It is the largest, most awesome geological feature on the face of the earth: a 40,000-mile-long, quake-prone chain of mountains and valleys that winds around the planet like the stitching on a baseball. Yet because most of this mid-ocean ridge system lies deep beneath the waves, little is known about how its activity affects the formation of mineral deposits, changes the ocean floor and even causes the slow movement of entire continents. During the next three months French and American scientists hope to learn much more about the mysterious undersea area by prowling the depths some 200 miles southwest of the Azores. Their goal: the exploration of a small section of the great volcanic rift valley that cleaves the Atlantic Ocean bottom almost all the way from the Arctic to Antarctica.
Inky Darkness. The expedition is part of Project FAMOUS (for French-American Mid-Ocean Undersea Study), and is the climactic phase of a three-year international program. It will involve some 60 dives in three of the world's most extraordinary undersea ships: the U.S. Navy's tiny Alvin,* operated by the Woods Hole Oceanographic Institution, and the French deep-diving submersibles Archimède and Cyana.
Each dive should be an adventure straight from Jules Verne. As the subs plunge two miles down, they will descend into a world of inky darkness where even their powerful spotlights will be unable to penetrate more than a few dozen feet. Pressure will be great enough (about 2 tons per sq. in.) to crush ordinary submarines. Indeed, the scientists have already had a preview of the project's perils. Last summer, during preliminary surveying, the Archimède crashed into rocks several times when it was tossed about by the strong bottom currents. The little sub had another close call when a small electrical fire filled the crew chamber with smoke and caused the premature release of ballast, sending the sub soaring rapidly to the surface. Even so, researchers seem unworried. Says Geologist Xavier Le Pichon, the chief French scientist: "The worst that could happen would be getting stuck under an overhanging cliff. But with three submersible craft in operation, we can come to one another's aid."
The potential payoff makes the risks seem worthwhile. The mid-Atlantic rift valley that the subs will probe is the place "where the earth's crust is created," says Chief U.S. Scientist James Heirtzler of Woods Hole. According to the revolutionary new view of geology called "plate tectonics," the earth's outer shell consists not of a single solid mass but of half a dozen or so giant plates on top of which the continents drift like extremely slow-moving ice floes. It was the gradual outpouring of lava from deep within the earth's mantle along the mid-Atlantic rift valley that began to split North America from Europe, Africa and South America some 225 million years ago. Even now, as fresh material attaches itself to the plates, the continents are being pushed apart at a barely perceptible rate of an inch or less a year. Project FAMOUS should not only provide further understanding of this sea-floor spreading, as it is called, but also shed new light on associated geological events along the ridge.