Geology of the United States' Seafloor - The View from GLORIA PDF
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Geology of the United States' Seafloor The View from GLORIA Edited by JAMES V. GARDNER, MICHAEL E. FIELD, and DAVID C. TWICHELL US Geological Survey CAMBRIDGE UNIVERSITY PRESS Published by the Press Syndicate of the University of Cambridge The Pitt Building, Trumpington Street, Cambridge CB2 1RP 40 West 20th Street, New York, NY 10011-4211, USA 10 Stamford Road, Oakleigh, Melbourne 3166, Australia 0 Cambridge University Press 1996 First published 1996 Printed in the United States of America Library of Congress Cataloging-in-Publication Data Geology of the United States’ seafloor : the view from GLORIA / edited by James V. Gardner, Michael E. Field, David C. Twichell. p. cm. Includes bibliographical references. ISBN 0-521-43310-X (hc) 1. Geology - United States. 2. Continental margins - United States. 3. Economic zones (Maritime law) - United States. I. Gardner, James V. 11. Field, Michael E. 111. Twichell, David C. QE77.G325 1996 557.3 - dc20 95-46492 CIP A catalog record for this book is available from the British Library ISBN 0-521-43310-X Hardback Introduction James V. Gardner U.S.G eological Survey, Menlo Park, California On the fog-shrouded morning of April 26, 1984, the USGS systems, as well as the other available sidescan sonar sys- research vessel Furnellu unceremoniously slipped its berth tems, can map a swath of only 5 to 10 km. Simple calcula- in San Diego, California, to begin one of the nation’s great- tions showed us that using any of these alternate systems est mapping expeditions ever undertaken. The mission was would require decades to complete the EEZ mapping. to map the newly declared territories of the United States - So, now a mixed team of USGS marine geologists and the Exclusive Economic Zone (EEZ). The U.S. EEZ was U.K. GLORIA experts were plowing through rolling seas proclaimed just a year earlier by then-President Ronald Rea- off San Diego to begin an eight-year EEZ-SCAN program gan. This single stroke of the presidential pen increased the to map the EEZ. It was well known to the team aboard size of the U.S. territory by more than loo%, a much larger Furnellu that morning that they carried with them the only increase in area than occurred with the Louisiana Purchase GLORIA I1 system in existence. The UK Institute of in 1803. Just as the area gained by the Louisiana Purchase Oceanographic Sciences (10s) developed the system in the was a region little explored, the more than 13 million km2 1970s for their own use but did not have the resources to of seafloor represented a vast term incognita (Figure 1). The construct a backup system. If, as often happens on scientific 1879 Organic Act of the U.S. Geological Survey (USGS) cruises, something were suddenly to go wrong during the provides a mandate for the USGS to map the territorial lands cruise and the GLORIA I1 system were severely damaged of the US., and mapping the EEZ was a natural extension or lost, it would mean the abrupt end of the survey and the of that mandate. However, how to map this vast region be- program, in something just shy of humiliation. Accordingly, came a problem. It was clear from the beginning that the this team of scientists, engineers, and ship’s crew, and every mapping budget would not be comparable to those set aside team that followed, had a large responsibility resting on its to map the Moon, Mars, or Venus. Yet, just a year after the collective shoulders. They had to return the GLORIA I1 sys- proclamation, and in the tradition of the late nineteenth- and tem to port in one month, intact and operating, so that the early twentieth-century USGS mapping expeditions of the next team could continue the survey. Over the eight years West, a USGS team ventured forth to map the newly ac- of mapping, this responsibility overrode all other shipboard quired national lands of the EEZ. considerations. In 1986, an improved GLORIA I1 system Although led by experienced marine geologists, the was constructed for the USGS, and this system provided for USGS team was unfamiliar with the principal instrument a backup in the event of mishap, but the precautions were chosen to map the EEZ. The USGS had selected the British- never relaxed and GLORIA was never lost. designed, -built, and -operated GLORIA I1 long-range side- Anticipating digital images of the seafloor allowed the scan sonar (Figure 2) to map the EEZ because it provided USGS to develop computer programs to correct distortions the state-of-the-art technology necessary for mapping large in the images and to digitally align the images into quad- regions of the ocean floor at reconnaissance scale. GLORIA rangle mosaics. Therefore reconnaissance-view quadrangles is a digital sidescan sonar system that has the unique capa- of the seafloor could be