‘91“? ' '3' X ‘1‘ It A :‘;3 U C L"‘..‘,g\...*....m :a-a a Law“ »> a Q " ‘ MAPS SEA FLOOR TOPOGRAPHY OFTHE CENTRAL EASTERN PACIFIC OCEAN United States Department of the Interior U.S. FISH AND WILDLIFE SERVICE BUREAU OF COMMERCIAL FISHERIES Circular 291 United, States Department of the Interior U.S. FISH AND WILDLIFE SERVICE BUREAU OF COMMERCIAL FISHERIES SEA FLOOR TOPOGRAPHY OFTHE CENTRAL EASTERN PACIFIC OCEAN BY Thomas E. Chase Circular 291 Washington, D. C. June 1968 5/ x) // 27“? fl 1'”: at?” } Created in 1849, the Department of the Interior—a department of conservation—is concerned with the management, conservation, and development of the Nation’s water, fish, wildlife, mineral, forest, and park and recreational resources. It also has major re- sponsibilities for Indian and Territorial affairs. As the Nation’s principal conservation agency, the Department works to assure that nonrenewable resources are developed and used wisely, that park and recreational resources are conserved for the future, and that renewable resources make their full contribu- tion to the progress, prosperity, and security of the United States— now and in the future. CONTENTS INTRODUCTION ......................................... CHART PROJECTION AND SCALE ........................... AREA COVERED ......................................... METHODS ............................................... Echo-sounding ......................................... Vertical exaggeration ............................... Other reflecting surfaces ............................. Compilation of Data ................................... Contouring ........................................... MAJOR GEOLOGICAL FEATURES OF THE EASTERN PACIFIC ..................................... Continental Shelf ....................................... Continental Borderland ................................. Continental Slope ..................................... Submarine Canyons ..................................... Oceanic Rises ......................................... East Pacific Rise ................................... Galapagos Rise ................................... Oceanic Trenches ..................................... Fracture Zones ....................................... Murray Fracture Zone ............................... Molokai Fracture Zone ............................. Clarion Fracture Zone ............................... Clipperton Fracture Zone ........................... Galapagos Fracture Zone ............................. Easter Island Fracture Zone ......................... Volcanic Ridges ....................................... Tehuantepec Ridge ................................. Cocos Ridge ..................................... Nasca Ridge ..................................... Malpelo Ridge ..................................... Coiba Ridge ....................................... Carnegie Ridge ..................................... Galapagos Platform ................................. Submarine Volcanoes or Seamounts ....................... Mathematician Seamounts ........................... Baja California Seamount Province ..................... Guyots or Tablemounts ................................. ACKNOWLEDGMENTS ................................... SELECTED REFERENCES ................................. APPENDIX—Charts ......................................... wwNNb—tn—Au—tt— \O\l\l\l\l\l\l\l\l\l\l\l\l\l\lO\O\O\O\O\UI€/IUIUI-lk-h-h-BA-FW ABSTRACT The offshore configuration of the floor of the eastern Pacific Ocean is presented on 26 topographic charts. A description of the methods and data used in their preparation is included with a general outline of the major topo- graphic features of the region. Innovations incorporated in the series of charts include a search and evaluation of all existing data pertinent to the sea floor topography, contouring of the region in detail, and labelling of prominent undersea geological features. 885308 INTRODUCTION The Bureau of Commercial Fisheries Tuna Resources Laboratory, La Jolla, Calif., in cooperation with the Institute of Marine Resources, Uni- versity of California, La Jolla, has prepared and issued a series of sea floor topography charts of the eastern Pacific Ocean. The Bureau of Commercial Fisheries has been studying the environment of the eastern Pacific Ocean as part of a long-range plan to forecast the availability of tuna and to increase the efficiency of the nation’s domestic tuna fisheries. The Institute of Marine Re— sources has been investigating the mineral content and the geology of the sea floor. Knowledge of the topography of the sea floor is important to both in- vestigations; the charts presented here summarize available sounding data col- lected over 15 years by many institutions and agencies. These charts represent a first attempt to describe the topography of this vast oceanic province in detail. Most marine charts published today are printed with the depths plotted as isolated sets of numbers and occasional contours. Such charts give water depth at a particular fixed point or along a single contour line but are mis- leading because the depth may change rapidly within a short distance. Existing marine charts of the eastern Pacific Ocean are inadequate for describing most deep-sea geological features. Fishermen cannot interpret many of the features because the charts do not show the configuration of the sea floor. To portray the sea floor in detail, depths must be plotted as closely as possible so that contour lines can be drawn through points of equal depths to give expression to heights and depths, and to show gradients of slopes. In re— cent years, continuously recorded echo-soundings along numerous ship tracks have provided the data necessary for preparation of contour charts. The main effort of the tuna fisheries in the eastern Pacific Ocean has been concentrated near continental shelves, slopes, and shoal areas around islands. Since the inception of the temperate zone fisheries in 1903 and the tropical zone fisheries in 1915, vast quantities of tuna have been caught in shelf and shoal regions. In 195 7, Hurricane Bank, later named Shimada Bank, was discovered by the tunaboat Hurricane at lat. 16°52' N., long. 117°32' W. (see fig. 1 and chart 11, Appendix A). Through 1964, a total of 16,398 tons of tuna had been caught at this bank.2 The large catches of yellowfin and skipjack tuna at Shimada Bank led to the question of the existence of other unknown submarine features that would offer new and productive fishing localities. The Scripps Institution of Oceanography, University of California, San Diego, has conducted extensive oceanographic and geological expeditions since the early 1950’s. Many of these expeditions have been specifically for the investigation of the eastern Pacific, and others have traversed this region enroute to other areas (fig. 2). Most of the vessels were equipped with echo- sounding devices that recorded the depth of the sea floor while the ships were underway. These expeditions have provided a wealth of high-quality sounding data from which many new geological features have been discovered. Many of these features have been illustrated in various scientific publications, but the enormous accumulations of sounding data have never been compiled onto regular charts. Although most of the sounding information for our charts came from expeditions of the Scripps Institution of Oceanography, other organizations also provided valuable data. Charts of the U. S. Navy Oceanographic Office contain spot soundings and the 100-fathom contour; these have been incor— porated on many of our charts. Additional sources of data were the British Admiralty, the International Hydrographic Bureau in Monaco, and vessel mas- ters of the southern California tuna fleet. The purpose of this circular is to present the complete series of topo- graphic charts under one cover for ease in referencing the floor of the eastern Pacific Ocean as it is known at the present time. The 26 individual charts are included in the Appendix, reduced to one-half of the original size. The ori- ginal topographic charts were issued at a standard size of 22 by 34 inches and distributed by the Bureau of Commercial Fisheries Tuna Resources Labora- tory, P. O. Box 271, La Jolla, Calif. 