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our Cayman Trough expedition, which was about to take place during the winter of 1976.

The Cayman Trough program had two primary purposes. The first was to use the submersible Alvin, the bathyscaph Trieste II, and the towed camera system Angus to investigate a small spreading center situated inside the transform fault system separating the North American Plate from the Caribbean Plate. Known as a "leaky transform fault," this boundary had a slight opening motion that led to the formation of an east-to-west spreading center bordered to the north and south by the steep walls of the Cayman Trough. The result was one of deepest spreading centers in the world, with the central volcanic axis occurring at a depth of 6,100 meters. The walls of the fault scarps within the trough also provided an opportunity for petrologists to obtain samples of the oceanic crust using the submersible Alvin.

The second reason for the Cayman Trough program was to maintain the momentum created by the success of the FAMOUS Project, while others like van Andel had an opportunity to define diving programs for funding given the scientific community's new positive attitude about submersibles.

The Cayman Trough investigation provided Corliss with an excellent opportunity to learn first-hand how to conduct a sophisticated research program using manned submersibles. It also provided him with the opportunity to make his first submersible dive.

By the time the Galapagos Hydrothermal Expedition got underway in February 1977, I had been asked to be co-chief scientist of the expedition with Dick von Herzen—not because I was a major scientific leader for this research program but because of my experience at conducting submersible programs. The real scientists behind the program were Jack Corliss and Jack Dymond from Oregon State University and John Edmond from the Massachusetts Institute of Technology. Jerry van Andel was also on the expedition, primarily to help these inexperienced scientists with the actual diving program to be carried out aboard Alvin's support ship Lulu.

The expedition's destination was a point 640 kilometers west of the coast of Ecuador, along the rift that separates the fast-spreading Cocos and Nazca plates in the Pacific Ocean. Our plan was to concentrate on the sites where seafloor temperature anomalies recorded by the earlier Scripps-Oregon State-Woods Hole expedition had suggested the existence of hydrothermal vents.

Woods Hole's research vessel Knorr, with Lulu under tow, began the expedition at Rodman Naval Base in the Panama Canal, but after several days at sea, it was decided to break the tow and let the two ships proceed under separate power to the dive site. This way, the faster Knorr could arrive ahead of Lulu, install a network of acoustic transponders within the rift valley, and conduct some preliminary reconnaissance runs with the towed camera system Angus.

The year before, I had been successful in convincing the U.S. Navy to conduct a detailed Sound Acoustic Surveillance System (SASS) sonar mapping effort of the Galapagos Rift dive area similar to the survey it had conducted in the FAMOUS area. The FAMOUS expedition and the 1976 program in the Cayman Trough had set a new standard for bathymetric detail that all future submersible diving programs would now seek to emulate.

Once the ship arrived in the area, Knorr's echo-sounder was used to collect a series of profiles perpendicular to the rift axis. Using this information, the buoy left the previous year by Corliss, and satellite navigation, we did our best to tie our present location to the estimated location of the thermal anomalies detected the year before.

Woods Hole's Angus camera sled was now lowered into the rift from the research vessel Knorr. Angus was equipped not only to take thousands of color pictures but also to register temperature changes as minute as one five-hundredth of a degree Celsius. Angus's sensitive thermistor at first recorded no variations in the near-freezing temperatures just meters above the ocean floor. Then, as the first day's run neared its halfway point in the early evening of February 15, recorders on board Knorr received an acoustically telemetered signal from Angus , revealing a sudden spike in water temperature, lasting less than three minutes. Since the time and temperature data were precisely keyed to the frames of film exposed by Angus's cameras as it canvassed the bottom, we were able to review the pictures taken at the exact moment of the temperature spike. But first, Angus had to be hauled back to the surface and the film developed.

All were eager for the first visual evidence of the hypothesized thermal vents—but nothing could have prepared us for what Angus had photographed, one and a half miles beneath the surface. The 122-m-long roll of color film revealed a bed of clams—hundreds of clams clustered in a small area on the lava floor of the rift—thriving as if they were in an environment no more hostile than a sunny mudflat on the New England coast. We couldn't help but wonder what these large clams were doing in such numbers at that depth, in that eternal darkness.

The next step in the research plan called for the deployment of Alvin to whatever promising sites Angus might reveal. It was February 16 when Lulu with Alvin aboard arrived in the dive area, and we lost no time in getting the submersible into the water at sunrise the next day, February 17.

After a descent lasting an hour and a half, pilot Jack Donnelly brought Jack Corliss and Jerry van Andel to a point less than 275 m from the clam beds and began the drive along the lava floor to the site. Along the way, the bottom appeared as might have been expected: fresh but relatively barren lava flows.

But when Alvin reached its goal, the scene the scientists observed through the viewports was remarkably different. Water that Alvin's sensors measured at 12°C, shimmered up from cracks in the lava flows and turned a cloudy blue as manganese and other minerals, which had been carried from

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