constructed, similar to Landsat im- bility of mapping swaths 30-, 45-, or 60-km wide, not just ages of the subaerial surface of the Earth. Once again, the the area directly beneath the ship. Other sidescan sonars USGS was almost uniquely qualified to tackle such a were available within the United States, but none of them problem because of experience gained in the planetary- have the capability of mapping such large swaths. Multi- exploration programs of the 1970s and 1980s. Consequently, beam-swath bathymetric systems were available in the U.S. the program began with all the elements in place to be suc- in 1983 and were considered for mapping the EEZ, but these cessful. Eight years later, on the balmy morning of June 15,1991, This Introduction is not subject to US copyright. with a quarter of a million kilometers of tracks behind them, 1 2 Geology of the United States' Seafloor: The View from GLORIA Hawaiian Figure Intro-1. Map showing the areas of the U.S. EEZ. Areas too small to show at this scale include Swains-Rose Islands and Northern Marianas. Figure Intro-2. The GLORIA I1 system during a launching operation in the eastern North Pacific. Introduction 3 an experienced team of USGS and 10s scientists brought none more important than the involvement of the team that Famellu to the pier in Hilo, Hawaii. This cruise terminated designed, built, and improved GLORIA 11. This team in- the first and largest stage by mapping more than 6 million cludes Jack Revie, Mike Somers, Mac Harris, Derek Bishop, kni2 of the U.S. seafloor. The deep-water portions (deeper Jon Campbell, Chris Flewellen, Eric Darlington, Brian Bar- than 200 m) off the U.S. East, West, and Gulf Coasts, and row, and Andy Harris. And then there are the masters, of- the Hawaiian, Aleutian, and Bering Sea EEZs had been ficers, and crew of IW Famella, managed by one of the mapped with virtually 100 percent coverage. The area was truly exceptional individuals of the entire program, Mr. no longer a terra incognita; it was now a familiar landscape James Hind. These gentlemen made our jobs infinitely eas- of seamounts, ridges, fracture zones, canyons, trenches, sub- ier through their unfailing humor, friendship, and assistance. marine fans, channels, and plains, all accurately mapped They also taught us to loathe mushy peas. wi@ state-of-the-art navigation and processed digital im- In his preface to the first atlas from the EEZ-SCAN Pro- ages. The surveys included more than 100 days at sea per gram, David Howell eloquently stated the spirit of EEZ- year for eight years, with less than one day per month down- SCAN with the following words: time over the entire period. That remarkable engineering Long before the American Revolution, explorers were achievement is testimony to the premier GLORIA develop- venturing westward on missions of discovery, motivated ment team at 10s and those 10s engineers that accompa- by the lure of the unknown and the quest for riches. The nied the USGS on each cruise. The entire survey cost the almost continuous westward stream of adventurers ebbed U.S. taxpayer only a penny an acre (in 1984 dollars), surely and surged in response to events as varied as the discov- one of the most efficient mapping expeditions of all time. ery of luxuriant furs in the Northwest, the addition of ma- jor land areas such as the Louisiana Purchase and Alaska, There is generally no place in a scientific book where one and the discovery of gold in California. can acknowledge all the people who were essential to make The rewards of expeditions extended beyond the bounty a program of this scope and magnitude a success. I’m taking of a particular voyage or trek. The more lasting treasures this opportunity to do so here. A program as large and un- involved new information about the discovered or more conventional as EEZ-SCAN is difficult to get funded, even fully explored territories. Private or corporate journals within a government agency that has experience with large were the repositories of the early findings, but when Presi- programs. There w& a certain urgency to begin a program in dent Thomas Jefferson in 1804 ordered Meriwether Lewis and Captain William Clark on an expedition to explore the newly formed Exclusive Economic Zone, brought on by the unknown country lying between the Mississippi River the withdrawal of the United States from the UN Law of the and the Pacific Ocean, the United States Government as- Sea proceedings and other political factors. The scientificj us- sumed a leadership role for all future surveys. It was not tifications for the program were easy to formulate, but often until 1879, however, that the Congress formally estab- scientificj ustification is not the most important criterion used lished the US.G eological Survey (USGS) to examine the by those managing the budget. For these reasons, the EEZ- substance of the