or important rock samples collected. For this reason, each vehicle had its own network of bottom-moored acoustic transponders. At the end of each dive, we were able to produce an edited plot of the submersible's x-y track across the rift valley floor. Adding the depth and altitude of Alvin along this track, we were able also to produce a bottom depth profile for the dive. Using these two plots and a transcription of the science divers' observations, we were able to produce a series of geological traverses across the rift valley floor. These annotated profiles included a wide range of observations dealing with the various volcanic and tectonic features we observed as well as the sediment cover, which reflected the age of the terrain.
In all, the American submersible Alvin conducted 17 dives, while the combined efforts of the French submersible Cyana and the bathyscaph Archimede completed 27 dives. Each vehicle was assigned to a particular operational area within the inner rift valley and the bounding transform faults. Alvin's work area included a central volcanic high called Mount Pluto and the southern portion of Mount Venus to the north. The Archimede overlapped Alvin's coverage of Mount Venus, working north up the rift valley toward transform fault A, which was the primary operational area for the submersible Cyana.
When the expedition ended and the final results were published in two volumes of the Geological Society of America Bulletin (1977, 1978), our detailed knowledge of the process of seafloor spreading had taken one giant leap forward illustrated by the following text that appeared in Science in 1975 (Ballard et al., 1975):
Observations confirmed that Mt. Venus and Mr. Pluto are the sites of most recent volcanic activity. The flanks of these hills consist of broad, steep-fronted flow lobes with relatively little sediment cover or attached organisms. The flow fronts consist of tubular lava extrusions elongated downslope, resembling in some respects terrestrial pahoehoe lava.
. . . in all traverses from the center of the valley outward to the flanks, we were impressed by the rapid increase in sediment cover and bottom life and by the intense tectonic degradation to which the extrusive lava forms were subjected. Generally, within 300 m of the valley center to the west and within 500 m to the east, most of the delicate extrusive forms had been destroyed, the flows were sliced and offset by numerous faults, and the surfaces were reduced to broken, jumbled lava blocks and extensive talus fans at the base of fault scarps.
In contrast to recent volcanic activity, which appears to be concentrated in a narrow central zone, recent tectonic movement is evident throughout the entire width of the inner rift valley floor. Faults and fissures are numerous, striking 020 degrees parallel to the rift axis.
Intrusive sills and dikes are exposed only at the base of one 300-m scarp on the west wall. Most fault displacements are less than 100 m and expose only breccia, truncated lava pillows and tubes.
In general, faulting appears to be a continuing process, while volcanic activity is episodic.
Simple and logical as these observations may seem, they confirmed the process of seafloor spreading, providing the first systematic documentation of a process that had global significance. Manned submersibles had finally come of age.
On the way back from the FAMOUS research site in the Mid-Atlantic Ridge, the Alvin was used to carry out a series of dives along the New England Seamount Chain, revealing ancient volcanic terrain covered by a thick layer of manganese and phosphorite similar to that encountered on the Blake Plateau.
Although Project FAMOUS was capturing the headlines in the early 1970s, scientists continued to use manned submersibles for their more traditional applications on the continental margins. The benthic biology community continued its studies of wood-boring organisms as well as efforts to quantify the biomass within deep-sea sediments and their rate of recolonization. Spurred on by the sandwich recovered from inside the lost Alvin, scientists expanded their research to include the decomposition of solid organic materials in the deep sea, with an eye toward the implications of using the ocean as a future dump site.
Geologists also continued using manned submersibles to study the carbon stratigraphy of the Bahama Platform, including its potential for hydrocarbon deposits and the occurrence of "lithotherms," deep-water coral structures that trap bottom transported sediments forming long linear ridges beneath the Gulf Stream in the Straits of Florida.
But clearly, Project FAMOUS had ushered in an entirely new phase of scientific use of manned submersibles, in particular, Alvin. Several factors were responsible. The first was the increased diving depth of Alvin from 1,800 to 3,050 m. The second was the integration of the manned submersible into a larger context, namely the lengthy preparation of a research site prior to the actual diving program. This preparation included the collection of detailed bathymetric maps and geologic traverses across the proposed study area using deep-towed vehicles such as Deep Tow and Angus. Most importantly, however, was the emergence of plate tectonics. In the final analysis, manned submersibles were in the right place at the right time.
For most of the scientists participating in Project FAMOUS, it was an unqualified success. But for one group, it was a bitter disappointment. Dr. Dick Holland had led a team from Harvard and Woods Hole that was keenly interested in finding underwater hot springs along the axis of the