Submarine Topography in the Gulf of Alaska

BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA VOL. 71, PP. 1087-1108. 12 FIGS.. 1 PL. JULY 1960

SUBMARINE TOPOGRAPHY IN THE GULF OF ALASKA

By WILLIAM M. GIBSON

ABSTRACT A bathymetric chart of the Gulf of Alaska and approaches covering an area of about 800,000 square nautical miles has been prepared from Coast and Geodetic Survey hydrography, 1925-1957, with a view to defining regional physiographic provinces. The basic data comprise 90 sounding lines across the gulf, 42,000 miles of graphically recorded profiles obtained during the last 5 years, and detailed surveys of 60 seamounts, seaknolls, and ridges. Tentative names are assigned principal features of the sea floor to facilitate discussion. The bathymetry and illustrated profiles reveal clearly the form of the Aleutian Trench, two submarine mountains, several seamount chains and groups, a ridge and trough province, a 200-mile trench west of Vancouver Island, a great trough paralleling the West Coast, and an inferred fracture zone extending in several wide echelon bands across the gulf. The submarine topography is discussed in relation to existing theories of earth science and correlated with features previously mapped on the mainland and in the Central Pacific Ocean.

TEXT ILLUSTRATIONS Page Figure Page Introduction 1087 1. Great Circle map of structural lineations. 1091 Acknowledgments 1088 2. Transverse profiles of the Aleutian Trench, Surveys 1088 Cape St. Elias to Unimak Pass 1092 Submarine terminology 1089 3. Axial profile, floor of the Aleutian Trench 1093 Description of the gulf coastal area 1089 4. Transverse profiles adjusted normal to General description of the gulf floor 1090 axis, Surveyor Deep-sea Channel 1094 Western and northern margin 1090 5. Transverse profiles of continental slope, General description 1090 eastern margin of Gulf of Alaska 1095 Continental shelf 1091 6. Transverse profiles, Baranof Sea Valley. . 1096 Continental slope 1091 7. Transverse profiles, Moresby Sea Valley. 1097 Aleutian Trench 1092 8. Transverse profiles, Explorer Trench 1098 Western floor of the gulf 1093 9. Transverse profiles, Ridge and Trough Eastern margin 1094 province 1099 Great Trough 1096 10. Transverse profiles, Mid-Gulf zone 1102 Ridge and Trough province 1097 11. Profiles along the Patton-Faris Seamount Kodiak Seamount Chain 1100 Group 1103 Mid-Gulf zone 1101 12. Transverse profiles across Parker-Bean and Parker-Bean and Patton-Faris seamount Patton-Faris seamount groups 1104 groups 1102 Unimak-Sirius Seamount Chain 1104 P ate Facing page Columbia fracture zone 1105 1. Bathymetric chart showing submarine to- Interpretation 1105 pography in the Gulf of Alaska and loca- References cited 1107 tions of illustrated profiles 1108

INTRODUCTION the Coast and Geodetic Survey initiated a program of running deep-sea traverses in 1925. This study of submarine topography in the For several years sounding lines were obtained Gulf of Alaska and approaches embraces an only on the return trip of survey ships after the area of about 800,000 square nautical miles. season's work in waters of western Alaska. In Although the whole area is referred to as the more recent years, because of modern naviga- Gulf of Alaska in this report, the name applies tion requirements and increased interest of to a more limited northern area. marine biologists, oceanographers, seismolo- Knowledge of this region was sketchy until gists, and geologists, sounding lines were run on 1087

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each crossing. Limited-area surveys of sea- by the Office of Naval Research and Bureau of mounts and other features were also made en Ships will add materially to existing knowledge route. It is a continuing program. of the northeastern Pacific area. The Gulf of Alaska was formerly included on Coast and Geodetic Survey Chart 9000 at very ACKNOWLEDGMENTS small scale, 1:5,000,000; but in 1952 the first edition of Gulf of Alaska Chart 8500 was pub- The officers and men of the ships and the lished at scale 1:2,100,000. The depth-contour cartographers in the Washington Office of the interval of 500 fathoms on this larger-scale Coast and Geodetic Survey have made this chart does not, however, reveal the secondary work possible, but special credit should accrue features so important to a study of submarine to those who set the initial and continuing topography. First details of the gulf topography policy of providing the hydrographic coverage were presented by Murray in 1941, followed in of this great area at little or no extra cost to the 1945 by his report on the Aleutian Trench. In Government. Rear Admiral H. A. Karo par- 1951 Menard and Dietz presented a compre- ticipated in both the field and office work, en- hensive geological study of the area. This study couraged preliminary study, and lent direction was based krgely on the Coast and Geodetic and assistance in the presentation. Survey deep-sea hydrography, supplemented Inasmuch as the study was made away from by sounding lines obtained by Navy ships. The the depository of survey records in the Washing- results of a joint exploration by the Navy ton Office, valuable assistance at that office was Electronics Laboratory and Scripps Institution given by G. F. Jordan in the preparation and of Oceanography in 1951, including the dredg- review of illustrative material. ing of tops of seamounts and coring the sea floor, were presented by Menard in 1953. In 1955 Menard reported further studies of the SURVEYS Gulf of Alaska. A considerable accumulation of original ship The hydrographic surveys from which the observations, including graphically recorded bathymetry on Plate 1 was developed are com- profiles of the floor and seamounts, was avail- posed of a continuing accumulation of deep-sea able for this study. The fathogram profiles are sounding lines obtained en route to and from reconstructed in several illustrations presented coastal areas of western Alaska. These recon- here, because various scales and vertical exag- naissance surveys have greatly improved in gerations resulted from the use of several types quality in recent years. of echo sounders and also from the effect of The early traverses relied solely on astro- different ships' speeds. nomic observations for positioning. Overcast Although bathymetric details of this report and storms were often experienced on return are considered to be almost complete in certain trips in September, and occasional dead-reckon- areas, considerable surveying is still needed to ing courses for long stretches resulted. Depths delineate all features in detail. Many sections were ascertained at intervals by sonic reflections of the depth contours could rightly be repre- read at an instant on a calibrated dial or timed sented by broken lines; solid-line bathymetry to hydrophone reception. Early improvements is presented with this qualification. An indica- in echo sounders were soon reflected in nearly tion of the density of deep-sea sounding lines continuous and more reliable soundings. An on which this study is based is given in the in- eventual adjustment of these traverses was con- dex-map inset on Plate 1. Numerous peak templated at a later date when the framework of depths of seamounts were deleted from copies well-controlled lines became established. The of the survey sheets used in this study. In very large amount of work required in the analysis of control data in the proposed adjust- recent years, survey information of this nature ment is now considered unwarranted. Inade- has not been available for unrestricted publica- quacies in the early lines do not materially tion. A discussion of flat-topped seamounts affect small-scale deep-sea charting. versus seapeaks is therefore not included in this Most traverses and all the limited-area sur- report. Reference is made to unpublished re- veys were made in more recent years with sults of the Chinook and Mukluk expeditions benefit of loran positioning and modern re- made by scientists of Scripps Institution of cording-type ultrasonic sounders. A large ac- Oceanography in 1956 and 1957. Geophysical cumulation of well-controlled graphic profiles data collected on these expeditions sponsored has resulted. On both outbound and inbound

