Anatomy of an Expedition
Henry W. Menard
Excerpted from Anatomy of an expedition / by Henry W. Menard.
Copyright © 1969 by McGraw-Hill, Inc. All rights reserved. Printed in the United States of America. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the written permission of the publisher.
To Robert Dietz and Roger Revelle, coleaders of the joint U.S. Navy-Scripps Institution of Oceanography Expedition Mid-Pac which, in 1950, took many young oceanographers into the deep sea for the first time.
Chapter One: fall 1965-march 1967
Genesis of an Expedition
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CHAPTER ONE An oceanographic expedition is the crystallization of an idea; it begins and ends in the mind with a little sailing around in between. The idea that became the Nova Expedition began to take form in the fall of 1965. At that time, I had not been to sea for fourteen months, which was my longest period on land since I became an oceanographer in 1949, and I started to think about another expedition. It is now March 1967 and the expedition is about to begin, and at this point I cannot remember exactly when or where the subject first came under discussion. After fifteen expeditions the preliminaries get rather vague. Most expeditions, and I suppose this was no exception, are conceived late in the evening after enough oceanographers have become sufficiently relaxed to be optimistic about work at sea. The reason for this is that everyone knows that the eventual output is going to require a lot of hard labor and discomfort. The conversation can be generalized as follows:
Ed, why don't we go drill an atoll and find out why it sank?"
"Say that's great. I need a sequence of reef limestones to test this new idea...."
"Which atoll? What about Fakarava?"
"You remember. Where we stopped on the Downwind Expedition in the central Tuamotus."
"Yeah, that was nice, and we can get fuel and plane service at Tahiti. When?"
"Well, there is a gap in the ship schedule for Argo next July because Sam canceled out. He can't get delivery on his equipment. We could take some students along."
"I was going to visit Cambridge that month on my way back from the meeting in Stockholm, but I could go there before the meeting."
"We'll need to know the crustal structure in order to pick the best spot to drill. I wonder if George would be interested. Where is George? Hey, George how would you like to go to Fakarava next July?"
Perhaps one out of five of these evening expeditions eventually puts to sea, and then it is at Majuro because the Navy will provide free air service and in August because the ship needs an overhaul in July.
Considering that it is the taxpayer's money, it may sound a little casual, but oceanographers constantly get new ideas to test, and they have to go to sea at one time or another, and there is no virtue in going to an unpleasant atoll if a beautiful one has the same geology. In any event, there is stringent product control. If you don't produce results, you can't get money for your next expedition. You may not get the results you expected—this is research, not bridge building—but you have to get significant results of some sort.
An expedition needs an idea, scientists who are interested in it, a ship capable of the work, and money. Bringing them together takes a lot of talking, adjustment, writing, modification, time, flexibility, and work. The steps have not changed in the last 150 years. The first United States Exploring Expedition in 1838 and the first great oceanographic expedition on the Challenger in 1873 followed the same path of organization as the Nova Expedition in 1967. Indeed, these and the intervening expeditions had similar problems, used about the same size ships, and cost similar amounts. The great changes have been in the ideas under investigation and the equipment on the ships. All this historical precedent, however, is little consolation as the painful process is repeated yet again.
The basic idea of Nova is to try to determine the development and geological history of the peculiar Melanesian region
It may be useful at this point to consider how oceanographic expeditions are financed and what they cost. Captain Cook's first voyage in 1768-1770 was supported by King George III with a grant plus a bark, Endeavour. The total cost for the ship and outfitting exceeded £8235, and it appears that the voyage cost at least £10,000 or in round terms about $28,000. This sounds very modest, but for comparison with modern expeditions we must allow for the decreasing value of money. At that time, for example, a man with an income of $1200 a year was able to "keep five or six servants indoors and out, to look well after his relations, to travel freely, and to exercise a generous hospitality to rich and poor."
A reasonable approach is to assume that the purchasing power of a given amount of money has decreased by two percent per year. Accordingly, it takes seven times as much money to buy something at the end of a century as it does at the start. Consequently, it cost King George about 1,400,000 modern dollars for Cook's voyage. In addition, the scientist, Banks, whose tax-free income in modern terms was about $1,000,000 per year, put in a considerable amount of his own
The cost of the first United States Exploring Expedition (Wilkes Expedition) in 1838–1842 is buried beyond recall in government records. However, in 1836 Congress appropriated $300,000 for the expedition, and the Navy reported that it was all spent in 1837, a year before the ships put to sea. The expedition involved four ships for four years and cost perhaps $10,000,000 in modern money. Each ship cost more than $2000 per day even though all were very small and some did not last for four years. A century and a quarter later, during Nova, we expect to land on the Exploring Islands, named after and surveyed by this expedition.
The value of the Challenger Expedition of 1873–1876 was enormous and so was its cost. The British government apparently paid out a sum equivalent to the estimated expense for the recent Mohole Project to drill a hole in the bottom of the sea. The modern project would have been so expensive that the American Congress in 1966 decided that the richest country in the history of the world could not afford it.
So, on historical precedent we needed to locate some rich and generous patrons if the Nova Expedition were ever going to sea. Fortunately for the success of American oceanography some far-sighted men established just such funding organizations fifteen to twenty years ago. No longer must appeals for support for each expedition be directed to king or Congress. Indeed, it would be quite impossible to have 50 to 100 American oceanographic expeditions per year without the existence and support of federal agencies. The most important for the past two decades has been the Office of Naval Research, which produced modern oceanography by supporting the expansion of marine institutions and fleets of research vessels. Somewhat later the National Science Foundation entered the picture and now provides about half the support.
The main cost of oceanography is for ship time. A research ship without support for operating funds is an albatross around the neck of an oceanographic institution. Not too long ago the cost of a ship had to be justified on the scientific merits
The total cost of Nova was initially estimated as follows:
|ARGO, ship time at $3000/day||$ 720,000|
|HORIZON, ship time at $2500/day||400,000|
|Direct support of expedition||270,000|
|Indirect costs of research||100,000|
|Scientific and technical salaries||200,000|
Due to the recent advances in federal money handling we did not need to ask for money to support the ships (which includes wages for the crew). Moreover, most of the salaries for scientists and technicians are paid by the University of California or by long-term state and federal research contracts. The indirect costs of research are those connected with this expedition but which are paid out of existing contracts with some broad objective. Thus the National Science Foundation supports a global study of carbon dioxide in the atmosphere, and some of this money will be used to make measurements
My colleagues, Harmon Craig, Edward Goldberg, Edward Winterer, Robert Fisher, and Manuel Bass, plus Charles Helsley of the Graduate Center of the Southwest, joined me in submitting a request to the National Science Foundation for this amount on 13 May 1966. As in all such proposals, we said what we want to do and why it is worth doing, who we are,
The general plan of Nova.
The detailed plan of Nova in the Melanesian region.
This evaluation process takes three to six months, and meanwhile planning for an expedition has to continue with the hope that it will not be wasted. My colleagues and I talked to other scientists who might be interested in problems in the southwestern Pacific. Gradually more of them decided to participate in Nova, and technicians and special equipment were organized and integrated into as comprehensive and efficient a whole as possible. We did not need to know which ports we would use for fueling when we submitted the request for funds. However, we did need such information before sailing so we examined various permutations of ports, distances, ship speeds, fuel consumption, water supplies, explosive handling, airplane connections, and general logistics. Some matters require a long lead time. My hair is very short because when I was a poor graduate student my wife cut my hair and she liked it short. However, like all blonds, I have a skin sensitive to the sun and my hair is getting thin. I usually wear a hat in the tropics, but it seemed prudent to have some natural covering between the top of my head and the tropic sun. Consequently, seven months before the anticipated departure time I started to let my hair grow.