92037. 1Present address, Department of Earth Sciences, Scripps Institution of Oceanography, Uni- versity of California, San Diego, La Jolla, Calif. 92037. 2Unpublished report, Inter-American Tropical Tuna Commission. By THOMAS E. CHASE, Geologistl Bureau of Commercial Fisheries; Fishery-Oceanography Center La Jolla, California 92037 Figure 1. Location map of Shimada Bank (formerly Hurricane Bank). Contours are in fathoms. The charts are not intended to represent definitive configurations of the sea floor but to provide a general picture of the major topographic features in the eastern Pacific Ocean. Regional features have been labelled for ease of identification. Reported shoal positions were checked against known accurate depths close by. All could not be surveyed and checked, however, owing to the time limitations of the project. Consequently, some reported positions have been labelled as “existence doubtful” or “reported” where verification was not possible. These charts are not designed for coastal navigation because the limitations of scale prohibited locating of all dangerous rocks and shoals on them. Publications of the U. S. Navy Oceanographic Office and the U. S. Coast and Geodetic Survey should be used for navigation in coastal regions. CHART PROJECTION AND SCALE The Mercator Projection was used for all charts. The nautical scale at lat. 20° N. is about 1:195,000. AREA COVERED The area of the eastern Pacific Ocean covered by the charts exceeds 4,530,000 square miles (fig. 3). Each chart covers 10° of longitude and 6° or 7° of latitude, except charts 12, 16, and 19, which cover 3° of longitude. A 1° Sea Floor Topography of the Central Eastern Pacific Ocean overlap of latitude occurs between charts 1 and 3, to give a complete portrayal of Guadalupe Island. A special, detailed chart of the Galapagos Islands area covers 7° of Ion— gitude and 4° of latitude. An additional chart was prepared to cover the area to the southwest of Clipperton Island (long. 110° to 120° W.; lat. 3° to 10° N.). This chart may also be requested from the Director, Bureau of Com- mercial Fisheries, Fishery-Oceanography Center. METHODS Preparation of a topographic chart involves the following steps: (1) col- lecting the sounding data by echo-sounding; (2) correcting the ship’s naviga— tional track to determine its true course; (3) plotting the soundings at appro- priate time intervals along the ship’s track; (4) compiling all available sounding data for the region to be entered on a single compilation sheet; (5) determin- ing an appropriate scale and contour interval; and (6) contouring and prepar- ing the chart. Discussion of these operations is given in detail so that the seagoing reader can interpret his own echograms and charts. Miles referred to on the topographic charts are nautical miles. ECHO-SOUNDING Echo-sounding is a method by which a sound impulse is transmitted from an instrument on the hull of a vessel, reflected from the sea floor, and received by an instrument on the ship as an echo. The length of time for the sound impulse to reach the sea floor and return to the ship as an echo is an ac- curate measure of depth at a given instant. With recording echo-sounding gear, depths of the sea floor may be recorded continuously while a ship is underway. Development of echo-sounding devices in the 1920’s marked the be- ginning of detailed portrayals of the sea floor. Few of the early models were capable of sounding the deep ocean, and detailed explorations were restricted to shallow regions until sophisticated instruments were developed during World War 11. Today, accurate depth measurements can be taken anywhere. Prior to 1956, the echo-sounder used by the Scripps Institution of Oceanography was the Edo Corporation Sonar Sounding Set AN/UQN-lB.3 The device was equipped with a transmitter-receiver, transducer, and a record- er which was modified to produce an echogram 91/2 inches Wide, with a scale in multiples of 600 fathoms. Two other models, the RCA NMC-l and the Submarine Signal Company NMC-2, were also used. In 1956, Scripps vessels were equipped with the Timefax Mark V Pre- cision Depth Recorder (PDR). This recorder, coupled with the Edo transmitter- receiver and transducer, gives a readout in multiples of 400 fathoms on an echogram 19 inches wide (fig. 4). thus permitting greater resolution of sea floor details. The frequency of the sound impulse leaving the Edo transducer is usually set at 12 kilocycles per second. Some soundings are taken with fre- quencies of 14 kilocycles per second but they constitute a small percentage of the total. The 12-kilocycle frequency allows the sound impulse to reach any depth of the ocean, whereas higher frequencies sometimes dissipate and do not attain the depths required for detailed topographic investigations. The speed of sound in sea water varies with the density of the water. The greater the density. the faster sound travels. A change in temperature or salinity, or both, causes variations in density and changes the speed of sound. The charts presented here have been prepared from uncorrected soundings, and incorporate an assumed constant average velocity of sound in sea water of 4,800 ft./sec. (800 fm./sec.). Maximum depth errors are 47 fathoms at depths of 2,000 fathoms.4 (Information concerning the correction values to be applied to echo-soundings is given by Matthews ( 1939). 3Trade names referred to in this publication do not imply endorsement of commercial products. 4Errors are conservative (i.e., depths recorded are too shallow) because the assumed sound velocity is slightly less than field experience indicates. 1 30° 25° 17° 130° |20° ”0° 100° 90° 80° 70° 35° 30° 25° 17° u o.- ''''' 10° 30 “52'... . ' .gv' . , in. ' . ' °° TRACK CHART OF OCEANOGRAPHIC EXPEDITIONS BY THE SCRIPPS INSTITUTION OF OCEANOGRAPHY ON WHICH SOUNDINGS WERE TAKEN 1950 -1965 Figure 2. Track chart of oceanographic expeditions by the Scripps Institution of Oceano- graphy on which soundings were taken, 1950-65 . The sound impulse leaving the echo-sounding transducer forms a sound cone that radiates outward with a beam angle of 60° at its apex (fig. 5). Be- cause the first return on an echogram comes from the first reflecting surface, the vessel may not always be directly over the spot which is being recorded. As the vessel travels over a protuberance on the sea floor, the trace on the echogram may be hyperbolic in shape, especially if the object is exceptionally narrow. Actually, the echogram consists of a series of hyperbolae (fig. 6), especially in areas of rugged topography. The roll of the ship further compli- cates the presentation on an echogram. An echo resulting from the sound cone passing over a high feature to one side of the ship’s track is depicted in figure 7. 4O /0" "' .' . [00 A /5° - "33121.12; 3'. - /5° 20°- 20, 24° = 24. 90° 80° 70° Changes in frequency resulting from fluctuations in the ship’s power source hampered operations of all early echo-sounders. Changes in frequency produce a speedup or slowdown of the recorder which results in recording an erroneous depth. Use of constant—frequency power sources in recent years has corrected this difficulty. Errors resulting from power fluctuations now are few. Vertical exaggeration—True slopes of the sea floor are much less steep than shown on the echograms and may be misleading unless vertical exaggera— tion is taken into account (fig. 8). At ship speeds of 10 knots the vertical exaggeration is about 20:1; that is, for every unit of horizontal distance tra- 130° 120° 110° 18821864 1882-8-64 30° 2 7 \\.