accumulating additional Columbia River sand, as indicated by comparisons of the present shoreline position with old coastal charts, and by annual beach profile surveys since 1951 (Phipps and Smith 1978; Schwartz et al. 1985). Figure 2.15 Chart of the North- ne west coast from Tillamook Head, Oregon, north past the Long Beach Peninsula and Willapa Bay in Wash- | ington, based on 1868-77 surveys. Based on 1868-1877 surveys. = @) 2 Long Beach a Peninsula 4 e) Zz Cape Disappointment PACIFIC OCEAN Columbia River Clatsop Plains NODAYO Tillamook Head “ Geological Evolution 29 Formation of the Northwest Estuaries The coastal rivers of the Northwest cut their valleys during the low sea lev- els that accompanied maximum glacial advances. When the water rose at the end of the ice ages, the valleys were drowned and developed into estuar- ies. Today these estuaries are important fisheries and harbors, and they serve as centers of community activity in many coastal towns. They also play a central role in sediment movements on the coast, which govern con- tributions of sand to the beaches. Each estuary is connected to the ocean through an inlet, which carries out to sea fresh water that enters the estuary from the river (fig. 2.16). Also important to maintaining the inlet are tidal flows into and out of the estu- ary or bay. Estuaries are zones where fresh water mixes with salt water. The fresh water is less dense and therefore tends to flow over the top of the seawater. At times, the fresh water may flow all the way through the estuary and into the ocean before finally mixing with the underlying seawater. When this oc- curs, the lens of denser salt water that lies below the fresh water exhibits a net flow from the ocean into the estuary. This type of flow, found in many Northwest estuaries, transports sediment from the ocean into the estuary and inhibits the movement of river sand from the estuary to the ocean beaches. The restriction of sand movement through Northwest estuaries was first demonstrated in a study of sediments in Yaquina Bay (Kulm and Byrne Figure 2.16 The Alsea Bay estuary on the mid-Oregon coast. A narrow inlet connects the bay to the sea. 30 NEWPORT Realms of Deposition marine mixed fluviatile YAQUINA BAY OREGON (Kulm and Byrne, 1966) Figure 2.17 Sediment patterns within Yaquina Bay result from the mixing of marine sand carried into the estuary by tidal flows and fluviatile sand derived from the river. After Kulm and Byrne 1966. 1966). Like the other rivers draining the Coast Range, the Yaquina River car- ries sand that has augite as its principal heavy mineral. The beach sand out- side the bay contains a large variety of minerals, including some derived from the Klamath Mountains. This difference in minerals makes it possible to trace the movement of the river and beach sands entering the estuary (fig. 2.17). River sand (fluviatile) forms 100 percent of the estuarine sedi- ment only in the landward portion of the bay. Marine beach sand carried into the bay through the inlet dominates the estuarine sediments near the mouth. The remainder of the bay contains river and marine sands mixed in varying proportions. Yaquina Bay is slowly filling with sediment, both fluviatile sand from the landward direction and marine sands from the ocean side. Sediment cores indicate that Alsea Bay began to fill as soon as the estuary was formed after the last rise in sea level and is continuing to fill (Peterson et al. 1982, 1984b). In fact, this is the fate of most estuaries. Formed from drowned river valleys at the end of the ice ages, they are envi- ronments out of equilibrium. Most estuaries are eventually reduced to channels that transport all of the river sediments to the ocean. However, such a development takes thousands of years, so we should not view our es- tuaries as temporary features. Geological Evolution 31 Although figure 2.17 indicates that little if any sand from the Yaquina River is presently reaching the ocean beach, this conclusion applies only to sand-sized grains. The fine clays remain in suspension in the water and are carried through the bay and into the ocean, evident in the brown plume that emanates from the inlet during river floods. Large estuaries separate most of the major coastal rivers of the Northwest from the Pacific Ocean and prevent them from contributing significant amounts of sand to mod- ern beaches. This in part explains why many Oregon beaches have relatively small volumes of sand, and why their mineralogies still reflect the along- coast mixing of sand obtained from different sources during low stands of sea level rather than more recent contributions. The one clear exception is the Columbia River, which transports more than 100 times as much sand as the next largest river (the Umpqua), and on the order of 1,000 times as much sand as the other coastal rivers (Clemens and Komar 1988a). Dune Fields of the Northwest Coast Impressive accumulations of dune sands occur along the Northwest coast. In many areas the dunes are still being actively molded by winds; in other areas vegetation now covers formerly mobile dunes. It has been estimated Figure 2.18 The Coos Bay dune sheet on the central Oregon coast. From the Oregon Highway Department. 32 Figure 2.19 The precipitation ridge at the landward edge of the Coos Bay dunes. The dune sand is slowly covering forests and blocking stream channels to form small ponds and lakes. that sand dunes are present along 45 percent of the Oregon coast and 31 percent of the Washington coast (Cooper 1958). All of the coastal dune fields are within 2 miles of the ocean shore; most are immediately adjacent to sand beaches. It is clear that the dunes along the Northwest coast were formed by winds blowing sand inland from the beaches. The Coos Bay dune sheet on the mid-Oregon coast is the largest coastal dune accumulation in the United States (fig. 2.18). It extends northward for nearly 150 miles from Coos Bay inlet to Heceta Head and is an impressive display of wind-blown landforms and processes. There is evidence of three episodes of dune advance in the Coos Bay dune sheet, and also in other dune fields (Cooper 1958). The earliest is rep- resented today by a strip of thoroughly vegetated dunes that in most places achieved the greatest landward advance. The second advance generally fell short of the first, and its present condition ranges from complete stabiliza- tion to still vigorous activity. The third episode is represented by the large areas of active dunes that until recently had open access to the ocean beaches that supplied them with sand. The landward edges of these dune fields are well defined by the presence of precipitation ridges (fig. 2.19), steep slip faces that slowly invade and bury forested areas. The precipitation ridge often blocks stream drainageways so that ponds and lakes develop along its base. People have played a major role in altering the surface cover of the dunes along the Northwest coast. In some cases this has been deliberate, in others Geological Evolution 33 Figure 2.20 Two views of the same area of the Clatsop Plains: top, active dunes in August 1937; bottom, July 1944, showing subsequent revegetation of the area using European beach grass. From Hanneson 1962. 34 Figure 2.21 Introduction of European beach grass in the Coos Bay dune field caused a foredune to build up at the back of the beach that cut off the inland move- ment of sand from the beach to the large dunes. accidental. When Europeans first settled the Clatsop Plains south of the Co- lumbia River in the nineteenth century, the extensive dune fields were cov- ered by dense grasses (Hanneson 1962). The settlers’ livestock ate the grasses, and overgrazing soon reactivated the dunes. By the 1930s, some 3,000 acres of sand had become mobile again (fig. 2.20), and blowing sand covered roads and homes. In 1934 the U.S. Soil Conservation Service took action to halt the advancing sand by first planting large areas with Euro- pean beach grass (which livestock generally will not eat). Once the dune grass took hold, plantings of Scotch broom and shore pine followed. These activities have been successful in revegetating the Clatsop Plains and simi- larly disrupted areas. This introduction of European beach grass had an unforeseen adverse consequence on the Coos Bay dune sheet. A hundred years ago these dunes existed as an unvegetated sand surface that extended from the ocean shore to the precipitation ridge at its landward edge. Sand was free to blow inland from the beach to supply material for the continued growth of the dunes. However, the European beach grass introduced during the 1930s in other areas of the coast quickly spread to the Coos Bay dunes and began to grow in the dunes immediately landward from the beach. These dune grasses captured sand blowing inland from the beach, resulting in the growth of high foredunes that have cut off the supply of sand to the large inland dunes. The impact was noted first in the area immediately landward of the foredunes (fig. 2.21), where the ground level was lowered to the water table. Geological Evolution 35 This in turn permitted the growth of shrubs and other vegetation atypical of dune areas. The areal extent of the active dunes has decreased substan- tially, and there is concern regarding their long-term preservation. Summary The ocean shores of Washington and Oregon have seen dramatic changes over the eons. Compared with other coasts, the Northwest is geologically young—it came into being only within the last five million years. Erosion of the emergent land mass supplied sand and gravel to the coast, and these sediments accumulated to form beaches and fields of windblown dunes. Ice age glaciers sculpted the far north coast of Washington, cutting the Strait of Juan de Fuca. However, the main impacts of glacial advances and retreats on the coast were indirect. The accompanying rises and falls in sea level cut stairways of marine terraces and drowned river valleys to form estuaries. The Northwest coast today displays the cumulative evidence of the roles played by geologic, climatic, and oceanographic processes. Tectonic activity within the earth continues to cause its uplift and shakes the Northwest coast every few hundred years with a major earthquake. 36 3. The Dynamic Northwest Coast The Northwest coast is one of the world’s most dynamic environments. Se- vere storms strike during the winter, generating strong winds, driving rains, and huge waves that crash against the shore (fig. 3.1). Waves and ocean cur- rents continuously reshape the shoreline. Sand is cut away in some spots and built up in others. Beaches give way, retreating inland and threatening homes, motels, and public parks. The reshaping of the shore can be under- stood only through a knowledge of ocean and beach processes—the waves, tides, and currents that interact with the land to modify shorelines. These change with the seasons of the year. Seasons and the Coastal Climate The difference between summer and winter in the Northwest is a difference of extremes. The summer months are dry with mild temperatures and winds. Vacationers can enjoy the sun and comfortable temperatures as they relax on the beaches or stroll through coastal towns. The weather begins to change in October, when temperatures fall and clouds and rain increase (fig. 3.2). Major storm systems generally begin to pass over the coast in No- vember, bringing heavy rains and strong southwest winds. Only those who enjoy witnessing the awesome power of the winter surf breaking against the shore venture onto the beaches. The return to summer conditions is gradual. From January through May the temperatures progressively rise while the rainfall decreases (fig. 3.2). Intense storms seldom occur after March. This extreme seasonality in climate creates parallel variations in ocean processes and is the strongest influence acting on the natural cycles that af- fect Northwest beaches. Winter storms generate much larger waves and stronger ocean currents than are seen in summer. The beaches erode under the onslaught of winter storms, then rebuild during the following summer. Figure 3.1 Large waves breaking against the rocks of Cape Disappointment, Wash- ington, along the north shore of the entrance to the Columbia River. Courtesy of the Daily Astorian. Cliff erosion also increases during the winter, not only because cliffs are at- tacked by storm waves, but also because the rain washes away loose cliff ma- terials and sometimes lubricates landslides. Examples of such cycles in coastal processes will be apparent throughout this chapter. Potential buyers should be aware of the difference between the summer Northwest and the winter Northwest. New retirees arrive from the Midwest in summer to settle into the comfort of a beach home fronted by a wide beach and gentle surf, only to see the sand disappear during the next winter and the waves lapping at their doors. Ocean Wave Generation The energy carried by ocean waves parallels the seasonality of storm winds, because the strength of those winds is the primary determinant of wave heights. In general, the greater the velocity of the wind blowing over the ocean surface, the higher the resulting waves. Other factors are involved as well, of course. One is the duration of the storm: the longer the wind blows, the greater the energy transferred from the storm winds to the waves. An- other factor is the fetch, the area or ocean expanse over which the storm winds are blowing. The importance of fetch is apparent when one compares wave generation on the ocean with that on an inland lake. The fetch on the 38 TILLAMOOK, OREGON 60 ZO we 7) ° o F © LJ « 55 = 15 ze, < 6 x uw 90 E 10 ao i= = a Gi a F 45 es oe a 40 O TRUMAN Min Um AN "SINO) IN] ID DFMAM dS DAS OM D Figure 3.2 Seasonal variations in temperature and rainfall measured at Tillamook, Oregon. lake can be no greater than its length, so the waves have time to acquire only a small amount of energy from the wind before they cross the lake and break on the far shore. Wind-generated waves are energy transfer agents. They obtain energy from the wind, transfer it across the expanse of ocean, and finally deliver it to the coastal zone when they break on the shore (fig. 3.3). Therefore, the storm generating the high waves need not be in the immediate coastal zone. Waves reach the Northwest coast from storms all over the Pacific, even from the Southern Hemisphere near Antarctica. However, our largest waves are derived from winter storm systems that move down from the North Pacific and Gulf of Alaska. Waves in the actual area of a storm are extremely irregular. Each wave changes rapidly in height, sometimes increasing but eventually decreasing until it disappears altogether. This complex pattern results because the storm generates many waves simultaneously; some are momentarily super- imposed to produce higher waves, then a few seconds later they move apart Figure 3.3 Wind energy is transferred to ocean waves, propagated in swell cross- ing the sea, and eventually delivered to the nearshore when the waves break. GENERATION PROPAGATION SHOALING AND BREAKING (Sea) (Swell) (Surf) (Foo in ri a D=storm duration i OE Ze VK P=ECn — = speed ea length, peers (oie ae Wee RR p eS ee energy transfer from energy carried with energy delivered to wind to waves = f(U,D,F) the waves the nearshore zone The Dynamic Northwest Coast 39 wave moving with phase velocity, C —_—___» +——— wave length, L crest —+— wave height, H trough Figure 3.4 Simple ocean waves consist of a series of crests and troughs that are measured by the wave length, L, and height, H. The wave period is the time interval between the passage of successive waves, for example, past the piling shown. From Komar 1997. and cancel one another. As the waves leave the storm area they begin to sort themselves and so become more regular. Waves distant from a storm are termed swell and are characterized by a series of crests and troughs (fig. 3.4). When waves are regular, like these, it is easier to measure their heights, lengths, and periods (the time it takes for successive crests to pass a fixed position such as a piling). Storm winds generate waves of many different heights and a wide range of periods. Long-period waves travel faster than short-period waves, and so move away from the storm area first and out- distance the short-period waves. This is a primary factor in converting the irregular waves found in the storm area into a regular swell. It also means that when waves generated by a distant storm reach the coast, the longest- period waves arrive first, followed by progressively shorter-period waves. In general, the waves that break on the coast are a mixture of swell from distant storms and more irregular waves generated locally by coastal winds. In the absence of a local storm, which produces high sea conditions in the nearshore, it is the lighter coastal winds that produce the “chop” that is al- most always present. Even when a strong chop due to local winds is present, however, the wave conditions along the coast still tend to be dominated by the regular swell generated in storms thousands of miles away. If there are two distant storms, then two sets of swell waves may reach the shore at the same time. These two sets may be superimposed for a short time to produce larger breakers, only to cancel one another out a few min- 40 utes later, yielding lower waves. It is such combinations of swells from dif- ferent storms that accounts for the common observation that the seventh wave is the largest; actually, the cycle can be every fifth wave to every tenth wave, depending on the difference in periods between the two sets of swells. The variability of wave heights makes it difficult to characterize ocean waves. What does it mean, for example, when the Coast Guard reports 10- foot seas? One could report an average height of all the waves at the mea- surement site, but this is not generally done because the smallest are too in- significant to be included. Instead, the wave conditions are commonly reported in terms of the significant wave height, defined as the average of the highest one-third of the waves (Komar 1997). The significant wave height can be determined using sophisticated instruments, but it turns out that it also roughly corresponds to a visual estimate of a representative wave height. This is because an observer naturally tends to notice the larger waves and ignore the smallest. Of course, there will be many individual waves that are higher than the observed significant wave height, which is something of an average. The largest wave height during any 20-minute in- terval will be a factor of about 1.8 times the significant wave height (Komar 1997). Therefore, when the Coast Guard is reporting 10-foot waves, be pre- pared to face individual waves that are approximately 1.8 x 10 feet = 18 feet. Ocean waves reaching the shores of the Northwest are measured daily with a unique system (fig. 3.5), a seismometer like those usually employed to measure earth tremors caused by earthquakes, but in this application tuned to sense the small ground movements produced by ocean waves as they reach and break on the shore (Komar et al. 1976b; Zopf et al. 1976; Creech 1981; Tillotson 1994; Tillotson and Komar 1997). A wave-measuring seismometer system at Oregon State University’s Hatfield Marine Science Center in Newport is connected to a recorder to obtain a permanent record of the waves. This system has been in operation since November 1971 and is the longest continuous record of wave conditions on the West Coast in existence. Since the 1980s, the National Oceanic and Atmospheric Figure 3.5 The seis- mometer at the Mark Hatfield Marine Science Center in Newport, Or- egon, is tuned to measure ocean wave conditions. The Dynamic Northwest Coast 41 Administration’s (NOAA) National Data Buoy Program has maintained a series of wave-measuring buoys in deep water off the shores of the coastal states, including Washington and Oregon. Wave measurements derived from the seismometer, and more recently from the deepwater buoys, have been invaluable in research examining the causes of beach erosion in the Northwest. It might come as a surprise that a seismometer in the Marine Science Center, which is 2 miles from the ocean, can provide records of ocean waves. But this seismometer differs from others in that it is tuned to am- plify minor tremors, whether these are caused by earthquakes too small to be felt or generated by ocean waves. Even more impressive is the fact that the waves can be detected with a seismometer located at Oregon State Uni- versity in Corvallis, 60 miles inland. When the surf is high on the coast, its effects show up as jiggles in the seismometer recordings. In order to use the record from the seismometer to measure ocean waves, it was first necessary to calibrate the system. This was accomplished by obtaining direct mea- surements of waves in the ocean at the same time their tremors were mea- sured with the seismometer. The direct measurements of waves were col- lected with a pressure transducer, an instrument which rests on the ocean bottom and records pressures that are directly proportional to the heights Figure 3.6 Daily variations in wave conditions on the Oregon coast measured with the seismometer, December 1972—January 1973 (1 meter ~ 1.1 yards). From McKinney 1977. OBSERVED HIGH-TIDE LEVEL (meters) BREAKER HEIGHT (meters) 1S 20 25 3 5 10 15 20 25 3 DECEMBER 1972 JANUARY 1973 42 PU pe eae ee re all ae 10k SIGNIFICANT WAVE < BREAKER HEIGHTS Ole Wise -| 30 ~s_monthly maximum ee = 8 Sg Bea on ‘ 9 ae T ¢ ~_ s *, y; 25 3 E 7 %, Gm 74 = = . # <7 € if rg D6 oe # 2 too 2 @o _ / z= ae ae / = 3 5 monthly mean and i 2 = __ standard deviation / S S seete . oO ig & 2 ~ o o o oo > > oO s = = 1 2 3 4 5 6 if 8 9 10 11 Month Number (January through December) Figure 3.7. The monthly variations of wave breaker heights on Northwest beaches (1981—present), computed from wave heights measured in deep water by a NOAA buoy offshore from Newport. The solid line indicates the mean monthly heights (significant wave heights), the short-dashed lines are one standard deviation above and below the mean, and the long-dashed line is for the maximum monthly breaker heights measured since 1981 (1 meter ~1.1 yards). After Tillotson and Komar 1997. of the waves passing over the transducer. Now only the seismometer is needed to monitor daily ocean wave conditions, which it does safely from within the Marine Science Center, far from the destructive impacts of the waves. Figure 3.6 shows daily wave measurements obtained from the seismom- eter from mid-December 1972 through mid-January 1973. Most apparent in this record are the storm waves that struck the coast at Christmas. The breaker heights reached about 25 feet—the height of a three-story building. But that figure represents the significant wave height (i.e., the average of the highest one-third of the waves), so there must have been individual waves with heights closer to 1.8 x 25 feet = 45 feet! As might be expected, there was considerable erosion along the coast during the December 1972 storm. The most severe erosion occurred at Siletz Spit on the mid-Oregon coast; we will examine that event in detail in chapter 6. The seismometer in the Hatfield Marine Science Center and the Noaa buoys yield measurements of the wave conditions offshore in deep water. As the waves travel toward the shore they become taller and taller, achiev- ing a maximum when they break on the sloping beach. Figure 3.7 is a graph of the yearly cycle of significant wave breaker heights experienced on The Dynamic Northwest Coast 43 swell (summer) profile swell profile shoreline mean water level ———~. trough / 7 bar po wet s storm (winter) profile Figure 3.8 Seasonal changes in the beach profile in response to seasonal variations in wave energy. From Komar 1997. Northwest beaches (Tillotson 1994; Tillotson and Komar 1997). The solid line gives the average breaker height for each month and shows that the breakers are on the order of 7 feet high during the summer, and nearly double that, about 13 feet, in the winter. Most breaker heights fall within the range delineated by the dashed lines on either side of the solid line. Of par- ticular interest