Early in August I got a phone call from Joe Creager, an oceanographer from the University of Washington who was doing his public service by working for a year with the National Science Foundation. He said that our proposal was approved on merit but that it cost more money than was available. Could we get along with less? I said we could, although with less I did not think that we could do everything we planned. How much less? Joe said "Half," and another time of troubles began.
What to cut? The categories in our proposal included salaries, assistantships for graduate students, supplies, equipment, travel, and a 42 percent markup to cover University
The next item was supplies and expenses. I quote from Sir Wyville Thomson concerning the outfitting of the Challenger Expedition in 1873:
It is almost inconceivable how difficult it is to keep instruments, particularly those which are necessarily made of steel, in working order on board a ship; or how rapidly even with the greatest care they become destroyed or lost. For this reason it is necessary to have an almost unlimited supply of those in most frequent use, such as scissors, forceps, and scalpels of all sizes.
We have the same problems and must constantly restock everything from pencils to expendable equipment which is used only once but is cheaper than the ship time necessary to recover it. We chopped our request for supplies mercilessly but again with the certain knowledge that we would have to ask for more for the next expedition. We did have one wind-fall. George Shor, who had decided to measure crustal thickness in the southwestern Pacific, needed a large supply of explosives for the purpose. This was in the Nova budget, but meanwhile a long-standing request for explosives from the Navy was at last granted and we did not need more from the National Science Foundation. That item alone saved $12,000.
Next we came to heavier equipment which we also wear out or lose in the normal course of oceanographic work. We are not the only ones. A Russian oceanographer, Gleb Udintsev, once learned that we were planning to dredge in the world's deepest water in the Marianas Trench. He told me that if we dredged up a deep sea camera it was his because he had lost one there. The camera cost about $10,000 and we did not find it—in fact we lost one ourselves. What can you expect when you attach a camera to six miles of wire and try to photograph
Finally we came to a whopping request for $76,400 for travel by air to various ports that the ships would touch. We got our Marine Facilities department which operates the ships to agree to pay for rotating the crew, and that cut the request in half. Of course, it also increased the ship operating cost, but that was covered by another budget. We could have eliminated all this air travel by merely returning the ships to San Diego every few months, but that would have been a waste of money—which is a very different thing from tailoring requests for money to fit the amounts available in different contracts.
After many a painful session we cut the budget request in half and resubmitted the proposal on 10 August. Creager knew how short the planning time was growing and soon phoned that the money was on the way. He also said that he had hoped that we might reduce the amount of ship time required because the Science Foundation was running short of money for ships. After our juggling this seemed a little ironical.
One problem we face at Scripps is naming an expedition after we create it. This does not arise at every oceanographic institution nor was it ever necessary in the past. If the Royal Society sent the Challenger around the world, the voyage was called the "Challenger Expedition," which was entirely adequate because no expectation existed that the ship would ever go on another expedition. Likewise the "Galathea Expedition" and the "Swedish Deep-Sea Expedition" clearly were conceived as unique efforts. When such ships as Atlantis and the E. W. Scripps began to be used for repeated cruises in the 1930s, the problem of identifying the results arose and two solutions were used. A sample is uniquely designated by the ship name, cruise number, and sample number, thus: Atlantis, Cruise 6, Sample 4, or by specifying the cruise location, thus: Scripps, Gulf of California, Sample 4. However, the second system may produce confusion if the ship returns to the Gulf of California, and it is not very useful if the expedition is to a
The first large Scripps expedition in the deep sea was focused on the mountains of the central Pacific and was named Mid-Pac. It was followed by Northern Holiday, which derived its name from the nautical term "holiday," meaning a place where no information exists. The name caused a little muttering among the financing agencies in Washington. When it was proposed that Northern Holiday be followed by Southern Holiday, the muttering became audible in La Jolla. Warren Wooster, who was in charge of the expeditions, decided the Navy was not ready for nautical terminology and changed the name. Then we had expeditions with a variety of names, such as Capricorn after the Tropic of Capricorn, which was the southern limit of the region explored, and Cascadia, which was the name of a continent thought to have once existed off Oregon where we were working. We had a great series of wind names typical of the region of operations: Chubasco, Chinook, Zephyrus, Downwind, Monsoon. We had momentary aberrations like Six-Pac and inspirations like Blue Flash, which was one of the first cruises using an arcer—which emits such a flash. We began to have so many similar names such as Dolphin and Dorado which means the same thing but in Spanish that we were in danger of confusing the samples. We all agreed not to name an expedition without the prior approval of Bill Riedel, curator of geological samples, who would ensure that the abbreviation of a suggested name would not be the same as one already used.
What to name the new expedition to Melanesia? Usually several weeks or even months pass before the natural name of an expedition emerges. It becomes increasingly inconvenient to organize a nameless expedition or one which different people call by different names. Finally Jerry Winterer noted that the region we would study contained New Caledonia, New Zealand, New Guinea, and the New Hebrides and suggested the name Nova. It was short, pertinent, and distinctive,
Next, or meanwhile, we needed to make base maps for our work. If you want a map to do something like hike in the Sierras or navigate a ship into Suva harbor you just buy one from the appropriate government agency. Not so in oceanography, where the maps have to be changed after each expedition and commonly are made on board in order to plan the next day's work. We needed to know about every unpublished geophysical observation anyone had taken in the southwestern Pacific, in order to avoid duplication and for making detailed plans. The only way to get such information is to write to or visit every person who might have it. There are both formal and informal worldwide information networks whereby oceanographers keep track of their colleagues' work. I had already acquired a large amount of information by making the usual carefully respected promises not to publish other people's unpublished data and by agreeing to make our own observations similarly available. There remained the problem of the most recent data collected by oceanographers in Australia, New Zealand, and New Caledonia. A lot is always known which has not even been processed to the point where it can be sent to anyone else. I needed that information but getting it would require work by other people whose time I did not want to waste. The only practical solution was to visit the laboratories and explain exactly what we hoped to do and what information we needed. The trip would also provide an opportunity to interest oceanographers in these countries in participating in Nova and thereby getting more scientific results from the same effort at sea. In any event, it is not very courteous to carry out a lengthy expedition in waters near other oceanographic laboratories without asking the scientists there if they would like to join in. Finally, the trip would give me a chance to inspect prospective ports once again and see whether the surrounding countryside would be suitable for geological field trips for the students.
My wife had never been in this region so we went through the necessary arrangements to leave our children. A month later we had talked to geologists and oceanographers and
Back in La Jolla my associates Stuart Smith, Tom Chase, and Isabel Taylor plunged into the compilation of the new data for our base charts. Tom and Stu were each to lead one of the early legs of the expedition and had a vital need for this information. I also had the assistance of several graduate students who would join in the work at sea and might eventually use some of the results for Ph.D. theses.
My own effort was concentrated on further planning. The possible permutations in an enterprise like this are beyond belief. Somehow all the senior scientists have to be satisfied that their work can be done, equipment and supplies have to be directed to the right places at the right times, and the budget has to be balanced. It always reminds me of planning an amphibious assault—as I did in the same region many years ago—except that money is important.