-. 188.11-30-64 188117764“ 230 4 3 ‘ 1881010460 188113064 [8811-30641 17° 7 6 5 ‘ 133.11'30'64 133.11'30'64 1.831130%]:358'26'60 N /" 10°17 10 9 ‘ _ SPECIAL ISS.12-4-63 [8812-4-63 ISS.12-4-6£ISS.11-50‘64 CHARTZ 3o 15 14 13 12 58.113664188113064 18811-3064 _—___ ————— EQUATOR-——— 4o 18 77 {16 133.12'19'62 ISS.11'30‘64 100° / .\ SPECIAL CHART 7 1/0 20 79 188121962 1888-14-62 INDEX OF TOPOGRAPHIC CHARTS 22 2' O ’8 18812-1962 33.121962} 24° 24 23 90° 80° Figure 3. Index of topographic charts of the eastern Pacific Ocean. 1200 800 ‘1‘“ SEA noes: "be” srco~o ecuo 34.43" mum ECHO 61*)1 R 4320 FATHOMS H "——‘-—— SJHDNI 1200 ' 800 400 Figure 4. PDR (Precision Depth Recorder) echogram showing scale changes in multiples of 400 fathoms. Second and third echoes have bounced off ocean floor and vessel two and three times, respectively. versed, the change in vertical distance recorded on the PDR is 20 times the true change in vertical distance, so that true slopes are 1/20th of recorded slopes. Other reflecting surfaces—Two other reflecting surfaces deserve men- tion. The most common is the Deep Scattering Layer, or DSL, (Dietz. 1961). which was found on almost all of the echograms. The DSL consists of count- less organisms which are sensitive to light and rise toward the surface at night and descend to depths of 100 to 350 fathoms during daylight (figs. 9 and 10). Thickness of the DSL varies from 50 to 200 fathoms. At times the DSL was hardly noticeable on the echograms, but on occasion the layer was so promi- nent that the sea floor trace was obscured. The DSL may have been the cause of many reported but unconfirmed shoals in the eastern Pacific Ocean. Echo- grams with a limited depth range may record a false bottom trace off this sur- face and could have been misinterpreted as the actual depth of the sea floor. Another reflecting surface commonly observed on the echograms was a series of hyperbolic-shaped traces known as “long-finned echoes” (fig. 11). I assume that these traces represent some kind of marine life and that the inverted-V shape was the result of the sound cone passing over either a fish or a school of fish. Depths of the reflecting organisms ranged from just below the sea surface to 300 fathoms; most were between the surface and 200 fathoms. The geographical distribution of long—finned echoes. appeared to be random, but further investigation is needed to determine their frequency. ‘1 55“ lEVEL FAYHOMS IN DEPTHS Figure 5. Spreading of sound cone on the sea floor. Illustration drawn to scale. Figure 6. PDR trace of series of hyperbolic echoes resulting from sound cone. These ec oes indicate that the sea floor has many small sharp hills. SIDE ECHO Figure 7. PDR trace of side echo. Echo is formed by sound cone passing over high topo- graphy to the side of the ship’s track. COMPILATION OF DATA On the high seas, most shipboard navigators record the location of the vessel at regular times each day (morning, noon, and evening) throughout a trip. For most expeditions this procedure is usually sufficient. Navigation ac- curacy was the most important and recurring problem in compilation of the data, for a sounding is useless for survey purposes if the location of the obser- vation is not known accurately. m E O I .. 4 IL Figure 8. Example of vertical exaggeration by PDR of sea floor slopes (top) to true slopes (bottom). Vessel size at same scale on true slope would be smaller than a single dot shown in the shading pattern. Star fixes provided the most accurate positioning. It was usually neces- sary, however, to correct each ship’s track between standard fixes to deter- mine the ship’s position at the time soundings were recorded. Some electronic positioning was obtained by Loran A navigation, and, where possible, fixes were taken on known landmarks. The ship tracks were first corrected to true course, and soundings were plotted at specific time intervals. The method used to determine the correct course between two true positions is shown in figure 12. The true positions are star fixes but could apply to land fixes or electronic positioning as well. The most convenient time interval for plotting soundings was 6 minutes (fig. 13). High peaks or low troughs, when present, were plotted between the 6-minute intervals. The corrected track with the soundings plotted (shown in fig. 13) was entered onto a compilation sheet with soundings from other sources (fig. 14). CONTOURING Contoured charts portray the configuration of the topography of the sea floor in more detail than do plots of series of soundings. A single contour line represents an imaginary horizontal line of equal elevation or depth throughout its length. On marine charts the values are al- ways referenced to mean sea level. Most marine charts display only one or two contours. Many depict the 100-fathom contour and some also have the 1,000- fathom contour. Others have contours of lesser depths depending on the scale of the particular chart. The vertical distance between contours is the contour interval. Whereas wide contour intervals are sufficient for general de- scription of an area, much more of the topography may be shown by reducing the contour interval. The contour interval used for the charts in this circular is 200 fathoms; every fifth contour line (starting with 1,000-fathom contour) is printed heavier than the others to indicate multiples of 1,000 fathoms. The 100-fathom contour is included also as a broken line. The special chart of the Galapagos Island area has a contour interval of 100 fathoms. Certain rules must be followed to give an accurate contour chart. These rules also assist in interpretation of the chart. They are: 1. A given contour line must close—though the closure may not be shown on each chart. 2. A contour line never crosses another contour line. Figure 9. Echograms of DSL (Deep Scattering Layer). Top echogram shows organisms rising toward surface during evening twilight. Bottom echogram shows animals decend at dawn. Horizontal distance across echogram is about 10 miles. Vertical white line on echo- gram denotes time lulls in recording. 3. Contour lines never divide or converge to a point. They may appear to do so when they represent a vertical cliff, where contour spacing is difficult to maintain on the chart. 4. The spacing of the contours represents slope gradients. Narrow spacing denotes steep slope; wide spacing denotes gentle slope. 5. Depressions lacking outlets are shown by contours with short lines called hachures pointing downslope toward the center. 6. When going upslope and then into a depression, the first hachured contour line of the depression always has the same value as the last contour line crossed. 7. The contour interval is given on each chart. The uses of contours to illustrate sea floor features are shown schemat- ically in figures 15, 16, and 17. In figure 16, a submarine mountain is shown as having imaginary horizontal lines encircling the feature at various depths (A). The same process is shown for a depression in figure 17, in which hachures point downslope (see rule 5 above). Figure 17 also illustrates the spacing of contours; the steeper the slopes, the closer are the contours (rule 4 above). Contours prepared from a compilation sheet are depicted in figure 18. MAJOR GEOLOGICAL FEATURES OF THE CENTRAL EASTERN PACIFIC The geology of the floor of the central eastern Pacific Ocean is com- plex. Although some relatively flat areas occur, the region has numerous and large submarine mountains, ridges, and trenches; and smaller, less prominent units are scattered about. The major physiographic features are shown in figure 19. A brief description of noteworthy features and their location on the topographic charts is given below. For a complete description of the geol- ogy of specific areas, the reader is directed to the selected references listed at the end of this circular. Figure 10. Echograms