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trips the ships survey seamounts and other and less regular topography than a rise; sea- features which lie on or adjacent to their trav- mount is defined as an isolated elevation of the erses. The traverses and limited surveys are deep-sea floor of about 3000 feet or more and planned each year to fill voids in untraversed circular or elliptical in form. The term "ridge" areas. Lines necessarily converge at the end of has been applied previously to immense struc- the Alaska Peninsula, Kodiak, and Strait of tures like the Mid-Atlantic Ridge. Throughout Juan de Fuca. Also, traverses have been con- the area of this study are weltlike forms 20-90 centrated in seamount areas to permit surveys miles in length and about 10 miles in width. of the features discovered on earlier crossings. These structures do not differ greatly from the These detached surveys have now covered 60 welts forming the Ridge and Trough Province seamounts, ridges, and knolls. Total crossings off the West Coast (Menard and Dietz, 1951, amount to 90, including the 1957 lines. In the p. 1274). They are termed ridges in this study. past 5 years 42,000 nautical miles of graphically The International Committee favors geo- recorded profiles were obtained in this area by graphic names over personal names (Wiseman ships of the Coast and Geodetic Survey. and Ovey, 1954, p. 93), but judgment is required in the application of geographic names derived from continental features to remote SUBMARINE TERMINOLOGY submarine forms on the floor of the Gulf of During the exploration and hydrographic Alaska in a different structural region. Ac- cordingly, new features that cannot be rea- development of the Gulf of Alaska and ap- sonably correlated with an existing geographic proaches, the names of ships and deceased hydrographers had been assigned to many under- name have been assigned appropriate ships' names or names of deceased hydrographers and sea features. In some cases the names were others identified with exploratory surveys of applied before the form and extent of a feature were adequately known. On the basis of present the region. knowledge some names might be appropriately changed or omitted, as in the case of several DESCRIPTION OF THE GULF COASTAL AREA peaks rising from a common elevated platform, each having in common usage the name of an The Alexander Archipelago and Vancouver early hydrographer. Clarity and simplicity Island stand like guards off the mainland of would be furthered if one name were used for Canada and Alaska for a distance of 750 miles the whole structure and the individual peaks between Cape Spencer and the Strait of Juan de named only if their importance warranted. Fuca. The islands are interspersed throughout a It is not the scope of this work to change broad and shallow trough lying between the names in current use, but the application of shelf edge and the mainland. The shallow names to currently mapped or previously un- trough, a variation from the usual continental recognized features of the sea floor is necessary shelf, fringes the entire Gulf of Alaska from to facilitate discussion. New names assigned in Queen Charlotte Sound to Unimak Island. It this study are in general accord with principles ends abruptly at the entrance of Queen Char- adopted by the International Committee on lotte Sound where it intersects the trend of the Nomenclature of Ocean Bottom Features, as continental slope at an angle of 45°. given in the minutes of the September 22, 1952, The islands of the Alexander Archipelago are meeting at the International Hydrographic mountainous throughout and are separated by Bureau at Monaco, and in accord with criteria depths to 400 fathoms. A large part of the recently established by the Undersea Features Behm Canal, which winds around Revillagigedo Nomenclature Committee at the Navy Hy- Island between peaks 2000-4000 feet high, is drographic Office. Since advance approval of a more than 300 fathoms deep. Clarence Strait large number of new names by The Interna- and Ernest Sound to the north of Dixon En- tional Committee, which meets only every 3 trance are 200-350 fathoms deep, as is Sumner years, is not considered practical, those used Strait. Chatham Strait is 3-8 miles wide, more in this study are tentative. than 400 fathoms deep in many places, and 200 The agreed general principles are an ex- fathoms deep at Skagway located 200 miles cellent guide but lack sufficient detail to permit north of the entrance. St. Amand (1957, p. 1351) noncontroversial selection. The International suggested that this strait is a portion of the Committee has defined a ridge as a long ele- great Denali fault curving west and southwest vation of the deep-sea floor having steeper sides to the Bering Sea.

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Northward from Cape Spencer the character GENERAL DESCRIPTION OF THE GULF FLOOR of the coastal zone has been modified by recent glaciation, general uplift, and local subsidence The floor of the Gulf of Alaska is in general a (Plafker and Miller, 1957; Miller, 1953; 1957; fairly smooth plain except where broken by Jordan, 1958; Gibson, 1958). The rapid reces- seamounts and ridges and cut by the major sion of ice in the prominent bays is well-known. Aleutian Trench and minor troughs. It dips The area lying between the coast and the Fair- westward and southwestward from the eastern weather and Chugach-St. Elias faults is the margin. The entire floor is traversed from south- Gulf of Alaska Tertiary province; high-angle east to northwest by echelon lines of seamounts faulting, great uplift, and numerous glaciers are and ridges. Three or four fairly definite linea- prominent features. The bases of the glaciers tions cross the Ridge and Trough province lie below sea level and are separated from the transversely and are in turn crossed by trans- sea by a low coastal plain consisting of recent verse structures in the Mid-Gulf zone. Most of accumulations along the western margin of the the significant features of the sea floor are ice. aligned in trends which converge upon the ap- The Gulf of Alaska Tertiary province has a proaches to Queen Charlotte Sound. Kodiak number of other known faults. The Sullivan Seamount Chain and the Ridge and Trough fault roughly parallels the Chugach-St. Elias province (Fig. 1) are the principal converging fault but turns abruptly seaward toward the lineations. A slight trough of great width paral- Aleutian Trench at Cape Yakataga (Miller, lels the coast southward from the Queen Char- 1957, Sheet 1, Map OM 187 Sheet 1). lotte approaches to the Mendocino Seascarp. An abrupt change in the trend and form of Explorer Trench, which resembles a great the shore line and continental shelf occurs at thrust fault, borders the trough for about 200 Kayak Island. The Copper River delta is miles on the west. fringed on the south by low offlying islands The continental slope constitutes a great and on the west by northeasterly trending escarpment that descends from the shelf edge Montague and Hinchinbrook islands which to a base at varying depths along the eastern tend to enclose the deep water of Prince William margin and to the bottom of the Aleutian Sound. The coast between Cape St. Elias and Trench on the west and north. The base of the Cook Inlet is everywhere deeply indented with escarpment is very irregular in depth on the deep bays in contrast to the more regular shores east and is broken off at Queen Charlotte Sound and shallow bays along the Gulf of Alaska by a trench and sea valley and off Queen Char- Tertiary province. Shelikof Strait and Cook lotte Islands by a parallel ridge and trough. Inlet have been inferred to occupy the site of The intermittent bench along the northwest an ancient trench in Mesozoic time (Menard wall of the gulf seems to describe in general an and Dietz, 1951, p. 1277-1279). Kodiak Island old base of the continental slope. The sea floor and the Alaska Peninsula have deeply indented south of the Alaska Peninsula and Aleutian coasts similar to those of the Kenai Peninsula. Trench rises from the bottom of the trench and The greater width of the continental shelf west- descends again to the general floor of the gulf, ward from Cape St. Elias contains a chain of thus describing a feature similar to an anti- islands including Kayak, Middleton, Kodiak, cline. The anticline contains a great variety of Chirikof, Trinity, Semidi, and the Shumagins. superficial forms and is cut by seamount zones. Many shallow canyons and submarine troughs Some significant features of minor relief have cross the sound transversely. been detected in the hydrography obtained in Field examinations of the entire coast and recent years with recording echo sounders, but, adjoining interior made by the U. S. Geological further survey work is needed before discussion Survey from the Alaska Peninsula opposite of minor relief is warranted. Kodiak to Cape Spencer show many alternating geanticlines and geosynclines ranging in age WESTERN AND NORTHERN MARGIN from Triassic to Tertiary (Payne, 1955). They General Description are practically continuous around the great bight of the Gulf of Alaska and include the The western and northern margin of the Yakataga geosyncline, a Tertiary element over- Gulf of Alaska comprises: (1) the wide trough lapping the coast and shelf and fronted by the or shelf containing Kayak, Middleton, Kodiak, Aleutian Trench. The geosynclines and geanti- Chirikof, Trinity, Semidi, Shumagin, and clines are progressively younger toward the sea. Sanak islands; (2) the shallow troughs ex-