I have mentioned the explosives before; the further problems connected with this item alone may illustrate something of what is involved. George Shor had about 12 tons of TNT stockpiled in the Navy ammunition depot in Pearl Harbor. Another similar amount would provide all we needed, and it was available in Southern California. However, Horizon could not carry its half of the explosives because its magazine had to take supplies needed for other work before we took it over in Kwajalein in April, 1967. It could have returned to Pearl Harbor, but that would have reduced time in the southwestern Pacific. We hit upon an elaborate scheme. Argo was scheduled to conduct oceanographic work from San Diego to Pago Pago to Pearl Harbor and then back south to Suva, where it would be joined by Horizon. We could load the local TNT on
At about this time a new development entered the explosives problem. Charles Helsley, of the Graduate Center of the Southwest, would also measure crustal thickness and structure on Nova. He flew to La Jolla, and he and George Shor developed some intricate negotiations whereby the TNT in California became an equal quantity of Nitramon, which is commercial fertilizer except when it is triggered by an explosive fuse. This safe stuff could be stored on Argo outside the magazine and would not have to be off-loaded at Pago Pago before the magazine was filled with TNT at Pearl Harbor. Consequently, Horizon need not go to Pago Pago and would be available for more important work. Moreover, Helsley would shoot off all the TNT between Suva and Brisbane, and we should have no problem entering the latter port, which had not yet replied to our inquiries about bringing in explosives. Then Brisbane said it would not let us enter even with the quantity of explosive fuses needed to set off the Nitramon.
So why were we going to Brisbane? Originally we planned to stop at that time in Noumea because it is more centrally located in the southwestern Pacific and it costs less to fly there from California than to Brisbane. However, Helsley had to ship some of his gear on to South Africa to join another oceanographic expedition. To meet this other sailing date he had to have the gear in a port with frequent sailings instead of Noumea, and so we put all other considerations aside. With the news from Brisbane about explosives, the port question was raised again. It turned out that a ship sails on an irregular
The above is a simplified version of the explosives problem. Helsley also shipped some Nitramon from Texas which was supposed to go by commercial truck. A trucking strike stopped that. The Nitramon came by truck driven by a graduate student and his wife. The truck broke down but was repaired and arrived just before sailing time.
There were also the mysterious and complicated affairs of the different air fares to Pago Pago, the missing magnetometers, the carbon dioxide program, and the perplexing problem of who would be working in the Coral Sea.
Finally, in April 1967, Horizon sailed south from Kwajalein and Argo sailed west from San Diego. The Nova Expedition was under way, seventeen months after it was conceived. Not a bad record, really; the Challenger Expedition took eighteen months and the United States Exploring Expedition took more than ten years to do the same thing.
Chapter Three: fall 1965-march 1967
Scientific Exploration of the Pacific Ocean
CHAPTER THREE One of my most distinguished colleagues at Scripps once designed a research ship. It was clear from the plans that none of the equipment would work when the ship was rolling in a normal swell. When queried, he explained that one could hardly expect a real scientist to work on something that pitched and rolled, and that the ship was a floating laboratory which would go to scientifically interesting places where the researchers would join it by airplane. The ship is a success.
Nevertheless, a very great scientist once sailed the Pacific and welcomed the opportunity even though he was wretched during every roll. Charles Darwin received a B.A. in theology, Euclid, and the Classics from Cambridge. By the time he was twenty-two, he had received some scientific training as an assistant to some very able men and knew how to stuff birds and collect fossils. As a result, on 24 August 1831, he received a letter from J. S. Henslow recommending that he take a position as unpaid naturalist on the circumnavigating voyage of H.M.S. Beagle with the words, "I have stated that I consider you to be the best qualified person I know of who is likely to undertake such a situation," a modest but realistic evaluation. Darwin first refused because his father had doubts about the merits of a position offered just before sailing. These doubts were resolved by family discussion, and young Darwin prepared to
We worked together for several years at the same table in the poop cabin of the Beagle during her celebrated voyage, he with his microscope and myself at the charts. It was often a very lively end of the little craft, and distressingly so to my old friend, who suffered greatly from sea-sickness. After perhaps an hour's work, he would say to me, "Old fellow, I must take the horizontal for it," that being the best relief position from ship motion; a stretch out on one side of the table for some time would enable him to resume his labours for a while, when he had again to lie down.
On 9 June 1834, the Beagle entered the Pacific and remained on the Chile coast until September 1835. During that time, Darwin was much ashore observing the uplifted ancient shorelines, collecting fossils, and otherwise working as a young naturalist. By Christmas Day 1835, he was in New Zealand, having spent a few weeks in the Galapagos Islands, about ten days at Tahiti, and the remainder of the time at sea. In that brief period, he made the observations that led him gradually to the Origin of Species and the theory of evolution. He also began to formulate ideas on the origin of coral reefs and the development of volcanic islands which were to influence greatly the future understanding of the geological history of the ocean basins. Darwin visited only one atoll and that was in the Indian Ocean in 1836, but he saw many volcanic islands in various stages of development from active eruption to almost total destruction by wave and stream erosion. He published The Structure and Distribution of Coral Reefs in 1842 and therein set forth his celebrated theory of the origin of
Not many scientists had either the grasp or vision of Lyell, and Darwin's ideas on coral reefs were hotly disputed. By the 1890s the Royal Society decided to resolve the matter by drilling an atoll to see whether it was a volcano capped by the thick coral demanded by Darwin's theory. I have not attempted
Most of Darwin's critics were concerned with the origin of the circular shape of atolls, whereas Darwin had been chiefly interested in whether large areas of the sea floor move up and down. Consequently, the scientific discussion in a remarkably large number of books was clouded by semantics. The matter was at last resolved when the atom bomb tests in the atolls of the Marshall Islands after World War II provided enough money for a thorough geological study. By this time the thickness of coral could be measured indirectly by geophysics and directly by the advanced drilling techniques developed to produce oil. Everything proved that Darwin was right. At Eniwetok Atoll the coral was almost a mile thick, and finally the drill brought up some basalt—the top of a volcano which had been near the sea surface more than 40 million years ago. With Darwin's theory of atoll formation confirmed, it was possible to turn to the, to me, more interesting question of movements of the sea floor. This will be one of the problems investigated during the Nova Expedition, so it is still not wholly resolved.
Between the Beagle and Nova the broad outlines of the
The Pacific was more remote, but some oceanography was being done—notably in the preparation of charts of surface currents and the distribution of whales—by Matthew Fontaine Maury, the Superintendent of the Depot of Charts and Instruments of the U.S. Navy from 1842 to 1861. Maury set himself the task of making order out of the countless entries in American ships' logs. He compared the course a ship appeared to be steering according to its compass with the course it proved to have steered according to the next position determined by star sights. The difference indicated the drift of ocean currents at that time and place. By plotting all the sightings of whales, he mapped migration paths which took great schools across half the ocean at different seasons. His objectives were the support of American commerce and the Navy, but his methods earned him international esteem and cooperation. From 1842 to 1847, his office processed 26 million observations specially collected for him in the world oceans. In addition to this work, he made the broadest studies of the ocean from the data then available. By 1859, his Physical Geography of the Sea was in its sixth edition, and he knew everything there was to know on the subject. Except for the North Atlantic, all he could say at that time was:
The first specimens have been received from the coral sea of the Indian Archipelago and from the North Pacific. They were collected by the surveying expedition employed in those seas. A few soundings have been made in the South Atlantic but not enough to justify deduction as to its depths or the shape of its floor.