are the largest breaking waves generated by the most severe storms. The long-dashed line indicates the maximum monthly breaker heights and reveals the dramatic increase that occurs during the winter months. The highest storm wave conditions occur during December and January, when the maximum breaker height is on the order of 35 feet. Once again, this is the significant wave height; individual breaking waves could be on the order of 1.8 x 35 feet = 63 feet. Although this is an awesome height, even higher waves appear to have occurred on the coast in the not-too-dis- tant past, but before the seismometer and buoys were in operation to mea- sure the daily wave conditions. In the early 1960s, a wave-monitoring sys- tem located on an offshore oil-drilling platform measured a wave 95 feet high (Rogers 1966; Watts and Faulkner 1968). This is close to the 112-foot height of the largest wave ever reliably measured in the ocean, observed from a naval tanker traveling from Manila to San Diego in 1933 (Komar 1997). All of the measurements on the Northwest coast confirm that it has one of the highest wave energy levels in the world. Beach Cycles on the Northwest Coast Beaches respond directly to seasonal changes in wave conditions. The re- sulting cycle is similar on most coastlines (fig. 3.8). The beach is cut back during the winter months when high waves erode sand from shallow water and from the dry part of the beach. The eroded sand moves out to deeper water and accumulates in offshore bars located approximately in the zone where the waves first break as they reach the coast. The sand reverses its movement during the summer months, moving back onshore from the 44 bars to widen the dry part of the beach. Although this cycle between two beach profile types occurs seasonally, the beach is really responding to the waves that strike the shore—high winter storm waves versus low regular swell waves. Sometimes low waves prevail during the winter and the dry beach may actually build out, although generally not to the extent of the summer beach. Similarly, beach erosion also occurs during summer storms. The same cycle occurs on the beaches of the Northwest coast (Aguilar- Tunon and Komar 1978; Fox and Davis 1978), although factors other than wave energy also help to determine the size and shape of the beaches there. During the winter of 1976-77, my student N. A. Aguilar-Tunon and I mea- sured profiles of two Oregon beaches: Devil’s Punchbowl at Otter Rock and Gleneden Beach south of Lincoln City. We chose those beaches because of their contrasting sand sizes. The grain size is the primary factor governing the slope of a beach; the larger the grain size, the steeper the slope. Gravel beaches are the steepest, with slopes sometimes reaching 25-30 degrees. In contrast, the overall slope of a fine-sand beach may be only 1-2 degrees. Gleneden Beach has coarser-grained sand than Devil’s Punchbowl (fig. 3.9) and is therefore steeper. Figure 3.10 shows the month-by-month changes in the Gleneden Beach profiles and the rapid cutting back of the dry part of the beach as the winter storms became more frequent. The erosion began as early as October and continued through the spring. Sand did not return to the dry beach until April, May, and June. The cycle of profiles at Devil’s Punchbowl Beach was basically the same, at least in its timing, but the magnitude of the change was much smaller than at Gleneden Beach. Sand elevations at Gleneden changed by as much Figure 3.9 Beach profiles from Gleneden Beach and Devil’s Punchbowl Beach (Ot- ter Rock), Oregon, on April 2, 1977, showing that the coarser-sand beach (Gleneden) is steeper. Vertical exaggeration is 10 times (1 meter ~1.1 yards). From Aguilar-Tunon and Komar 1978. Both profiles 2 April 1977 GLENEDEN BEACH 10x vertical exaggeration (median grain size = 0.35mm) high-tide level DEVIL’S PUNCHBOWL BEACH (median grain size = 0.23mm hh meter Va low-tide level 0 20 40 60 80 100 120 140 160 180 200 DISTANCE (meters) The Dynamic Northwest Coast 45 BEACH PROFILES GLENEDEN BEACH (1) 27 AUGUST 1976 (2) 7 OCTOBER 1976 (3) 6 NOVEMBER 1976 (4) 20 NOVEMBER 1976 (5) 5 DECEMBER 1976 (6) 19 JANUARY 1977 (7) 2 FEBRUARY 1977 (6) 17 FEBRUARY 1977 (9) 5 MARCH 1977 (10) 16 MARCH 977 (i) 2 APRIL 1977 (vertical exaggeration 10x) ELEVATION IN METERS a 1 a T Alp J st mit I =f wot 30 ; $0 = 80 = 700 120 140 160 160 200 DISTANCE IN METERS 1. al BEACH PROFILES (re ee GLENEDEN BEACH - % (10) 16 March 1977 © -2 (Il). 2 April 1977 ee . ~, (12) 7 May 1977 - . ws 43 [ronge"5} (13) 3 June 1977 . (14) 23 July 1977 z . Erde ? Sy S 12 [renge™4] < -5p > WwW =| w -6 ah ee a a ae S> Nia [range] a8 1 L 1 Nl ef 1 n ay SSS si 1 [ie eae LS Ey ) 20 40 60 80 100 120 140 160 180 200 DISTANCE IN METERS Figure 3.10 A series of beach profiles obtained at Gleneden Beach, Oregon, illus- trating the seasonal variations on Northwest coast beaches (see fig. 3.9). There was considerable variation in the beach profiles along the length of the beach during May and June, as indicated by the different profile ranges included in the lower graph (1 meter ~1.1 yards). From Aguilar-Tunon and Komar 1978. as 8 feet (fig. 3.10), while the changes at Otter Rock amounted to less than 3 feet. In general, the coarser the beach sand (i.e., the larger the grains) the steeper the beach, and the more its profile changes in response to varying wave conditions. Coarser-grained beaches also respond to storms more rapidly than do finer-grained beaches—storm waves not only cut back the coarser beach to a greater degree, they also erode it at a much faster rate. The waves’ energy is concentrated in a smaller area on a coarse-sand beach, which has a narrower surf zone than a fine-grained beach, whose low slope causes the waves to break farther offshore. Therefore, the same amount of wave energy strikes a substantially smaller area on a narrow coarse-sand beach; the wide surf zone of the fine-sand beach acts to dissipate the energy. The greater response of coarser-grained beaches to storm waves is an im- portant factor in coastal erosion. Waves that strike a coarse-sand beach are able to cut rapidly through the beach to reach the land and buildings be- hind it. This points to the general role of the beach as a buffer between the 46 ocean waves and coastal properties. During the summer, when the dry beach is wide, the waves cannot reach beach properties, and erosion is not a problem. When the beach is cut back during the fall and early winter, how- ever, it progressively loses its buffering ability and property erosion is more likely. Generally speaking, a storm that strikes the coast in October, when there may still be enough dry beach to serve as a buffer, will do much less damage to property than a storm that strikes from November through March, when the dry beach has disappeared and cannot serve as a buffer. In fact, however, the extent of the remnant beach is extremely variable along the coast, as is the parallel threat of property erosion. This variability in the width of the dry beach is the result of patterns of the nearshore currents that assist the waves in cutting back the beach. We know much less about seasonal changes in the offshore sandbars, be- cause it is difficult to measure beach profiles all the way out through the breaker zone along this high-energy coast. The best information we have concerning the offshore bars on Northwest beaches comes from profiles ob- tained during World War II as part of preparations for landings in the Pa- cific and on the Normandy beachhead in France. The profiles were acquired using an amphibious vehicle that could cross the beach and go out through the breakers (fig. 3.11). This was a dangerous operation, and on one occa- sion a breaker heaved the vehicle onto its side with its wheels pointing out Figure 3.1! The surveying technique used to measure beach profiles in studies un- dertaken during World War II (employing an amphibious vehicle). From Bascom 1964. The Dynamic Northwest Coast 47 to sea (Bascom 1980). Fortunately, the next wave set it upright again without damage. Three amphibious vehicles were lost during the course of the study; two were lost in the surf and one rolled off a cliff and plunged 200 feet down into the sea. Amazingly, no one was seriously injured. Profiles were obtained for nine beaches on the Washington coast and six on the Oregon coast (Komar 1978a). Figure 3.12 shows a profile from Solando, Washington, revealing a system of three offshore bars. (The pro- files at other locations typically showed one to three bars.) When the profil- ing operation was repeated at Solando about three weeks later, the profile showed that the bars had grown and the troughs had deepened, probably in response to increased wave and current intensities. There was appreciable alongshore variation in the size and even occurrence of offshore bars, the re- sult of systems of nearshore currents and rip currents. Nearshore Currents and the Movement of Beach Sand Waves reaching the coast generate currents near the shore that are impor- tant to sand movements on the beach, and thus to erosion processes. These wave-generated currents are independent of ocean currents, which exist farther offshore and do not extend into the very shallow waters of the nearshore. Most of the time, waves along the Northwest coast approach the beach with their crests nearly parallel with the shoreline. Under such circum- stances the nearshore currents take the form of a cell circulation (fig. 3.13), with seaward-flowing rip currents being the most prominent feature. The rip currents are fed by longshore currents that flow roughly parallel with the shore, but only for short stretches. The currents of this cell circulation can move sand, and therefore can affect the beach’s shape. The longshore cur- Figure 3.12 Beach profiles from Solando, Washington, show three offshore bars, measured in 1946 with an amphibious vehicle, as shown in figure 3.12. From Komar 1978 a. DISTANCE (meters) 0 200 400 600 800 BEACH PROFILE SOLANDO, WASHINGTON Range 3000N y6 October 1946 ELEVATION (feet) ELEVATION (meters) 0 500 1000 1500 2000 2500 3000 DISTANCE (feet) 48 Cae) ie rat) . Saat ae { GD ors - oD ed sie a MAle \ ’ & RETURN FLOW Al S S + Va ‘ ¢ 4 —— I =e hs vA + LONGSHORE CURRENT. Ss : vs Figure 3.13 The nearshore cell circulation consists of seaward-flowing rip currents and longshore currents that feed water to the rips. From Komar 1997. rents hollow out troughs into the beach, which generally increase in depth as a rip current is approached. Rip currents can be very strong, cutting through the offshore bars to produce deeper water and a steeper but more uniformly sloping beach. They move sand offshore and erode crescent-shaped embayments into the beach. Aerial views of the beach typically show series of extremely irregular rip embayments of various sizes together with troughs cut by the longshore currents and rip currents (fig. 3.14). Rip current embayments sometimes extend across the entire width of the beach and begin to cut into foredunes and sea cliffs. Such rip embayments play a major role in erosion because they eliminate the buffering effect of the beach. Storm waves pass right through the deep water of the rip embayment and do not break and expend their energy until they reach the land behind the beach. Thus, a rip embayment may focus storm waves on a relatively small area (fig. 3.15). This type of erosion is commonly limited in extent to only 100 or 200 yards—the longshore span of a rip embayment that reaches the foredunes or sea cliff. When waves approach the beach at an angle rather than head-on, they generate a current that flows parallel to the shore. Even then, however, seaward-flowing rip currents may be present. The longshore currents, to- gether with the waves, transport sand along the beach in a type of move- ment known as littoral drift. This is more than a local rearrangement of the sand with an accompanying change in the shape of the beach. Littoral drift may displace sand hundreds of miles along a coast. On the Northwest coast, the waves tend to arrive from the southwest during the winter and from the northwest during the summer (corre- The Dynamic Northwest Coast 49 = Sr. Figure 3.14 The beach at Nestucca Spit, Oregon, photographed during low tide, showing the troughs and embayments eroded by longshore currents and rip cur- rents. sponding to the prevailing wind directions). As a result, there is a seasonal reversal in the direction of littoral drift; north during the winter, south dur- ing the summer. The net littoral drift is the difference between these north- ward and southward sand movements. Along most of the Oregon coast the net drift is essentially zero, at least if averaged over a number of years. This is demonstrated by the absence of continuous sand accumulation on one side of jetties or rocky headlands and erosion on the downdrift sides (Komar et al. 1976a). Patterns of sand accumulation and erosion on opposite sides of jetties (fig. 3.16, top) occur OCEAN Figure 3.15 Rip currents erode em- bayments into the dry beach and lo- breaking waves cally threaten prop- gan Zao ee erties backing the >= ne ae oe ~ spent eddies edge beach. eae dune ee Ca) ee pee Py SPIT endangered homes 50 OCEAN st Rese net littoral 7 Qe aw Ww drift © deposition wave crests erosion erosion \ deposition deposition Figure 3.16 Patterns of sand accumulation around jetties: top, the jetties are block- ing net littoral drift, and sand accumulates in the updrift direction and erodes downdrift of the jetty; bottom, there is no net littoral drift for the jetties to block. Jet- ties on the Oregon coast exhibit the latter condition. on coasts where there is a net littoral drift; for example, along the shores of southern California and most of the east coast of the United States. Jetties on those coasts act like dams to the longshore movement of beach sand, ac- cumulating sand on their updrift sides and causing erosion downdrift. This often causes major losses of beach and property. Jetties built on the Oregon coast, which has no net littoral drift, tend to accumulate sand on both sides (fig. 3.16, bottom). The accumulated sand comes from small-scale erosion of beaches more distant from the jetties, so that an overall symmetrical pat- The Dynamic Northwest Coast 51 tern emerges. The shoreline soon reaches a new equilibrium, so the erosion does not continue for very long. In sum, the Northwest coast is less likely than other coasts to experience major erosion and property losses due to the construction of jetties. One severe erosion problem did occur on the Oregon coast in direct response to jetty construction, however, and it led to the destruction of the town of Bayocean in the early half of this century (see chapter 5). The reason for the zero net littoral drift of sand along the Oregon coast is that the beaches are contained within pockets between rocky headlands that are large enough and extend into sufficiently deep water to prevent beach sand from passing around them (see chapter 2). The sand in each pocket beach is isolated within its cell. It may move north and south within its pocket in response to seasonal wind and wave directions, but the long- term net movement is zero. The one beach on the Oregon coast that does not fit the pattern of a zero- drift pocket is the Clatsop Plains, the shoreline that extends south from the Columbia River past Seaside to Tillamook Head. The plains were formed by the accumulation of sand derived from the Columbia River, a small part of which moves south until it is blocked by Tillamook Head. The bulk of the Columbia River sand moves northward along the coast of Washington. Most of it stays on the beaches just north of the Columbia River, but some continues farther north, in decreasing amounts, until beyond Copalis Head net erosion prevails. On many coasts, sand spits grow in the direction of the net littoral drift. The Long Beach Peninsula, which extends northward from the Columbia River, likely reflects the net sand movement along the Washington coast. It is unclear whether this northward growth has continued within historic times, however, because there have been many cycles of growth and erosion at the tip of the peninsula. Some of the shifts at the end of the spit have been caused by migrations of the entrance to Willapa Bay, which has pro- duced major erosion problems at Cape Shoalwater just north of the inlet (see chapter 6). There are a number of sand spits along the northern half of the Oregon coast; some point north, others point south. Those spits are located within the beach cells where zero net littoral drift prevails, and their directions do not provide testimony of net longshore sand movements. Tides along the Northwest Coast The oceanographer Albert Defant described tides as the “heartbeat of the ocean” (Defant 1958), an appropriate characterization of these rhythmic rises and falls, predictable and unexciting. Tides along the Northwest coast are moderate, with a maximum range of about 13 feet and an average range 52 TIDAL ELEVATIONS NEWPORT, OREGON (after Div. of State Lands) Tide Elevations (feet) M.L.L.W. 14.5 Extreme High Tide f ; 12.63 Highest i A Typical Day’s Tide ighest Measured Tide nha high | | | halle heal 71 \ tide FH c lower high 10.3 Highest Predicted Tide 8.38 Mean Higher High Water 7.62 Mean High Water 4.58 Mean Tide Level 4.51 Local Mean Sea Level 4.11 Mean Sea Level 1.54 Mean Low Water 0.00 Mean Lower Low Water lower lo | tide -2.9 Lowest Predicted Tide -3.14 Lowest Measured Tide “3.5 Extreme Low Tide Figure 3.17 Daily tidal elevations measured in Yaquina Bay on the mid-Oregon coast are typical of tides along the Northwest coast. From Hamilton 1973. of 6 feet. There are two highs and two lows each day, with successive highs (or lows) usually having markedly different levels. Tidal elevations are given in reference to the mean of the lower low water levels (abbreviated MiLw). Accordingly, most tidal elevations are positive numbers; only the extreme lower lows have negative values. In Yaquina Bay, Newport (fig. 3.17), the highest predicted tide is 10.3 feet MLLw and the lowest predicted low is -2.9 feet MLLw, giving a total range of 13.2 feet. When the moon, sun, and earth form a straight line in space (termed “syzygy’), their gravitational forces combine to produce the highest monthly tidal range, the spring tide. This alignment occurs at full moons and new moons, and spring tides thus occur each month. Once a year the moon makes its closest approach to the earth (termed “perigee”), and its gravitational attraction on the ocean reaches a maximum. The resulting perigean spring tide is accordingly the largest range of the entire year—this is the 13.2-foot maximum range for Yaquina Bay. When the earth, moon, and sun are not aligned, the net gravitational forces are reduced and the tidal ranges are lower. The lowest tidal range occurs when the moon and sun are at right angles with respect to the earth, so their tide-producing forces are in direct opposition and tend to cancel; this lowest tidal range of the month is called the neap tide. Tides are an important factor in coastal erosion because they govern the hour-by-hour level of the sea and hence the position of the shoreline and the zone where the ocean waves expend their energy. Spring tides, and espe- The Dynamic Northwest Coast 53 cially perigean spring tides, may bring water levels high up on sea cliffs and foredunes so that waves reach and attack coastal properties. High spring tides contributed to the breaching of Nestucca Spit, Oregon, in 1978 (see chapter 6) and are a significant factor in sea cliff erosion (see chapter 8). Tides also affect the currents in bays and estuaries. In bays such as Netarts and Willapa, which receive little freshwater flow from rivers, the tidal cur- rents are the sole factor keeping the inlets open to the sea. Water Level Fluctuations The measured water levels are usually different from those predicted by tide tables. Tidal computations are made using ideal conditions and consider only the gravitational forces of the moon and sun together with the influ- ence of the overall shape of the ocean basin. The “errors” in the tide table predictions result from other processes that act on water elevations, such as winds, atmospheric pressures, ocean currents, and water temperatures. On many coasts, the most significant water level changes are brought about by meteorological factors such as strong winds and changes in atmo- spheric pressure. When the wind blows toward the shore, water can pile up against the coast and reach levels above the predicted tides; offshore winds lower water levels. The stronger the wind and the longer its duration, the greater its effect on the water level. If the winds are part of a storm system, reduced atmospheric pressure is another contributing factor because storms are associated with low-pressure centers. The local reduction of at- mospheric pressure causes a “humping” of the water on the ocean surface, which acts as an inverse barometer. Together the winds and reduced atmo- spheric pressures of a storm can create a storm surge. As the name implies, this is a surge of water over low-lying areas of the coast, sometimes reaching levels several feet above normal. Storm surge is most dramatic during hur- ricanes and cyclones, and has been the cause of extreme destruction and loss of life along the east and Gulf coasts of the United States. Fortunately, storm surge has not been a significant problem in the Northwest. The rise in water level beyond that expected from tides amounts to only 6-12 inches on our shores (McKinney 1977). Although small, such increases in water levels may nevertheless intensify the processes of coastal erosion. Many of our beaches have very low slopes, and even a small vertical rise in the water level due to a storm surge can produce a significant landward shift of the shoreline—in some cases 50-100 feet—placing the water closer to beach properties and allowing ocean waves and currents to act more directly against the land. Water levels along the Northwest coast are consistently higher during the winter than in the summer (fig. 3.18). The average water levels may be any- where from 4 to 15 inches higher than expected from the tides alone, but 54 SEA LEVEL after Huyer et al. (1983) Newport, Oregon Sea Level (cm) Sea Level (inches) 1982 1983 Figure 3.18 Monthly variations in mean sea levels measured by the tide gauge at Newport, Oregon, illustrate the annual cycle, with higher water levels during the winter (10 centimeters ~ 4 inches). After Huyer et al. 1983. they are always greatest during the winter. The data shown in figure 3.18 were obtained from the tide gauge in Yaquina Bay on the mid-Oregon coast, determined by averaging the actual measured water levels. This aver- aging has the effect of removing the daily tidal fluctuations, so the averages given represent deviations from the worldwide sea level as well as from the tide level in Yaquina Bay during any given hour. A number of processes combine to produce the higher winter water lev- els, including storm surge (because onshore winds tend to be strongest in the winter) and seasonal variations in ocean currents and water tempera- tures. During the winter, the ocean currents off the Northwest coast flow primarily northward in response to the prevailing winds of that season. Al- though the dominant current direction is parallel with the coast, there is a component directed toward the shore, caused by the earth’s rotation. When a wind produces a current in the Northern Hemisphere, the flowing water tends to rotate slightly to the right of the wind’s direction (in the Southern Hemisphere the rotation is to the left). This onshore component of the northward current during the winter raises water levels along the shores of Oregon and Washington. In the summer the currents flow toward the south and the rotation is directed offshore, lowering the sea level along the coast. Another factor that contributes to the lower summer water levels is coastal upwelling produced by the offshore component of the ocean cur- rents, which moves the near-surface warm water away from the land. The warm water is replaced by cold water that moves up from the depths, with several