of DSL displaying undulations but remaining at the same general depth. CONTINENTAL SHELF The Continental Shelf of the central eastern Pacific is extremely nar- row. It widens only where a bight into the continent creates bays and gulfs. The Gulf of Panama has the widest shelf in the region and extends a maximum of 85 miles seaward at long. 79°12' W. (chart 12). The Gulf of Tehuantepec also has a wide shelf. At lat. 10°17I N. the shelf is 40 to 60 miles wide, and at lat. 15°40' N. it narrows to less than 5 miles (charts 8 and 9). Tuna fishing occurs regularly in both regions. Other bights and wide shelves may be seen on charts 3, 5, 13, 16, 19, and 21. CONTINENTAL BORDERLAND Off the coast of southern California, the exact limit of the shelf (chart 1) is difficult to determine. This area has a rugged topography con- sisting of ridges and deep troughs similar to adjacent continental land forms and is known as the Continental Borderland (Shepard and Emery, 1941; Emery, 1960; Krause, 1961). Within this borderland are several sharp breaks in slope that might be interpreted as the limits of the Shelf. These slopes, however, descend into basins and rise again to form ridges. Cortes Bank and Sixty Mile Bank are on two of these ridges. A steep slope at long. 119° W., lat. 31 o15'N. bearing in a northwest direction is known as the Patton Escarpment. It drops from a ridge at depths of 600 to 800 fathoms to the deep-sea floor at depths greater than 2,000 fathoms (charts 1 and 2). This escarpment marks the western edge of the Continental Borderland and the Continental Shelf. Albacore and bluefin tunas are taken regularly each year by fishermen operating along the edge of this escarpment and near the offshore banks. San Juan Seamount is 22 miles west of the Patton Escarpment. It rises from the deep-sea floor and is not associated with the borderland (chart 2). CONTINENTAL SLOPE The Continental Slope displays varying widths and slope gradients. Several of the eastern Pacific slopes are among the steepest in the world owing to the presence of deep oceanic trenches adjacent to the continents (charts 5, 8, 9, 19, 20, 21, and 23). Figure 11. Echograms of “long-finned echoes” showing abundance and range in depth. Distance across echograms is about 10 miles. Note distinctive inverted V’s in lower illustration. SUBMARINE CANYONS Incised into the Continental Shelf and Slope in many locations are steep—walled features known as submarine canyons (charts 1, 3, 5, 8, 9, 10, 12, 13, 16, 19, 21, and 23). Known canyons are shown on the topographic charts by contours pointing toward the shore in V-shaped patterns. Submarine canyons are variable. Some describe a curve as they descend in depth, and others are nearly straight, with branches of tributaries entering the main canyon. Submarine canyons often are favored fishing locations, be- cause local currents tend to cause fish to concentrate nearby. OCEANIC RISES The oceanic rise system in the Atlantic, Indian, Antarctic, and Pacific Oceans is essentially continuous between oceans (Heezen, 1962; Menard, 1960). In the Atlantic, Antarctic, and Indian Oceans, the feature is near the center of the basin and is called the Mid-Ocean Ridge. The eastern Pacific Ocean sea floor has bulges in two places that are named the East Pacific Rise and the Galapagos Rise (charts 5, 10, 13, 15, and 17). lEGEND sun FIX A srAr|0N(srA) DATE (SE 157° SP 10.5 K" ARRIVE DEPAR 1 SPEED COURSE CHANGE COURSE 0900 ‘1: 090° 1000 9, no" I C E b 1100 5109 SH. 3 (5! 196° SP 10.5KcsEI DAVE Figure 12. Example of method used to achieve correct ship’s track. Broken lines represent inferred track. Solid line represents corrected track. An oceanic rise may not be detected by an observer unless he is aware of the general character of these features, for it may comprise areas as large as the North and South American continents combined (Menard, 1960). Oceanic rises are generally long, low bulges on the sea floor. These rises often are off- set by fracture zones, and segments may be as long as 6,000 miles. Height above the adjacent sea floor is as much as one-half mile (440 fathoms) and can be even higher when the crest has submarine volcanoes. The width of the flanks may range from 600 to 2,400 miles. East Pacific Rise—The East Pacific Rise appears at about long. 102° 10 W., lat 3°40 N. It has a 2- to 20-mile wide crest (as described by the 1,600-fathom contour) bearing almost true north (chart 15 ). On either side of the crest the rise slopes off to depths greater than 1,800 fathoms, and a series of small fault blocks produce a series of ridges and troughs trending parallel to the crest. At about long. 1030 W., lat. 9° N., the 1,600-fathom crest is offset toward the west about 60 miles, appearing again at long. 104° W., lat. 10° N. 4 MINUTE INTERVALS 0900 ‘1; 091° q- 1000 9: 182° noo STOP SM n 1500 0:9 51A s on; CSE198° SP1] Kts DATE Figure 13. Example of corrected track with time marks and depths plotted at 6-minute intervals. This discontinuity coincides with the Clipperton Fracture Zone and an un- determined but probable fracture zone at about lat. 8° N. North of the Clipperton Fracture Zone the crest displays entirely dif- ferent characteristics than to the south (chart 10). No longer is there a simple north-trending 1,600-fathom contour; here the crest is broken into smaller 1,600-fathom segments rising from a base about 200 miles wide having depths less than 1,800 fathoms. The general trend, however, is still toward the north. On the rise in this region are many volcanoes with peaks ranging from 710 to 1,165 fathoms deep. Further north, the crest narrows to about 120 miles and the 1,600—fathom contour is again more pronounced. The rise continues into the Gulf of California (Menard, 1960) and possibly under the western portion of the United States (Menard and Chase, 1965). Galapagos Rise—Extending south from Panama between lat. 82° and 83° W. is an area of rough topography which appears to be the northern por- tion of the Galapagos Rise. This rise, though not as well defined as the East Pacific Rise, appears east of the Galapagos Islands and south of the islands bends toward the southwest as displayed by the contours at long. 91° W., lat. 3° S. (charts 17 and 18; Menard, Chase, and Smith, 1964). OCEANIC TRENCHES The deepest portions of the eastern central Pacific Ocean are near the continents, as illustrated by the presence of oceanictrenches adjacent to Central and South America. Figure 14. Example of a compilation sheet with all available soundings entered. Of the 11 oceanic trenches in the entire Pacific basin, 2 are in the east- ern Pacific. These are the Middle America and Peru‘Chile trenches. The Middle America Trench (Fisher, 1961) begins west of the Tres Marias Islands off Mexico, extends the length of Middle America, and ends off the Gulf of Dulce, Costa Rica—a distance of 1,550 miles (charts 5, 8, 9, 10, and 13). The Peru- Chile trench (Fisher, 1962) extends from southern Ecuador to central Chile (charts 17, 19, 20, 21, and 23), and extends south of lat. 24° S., the southern limits of chart 23 of this circular. Both trenches parallel the shoreline of the continents and remain close to the edge of the landmass (about 20-100 miles). Both trenches have ridges approaching from the southwest and shoal where they intercept each other. In each case the deepest part of the trench lies south of this junction. The Tehuantepec Ridge intercepts the Middle America trench at about lat. 15° N., long. 95 °30' W., where the trench shoals to a depth of about 2,800 fathoms (chart 10). North of the Tehuantepec Ridge, the depths of the trench range between 2,600 and 2,800 fathoms. South of the ridge the depths range to over 3,400 fathoms. This same situation occurs in the Peru-Chile trench. The Nasca Ridge intercepts the trench at approximately lat. 15°20' 8., long. 76°20' W., where it shoals to less than 2,600 fathoms (chart 21). Depths