This lack of knowledge led the Royal Society to send the Challenger Expedition around the world in 1872–1876. The ship was specially fitted out to sound and dredge in very deep water and was blessed with a captain who was a Fellow of the Royal Society. The ship displaced 2306 tons, which is far larger than most oceanographic ships now in use, but, of course, it was due to be away from its home port for a very long time. There were twenty-three officers and a large crew but only six scientists even though the objectives were wholly scientific. The chief scientist was Sir C. Wyville Thomson, who only reluctantly accepted such a lengthy assignment. The results of this expedition came out in a vast array of scientific volumes, logs, reminiscences, and popular accounts. Its scientific impact was enormous. The samples collected are still being used today. I have collected some fragments of the geological samples for study myself while in London. They are protected in an underground civil defense center, left over from the blitz, which is situated on the grounds of the British Museum, Natural History.
The ship departed England at 11:30 A.M. on Saturday, 21 December, which I find rather amusing because these days we hardly dare antagonize our crews by leaving or even arriving home on a weekend. Our ship Argo is due to return from the Nova Expedition on 18 December for no special reason except to have everyone home for Christmas. The attitudes of pioneers are understandably different from those of present oceanographers who go to sea again and again and again.
One of the junior scientists on the Challenger was Mr. John Murray. By 1908, he had become Sir John Murray K.C.B., L.L.D., F.R.S., and anyone who collected a deep sea bottom sample or even measured the depth, took care to send it to him at the Challenger Society Office in Edinburgh. Consequently, when we look at his maps of that date stating "compiled from the latest sources," we can be confident that they are complete. His chart of the Pacific shows about 500 soundings except in the southwestern Pacific to which I shall return. Of those in the deep open Pacific, almost all came from two sources: oceanographic expeditions and surveys for submarine telegraph cable routes. The chief oceanographic expeditions
The situation in the north and central Pacific was entirely different. There bands of soundings are shown on Murray's map along lines from the United States to Hawaii and thence to Fiji and to Guam and the Philippines. Another line went directly from Japan to Seattle. It will be apparent enough that these were the major political and commercial centers in the Pacific and that the routes were surveyed in order to pick locations for submarine cables. The surveys, seeking to avoid great depths which would destroy the cables, found the deep trenches that border the western Pacific. In its broad outlines, the Pacific known to Murray was about the same as we know sixty years later, but the "details" discovered since include numerous mountain ranges as big as the Alps.
In a second map, Murray shows the distribution of the curious sediments which he was first to discover in the Pacific. These included volcanic and coral mud around islands which were not very different from the muds and sedimentary rocks
In an earlier report, Murray had described the sea floor relief and sediments of Melanesia which is to be the focus of the Nova Expedition. The cumulative effort of British surveys, chiefly along cable routes, is really astonishing for 1906. At that time, the oceanic soundings were so numerous that the 2000 plotted were only a small fraction of those available. There were 1019 measurements of the sea water temperature directly above the bottom and over 700 samples of bottom sediments. Murray was able to describe the general geography as:
extremely diversified, ridges and valleys running approximately in a north and south direction alternating with each other, the valley nearest Australia being the deepest.... This deep valley ... is broken up by several elevations which do not reach the surface of the sea, the latest additions to these elevations being the "Britannia Hills," discovered by Mr. Peake in 1903.
Elucidating the origin of these very ridges and troughs and elevations is a major aim of Nova, and we hope to dredge the first samples of the Britannia Hills.
For almost forty years after Murray and Agassiz, little more was learned about the Pacific sea floor. Some samples of sediment were collected by the nonmagnetic ship Carnegie before she blew up in Apia harbor in 1929, but the invention of the echo sounder eliminated the opportunity to sample whenever a sounding was taken. Indeed, a large number of the new echo soundings were erroneous and, if anything, the oceanic charts of the Pacific in 1940 were worse than those of 1910. This was because measurement of depth with a wire was replaced by measuring the time it took an echo to bounce off the sea floor. This was tricky even when done by skilled
The marvels of technology developed by the Navy to look for submarines in the 1940s changed everything, and ships, instruments, and money became available for modern oceanography. The first work in the Pacific, however, was done as a part of three world-circling expeditions by British, Swedish, and Danish scientists, some of whom had used their time during the war to make preparations. The first was the Swedish Albatross (once again that wonderful name) Expedition of 1947–1948 headed by Hans Pettersson. Superficially, it seemed a little like the Challenger Expedition in that a small number of scientists were on a large and carefully outfitted ship. However, the problems of interest and the equipment to study them were very different indeed. The ship had a special winch with a great tapered wire capable of reaching the deepest parts of the sea. It had a newly invented corer which could plunge a steel pipe 30 to 60 feet into the sea floor, which previously had only been scraped. It had devices to measure the thickness of sediment between the sea floor and the hard igneous rock of the oceanic crust, and the amount of heat flowing through the sea floor because of the decay of radioactive minerals in the interior of the earth. And, wonder of wonders, it had an echo sounder which recorded a continuous profile of depths and thus gave a real picture of the shape of the sea floor. I can still remember the excitement when Robert Dietz and I first projected microfilms of these precious records in 1950. Now just my own collection of such depth recordings would form a continuous strip more than 100 miles long, and our Scripps fleet sometimes records 10 million soundings in a month.
With all these new devices, the Swedish scientists discovered undersea mountains and traced the fluctuations in oceanic
The Danish Galathea Expedition of 1950–1952 was headed by another famous scientist, Anton Bruun, whose name now graces a ship dedicated to international oceanographic research and cooperation. The expedition was partially financed by the Carlsberg Brewery in Copenhagen, which had supported research at sea on previous occasions. The objectives were primarily biological and were spectacularly successful. Galathea dredged animals from the deepest trenches and off Central America found a "living fossil," an animal of a type which was previously known only in rocks tens of millions of years old.
The last of these three circumnavigating expeditions was British and named Challenger II, but unlike its predecessor its primary aim was surveying possible hazards to navigation. One can only shudder at the story that the ship had been presented with a complete set of the great volumes of scientific results of the Challenger Expedition and that one day someone threw the lot overboard because the old books were taking up space. Perhaps this was apocryphal; in any event, very valuable measurements were made of the thickness of the crust of various ocean basins, which turned out to be much thinner than continents.
About this time, the general complexion of oceanography in the Pacific, and elsewhere, began to change. No longer was it assumed that each expedition would be followed by years of study of samples before planning began for the next one. Russia and the United States almost simultaneously began a
Chapter Four: fall 1965-march 1967
Objectives of the Expedition
CHAPTER FOUR The Nova Expedition includes many independent scientific experiments on land, sea, and air. Some of the studies are only very broadly related, and describing the reasons for and expectations from each would take an encyclopedia. These programs are part of the expedition only because ships are expensive and we try to make our operations as varied and efficient as possible. However, most of the investigations are parts of an integrated study of a general problem, namely, the origin and geological history of continents and ocean basins. This includes such questions as: Do continents drift about on the surface of the earth? Do continents grow and shrink? Are they torn into fragments by the convective flow of rocks within the interior of the earth? Does the sea floor move from one place to another? And so on. These ideas may seem a little bizarre even to people who know that the elements are transmutable and are prepared to believe that the universe is expanding. I shall have to review some recent geological discoveries in order to explain why they are taken seriously and thus how we hope to test them.