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tending across the continental shelf transversely Continental Slope and including Cook Inlet and Shelikof Strait; (3) the continental slope and north slope of the The steplike descent of the continental slope Aleutian Trench including Pamplona Ridge, and the north slope of the Aleutian Trench is

FIGURE 1.—GREAT CIRCLE MAP or STRUCTURAL LINEATIONS

Shuyak Seamount, Unimak Seamount, a few illustrated on the transverse profiles in Figure seaknolls, and numerous steps and benches; 2. Most prominent of the steps is the Aleutian (4) the Aleutian Trench with Kodiak Sea- Bench first recognized by Murray (1945, mount; (5) the southerly slope of the trench p. 775). He described this 20-by-70-mile feature with Dall and Derickson seamounts, Surveyor as extending from Unimak Island to the Islands Deep-sea Channel, and the western base of of the Four Mountains, the western limit of the the Patton-Faris Seamount Group; (6) the offshore surveys at that time. Subsequent sur- southerly rise from the Aleutian Trench, which veys reveal the westward continuity of the includes many isolated seamounts; seamounts bench (Gibson and Nichols, 1953, "p. 1178: and lesser features associated with the Patton- Gates and Gibson, 1956, p. 143). Profile A6 Faris and Parker-Bean seamount groups, and (Fig. 2) shows that the bench is a smooth level the Unimak-Sirius Seamount Chain. plain 15 miles wide, but it becomes troughlike westward, particularly midway in the Aleutian Continental Shelf Arc where a broad trough is flanked seaward by extensive ridges rising more than half a mile Detailed discussion of the coastal margin above the trough floor. Profile A5 shows the with its broad shelf, islands, and submerged eastern end of the bench broken by Unimak rises and transverse troughs is omitted from Seamount, a ridgelike structure 10 miles wide this study. The continental shelf is referred to and 30 miles long. A very irregular bench of below only where regional considerations are limited extent lies in 1500-fathom depths south involved. of Middleton Island. Shuyak Seamount and

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several lesser structures rise from this bench, continental slope, superimposed seamounts At the head of the trench south of Cape St. and seaknolls, and varied depths are indicative Elias (Profile Al), a prominent seaknoll marks of echelon faulting along lines parallel to or a step, also in 1500-fathom depths. Immediately slightly converging northeastward toward the beyond the head of the trench is an extensive axis of the Aleutian Trench.

70 > I I I „ I I I I I © Surveyor, 1933 0

base or SeamounDericfcsonf

Depths in fathoms Distances in nautical miles Vertical X 10

FIGURE 2.—TRANSVERSE PROFILES or THE ALEUTIAN TRENCH, CAPE ST. ELIAS TO UNIMAK PASS

spur, Pamplona Ridge (Jordan, 1958), which Aleutian Trench projects 15 miles out over the continental slope. Jordan suggested that this is a bedrock struc- No major trench is so well charted as the ture which was uplifted and subsequently Aleutian Trench. Since the inception of the foundered. Coast and Geodetic Survey's program to explore Although the benches lie well above the major bottom features the hydrographic cover- general level of the gulf floor, they are roughly age has become almost complete. Unfortunately at a depth of the foot of the continental slope most of the lines for which fathograms are in other sections. In other portions of the con- available crossed the trench at acute angles. tinental slope no definite line of demarcation Most of the normal crossings were obtained be- may be seen between the slope and the fore the advent of recording fathometers. These trench. The Aleutian Bench appears to lie were specific transverse profiles reported by at or near the geographic extension of the Murray (1945, p. 765-773). No attempt has axis of the Yakataga geosyncline, a Tertiary been made to illustrate the actual fathograms tectonic element mapped by the U. S. Geologi- obtained over the trench and continental slope cal Survey westward to western Kodiak (Payne, because of various scale factors and difficulty 1955). The more or less troughlike forms of the in comparing profiles run in opposite directions.

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Plate 1 shows the Aleutian Trench as an asymetrical depression bordering the foot of the 1 V JB continental slope, and Figure 2 contains six E profiles for illustrating the detailed form at « ~*1 "J 1 m.J widely separated crossings. Figure 2 is intended \ o m to supplement the numerous excellent profiles \ S.E S by Murray (1945). .E S x The strike of the trench axis ranges from S. £ C t 40° W. between Middleton and Kodiak islands Is I to S. 67° W. near Unimak Seamount. There is - an apparent reversal to the east in the area southeast of Middleton Island. The principal 1 changes in direction occur about 60 miles south- J, i ! ! west of Cape St. Elias, at Kodiak Seamount, ll 1 1 and at the western end of the Patton-Faris *jvy Seamount Group. The trench floor south of Cape St. Elias (Fig. 3) slopes downward to the southwest for about 400 miles at the approximate rate of 4 feet per mile to a point southeast of Chirikof Island where the trench is intersected by the Patton- .! Faris Seamount Group. The rate of descent - increases to about 21 feet per mile for the next ; 200 miles to depths of about 3700 fathoms and H then flattens to general depths of about 3950 tf fathoms beyond the limit of Figure 3. If the lesser gradient, comparable to the slope of the sea floor east of the trench, is projected up- trench from Unimak Seamount then the raised u~ floor of the trench might be due to a large build-up of sediments. This possibility was originally suggested by Menard and Dietz (1951, p. 1279-1282). Their hypothetical blan- ket of sediment at the base of Kodiak Sea- 8- mount (GA-1) is of the same general magnitude as that inferred in Figure 3 of the axial profile of the Aleutian Trench. * ~5 £~ WESTERN FLOOK OF THE GULF \ The floor of the gulf east of Kodiak Island and the Aleutian Trench is a vast plain sloping downward to the axis of the trench from the continental slope on the east. These slopes are traversed by seamount zones but not materially Ij^^" altered in general. The floor flattens between the 2000- and 2200-fathom curves, and in this area major tablemounts and the Surveyor Deep-sea Channel (Gibson, 1958) are found. The latter feature parallels the Aleutian Trench for about 250 miles, then curves west and northwest to CM 1 1 intersect the Aleutian Trench at a point about 60 miles southwest of Kodiak Seamount. It is 2-3 miles wide and 500-1000 feet deep over most of its length. Profile B4 (Fig. 4) shows the form of the channel at a point about 5 miles

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northwest of Giacomini Seamount. It has a marked by a cluster of seaknolls circumscribed more regular cross section and is deeper south- by the 2500-fathom curve, Wildcat and Sirius west and west of this point. The maximum seamounts. It is also marked by a low western depths are on the south slope of the Aleutian extension of the Parker-Bean Seamount Group.