national domain. The USGS has re- SCAN program was inordinately fortunate in its early stages mained intact for more than 100 years owing to the im- portance and lasting relevance of its charge: to provide of development to have the support and leadership of two key geologic, topographic, and hydrologic information that science administrators who had vision and perseverance: Dr. contributes to the wise management of the nation’s natural David G. Howell, then Branch Chief of the Branch of Pacific resources and that promotes the health, safety, and well- Marine Geology, and Dr. Gary W. Hill, then Deputy Chief, being of the people. Office of Energy and Marine Geology. David enthusiastically The western limit of exploration for many years was encouraged the initiation of the project because he had the vi- the shoreline of the Pacific, for the ocean beyond was too sion of road maps of the seafloor to guide generations of more hostile and the prospect of natural resources seemed mini- mal. It was ignorance, not information, that temporarily detailed follow-on studies. Gary actively supported and pro- thwarted our manifest destiny. moted the program because he saw the scientific results as being a vital function of the mandate of the USGS-to map This book represents the first compilation of derivative the nation’s lands and inventory potential resources and haz- studies from the GLORIA surveys of the U.S. undersea ards. Without the leadership of these two key people, the goal territories. The primary sidescan, seismic-reflection, grav- of mapping the nation’s vast new territories would never have ity, and magnetic data have been published, or are been achieved. presently in preparation, in an ongoing series of USGS at- Other individuals critical to the successful implementa- lases. CD-ROMs of the data have been produced and dis- tion of the EEZ mapping initiative reside in the United King- tributed by the USGS free of charge to anyone interested dom. The then-Director of IOS, Sir Anthony Laughton, was in the data. Many studies and areas are not included in a strong supporter of the project from the very beginning, this volume because of limitations imposed by time and and he was instrumental in the formulation of a strong volume size. For example, interpretative papers on the en- USGS-IOS collaboration that integrated the collection of tire Hawaiian EEZ are planned to appear in a separate vol- data with the interpretations. Our cooperative mapping pro- ume. More than a hundred derivative studies have already ject enjoyed eight years of success for many reasons, but been published in numerous journals, and many more are 4 Geology of the United States‘ Seafloor: The View from GLORIA in various stages of conception, formulation, and draft h2of the U.S. Trust Territories remain unmapped, as well writing. Like the first cruise in April 1984, this book is as more than a million km2 of U.S. continental shelf, an area just the beginning. too shallow to be efficiently mapped with GLORIA 11. These The second stage of mapping America’s Exclusive Eco- areas await both the funding base and the technologies only nomic Zone is designed to enhance understanding of the ge- now emerging, so that mapping the nation’s frontier can be ology represented by the acoustic images of the GLORIA completed. I1 sidescan sonar. Collecting, processing, and displaying im- ages of the seafloor has been difficult, but in comparison to References what follows, it was the easy part. The more difficult job lies ahead. The imagery produced by the GLORIA I1 side- EEZ-SCAN 84 Scientific Staff 1986. Atlas of the Exclusive Eco- scan sonar represents the backscatter from the acoustic prop- nomic Zone, Western Conterminous United States. US.G e- erties of a variable-thickness volume of seafloor. The more ological Survey Miscellaneous Investigations Series I-l 792, challenging job for marine geologists is to find the Rosetta 152 p., scale 1:500,000, Reston, Va. stone, or stones, that can be used to decipher the backscat- EEZ-SCAN 85 Scientific Staff 1987. Atlas of the Exclusive Eco- nomic Zone, Gulf of Mexico and Eastern Caribbean areas. ter images and produce true geological maps. That task US.G eological Survey Miscellaneous Investigations Series stretches into the 21st century. This stage will require a gen- I-I864-A,B, 104 p., scale 1:500,000, Reston, Va. eration of geoscientists and a major commitment to unravel EEZ-SCAN Scientific Staff 1991. Atlas of the Exclusive Economic the physics of the interaction of sound with sediments to Zone, Bering Sea. US.G eological Survey Miscellaneous In- provide interpretations equal in detail to those now provided vestigations Series 1-2053, 145 p., scale 1: 500,000, Reston, Va. by satellite-mapping systems for the land areas. This second EEZ-SCAN 87 Scientific Staff 1991. Atlas of the Exclusive Eco- stage is only in