To begin with, we may consider the origin of the continents and ocean basins. In attempting to answer this question, scientists have used their imaginations to the fullest to make up for a paucity of facts. It is known that continents and ocean basins are very different but they float on a common material
How did these two very different types of material come to be on the surface of one planet? One group of ideas involves celestial catastrophes. It has been proposed that the continents are asteroids which hit an earth which was once all ocean basin. A diametrically opposed view is that the earth was once completely covered with continent and that part of it was pulled away to form the moon or that several parts of it were blasted away by the explosive impact of asteroids. Quite a different type of idea is that the earth was once covered entirely by continent but has been, and is, expanding and that the ocean basins are the opening cracks between continental fragments. Finally, there is the hypothesis that everything on the surface of the earth is the froth produced by gradual migration of low-density material from the interior. This idea has the great virtue that it accounts not only for continental rocks but also for sea water, which is another light-weight
At present, no one is sure which of these ideas is correct. All may have had some effect, but which have been important? This is the sort of problem which perhaps will be answered only when we have more information about other planets and the moon.
On a more modest scale we may wonder what has happened to the continents and oceanic crust since they were formed. Many geologists think that the continents have grown. Lava comes from the mantle and volcanoes spread it on the surface of continents. Consequently, new continental material is accumulating even now. Similar volcanic rocks have flowed out for several billion years. If the rate in the past was the same as during historical times, this vulcanism alone could have produced the whole volume of the continental crust and probably sea water as well. There is also a suggestion that the area of continents has increased because the oldest rocks, in North America at least, are in the center and younger ones lie closer to the edge. As we might expect, considering the speculation involved, the alternative idea that the continents are now shrinking has also been suggested. This is one of the possible interpretations of the fact that many mountain ranges simply disappear when they come to the edge of a continent and that many sedimentary rocks seem to have been eroded from mountains located where ocean basins now exist.
Another way to explain this same evidence is to say that continents which are now widely separated were once joined together and thus that the continuations of the mountain ranges, for example, still exist but are now separated by an oceanic gap. This is the famous theory of continental drift proposed in its best-known form by Alfred Wegener fifty years ago. Wegener started with the fact that the Atlantic sides of Africa and South America can be fitted together with hardly any gaps or overlap. This can be seen on any world map. He also noted that very peculiar and distinctive plants flourished in Africa, southern South America, and India at about the same time in the geological past. Likewise, evidence of more
By permission of the Royal Society
Then a new approach developed, based on the discovery that the position of the ancient magnetic pole was preserved in different types of rocks regardless of age. Although the origin of the earth's magnetic field is still somewhat obscure, for the last 60 million years the magnetic poles have corresponded roughly with the poles of rotation. Thus, the magnetic pole positions evident in the rocks probably indicate the approximate position of the geographic pole. The new magnetic data suggest widespread drift of continents and that the various components of Wegener's great southern continent, "Gondwanaland," were very near the southern pole at the time of the glaciation. Many ambiguities were discovered, and doubtful geologists had reason for continuing skepticism, but it was quite striking that the new type of observations strongly supported continental drift as originally conceived on quite different evidence.
In the late 1950s it was discovered that an enormous mountain range lies in the center of most ocean basins and particularly in those basins which separate the supposed fragments of Gondwanaland. The suggestion was rapidly advanced that this mountain range, or midocean ridge system, marked the initial crack along which Gondwanaland had split and from which the fragments had spread. The ultimate confirmation of this idea required large-scale investigations of the sea floor and a gradual understanding of how the midocean ridge system develops. To a certain extent, marine geology during the past two decades has only accidentally provided evidence bearing on this question, which is hardly surprising because the question itself is not that old. In more recent years, however, considerable effort has been spent in trying to answer this question with the happy result that the answer is now known.
How this came about involves a brief history of the course of oceanographic exploration and the development of
Shattered beliefs soon became a commonplace as it developed that almost everything supposed about ocean basins was wrong. The crust under ocean basins is not as thick as continental crust but in fact is much thinner and also astonishingly uniform. The sediment in the basins is not a mile or more thick as anticipated from the known rate of erosion of continents. Instead it is only a thousand feet thick, which is the amount of sediment that would accumulate in only a few hundred million years rather than in the total age of the earth. Moreover, no really ancient rocks can be found in the basins comparable to the three-billion-year-old rocks of the continents. At first, this was attributed to inadequate sampling but as the number of bottom samples continued to mount, the suspicion grew that ocean basin rocks are all relatively young. The midocean ridge system was found to be the locus of many earthquakes and a great trough was discovered running along the crest of the Mid-Atlantic Ridge. Soon a belt of unprecedentedly high heat flow was found along the crest of the midocean ridges.
All of these features were accepted as evidence of modern mountain building and the supposedly quiet ocean basins began to emerge as the very focus of global deformation. The largest faults on the surface of the earth were discovered in the Pacific, features thousands of miles long which follow straight lines even when plotted on a globe. Similar faults were soon found extending across the Atlantic ocean basin and indeed everywhere on the flanks of the midocean system.
Patterns of magnetic anomalies were discovered in the northeastern Pacific which have the peculiar properties that they are perpendicular to the great faults and are offset along them. That is, a distinctive anomaly can be traced to a fault and then is found again on the other side but displaced by a great distance. The maximum displacement is 700 miles. A comparable discovery on land would be that a road in California would stop at a great crack and that when this crack was traced to the east, a continuation of the road would appear in Utah. No such offset has been found anywhere on the continents and, once again, the sea floor assumed more importance in geological thinking.
As oceanographers made these discoveries, they proposed explanations but they were very specific—the number of explanations was at least equal to the types of facts and no common unifying hypotheses were proposed. After a while broader syntheses were attempted and they succeeded in explaining large groups of facts. One such idea, that the earth is rapidly expanding, could explain young ocean basins, thin sediment, and the position, topography, and earthquakes of the midocean ridge system. Another idea, mantle convection rising and spreading from the centers of the midocean ridge system, offered an explanation for most of the same features and also for the orientation and length of great oceanic faults, the surprising equality of average continental and ocean heat flow, the high heat flow near the crest of rises and ridges, and the tendency for large regions of the sea floor to sink.
However, it remained for the same Harry Hess who discovered guyots to propose a truly comprehensive hypothesis which explained just about everything known, and as it turned out, was capable of explaining many things discovered later. Hess rarely goes to sea on an oceanographic ship any more and thus this is a classic example of a broad synthesis created by someone who is not involved with the trivia which blind people who are involved with day-to-day collection of data. The example is highly exceptional, however, because the synthesizer was also a pioneer data collector in the same field more than two decades earlier.