north of the ridge average 3,200 to 3,600 fathoms, and to the south, greater than 4,000 fathoms; the deepest part is over 4,200 fathoms at lat. 21° S. (chart 23). FRACTURE ZONES The eastern Pacific sea floor is divided into segments by six major frac- ture zones. These zones are extremely long; some extend thousands of miles in an almost true east-west direction. Their width, however, is usually less than 100 miles. They are characterized by narrow bands of rough topography with high ridges and steep troughs. Faulting is the main cause of fracture zones. Volcanism may be indicated by either single cones or elongate ridges trending in the direction of the zone (Menard, 1965). The fracture zones have offset the East Pacific Rise in several locations (charts 5, 10, and 15). A pronounced change in depth across the zones, where faulting has shifted flanks of the rise, can be noted in charts 5, 10, and 15. Murray Fracture Zone—The Murray Fracture Zone enters the region at long. 130° W., lat. 33°25I N., and has an almost true east-west bearing of about 085° to 087° (charts 1 and 2). Topographically, the east-west orienta- tion of the 2,400-fathom contour displays the lineation common to all fracture zones. Between long. 125° and 127° W., vertical displacement is not extreme, except for a small trough greater than 2,600 fathoms at long. 126° W. Between FLAT SURFACE INCLINED FOR lLLUSTRATlVE PURPOSE FLAT SURFACE INCLINED FOR ILLUSTRATIVE PURPOSE FLAT SURFACE INCLINEO FOR ILLUSTRATIVE PURPOSE B Figure 15 (top). Projection of a submarine mountain onto a flat surface as contours. Figure 16 (center). Projection of a closed basin or depression onto flat surface as contours. Figure 17 (bottom). Example of slope variation. Closely spaced contours represent steep slopes, widely spaced contours represent gradual slopes. long. 129° and 130° W. the close spacing of the 2,400- to 2,600-fathom con- tours shows an escarpment of over 200 fathoms. A seamount at long. 121° W., lat. 34° N., and four of the Channel Islands (San Miguel, Santa Rosa, Santa Cruz, and Anacapa) all fall in the trend 5 Figure 18. Preparation of contour charts from soundings on compilation sheet. Contour interval is 200 fathoms. of the zone. This is about 45° off the trend of the Continental Borderland to the south and southeast of the zone (chart 1). The Murray Fracture Zone is the northern boundary of the Continental Borderland. Molokai Fracture Zone—The Molokai Fracture Zone occurs at about lat. 25° N., long. 130° W. (chart 4). This zone, named after Molokai Island in the Hawaiian Island chain, is an example of the length these fracture zones may attain. It extends from Molokai Island in the Hawaiian group to the coast of Baja California (Smith and Menard, 1964). An offset occurs at about long. 125° W. where the zone is shifted toward the northwest about 60 miles (chart 4); it then heads almost true east along the Shirley Trough until it joins the Cedros Deep off Baja California (chart 3). Clarion Fracture Zone—The Clarion Fracture Zone (charts 5 and 7), named after Clarion Island, the westernmost of the Revillagigedo Islands, en- ters the area at long. 130° W., lat. 17°30' N. This zone, marked by rugged topography for about 60 miles wide, has traces as far as 3,000 miles to the west (Menard, 1960). West of long. 116° W., the zone is characterized by nar- row ridges and long narrow troughs (chart 7); the ridges deepen from 1,800 to 2,000 fathoms at long. 117° W. to 2,400 fathoms at long. 129° W. Troughs greater than 2,600 fathoms are frequent between long. 127° and 1300 W. Two good tuna fishing banks, Alphecca Bank (chart 6), and Shimada Bank (chart 11), are along this zone. East of long. 116° W. the zone rises from depths over 2,000 fathoms to about 1,800 fathoms. Clarion Island (chart 6) rises from the western side of the ridge delimited by the 1,800 fathom contour. Echograms of SCOT Expe- dition in 1958 showed an abundance of long-finned echoes on both sides of the island. Between long. 112° W. and 110° W., the east-west trend is inter- rupted by the Revillagigedo Islands and Mathematician Seamounts, where the contours display a north-south lineation. East of the Revillagigedo Islands the zone is further complicated by the presence of the EaSt Pacific Rise. A ridge and trough between lat. 19° 10' N., long. 110° W. and lat. 18°30' N., long. 105° W., is an extension of the Clarion Fracture Zone (chart 5). Clipperton Fracture Zone—The Clipperton Fracture Zone, located at about lat. 10° N. is named after Clipperton Island (chart 10). The Clipperton Ridge (charts 10 and 11) is the most prominent feature of the zone found in the eastern Pacific. When surveyed in detail (Menard and Fisher, 1958), the ridge is found to consist of a series of elongate peaks rising from a single con- tinuous ridge. The good fishing areas west of Clipperton Island are on this ridge. The average depth of the base of the ridge is 2,000 fathoms. A steep narrow trough with depths greater than 2,800 fathoms is along lat. 10°40'N. at long. 109°50' W., where the eastern ends of the trough and ridge curve toward the south and end at lat. 9°55' N., long. 107° 10' W. .L A“ P R o VIN c E .- 5. ~ .‘ h\‘ A A SULTCASE ‘ “:SFZAMOU'NIE SHIMADA BANK" ' MATHEMATICIANS SEAMOUNTS . - 'T ' 71'. C, ,GUATEMALA - ’ _: BASIN , MAJOR GEOLOGlC FEATURES OF THE EASTERN PACIFIC Figure 19. Major geologic features of the central eastern Pacific. The Clipperton Fracture Zone intercepts the crest of the East Pacific Rise at about lat. 10° N., long. 1050 W., causing an offset of about 60 miles. East of the crest there is no prominent ridge Similar to the Clipperton Ridge, but the zone is expressed by the east-west orientation of the 2,000 and 2,200- fathom contours (charts 9 and 14). Galapagos Fracture Zone—West of Darwin Island in the Galapagos Islands lies the Galapagos Fracture Zone. The width narrows from about 200 “fig eGAL/A‘PA’GQSLMTUREA A .51 mm ZONE ‘ ‘ EASTER FRACTURE g... W' . l ‘\‘\ M\\\\v\ ‘ _ Q . . . miles at long. 95° W., to about 120 miles at lat. 97°30' W. (Shumway and Chase, 1961; chart 18). Easter Island Fracture Zone.—A small portion of the Easter Island Fracture Zone is shown on chart 24 from long. 84° W. to 90° W. at lat. 23°40' S. The major part of the zone is beyond the southern limits of this circular. This zone intercepts the Nasca Ridge at about lat. 23°40' 8., long. 84° W.; depths are greater than 2,000 fathoms between the two features. An elongate sea- mount with two unnamed peaks (178 fathoms and 474 fathoms) is at lat. 23°42' S., long. 85° 18' W., and lat. 23°42' 8., long. 85°39' W. 6 VO LCANIC RIDGES The eastern ends of the Clipperton, Galapagos, and Easter Island Frac— ture Zones are characterized by three major volcanic ridges (Tehuantepec, Cocos, and Nasca) which are parallel and branch off in a northeast direction extending almost to the coastline of the continents. Each ridge is the result of movement of its own fracture zone and is a branch of the fracture zone (Menard, 1964). Tehuantepec Ridge—The Tehuantepec Ridge begins at about long. 11° N., lat. 99 W. and trends toward the Gulf of Tehuantepec where it inter- cepts the Middle America Trench at long. 14°50' N., lat. 95°30' W. (chart 9). The ridge is about 300 nautical miles long, and about 40 nautical miles wide. The base of the ridge is shown by the 2,000-fathom contour; it consists of 10 submarine volcanoes along a line; the highest peak, at lat. 13°09' N., 96°51' W., is 988 fathoms deep. , A regional change in depth of about 200 fathoms occurs across the ridge from the northwest to the southeast. The northwest side has an average depth of 1,800 to 2,000 fathoms; the southeast side ranges from 2,000 to 2,200 fathoms. This deep is called the Guatemala Basin (chart 9). Cocos Ridge—Named after Cocos Island, which rises from one of the smaller elongate volcanoes on the main ridge, this ridge extends from the southern end of