consequences. When the cold water meets the warm air, fog is pro- The Dynamic Northwest Coast 55 duced. The cold water contributes to the lowering of ocean surface levels along the shore during the summer (fig. 3.18) because it is denser than the warmer water that covers most of the ocean. The ocean waves themselves raise water levels in the nearshore, an in- crease that is called wave setup. The energy of the waves approaching the beach is partly expended in causing the mean water level to slope upward toward the shore. The effects of the wave setup are maximum at the shore- line itself and are reduced to approximately zero at the breaker zone. The higher the breakers on the beach, the higher the setup above the horizontal still-water level (the level that the sea would have if there were no waves). The maximum setup at the shoreline is about 0.17 times the height of the offshore ocean waves (Guza and Thornton 1981; Holman and Sallenger 1985; Komar and Holman 1986). Accordingly, 10-foot waves will produce a setup of 1.7 feet, or 20 inches, at the shoreline. If a storm should increase the wave height to 20 feet, the setup elevation would be raised to 40 inches. A rise in setup can cause a significant landward migration of the shoreline. On a 1-in-50 beach slope, a 20-inch rise during a storm would move the mean shoreline landward by more than 80 feet. Wave Run-up and Sneaker Waves You might also expect storms to cause a considerable increase in the energy of the waves at the point where they swash up and down the beachface. But here nature has a surprise, at least on beaches with a low slope. Ocean waves directly generated by winds have periods less than 20 seconds. Therefore, the interval between successive breaking waves will be 20 seconds or less, as will the swash of the wave surf after the bores have crossed the beach and run up on the shore. But if we actually measure the swash run-up on a beach with a low slope under such conditions, we find that an increase in breaker heights does not produce the expected increase in swash energy and height at the shoreline (Guza and Thornton 1982; Holman and Sallenger 1985; Komar and Holman 1986). Why not? A wave breaks as it approaches the shoreline at a point where the depth of the water is approximately equal to the wave’s height; that is, a 10-foot wave will break in approximately 10 feet of water. Thus, if the offshore waves double in height during a storm, they break in water that is twice as deep, and roughly twice as far offshore. The surf bores now have farther to travel before reaching the shoreline, los- ing energy as they go. Thus, it seems clear that a doubling of the breaker heights will not double the swash run-up on the shore. At this point nature adds a further complication, however, one that is not fully understood. Even though the run-up of wave motions with periods less than 20 seconds does not increase significantly when breaker heights 56 increase, there is a considerable increase in run-up associated with water level motions having periods greater than 20 seconds. As the ocean waves approach the coast and break, all of their energy is contained within wave oscillations that have periods less than 20 seconds. But somehow that en- ergy is transferred to longer-period motions within the surf zone; it is the mechanism of this energy transfer that is poorly understood. The swash run-up related to these longer-period cycles does depend directly on the offshore breaker heights and energy, so it is clear that normal ocean waves are at least indirectly the source of this energy. The long-period cycles are observed as horizontal movements of the mean shoreline, especially during storms: the shoreline slowly migrates up the beach, reaches a maximum landward position, and then slowly shifts seaward, only to return again. The entire cycle may take 2-5 minutes. Su- perimposed on that cycle is the swash of the incoming wave bores that have the shorter periods of regular ocean waves (i.e., less than 20 seconds). Ac- cordingly, the zone of wave swash and run-up migrates slowly back and forth across the beach. This is the process that creates “sneaker waves,” so called because they sneak up and suddenly drench a person walking along the beach. You may be on what you think is the dry part of the beach, well above the action of the wave swash. But the long-period motions cause the water’s edge to shift slowly landward, and if there is suddenly a larger-than-average wave bore, you may abruptly be overtaken by the combined run-up—you have experi- enced a sneaker wave. The consequences can be serious. The water may suddenly be up to your knees or deeper, accompanied by strong currents and wave swash. The danger to children is obvious. Some people try to es- cape the water by jumping atop a drift log, only to have the waves roll the log over them. Lives have been lost in this way. Tsunami: The Extreme Coastal Hazard There is one type of destructive wave that is not generated by winds: the tsunami, often incorrectly called “tidal wave” (tsunamis have nothing to do with tides). Tsunamis are produced by a displacement of the seafloor by an earthquake, explosive volcanic eruption, or submarine landslide. The sud- den upward or downward movement of a portion of the seabed momen- tarily raises or lowers the overlying water surface. That disruption then travels outward from its site of origin as a series of waves moving at veloci- ties of 350-500 miles per hour. In the deep ocean these waves are small, typically less than 3 feet, too small to be noticed as they pass beneath a ship. But tsunamis have very long periods; the time between successive waves in a series is 10-20 minutes. One effect of this long period is that tsunamis “feel” The Dynamic Northwest Coast 57 the bottom as soon as they reach the continental shelf. The shallower water slows their rate of movement, which causes their heights to progressively in- crease. As the tsunami waves cross the wide continental shelf, they get higher and higher, until at the shore itself they may achieve heights up to 50 feet. Their breaking and swash on a sloping beach can carry water far be- yond the normal reach of the ocean. The first sign of an impending tsunami is often an unusual and sudden lowering of the water level along the shore. Basically, this low water is a trough between the crests of the tsunami waves. Each wave is separated Figure 3.19 Heights of tsunami waves measured within bays and estuaries along the Northwest coast on March 28, 1964. The solid line shows the approximate loca- tion and time of the tsunami wave front; the dashed lines show the approximate lo- cations and times of the spring tide crest. From Wilson and Torum 1988. 124° Ww 122°w 120° W fe ’ Jf VICTORIA NEAH BAY ~ 4.7(R)) LEGEND i“ ome APPROX. LOCATION & TIME LAPUSH-5.3(R) OF TSUNAMI WAVE FRONT ‘ u \ 4 EVERETT ——— APPROX. LOCATION & TIME 48°N BREMERTON CAPE FLATTERY,, FRIDAY HARBOR - 2.3(R) HOH R.-1.7(R) | OF CREST OF SPRING TIDE \ \ SEATTLE - 0.8 (F) 2.3(R) FIGURES ARE HEIGHTS (in ft) wal OF MAXIMUM TSUNAMI WAVE TAHOLAH - 2.4(R) BASED ON RISE (R) OR a CREEK -14.9(R ) FALL(F) ABOVE TIDE LEVEL Fa DATA FROM SPAETH AND \ t \ BERKMAN, |967, SCHATZ, abl SHORES 9.7(R ) of of, 1964, HOGAN, et of, 1964 U.S. COAST GUARD GRAYS. HARBOR WHIPPLE @ LUNDY, 1964, wiapa BAY T° SEAVIEW -12.51R) Wks 2. TIDE CREST | WASHINGTON ° ° \ \ Ve \ {7 ooo-| 0900 & !030_ COLUMBIA = RIVER WAVE HEIGHT ABOVE MEAN HIGH WATER TSUNAMI FRONT ---| 46°N ———_—— NEHALEM R R 28, 1964 EN: YAQUINA BAY mire ee eee SIUSLAW R fice wolf? ssl ng cmp EUGENE ° UMPQUA R 4aeN coos BAY ae eee ee | COQUILLE R. fe es ee o7 os 09 10 W 12 13 TIME IN HOURS — G.M.T. MARCH 286, 1964 < = e = o ° o | l 08 e FOLEDO coRVALLIS OREGON 42°N CALIFORNIA 58 from the one preceding it by such a low. Just as it would be extremely un- wise to stay on the beach when such a sudden lowering occurs, so it is also not advisable to rush out onto the beach after the first wave to see the re- sulting damage. Most of the significant tsunamis that reach the Northwest coast are caused by earthquakes in and around Alaska. Two struck our shores during the 1960s—on March 28, 1964, and May 16, 1968 (Schatz et al. 1964; Schatz 1965; Wilson and Torum 1968). Figure 3.19 shows the heights of the tsuna- mis during the 1964 event as measured on tide gauges in several bays; unfor- tunately, no measurements are available for the open coast, where the wave heights undoubtedly were much greater. Each location experienced a series of waves, and the first was not necessarily the largest (fig. 3.19). Maximum wave heights in the bays and estuaries reached approximately 10 feet, an ex- tremely high level for those sheltered environments. The 1964 tsunamis damaged bridges and dwellings along the shores of the Necanicum and Neawanna Rivers where they flow through Seaside, Or- egon; the cost of the damage was assessed at $276,000 (Wilson and Torum 1968). Other hard-hit areas were Cannon Beach ($230,000), Waldport on Alsea Bay ($160,000), Florence ($50,000), and Coos Bay ($20,000). Fortu- nately, there were few reports of destruction along the open-ocean shores of Oregon and Washington during the 1964 and 1968 tsunamis. Four children were drowned as their family slept on the beach at Beverly Beach State Park in Oregon when the 1964 tsunami struck. Greater damage occurred at Cres- cent City in northern California. During the 1964 tsunami, one wave washed about 500 yards inland, destroying 29 blocks of the business district and causing some $29 million in damage. However great, those impacts are substantially smaller than those that have been experienced in Japan, Ha- wali, and Alaska, which are periodically devastated by tsunamis. Hanging over the Northwest coast is the threat of a truly catastrophic tsu- nami that could be generated by a local subduction earthquake. As dis- cussed in chapter 2, there is firm evidence that a major subduction earth- quake occurs immediately offshore every few hundred years. These must generate tsunamis of awesome proportions. The main evidence that such events have transpired lies in the layers of sand carried inland from the beaches. Dr. Curt Peterson of Portland State University has examined such layers at several sites. Figure 3.20 shows his map tracing the surge of the tsu- nami that occurred about 300 years ago (in the year 1700) as it moved up into Yaquina Bay (Peterson and Priest 1995). The main path of the giant waves was along the length of the bay and up the river; sand layers attribut- able to those waves have been found as far upriver as Grassy Point, 8 miles from the mouth of the bay. The flows also surged up side channels as the tsunami passed through the bay (fig. 3.20). Even elevated areas are not safe from inundation by tsunami waves asso- The Dynamic Northwest Coast 59 Figure 3.20 Map of Yaquina Bay showing the path followed by the tsunami surge generated by the subduction earthquake in 1700. Evidence of this penetration comes from layers of beach sand that covered marshes. From Peterson and Priest 1995. ciated with subduction earthquakes. Cores drilled by Dr. Peterson through- out the city of Cannon Beach reveal the existence of a sand layer that was laid down by the 1700 tsunami. The layer extends inland to at least Highway 101 east of the city, evidence that the run-up of the tsunami and its destruc- tive impacts can reach more than a mile inland even when passing over el- evated areas. An early warning system assesses whether or not earthquakes in such dis- tant areas as Alaska and Japan have the potential to generate tsunamis. The system’s predictions are not absolute, however, and there is usually a wait- and-see period before it can be established that destructive waves have actu- ally formed. The system provides adequate warning time for people to evacuate beaches and other low-lying areas, but it also has the opposite ef- fect: people flock to the coast to see the giant waves. After a recent warning the roads were clogged by thousands of cars carrying people from the valley to the Oregon coast. Fortunately, it turned out to be a false alarm. Such false alarms may create a “cry wolf” syndrome and make people less responsive to warnings and less heedful of the danger, even in areas that have been dev- astated by tsunamis in the past. People can be evacuated from areas threatened by a tsunami, but their homes and possessions remain in the zones of potential destruction. Since the last tsunami in 1968, there has been a great deal of construction on the 60 Northwest coast. Many more homes now line ocean beaches and the shores of bays and estuaries. It can be expected that future tsunamis will cause considerably more property losses than in 1964 and 1968. Many communities have developed local warning systems and evacua- tion routes to prepare for future tsunamis associated with subduction earthquakes. The earthquake itself will, of course, provide the first warning. People who live in hazardous zones must be made aware that the earth- quake will likely be followed by a tsunami. The first wave can be expected to arrive 10 to 20 minutes after the quake. Summary The Northwest coast is shaped by powerful ocean and beach processes. Winter storms generate huge waves that combine with rip currents to erode beaches and attack coastal properties. The wave swash at the shore is the biting edge of the sea, the area where the conflict between the ocean and land reaches a maximum. During the winter the zone of wave swash moves landward due to a number of processes that combine to raise water levels in the coastal zone. This inland movement can bring erosion processes di- rectly up against sea cliffs and the foundations of buildings. Examples of the resulting problems are examined in later chapters. The most fearsome force of nature threatening the Northwest coast is the tsunami. In 1964 and 1968, tsunamis generated in Alaska caused some dam- age in Oregon and Washington, although the most extensive damage oc- curred in Crescent City, California. Extreme tsunamis generated by subduc- tion earthquakes immediately off the coast have struck the Northwest coast in the past and pose the greatest threat to the coast in the future. The Dynamic Northwest Coast 61 T ) eur ue en wir rere nigh vale love ss eo! 65 The¢i-1 ‘iP eig if pyoel 9 ° riot: i gute a heer, a Oar i ae Be) A! Y ei. oo ibm ” ques 4 The Arrival of Man—Erosion Becomes a Problem For countless ages the Northwest coast remained untouched by humans. The Pacific waves crashed against the high cliffs and sandy beaches, ob- served only by the abundant seals and sea lions that frequented the shoals of bays and ocean beaches. Their existence must have been idyllic until the day about 10,000 years ago that human beings first walked the shores of the Northwest coast. They were Asians from what is now Siberia, hunters who crossed over to Alaska on the land bridge that emerged when sea levels fell during the last ice age. It is possible that humans first arrived on the Northwest coast in pursuit of game—not necessarily deer or elk, but larger game, the now-extinct mastodons. In the summer of 1977, a farmer near Sequim, on the south shore of the Strait of Juan de Fuca, turned up tusks and bones from a mast- odon with his backhoe (Borden 1979). Firmly stuck into one of the ribs was the broken tip of a sharpened bone projectile, a clear indication of the pres- ence of big-game hunters. Radiocarbon analyses of plant material from the site established that this ancient hunt took place about 12,000 years ago, soon after the glaciers had withdrawn from the strait. The oldest material associated with Indians in what is now Oregon and Washington was found inside Fort Rock Cave in eastern Oregon and has been dated at about 13,000 years before the present. Still older material, dat- ing back 15,000 years, has been found in Idaho. This supports archaeolo- gists’ hypothesis that the Indians moved down into the Northwest from Alaska by first moving eastward to skirt the still glaciated mountains. Ac- cordingly, the general view is that the interior was settled first, the banks of the Columbia River next, and the coast last. The oldest dated Indian mate- rial found on the coast is about 8,000 years old. That age may be mislead- ing, however, because earlier occupation sites directly on the coast would now be covered by the ocean, which rose at the end of the ice ages. The Native Americans must have lived a reasonably carefree existence be- fore Europeans arrived in the Northwest. Food was plentiful—berries and game on the land, salmon and shellfish in the sea. The native people used cedar for almost all of their material needs: clothing, shelter, utensils, con- tainers, and their superb canoes. They lived in small villages of plank houses, generally on the shores of estuaries and streams rather than on open-ocean beaches. The coastal Indians were animists who believed that all things—rock and tree, animal and man—were imbued with spirit. And with this living world the Indians lived in close communion. It is uncertain when Europeans first appeared on the Northwest coast, or even who they were. The first explorers probably arrived during the six- teenth century, and they probably were Spanish. Many historians credit a Spanish expedition that sailed in 1542 from Navidad, Mexico, under the command of the Portuguese explorer Joao Rodrigues Cabrilho (Juan Rodriguez Cabrillo in Spanish). Following Cabrilho’s death, the expedition was directed by the pilot, Bartolomé Ferrelo. It is believed that they reached the vicinity of the Rogue River in the spring of 1543. They were prevented from landing, however, by storms so severe that the crew was assembled to make their last confessions. Other explorers followed. One was the Greek mariner Valerianos, who sailed under the Spanish flag as Juan de Fuca. His course took him along the coast of New Spain and California, and he claimed to have sailed as far north as latitude 47 degrees, where he found the broad inlet to the sea that now bears his name. He saw people clad in animal skins and decided not to land. The Spanish did not attempt to lay permanent claim to this new land. Their search for gold and wealth drew them instead toward the west, across the Pacific to the Philippines. For nearly 300 years there was extensive travel and trade between Spain’s possessions in Mexico and the Philippines. The course followed by the great galleons was generally south of the latitudes of Washington and Oregon, but occasionally ships were blown off-course to the north. One of them, believed to be the San Francisco Xavier, wrecked at the base of Neahkahnie Mountain on the north Oregon coast, spilling its cargo of beeswax, remnants of which are still sometimes found on the nearby beaches. It is almost certain that Spanish treasure lies somewhere off the Northwest coast, perhaps buried deep within the beach sand, but none has ever been found. The Spanish were not the only seamen to wash up as castaways on the shores of the Northwest coast, and they may not have been the first. Some castaways originated in the Orient, from China, Taiwan, and Japan. In their book Ten Years in Oregon, published in 1844, missionaries Daniel Lee and Joseph Frost wrote: “About 30 or 40 miles to the south of the Columbia are 64 the remains of a vessel which was sunk in the sand near shore, probably from the coast of Asia” (quoted in Gibbs 1978). During a trip along that stretch of coast in 1848, Sol Smith and John Hobson reported seeing “sev- eral pieces of a junk” which they concluded was Chinese. Dozens of Asian junks have been found wrecked or adrift off the Northwest coast, and many were undoubtedly carried ashore, much as glass floats originating in the Orient still arrive during winter storms (Weber 1984; Plummer 1991). Perhaps the most intriguing of the stories of Asian visitors is the Indian legend that about 500 years ago, just before Columbus discovered the New World, an old Chinaman survived the wreck of his junk on the shores of Oregon (Plummer 1991). The legend relates that he enlisted “bad” Indians, who pillaged and plundered one native village after another along the coast. The fierce Asian brought with him knowledge of how to make and wield weapons of metal, which were used with frightening results on their vic- tims. Whether or not this legend is true, it foretold the later arrival of Euro- peans with their vastly superior capacity to wage war and subjugate the In- dians. Exploration of the Northwest coast began in earnest in the last quarter of the eighteenth century. Some of the explorers were still searching for the Northwest Passage, the mythical route that supposedly connected the At- lantic and Pacific Oceans and would provide a direct sea route from west- ern Europe to Asia. However, the new objective was “the great river of the west,’ sometimes called the “Oregon” but now known as the Columbia (Nokes 1991). In August 1775, the distinguished Spanish explorer Bruno de Heceta located the river’s mouth, but his crew were too weakened by scurvy to handle the sails and cross the bar. Two years later, the English mariner James Cook passed the river mouth unknowingly during a stormy night. He was followed in 1778 by his countryman John Meares, who concluded that there was no river at all, and so named its estuary Deception Bay and its northern promontory Cape Disappointment. While surveying the Northwest coast in 1792, Captain George Vancouver passed the river’s mouth. Although he noted the presence of earth-colored water, drifting logs, and cross currents, he wrote in his log, “Not considering the opening worthy of more attention I continued our pursuit to the N.W.” (quoted in Nokes 1991). The Columbia River was finally found in 1792 by an American, Captain Robert Gray, on his second voyage to the Oregon coast. The American mer- chants of New England were anxious to trade with the Chinese, but they produced little the Chinese wanted. However, they had heard that Russian and British traders earned great profits by selling Northwest furs in the Ori- ent. In October 1787, Captains John Kendrick and Robert Gray were sent out from Boston with a cargo of beads, cloth, and bits of iron and copper to The Arrival of Man 65 trade for sea otter pelts. The pelts were sold in China, and the money used to buy tea and perhaps silk and spices. Having completed these transac- tions, Gray set sail for Boston, the first American to circumnavigate the globe. ; On his second voyage to the Northwest coast, Captain Gray found him- self off the mouth of a great river. Like Vancouver, he noted a large flow of muddy water fanning out from the shore. Even more so than now, the Co- lumbia bar was one of the most treacherous on earth. At eight o'clock in the morning of May 11, 1792, after waiting several hours for the right combina- tion of wind, tides, and currents, Gray gave the command and his ship, the Columbia Rediviva, crashed through the breakers and entered the Great River of the West. The Columbia River was finally discovered. The next major thrust of exploration came from inland. On November 15, 1805, after an arduous 19-month journey, Meriwether Lewis and William Clark reached the Pacific Ocean at the mouth of the Columbia River. There they passed a miserable winter in a small log stockade, Fort Clatsop, built on a low hill above a bog and tidal creeks. It rained every day but six. There was much sickness—colds, dysentery, and rheumatism—and the men were plagued by fleas. Food was scarce. On Christmas they celebrated with “pore Elk, so much Spoiled that we eate it thro mear necessity, Some Spoiled Pounded fish and a fiew roots” (quoted in O’Donnell 1988). In spite of the adversity they faced, Lewis and Clark recorded a detailed account of the ge- ography, fauna, and flora; they returned east with reports that this was a place suitable for settlement. The first permanent community established by white men on the North- west coast came soon after the departure of Lewis and Clark, and at the same locality—Astoria, on the south bank of the Columbia about 4 miles upriver from the mouth. John Jacob Astor was a German immigrant who had achieved the American dream of acquiring great wealth. One of his ideas was to establish a fur-trading center at