Hess proposes that convection currents in the mantle rise
Hess conceived that peridotite and water in the mantle convect upward along lines under the ocean basins and elevate the midocean ridge system. As the mantle moves upward, it cools and passes through the level which is at 500°C, and the water and peridotite combine and form serpentine. Laboratory tests indicate that whereas peridotite transmits earthquakes with the velocity of the mantle, serpentine transmits them like the oceanic crust. Consequently, Hess had a mechanism for producing crust from mantle as a consequence of the convection which was already suggested by many types of evidence. But now he could explain many new things. The oceanic crust has its astonishingly uniform thickness because it is formed above a certain temperature which occurs at a uniform depth. The crust can move very large distances without leaving central gaps because new crust forms at the center of spreading. It does not pile up in great thicknesses at the edges of the ocean basins because as it is pushed down below the 500°C level, it is reconverted to peridotitic mantle. Continents do not drift through the mantle but merely float on it as it moves away from rises and ridges.
The sea floor spreading hypothesis.
The theory can also explain many other things provided the duration of the most recent mantle convection is known. The evidence available is rather tenuous but it suggests that most of the sea floor has been produced in this way during the last few hundred million years. For example, the Atlantic Ocean apparently was opened by continental drift during that time. If so, the oceanic sediment is thin because it is sitting on a young crust and has not had much time to accumulate. This does not mean that all ocean basins are necessarily very young but merely that older sediment has been skimmed off and plastered against the continents while older crust has been reconverted into mantle. The elimination of older crust likewise explains why no old rocks are found in ocean basins no matter how many times they are sampled. The older rocks have been moved out of ocean basins and either pushed into continents or pulled down into the mantle where they cannot be dredged.
Although an impressive display of imagination, this idea, soon named the "sea floor spreading hypothesis" by Robert Dietz, did not quickly gain acceptance. Geologists and geophysicists on average are as conservative in their own fields as any other group. It is hard enough adjusting to a growing flood of new work and ideas which surely are proven without also trying to understand the implications of everything which is not proven. The sea floor spreading hypothesis was not the
The confirmation of sea floor spreading came from the proof of a really outlandish corollary. Fred Vine and Drummond Matthews, respectively a graduate student and young instructor at Cambridge University, suggested that the spreading sea floor is a tape recorder. About the time Hess published his hypothesis, it was being established that the magnetic field of the earth is periodically reversed. Certain iron-rich minerals in solidifying volcanic rocks become oriented in the direction of the earth's magnetic field. When the rocks cool through the Curie point the orientation of the magnetic minerals is fixed and cannot readily be altered without reheating. Thus by measuring the direction of magnetization of the minerals in an ancient rock it is possible to determine the location of the magnetic north pole at the time the rock cooled. When the position of the pole was studied in detail in a given locality, it appeared that the north and south magnetic poles occasionally reversed. This was rapidly explained in several different ways and the significance of the observations was obscure. The field measurements continued and more effort was made to date the time of reversals by newly refined methods of measuring rock ages by the decay of radioactive elements. The origin of the reversals was established in an elegant way when it was gradually proved that the reversals occurred at the same time in widely separated places. That is, there were several distinct and worldwide times of reversal which could only mean that the whole magnetic field had reversed during a period of a few thousand years. It is interesting to speculate how navigation would have been affected if the field had been reversing,
Vine and Matthews reasoned that the long parallel magnetic anomalies characteristic of the oceanic rises and ridges are produced by reversals of the magnetic field combined with sea floor spreading. The lava that pours out and cools in the center of a rise preserves a record of the orientation of the magnetic field at that time. Spreading splits the solidified lava and moves it to the flanks of the rise. Meanwhile, the widening gap is again filled with cooling lava. If the magnetic field reverses during this period, the newer rocks preserve a record of a reversed field. Field measurements of the present total intensity of the field would show a strong field where the present one is reinforced by an ancient field with the same polarity and a weakened field where the modern and ancient field are in opposite directions. A tape recorder works in the same way, preserving the intensity of a varying magnetic field to which the moving tape is exposed.
Within a few years two new facts about the long parallel magnetic anomalies were discovered and both agreed exactly with the tape recorder hypothesis. First, it was found that the anomalies, which have quite distinctive shapes, are symmetrical around the centers of rises and ridges; in short, the sea floor is a stereo tape recorder with almost identical volcanic rock "tapes" spreading out in enormous sheets from the center. This was beyond the fondest expectations of Vine and Matthews because no one ever conceived of the enormous mountain-building deformation of the earth behaving in such a remarkably orderly manner. In any event, the idea of the moving crust preserving a history of reversals of the earth's magnetic field is the only one that offers a reasonable explanation for the symmetry. The other discovery was that the distance between the sea floor anomalies is generally proportional to the spacing between the times of reversals of the magnetic field measured on land during the last 3 million years. Consequently, particular sea floor anomalies can be paired with particular reversals. This not only reconfirms that the anomalies
The origin of these magnetic anomalies confirmed Hess's hypothesis of sea floor spreading and numerous other confirmations followed in short order. J. Tuzo Wilson of the University of Toronto observed that the large earthquakes along the great sea floor faults which offset the center of midocean ridges have a very peculiar distribution. The faults are thousands of miles long, but the earthquakes generally occur only between the offset centers of the rises. He reasoned that if the sea floor is spreading from each of the offset centers, this distribution can be explained. Between the centers, the oceanic crust on the two sides of the fault is moving in opposite directions, and this causes earthquakes. Beyond the centers, however, the crust on both sides of the fault is moving in the same direction and no earthquakes occur. If this is correct, it means that the motion on the faults is in the opposite direction from the indicated offset of the centers of a rise. He assumed that the faults are very old and that the younger rises and ridges were offset
when they were created by convection. He did not attempt to explain the origin of the faults or the offsets, merely the earthquakes. His prediction of the direction of motion of the crust was subject to testing because the first motion on earthquakes can be measured by studying the motion they produce in instruments on land. Lynn Sykes of Lamont Geological Observatory quickly proved that Wilson was right and, since the prediction assumed sea floor spreading, also proved that Hess was right.
Shortly everyone got into the act. Vast quantities of oceanographic observations were available to evaluate the reality of sea floor spreading. The thickness of sediment increases at greater distances from the centers of spreading. Although no fossils in ocean basins are very old by geological standards, the oldest ones occur at the margins of parts of the sea floor that have spread, and younger and younger fossils are found as the centers of spreading are approached. There is even a correlation with the rate of spreading. The solidified lavas are thick where spreading is slow and they are thin where it is fast. Likewise, mountainous ridges and a central rift are associated with slow spreading and low rolling hills with fast spreading. Most of the topography of the sea floor, like the magnetic anomalies and crust, is formed at the center of a rise or ridge and then spreads to one side or the other.
These correlations and confirmations of sea floor spreading have appeared very rapidly and are still coming. As I write this in preparation for the Nova Expedition, many of these discoveries have yet to be published in the scientific literature. Thus we go to sea in a time of great intellectual ferment and excitement. What remains to be done? For one thing, we have before us the opportunity to prove that more than one period of convection has occurred during the history of the earth. This is a particularly important point because our present knowledge about sea floor spreading is concerned with only the last small fraction of geological time. We need quite different information to tell whether the same process has occurred again and again, sweeping the sea floor clean and causing continents to drift about during the last several billion years.
The most favorable place to look for such evidence is in the region between Hawaii and the southwestern Pacific which we shall be traversing repeatedly during Nova. In this region it appears that about 100 million years ago the sea floor was elevated into a broad oceanic rise which has since slowly subsided. Charles Darwin first observed that this region had subsided, and consequently this broad feature is called the Darwin Rise in his honor. Since Darwin's time, Hess and various following oceanographers have found and dredged numerous drowned ancient islands in this region. The few that are sampled were islands at about the same time.