the Middle America Trench off Costa Rica to the Galapagos Islands, a distance of about 700 nautical miles(charts 13, 14, 17, and 18). The width is about 200 nautical miles at the eastern end, narrowing to about 80 miles at long. 89°54' W. From this position to the Galapagos Islands, it is bro- ken into smaller segments displayed by the 1,000-fathom contour (charts 13, 17, and 18). The area traversed by this ridge has produced excellent tuna fishing for many years. Paramount Bank is located on the north side of the ridge (chart 14). Nasca Ridge—The southernmost of the major ridges in the eastern Pacific is the Nasca Ridge. Branching off the Easter Island Fracture Zone, between long. 83° and 84° W., lat. 23°50' S., the ridge proceeds in a northeast direction toward the coast of Peru (charts 21, 23, and 24). Several seamounts along this ridge remain unexplored by U. S. tuna fishermen. One, located at lat. 21°31' S., long. 81°45' W., has a minimum depth of 175 fathoms. Peaks having depths of 170 fathoms at lat. 20°41' S., long. 80°51' W., and 176 fathoms at lat. 23°42' S., long. 85°18' W., are also located on this ridge. This region lacks detailed sounding information, and the probability of discovering additional submarine volcanoes is high. Malpelo Ridge.—The Malpelo Ridge is an elongate northeast-southwest feature with a width of 48 miles at the widest point and length of about 150 miles (charts 13 and 17). The Malpelo Ridge has a series of volcanoes rising to depths less than 800 fathoms. Malpelo Island rises from one of these volcanoes situated on the northwest side of the main ridge. Coiba Ridge—North of the Malpelo Ridge along the 82° W. meridian between lat. 5°30 N. and 7° 15' N. (chart 13) is the Coiba Ridge. A huge fault escarpment on the western side of this ridge at long. 82° W. has depths ranging from a 380-fathom peak to a trough greater than 1,600 fathoms within a dis- tance of about 7 miles. Carnegie Ridge.—The Carnegie Ridge lies in an east-west orientation at about 1° S. (chart 17). The Carnegie Ridge is in line with the Galapagos Plat- form; deeps greater than 1,200 fathoms lie between the features. Galapagos Platform.—The volcanic islands of the Galapagos region are perched on the top of a distinctive platform. The most striking characteristic of the platform is the steepness of the western and southern sides and the grad- ual slope toward the eastern end. The main portion of the platform is relatively flat and is shallower than 500 fathoms. Many banks less than 100 fathoms deep are between the islands. The general shape of the platform is described by the 1,000-fathom contour (special chart 1; charts 17 and 18). Yellowfin tuna are taken regularly from several locations on this platform. This region is active volcanically, and new banks may appear in the future.5 SUBMARINE VOLCANOES OR SEAMOUNTS A seamount is a submarine volcano with a relief or vertical distance from peak to base of 500 fathoms or more. Seamounts are usually conical and 5Vessel operators are requested to note the position of any shallow banks not indicated and report them to the Director, Bureau of Commercial Fisheries, F ishery-Oceanography Center, P. O. Box 271, La Jolla, Calif. 92037, or Department of Earth Sciences, Scripps Institution of Oceanography, La Jolla, Calif. 92037. have steep slopes, but they may be elongate. Many rise directly from the deep- sea floor, whereas others rise from volcanic ridges. Directional trends may be found even though a ridge is not present. Many have a moatlike depression that partially or completely surrounds the base (Menard, 1951). A seamount shallower than 100 fathoms is called an oceanic bank (examples: Shimada Bank, 15 fathoms; Paramount Bank, 95 fathoms; chart 14). To date, 229 seamounts have been found throughout the eastern Pacific Ocean; several areas stand out as having abundant evidence of volcanic activity. Two of these areas are described below. Mathematician Seamounts—This group, consisting of massive sea- mounts and deep, narrow troughs, is on the western flank of the East Pacific Rise. The area is one of extensive faulting and volcanism which is responsible for the extremely rugged topography. An example is the trough more than 3,000 fathoms deep at lat. 13° N.; 11 miles north and 6 miles south of it, two seamounts rise to depths less than 1,000 fathoms (charts 5, 6, 10, and 11). Baja California Seamount Province.—The largest number of seamounts in the eastern Pacific are within the Baja California Seamount Province (charts 1, 2, 3, 4, 6, and 7). Located between the Murray and Clarion Fracture Zones, this province has about 40 known seamounts. Jasper Seamount (sometimes called Showboat by albacore tuna fishermen), San Juan Seamount (chart 2), and Rosa Bank (chart 3) are within this province. A cluster of deeper volcanoes known as the Suitcase Seamounts exists between the Revillagigedo Islands and Baja California (chart 6). The name seamount is slightly misleading, for many of the volcanoes have not been sur- veyed in detail and the exact depth of their peaks is not known. GUYOTS OR TABLEMOUNTS A seamount with a broad flat top is known as a guyot or tablemount. The flat top is usually considered indicative of erosion by the surf zone at some time in the geologic past while the feature was an island. During the erosion process, the island may experience either slow or rapid subsidence. If the feature existed as an island in the tropical regions, coral reefs may also be present. If subsidence of the feature is faster than the growth rate of the coral, it sinks below the life zone of the coral (which then dies and becomes fossilized). If the rate of subsidence is less than the growth rate of the coral, the result may be a coral atoll. Clipperton Island is the only coral atoll in the eastern Pacific (chart 10). Several of the seamounts rising from the Nasca Ridge appear to be guyots.6 The entire ridge may have subsided, as the area outlined by the 800- fathom contour has the appearance of a truncated surface. Fieberling Guyot (chart 2) has been surveyed in detail (Carsola and Dietz, 1952). The existing sounding data are admittedly scarce in some sections of the eastern Pacific (see track chart, fig. 2). The larger geological features of the region are known. Many smaller details, such as seamounts, have not been discovered and vessels equipped with echo-sounders will certainly find new ones in the future, especially in regions where volcanism is common. Further investigations may change the configuration of the major features slightly, but at the present time these charts represent our best knowledge of the sea floor. ACKNOWLEDGMENTS Many persons offered assistance during the course of this project. The project was initiated and originally supported by the American Tunaboat Asso- ciation and implemented by John Newton. H. W. Menard offered guidance and encouragement from conception to completion and made available most of the data required for the project. Many members of the Scripps Institution of Oceanography made avail- able published and unpublished sounding data: R. L. Fisher, the Gulf of Cali- fornia, Cedros Deep, Middle America, and Peru-Chile Trenches; F. P. Shepard, the Continental Borderland off southern California,; D. C. Krause, the southern portion of the Continental Borderland. J. R. Moriarty, Bonnie Swope, and Janet Pyle made valuable suggestions in the drafting of the charts. S. M. Smith and T. W. C. Hilde offered assistance countless times throughout the project. Franklin Alverson and Nannette Clark of the Inter-American Tropical Tuna Commission provided information on locations and depths of submarine banks that are included on many of the charts. Lastly, appreciation is given to those tunaboat masters and navigators whose careful logbook entries served to pinpoint submarine features otherwise unobserved by the merchant marine and naval community. 