the mouth of the Columbia. The furs brought in by Indians would be shipped out and sold in the Ori- ent. In theory the idea was a good one, but in practice it was a disaster. Two contingents were sent to establish the post, one by land, the other by sea. The Tonquin was captained by Jonathan Thorn, who turned out to be a psychopath. Due to his madness, eight men died while crossing the Colum- bia bar. It must have been something of a relief to everyone when Thorn was killed a few months later by Indians on Vancouver Island after he struck their chief. The overland contingent also was plagued by disaster. They be- came lost in the uplands of the Snake River and were reduced to eating their moccasins. Matters did not improve much on their arrival at Astoria. They first had to clear a site for the trading post, and many of the trees in the surrounding 66 forest were 50 feet in girth. After two months, barely an acre had been cleared, two men had been badly injured by falling trees, and one had blown his hand off; three of the company had been killed by Indians. In June 1812 the United States declared war on England. In the expectation that the British would arrive at any moment to seize the post, it was wisely sold to the British-owned North West Company. In December 1813 the Stars and Stripes came down and Astoria became Fort George. The British domi- nated the area for the next three decades, but a negotiated agreement even- tually returned the mouth of the Columbia to the United States. The arrival of white men inevitably meant the demise of the native in- habitants. Europeans brought disease, whiskey, guns, greed, and superior power. Disease was the first to strike, and it is certain that it arrived well be- fore white men physically reached these shores in significant numbers. Some anthropologists and historians believe that the native population had already been reduced by half before Europeans arrived on the scene. The noted botanist David Douglas described the impacts of disease on the Indi- ans, although at a much later date. During a visit to Clatsop County during October 1830, Douglas recorded the following entry in his journal: “A dreadfully fatal intermittent fever broke out in the lower parts of this river (the Columbia) about eleven weeks ago, which had depopulated the coun- try. Villages which had afforded from one to two hundred effective warriors are totally gone; not a soul remains. The houses are empty and flocks of famished dogs are howling about, while dead bodies lie strewn in every di- rection on the sand of the river” (quoted in Gibbs 1978). As white men arrived in increasing numbers, massacre as well as disease decimated the populations of Native Americans. An Indian agent recorded in his journal on February 5, 1854, that a most horrid massacre, or rather an out-and-out barbarous mass murder, was perpetrated upon a portion of the Nah-so-mah band re- siding at the mouth of the Coquille River on the morning of Jan. 28, by a party of 40 miners. The reason assigned by the miners by their own statements, seem trivial. However, on the afternoon preceding the murders, the miners requested the chief to come in for a talk. This he refused to do. Thereupon the whites at and near the ferry-house as- sembled and deliberated upon the necessity of an immediate atack upon the Indians. A courier was sent to the upper mines, some seven miles to the north, for assistance. Twenty men responded, arriving at the ferry house in the evening proceding the morning massacre. At dawn on the following day, led by one Abbott, the ferry party and the 20 miners, about 40 in all, formed three detachments, marched The Arrival of Man 67 upon the Indian raches and consumated a most inhuman slaughter, which the attackers termed a fight. The Indians were aroused from sleep to meet their deaths with but a feeble show of resistance; shot down as they were attempting to escape from their houses. Fifteen men and one squaw were killed, two squaws badly wounded. On the part of the white men, not even the slightest wound was received. The houses of the Indians, with but one exception, were fired and entirely destroyed. Thus was committed a massacre too inhuman to be readily believed. (Quoted in Gibbs 1978) In spite of such blatant atrocities, the Indians were slow to seek revenge, perhaps recognizing the hopelessness of their situation. Finally, on the night of February 22, 1856, the Indian tribes in the Rogue River area rose in desperation and went on the warpath. Practically every home inhabited by white settlers in Curry County was burned to the ground; many were killed. The Rogue River War of 1855-56 was a significant uprising of Northwest coastal Indians, but it came too late. It was soon put down by American troops, and the Indians who survived were herded onto reservations, whether or not they had participated in the uprising. The disease and killing went on for more than a century, almost obliter- ating the native people from the Pacific shores. Their former existence is re- Figure 4.1 Early settlers on the Northwest coast lived initially in log cabins. From the Oregon Historical Society, Portland. Newport, Oregon. Figure 4.2 The initial settlement of Newport occurred along the shores of Yaquina Bay. Courtesy of Betty Troxel, Newport, Oregon. corded in the geography of the Northwest coast: Yaquina, Siletz, and Willapa are derived from the names of Indian tribes. Their presence is also recorded in the great mounds of their shell middens—little evidence of a people who lived in relative peace in a plentiful land for thousands of years. With the Indians out of the way, settlement by Europeans began in ear- nest. The first homes were crude cabins built of readily available logs (fig. 4.1). These were later replaced by more elegant dwellings. It is sometimes difficult to believe that all the development we see on the coast today— homes, shops, roads, bridges—has come about within the last 100-150 years. For example, attention was first drawn to Yaquina Bay in 1852 when the schooner Juliet was wrecked on the nearby ocean shore (Price 1975) and rescue attempts dramatized the bay’s potential as a harbor. Settlers were slow to come to the area, however, and it was not until 1875 that the first plat was filed for the city of Newport. It covered a small area along the wa- terfront of Yaquina Bay, the present-day “old town” (fig. 4.2). During those formative years the town’s day-to-day activities centered on the bay, and the same was true in towns and villages all along the coast. “Summer people” began coming to the coast as early as the 1860s, arriv- ing either by boat or by wagon on muddy roads that crossed the Coast Range. Like tourists today, they were drawn to the ocean beaches, where they set up tents and stayed for much of the summer. In Newport, the camping centered on Nye Beach (fig. 4.3). Completion of the railroad be- tween Corvallis and Yaquina City in 1885, with ferry service to Newport, greatly increased the numbers of summer people. The Arrival of Man 69 F - QREGUINV. -7ee- Figure 4.3 Many of the “summer people’ visiting Newport at the turn of the cen- tury stayed in tents along the shore at Nye Beach. Courtesy of Betty Troxel, New- port, Oregon. Figure 4.4 As the number of visitors to Nye Beach grew, more permanent and comfortable accommodations were built, including a hotel and a sanatorium that provided hot seawater baths. Courtesy of Betty Troxel, Newport, Oregon. 70 Figure 4.5 The Burton expedition in July 1912 was the first automobile trip from Newport to Siletz Bay (see Stembridge 1975a). That arduous trip took 23 hours; to- day the 47-mile distance is easily covered in less than an hour. From the Burton Col- lection of the University of Oregon, Eugene. The growing interest in beach recreation inevitably led to the construc- tion of permanent buildings along the ocean shores. The tents at Nye Beach gave way to cottages and cabins, and stores were constructed to serve the growing community (fig. 4.4). In 1901 a bathhouse was built close to the shore at Nye Beach; the next year a sanatorium featuring hot seawater baths was constructed. And so went development all along the Northwest coast. The railroads completed in the late 1800s facilitated east-west travel be- tween the coast and the inland valley. North-south movement along the coast remained extremely limited, however, and coastal communities were isolated except for uncertain boat traffic between the bays or travel along the beaches at low tide. The problem of movement along the coast is illus- trated by the Burton “expedition” of July 1912, which took 23 hours of ardu- ous travel in a Flanders “20” car to cover the 47 miles between Newport and Siletz Bay (fig. 4.5; Stembridge 1975a). The eventual construction of High- way 101 along the coast was done piecemeal. The building of the Roosevelt Coast Military Highway began in 1919 with projects in Tillamook and Curry Counties (Boxberger and McFeron 1983). The section through Lincoln County was completed in 1922, but it was not possible to traverse the entire length of the coast on a quality road until 1932. Even then the numerous bays and estuaries had to be crossed on ferries. The magnificent bridges we The Arrival of Man 7I Figure 4.6 As indicated by the handwritten caption on this photo taken at Barview, at the entrance to Tillamook Bay, even early development along the coast was affected by erosion. From the Pioneer Museum, Tillamook, Oregon. use today were completed during the 1930s. Only at that stage was the coast fully ripe for development. The processes of wave erosion were readily apparent even in those early days of settlement (fig. 4.6), and it was inevitable that erosion would con- flict with the growing pressure to develop land adjacent to the beaches. Houses, hotels, and roads inevitably were lost to the waves of winter storms. It might be a natural process, but coastal erosion did not fit in with human plans for development, and accordingly it became a “problem.” 72 5 The Development and Destruction of Bayocean Spit In 1906, T. B. Potter traveled from Kansas to Portland, Oregon, on vacation. Potter, a real estate promoter, had made a fortune as the head of the T. B. Potter Realty Company, which had offices in Kansas and San Francisco. In Portland he inquired about good places for fishing and hunting, and was advised to travel to Tillamook Bay on the coast (fig. 5.1). He found a large, beautiful bay teaming with fish and waterfowl. Beyond it lay a 4-mile-long peninsula covered with dunes and forest. Along its edge a wide, sandy beach met the surf of the Pacific Ocean. Potter’s business instincts were aroused, and he vowed to develop the “Atlantic City of the Pacific Coast.” Potter’s vision was the opening chapter of the first, and still the grandest, attempt at development on the Northwest coast. It was to meet with trag- edy, first in the form of economic problems, and subsequently in the form of catastrophic erosion that ultimately led to the destruction of his resort. The Development of Bayocean Park The initial settlement of the Tillamook area had occurred less than a half century before Potter arrived there. Tillamook County deed records show land claims for portions of the peninsula, later to be called Bayocean Spit, dating back to 1867. One of the early landholders was A. B. Hallock, who constructed a wharf and warehouse on the bay side of the spit. In April 1891, Hallock established a post office in his home, primarily to serve the personnel at the Cape Meares lighthouse. He called his small holdings Barnegat, after a popular Atlantic coast resort. Alight with his vision to establish an elegant resort on the spit, Potter re- turned to Portland and teamed up with H. L. Chapin to form the Potter- Chapin Realty Company. Potter purchased much of the spit, and in 1907 he submitted a plat map to Tillamook County. The map is an impressive dis- play of some 3,000 lots, each 50 by 100 feet. Lots were to be priced from = 1 S \ © north jetty \ ES 1914-17 \ & \ N w° south jetty Geribaldi 1974 v2 Ke ° | 2 miles ———— nt ° | 2 3km Bayocean Spit aS af ms G6 UG = ie) is 6 = a 2 rs ac 2 5 @ ac Z4 ac 2) S s “y 3 ir 3 0 < x x =x ui 2 uu fae 2a oO 0 1 1 0 0 AUG SEPT OCT NOV DEC JAN FEB MAR APR 1982 1983 Figure 7.4 Wave breaker heights derived from the seismometer system at New- port, Oregon, during the 1982-83 El Nino (1 meter ~1.1 yards). From Komar 1986. seasonal variations, and the dashed lines give the previous maxima and minima measured at Newport. As discussed in chapter 3, these curves in part reflect the normal seasonal cycle of sea levels produced by parallel variations in atmospheric pressures and water temperatures. However, it is apparent that the 1982-83 sea levels were exceptional, reaching some 10-20 centimeters (4-8 inches) higher than previous maxima, about 35 centime- ters (14 inches) above the average winter level. Most of this unusually high sea level can be attributed to the effects of a coastal sea level wave arriving from the equator. Similar extreme sea levels occurred along the coast of California at the same time and were important causes of the erosion at Malibu Beach and other coastal communities (Flick and Cayan 1985). Wave conditions on the Oregon coast were also exceptional during the 1982-83 El Nifio (Komar 1986). Measurements from the seismometer at Newport (fig. 7.4) collected daily from August 1982 through April 1983 show that several storms generated high-energy waves, with three achiev- ing breaker heights on the order of 6—7 meters (20—25 feet). Breaker heights of this magnitude are rare in the Northwest; they occur on average only about every two years. It is therefore not surprising that extensive erosion took place during the winter of 1982-83. The unusual severity of the 1982-83 storms illustrates the fact that there is more to El Nino than a decline in the trade winds at the equator and fish kills off Peru. In fact, as residents of the Northwest learned firsthand, El Nino represents a major disturbance of meteorological and oceanographic conditions throughout the Pacific. Also associated with the 1982-83 El Nino were droughts in Australia and floods in the United States and in the Peru- The 1982-1983 El Nino 121 vian desert. The high-altitude jet streams narrowed and intensified, and spun off cyclonic storms over the Pacific that were stronger than usual. The jet streams were also farther south than normal, so the storms crossed the North American coast in southern California rather than passing over the Northwest, giving places like Malibu Beach a taste of wave energies to which they are not accustomed. The erosion that occurred on the Oregon coast during the 1982-83 El Nino was in response to these combined processes. The large storm waves that struck the coast arrived at the same time the sea level was approaching its maximum (figs. 7.3 and 7.4). High spring tides were also a factor. During the December 1982 storm, high tides reached +11.0 feet MLLW, 23 inches higher than the predicted tide, due to the raised mean sea level. The tides during the January 1983 storm were still more impressive—+12.4 feet, 34 inches higher than predicted. This pattern continued during the February 1983 storm, when high tides up to +10.3 feet—17 inches above the predicted level—were measured. These tides were exceptional for the coast of Oregon, where a spring-tide level of +9.0 feet is normal (chapter 3). CAPE FOULWEATHER Figure 7.5 Beach erosion and sand accumulation along the central Oregon coast resulting from the Rock. Horthward transport of sand during the 1982-83 El Nino Sand accumulation and shoreline buildout. <-> (1 kilometer ~ 0.6 mile). From Komar 1986. BEVERLY BEACH 1982-83 longshore sand transport Sand losses with ———> beach erosion = la Sand accumulation with shoreline buildout and dune development YAQUINA HEAD AGATE BEACH 122 Responses of Oregon Beaches to El Nino As expected, the intense storm activity and high water levels during the winter of 1982—83 cut back the beaches of the Northwest coast. However, for a time the patterns of erosion were puzzling. There were numerous reports of erosion along the coast, yet beaches in some areas clearly were building out. It took some time to determine what was happening. Normally, summer waves approach the coast from the northwest and winter waves arrive from the southwest, so there is a seasonal reversal in the direction of sand transport along the beaches. As discussed in chapter 3, most of the Oregon coast consists of a series of large littoral cells, pocket beaches separated by headlands. Over the long term there is something of an equilibrium between the north and south sand movements within any pocket, yielding a net littoral drift of zero. This equilibrium condition was upset during the 1982-83 El Nifio as a re- sult of the southward displacement of the storm systems. The waves ap- proached the Oregon coast from a more southwesterly direction, and this together with the high wave energies of the storms caused an unusually large northward movement of sand within the littoral cells (fig. 7.5). The result was sand erosion at the south end of each pocket beach and sand ac- cumulation at the north end. In other words, the pocket beaches reoriented themselves to face the waves arriving from the southwest, and each head- land acted like a jetty, blocking sand flow south of it and causing erosion to its immediate north. Figure 7.5 illustrates this pattern for the littoral cell be- tween Cape Foulweather and Yaquina Head. Directly north of Yaquina Head the beach eroded down to bedrock, while south of the headland, at Agate Beach, so much sand accumulated that it formed a large dune field (fig. 7.6). Residents of areas north of the headlands, at the south ends of the pocket beaches, experienced some of the greatest beach and property losses that occurred during the 1982-83 El Nino. The beaches eroded far more than during normal winters, with the sand moving not only offshore into bars but also northward along the shore. Once the fronting beaches lost their sand buffer, properties north of headlands were exposed to direct at- tack by storm waves, often suffering further large erosional losses. Alsea Spit Erosion The area that experienced the greatest erosion during the 1982-83 El Nino was Alsea Spit on the central Oregon coast (fig. 7.7). Erosion there was mainly in response to the northward longshore movement of beach sand, which deflected the inlet leading into Alsea Bay (Komar 1986). Although the problem originated during the 1982-83 El Nino, the erosion continued for several years as a result of the disrupted inlet. The 1982-1983 El] Nino 123 Figure 7.6 Sand level changes north and south of Yaquina Head (fig. 7.5). The beach north of the headland (top) was totally depleted of sand while large quanti- ties of sand accumulated to the south at Agate Beach (bottom). A 1978 photograph of Alsea Spit (fig. 7.7) shows the spit in the early stages of development; streets had been installed, but large-scale home construc- tion had not yet begun. The photo illustrates the normal configuration of the spit and inlet, with a narrow mouth to the far south pushed against a rocky portion of the mainland. Alsea Spit appeared to have been relatively stable over the preceding years (Stembridge 1975b), and there was little no- ticeable change in its morphology before the 1982-83 El Nino. 124 Figure 7.7 Aerial view of Alsea Spit in 1978 showing the normal configuration of the inlet. From Komar 1986. Ordinarily, the channel from Alsea Bay continues directly seaward be- yond the inlet mouth (fig. 7.7). During the 1982-83 El Nifio, however, the channel was deflected well to the north (fig. 7.8). The inlet mouth itself moved very little, the deflection instead taking place in the shallow off- shore. Apparent in this aerial photograph is an underwater bar extending from the south and covered with breaking waves. It was the northward growth of this bar, which occurred as a result of the northward sand trans- Figure 7.8 The channel leading into Alsea Bay was deflected when the longshore bar grew northward in response to storm waves that arrived from the southwest during the 1982-83 El Nino. From Komar 1986. The 1982-1983 El Nino 125 Figure 7.9 House on Alsea Spit located in the area most eroded during the early stages of the 1982-83 El Nino: top, soon after the initiation of spit erosion, before rip-rap placement; bottom, later, threatened from the side because the adjacent va- cant lot was not protected. From Komar 1986. port during the 1982-83 El Nino, that diverted the channel from its normal course. The erosion on Alsea Spit continued for about three years and was di- rectly attributable to the northward deflection of the channel. The earliest property losses occurred during the winter of 1982-83 on the spit’s ocean side well to the north of the inlet (fig. 7.9). The center of this erosion was di- rectly landward of the point where the channel turned seaward around the end of the northward-extending offshore bar. The erosion appeared to be 126 caused by the oversteepened beach profile leading into the deep channel and by direct wave attack; waves passing through the channel did not break over an offshore bar, and therefore retained their full energy until they broke directly against the spit. Placement of rock rip-rap initially protected homes in the eroding area, but when adjacent lots were left unprotected, erosion flanked the rip-rap and continued along the sides of the houses. The house shown in figure 7.9, flanked by wave erosion of the foredunes, was deliberately burned down before it fell into the sea. The erosion of the spit continued for several years while the deflected channel slowly migrated southward toward its former position. By July 1985, the opening had moved well south of its most northerly position dur- ing the winter of 1982-83. As the channel shifted southward, the center of maximum erosion along the spit similarly shifted toward the south. In Sep- tember 1985 there was an abrupt increase in the rate of erosion as the focus moved onto the unvegetated, low-lying tip of the spit (figs. 7.7 and 7.8). Within just a few days, this tongue extension of Alsea Spit completely eroded away. At the same time, the deep water of the offshore channel shifted landward, directly eroding the developed portion of the spit where it curves inward toward the inlet. Seven houses were threatened by this ero- sion, in particular one that was adjacent to an empty lot initially left unpro- tected (fig. 7.10). Figure 7.10 During the later stages of erosion on Alsea Spit, after the 1982-83 El Nino, the main center of beach and property losses shifted progressively toward the inlet. The beach had completely disappeared, and erosion was cutting back the dunes where homes had been constructed. From Komar 1986. The 1982-1983 El Nino 127 The beach fronting Alsea Spit grew significantly during the summer of 1986, and the tongue of sand began to reform at the end of the spit. Erosion during the winter of 1986-87 was minimal, and Alsea Spit and the inlet finally returned to their normal conditions—those that had prevailed for many years prior to the 1982-83 El Nino. The Erosion of Netarts Spit The effects of the 1982-83 El Nino persisted much longer in the erosion of Netarts Spit, about 60 miles south of the Oregon-Washington border. That erosion was of particular concern because it affected Cape Lookout State Park, a popular recreation site (Komar et al. 1988; Komar and Good 1989a). Netarts Spit forms most of the stretch of shore between Cape Lookout to Figure 7.11 Netarts Spit Cape ree on the northern Oregon coast lies within the lit- ThrSeuATER toral cell bounded on the Rocks 4 north by Cape Meares ee and on the south by Cape Oceanside = | ookout. Cape Lookout Maxwell Point State Park, where most of the El Nifo-related ero- sion occurred, is on the south end of the spit. PACIFIC OCEAN From Komar et al. 1988. Netarts Spit park sea cliff Cape Lookout (@) Ss SI O 3km S=——E=== 128 the south and Cape Meares to the north (fig. 7.11). It is one of the smallest pocket beach littoral cells on the Oregon coast. The spit together with its dunes contains a large volume of sand (fig. 7.12), yet there is no significant