The load of these ancient islands cracked the surrounding crust and enormous volumes of volcanic rock poured out of the cracks. Then the rise sank. But was it really a rise like the existing ones, and will the Mid-Atlantic Ridge and the East Pacific Rise sink like the Darwin Rise? It is now clear that one
Of course, we cannot expect too much of six profiles measuring magnetic anomalies, and we may not be much further along toward solving these problems next fall than we are now. If so, we shall have to return. One of the complications making it difficult to map magnetic anomalies is that they are so commonly offset along perpendicular faults. If the faults are not located, it is difficult to determine the trends of anomalies. Unfortunately, it is not easy to map faults and anomalies at the same time because they are mutually perpendicular. If we go in one direction, we cross anomalies but not faults; and if we go in the other, we cross only faults and run along the anomalies, which is not much help. Some faults are already mapped, however, and they will help us determine what has happened and where to explore. The faults themselves are not without interest because they are so long and straight, and in some places they have formed very deep troughs. One just east of the Phoenix Islands is almost 25,000 feet deep and the
The sea floor spreading hypothesis will also provide a guide for our studies of the southwestern Pacific, and in that region we shall have information from islands to guide us. In fact, the great peculiarity of Melanesia is that it is a jumble of large continental islands and small ocean basins on a scale which exists nowhere else on earth. The Pacific edges of Melanesia generally are marked by "island arcs," which is the geological term for chains of volcanic and uplifted coral islands bordered by a very deep oceanic trench and with associated earthquakes. These island arcs are different from others around the margins of the Pacific. The Tonga-Kermadec "arc," for example, is straight except at the northern end where it curves sharply to the west. In other respects, it is relatively normal in that the trench is on the Pacific side of the islands and the earthquakes dip from near the surface below the trench to about 400 miles below the sea floor west of the islands. Dipping planes marked by earthquakes of this sort occur only below island arcs or continental equivalents, and they are usually intepreted as faults on which the islands are being pushed over the trenches. Most dip away from the Pacific, but in this respect, the island arcs of northwestern Melanesia are peculiar. The New Britain, Solomon, and New Hebrides arcs are linked in a wavy chain. The trenches next to these arcs are all on the side away from the Pacific Basin and the fault planes all dip toward the basin. Everything is backward, and the cause for this is one of the puzzles that besets us.
Many puzzles exist regarding the small faults at the top of the crust around island arcs, and these will be studied to see what they reveal about the existence of deep thrusting and the formation of trenches. The filling of trenches by sediment is also little understood and will be elucidated by mapping
Between the island arcs and Australia are the small continents and ocean basins of prime interest to Nova. The islands of New Zealand, the Fijis, and New Caledonia have been mapped by geologists and are relatively well known compared to the sea floor. They are considered to be little continents because they are above sea level and because they consist of rocks which occur in typical continents but not in ocean basins. Most of the rocks are produced by weathering and redeposition and sometimes reheating of fragments derived from older volcanic outpourings and intrusions of igneous rock. What are the sources from which the sediments were eroded? The geologists who have mapped Fiji are inclined to believe that the sources were all local and that erosion and redeposition have merely shifted sediment from one place to another on the islands. All the rocks in Fiji seem to be relatively young, and shifting them about does not seem unreasonable. New Caledonia is much more puzzling. Many of the rocks are much older, and they were deposited in an elongate submarine trough which was at least as extensive as the present island. Where did the sediments come from to fill the trough, if the present island was all under water? New Caledonian geologists tend to call on a former bordering mountain range which has now disappeared. There are two possible positions for this former range. If New Caledonia has not moved, then the range has been changed into the deep ocean basin which is now west of the island. However, continental drift is another possibility. Perhaps New Caledonia was once next to Australia or perhaps next to a supposed continent midway between the present positions of Australia and New Caledonia. New Zealand is more like New Caledonia than Fiji, and many geologists think that it, too, derived sediment from a source which has sunk or drifted away. The concept of one or
In a few months we can hardly expect to do much productive work on these islands because it has taken many years to learn the little that is already known.
Mostly we shall try to solve the problems of the land by looking at the sea floor between islands. This may seem rather indirect, but it has been a revealing approach in other regions. We shall map the topography, measure the thickness of the layers of the crust, measure variations of the magnetic and gravity fields, determine heat flow, and obtain samples of sediment and rock. Hardly anything is known about the Melanesian ocean basin because of a peculiarity of oceanographic exploration. The general topography and sediment distribution were discovered early because of the necessity of laying submarine telegraph cables. Since the development of modern marine geology, however, the region has largely been skirted. It is extremely distant from the older Pacific oceanographic centers in the United States, Siberia, and Japan; and the newer centers in New Zealand, Australia, and New Caledonia are only beginning to develop the necessary technology. Fortunately, a special international effort was made to study the even more remote Indian Ocean a few years ago. Much was learned along the tracks of ships going to and from the Indian Ocean. Even so, Melanesia was almost completely neglected because the ships had to go either north or south of Australia and Melanesia is, so to speak, in a lee of the continent. All we have are a few intriguing clues regarding what we may find.
We know more about the bottom topography of Melanesia than anything else, but we do not know enough for our purposes. The older spot soundings simply do not give the same kind of information as modern, recorded echo soundings. Older methods yielded a generalized map. New ones produce a continuous picture of the sea floor under a moving ship. The difference in what can be learned is about the same as the difference between looking at the moon with the naked eye and taking pictures of it with a rocket which flies just above it. We have
With the echo sounder we can also try to find flat-topped submarine volcanoes, guyots, like those first discovered by Harry Hess in the central Pacific. A few have already been found in the deep Tasman Basin east of Australia. They lie along a straight line about midway between the Australian coast and the Lord Howe Rise, and their history, can we but discover it, will tell us much about what has happened in this
We shall have no difficulty distinguishing a blanket of sediment from truncated rock on the Lord Howe Rise because we shall make continuous profiles of the upper layers of the sea floor. This is done with instruments like echo sounders but more powerful. A loud noise can be generated in the sea in many ways: by explosives, by electrical sparks, by igniting blobs of natural gas, or by compressed air bursts. We use an electrical spark for the gear on Horizon and compressed air on Argo. This is because these sub-bottom profilers, now abbreviated to "profilers," are still in experimental development and one type is better than the other, depending on the detail desired. The chief problem with profilers is that the listening hydrophones are affected by the noise of water moving past them, and this means that ships cannot go at full speed. Considering that ideal speeds for profiling are only 4 to 6 knots, it costs a lot of ship time to obtain the records. We are now conducting experiments which may enable us to go faster and thus do more profiling. These newly developed profilers give records that oceanographers find almost miraculous. In the past, we had to deduce the thickness and structure of sediment in most places from the details of the surface topography as revealed by echo sounders. Now when everything is just right we can see the layers far below the bottom, watch them thicken and thin, and see whether they are flat or have been folded or faulted and then buried. With these marvelous instruments
By measuring the thickness and layering of the crust we hope to establish whether its general character is that of a continent which is being destroyed or an ocean basin which is being built up into a thick continent. This is done by setting off explosions in the ocean and recording the times at which they are detected on a ship or at several floating buoys. There are few precedents to guide us, but that is one reason the region is interesting. The velocity at which explosive-generated waves move through typical continental crust is less than through typical oceanic crust. Consequently, unusually thin continent may not be the same as unusually thick ocean crust. The layering might also differ depending on the history of the upper crust. Thick mud on an old oceanic crust would not resemble the hard sedimentary and metamorphic rocks characteristic
The sea floor and the crust below as seen with instruments with different power and resolution.