I I NW 2000 SE 2100 Discoverer, 1933 NW 2100 SE Explorer, 1956 2200

W 2100 Explorer, 1945

2100 E I Pathfinder, 1956 2200

_W 2100 2200 Surveyor, 1946

2200 SE

2700 ./ Surveyor, 1946 Depths in fathoms Distances in nautical miles Vertical X 10 FIGURE 4.—TRANSVERSE PROFILES ADJUSTED NORMAL TO Axis, SURVEYOR DEEP-SEA CHANNEL

Trench. In the original report this author de- In addition to the Aleutian Trench rise the scribed the feature as a trough, but subsequent western margin of the gulf floor is marked by consensus reveals "deep-sea channel" to be a seamounts along the south slope of the trench. more generally acceptable term. Derickson, Walls, Chirikof, and Dall seamounts South and west of the junction of the channel arc aligned at a distance of 30 miles from the with the Aleutian Trench, the plain of the trench axis. western gulf floor slopes southward and is ex- tensively broken by groups and chains of sea- EASTERN MARGIN mounts and lesser rises. The Patton-Faris Seamount Group rests on a transverse rise The Aleutian Trench is not evident east- which constricts the trench. Southwest of this ward of a line passing south from Kayak Island, constriction the southern slope of the Aleutian although there are slight indications of a sub- Trench culminates in a slight rise. This rise marine canyon traversing the continental slope resembles an anticline which continues to the along the approximate alignment of the axis limit of Plate 1 and probably for most of the (Fig. 5). Here the Gulf of Alaska Tertiary distance to the end of the trench. It is delineated province extends about 30 miles back from the by a loop of the 2600-fathom curve and is coast line between Copper River and Lituya

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30 2Q_

Depths in fathoms Distances in nautical miles Vertical X 10

FIGURE 5.—TRANSVERSE PROFILES OF CONTINENTAL SLOPE, EASTERN MARGIN OF GULF OF ALASKA

Bay (Menard and Dietz, 1951, p. 1279; Miller, Pamplona Ridge (Jordan, 1958) and Yakutat 1957; Plafker and Miller, 1957). The province Bay are examples of local subsidence in a zone is bordered on the east by the Chugach-St. lying roughly on the extended axis of the Aleu- Elias and Fairweather faults and is occupied tian Trench. Middleton Island on the north by a number of glaciers. A low flat coastal area side of the trench is an example of pulsating has built up on the seaward side of the glaciers. emergence in late Pleistocene or Recent time,

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marked by five terraces up to 105 feet above tectonic elements shown by Payne (1955) on sea level (Miller, 1953, p. 17). The Tertiary the mainland with the Aleutian Trench and province contains many high-angle faults, Surveyor Deep-sea Channel beneath the sea synclines, and anticlines and is featured by (Gibson, 1958) an inferred former trench or deep sediments and general uplift. Assuming its geosyncline might be expected to lie beneath

n i r I Pioneer, 1940 1300 1400 ) Surveyor, 1945 1500

) Explorer, 1945 1600 1700 1500 sS-—-""sm-veyor, 1946 1600 Depths in fathoms 1700 Distances in nautical miles Vertical X 10 FIGURE 6.—TRANSVERSE PROFILES, BARANOF SEA VALLEY northern border to continue southwesterly from the present coast line and continental slope the Katalla district (Miller, 1957) along the along the Alexander Archipelago. Queen Char- continental shelf to the fault crossing southern lotte Trough lies between the Queen Charlotte Kodiak Island, the province approximates the Islands and a rise emanating from Queen Char- Yakataga geosyncline (Payne, 1955). Surveyor lotte Sound and marked by Graham Seamount. Deep-sea Channel may mark the southern limit The steepness of the continental slope here and of the Yakataga geosyncline. the probability of heavy silting from glacial The Chugach-St. Elias fault is inferred by melt suggests a great wall of deposition only St. Arnand (1957, p. 1358-1359) to continue partially filling the embayment (Queen Char- southeastward along the coast to form a junc- lotte Trough) lying inshore from the Kodiak tion with the Denali fault just south of the Seamount Chain. entrance to Chatham Strait at a small The long, low, and broad rise forming the depression in the continental shelf described northwest side of Baranof Sea Valley (Fig. 6) by Murray (1941, p. 337) and Heck (1927). A suggests tectonics more than turbidity-current single deep sounding at the foot of the con- deposition because of its great extent. Moresby tinental slope near the axis of Baranof Sea Sea Valley and Explorer Trench cut the con- Valley and due west of the small depression tinental slope in the entrance of Queen Char- indicates the possibility of a similar deeper de- lotte Sound where turbidity currents would be pression. The sounding is 300 fathoms deeper expected to flow out along their axes. However, than other consecutive soundings and needs their cross sections favor tectonic origins. The substantiation before delineating on the submarine topography between Moresby Sea bathymetric chart. St. Amand's inferred sub- Valley and Explorer Trench may be a dropped marine fault running along the seaward side of block marked by the two limiting faults. Ex- the Queen Charlotte Islands has some very plorer Trench (Fig. 8) has the form of a thrust tenuous confirmation from the ridge and trough fault with a raised escarpment on its east rim off Dixon Entrance and the few seaknolls along similar to that lining the north wall of Mendo- the margin to the head of Moresby Sea Valley cino Seascarp ridge. (Fig. 7, profile El). If a submarine fault existed here it would be buried deeply by sediment ex- GREAT TROUGH cept where recent movement might be reflected in the topography. The Great Trough (Menard, 1955a, p. 239) In view of the general parallelism of the lies between the foot of the continental slope

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off the coasts of northern California, Oregon, two troughs at Queen Charlotte Sound eri- Washington, and Vancouver Island and the trance by cutting across diagonally at a east face of the southwest-trending forms of 45-degree angle.

10 12 14 16 18 r i 1100 ©Surveyor. 1300 \ I Pathfinder, 1954 1400 \ 1400

I Pathfinder, 1953 1700 1800

Depths in fathoms Distances in nautical miles Vertical X 10 FIGURE 7.—TRANSVERSE PROFILES, MORESBY SEA VALLEY

the Ridge and Trough province (Fig. 9, pro- RIDGE AND TROUGH PROVINCE file F3). It has a remarkably smooth floor that is indicative of heavy sedimentation and is The northern portion of the Ridge and cut by channels trending south and west Trough province (Menard and Dietz, 1951, (Menard, 1955a, p. 243). Nautical charts of the main plate) included in Plate 1 lies between the Coast and Geodetic Survey show prominent Great Trough on the cast and Moresby Sea terraces in the continental slope which are also Valley on the west. The latter feature is not a cut by submarine canyons. The deep-sea hy- definite border because some less distinct ridge drography is not sufficient detailed off the west and trough forms are found farther west. Ex- coast for the mapping of minor relief. plorer Trench, approximately defining the east The east limit of the Great Trough is notable border, and Moresby Sea Valley have parallel for the smooth junction with the continental strikes of about S. 30 W. The province extends slope and an initial steep rise of about 400 to the Mendocino Seascarp on the south, al- fathoms followed by a falling off and subsequent though intersected by ridges and lines of sea steep rise (Fig. 5, profile C7). The bordering mounts trending transversely. topography of the Ridge and Trough province The hydrographic development consists on the west converges upon Heck Seamount mostly of sounding lines fanning out from the lying off tho Strait of Juan de Fuca, makes a Strait of Juan de Fuca. On account of the di- radical turn left, and ends abruptly in a smooth vergence of the lines the development becomes plain. At this point a long narrow ridge skirts weaker with the distance offshore, except for the smooth plain on the east and north, then limited-area surveys of numerous seamounts. veers northward along Explorer Trench toward Most of the larger forms of the gulf floor have Queen Charlotte Sound, thus forming a border been well charted, but more hydrography is of the Great Trough. The southward prolonga- needed to develop in detail the minor features of tion of the axis of the trough occupied by the relief. An 80-mile belt extending the approxi- Queen Charlotte Islands and Hecate Strait mate width of the province near Queen Char- coincides with the axis of the Great Trough, lotte Sound is not sufficiently surveyed to although the continental slope separates the warrant more than general discussion. Moresby

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Sea Valley (Fig. 7) lies within the area of in- Moresby Sea Valley, Explorer Trench, the sufficient hydrography, but it has been crossed continental slope, and lines of seamounts. The hi enough places to define its cross section and unscrambling of these converging elements may continuity. be subject to differences of opinion with regard The complexity of topography of the gulf to details, but the broad pattern seems clear.