local sediment source within this isolated cell. Only a few minor streams enter Netarts Bay. Cliff erosion south of the spit and in the Oceanside area may contribute some sand to the beach, but the quantities would be small. The mineral structure of the sand forming Netarts Spit also demonstrates that most of it does not have a local source; the sand contains heavy miner- als derived from rocks found in the Klamath Mountains of southern Or- egon and northern California (Clemens and Komar 1988a). The presence of Figure 7.12 Oblique aerial photo of Netarts Spit and the inlet to Netarts Bay, March 10, 1978. Photo A682-23 from the Oregon Highway Department. The 1982-1983 El Nino 129 Figure 7.13 The log seawall fronting the park on Netarts Spit prior to the 1982-83 El Nino. From Komar et al. 1988. Klamath minerals in Netarts Spit can only be explained by a northward longshore sand transport during the lowered sea levels of the ice ages, when headlands did not block such movements, followed by a landward migra- tion of the beaches when the glaciers melted and water levels rose (chapter 2). The significance of this to the recent erosion of Netarts Spit is that the spit does not have present-day sources of sand that can be added to the beach. Before the 1980s, erosion of Netarts Spit during historic times had been minimal. In the late 1960s, a seawall was constructed at the back of the beach in the park area (fig. 7.13). Its construction was not entirely a response to wave erosion problems, but also in part to keep people from walking on the dune face, which disturbed and mobilized the dune. The sudden and dramatic erosion during the 1982-83 El Nino therefore came as a surprise. The pocket beach within the Netarts cell underwent a marked reorientation due to the approach of the storm waves from the southwest. This depleted the beach immediately north of Cape Lookout of sand, leading to erosion of the low-lying sea cliffs in that area. Of more lasting significance was that much of the sand transported northward along the beach apparently was swept through the tidal inlet into Netarts Bay, and perhaps also offshore. This effectively removed the sand from the beach system, leaving the beach depleted and less able to buffer park properties from storm erosion pro- cesses. Because of this, erosion along Netarts Spit has continued even though the direct processes of the 1982-83 El Nino stopped long ago. Rip currents and storm waves have been the chief agents of erosion on the sand-depleted Netarts Spit. They cut back the beach in the park area, leav- 130 ing much of it covered with cobbles rather than sand (fig. 7.14). The seawall was destroyed, and the erosion of park lands was substantial. Park officials considered placing rip-rap to prevent additional loss of park lands, but the fact that rip currents change position from one winter to the next, focusing erosive forces in different areas, would have made that a futile and expensive exercise. Figure 7.14 Progressive erosion of Cape Lookout State Park following the 1982-83 El Nino: top, the destruction of the log seawall and the initiation of dune erosion during October 1984 (photo by J. W. Good); bottom, erosion during the winter of 1988 left the beach composed of cobbles and gravel rather than sand. The I-beams of the log wall are now located at mid-beach. From Komar et al. 1988. The 1982-1983 El Nino 131 The fundamental problem at Netarts Spit is the depleted beach, and the most recent conservation efforts have been directed toward solving that problem. State parks officials have considered beach nourishment, bringing in sand from elsewhere to replenish the beach sand, as one solution. Sand nourishment would restore the beach along its full length, making it once again both a buffer and a recreational site. The Corps of Engineers’s yearly dredging operations within Tillamook Bay and the Columbia River are possible sources of sand for the project, but a more logical source would be the sandy shoals within Netarts Bay itself, in effect returning sand to the beach from which it was swept during the 1982-83 El Nifo and afterward. An associated positive effect would be the restoration of the bay, which has undergone considerable shoaling. However, Netarts Bay contains many acres of protected wetlands and has the highest diversity of clam species of any estuary in Oregon. The benefits to the bay from dredging and sand re- moval would have to be balanced against the probable negative impacts of such operations. EI Nifio and Previous Erosion The importance of the 1982-83 El Nino to erosion along the Northwest coast raises the question of whether previous El Nifios played a similar role. Although not truly periodic, El Nifos occur some 20 to 25 times per cen- tury. Dr. William Quinn of Oregon State University investigated the historic occurrences and classified them according to their intensity. Table 7.1 lists El Nifios since 1900 that have been assessed as “moderate” or “strong.” Recall that the two major erosion periods on Siletz Spit took place during the win- ters of 1972-73 and 1976 (chapter 6)—both El Nino years. On the other hand, the serious erosion that took place during 1978 and led to the breach- ing of Nestucca Spit did not coincide with an El Nifio. Unfortunately, little Table 7.1. El Nino Intensities during the Twentieth Century Year(s) Intensity Year(s) Intensity 1991-92 medium 1929-30 medium 1982-83 very strong 1925-26 strong 1976 medium 1918-19 strong 1972-73 strong 1914 medium 1965 medium 1911-12 strong 1957-58 strong 1905 medium 1953 medium 1902 medium 1941 strong 1899-1900 strong 1939 medium Source: Quinn et al. 1978. 132 is known about earlier erosion. We have aerial photographs of the coast dating back to 1939, but there are not enough of them to determine the ex- act timing of erosion events. Newspaper accounts of earlier erosion (Stembridge 1975b) do not show a strong correspondence between large- scale erosion and the El Nino years listed in table 7.1, but newspapers typi- cally report local erosion, not coastwide problems. In sum, it appears that erosion on the Northwest coast cannot in general be attributed to El Ninos, although there is evidence that El Ninos can in- tensify erosion by increasing storm intensities and raising sea levels. It is possible that the unusual storms that eroded the coast during 1972-73 and 1976 were related to El Ninos. One study found a strong statistical correla- tion between large waves in southern California and El Nino periods (Seymour et al. 1985). The 1972-73 and 1976 storm systems were not dis- placed to the south, as the 1982-83 storms were, and instead passed over Or- egon. There was thus no strong northward littoral drift of sand along the Northwest beaches during those earlier El Ninos, and the coastal response differed from that during 1982-83, when sand movements played an impor- tant role in causing erosion. Summary The 1982-83 El Nino produced considerable erosion along the Oregon coast as well as in California. The main contributing factors were exceptionally high sea levels, storms that generated intense wave conditions, and the northward transport of sand along Oregon beaches. This northward move- ment of sand, caused by the southward displacement of storm paths during El Nino, was unusual for Oregon beaches, where near-zero net littoral sand transport normally prevails. The sand movement was particularly impor- tant in governing locations of beach erosion, which occurred primarily on the north sides of headlands. Particularly severe erosion occurred on Alsea Spit, where the northward sand transport deflected the inlet, and in subse- quent years on Netarts Spit, which lost a good deal of its sand into Netarts Bay. It took several years for the beaches to return to normal, for the Alsea Bay channel to migrate back to its usual position, and for beach sand to move southward again within the littoral cells. We now understand that El Ninos affect far more than the fisheries of Peru; they can also have major impacts on erosion on the Northwest coast. Now when we hear news reports that another El Nino may be developing, we have a justifiable feeling of apprehension. The 1982-1983 El Nifo 133 7: 009), GOA !, & =e = iy aw ve 4 rn -& = & ut)o=zn¢ tq Ais sty" 1) oa Or oy 8 Sea Cliff Erosion and Landsliding along the Northwest Coast Although the erosion of sand spits such as Bayocean, Siletz, and Alsea has been rapid and dramatic (see chapters 5, 6, and 7), the long-term progres- sive retreat of sea cliffs along the Northwest coast accounts for greater prop- erty losses and affects more citizens. This is especially true in Oregon, where many coastal communities are built on nearly level marine terraces or alluvial slopes emanating from the nearby Coast Range, the areas af- fected most by cliff erosion (fig. 8.1). Communities such as Lincoln City, Gleneden Beach, and Newport have experienced sea cliff retreat and the parallel problem of landsliding in the undercut bluffs. State parks are being lost as cliff erosion and landsliding destroy parking lots, picnic areas, and camping facilities. In total, cliff retreat and landsliding affect hundreds of miles of the Oregon coast. Sea cliff erosion also occurs along the northern half of the Washington coast, but it is considered to be less of a problem there due to the light de- velopment. Only a few homes and condominiums are in the path of the erosion. In Olympic National Park, cliff retreat is accepted as a natural pro- cess rather than viewed as a problem. Considering the extent and importance of sea cliff erosion and landsliding to many citizens and communities, it is surprising how little is known about these processes and their associated problems. We do not even know the rates of cliff retreat in most areas of the Oregon coast, and so cannot determine adequate setback distances for safe development. In this chapter we will examine what is known about the extent and processes of sea cliff erosion and landsliding along the Northwest coast. Processes of Sea Cliff Erosion Sea cliff erosion is often viewed as the process of waves attacking and un- dermining the cliff, which in turn triggers landsliding or sloughing of the Figure 8.1 Examples of sea cliff erosion on the Oregon coast: top, Lincoln City; bottom, south of Newport. upper portions of the undercut bluff. This view is oversimplified in that a large number of processes can be involved and the cliff may respond to them in a number of ways. Figure 8.2 summarizes the erosion processes and the factors that govern rates of cliff retreat. These include the energy of the waves and their run-up intensity, tides, and sea level—factors that deter- mine the elevation of the water against the cliff and hence the position of the wave attack. The width of the beach fronting the cliff is clearly impor- tant, too, because it controls the degree to which the beach buffers the cliff from the attacking waves. Relevant to the buffering ability of the beach is 136 the presence or absence of rip currents, which hollow out embayments in the beach and bring waves closer to the cliffs. An example of the resulting erosion is shown in figure 8.3, a photograph from Gleneden Beach, Oregon, where a rip current embayment directed the wave attack during high tides. In this case the erosion was limited to four or five lots and two houses, the longshore extent of the rip embayment. The processes that cause sea cliff erosion are the same as those discussed in chapters 3 and 6, although there the emphasis was on sand spit erosion. The ocean and beach processes are essentially the same in both cases, but the erosion of cliffs is, of course, much slower than that of sand spits, where the loose sand of the foredunes offers virtually no resistance to wave attack. On the other hand, cliff retreat is permanent, whereas foredunes may subsequently build back out by natu- ral processes and restore lost property (see chapter 6). A series of laboratory experiments conducted in Japan to simulate sea cliff erosion illustrate the role of the beach and its sediments (Sunamura 1983). Artificial cliffs were constructed of loosely cemented sand. Initially there was no fronting beach, so the cliff was under the direct attack of waves (generated by a paddle in the laboratory wave basin). As the cliff re- treated, the erosion generated a supply of sand that accumulated at the base of the cliff. Initially the released sand increased the rate of cliff erosion be- cause the waves used it as a “blasting” agent. Later, however, after more sand had accumulated and a beach had developed, the beach became a buffer that caused the waves to break offshore, away from the cliff. At that Figure 8.2 A summary of the many processes and factors involved in the erosion of sea cliffs. Ocean factors 1. Waves: heights and periods (energy or energy flux) approach angle (longshore currents and littoral drift) Set-up and run-up Cliff factors . Cell circulation with rip currents . Tidal variations . Storm surge . Sea level (seasonal and long- term net changes) 1. Composition: “hardness” (e.g. com- pressivestrength) talus production Source of beach sediments 2. Layering (bedding), joints, and faults 3. Inclination of rock layers 4. Height and slope of cliff face af WP Other factors 1. Rain wash on cliff face Beach factors Va 2. Ground-water flow and pore pressures 1. Volume of beach sediments (buffering ability) 3. Vegetation cover 2. Composition and grain size: 4. Burrowing by rodents, etc. control on beach morphology 5. People: sand “blassting” walking on cliff and talus 3. Presence of drift logs carving graffiti on cliff face watering lawns culverts, etc. protective structures (seawalls, etc.) Sea Cliff Erosion and Landsliding 137 Figure 8.3. An example of rapid cliff retreat in Gleneden Beach, Oregon. A rip cur- rent cut an embay- ment through the beach, allowing waves to attack and undercut the cliff. stage the cliff erosion was reduced. It is likely that similar processes are at work on cliffs backing ocean beaches. The wide summer beaches act as buffers and prevent the waves from reaching the cliffs. In the winter the beaches are cut back by storm waves and nearshore currents, and the waves can reach and attack the sea cliffs. At such times, the remaining beach sand might become an agent enhancing cliff erosion. Drift logs are common on Northwest beaches, and it has been suggested that waves sometimes crash them against the sea cliffs like battering rams, increasing their erosive force. This may indeed be the case, although I have never seen it. Generally the logs are floated offshore during storms and epi- sodes of beach erosion. It has also been suggested that drift logs on a beach enhance its buffering ability, and therefore prevent or limit erosion. This view might be supported by the sea cliff erosion at Taft, Oregon, that fol- lowed removal of a significant portion of the logs in 1976. The Taft beach tends to accumulate large masses of driftwood—so much, in fact, that it hinders recreational use of the beach (fig. 8.4, top). To remedy 138 the situation the state of Oregon permitted log removal during the summer of 1976. Before the driftwood was removed, the cliffs backing the beach had not eroded for many years. Soon afterward, however, during the winter of 1977-78, there was major erosion of the cliff (fig. 8.4, bottom). Since that time, logs have returned to the beach and there has been no subsequent cliff erosion. The obvious conclusion is that the log removal was Figure 8.4 Cliff erosion in Taft, Oregon, may have been caused by the removal of drift logs from the fronting beach. Top, the large accumulation of driftwood may have protected the sea cliff. Bottom, erosion began soon after the logs were removed to improve the recreational use of the beach. From Komar and Shih 1993. idibas ae A! Sea Cliff Erosion and Landsliding 139 a primary factor in the cliff erosion at Taft, supporting the hypothesis that masses of logs do offer some protection. On the other hand, the log removal and subsequent erosion might be simple coincidence. The storm that caused most of the erosion was severe and took place during exceptionally high water levels produced by spring tides. Erosion took place at other beaches along the Oregon coast, too, not just at Taft. In addition, a large rip current embayment cut into the beach immediately south of the Inn at Spanish Head (fig. 8.4), and this clearly contributed to the erosion of the sea cliff at Taft. Although we cannot be certain that log removal was an impor- tant factor in the cliff erosion at Taft, this episode should cause us to pause before undertaking whole-scale log removal from beaches. Cliffs respond to erosion processes in different ways because there are many factors governing their resistance (fig. 8.2). Of primary importance is the composition of the rocks forming the cliff. The difference this can make is well illustrated on the Northwest coast. We need only think of the ex- tremely hard basalts of the headlands, which can resist the onslaught of even major storm waves, and compare them with the weaker sandstones and mudstones that more readily give way to wave attack and form the cliffs that back stretches of beach. Even these sedimentary rocks exhibit variable resistance due to differences in rock compositions. Many cliffs consist of Tertiary mudstones and siltstones (fig. 8.5, top), which can be quite resistant to wave attack. Other cliffs are composed en- tirely of Pleistocene terrace sands (fig. 8.5, bottom) that are only moderately cemented and therefore succumb easily to wave attack. The cliffs in many areas of the Northwest coast are composites of less resistant Pleistocene sandstones lying above Tertiary mudstones. This layering complicates cliff retreat. Groundwater tends to flow out at the interface of the porous sand- stone and the nonporous mudstone, eroding the Pleistocene sandstone layer in a process separate from ocean processes. The composition of the cliff material also determines whether or not eroded material accumulates as talus at the base of the cliff. If too fine grained, the loosened material is carried away by rain or groundwater flow. This is the case with mudstone if it is relatively homogeneous and does not contain resistant layers that can break off as individual blocks. The Pleis- tocene terrace sands are more likely to accumulate as cliff-base talus (fig. 8.6, top), usually soon after an episode of wave attack and erosion. The waves first remove the talus that accumulated since the previous ero- sion episode, perhaps several years earlier, leaving a nearly vertical cliff face. During the week or two following the erosion there is active sloughing of the terrace sands and a rapid new talus accumulation. Such sloughing may involve minor slumps of the cliff sands—effectively a vertical drop of blocks of intact sandstone—as well as increased groundwater seepage and direct runoff of winter rain from the newly exposed cliff. As time passes and the 140 accumulating talus protects the cliff, the latter processes diminish. In many areas, cliff retreat is due more to these processes than to direct wave attack. The main role of the ocean processes is to remove the accumulated talus sheltering the cliff, permitting renewed groundwater sapping and rain wash. The extent of the talus and its degree of vegetation cover are evidence of how recently the area has experienced wave attack. The absence of talus at Figure 8.5 Examples of sea cliffs: top, the cliff at Fogarty Creek State Park is com- posed mainly of Tertiary mudstones with only a thin layer of Pleistocene terrace sand at the top; bottom, the cliff at Lincoln City consists entirely of Pleistocene ter- race sandstones. Sea Cliff Erosion and Landsliding 141 Figure 8.6 A sea cliff at Gleneden Beach State Park, Oregon: top, new talus began to accumulate at the base of the cliff soon after erosion had removed the older talus covered with vegetation; bottom, another episode of erosion removed the newly ac- cumulated talus, leaving a vertical cliff face. the base of a sea cliff indicates recent erosion, but only if the cliff materials are suitable for the development of talus. Where the fronting beach is nar- row, wave erosion may occur each winter so that only minor talus accumu- lations build up during the summer months. Such areas generally have the fastest rates of sea cliff recession. In other areas, Taft being an example (fig. 8.4), wave attack is infrequent and the talus may accumulate over several 142 years or even decades. This permits the development of a vegetation cover, even small trees. The extent of that cover and the ages of the trees are a good indication of how long ago the last erosion took place (fig. 8.7). In some areas vegetation grows on the bluff itself as well as on the accu- mulated talus. Such bluff vegetation can be important in reducing erosion in that it protects the cliff from attack by winter rains and may also resist sapping by groundwater. Burrowing by rodents weakens the cliff material and funnels the groundwater, effectively enhancing erosion. Unfortunately, people do the same sort of damage when they carve graffiti or cut tunnels into the exposed bluff (fig. 8.8). Since natural processes of sea cliff erosion produce retreat rates amounting to only a few inches per year, the human factor is far from negligible. In some places it is the most important agent in sea cliff retreat. Cliff erosion is also affected by the geometry and structure of the cliff rocks—particularly rocks that are otherwise fairly resistant (e.g., basalt headlands and ‘Tertiary mudstones), because the bedding and fractures pro- vide lines of weakness. A good example of structural control of basalt ero- sion is the wave-cut bench near Cape Perpetua on the Oregon coast (Byrne 1963). Here, the principal set of joints is oriented in a northwest-southeast direction. Although the greatest wave energy comes from the southwest, erosion is predominantly along the northwest joint direction and has pro- duced a series of surge channels, crevices, caves, and blowholes (fig. 8.9). In general, irregularities and small bays and inlets in the headlands are gov- erned by joints and fault-controlled erosion or by dikes and layering within the ancient lavas. Figure 8.7 A heavily vegetated sea cliff. Sea Cliff Erosion and Landsliding 143 Geometry and structure are also important in the erosion of Tertiary mudstones. Although faults and joints do play a role, more important here is the layering of the deposits. Mudstones were originally formed by sedi- ments deposited on the seafloor in the deep ocean (see chapter 2), and therefore accumulated as nearly horizontal layers. Some layers were origi- nally mud, others were silts or sandy sediments. Variations in the composi- tion of the deposited sediments produced the layers that we now see in the cliffs backing the beaches (fig. 8.10). Some layers are more resistant than others, and so project further out from the cliff face. Particularly durable layers may break off as blocks and accumulate at the base of the cliff, where they offer some protection from erosion. Differences in the permeability of the various layers channel groundwater flow and determine patterns of sap- ping of the cliff face. However, the most important feature of these Tertiary Ee 4 nn neem ni gi pe a Ve oii Tw, es Figure 8.8 Graffiti carved into the sea cliff at Lin- y ‘at iGo a coln City. Such human handiwork may do more to fa lrav? : Cs awiNo 3 _ produce cliff retreat than natural processes. 