6Downwind Expedition, 1958. SELECTED REFERENCES CARSOLA, ALFRED J., and ROBERT S. DIETZ. 1952. Submarine geology of two flat-topped northeast Pacific seamounts. Amer. J. Sci. 250: 481-497. CHUBB, L. J. 1933. Geology of Galapagos, Cocos, and Easter Islands. Bernice P. Bishop Mus. Bull. 110: 1-44. DIETZ, ROBERT S. 1962. The sea’s deep-scattering layers. Sci. Amer. 207(2): 44-50. DOWNWIND EXPEDITION. 1958. International Geophysical Year, General Report, No. 2. Nat. Acad. Sci., Nat. Res. Counc.: 58 p. EMERY, K. O. 1960. The sea off Southern California. John Wiley and Son Inc., New York, 366 p. ENGEL, CELESTE G., and THOMAS E. CHASE. 1965. Composition of basalts dredged from seamounts off the west coast of Central America. U. S. Geol. Surv. Prof. Pap. 525C: C161-C163. ENGEL, A. E. J ., and CELESTE G. ENGEL. 1964. Igneous rocks of the East Pacific Rise. Science 146: 477-485. FISHER, ROBERT L. 1961. Middle America Trench: Topography and structure. Geol. Soc. Amer., Bull. 72: 703-720. 1962. Pacific Ocean. ka. Sci. Technol.,McGraw-Hill,New York: 384-390. FISHER, R. L., and H. H. HESS. 1963. Trenches. I_nThe Sea 3: 411-436. Interscience Publishers, New York. FISHER, ROBERT L., and RUSSELL W. RAITT. 1962. Topography and structure of the Peru-Chile trench. Deep-Sea Res. 9: 423-443. FISHER, ROBERT L., and ROGER REVELLE. 1955. The trenches of the Pacific. Sci. Amer. 193(5): 36-41. HAMILTON, EDWIN L. 1956. Sunken island of the Mid-Pacific Mountains. Geol. Soc. Amer., Mem. 64, 97 pp. HEEZEN, B. C. 1962. The deep-sea floor, 235-288. I_n S. K. Runcom (editor), Continental Drift. International Geophysics Series 3, Acad. Press, New York and London, 380 pp. KRAUSE, DALE C. 1961. Geology of the sea floor east of Guadalupe Island. Deep-Sea Res. 8: 28-38. LUSKIN, BERNARD, BRUCE C. HEEZEN, MAURICE EWING, and MARK LANDISMAN. 1954. Precision measurement of ocean depth. Deep-Sea Res. 1: 131-140 MATTHEWS, D. J. 1939. Tables of the velocity of sound in pure water and sea water. (2nd ed.), H.D. 282, Admiralty, Hydrogr. Dep., London, 52 pp. MENARD, HENRY W. 1955. Deformation of the Northeastern Pacific Basin and the west coast of North America. Bull. Geol. Soc. Amer. 66: 1149-1198. 1956. Archipelagic aprons. Amer. Ass. Petrol. Geol.,Bull. 40: 2195-2210. 1959. Minor lineations in the Pacific Basin. Bull. Geol. Soc. Amer. 70: 1491-1495. 1959a. Geology of the Pacific sea floor. Experientia 15(6): 205-213. 1960. The East Pacific Rise. Science 132: 1737-1746. 1964. Marine geology of the Pacific. McGraw-Hill Book Co., New York, 271 pp. MENARD, H. W., and ROBERT L. FISHER. 1958. Clipperton fracture zone in the northeastern Equatorial Pacific. J. Geol. 66: 239-253. MENARD, H. W., and V. VACQUIER. 1958. Magnetic survey of part of the deep—sea floor off the coast of Califor- nia. Office of Naval Research, Res. Rev., June: 1-5. MENARD, H. W., T. E. CHASE, and S. M. SMITH. 1964. Galapagos Rise in the southeastern Pacific. Deep-Sea Res. 11: 233-242. 7 SELECTED REFERENCES (continued) RICHARDS, A. F. 1959. Geology of the Islas Revillagigedo, Mexico. Bull. Volcan. Ass. Volcan. Int. Union Geol. Geophys., Ser. 2, 22: 73-123. RUSNAK, G. A., and R. L. FISHER. 1964. Structural history and evolution of the Gulf of California. Amer. Ass. Petrol. Geol., Mem. 3: 144-156. RUSNAK, G. A., R. L. FISHER, and F. P. SHEPARD. 1964. Bathymetry and faults of the Gulf of California. Amer. Ass. Petrol. Geol.,Mem. 3: 59—75. SHEPARD, F. P. 1963. Submarine geology. ed. 2. Harper Bros., New York, 557 pp. SHEPARD, F. P. 1964. Sea floor valleys of Gulf of California. Amer. Ass. Petrol. Geol.. Mem. 3: 157-192. SHEPARD, FRANCES P., and K. O. EMERY. 1941. Submarine topography off the California coast. Spec. Pap. Geol. Soc. Amer., 31, 171 pp. SHUMWAY, GEORGE. 195 4. Carnegie Ridge and Cocos Ridge in the east equatorial Pacific. J. Geol. 62: 5 73-5 86. SHUMWAY, G., and T. E. CHASE. 1963. Bathymetry of the Galapagos Region. Occas. Pap. Calif. Acad. Sci. 44: 11-19. SMITH, STUART M., and H. W. MENARD. 1965. The Molokai Fracture Zone. I_n Progress in Oceanography. Pergamon Press, London, 3: 333-345. VON HERZEN, R. P., and S. UYEDA. 1963. Heat flow through the eastern Pacific Ocean floor. J. Geophys. Res. 68: 4219-4250. WILDE, P. 1966. Quantitative measurements of deep-sea channels on the Cocos Ridge, east central Pacific. Deep-Sea Res. 13: 635-640. APPENDIX Charts lA JOllA SUIMAIIN! 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I I I _ _ -- '-~,._: IT' ”0- I09° IOB’ ‘ ° ' ' ' IOI‘ IOO‘ 14 22' 2|' _ n I I I '0' d I I I" v I {:39 o _ g /m° 0 O 0 ~ €39 - 0 _ @ o _ o @ CA5£©T""SEAM <::> ° @O 3% A flwlwwmy o i 2 O‘ TOPOGRAPHIC CHART N O. 6 O (\ u 6% Y5 Q 06 o CAUTIONIDO NOT USE THIS CHART FOR COASTAL NAVIGATION 15 22°: OW I7l5 360 In” H ”11mg Ammm “:1” 21- 00 gal- 20': ¥ : I [9' Cm) CA L IraNN/A 5y 7 TOPOGRAPHIC CHART N O. 7 IZO' . u 23' 90’ IT' 88' 37‘ 86' 85' 84‘ TOPOGRAPHIQ C_:A_RT N‘O. 8 CAUTIONIDO NOT USE THIS CHART FOR COhSTAL NAVIGATION GULF OF HONDURAS HAL . a m I5' :_ Imam,” HIIIIII I/ HM \ MI,” . \\\\“\ 0/ : N‘Q fi' ’- " / (7% - \‘\ a ~ ”0/ : \\\ /’/// — ° ”0/ CONTOURS OF MIDDLE AMERICA TRENCH FROM ROBERT L‘ FISHER SCRIPPS INSTITUTION 0F OCEANOGRAPHY '4' I4' EL a o ’6‘ _ ” w _ __ IA LllElr‘D _ r HONDURAS : V _ , 8 _ EULF 0F FONSECA _‘ ‘ :l3' N/ c A I? A G U A ‘5 OWMHMN.%M 3 1 I? II' E I I I I I I I. I I .III. I “and .I...I....l..III..IIImIIIII ”I... l l I I I I I l I I I I. I I 1 I 1 I I I | I I 1 “min I I II I I l 1 ' a '030' 89‘ 88° 02' BI' 30? 17 TOPOGRAPHIC CHART NO. 9 MEX/00 CAUTIONIDO NOT USE THIS CHART FOR COAQTAL NAVIGATION CONTOURS OF MIDDLE AMERICA TRENCH FROM ROBERT L. FISHER SCRIPPS INSTITUTION OF OCEANOGRAPHY GUATEMALA ‘3 , SAN JOSE , ,. '” m “g 100 CLIPPERTON FRACTURE ZONE? @4006.” II. .lII II I IIIIIIII IIlIIIIJIIIIIIIIIIIIIIJII IIIIII I. I .IIII IIIIIIIII.IIIIIIIIIIIIlIIIIlIIIJIIIIlI .I IIIII .IIII. IIIIIIIlIIII I.I.I III I .III I IIIIIIJ 1. IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIlIIIIlIIIIIIIIIIIIII I III.. 96' 95‘ 9 4' 93' 18 ”0' I09' IOB' I07' l06‘ l05’ l04' IOS‘ IOZ' IOI' "3?;- TOPOGRAPHIC CHART NO. IO \KM. '00 6 ”00 e 445 U 0 |09' IOB‘ IOT' IOG' l05' IO4' l03‘ l02' IOI' I059 CAUTIONZDO NOT USE THIS CHART FOR COASTAL NAVIGATION 19 TOPOGRAPHIC CHART NO. || 9 {3 I6° 0 CO) on : l5' it \\1\ 1 1 1 “\MWS.‘ L .I [WWI/4% « u» \ \\\“\\\\\\\ .m\1\1\\\\ l4’. : 14- \|1\|I||IIIHIIH “\\\““\1111\ I l / 1/1/1117”, \ '1' M“ a "' "' ~ \y . 1‘ I/ 1/ I 7' ”Will 52' \\ \ \y §\9 ngo $ // /§ ///l /, ’l/ \4 \ ’1”? "\u \‘\ \ ”W" ’11::11411 :ulnn\m\\\\\\"\ : 13- J. \|l||||1!llll ' \""\\ \“"\' 1 l “rm/WW ._ :4 Mo E \\\\\‘3 9' 'v 10%,, O O - \‘\ ///// 7 ° Q I v ”I, _ Q. 2/, o , ‘ fl 2” E D ‘ V2 0 : $3 1% : é! -: CD - l2’; 3 f. - 5 [2° 2* it 11 \\\\\ ‘ f 2200 \ / ” \\ : ~ \\\\\ ”0/ \\ // \\ ”11%”; u I I. n- T\\\\\\\\\\\ ® @~ 19 1 a :_ MIMI/111111111 Imlun\\\u\\\ \‘mng‘p Q/e‘ _;'.. E o OCLIPPERTON FRRTURE.,.\ZONE . e c; 5 / l ° 3 E 0 ”0° (00‘ 1:00 “°° Azoo "00 2°: _: E: a 7'1 ‘1" O 1450 3/ E > W. 00E 1 A A l I 1 A 1 | A A A I 1AAA 1. .l I. I l 1 1. 1.. 1 .. 1 l 1 I 1 I l ”.1..“ A”.1... . ... .. . . u... . .fl1...I....1....l....]....|....1....I..“kn/“..1....I....1....l....1....l....1....l.m@ “@1111“ AAA . AA AA u/ . .......1...l...1. |. 1. ..|.. .1....l....1..|.. 1... .1. l. .l 1 .1.. ..1 .1. h III/ll""’"“I/.;11hnl O ( . fl IN 20 90‘ 9’ B loo :"”l""l""|" y]..,.,....l....lm.l..,., 'I' ., "I....[nulnup I'” Hill .1." I Vvvvlny Hllllllvlvnv'uull "Inuluulu [nu] u. OOII O @" IIOO / ' \ moon" I ’ouMp/M u.‘ \© © \EI/SYENCE DOUHJ‘FUL \ I fix @Izos O nu] n Inup. 'I u I ”I....I. "lump" 8 6' 8 5' 84‘ n. . I "I"' luvqnnlv ynTn |v ..|. .l I' COSTA R/CA 9': 1’ ‘13:: I430 0/ a MOO lvvv n. m]. ‘m'.u.l.mln “ml" I ‘PA ”IDA I5 ., "I 1 . I" CAUTIONIDO NOT USE THIS CHART FOR COASTAL NAVIGATION quunw * “HIM/"WW. n ,/ \l0° A . |\.. “upon: I: I2 lo I? TOPOGRAPHIC CHART NO. I3 BI' 80' .,. , . I“ .,..,.,....l ...l ,,,,. , I , IO' lIllA ...I....I....1....I....1....I. ..1... 