Depths in fathoms Distances in nautical miles Vertical X 10 FIGURE 8.—TRANSVERSE PROFILES, EXPLORER TRENCH floor between Eickelberg Ridge and Queen The alignment of ridges and troughs Charlotte Sound precludes portrayal of de- (S. 30°W.) is not precise because of many varia- tailed physiography at the scale of the basic tions due to the interposition of Eickelberg hydrographic sheets and results in excessive Ridge and numerous seamounts. Most of the generalization at the scale of Plate 1 which is linear forms lie to the east of Eickelberg Ridge one-third reduction. The importance of this in a comparatively narrow 60-mile belt, al- area warrants a complete study, which would though some lie on either side of the ridge to best be made at a scale about 6 times that of the north and south. The right-angle bend in Plate 1. The importance stems from the con- the 1700-fathom curve 25 miles southeast of vergence upon the approaches of Queen Char- Eickelberg Ridge may represent its merging lotte Sound of the Queen Charlotte Islands, with one of the linear forms, which then veers Hecate Strait lying back of the continental to S. 40° W. and continues for 200 miles. The shelf, the Ridge and Trough province, Kodiak alignment of the ridges and troughs becomes Seamount Chain, Queen Charlotte Trough, S. 45° W. near the Mendocino Seascarp, and

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they arc more numerous. The underlying ridges mount has been completely delineated by and troughs are not characterized by much numerous lines of hydrography, but these lines relief and are in reality long linear rises with were run parallel to its axis, and no transverse intervening flat sea-floor or shallow troughs. fathogram is available for determining ridged They rise from a gentle plain which slopes slopes. downward to the west at the rate of about 2 fathoms per mile (Fig. 9). Explorer Trench and KODIAK SEAMOUNT CHAIN Moresby Sea Valley have definite deeps at their heads near the entrance to Queen Charlotte Kodiak Seamount Chain is featured by a Sound. There are indications of smaller and line of great seamounts extending for 650 miles shorter features similar to Moresby Sea Valley across the Gulf of Alaska without evidence of streaming out from Queen Charlotte Sound. intervening sea-floor topography that would Extensive morainal features that are not ade- normally be expected in a fault zone. It is not quately surveyed lie close to the foot of the clear whether the chain comprises two arcs continental slope southeast of Queen Char- intersecting at Welker Seamount or one long lotte Sound. arc accompanied by short shear or tension fea- The eastern margin of the Ridge and Trough tures. The preferred assumption is that the province contains the Explorer Trench with main fault is marked by Kodiak, Giacomini, fringing scarp, a short ridge surmounted by Ely, Quinn, Surveyor, Welker, Denson, Explorer Seamount, and an extensive low rise Hodgkins, Bowie, and Graham seamounts. running from the entrance of Queen Charlotte Shuyak and Dall seamounts seem to be asso- Sound parallel to Explorer Trench to a right- ciated with the Aleutian Trench. Although angle junction with the southeasterly exten- Kodiak Seamount is in the Aleutian Trench its sion of Eickelberg Ridge, at Warwick Sea- precise alignment with the axis of this zone mount. cannot be disregarded. One secondary lateral Explorer Trench, one of the most striking shear pattern may be represented by Durgin features of this province (Fig. 8), can be traced and Pratt seamounts and another by Brown for 200 miles from the deep off Vancouver Is- and Dickins seamounts. land S. 30° W. to the east end of Eickelberg The northwest end of Kodiak Seamount Ridge. Indications of its continuance to the Chain appears to join the Aleutian Trench at southwest require additional confirmation. Its Kodiak Seamount, although a 100-mile gap width is 7-10 miles, and the depth below the separates it from Giacomini Seamount. Judging east scarp ranges from 250 to 725 fathoms. The by alignment, the southeast end of the chain general sea-floor level is difficult to judge be- comprises a seaknoll lying 60 miles southwest cause of the complex topography, but on the of the northwest tip of Vancouver Island, west it is estimated to be 100-200 fathoms Dellwood Hills, and the rise flanking Queen deeper than that to the east of the scarp. It Charlotte Trough. The first two features seem does not have a graded profile along its axis. to be superimposed on the ridges and troughs. Moresby Sea Valley (Fig. 7) also can be The rise emanates from Queen Charlotte Sound traced for 200 miles, to the west end of Eickel- and extends northwesterly to Baranof Sea berg Ridge. It is about 50 fathoms deep, 2 miles Valley. Its crest is lined with a seaknoll, wide, and has a well-graded profile along its Graham Seamount, another slight linear rise, axis. and Dickins Seamount. Low saddles tend to Heck Seamount is the middle high of a group separate the latter three features. Bowie, of three northwesterly trending ridges. The Hodgkins, Denson, and Davidson seamounts unusual configuration of the group consists of rise from the steeper west slope of this flanking the ends of three low ridges which trend north- rise. The shallow irregular depression lying eastward and abruptly turn northwestward, close to the bases of the seamounts could in- each terminating in a seamount. The area sur- dicate subsidence due to loading of the crust or rounding and between the three seamounts scouring through the action of turbidity cur- forms a flat featureless plain of great extent bounded on the east and north by the west rents. scarp of the Great Trough, and on the west by The floor along the seamount chain extending a long narrow scarp rising above the east wall northwestward from Brown Seamount is al- of Explorer Trench. The ridged slopes of Ex- most devoid of relief and has a slight uniform plorer, Stirni, Union, and other seamounts are downslope to Giacomini Seamount. A fault illustrated in Profile FJ of Figure 9. Heck Sea- zone such as this is presumed to be might nor-