144 Ae PE heb late Figure 8.9 A wave surge channel on Cape Perpetua follows a northwest-oriented fracture that provided a zone of weakness for the erosion within the otherwise highly resistant basalt. sedimentary rocks is their seaward slope (fig. 8.10). Combined with wave erosion that creates nearly vertical surfaces, such slopes yield unstable cliffs prone to massive landslides. Landslides and Property Losses Landslides that occur suddenly and affect large areas can have major conse- quences for homes, parks, and highways. It has been estimated that sea- ward-sloping rocks like those shown in figure 8.10 are present on more than half of the northern Oregon coast (Byrne 1964; North and Byrne 1965). The muddy consistency of their Tertiary sediments makes these cliffs particu- larly susceptible to landsliding, although major landslides have also oc- curred on the steep slopes of headlands. The term /andslide has been used to represent a variety of types of dis- placements of masses of rock, soils, and sediments. The common ingredient of all such movements is gravity, which acts on the mass, causing it to move downward and outward. The classic landslide, or slump (fig. 8.11), is the type most likely to take place on sea cliffs, which lack support in the sea- ward direction. Without support, stress develops in the cliff materials. When the stress exceeds the resistance of the rock, a landslide occurs. The failure often takes place along a concave up surface, and this becomes the rupture plane over which the slump moves (fig. 8.11). As the slump moves downward and out onto the beach, the upper portion of the rupture surface Sea Cliff Erosion and Landsliding 145 Figure 8.10 A sea cliff in the Jump-Off Joe area of Newport, Oregon, shows the seaward-dipping layers within the Tertiary mudstones and the upper layer of Pleis- tocene marine terrace sands. The steep slope of the layers within the mudstones contributes to the massive landsliding that has occurred at this site (see fig. 8.12 and chapter 9). is exposed, forming a nearly vertical scarp at the landward limit of the slump. As the slump progresses, the material rotates such that originally hori- zontal surfaces tilt landward. This rotation is particularly evident when the slump occurs in a marine terrace. Portions of the formerly horizontal ter- race now slope toward the land, and trees that once grew vertically tilt in- land with uniform orientations (fig. 8.12). The farther the material moves, the more jumbled it becomes; eventually, intact portions of the terrace no longer exist and the trees slant in all directions. By the time the material flows out onto the fronting beach, it is generally a tangled mass of rocks, soil, trees, and brush. This portion comprises the foot and toe of the slump (fig. 8.11). Waves quickly go to work to erode away this mass, which may extend across much of the beach and even into the sea. It is surprising how resis- tant slide masses can be to wave attack. It sometimes takes months for the waves to cut back a landslide that flowed across the beach and into the surf zone. Wave erosion of the slump toe produces a temporary cliff, or scarp, and removes the basal support of the slide mass, creating additional instability. This type of erosion may result in repeated movements of the mass. In the case of very large slumps, the process may continue for years, with the slump mass slowly moving seaward at the same rate the waves cut away the cliff formed in its toe. Sometimes this type of movement occurs in large 146 rupture slip surface LANDSLIDE NOMENCLATURE Figure 8.11 The classic form of a slump or landslide. blocks of land that are still relatively intact, never having gone through a phase of rapid sliding. The movement may amount to only a few inches per year, but that is enough to disrupt roads and progressively shift foundations of homes. Such unstable sites are obviously undesirable locations for per- manent structures, yet developers persistently build on them. A good ex- ample is the destruction of the Stratford Estates development north of Newport (fig. 8.13), where streets and sewers placed on a slow-moving land- slide were quickly disrupted. Most movement on landslides occurs during the winter months (fig. 8.14), primarily December and January, which are also the months of maxi- mum rainfall. This is hardly surprising, since rainfall and groundwater are primary agents in landslide generation. The winter months are also a time of intensified ocean wave activity (see chapter 3), and winter waves may also contribute to landslides by undercutting cliffs and thus increasing their in- stability. The largest landslides on the Northwest coast occur on headlands or within the loose debris along their immediate margins. A good example is the huge slump on Cascade Head, Oregon (fig. 8.15), which abruptly gave way in 1934 (North and Byrne 1965). The surf has cut away at the toe of the landslide, forming a high cliff in the debris. Massive landslides associated with headlands also affect developed areas. The large landslides that cross Ecola State Park on Tillamook Head, immediately north of Cannon Beach, become active every few years, disrupting access roads and other facilities (fig. 8.16; Schlicker et al. 1961; Byrne 1963). Alongshore Variations in Sea Cliff Erosion One of the difficulties with managing sea cliff erosion on the Northwest coast is its extreme variability, both spatially and temporally. This variabil- Sea Cliff Erosion and Landsliding 147 ity makes it difficult to establish reasonable setback distances to ensure safe development and to judge whether or not cliff protection structures such as seawalls are justified. My colleagues and I have focused on this variability in our investigations of sea cliff erosion along the Oregon coast, particularly that in the littoral cells on the northern half of the coast (fig. 8.17; Komar and Shih 1991, 1993; Shih 1992; Shih and Komar 1994; Shih et al. 1994; Ruggiero et al. 1996). Each cell exists as a nearly isolated pocket beach bounded on the north and south by headlands that prevent alongshore exchanges of beach sand. In addition to investigating cliff erosion within this series of cells, we also examined Figure 8.12 ‘Tilted trees and inclined ground on what was once the horizontal sur- face of a marine terrace are evidence of the disruption produced by the Jump-Off Joe landslide in Newport. These photos, taken in 1975, predate attempts to build condominiums on the landslide (see chapter 9). Figure 8.13 A street and sewers in the Stratford Estates development north of Newport were destroyed by a slow-moving landslide. The disruption has caused the street to be “cloased.” after Byrne (1963) Figure 8.14 Number precipitation of landslides versus monthly precipitation amounts. Most land- slides on the Oregon coast occur during the months with highest precipitation, reflecting PRECIPITATION (inches) the importance of rain- fall and groundwater in LANDSLIDES/MONTH the generation of land- slides. From Byrne 1963. specific sites of potential erosion along the southern half of the coast, as- sessing vegetation cover on the cliffs, the quantity of accumulated talus at the cliff base, and the occurrence or absence of wave attack in recent years. We identified a coastwide pattern of cliff erosion that parallels the pattern of tectonic uplift along the coast relative to the global rise in sea level (Komar and Shih 1993). Recall from chapter 2 (fig. 2.7) that the sea level Sea Cliff Erosion and Landsliding 149 along the north-central portion of the coast is presently rising at a rate faster than the rate of tectonic uplift. Sea cliff erosion is active on this por- tion of the coast, illustrated by the bluffs within the Lincoln City and Beverly Beach littoral cells (fig. 8.18, middle). The relative water level aver- Figure 8.15 A massive landslide occurred on Cascade Head, Oregon, in 1934. Courtesy of J. V. Byrne. Figure 8.16 Landslides in Ecola State Park on Tillamook Head, Or- egon, periodically dis- ECOLA STATE PARK after Schlicker et al. (1961) 1000 ft PACIFIC rupt park facilities. After OCEAN j S Schlicker et al. 1961. 20° active landslide old landslide scarps Miocene siltstones, shale and sandstone Miocene volcanics 150 Cape Lookout SAND LAKE CELL Cape Kiwanda NESTUCCA columbia River CELL Cascade Head LINCOLN CITY CELL Tillamook Head Cape Foulweather CANNON BEACH CELL Cape Falcon BEVERLY BEACH CELL Yaquina Head ROCKAWAY CELL NEWPORT LITTORAL CELL Cape Meares NETARTS CELL Cape Lookout Cape Perpetua to) 50 km Figure 8.17 A series of littoral cells on the northern half of the Oregon coast form beach embayments between rocky headlands. Cliff erosion within each cell depends on the tectonic rise of the land relative to the increase in sea level, and on local fac- tors such as the rock composition of the cliff and the extent of the fronting beach that buffers the cliff from wave attack (1 kilometer ~ 0.6 mile). From Komar and Shih 1993. ages slightly higher here each year, and this accounts for the continued cliff erosion. In contrast, there has been essentially no wave-induced cliff ero- sion within the Cannon Beach cell near the Oregon-Washington border in the north (fig. 8.18, top) or at Bandon on the south coast (fig. 8.18, bottom). The sea cliffs at these sites are heavily vegetated, and there has been no sig- nificant erosion resulting from direct wave attack during historic times. In addition, these sites lie within stretches of coast that are rising tectonically at rates that exceed the present rise in the global sea level (fig. 2.7). The lack of cliff erosion in these areas can be explained simply by the uplift of the land: each succeeding year the waves are less able to reach the cliffs to erode them. It is apparent, then, that the extent of cliff erosion along the Oregon coast roughly parallels the net change in relative sea level, the difference be- tween the tectonic uplift of the land and the global rise in sea level. Sea Cliff Erosion and Landsliding 151 Figure 8.18 Sea cliffs on the Oregon coast: top, in the Canon Beach cell on the northern Oregon coast; middle, in the Lincoln City and Beverly Beach cells on the middle coast; bottom, at Bandon on the south coast. The variable rates of sea cliff erosion at these sites parallel the north-to-south trends of tectonic uplift of the coast relative to the global rise in sea level. From Komar and Shih 1993. 152 The minimal erosion during historic times of sea cliffs within the Can- non Beach cell and at Bandon is particularly intriguing. The little cliff re- treat that occurs there is mainly the result of groundwater seepage, and not direct attack by ocean waves. Yet the steepness of the cliffs at those loca- tions, and their alongshore uniformity without appreciable degradation by subaerial processes such as rainfall and groundwater flow (fig. 8.18, top and bottom), suggest that these cliffs experienced wave-induced erosion in the not-too-distant past. In addition to the steep cliff backing the beach at Bandon, there are a number of sea stacks in the immediate offshore, many with flat tops that continue the level of the marine terrace, further attesting to comparatively recent and major cliff erosion and retreat. Our interpretation of both the Cannon Beach cell and the Bandon area is that cliff erosion occurred following the last major subduction earthquake, about 300 years ago (Komar et al. 1991; Komar and Shih 1993). As discussed in chapter 2, major portions of the coast may drop several feet during a subduction earthquake, which releases the strain that had previously caused coastal uplift. An abrupt coastal subsidence 300 years ago would have resulted in massive erosion and retreat of sea cliffs as well as sand spits. In the case of Cannon Beach and Bandon, the uplift that has occurred since the earthquake has been sufficiently rapid to diminish and then stop cliff erosion. The other littoral cells along the north-central part of the Oregon coast likely also experienced subsidence and massive cliff erosion 300 years ago, but subsequent uplift there relative to the rising sea level has been in- sufficient to completely halt cliff erosion, which is still apparent in the Lin- coln City and Beverly Beach cells (fig. 8.18, middle). Although cliff recession on the Oregon coast is directly related to tec- tonic uplift relative to sea level rise, there is a great deal of local variability (spatial and episodic) that is attributable to local factors. These include the overall ability of the fronting beach to buffer the cliffs from the waves, beach processes such as run-up and erosion within rip current embay- ments, and the composition of the cliff materials (fig. 8.2). The importance of cliff composition to erosion is evident in a compari- son of the Newport and Beverly Beach littoral cells with cells farther north. The sea cliffs in the Newport and Beverly Beach cells consist mainly of Ter- tiary mudstones. These deposits dip seaward at an angle of 30 degrees in the Nye Beach area of Newport (fig. 8.10), a factor important to the generation of the large Jump-Off Joe landslide (see chapter 9). Although also impor- tant in the Beverly Beach cell, landsliding is less catastrophic and rapid than in the Newport cell, probably because the mudstones at Beverly Beach dip seaward at lower angles. Landsliding also has been important in the Can- non Beach cell, where the cliff material consists of muddy alluvium and an- cient debris. Major efforts have been made to control these slides (drainage, Sea Cliff Erosion and Landsliding 153 etc.) because they affect Highway 101. Landslides have not been a significant problem in the other littoral cells. The cliff in the Lincoln City cell is com- posed entirely of Pleistocene terrace sands (fig. 8.5), which generally fail in small-scale vertical falls rather than in the massive landslides typical of the mudstones. Cliff erosion has been most active in the Beverly Beach littoral cell (fig. 8.18, middle). Some of the erosion is occurring in intact land masses that are slowly moving toward the sea. Further, the beach within this cell is a poor buffer because of its small sand volume. My colleagues and I documented the lack of buffering protection by measuring wave run-up elevations on the beach (Shih 1992; Shih et al. 1994). Our objective was to investigate the frequency with which waves reach the talus at the base of the sea cliff and the intensity of the swash run-up. We found that the wave swash commonly reaches the cliff base in the Beverly Beach cell but rarely does so in the other cells. This is because the beach profiles within the Beverly Beach cell have low elevations compared with mean sea level and high-tide elevations. Most of our research has centered on the Lincoln City cell (fig. 8.19; Shih 1992; Shih and Komar 1994), which is of particular interest because of the extensive development on the cliff edge along this stretch of coast (fig. 8.1, top). In addition, one unusual feature of this cell enhances its scientific in- terest: there is a marked longshore variation in the coarseness of the beach sand, and this produces longshore changes in the beach morphology and the nearshore processes that are important to cliff erosion. The beaches on the central to southern part of the cell, including the beaches fronting Siletz Spit and the community of Gleneden Beach, have the coarsest sand (fig. 8.19). Sand grain size decreases somewhat south of there but much more so in the northern part of the cell, where the sand is finest in the Roads End area of Lincoln City. The effect of sand size on the beach morphology is significant. The coarse-grained beach at Gleneden Beach is much steeper than the beach at Roads End, which has a very low slope. Recall from chapter 3 that coarse- sand beaches respond faster to storm waves and exhibit larger profile changes than fine-grained beaches. The large profile shifts at Gleneden Beach make that beach a poor buffer, and as a result, cliff erosion is much more active there than it is north of Lincoln City, where the cliffs are fronted by a fine-sand beach with a low slope. Rip current embayments also cut more deeply into coarse-sand beaches, and they have been a significant factor in the sea cliff erosion at Gleneden Beach (fig. 8.3). The rip current embayments on the fine-sand beach north of Lincoln City are broader in longshore extent but do not cut as deeply into the beach. In contrast, bluff retreat in north Lincoln City is caused mainly by rain- fall beating against the cliff face and groundwater seepage, aided consider- ably by the carvers of graffiti (fig. 8.8). The fallen material accumulates as 154 LINCOLN CITY CELL Cascade Head Salmon Gleneden Beach Fishing Rock “Fogarty Creek 030 O35 O40 045 O50 MEDIAN DIAM. (mm) Q25 Government Point Figure 8.19 Sand grain diameters on the beaches of the Lincoln City littoral cell. The beach sand is coarsest in the vicinity of Gleneden Beach and Siletz Spit, and be- comes progressively finer toward the north and, to a lesser extent, toward the south (a inch = 25 millimeters; 1 kilometer ~ 0.6 mile). From Komar and Shih 1993. talus, sometimes for years or decades, until it is removed by wave action during an unusually severe storm accompanied by extreme high tides. Rates of Sea Cliff Recession The spatial variability and episodic nature of sea cliff erosion along the Northwest coast make it extremely difficult to obtain accurate and mean- ingful measurements of long-term average cliff recession rates. We tried to use sequences of aerial photographs to measure these rates, but our at- tempts were not particularly successful, even in the Lincoln City and Beverly Beach cells, which are known to have experienced wave attack in re- cent years (Shih 1992; Komar and Shih 1993). Sea Cliff Erosion and Landsliding 155 We concentrated on the Taft area of the Lincoln City cell, which eroded extensively during the winter of 1977—78 (fig. 8.4). A series of aerial photo- graphs of that area dating back to 1939 is available. Even in the area that was thought to represent significant cliff recession, however, we were unable to determine the long-term erosion rate. The photographs show episodes of talus removal by waves followed by decades of accumulation, but recession of the top of the bluff has been too small to measure accurately on the aerial photographs. Ground photos taken over the years substantiate the negli- gible cliff retreat in Taft. Old photos, undated but known to have been taken in the 1920s (fig. 8.20), differ little from modern ones, confirming that there has been little retreat of the bluff top. My own photographs of the coast span some 25 years and further verify that cliff retreat has been very slow. Even in areas of the coast perceived to be undergoing significant cliff ero- sion, the long-term retreat rates are a couple of inches per year at most. In a few locations the retreat has been dramatic when rip current embay- ments reached the base of the cliff and allowed direct wave attack, at least for a few days. That erosion is measurable on aerial photographs, but it is local and episodic, and in the long term represents a small rate of average recession. Another factor that makes it difficult to measure cliff recession along the Oregon coast is the mass movement of the cliff itself. In the Beverly Beach and Newport littoral cells, large blocks of the mudstones, some several acres in extent, move seaward a few inches each year. These blocks remain largely intact because of their slow movement. As a block slides toward the ocean, wave erosion cuts back its seaward edge at just about the same rate as its movement. Although bluff erosion is occurring locally on these moving blocks, and homes built atop them slowly shift toward the cliff edge, the cliff itself remains approximately stationary in position as viewed in aerial pho- tographs. We had hoped to determine long-term recession rates that would enable coastal communities to establish setback distances to protect new construc- tion. Although we were unsuccessful, we did learn that long-term retreat is much less than initially thought. The establishment of setback lines is a valid management approach, but it should be based on an assessment of the capacity of a particular beach to serve as a buffer and the susceptibility of the cliff material to landsliding. These factors, and thus reasonable setback distances, differ from one littoral cell to another, and secondarily within the littoral cell depending on local conditions. Structures that Prevent Cliff Erosion There have been many attempts to limit or prevent sea cliff erosion by con- structing protective structures. These structures have taken a variety of 156 Figure 8.20 Photos of the Taft area of Lincoln City taken in the 1920s (top) and re- cently (bottom) demonstrate that bluff retreat there has been minor over the past 60 to 70 years. From Komar and Shih 1993. forms—including rip-rap and seawalls—depending on the magnitude of the erosion and the height of the sea cliff. Some have been successful; oth- ers were a complete waste of money. Some structures have minimal visual impact; others are noted mainly for their ugliness. The minimum protective structure is represented by a line of rip-rap that protects the toe of the accumulating talus at the base of the sea cliff (fig. 8.21). In most cases the structure can be small, especially if the fronting beach is composed of fine sand and has a low average slope. In Sea Cliff Erosion and Landsliding 157 Figure 8.21 A low line of rip-rap has been successful in protecting the accumu- lated talus from wave attack during storms; the talus in turn shelters the sea cliff from rain wash and groundwater flow. such circumstances the structure need only protect the talus from the run- up of weak waves that have lost nearly all of their energy in crossing the wide beach. By protecting the talus, the rip-rap reduces erosion on the cliff itself, because the talus shelters the cliff face from wind-driven rains and also reduces sapping from groundwater seepage. Growth of vegetation on the talus should be encouraged because it helps to stabilize the talus and thus protects the cliff from further erosion. Rip current embayments that cut down the level of the beach can also play an important role in cliff erosion, particularly on steep coarse-sand beaches. In such circumstances, a more massive structure is required to withstand the stronger forces of waves that may break directly against it. To prevent undermining, the base of the structure must be placed below the lowest level the beach may reach when subjected to combined waves and rip currents; if possible, the base of the structure should rest on the bedrock be- neath the beach sand. Very high cliffs cannot be adequately protected by walls or other struc- tures; no reasonably sized structure can protect the full elevation of the cliff. In that case, it is preferable to move a threatened dwelling back from the cliff edge. This approach usually costs less than building a seawall and pro- vides the greatest certainty of success. The disposition of two houses threat- ened by erosion at Gleneden Beach will illustrate the point. Following the erosion, the two dwellings projected well beyond the cliff edge (fig. 8.3). The one on the right was moved and is now safely beyond the reach of continued cliff recession. The dwelling on the left was not moved, 158 Figure 8.22 The homeowners’ responses to the erosion at Gleneden Beach pic- tured in figure 8.3. One of two threatened houses was moved back from the cliff edge; the other was left in place and is now supported by I-beams, with railroad ties filling the space between them. possibly because its concrete foundation was too massive. Instead, the por- tion of the house hanging over the cliff edge was supported by steel I- beams, and the spaces between were filled by railroad ties in order to reduce cliff erosion (fig. 8.22). Without a doubt, the result is the ugliest structure on the Northwest coast. Most commonly, a structure, generally rip-rap, is placed at the base of a cliff to protect its toe and accumulated talus from wave attack. This leaves the upper portion of the cliff unprotected, and it continues to retreat due to rain wash, groundwater sapping, and human activities (graffiti carving, etc.). A number of schemes have been devised to protect bare upper cliff faces, including board walls and concrete gunite. These approaches have had mixed success in reducing the continued retreat of the bluff top. Summary Cliff erosion along the Northwest coast is extremely variable in extent and intensity. Particularly evident are spatial variations. For example, sea cliffs in the communities of Lincoln City and Gleneden Beach have undergone noticeable erosion during historic times, while cliffs in the Cannon Beach cell and at Bandon have experienced minimal wave erosion. On the other hand, the steep cliffs and offshore sea stacks at Cannon Beach and Bandon are clear evidence of extreme cliff retreat in the not too-distant past, per- Sea Cliff Erosion and Landsliding 159 haps initiated 300 years ago by the last subduction earthquake to affect the area. Subsequent uplift of the coast has reduced or eliminated continued erosion. We can expect renewed massive cliff erosion should there be an- other subduction earthquake. A great deal of the spatial variability in sea cliff erosion is due to local fac- tors that include the extent of the fronting beach, which determines its abil- ity to act as a buffer between the waves and cliffs, and the composition of the bluffs, which governs their susceptibility to landsliding. Landslides are significant problems in some areas, the most notable example being the large Jump-Off Joe landslide in Newport, which is examined in detail in chapter 9. Cliff erosion has been episodic as well as spatially variable in ar- eas such as Gleneden Beach, where the cliff is fronted by a coarse-sand beach. Even in areas where sea cliffs are perceived to be undergoing significant erosion, however, the long-term retreat is small. In view of this, reasonable setback distances can be established that will keep new construction safe from continued cliff retreat. It is better to move threatened homes back from the cliff edge than to build protective structures, especially since the construction of seawalls and rip-rap revetments cannot guarantee adequate protection. 