its infancy in 1995. nomic Zone, Atlantic continental margin. US.G eological That sunny morning in June 1991 terminated the first Survey Miscellaneous Investigations Series I-2054, 174 p., stage of EEZ-SCAN mapping, but an additional 3.5 million scale 1:500,000, Reston, Va. Contents Contributors vii 5 Breaching the Levee of a Channel on the Mississippi Fan 85 Foreword xi David C.T wichell Gary W. Hill William C. Schwab Introduction 1 Neil H. Kenyon James V. Gardner Homa J. Lee 6 Morphology of Carbonate Escarpments as an Indicator of Erosional Processes 97 Part I The GLORIA System and Data Processing 5 David C. Twichell 1 The USGS GLORIA System 5 William P. Dillon Michael L. Somers Charles K. Paul1 Neil H. Kenyon 2 Processing and Manipulating GLORIA Sidescan Sonar Images 29 7 Sedimentary Processes in the Salt Pat S. Chavez, Jr. Deformation Province of the Texas-Louisiana Jeff A. Anderson Continental Slope 109 Stuart C. Sides David C. Twichell JoAnn Bowel1 Catherine Delorey 8 Sedimentary Processes in a Tectonically Active Region: Puerto Rico North Insular Part 11 U. S. East Coast EEZ 43 Slope 123 James M. Robb Kathryn M. Scanlon William P. Dillon Douglas G. Masson Dennis W. O’Leary Peter Popenoe 9 A Review of the Tectonic Problems of the 3 The Timing and Spatial Relations of Strike-Slip Northern Boundary of the Submarine Canyon Erosion and Mass Caribbean Plate and Examination by Movement on the New England Continental GLORIA 135 Slope and Rise 47 William P. Dillon Dennis W. O’Leary N. Terence Edgar Kathryn M. Scanlon 4 Characteristics of the Continental Slope and Dwight F. Coleman Rise off North Carolina from GLORIA and Seismic-Reflection Data: The Interaction Part IV U. S. West Coast EEZ 165 of Downslope and Contour Current James V. Gardner Processes 59 Michael E. Field Peter Popenoe William P. Dillon 10 Discrimination of Fluid Seeps on the Convergent Oregon Continental Margin with GLORIA Imagery 169 Part 111 Gulf of Mexico and Caribbean EEZ 81 Bobb Carson David C. Twichell Valerie Paskevich Kathryn M. Scanlon Erol Seke William P. Dillon Mark L. Holmes V vi Contents 11 A Meandering Channel at the Base of the 15 Sediment Pathways in Gulf of Alaska from Gorda Escarpment 181 Beach to Abyssal Plain 255 David A. Cacchione Paul R. Carlson David E. Drake Andrew J. Stevenson James V. Gardner Terry R. Bruns Dennis M. Mann 12 The Morphology, Processes, and Evolution Quentin Huggett of Monterey Fan: A Revisit 193 James V. Gardner 16 Sedimentation Along the Fore-Arc Region of Robert G. Bohannon the Aleutian Island Arc, Alaska 279 Michael E. Field Max R. Dobson Douglas G. Masson Herman A. Karl Tracy L. Vallier 13 Ground-Truth Studies of West Coast and Gulf of Mexico Submarine Fans 221 17 Aleutian Basin of the Bering Sea: Homa J. Lee Styles of Sedimentation and Robert E. Kayen Canyon Development 305 Brian D. Edwards Herman A. Karl Michael E. Field Paul R. Carlson James V. Gardner James V. Gardner William C. Schwab David C. Twichell 18 Geology of the Kula Paleo-Plate, North Pacific Ocean 333 14 Morphology of Small Submarine Fans, Inner Tracy L. Vallier California Continental Borderland 235 Carlos A. Mortera-Gutierrez Brian D. Edwards Herman A. Karl Miohael E. Field Douglas G. Masson Neil H. Kenyon Libby Prueher Thomas E. Chase Part V Alaskan EEZ 251 Herman A. Karl Paul R. Carlson Index 355 I The GLORIA system and data processing 1 The USGS GLORIA system Michael L. Somers Institute of Oceanographic Sciences, Southampton, United Kingdom The sidescan sonar technique the sonar system, whereas along track it is the physical translation of the array. The former process is essentially The sidescan technique is, as the name implies, a scanning continuous, though it is usually sampled in modern sys- process in which attention is directed successively at each tems for digital recording, whereas the pulsing of the point in the target field. It detects and records the energy transmitter makes the scanning along track inherently dis- backscattered from the scanned point onto an image field. continuous. The difference is that the designer has much The imaging process is a one-to-one mapping from the ob- less control over the sampling along track. The minimum ject field to the image in which the geometry, though con- size of the patch on the seabed that may be independently taining distortions, is recognizably close to true plan. The mapped, or resolved, on the image is determined by the technique is commonly applied to radar imaging from the pulse length across track and, in the limit, by the distance air over land and sea and to sonar imaging of the seabed. traveled by the survey vessel between pulses along track. GLORIA is an example of the latter. The strength of the In principle this is not rigorously true. Different consid- technique lies in the fact that with the nearly true geometry, erations apply if the so-called near field