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mally contain a considerable number of sig- east-west axes. On the west, Hook Ridge and nificant features of moderate relief on the sea a parallel westerly chain of seamounts and floor in contrast to the apparent evenness. A ridges are aligned in a south-southwesterly narrow dikelike form extends from a point direction. West of Whitney Ridge, several about 60 miles southwest of Welker Seamount ridges and Pathfinder and the Campbell-Scott for more than 100 miles to the northwest. It seamounts have southwesterly axes. Path- is about 2 miles wide, 200 fathoms high, and finder and Campbell seamounts were originally approximately symmetrical. This feature ap- reported and illustrated by Nichols (1950). pears to mark the southern limit of Kodiak This area has been traversed by a large num- Seamount Chain. Most of the sounding lines ber of sounding lines, and many limited-area constituting the hydrographic development surveys have been made. Sounding lines have traverse east-west and should have revealed crossed the generally south- to southwest- any existing related structures. However, closer trending features at right angles in recent spacing of sounding lines is needed before the years and provide excellent transverse profiles. lateral extent of the seamount zone is defined. Some of these crossings are illustrated in A wide and shallow trough extends north- Figure 10. Whitney, Schoppe, and Peters eastward between Quinn and Surveyor sea- ridges are not included because the numerous mounts and into the embayment described by parallel crossings were made at acute angles to the 2000-fathom curve north of Pratt Sea- the trend of the ridges. mount. North of the embayment, a slight These easterly ridges may mark a zone of trough may be traced northeastward for 95 weakness along the southeasterly prolongation miles. Its existence as a continuous feature of the Parker-Bean Seamount Group. A paral- needs confirmation from additional traverses lel alignment includes Twin, Scott-Campbell, and fathograms. Present indications on adjacent Pathfinder, and Laskowski seamounts. The sounding lines are soundings ranging from 25 Mortons Seamounts are south of this alignment to 115 fathoms below the general floor. The and on a southwesterly extension of a trend trough appears to be about 2 miles wide, and marked by the ridge west of Whitney Ridge it may extend up the continental slope toward and minor elevations enclosed by a spur in the Alsek Canyon. 2100-fathom contour. Murray (1941, p. 344, 348) illustrated the This southwesterly alignment predominates profiles of the flat-topped seamounts in this westward, in the base of Pathfinder Seamount zone. Menard and Dietz have studied and and lesser features 60 miles northeastward. reported on them (Menard and Dietz, 1951; Similarly, Laskowski Seamount and other Menard, 1955b). The form of the tops of those elevations trending past the east side of Miller seamounts that have not been completely sur- Seamount have an alignment transverse to veyed is difficult to judge, for the sounding the major seamount zones to the west. Hook line may not have crossed the highest point. Ridge has a comparable trend, which is in Almost any profile along slope may show a part distorted into a north-south alignment. flattened crest. Fathograms for sounding lines The ridge consists of echelon ridges separated following the crest of a ridge show a definite by low saddles and the severely ridged north- flat crest. Some of the seamounts have been eastern extensions (Fig. 10, profile Jl). The determined to be flat-topped by numerous numerous ridges and troughs in this area and sounding lines across the crests, preferably in IS miles eastward, delineated from several different directions. Not all seamounts have had northwestward sounding lines, strongly suggest this type of development. Welker Seamount has southwesterly aligned folds. been crossed by only two sounding traverses. The western margin of the Mid-Gulf zone is Detailed surveys of Pratt, Surveyor, Quinn, marked by Miller Seamount. Separated from and Giacomini seamounts reveal them to be the Patton-Faris Seamount Group by 100 tablemounts. Brown and Denson seamounts miles of generally smooth bottom, and having have been closely surveyed except for the full a base with northeasterly trending extensions, extent of their crests. it appears to be related with the southwesterly alignments. Additional sounding lines are MID-GULF ZONE needed in this area to trace the extent and direction of minor features on the sea floor. This zone comprises a variety of submarine In the extensive area south west ward, low forms in various alignments. On the east are linear rises, depressions, and narrow deep Peters, Schoppe, and Whitney ridges with their embayments in the depth contours are aligned

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in a similar southerly to southwesterly direction. and Scott-Campbell seamounts which have The area does not warrant discussion at this been described in the Mid-Gulf zone. The time, however, because the sounding traverses Patton-Faris and Parker-Bean seamount are widely spaced, and future revisions and groups, which have been described as sub-

FIGURE 10.—TRANSVERSE PROFILES, MID-GULF ZONE

additions of contours as delineated on Plate 1 merged mountains, consist mainly of great are very likely. seamounts and sea ridges rising from elevated platforms that are separated by and bordered PARKEE-BEAN AND PATTON-FARIS on the north and south by embayments from SEAMOUNT GROUPS the Aleutian Trench. Surveyor Deep-Sea Channel, descending the southern slope of the The sea floor west of the Mid-Gulf zone Aleutian Trench, separates the Patton-Faris slopes down to the south-southwest and down and Kodiak seamount groups. The poorly toward the Aleutian Trench to the northwest defined southern limit of the Parker-Bean (Figs. 11, 12). Many of the features of the Gulf seamount group includes many seaknolls and of Alaska seamount province are found here long narrow ridges lying in northeasterly (Menard and Dietz, 1951, p. 1270). Murray alignments. Hecht Seamount lying in the (1941, p. 351, 354, 359) described individual embayment midway between the two seamount seamounts from illustrated profiles. groups is flanked by a shallow depression as is The principal features are found in two also Bean Ridge and detached Faris Seamount. parallel seamount zones aligned transverse to Deeper depressions lie close to the southern the Aleutian Trench. The northerly one, i.e., base of the Parker-Bean group. The topography Patton-Faris Seamount Group, extends 270 of the two zones suggests extrusions through miles S. 75° E. from the bottom of the Aleutian the crests of underlying rises in the form of Trench opposite Chirikof Island. The southerly, seamounts and ridges, followed by partial Parker-Bean Seamount Group, extends about collapse of the sea floor flanking the extruded 380 miles S. 75° E. from the crest of the southern structures or by subsidence of the structures slope of the Aleutian Trench. Its axis prolonged due to overloading the crust (Daly, 1951, p. 30). would contain Laskowski, Pathfinder, Mortons, The Patton-Faris Seamount Group restricts

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the width of the Aleutian Trench southeast of crest is occupied by four peaks. The southeast Chirikof Island where the ridge or rise may be rise, Guide Ridge, has a serrated crest with seen in the bathymetry above the 2900-fathom several peaks at depths of 1800 fathoms. Wood- curve. The Chirikof and Marchand seamounts worth and Jones seamounts have the same seem to be isolated structures lying on the underlying north-south ridges resembling folds.

250 200

FIGURE 12.—TRANSVERSE PROFILES ACROSS PARKER-BEAN AND PATTON-FARIS SEAMOUNT GROUPS

up-bulged slope of the Aleutian Trench. The UNIMAK-SIRIUS SEAMOUNT CHAIN remainder of the zone comprises a single large structure 30-40 miles wide and 110 miles long, The Unimak-Sirius Seamount Chain extends which lies inside the 2100-fathom curve, except southeast across the Aleutian Trench from for flanking features such as Smook and Faris Unimak Island and the Sanak Islands. Unimak seamounts. The 80-mile-wide section of the sea Island is well dotted with major peaks and floor eastward from Faris Seamount and Mur- volcanoes. Unimak Seamount rises from the ray Seamount is slightly bowed down. The northern slope of the trench or continental seamounts on the large structure may consist slope, and Derickson from the southern slope of two parallel east-west lines of seamounts of the trench. Wildcat Seamount is the southern that have only partially coalesced except at culmination of a long and narrow ridge. Mani- Patton Seamount. In that case the two peaks festations of the zone are lacking from this of Patton Seamount lying above the 1000- point southeasterly to lat. 50° N. and long, 155° fathom curve would represent the partially W. About 17 seamounts form a gently curving coalesced western termination of the two lines. arc along the southern flank of the Parker- The width of Parker-Bean Seamount Group Bean Seamount Group and southeastward ranges from 10 miles on the east to 50 miles on across the Mid-Gulf zone. the west, and the sill depths between structures The axis of Sirius Seamount branches off to indicate that the ridge was built on a raised the south at an angle of 50° to the main zonal platform or arch in the sea floor. The arch is axis. It rises about 9000 feet above the crest folded as if it were compressed from the east or of the Aleutian Trench rise. All the seamounts west. The strike of the folds ranges from north- of this zone seem to rise above lower linear cast at Parker Seamount to north at Jones forms. Seamount. The next rise eastward also trends Unimak Seamount, 10 by 30 miles in extent, northerly but then turns nearly 90° eastward rests on an 8-degree slope with its longer axis into alignment with Bean Ridge, which has a parallel to the Aleutian Trench (Fig. 2, profile serrated crest. A5). Its north base lies in 1235 fathoms and The great seamounts of the Parker-Bean the south base in about 2000 fathoms. A deep seamount group seem to be structural accumu- boxlike canyon extending down the slope from lations overlying the ridged arch, although the the direction of Sanak Islands borders the possibility exists that the seamounts were seamount on the east, and two other canyons compressed and folded with the underlying diverge from the west end down the slope toward arch. the bottom of the Aleutian Trench. The form The main structure of this zone is marked suggests horizontal flow through a horizontal or by two parallel northeasterly trending open north-plunging fissure. The ridge containing folds with intervening troughs. The northwest Derickson Seamount projects into the 3200-