160 9 The Jump-Off Joe Fiasco The rocky promontory called Jump-Off Joe was once one of the most pic- turesque spots on the Oregon coast (fig. 9.1). Legend has it that Joe, an In- dian, jumped to his death while being pursued for a crime he had not com- mitted. His lover, Mishi, who also jumped but survived, put a curse on the bluff. In view of subsequent events at Jump-Off Joe, the curse seems to have had its intended effect. In 1942, a large landslide in the bluff at Jump-Off Joe carried more than a dozen homes to their destruction (Sayre and Komar 1988). In spite of con- tinued slumping, a condominium was built on the remaining bluff in 1982. A certified geologist had determined that the site was stable even though it was adjacent to the 1942 landslide and in the area with the highest rate of erosion on the entire Oregon coast, and the Newport city government gave its approval to the project. Within three years, before the construction was even completed, slope retreat caused the foundation to fail, and the city or- dered the destruction of the unfinished structure. The developers, the con- tractor, a lumber company, and the insurance company that had insured the project against slippage went bankrupt. Creditors with claims of $1 mil- lion were paid between 18 cents and 1 cent on the dollar. The consulting ge- ologist lost his certification. The debate over Jump-Off Joe was the most divisive land-use battle ever fought on the Oregon coast, and people still have strong feelings about the project. It was a classic confrontation between developers who thought their project would help a city grow and environmentalists who wanted to preserve the coastline. In the end, the issue was decided by Nature. History of Erosion at Jump-Off Joe Newport was founded in the 1860s by settlers who were attracted by the natural resources of the area, particularly the timber and abundant oysters. WHO REMEMBERS REMEMBERS TMAT RUGGED PIONEER, TMAT WEATRERED THE STOR WMER COAST WAS TUE SUDAMER BAYS OF LONG AGO, WHEN WE CLIMBED ON THE BACK OF SOMP-OFF LIKE THE PICNEERSWENMAS PASSED DARK, AND HOT A SIGN ISLEFT TODAY, TO MARK LME SPOT WHERE ONCE WE PLAVED—On GOMER DANS FOUND REST Ann SHADE- THE WAVES AND SURE AND BLL0WS WILL FLOW, BUT WEVER AGAIN WASH JOMP-oFF-SOE- ) WESIEX prnoanHs © 5. Figure 9.1 The picturesque Jump-Off Joe sea arch inspired early tourists to pen lines of descriptive poetry. From the Oregon Historical Society, Portland. The beauty of the coast also attracted tourists, who began to arrive in sig- nificant numbers in the 1890s. One of the major tourist attractions in the Newport area was Jump-Off Joe, a rocky promontory just north of Nye Beach (figs. 9.1 and 9.2). Through the years Jump-Off Joe has been a much-photographed spot, and its rapid erosion is thus well documented (fig. 9.3). The earliest photo- graphs, taken in the late 1800s, show the promontory still connected to the coast. Later photos show its separation and development into an arch. The arch eventually collapsed, and the resulting stacks continued to erode, so that today only small nubs remain, visible at low tide. After the loss of the original promontory, the name Jump-Off Joe was adopted for the area in general and has been used to refer to the landslide that developed in the 1940s as well as to the small remnant of terrace left behind as a promontory. Development of the Jump-Off Joe area began in the early 1900s (Price 1975). Some landsliding endangered structures as early as 1921 (Baldwin 1985), but most of the damage occurred when a large slump developed over a period of months from late 1942 to spring 1943 (figs. 9.4 and 9.5). The slump is located between Sixth and Eleventh Streets, and the escarpment is west of and parallel to Coast Street (fig. 9.2). The 1942-43 slump involved about 15 acres and affected 15 houses. A few homes rode the slump block down intact and were occupied until 1966 (see figure 9.5). Eventually they were in danger of being undermined by wave erosion of the toe of the slide and were intentionally burned. The Yaquina Bay News of March u, 1943, made an interesting suggestion regarding the cause of the slump and earlier activity: “There was a forma- 162 tion of soapstone underneath and when the earth became saturated with water it would form a stream causing a crevice and pushing the ground up.” The state geologist investigated the site a few weeks later and provided the earliest scientific account of the slump (Lowry and Allen 1945). The Jump- Off Joe bluff is a remnant of a marine terrace. Tertiary marine mudstones contained within the bluff are layered and dip steeply toward the sea (see fig. 8.10); most of the slumping takes place on shear zones within these mud- stones. The bluff retreat at Jump-Off Joe over the past century is documented in coastal charts and aerial photographs (Stembridge 1975c). Figure 9.2 shows the location of the cliff edge in 1868, 1939, and 1967. This diagram also shows that major slumping took place more than a century ago just north of the 1942-43 slump. The two slumps left a small segment of uneroded bluff be- tween them, and it was this segment that became the site of condominium construction in 1982. Figure 9.2 indicates that the long-term sea cliff retreat Figure 9.2 Cliff retreat at Nye Beach, Newport, from 1868 to 1976. Cliff edge lines were determined from old charts and aerial photographs (Stembridge 1975c). The black squares represent homes affected by the 1942-43 landslide. Jumpoff Joe Nye Beach Cliff Retreat L 1868 —- 1967 “C___ (Stembridge, 1976) 1982 Condominium L fo) 500 ft. fe © 100 200m 7 Landslide ie iE i | GS Yaquina te (ie <= ie G z I 5 re Q Nye Beach Turnaround yf The Jump-Off Joe Fiasco 163 bene Figure 9.3 Photographs of Jump-Off Joe taken by tourists in 1880 (top), c. 1915 (middle), and 1978 (bottom). From the Lincoln County Historical Society, Newport. 164 was spatially variable but averaged several feet per year, a rate that is by far the highest on the Oregon coast. An inventory of geological hazards along the Lincoln County coastline completed in 1975 gives an erosion rate of 7 feet per year for Jump-Off Joe and correctly concludes that such active landslides should remain undevel- oped. This conclusion is ironic in view of the fact that the chief author of this report was to become the principal consulting geologist for the devel- opers of Jump-Off Joe. Figure 9.4 Photos taken on February 3, 1943, show some of the damage caused by the 1942-43 landslide at Jump-Off Joe. From the Lincoln County Historical Society, Newport, Oregon. The Jump-Off Joe Fiasco 165 Figure 9.5 Aerial view of the 1942-43 landslide area in 1961. Some of the houses on the slump block were occupied until 1965. From the Lincoln County Historical Soci- ety, Newport, Oregon. The Development of Jump-Off Joe The story of condominium development at Jump-Off Joe begins in 1964 when the developers, Mr. and Mrs. Anderson of Newport, acquired the down-dropped block involved in the 1942-43 landslide and the adjacent uneroded bluff at the end of Eleventh Street (fig. 9.2; Sayre and Komar 1988). The city gave the Andersons these parcels in exchange for land to the north of the bluff. The earliest geological investigation carried out for the developers, con- ducted by the well-known engineering firm of Shannon and Wilson, indi- cated that the down-dropped slump block was still active, as evidenced by fissures, its irregular hummocky topography, and back-tilted trees (see fig. 8.12). The investigators noted that wave erosion at the toe of the block was causing constant movement into the intertidal zone. In spite of this reported slump activity and known high rates of erosion on the Jump-Off Joe bluff, the Andersons decided to go ahead with their plans for development. Grading and removal of vegetation on the down- dropped block began in December 1980 (fig. 9.6). Opposition to the project appeared along with the bulldozers. By mid-February 1981, the developers’ attorney and geologist were meeting with neighboring homeowners to as- sure them of the appropriateness and benefits of the project. Shannon and Wilson prepared a geotechnical report of the site for the developers that acknowledged the geological hazards at the site but pro- posed three measures to stabilize it: 166 1. A drain field to control groundwater seepage 2. Reduction of the steep slope paralleling Coast Street to a 1:2 slope using a combination of cut and fill 3. Construction of a seawall at the toe of the 1942-43 slump On the basis of this report, a plan for the construction of 39 single-family homes was submitted to the Newport Planning Commission in early March 1981. Several opponents of the project also made presentations to the Plan- ning Commission, arguing that the project endangered nearby private property, questioning the plans for reducing the landslide hazard, and stat- ing that development should not be considered so close to the beach. In ad- dition, a representative of the Oregon Land Conservation and Develop- ment Commission (Lcpc) indicated that statewide land-use planning goals were not being satisfied. Oregon requires that all cities and counties have comprehensive land-use plans and that all plans conform to goals set by the Lcpc (see chapter 10). The Newport Planning Commission found the project attractive because it proposed new homes for a part of the city characterized by smaller, older homes, but postponed a decision on the subdivision. The next meeting of the Planning Commission was held in mid-April and focused on geological and geotechnical testimony from experts on both sides of the issue. The op- ponents were now represented by the Friends of Lincoln County (Ftc), a group formed in the 1970s to oppose the development of wetlands in the Newport area. The Fic brought several letters from geologists and oceanog- Figure 9.6 Grading on the 1942-43 Jump-Off Joe slump block in December 1980 in preparation for its development. From the Lincoln County Historical Society, New- port. The Jump-Off Joe Fiasco 167 raphers that raised questions about the proposed hazards mitigation. An engineering geologist from Oregon State University questioned whether the developers’ consultants had located the toe of the 1942-43 slump. If the fail- ure zone was deeper than suspected and the toe was actually seaward of the proposed seawall, construction of the wall would further destabilize the slump block rather than providing support. Once again the Planning Com- mission postponed its decision. The developers finally convinced the Planning Commission at a meeting in late April, and the project was given tentative approval as long as certain conditions were met. These included the completion of a detailed geotech- nical study, an independent review of the developers’ plans for stabilizing the block, and the establishment of beach access. In response, the Fic hired legal counsel and a professional geologist and asked the Newport City Council to review the Planning Commission’s decision, alleging that the project violated state land-use goals. The Fic’s attorney charged that the city government was unresponsive to the involvement of citizen groups in its decision-making procedures. A prodevelopment member of the Plan- ning Commission and City Council characterized the FLc as combative and unwilling to compromise (Sayre and Komar 1988). The developers’ attorney felt that too many conditions were placed on the developers at this stage of their plans and that the City Council took too long in ratifying the Planning Commission’s decision. The City Council was trying to balance the oppos- ing points of view and did not see any need for urgency. It did not complete its review until January 1982, more than six months later. In the meantime, in May 1981, the Andersons advertised the property for sale. They were unable to find a buyer and continued with their develop- ment plans. The detailed geotechnical study of the site requested of the developers by the Planning Commission was completed by Shannon and Wilson in July 1981 (Sayre and Komar 1988). Deeper drilling did reveal an older failure zone which had been active when the slump was much larger than present. At the city’s request, the engineering firm CH,M-Hill reviewed the report. Their resulting assessment noted that adding fill to reduce the slope along Coast Street would place a large load on the slump block, reducing its sta- bility as well as occupying space originally planned for development. Cut- ting this slope would also require the purchase of private property and would expose a larger area to surface water erosion. They recommended that the developers take additional measures to stabilize the scarp. The engineering report also placed the rate of erosion in the Jump-Off Joe area at several feet per year and expressed concern that the site and its seawall might become a peninsula over time, requiring the construction of wing walls. The designed seawall was not tall enough to stop overtopping by ocean waves, which would saturate the backfill and increase the weight the 168 seawall was required to hold. Overtopping could also wash away some of the backfill. In addition, the report concluded that the footings were not deep enough to protect the structure from wave scour. In early 1982, the developers applied to the Oregon Division of State Lands (psx) for a permit to build a seawall, because Oregon’s removal-fill law applied to the excavation and backfilling operations that would be in- volved in the construction. The pst denied the application, stating that the seawall would produce only an illusion of safety in an area of known geo- logical hazards, and that there would be no public benefit from its con- struction. The developers filed an appeal but later withdrew it. In mid-January 1982, the City Council agreed with the Planning Com- mission’s decision to allow the slump block to be resubdivided and devel- oped, but then announced a few days later that it would reconsider its deci- sion at a February 1 meeting. Most likely the council was going to postpone the decision once again because a cul-de-sac in the plan required a variance that had not been applied for. However, before the council could take that action, the Andersons suddenly withdrew their plans for development on the landslide itself and announced new plans to build 10 condominiums on the small remnant of bluff adjacent to the landslide. Their application for a building permit for that construction was granted a few days later. A report written by the Andersons’ consulting geologist was the first study prepared for the developers that focused on this small section of uneroded bluff. It was completed in the fall of 1981 while preliminary work was still under way on the down-dropped block. The report acknowledged the close proximity of massive landslides to the immediate north and south but concluded that the rate of cliff retreat was only 1 foot per year or less at the bluff itself, based on a comparison of aerial photographs taken in 1939 and 1972. The geologist did not explain the disagreement between this esti- mate and the 7-foot-per-year erosion rate given in the report he prepared for Lincoln County in 1975 (Rohleder et al. 1975), a rate that was confirmed by the 1981 CH,M-Hill study. Based on his new lower rate of estimated ero- sion, the geologist established a setback line that would keep structures on the bluff safe from cliff retreat for 20 years. This setback line was followed in the later construction. The 1981 report by the developers’ geologist appears to have been critical in the City Council’s decision to approve construction on the bluff (Sayre and Komar 1988). City Planner Jan Monroe said that “if (the geologist) hadn't issued that report, they would never have given the project a build- ing permit. If a person meets all the requirements and goes through the steps, they are issued a (building) permit. We have no discretionary author- ity to deny a permit based on gut feeling or knowing it’s not good sense” (Oregonian, July 21, 1985, E10). Shannon and Wilson reviewed the hazards report prepared by the geolo- The Jump-Off Joe Fiasco 169 gist for the developers and suggested that a drainage system be installed. A 6-inch pipe was placed beneath the condominium to control groundwater saturation. It would later burst and accelerate erosion on the site. The opponents of the development were unable to stop the construction of the condominium on the remnant of uneroded bluff. Building began in earnest in March 1982 (fig. 9.7), and by the end of the year all but the inte- rior was completed. The precarious position of the building, on a rapidly eroding bluff with landslides on both sides (fig. 9.8), should have been ample warning to potential buyers. Opponents of the development who lived near the construction site placed signs in their front yards as an addi- tional warning of the landslide hazard (fig. 9.9). Each unit was to sell for $250,000, but sales were slow. The early 1980s was a time of high interest rates and a depressed real estate market. Con- struction was halted in December 1982 before the interior was completed. The developers had been unable to obtain a construction loan and ran out of money. Most of the subcontractors had placed liens on the condo- minium. An appraisal placed the value of the unfinished project at $1 mil- lion (Sayre and Komar 1988). As early as September 1981, the Andersons had stopped making payments on a loan for the subdivision project, although this was not known publicly until near the end of 1982. Accumulated interest during the delay and de- mands by their lending institution ultimately led in late 1982 to foreclosure and auction of the down-dropped landslide block. The land was sold to the Figure 9.7_ Condominiums under construction in 1981 on the ter- race remnant at Jump-Off Joe. From the Newport News-Times. 170 Figure 9.8 This site on a rapidly eroding bluff with landslides on both sides was ex- tremely precarious for development. The southwestern portion of the structure (lower right) is already beginning to tilt. bank for more than $850,000. Within a year, this bank found itself in trouble because of poor loan practices and was forced to merge with an- other bank. The Andersons filed for bankruptcy in May 1983. Just prior to that, they purchased insurance against slippage of the condominiums. The insurance premiums were paid by a committee of the 19 secured creditors who held liens on the construction; among this group was the city of Newport (Sayre and Komar 1988). By September 1984, sloughing of the bluff had undermined the perimeter fence around the condominium. The drainage pipe burst, probably due to Figure 9.9 The Friends of Lin- coln County erected lawn signs in the Jump-Off Joe area to dis- courage buyers. From the Newport News-Times. The Jump-Off Joe Fiasco 171 Figure 9.10 The foundation of this condominium failed during renewed slumping in 1985. The stress placed on the = _ building by the ground 2 movement and loss of se ite igiee support caused the Cee ae wis ; windows to shatter. Figure 9.11 The final demolition of the condominiums in October 1985 brought to an end the contention over developing the Jump-Off Joe landslide site. From the Newport News-Times. 