of the array ex- the patterns formed by the recorded backscattered energy tends across an appreciable portion of the swath. This con- give powerful and important clues to the processes at work dition certainly does not apply to GLORIA, but it on the object field surface. In neither radar nor sonar is there sometimes does for very high frequency sonars. In prac- much penetration of the radiation below the surface, though tice the resolution along track is limited for most of the there are minor exceptions in both cases, and sidescan is survey swath by the angular spread of the sound beam in generally classed as a 2D process. The choice of acoustic the fore and aft direction. The spread is related to the energy for sidescan mapping of the seabed is dictated by the acoustic frequency and the array dimensions, which are failure of electromagnetic energy of any wavelength to pen- crucial considerations in the design of sidescan sonar sys- etrate useful distances under water. Sidescan differs radi- tems. cally as an imaging technique from the well-known func- Figure 1-2 shows these basic facts of sidescan sonar. tion of a lens in optics where all points on the object field There are inherent distortions in the images arising from are imaged simultaneously and continuously on the image both the geometry of the technique and the propagation of surface. sound in the sea, but much can be done by suitable pro- The scanning process uses a narrow fan-shaped beam cessing to alleviate the effects. The real strength of side- of sound directed at right angles to the survey track, as in scan sonar reveals itself when the sonar energy impinges on Figure 1-1, to illuminate a narrow strip of the seabed. A the seabed at near-grazing incidence. Not only are the geo- short pulse of sound is emitted at regular intervals, and metrical distortions much less evident, but the variation of the returning echoes are recorded between the transmis- backscattering with angle is more rapid at shallow angles, sions. The transmission interval is the time required for which aids in revealing more subtle processes. The aim of the sound to travel to extreme range and back. Between the designer is almost always to have the widest swath pos- pulses, the survey vessel advances a known distance along sible, and in any case a ratio of maximum range to vehicle its track. The use of a short pulse ensures that energy re- altitude of at least 5:1 . flected from any point on the scan is not confused with This chapter starts with a short resume of the history of that from neighboring points at slightly different ranges. sidescan sonar, follows with an expansion of the foregoing Thus the scanning comprises two mechanisms. Across material, and ends with a treatment of topics relevant to the track, it is the propagation of the sound pulse away from USGS GLORIA system. 5 6 Geology of the United States' Seafloor: The View from GLORIA Figure 1-1. The principle of sidescan sonar. The sonar array is shown being towed behind the survey ship in the direction of the arrow. Short pulses of sound are transmitted in the fan-shaped region shown and intercept the seabed along the narrow high- lighted strip. The lower part shows the record formed by a large number of recorded pulses laid side-by-side on a facsimile recorder. The correspondence between points on the seabed and features on the image is indicated by the thin arrows. The reader will note that on the image the seabed vertically below the sonar is printed some distance into the record, as though it belonged well off to one side of the track. The delay is the time the sound takes to traverse the water column. Also, features a small distance off the vertical are foreshortened on the image. These two effects, the presence of the water column and the slant- range distortion, are the result of the geometry of the propagation-the recorder simply records events in linear time as they oc- cur. These distortions are normally corrected in a digitally recorded image. Note that, for clarity, only the port-side operation is shown; GLORIA has both port and starboard arrays. History of sidescan and the ized, leading shortly to the publication of results in the ge- GLORIA system ological literature (Chesterman, Clynick, and Stride 1958). The first sidescan sonar designed and built in the civilian Sidescan sonar in the civilian field dates from the late 1950s. field was described in 1961 (Tucker and Stubbs) although At that time military sonar work was giving information on it was originally intended for fisheries research, and it used the backscattering of sound by the seabed, and the geolog- military transducer hardware. This fact set the operating fre- ical implications of the patterns observed were soon real- quency at 36 kHz and thereby optimized the design for use
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