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W“ \\\\ [111111111 1nvlnn\111\\\\\\ :_ C) M c /‘°°° “a O 000 O - o : o m _ *‘ M m o 1300 » moo / ‘1 4- m 4- W ‘ h 3:; 12" 1 _ O b (g 3):? 59 0 // — woo woo— 1A°° _. _ _.m/ > _ S\un ‘ _ PARANOVNT ax __ 3:): 125 r1701": _ — 100° m 95 0 Z _ — moo 1I° dz? 0 o r c HANLENE snr (? _ /f — CD 550 L34], (41,200 REPORTEQV'ZW _ 1 1 1 1 1 1 1 1 1 1 1 .11. 1 1 1 1 . 1. 1 .l 1 1 1 1 1 1 1 1 1 1 1 1 1 . .1 1 1 1 1 1 1 1 1 1 1 l. 1 l 1 l 1 1 1....1....1....1.. .1... 1.11 . 1.. .1 ..1. ....l. .11....I ...1....1...1 3- 99' 98‘ 95‘ 94’ 93’ SI. 90' 22 TOPOGRAPHIC CHART NO. l5 IOI' IOO' , In ,myl , ”I "l"'['"l "I la § ’72 _= F: «’2 s “g 3‘5 13:; 5' , : - E _ 5. 4! IE _: _ 2% ti .2 ”z \ _ s‘ 0’ fl “1 / — 6o » \ _: ’4” '- » \\\\\\\\ . 04/ a. a \x\\ ”0/0 / u I- 0' \\\\ T— I ”’I/Im/vau unImI “W“ —. " °3 3 : Q Q, Q ..1. l. ..1 .1. ”I . .I ...1....I l. .l 1 ml“ IQQI I I. I. ..I ...|.. .I . 3- . |o|o l00° CAUTIONIDO NOT USE THIS CHART FOR COASTAL NAVIGATION 3. ....I.... I... 1 I. . 1.. . ....I.... ....I... .I. . . l .1 .|.. .l I.. I. 1. . 1 I l I . I. 1.. 1 . ....1. ..I....1.... ....I. . . . I "0' I09' IOS' I07' 23 TOPOGRAPHIC CHART NO. l7 8" .l.... . up. “my..." 80. I Jaw 3 HOOVflOSJ’ TOPOGRAPHIC CHART NO. I8 99° 96° 95' 94' 9 3' 9 2' 9 I‘ 9%: H , . . ... .. . .... r . ... .. y. . mum!” ,y.. l' , I , H ., ml. ,m .,. ”I”... "In ., m, 1.... .. ,u .l u,” I. v.0 In “ml. , .l . ., "Wyn," 1' mm,...... 1. m , q. ,,.,.|,nlv,.l...vl.wnmr Ill! I|lFl|lIYIl IIIIIIIII|I III[ p\ O Q 'o" o o / “<3 0 W 1290 CD ,.00\ 61/‘I‘OO-V 1960 o oo’# 0 ' “W A LWWFRAM Z 9M3” GM 0 0 cm ’L - C? mm m 6/ moo CULPEPFEfl / (:2; 5 B 4’00 I70 .3 : a . :— O 9 —f ?- (:) 1,0012%}:3 200°”fl;? _§ /3- ' J m 0 Ia' 2'00 6:“ .63 5f as... @3369 “E3 ”3»! “N O 9 0 O a? a 63 exec % o QC»? 63f {:3 N Q1. . o . %\\? (3/3 ° W f“ 2300 /4' [4’ \\_—/’ Q9 \ I....I....I....I....I. ..I. ..I. .I . .. .I ...L...I....l. .I....I. l ..1. ..I ..I w 0 :y (D [5’ — €329 KWOM >99); 15. _ ¢:’ (3 <::) : mm WW /6" / ”9° w . IIIIIIIH . \\‘\\\\ v‘ ’u " [7/ \\ ¢ ~ 1‘63 ... I. .I... I.. I .I. I. 2.00 .I [IV .... ... I. .I.. .I. .I ...I. .I . .l I. ......l.........I I'""l' 'I /7’ [7’ lo,“ 4%% 6%”4H s // 44,) u \\\\\ 0 in 1| \“ [WM/I I I. M I\\\\\\‘\\ mhthMuuMufimM“ II. I. .I.. I ..I-...I.... ....IIIIIIIIIIIII W' a 1 90 .I 'I""' Go I E“; I.. i:}\d‘nllllll||‘nl .IIIIIl f\ee I..I....l....I...I....I....I....I....I. I.. I II ....I....I...I....I....I.. I... I....I... I. I.I..I.... ... I. I I I I...I...1...I...I....I....I........I....I. I..I....I..I. I .I....I..I l .. I. I I....I....I....I....I....I....I....I....I ....I. I I .I I I I...I...I I I I I I .I.. I. ..I.. I....I. .I. l I... . I. I I .I .I. .I I...I....I I I I I .I. |..I I. .l I I I... .I I I...I....I..I. .I I.I 89‘ 88' 87‘ 96“ 05' 94' 53' 02’ 8I' 3. Q [8‘ (I O u 29 TOPOGRAPHIC CHART N O. 23 7 6" 75’ 74' 70' ' l ' " 'I' " l""l' ”I' 'I' I I ' "'"I I I' "I l | I "I 'l 'l I" l' ""'I"""' 'I ' 'I "I I ' 2 la. p00 ’ l9‘ .o° ‘ ‘ . a ‘5‘“- \u M “Human” 3;, I \\\\“‘\\\‘\\\'\a\ L '/ WWI/0%, ‘- 0 1000‘" ' v22. [6“ «"i? by f 20. I14, / '~ ~ "I ‘0 o :— ”I’ll/’W/Hfl/HIIIIIIT: IIII\\\I\\\\\“‘“\\\ * .9 \\ \\A‘\\\II\IIII‘|IIIIll'llH/lr‘Hl/W ‘ o x” v.1- “ - O 56:, XXV 2/. C) "°° ”’40? ~ a “xv“ . ‘ w I l \ , ‘ '/ We /’//”ll/l”//IIIITIHIIII.I:IIIII:\Y\\\\\““\\\\\\\\\\ ' . ‘ ._ w . : . _ cam O V I . - .— 59 uo/ — — o 5 o. 3. q: :— .Iuwmmmzcooumumu . ' ‘ 1 :— PROFILE ACROSS THE PERU-CHILE W _ . ‘ t E TRENCH ON A counss BEARING ‘ ‘ ‘ V 7 22' zoo ZTO'TRUE AT 2|‘S.LATITUDE _ I _ I. g“ i 2‘ — 6" I; _ O - < m— i ' _ ; a ,x — 2000— i 3 ‘3' ‘ g 1 g I, . _ i use _ ‘ ‘3 _ l . E : ‘ l » _ = "°°‘ % 23' . ,. —' 23- ; uoo— j '— 63 -. _ 3000 — t _ , \ r " ‘= ' 4000 — "I ‘ . z E 00 0 O 4400 1 < -_ 9 N . 4 7 HOR|ZONTAL SCALE IN MILES I _ 24¢ - I | I .I I I I I l l I I l I .l I...l I .l I l I. .. I l l .l “I .l I I I I I I I I I l I I I I I ..I l . ' , 24. ago 79- 7,- 77- 73' 7/‘ cnunonwo nor us: THIS 70‘ CHART FOR COASTAL NAVIGATION 30 86 ' 85‘ 84‘ TOPOGRAPHIC CHART NO. 24 a. /8' u ‘ n p 'l‘ I 'I I. '| I I' I'm-In. "u. I Ivvqnnlnvv‘nul m n . ”nun-”Inn“ . . '[ 'lvllnv‘vylvl | "I. vlnvlllvn'vlulvivv n I. n l9' 20’ NW N ,- mmm Immu/ if u WWI/1,,” 0/ / I. ”(a I /90 .1“. I n1! .n1 . ‘ 20' ,|,l. ,,.,,,,l.'. ....,....,....]n.w...,...,,,,,m,,m.,ml,m g lvv'lllvwl" \z-w —/ unnu‘hmlunl A Q . 22' DfPYN m rum-S su LEVEL loo - no . IZOO — moo L 2000 - u..h.uLm1Lu,I....nun... ....Lm1.u.l.u.1 22 ‘ PROFILE ACROSS NASCA RIDGE . . . L . . x_ ——_i HORIZONTAL SCALE IN MILES “In: I“ h XI. 23' 23' V?ITI'TTYTTVTVTY‘Y‘|—'TTTVTTY1VIVVW‘W'VYT‘V'WWTTITVTYIVIYTIYTTTIYYYYPYIIIIIIl yylv .vnvlrnqvn r]. H” V'llll'lxnvly , n [H ”In! mu. w n v “ml” my I. “1 C900 EASTERM l uh © . .uluuhml /—:100 x. O F RACTHREJZW .1...l....l ..l.m1“ul...1... I I ..1.. O “l AlmuuulI ...n...l...u..uhu.| m1“. 24‘ 90‘ 8 ISLADH) 88‘ 87‘ 06' 04‘ 31 93° SPECIAL CHART NO.| 92° 9 P 89° 88° 87" 36° II 1 ””l””l"”[l"‘II"‘[""[”“I””[””I'I'III'” llll I'll] "'IHHI” llvvvrlllllllllllu'IlllvllHIIIIHIIH O o l \IIIIIIIIV Illllllllllllllllli /°— "I'llllllllllllllnll]llllllllllIIIIIHHIIIHIIIIIIIHI IllllnnlIlllllnlllllll . o 9 0° 20° IEO' \300 L OCA 770/1 MA P .0. I 0 2 nullnllIlllllllllllvlllnv IIulllilllvllllllll'll'lIIIl VIIIIIIIIIIIIIII'IIIIIIYIYV' ' . ‘Illll'll']"" vrvvllvvvlvnqnuI-Iv 70' - - -EQUATOI- - - -E ------ ‘0' >0° |20° 90° 7 20‘ 1....l....1.mlu..l.... [300 770 \200 D @ @926 PICOROTO BK (EXACT POSITION UNKNOWN) 0 _ [—BK REPORTED, NO DEPTH 75 (fl) I40 PINTA BK, 598 944 W00 I240 ~L E 6‘ E ND~ o \a°° sounomes m FATHOMS {:9 conroun INTERVAL - Ioo FATHOMS LOCAL DEPRESSION - m ISSUEO= MAR. 29, I962 CAUTIONiDO NOT USE THIS CHART FOR COASTAL NAVIGATION luulluullIlnllunlnuluulunluu AIIIIIAJAIIIAIlllIlllllll‘llllllil I O o O Iulun l‘llllllllll‘ In Alll|lllll uuluulunlunllluluu unluulunlu 5 , \ mas/0A /,I;’.:‘5,,,,,,VE ‘ {WW I. ‘ , I I . . BALTRA / I 6 , , ‘\ \JM nuts I. _... _: .. .. 7eo’<@) Iao &§\ SUN RAY 8K. (x GA ‘ ‘ “x ' ‘x l 260 \ \ .’ \ ~ TORTUGA I, ‘. ‘ ‘ \ _ _ _ ‘ , , . ‘ \ 500 \@ 900 o a, —' ‘ " I \ ARRECIFE —/ _ \gIZ/aiu , 20° .\ ,Io x‘ MACGOWEN 7o 00 , .\ / ~_- HANCOEK BK. .\| H/ \‘ a0 20° P ‘ .’ ‘IOO' ' -~ “00' , ' ' O , ‘ bin/Dan I. \ - ,00' '02 ISA/v74 MAR/A \ CALDWELL /. /. 10 2 ’11,; gfnmvn L ______ (:0\ . ~ 1’ ‘1 3 ,’ o g ‘ ‘ - 300 . - FAA/OLA I. _ / ”new I. (LOO , ‘55; llllll‘llllllllllll unlunlun “I Illlllllllllllllll IllluLlllllllllAllllllllll: 20 N o 93" I D. llAlllllllllllllAlllllllllllllllllllllll|IlljjllllllllllIIIIIAIIIIIIIIIIjillijlllllllellll‘AllAllJJJlllllll'Illllll Aluulu.IIIIuLquInIIIII“In”IIIIIIIIIIIIIIII ll Illlllllllllll u IIllIIIIIIInInnlnnllulIlnllllnllul lIllluuhlulllllInuIIIIlluuLII”Illnllllllnlllnn unlunnjuulunllllI[null“All“lllllllnulunllIn[IIIIIIII 92° 9/° 90° 89° 88° 87° 86° BATHYMETRY OF THE GALAPAGOS REGION PREPARED BY U. S. BUREAU OF COMMERCIAL FISHERIES AND UNIVERSITY OF CALIFORNIA INSTITUTE OF MARINE RESOURCES 32 SPECIAL CHART NO. 2 ”3’ "2' Ill“ ”0' \‘41;/ my o 5: 0° W“? W fiéffFRACTUR’l z o /“° ,W ) 31g)“; moo/h ./:”°° ‘a/ / o 5:??? Waco D ,_./ {a / <1 / 2 C3; ~—\ zooo—————'—*?/ E— mzzoo % EXISTENCE oouarsm. .— ° a w Cfl r r o u ° €22 a o €29 /OA 1" 5:3 : “A l\““‘“”""“l“"/1m,”,, 0 : , W 2 00 _:_ \\\\\w 9. an n 3' L m. “' 0 fig) \ m > <9 ZIOO J 2.0M r\ K f.\ \Ja «[7ij 7%, \ \g s v 0% (a \ \\1=:- 0001 s‘ \é €13 /1 e ’I// ~ In m ‘“ \\\\\ Q 3 / 06:; ea I(”WWI/15min”‘uuluH\““\‘\““\\\\ Q3 / z\ / a N fij \— ——I4 ’/ K1 1.00 a m" @‘V 5"“? b\ C) Q % 220° 2200 \‘\ C 53:2 9 CD, 0 i O 1 V {"555} 6. A E e a E E— /"‘°° 63 ago \ ': é ‘5 ° ‘9 0 o 0 MI} _ k\\m mu m y A‘me n 5. zzoo \ Q m ,, n W E ~ , I- Q) 00 . fl, 50 III 5-? WWW. "“N” | \ “I : ‘ 2100 C ‘I, (\o h I. a \ ‘ E n 0/01..“ :9 \\\\\\\““ :— /_ u m/m )u'fiulull thm\uu\“‘ a V l 001.: O E 1100 A 4" 4o 963 \ C‘ /tlco ~——-‘ _ E A IES \MW“T\Ili\i\f\|'\i‘\ii\lifl\\\fl$\\i\i\l|lii\l\ I“ MAY 05 1995 _ UBRARY UMVERSIW OF CALIF: M RETURN TO —) MAP ROOM 642-4940 LOAN PERIOD 1 2 3 I DAY 4 5 6 DUE As STAMPED BELOW UNIVERSITY OF CALIFORNIA, BERKELEY FORM NO. DD BERKELEY, CA 94720