172 slippage, exacerbating the problem. A larger slump developed on the rem- nant bluff, causing the foundation to fail (fig. 9.10). Slump movement was not directly seaward, but had a southerly component, suggesting that re- grading of the 1942-43 slump surface during development may have been a contributing factor. In January 1985, the city ordered the demolition of the condominiums, and they were torn down later that year (fig. 9.11). The sal- vager paid the city $4,000. The developers filed a $375,000 claim with the insurance company, but the claim was not settled for more than a year because the insurance com- pany had also filed for bankruptcy. By the time the company was ready to investigate the claim, the condominium had been destroyed by the city. In the end, the insurance company paid out $225,000. After administrative ex- penses, legal fees, and other costs were subtracted, there was only $131,000 left to meet the secured creditors’ claims, which totaled $720,000 (Sayre and Komar 1988). The largest settlements went to the contractor and the lumber company, both of which were also bankrupt. The 43 unsecured creditors, including the developers’ attorney and their consulting geologist, requested a total of $283,000 but received only $3,544. The Oregon State Board of Geologist Examiners filed a complaint against the developers’ geologist over this and five other projects (Sayre and Komar 1989). The board decided to revoke his certification, citing in a news re- lease his “incompetence and gross negligence.” The Newport City Council adopted a new subdivision ordinance and a new comprehensive plan. Friends of Lincoln County was involved in the proceedings and contended that no development should be allowed at Jump-Off Joe. Nevertheless, the area remains zoned for high-density multifamily dwellings, although now with a geological hazards overlay that allows the city to request additional information and more exploration. The ownership of the bluff is still in question, but the down-dropped block is owned by a Los Angeles devel- oper. The city hopes eventually to acquire the land. The Jump-Off Joe Fiasco 173 174 10 The Northwest Coast— A Heritage to Be Preserved As the twenty-first century approaches, we face new challenges on the Northwest coast. Behind us is a century of development, and now is a good time to reflect on where we are and what must be done to manage and pre- serve our coastal resources. We have a much better understanding of the processes of coastal erosion and its impacts than we did even a decade ago. Will it be possible to use that information to make management decisions that will limit erosion and financial loss on the coast? Can midcourse cor- rections help us avoid further proliferation of the seawalls and rip-rap re- vetments that have begun to mar our coast? The decision is ours to make. Will it be seawalls or wise management? We are fortunate in having established public ownership and good access to the beaches of the Northwest. On the Washington coast, the 25-mile stretch of shore on the Long Beach Peninsula is open to the public along its full length. Farther to the north is Olympic National Park, with complete public access to beaches and trails along the rocky stretches of coast. Even in areas of the Washington coast that are privately owned, the public has ac- cess to the beaches. This is also the case along the Oregon coast, where an unparalleled system of state parks, waysides, and paths provides more than 600 beach access points. We in the Northwest tend to take for granted our ready access to any beach. We come to more fully appreciate that freedom only when we travel to other states where those rights have not been established. For example, only 10 miles of the 1,300-mile coast of Massachusetts are publicly owned (Straton 1977). Most of the Florida coast has been claimed by hotels, exclu- sive beach clubs, and private homeowners. Less than one-fifth of the 1,200 miles of coast in California is open to the public. The public ownership of beaches in the Northwest came about in part through happenstance. The first white settlers lived in relative isolation along the shores of bays and estuaries (see chapter 4). North-south travel Figure 10.1 The beaches were the best routes for north-south travel along the Northwest coast prior to the construction of highways. From the Oregon Historical Society, Portland. was easiest along the wide ocean beaches, which were adopted as ready- made roads (fig. 10.1). This use was formalized in 1899 when the Oregon legislature designated the 30 miles of ocean beach between the Columbia River and the south line of Clatsop County a public highway (Straton 1977). In 1913, the law was amended to make all ocean beaches highways. This placed beach ownership firmly in public hands, or so people thought until the right of full access to the dry-sand beach was challenged during the 1960s. Figure 10.2 Recreation on Northwest beaches over the decades was important in establishing legal public access. From the Oregon Historical Society, Portland. ss Figure 10.3 Former governor Tom McCall surveying the log barricade placed on the sandy beach in front of the Surfsand Motel in Cannon Beach on May 13, 1967. This denial of public access to the beach eventually resulted in the passage of the Or- egon Beach Bill. From the Oregonian, May 1967. The designation of beaches as highways was limited by law to the area ex- tending from extremely low tide landward to “ordinary” high tide. Most people assumed that this meant the entire sand beach and became accus- tomed to unquestioned use of it as a recreational playground (fig. 10.2). Ac- cordingly, there was a great deal of public concern during the summer of 1966 when the owner of the Surfsand Motel in Cannon Beach built a low barricade of logs around the dry-sand area adjacent to the motel and erected signs stating “Surfsand Guests Only Please” (fig. 10.3). This chal- lenge to public ownership and access resulted in the passage of the Beach Bill in 1967, which established the public’s right by long-established custom to recreational use of the dry sands of beaches along Oregon’s coast. Immediately after the Beach Bill became law, the state Highway Commis- sion began a survey of the entire coast to establish a permanent beach zone line, and the coordinates of that survey line became an integral part of the law. The line, which roughly corresponds to the edge of the vegetation backing the sandy beach, remains today as the jurisdictional limit of the state’s easement with rights of its citizens for recreational use. The first legal challenge to the Beach Bill came not from the Surfsand Motel in Cannon Beach, but rather involved an attempt to build a private road across the beach at Neskowin (fig. 10.4). Built to provide access to property along the bluff to the south on Cascade Head, the road extended in a U across the sandy beach, approximately 200 feet beyond the newly es- tablished beach zone line. The state challenged the road in the courts. The A Heritage to Be Preserved 177 judgment, handed down on August 26, 1968, ruled that the road was not in the public interest and affirmed that the public had acquired an easement. The Surfsand Motel case was similarly decided in 1969. State jurisdiction over the beaches further requires that coastal property owners obtain permits before constructing seawalls or rip-rap revetments that would extend across the beach zone line. Denial of such permits has been one of the main factors limiting the proliferation of shore protection structures along the Oregon coast. If the public has the right to use the beaches, it must also be guaranteed access to them. Fortunately, state officials recognized this at an early date, and in 1964 the Oregon State Parks Division began a program to improve and guarantee access by acquiring parcels of land at approximately 3-mile intervals. These now constitute our numerous state parks, waysides, and pathways leading to the beach. Although our rights to reach and use beaches have been preserved, our shores are not yet safe. Rapacious land developers and urban sprawl have become a serious threat to the Northwest coast. Many a once-quiet seashore resort has been lost to excessive development. Urban sprawl is insidious along the coast. The growth tends to follow Highway 101, which is pressed between the sea and the mountains of the Coast Range. Each year, more of the green space between successive communities vanishes as the highway is lined with ever more rv parks, motels, and fast-food restaurants. During the height of the tourist season, parts of Highway 101 feel like downtown Los Angeles. Nowhere is this worse than in Lincoln City, which has grown into a hodgepodge of unplanned and unattractive commercial develop- Figure 10.4 Construction of a road across the beach at Neskowin triggered the first court test of Oregon’s Beach Bill. From the Oregon Department of Transporta- tion. 178 ments. Touted by the Chamber of Commerce as the “Twenty Miracle Miles,” visitors more often glumly refer to it as the “twenty miserable miles.” The urban sprawl extends all the way to the beaches. The sea cliffs and sand spits are lined with houses, motels, and condominiums, interrupted only by state parks. The wholesale development of properties backing the beaches has resulted in increased problems with erosion because natural processes continue to act without regard to humans’ presence. The erosion has led to the proliferation of seawalls and revetments. The natural beauty of the coast is increasingly marred by the presence of these structures. This is where the challenge now lies if we are to preserve the beauty and natural- ness of the Northwest coast for future generations. Increasing development and its associated problems have led nearly all the coastal states to adopt plans for the management of their coastal zones. While these programs vary in their emphasis, most reflect a concern for the preservation of coastal environments. The main initiative has been the Coastal Zone Management Act passed by the U.S. Congress in 1972 with four main objectives: (1) to protect fragile coasts; (2) to minimize life and property losses from coastal hazards; (3) to create better conditions for coastal resource use, including better access for recreation; and (4) to pro- mote intergovernmental cooperation, leading to a reduction in bureau- cracy. The federal government provided grants to the states to establish coastal management programs, and the states were required to submit their programs to the federal government for evaluation and approval. In 1976, Washington became the first state to have its coastal manage- ment program approved and implemented; approval of Oregon’s program followed soon thereafter in 1977. Both states delegated much of the devel- opment of their coastal zone management programs to the counties and cities. This has turned out to be an unfortunate decision. Each community has somewhat different regulations, and too often the county or city offi- cials are lax in enforcing the management policies. A tragic example is the attempt to develop the Jump-Off Joe landslide site discussed in chapter 9. One of the basic principles of coastal zone management is to avoid plac- ing homes and other structures in hazardous zones. Jump-Off Joe was by far the best-known geological hazard along the Oregon coast, yet approval to develop was forthcoming at the local level, from the city of Newport. The consequences of this unwise development became obvious when the still-unfinished condominium was destroyed by slumping and bluff ero- sion. An enlightened and well-implemented coastal zone management pro- gram should prevent construction in areas prone to rapid erosion and landslides. We don’t need any more Jump-Off Joe fiascoes. More uncertain is the regulation of development close to cliff edges that are retreating at A Heritage to Be Preserved 179 slow rates from episodic erosion. In most cases it is difficult to predict the rate and degree of future erosion, and the wisest policy is to stay well back from the cliff edge. The establishment of reasonable setback lines based on long-term recession rates of the sea cliff would do much to ensure building safety. Setback lines are particularly important on sand spits and in other dune areas because of the rapidity with which erosional processes cut back such areas. Our analyses of predevelopment aerial photographs of Siletz Spit (see chapter 6) showed that erosion could cut back the foredunes by up to 50 feet within just a few weeks. Had setback lines been established on Siletz Spit, development in that naturally ephemeral zone could have been prevented. Unfortunately, the developers did not commission studies of the spit’s sta- bility before building, and homes were placed in foredune areas that had eroded away only a decade earlier. Potential increases in sea level and subsidence associated with subduction earthquakes should also be considered when drawing setback lines, both for sea cliffs and for foredunes backing beaches. New homes could be designed to be more readily movable should erosion be greater than expected. Setback lines have been established for many areas of the Oregon coast, yet they are commonly ignored and development in hazardous areas has not been significantly curtailed. The Siletz littoral cell is one of the most ero- sion-prone areas on the Oregon coast, and one of the most extensively de- veloped (Good 1994). Nearly 20 percent of the construction there has oc- Figure 10.5 Annual construction of shore protection structures in the 14-mile- long Siletz littoral cell and their cumulative length (6.8 miles as of 1991). Construc- tion increases immediately after El Nino events, which can be ranked as moderate (M), strong (S), or very strong (VS) depending on the intensity of the coastal ero- sion processes they generate. From Good 1994. 8 ALONGSHORE LENGTH OF SHORE PROTECTION 6 Lincoln City Littoral Cell cumulation length of structures Length in miles El Nino Years strong medium very strong — — — 180 Figure 10.6 A massive rip-rap revetment on the beach in the Siletz littoral cell restricts access to the beach and is a visual blight. curred since Oregon’s coastal zone management program was adopted and went into effect in 1977. The spit’s shoreline has been gradually hardened with protective structures, mostly large rip-rap revetments and concrete seawalls (fig. 10.5; Good 1994). By 1991, 6.8 miles, or 49 percent, of the 14 miles of beachfront shoreline within the Siletz littoral cell had some sort of protective structure. A review of the permits that were issued for these structures showed that in 35 per- cent of the cases there was no threat from erosion or land instability that ac- tually warranted building a shore protection structure (Good 1994). In 28 percent of the cases the lots were vacant, so no homes could have been in danger. Local policies require property owners to install a hard shore protection structure in order to obtain a building permit. A number of vacant ocean- front lots are shallow and virtually unbuildable without an erosion preven- tion structure, but new construction can ignore the setback zone so long as the property can be adequately “stabilized.” Too often, this means that a new seawall or revetment is constructed whether or not there is any danger from active or potential erosion. The end result is that much of the beauty of the coast within the Siletz littoral cell, and especially within the area of Lincoln City, is marred by large seawalls and great heaps of rip-rap (fig. 10.6). In addition to their aesthetic effects, shore protection structures block new sand from reaching the beach. As more and more structures are con- structed, the supply of sand will further diminish, and “protected” beaches will become ever narrower as the sea level continues to rise. Coastal man- agement policies were intended to give preference to hazard avoidance and nonstructural means of erosion control. In practice, however, as seen in the Siletz littoral cell, seawalls and revetments have become the preferred haz- ard-reduction strategy, much to the detriment of the coast (Komar and Good 1989b; Good 1994). A Heritage to Be Preserved 181 ae wé ( Fai a Figure 10.7 This massive creosote-covered seawall is an unnecessary eyesore; there was minimal bluff erosion at this site. Too often, those who decide whether or not a property should be devel- oped or whether the construction of a shore protection structure is war- ranted do not adequately assess the property’s susceptibility to erosion. Such an assessment requires determining the expected wave run-up during extreme storms at high tides versus the capacity of the fronting beach to act as a buffer (see chapter 3). This information must be determined for each oceanfront lot that is to be developed or protected. Detailed site evaluations by registered engineers or geologists are required when a development is proposed, but their reports almost never include analyses of the potential susceptibility to erosion. It is surprising how many expensive seawalls and revetments are built to protect areas that do not need them. Such is true of a massive seawall on the scenic north Oregon coast (fig. 10.7) that creates both a visual blight and an olfactory one—it can be smelled for a considerable distance because it is coated with creosote. In this case, the developer was told to build the home well back from the cliff edge so there would be no danger from erosion. This would have involved a relatively small setback distance since the long- term erosional retreat of the cliff at that site has been negligible. Unfortu- nately, this reasonable recommendation was ignored, and the house was placed as close to the cliff edge as possible. As soon as the house was com- pleted the owner requested permission to build a seawall, and it was granted even though he had ignored the previous warning and no erosion had occurred subsequent to construction. 182 In another example, permission was given to construct a large seawall in front of an older house (fig. 10.8), in spite of objections from neighbors and even though the bluff has not experienced erosion within historic times. The absence of erosion was readily apparent in the thick vegetation cover- ing the bluff, including sizable trees that could also be seen on old photo- graphs of the site. The geologist who performed the site inspection for the homeowner reported that the property was undergoing 2 feet of bluff re- treat per year. This would seem to be another case of a consultant tailoring his conclusions to fit the desires of his client. Unfortunately, these two cases are not unique. County commissions and city councils almost always grant requests for the construction of seawalls, whether or not they are needed to halt erosion. Only the state has at- tempted to prevent seawall construction, but the state has a say in the mat- ter only if the proposed structure crosses the beach zone line or if a large volume of material is to be excavated during construction. A new element that must be considered in management decisions on the Northwest coast has been recognized within the last decade: the potential for a subduction earthquake and accompanying tsunami. Only recently have we learned that such events have already occurred a number of times in the past, the last one on the evening of January 26, 1700 (see chapter 2). Based on the time intervals between past events, the 300 years since the last major earthquake places us well within the window for another. We do not know whether it will occur today, tomorrow, or not for another century or more, but without a doubt such an event is on the agenda for the Northwest coast, and we must be prepared for it. Figure 10.8 An unnecessary seawall now mars the natural beauty of the coast south of Cannon Beach, Oregon. A Heritage to Be Preserved 183 The next subduction earthquake will probably have a magnitude on the order of 8 to 9 and will cause mass destruction along the coast and well in- land, effectively isolating communities from outside help. It is estimated that the tsunami waves generated offshore by the earthquake will reach the shore within 10-20 minutes. According to studies of sediments deposited by past tsunamis (chapter 2), these immense waves may wash over low-lying coastal areas and travel many miles up bays and estuaries, causing destruc- tion all along their shores. It is imperative that residents disregard the earthquake shaking and destruction and get out of the path of the expected tsunami. This danger is being recognized by more and more coastal com- munities, and a few already have evacuation plans, including warning sirens and evacuation routes that lead to safe elevated areas. A number of schools teach their students about earthquake and tsunami hazards, and a few have annual drills. Unfortunately, the extreme tsunami hazard has not yet significantly af- fected development along the coast. It is expected that the primary response will be to place schools and hospitals in safer areas and in buildings with re- inforced construction. Little consideration has been given to the thousands of homes—and people—that will be in the path of the destructive tsunami waves. It would be easy to become despondent in the face of the rapidly expand- ing development and the proliferation of shore protection structures on the scenic Northwest coast. 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References 191 Index figure numbers appear in italic type Agate Beach, 123, 7.6 Alsea Bay, 31, 123-128, 2.16, 7.7, 7.8, 7.9, 7.10 Alsea Spit, 123-128, 7.7, 7.8, 7.9, 7.10 Astoria, 22, 66—67, 2.11 Bandon, 19, 151-153, 8.18 Bayocean Spit, 73-92; breach, 84-86, 5.9; development of, 73-78, 5.2, 5.3, 5.45 erosion, 80-92, 5.7, 5.8, 5.9, 5.11; jetties 78-80, 5.5 Beach: access, 175-178; embayments, 49, 99-100, 104-105, 111, 154, 3.14, 3-15, 6.7, 6.9; mining, 102-103; nourishment, 132; ownership, 175-178; profiles, 44— 48, 3.8, 3.9, 3.10, 3.12 Beverly Beach, 153, 154, 156, 8.18 Black sand, 16, 25 Breaching, spit, 84-86, 109, 111, 5.9, 6.15, 6.18 Budget of sediments, 102-103, 6.8 Cannon Beach, 153, 177, 8.18, 10.3 Cape Blanco, 20, 2.8 Cape Disappointment, 3.1 Cape Foulweather, 13 Cape Lookout, 13, 130, 2.3, 7.11 Cape Perpetua, 143, 1.2b, 8.9 Cape Shoalwater, 113-116, 6.19, 6.20 Cascade Head, 8.15 Chehalis River, 15, 2.4 Clatsop Plains, 28, 35, 52, 2.20 Climate, coastal, 37-38, 3.2 Coastal management, 179-184 Coastal Range, 12-13, 14, 16, 18, 25, 2.13 Coastal Zone Management Act, 179 Columbia River, 15-16, 24, 25-26, 27, 29, 65-66, 2.13, 2.15 Coos Bay dune sheet, 32, 33, 35, 2.18, 2.19, 2.21 Crescent City, 59 Currents, nearshore, 48—49 Drift logs, 104, 111, 113, 138-140, 6.10, 6.11, 8.4 Dunes, 1, 20, 32-36, 1.2¢, 2.18, 2.19, 2.20, 22In Onl Earthquakes, 9-12, 59, 153, 180, 183-184, 2.1 Ecola State Park, 147, 8.16 El Nino, 117-133; and Alsea Spit erosion, 123-128, 7.7, 7.8, 7.9, 7.10; beach re- sponse, 123, 7.5, 7.6; and Netarts Spit erosion 128-132; occurrences, 132-133; origin of, 117-118; sea level, effects on, 118-121, 7.2, 7.3; and tides, 122; and wave conditions, 121, 7.4 Embayments, 49, 99-100, 104-105, 111, 154, 3.14, 3.15, 6.7, 6.9 Erosion, coastal: bayside, 106-109, 6.9, 6.12, 6.13; beach, 72, 4.6; and jetties, 86-91; and rip currents, 48, 49, 98-100, 137, 3.13, 3-14, 3.15, 6.7, 8.3; and storms, 95-99; and tides, 53-54, 100-101. See also entries for individual sites Estuaries, 30—32, 6.12 European beach grass, 35, 2.20, 2.21 Fogarty Creek State Park, 8.5 Foredunes, 104-106, 6.2, 6.10, 6.11 Glaciers, 14, 15 Gleneden Beach, 45, 102, 154, 158-159, 3.9, 3.10, 8.3, 8.6, 8.22 Global warming, 24 Gorda Plate, 9, 2.2 Gorda Ridge, 9, 2.2 Grays Harbor, 15 Greenhouse effect, 2 Headlands, 1, 27, 1.3, 2.3 Indians. See Native Americans Jetties, 502-52, 78-80, 86—91, 3.16, 5.5, 5.10, Sill, 5215013 Juan de Fuca Plate, 9, 2.2 Juan de Fuca Ridge, 9, 2.2 Jump-—Off Joe landslide, 161-173, 179-180, 8.10, 8.12, 9.2, 9.4, 9.5; and cliff retreat, 163-165, 9.2; and development, 162, 166, 9.6, 9.7, 9.8; property destruction and, 9.4, 9.10; sea arch, 9.1, 9.3 Klamath Mountains, 25, 26, 27, 2.13 Landslides, 145-147, 8.11, 8.13, 8.15. See also Jump-—Off Joe Lincoln City, 154, 181, 8.1, 8.5, 8.8, 8.18. See also Taft Littoral cells, 27, 102-103, 123, 128, 148, 180-181, 6.8, 7.5, 7.11, 8.17 Littoral drift, 49, 50-52 Long Beach Peninsula, 1, 29, 52, 114, 175, 1.24, 2.15, 6.19 Management, coastal, 179-184 Mining, sand, 102-103 Native Americans, 67—69 Nearshore currents, 48—49. See also rip currents Neskowin, 177-178, 10.4 Nestucca Spit, 54, 109-113 Netarts Spit, 128-132, 1.2b, 7.11, 7.12, 7.13, 7:14 Newport, 69-71, 135, 4.2, 4.3, 4.4, 8.1, 8.13. See also Jump—Off Joe; Yaquina Bay 194 North American Plate, 9, 2.2 Olympic National Park, 175 Oregon Beach Bill, 177, 10.3, 10.4 Oregon Dunes, 1, 20, 1.2¢ 4 Otter Rock, 45-46, 2.5, 3.9 Plate tectonics, 7-14 Rip currents, 48, 49, 98-100, 111, 130-131, 1375 154, 3.13, 3-145 3.15, 6.7 Rip-rap, 95, 97, 110, 157, 181, 182, 6.4, 6.13, 6.17, 7.9; 7.10, 8.21, 10.6 Sand: black, 16, 25; budget of sediments, 102-103, 6.8; grain diameters, 8.19; minerals, 24—27; mining, 102-103 Sand bars, 47, 48, 3.12 Sea cliffs, 135-160; erosion processes and, 135-145, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.8; erosion variations, 147-155; graffiti on, 143, 8.8; recession of, 155-156; rock compositions, 140, 144-145, 153-154, 8.5, 8.10; structure protection and, 156— 159; vegetation, 143, 158, 8.7 Seafloor spreading, 8, 9 Sea level, 14-24, 27, 118-121, 2.9, 2.10, 2.11, DiI 2727.3 Seaside, 59 Seawalls, 130, 169, 181-183, 7.13, 7.14, 10.7, 10.8 Setback lines, 156, 180-181, 182 Shoreline embayments, 49, 99-100, 104— 105, 111, 154, 3.14, 3.15, 6.7, 6.9 Shore-protection structures, 156-159, 179, 180-181, 10.5, 10.6 Siletz Spit, 93-109, 180-181; and bayside erosion 106-109, 6.9, 6.12, 6.13; devel- opment, 93-95, 6.2; erosion 95-109, 6.3, 6.4, 6.5, 6.6, 6.7, 6.11; and shore protection structures, 180-181, 10.5, 10.6 Siuslaw jetties, 87—91, 5.10 Sneaker waves, 57 Solando, 48, 3.12 Storm surge, 54, 101 Storms, 95-101, 109-113, 121-122 Subduction earthquakes, 9-12, 59, 153, 180, 183-184, 2.1 Taft, 138-140, 156, 8.4 Tectonic rise, 18 Terraces, marine, 16, 17, 18, 19, 2.5 Tides, 21, 52-54, 100-101, 122; El Nino dur- ing, 122; gauges, 21; neap, 53; perigean, 533 Spring, 53, 109 Tillamook Bay, 73, 5.1, 5.5 Tillamook Head, 27, 28 147, 2.14, 2.15, 8.16 Tsunami, 10-12, 57—61, 183-184, 3.19, 3.20 Upwelling, 55-56 Water levels, 54-56, 100-101. See also sea level; tides Waves, 38—44, 49-50; and El Nino, 121, 7.4; generation, 38—41, 3.3; heights, 41, 3.4, 3.6, 3.7, 6.16, 7.4; Measurements, 41—43, 109, 3.5, 3-6, 3.7%) 6.16, 7.4; periods, 56— 57; runup, 56-57; seismometer mea- surement, 41—43, 109, 3.5, 6.16, 7.43 setup, 56; significant height 41; sneaker, 57 Willapa Bay, 113, 6.19, 6.21 Yaquina Bay, 30-32, 53, 55, 59, 69, 120-121, Dip, SiG AO, 763} Yaquina Head, 13, 123, 7.6 Index 195 Paul D. Komar is Professor of Oceanography at Oregon State University. He is author of Beach Processes and Sedimentation and editor of Hand- book of Coastal Processes and Erosion. Library of Congress Cataloging-in-Publication Data Komar, Paul D. The Pacific Northwest Coast : living with the shores of Oregon and Washington / Paul D. Komar. p. cm.—(Living with the shore) Includes index. ISBN 0-8223-2010-x (alk. paper).—1sBN 0-8223-2020-7 (pbk.: alk. paper) 1. Shore protection—Washington (State) 2. Shore protection—Oregon. 3. Coast changes—Washington (State). 4. Coast changes— Oregon. 5. Northwest coast of North America. I. Title. II. Series 10€223.8.K66 1998 627'.58'09797—dc21 97—23870 CIP - Soe oe Im | ibraries 2 i = o = Sai 3S N ———S=A = a £ fo) S a) Wi Se Poe oee rece arty: L saree sions SSS Sse eresseeeee