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fathom contour of the Aleutian Trench, almost west of Eickelberg Ridge, the nearly continuous 600 fathoms lower than its south end. The line of northwesterly trending rises appears to structure comprising Sirius Seamount and the terminate at the southwesterly extension of low seaknoll to the north, together with the Moresby Sea Valley. The flanks are depressed embayment to the south in the 2600-fathom as if from loading of the crust, and the numer- curve and enclosed basin, suggests a fault ous flanking rises may be related to transverse zone extending southwesterly from the line of or normal faulting of the ridge. Another parallel the Derickson-Unimak seamounts. fracture to the north is believed to be mani- fested by Heck, Stirni, Union, and Tucker COLTJMBIA FRACTURE ZONE seamounts. Intermittent seamounts and ridges carry the Assuming that topography of the gulf floor is alignment northwesterly through Peters, characterized by north- to northeast-trending Schoppe, and Whitney ridges and across the ridges and troughs generally, then some expla- Mid-Gulf zone at the north end of Hook Ridge nation of the numerous transverse features is to the Parker-Bean Seamount Group and the needed. The latter features seem to be super- Aleutian Trench rise. imposed on the ridge and trough topography The Patton-Faris Seamount Group is inferred and consist of ridges and lines of seamounts. to constitute two parallel lines of fracture as They are inferred to be the result of some far east as Miller Seamount. The Unimak- great stress in the earth's crust, such as might Sirius Seamount Chain projected eastward have caused the San Andreas fault and various aligns with a large number of seamounts and fracture zones. Sea-floor manifestations of this seaknolls lying about 150 miles south of the inferred fracture zone extend northwesterly Parker-Bean Seamount Group. The former from the vicinity of the Gorda Seascarp at line appears to mark the most southerly frac- Cape Mendocino (Fig. 1), across the Great ture of the zone. Trough and the Ridge and Trough province to the Aleutian Trench rise. Unlike the fractures INTERPRETATION to the south described by Menard (1955b, p. 1153) the difference of elevation of the sea Bathymetry of 800,000 square miles of the floor on the northeast and southwest of the deep ocean based on such comprehensive and zone is not great and could be ascribed to the accurate reconnaissance surveys should pro- general slope. However, the difference on either vide some confirmation or modification of side of Eickelberg Ridge and the Parker-Bean existing theories of earth science. Comparison Seamount Group is about 100 fathoms. This of submarine topography with mapping along difference is not conclusive, since it occurs the contiguous shores should provide correla- where local subsidence is evident. This inferred tion and lend direction to further investigations. fracture zone consists of lines of seamounts and However, inferences based on physiography ridges in echelon form extending over a wide are extremely tentative without collateral belt of the sea floor. Kodiak Seamount Cham evidence. is inferred to be the most northerly line and The Aleutian Trench is interpreted as an the least definitely fractured. Thus, the line open geosyncline fringed on the north by an of seamounts would represent volcanic out- advancing wall of deposition (continental pouring along separated vents in contrast shelf and slope) and on the south by a slight to those farther south which appear to have anticline or rise. The northeastern end of the poured from fissures. trench, obscured by heavy sedimentation, The main fracture transverse to the Ridge makes a reverse turn southeastward in general and Trough province comprises Eickelberg parallelism with the curving tectonic elements Ridge and its southeastern and northwestern mapped back of the coast line by the U. S. extensions. Over its 170-mile generally north- Geological Survey (Payne, 1955). Recent and westward trend, the fracture is marked by perhaps continuing orogeny is deduced from distorted topographic manifestations in the the pulsating uplift at Middleton Island (Miller, form of abrupt changes in trend, major sea- 1953), by general uplift of the Gulf of Alaska mounts, and low saddles. Warwick Seamount Tertiary province and high wave-cut terraces on its southeasterly extension rises nearly 10,000 near Lituya Bay (Miller, 1957, personal com- feet to a depth of 250 fathoms. It occurs at an munication), and by subsidence along the abrupt change in trend and at the southwestern extended axis of the Aleutian Trench at end of an extensive, low transverse rise. North- Yakutat Bay and Pamplona Ridge (Jordan,

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1958, p. 12). The recent discovery of Surveyor Mendocino Seascarp. Drag fractures making Deep-sea Channel paralleling the Aleutian angles of 8°-15° with the zone of displacement Trench near the crest of its southeastern slope have been produced experimentally by Cloos tends to confirm this possibility. The similarity (1955, p. 244-246) as a result of rotational between Dutoit's (1937, p. 324-326) theoretical forces. A model, free to rotate externally and marginal geosyncline and moving anticline and internally to a couple, opened two sets of the Aleutian Trench and rise is evident. The fractures, one 45°-65° and the other 70°-90° Aleutian Trench rise would conform to the from the direction of pull. The drag fractures present position of the moving anticline and would be similar to those of the Kodiak Sea- the Aleutian Bench to a former one. The fact mount Cham, and the two sets produced by that the geosynclines and geanticlines are the couple are similar to the transverse Ridge progressively younger toward the sea (Payne, and Trough and Columbia fracture zones. A 1955) may tend to confirm Dutoit's theory of common origin or constructional process may sliding continents. In that case the Aleutian be inferred from the close agreement in general Trench rise would have to develop into a far form of cross sections of the Hawaiian Islands greater feature hi order to provide sediments and Bean and Eickelberg ridges. In each case for filling the next foredeep to the southeast. the ridges may be attributed to fissure eruptions However, conditions seem to be more indica- from upwelling and thermal expansion of the tive of a gradual outbuilding of the continental hot magma of a subcrustal convection current margin than of a sliding mass. followed by volcanism through tensional The Alexander Archipekgo, occupying a fractures at the crest of the swell, followed by slight trough at the site of a former Cretaceous regional and isostatic sinking as indicated by geosyncline, projected southward beneath the the flanking depressions. However, Bucher sea coincides with the axis of the Great Trough (1956, p. 1313), who long postulated the need off the west coasts of Washington, Oregon, and for surface tension in the mechanism, now northern California. This trough may mark believes that deep-seated tension caused by the site of the geosyncline postulated by deep earthquakes will create channelways for Eardley (1951, p. 62-68) as persisting from heat to traverse the earth's crust. In some Silurian to Cretaceous time, and its west places, especially hi the Mid-Gulf zone, erup- bordering ridges and seamounts are remnants tions may have taken place through the crests of the postulated archipelago constituting of folds or through inclined vents along the sources for volcanic rocks found in the western flanks. Figure 2 shows that the general axis of part of the Cordilleran geosyncline. The con- the Columbia fracture zone falls on the pro- tinental slope, cutting across at an angle of 45° longation to sea of the axis of the Coast Range at Queen Charlotte Sound and tending to and the San Andreas fault. separate the two troughs, was more recent. St. Amand (1957, p. 1366) pointed out the The axes of the Great Trough, Alexander possibility that the North Pacific basin may Archipelago, Gulf of Alaska Tertiary province, have been rotating counter-clockwise for a Chugach-St. Elias fault, Sullivan fault, Aleutian very long tune and quoted a suggestion by Hill Bench, Aleutian Trench, Aleutian Trench rise, and Dibblee of about 225-mile offsets along the and Surveyor Deep-sea Channel all tend San Andreas fault since late Eocene tune. No toward parallelism and conform hi general with direct confirmation of that movement may be the axes of the tectonic elements mapped along seen in the bathymetry, but there are sugges- the margins of the land (Payne, 1955). tions of rotational movements. The Bowie, The deep-sea-floor features comprising the Hodgkins, Davidson, and Denson group com- Ridge and Trough province and the Mid-Gulf prises four seapeaks in a 75-mile line that are zone consist mainly of north-northeasterly roughly similar to the four seapeaks extending patterns, and the Columbia fracture zone and Kodiak Seamount Chain consist mainly of over a 75-mile line northwest of Durgin Sea- transverse northwesterly trends. These orienta- mount. The vents under the latter line are tions happen to agree closely with the axes of spaced the same as the four seamounts com- the Hawaiian Islands and sunken islands of the prising the Surveyor-Giacomini group. The Mid-Pacific Mountains at their junction near distance between Peters and Whitney ridges, Necker Island (Hamilton, 1956, p. 38-44). Pos- Scott, and Pathfinder seamounts, Sirius to sibly the same alignments will be found between Derickson seamounts and Derickson to Unimak the Hawaiian Islands and Columbia fracture seamounts is about 75 miles. The most likely zone, except for the anomalously trending correlation with a rotational movement would

