spending their lives attached by their threadlike filaments to the rock formations of the bottom. Each of the creature's "petals," dissection showed, has a different purpose. Some capture microorganisms; others digest them; and still others are involved in reproduction. All surround a buoyant pocket of gas, which allows the animal to bob at the end of its tethers.
As our time on the rift went on, we collected new species of leeches, worms, barnacles, and whelks. We even took away some 200 strains of bacteria, which were brought alive to Woods Hole for whatever clues they might offer to the basis of this remarkable food chain. Throughout our observations—whether they involved the humblest microorganisms or the most extravagantly sized and colored worms and bivalves—we were tantalized by the thought that surely such phenomena could not have been confined by evolution only to this obscure stretch of the Galapagos Rift. At how many other places on the bottom of the oceans do such communities thrive, and how many other yet-unknown species draw life from the interplay of seawater with the steaming, mineral-rich depths of Earth's developing crust?
Before the 1979 return trip to the Galapagos Rift took place, plans were already underway for a major expedition to the East Pacific Rise by many of the same French and American scientists who participated in Project FAMOUS. After Project FAMOUS was completed, the French were eager to conduct another large joint program with the United States on the Mid-Ocean Ridge. Since Project FAMOUS was conducted on a slow-spreading segment of the ridge where the plates are moving apart at a rate of 2.5 cm per year, the French wanted to compare what they had learned about the volcanic and tectonic processes of the Mid-Atlantic Ridge with a faster-spreading ridge in the Pacific Ocean.
Spearheaded by Dr. Jean Francheteau, the French chose the East Pacific Rise (EPR), where the plates separate at a range of 6 to 12 cm per year. Based on a series of studies of the rise conducted by U.S. oceanographers, the French selected a segment of the EPR at 21°N latitude, at a spot off the Mexican coast where the Pacific and North American plates diverge. As the program took shape, the French asked a number of U.S. scientists, including myself, if we would be interested in such a joint investigation.
While it had been fitting for Woods Hole to play the lead role in Project FAMOUS since the program was conducted in the Atlantic Ocean and involved the use of its submersible Alvin, Woods Hole was not the logical choice for the East Pacific Rise program. The Pacific Ocean was the territory of the Scripps Institution of Oceanography. And since scientists at Scripps had carried out most of the research on the East Pacific Rise on which the French were basing their study, it was decided at a workshop held in La Jolla, California, that Scripps would be the lead U.S. institution for this joint program. Dr. Fred Spiess of Scripps would play the role Jim Heirtzler had played during Project FAMOUS.
As with FAMOUS, the French wanted to carry out the first series of dives of the East Pacific Rise using their submersible Cyana and I was invited to participate. This initial dive series was scheduled for February 1978. The French named their phase of the program RITA, for the two transform faults (Rivera and Tamayo) that bounded the spreading segment of the EPR to be investigated. Their plan was similar to the approach they had taken during FAMOUS—to conduct a series of long dive traverses at right angles to the axis of the rise. This meant that they would be diving across time lines, beginning in the center of the rise where young lava is flowing out onto the seafloor and exploring in both directions away from this central zone of injection. They would head east toward the coast of Mexico and the North American plate, and west toward the Pacific Ocean and the Pacific Plate.
The French dive series in 1978 using Cyana at 21°N was highly successful, completing 21 dives. Like the FAMOUS study area, the central volcanic axis was found to be relatively narrow, flanked on either side by older tectonically altered terrain characterized by fissures and small-scale fault scarps. Reconnaissance dives were made between the EPR crest and the Brunhes-Matuyama reversal area 21 km to the west (three dives) and in the Tamayo transform (six dives). The extrusion zone is narrow (0.4 to 1 km), like that of slow-spreading centers. The extension zone, bracketed by a nearly continuous bottom traverse, has a half-width of 7-8 km. The Brunhes-Matuyama area was thus tectonically dead.
In contrast, the extension zone of slow-spreading centers is thought to be wider, although there are no field observations. Hydrothermal activity is demonstrated by colored deposits of rocks, tall cones of variegated deposits, and fields of giant clams (dead). Intense hydrothermal activity is probably a general feature of the EPR in contrast with its scarcity in the FAMOUS rift. Large areas of the young seafloor are covered by pahoehoe flows (sheet flows) and by lakes with pillars, expressing the greater fluidity of EPR extrusives compared with Mid-Atlantic Ridge (MAR) pillows and perhaps reflecting readier access to a larger magma pool.
A fascinating find associated with the East Pacific Rise expedition as well as those to the Galapagos Rift in 1977 dealt with the undersea lava flows encountered along these faster-spreading centers. During Project FAMOUS, the dominant extrusive lava form was an endless variety of pillow lavas, which scientists considered to be the classic underwater flow form. But when submersibles began diving in the faster-spreading centers of the Pacific, we encountered an entirely different type of lava feature termed "sheet flows." Unlike pillow lavas, which consist of a network of small lava tubes intertwined like a pile of spaghetti with individual "pillows" budding off from lava tubes, sheet flows form vast lakes or pools of molten lava. Fluctuations in the level of these lakes—caused by drainback into the magma chamber deep beneath the ocean floor—are indi