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Images: Exploring The Global Mid-Ocean Ridge

This 1977 World Ocean Floor image was the last in a series produced by Bruce Heezen and Marie Tharp at Lamont-Doherty Geological Observatory of Columbia University from somewhat eclectically collected and widely spaced seafloor data taken over a 30-year time span.

By the mid 1980s, this map could be produced from many wide-beam echo sounder data sets assembled by the National Geophysical Data Center. The figures opposite and on the back cover are products of later, more sophisticated multi-beam echo sounder data.

Shaded relief image of the fast-spreading East Pacific Rise at 12°35’ to 13° N enlarged from the northern part of the image above. The 12°37’ N overlapping spreading center is in the foreground; the 12°54’ N overlapping spreading center is in the background. These discontinuities offset the ridge axis only 1 to 2 kilometers and define a fundamental segmentation of the spreading center that went unrecognized until multibeam echo sounders were available. The axial summit trough is large enough here (some 500 meters wide by 50 meters deep) to show up as a small axis parallel groove along the crest of the East Pacific Rise.

French and American Project FAMOUS scientists laid out US Navy supplied mid-ocean ridge photos on a gymnasium floor as part of their pre-cruise planning.

Alvin and the French submersibles Cyana, shown here, and Archimède, a bathyscaphe, took Project FAMOUS diving scientists to the seafloor. Archimède made preliminary dives in 1973 and all three subs dove in 1974.

This photo, taken in 1979 on the East Pacific Rise at 21°N, is the first ever taken of a black smoker vent. Scientists didn’t realize how hot the erupting water could be until their temperature sensors came back charred!

The Alvin group prepares to lift the sub to Knorr’s fantail for the trip to the Mid-Atlantic Ridge dive sites of Project FAMOUS (French-American Mid-Ocean Undersea Study) in 1974. Knorr towed Alvin’s tender Lulu to the Azores, where the sub was transferred back to its support vessel.

Mid-ocean ridges have segmented architectures. The underlying processes differ somewhat in fast- and slow-spreading centers, but in general, first-order segments are hundreds of kilometers long, persist for millions to tens of millions of years and are bounded by relatively permanent, rigid-plate transform faults. First-order segments are divided into several second- or third-order segments, bounded by a variety of nonrigid discontinuities. These smaller segments lengthen, shorten, or even disappear in 10 million to 100,000 years, respectively. At the finest scale, fourth-order segments, about 10 kilometers long, may survive for only 100 to 10,000 years. These segments are the products of dike intrusion events, the fundamental units of crustal creation.