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be between the Durgin-Pratt group and the parallels Aleutian Trench: Geol. Soc. America Bull., v. 69, p. 611-614 Surveyor-Giacomini group, if it is real. Gibson, William, and Nichols, Haven, 1953, Con- Inasmuch as Vancouver Island has risen, figuration of the Aleutian Ridge: Geol. Soc. subsided, and risen again it is not surprising to America Bull., v. 64, p. 1173-1181 find that the Explorer Trench and parallel Hamilton, E. L., 1956, Sunken islands of the Mid- Pacific Mountains: Geol. Soc. America Me. 64, escarpment lie westward. The relief of the 98 p. trench and escarpment favors an interpretation Heck, N. H., 1927, Some unusual submarine fea- of a thrust fault. It is similar in size to the tures in the North Pacific: Geog. Rev., v. 17, Denali fault of Chatham Strait. Heck Seamount p. 448-452 Jordan, George F., 1958, Pamplona searidge: Intern. appears to rest in the mid-portion of a great Hydrog. Rev., v. 35, no. 1, p. 3-12 downfaulted block. Menard, H. W., Jr., 1953, Pleistocene and Recent The planation of the tops of the tablemounts sediment from the floor of the Northeastern of the Kodiak seamount province has been Pacific Ocean: Geol. Soc. America Bull., v. 64, p. 1279-1294 attributed primarily to a combination of 1955a, Deep-sea channels, topography and sedi- lowered sea level and local or regional sub- mentation: Am. Assoc. Petroleum Geologists sidence. During periods of lower sea level crests Bull., v. 39, p. 236-255 of the seamounts may have been modified by 1955b, Deformation of the Northeastern Pa- cific basin and the west coast of North America: floating ice islands or a deeply frozen sea in Geol. Soc. America Bull, v. 66, p. 1149-1198 the early stages of volcanism. Riesenberg Menard, H. W., and Dietz, R. S., 1951, Submarine (1941, p. 366-376) quoted reports of ships in geology of the Gulf of Alaska: Geol. Soc. Amer- the Antarctic sighting ice islands 50 km long ica Bull., v. 62, p. 1263-1285 Miller, Don J., 1953, Late Cenozoic marine glacial and 500 feet high. The underwater portions of sediments and marine terraces of Middleton horizontal masses would then have been 3000- Island, Alaska: Jour. Geology, v. 61, p. 17-40 4000 feet and deeper if irregular. Extremely 1957, Geology of the southeastern part of the large ice islands are known to be moving in the Robinson Mountains, Yakataga district, Alaska: U. S. Geol. Survey Oil and Gas Inv. Arctic Ocean. Present currents off the south- Map OM-187 east coast of Alaska would tend to carry ice Murray, H. W., 1941, Submarine mountains in the toward the tablemounts. Kreichgauer (Schei- Gulf of Alaska: Geol. Soc. America Bull., v. degger, 1958, p. 5) estimated positions of the 52, p. 333-362 1945, Profiles of the Aleutian Trench: Geol. north pole in Carboniferous time at lat. 35° N., Soc. America Bull., v. 56, p. 757-782 long. 145° W., and in Tertiary tune at lat. Nichols, Haven, 1950, New seamount in the North 51° N., long. 154° W. The latter Tertiary Pacific Ocean: Geog. Rev., v. 40, p. 457-461 position is about 100 miles southwest of Parker Payne, Thomas G., 1955, Mesozoic and Cenozoic Seamount. tectonic elements of Alaska: U. S. Geol. Survey Misc. Geol. Inv. Map 1-84 Plafker, George, and Miller, Don J., 1957, Recon- REFERENCES CITED naissance geology of the Malaspina district, Alaska: U. S. Geol. Survey Oil and Gas Inv. Bucher, Walter H., 1956, Role of gravity in orogene- Map OM-189 sis: Geol. Soc. America Bull., v. 67, p. 1295- Riesenberg, Felix, 1941, Cape Horn: London, Rob- 1318 ert Hale, 452 p. Cloos, Ernst, 1955, Experimental analysis of fracture St. Amand, Pierre, 1957, Geological and geophysical patterns: Geol. Soc. America Bull., v. 66, p. synthesis of the tectonics of portions of British 241-256 Columbia, Yukon Territory, and Alaska: Geol. Daly, R. A., 1951, Relevant facts and inferences Soc. America Bull., v. 68, p. 1343-1370 from field geology, p. 23-49 in Gutenberg, B., Scheidegger, A. E., 1958, Principles of geodynamics: Editor, Internal constitution of the earth: New Berlin, Springer-Verlag, 280 p. York, Dover Publications, Inc., 439 p. Wiseman, John D. H., and Ovey, Cameron D., 1954, Dutoit, Alex L., 1937, Our wandering continents: Proposed names of features on the deep-sea London, Oliver and Boyd, 366 p. floor: Deep-Sea Research, v, 2, p. 93-106 Eardley, A. J., 1951, Structural geology of North America: New York, Harper & Bros., 624 p. 101 WILDWOOD AVE., PIEDMONT 10, CALIF. Gates, Olcott, and Gibson, William, 1956, Interpre- MANUSCRIPT RECEIVED BY THE SECRETARY OF THE tation of the configuration of the Aleutian SOCIETY Ridge: Geol. Soc. America Bull., v. 67, 127-146 PUBLICATION AUTHORIZED BY THE DIRECTOR, COAST Gibson, William M., 1958, Gulf of Alaska Trough AND GEODETIC SURVEY

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SUBMARINE TOPOGRAPHY IN THE GULF OF ALASKA

BATHYMETRY FROM DEEP-SEA SOUNDING LINES AND LIMITED-AREA SURVEYS OBTAINED BY SHIPS OF THE COAST AND GEODETIC SURVEY 1925-1957

Depth Contours at 100-Fathom Intervals to Bottom of Rises and Rim of Deeps Depth Contours at 200-Fathom Intervals on Continental Slope and Seamounts Dashed Numbered Lines Indicate Profiles on Separate Illustrations TRACKS OF C. & G. S. SQUNDING LINES 1925-1957 Compiled by W. M. Gibson, Const and Geodetic Survej NORTHEAST PACIFIC OCEAN (Limited-Area Surveys of Seamounts are Not Indicated)

Nautical Miles at Different Latitudes

'-_L _ , f~- SGamounl J^*-m-~ '^^^ ^^.-^—^'•i V1 ~^~^~~ ' :rr~-*X>°-^-J/

BATHYMETRIG CHART SHOWING SUBMARINE TOPOGRAPHY IN THE GULF OF ALASKA AND LOCATIONS OF ILLUSTRATED PROFILES

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