Variations in the intensity of gravity from place to place result from variations in the thickness and density of the underlying rocks. Geophysicists learn early that gravity observations can be interpreted in an infinite number of ways if nothing else is known. Given the discrete measurements of crustal structure by explosive seismology, however, the interpretation of gravity can be quite informative. The gravity interpretations can be adjusted to agree with the seismic data. This might seem rather pointless and would be if nothing else could be achieved. The value of gravity measurements is that they can be made continuously while the ship is underway between seismic stations, which are limited in number by time and the amount of explosives that the ships can carry. If all goes well and the weather is not too rough for sensitive instruments, we shall have continuous profiles of gravity which can be equated with some confidence to continuous profiles of the crust of Melanesia.
Profiles of magnetic intensity are obtained by towing a magnetometer behind each ship at a distance such that it is unaffected by the steel hull. We shall be seeking the distinctive local magnetic anomalies which have elsewhere demonstrated sea floor spreading. Pre-expedition observations have been made in Melanesia by the U.S. Navy in Project Magnet, using low-flying airplanes. These indicate local magnetic anomalies, which is promising, but flight lines are too few to show whether the anomalies have the characteristic elongate shapes produced by sea floor spreading. If the anomalies are elongate and parallel we shall look for symmetry and centers of spreading. We shall also try to identify the identical sequences of anomalies already found in other places where spreading has occurred. This will give some clues regarding the time of Melanesian spreading. We already have some ideas about where to look for spreading because of the possibility that the
Heat comes to the surface of the sea floor from deep in the interior of the earth. I do not mean that the abyssal sea floor is warm; on the contrary, it is very close to freezing. But if we plunge a long probe into the bottom sediment and measure the temperature at different points along the probe, we find it is warmer the deeper we go. If we also measure the thermal conductivity of the sediment, we can calculate the flow of heat moving upward from the interior. Were there no complications and if all the heat came from great depth, these measurements would tell us where the mantle is hot and rising and where it is cold and sinking. Such information would be very helpful in trying to establish the origin of the small crustal blocks of Melanesia and whether they are moving. Unfortunately, there are complications. If sediment accumulates rapidly, the heat flow seems low. If a measurement is made on a hill, heat flow seems low and if in a valley, it seems high. Consequently, measurements must be numerous and at carefully selected sites for meaningful interpretation. Existing measurements suggest that heat flow is relatively normal in northwestern Melanesia and relatively high elsewhere in the region. It remains to be seen if these relationships are still true when we have a hundred measurements instead of twenty. If there are centers of sea floor spreading, we may expect to find that
Having examined the sea floor with every type of modern instrument, we can also fall back on the oldest method of doing geology, namely, taking samples. We do this in several ways: by photographs, cores of sediment, and dredge hauls of rock. Modern deep sea cameras can be located accurately a few meters above the bottom and can take several hundred pictures as the ship drifts along. The photos are developed immediately and provide a guide for other types of sampling. By themselves they show such things as whether ocean currents are intense at the bottom; whether animals and animal borings are abundant; and whether the bottom is paved with nodules of manganese oxide or phosphorite, which are minerals of potential economic importance. Cores are a few inches in diameter and three to thirty feet long. Heavy weights propel the coring pipes vertically into the bottom so the cores show not only the surface sediments but also the layers just below. Sediment accumulates slowly in the ocean, and may not accumulate at all on small hills. Consequently, even these short cores may recover sediment millions of years old. With our profilers we can follow deep layers to places where they reach the surface, on a cliff for example. When we core such a place, we are able to deliberately sample old sediment which we would be very lucky to hit if we did not have profiler records. This is also true for dredge hauls of rock. We used to try to dredge rock from cliffs which often turned out to be covered with mud. Now our chances are better. If our dredging is successful, we should have no difficulty in resolving the nature of the submarine rises and ridges in Melanesia. Continental rocks are strikingly different from those of the ocean basins. If they contain fossils or are fresh enough for radioactive mineral dating, we can also tell their age and a great deal about their history. If they are very old or otherwise unusual, we shall want to make more dredge hauls.
When the expedition was first planned we had the choice of trying to do all these things at once or doing them in stages. We elected the latter course because so many programs are
The General Schedule of The Nova Expedition
LEG I E. Goldberg*
17 Apr., San Diego to
16 May, Pago Pago
LEG II W. G. Van Dorn*
19 May, Pago Pago to
9 June, Honolulu
LEG III H. B. Craig*
16 June, Honolulu to
8 July, Suva
LEG IV E. L. Winterer*
12 July, Suva to
8 Aug., Noumea
LEG V H. W. Menard*
|(1st half)||11 Aug., Noumea to|
|23 Aug., Brisbane|
|(2nd half)||25 Aug., Brisbane to|
|12 Sept., Auckland|
LEG VI H. B. Craig*
18 Sept., Auckland to
2 Oct., Suva
LEG VII R. L. Fisher*
|(1st half)||7 Oct., Suva to|
|16 Oct., Tonga Islands|
|(2nd half)||16 Oct., Tonga Islands to|
|26 Oct., Pago Pago|
LEG VIII V. Vacquier*
|(1st half)||29 Oct., Pago Pago to|
|4 Nov., Suva|
|(2nd half)||4 Nov., Suva to|
|19 Nov., Pago Pago|
LEG IX A. E. Engle*
22 Nov., Pago Pago to
11 Dec., Hilo
LEG X P. Crampton*
11 Dec., Hilo to
19 Dec., San Diego
* Scientist in charge (SIC)
|(1st half)||T. Chase*|
|18 Apr., Kwajalein to|
|3 May, Brisbane|
|(2nd half)||S. M. Smith*|
|6 May, Brisbane to|
|29 May, Noumea|
LEG II E. L. Winterer*
1 June, Noumea to
1 July, Suva
LEG III H. W. Menard*
4 July, Suva to
11 July, Suva
LEG IV H. W. Menard*
13 July, Suva to
7 Aug., Noumea
LEG V G. G. Shor, Jr.*
|(1st half)||11 Aug., Noumea to|
|23 Aug., Brisbane|
|(2nd half)||25 Aug., Brisbane to|
|12 Sept., Auckland|
LEG VI D. E. Karig*
|(1st half)||12 Sept., Auckland to|
|26 Sept., Pago Pago|
|(2nd half)||26 Sept., Pago Pago to|
|14 Oct., San Diego|
* Scientist in charge (SIC)
Excerpted track charts from Chapters 8, 9 and 14.
Track of R/V Argo Nova Expedtion Leg IV (July 12-August 8, 1967), Page 115
Track of R/V Horizon Nova Expedition Leg V (August 11 -September 12, 1967), Page 146
Tracks of R/V Argo Legs VI-IX and R/V Horizon Leg VI (October-November 1967), Page 230
Courtesy of Scripps Institution of Oceanography Library; http://scilib.ucsd.edu/sio/
Title: Anatomy of an expedition
By: Menard, Henry W. (Henry William), 1920-1986, creator
Date: 2003] (issued)
Contributing Institution: Scripps Institution of Oceanography Library; http://scilib.ucsd.edu/sio/
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