Down in the Valley

During some 50 dives this summer as part of Project FAMOUS, the American submersible Alvin and its French counterparts Archimede and Cyana explored one of the earth's last great frontiers: the rugged, seismically active rift valley that cleaves the floor of the Atlantic almost all the way from the Arctic Ocean to Antarctica. Last week, as the scientists who took part in FAMOUS (for French-American Mid-Ocean Undersea Study) returned home from their expedition to the bottom of the sea, they reported that their little craft had discovered important new clues to the secrets of continental drift.

Buried under nearly two miles of water, the huge valley probed by the subs is the place where the Americas began to part from Europe and Africa some 180 million years ago. The continents are still drifting away from one another at a snail's pace of one inch or so a year.

But the mechanism that continues to propel these great land masses away from the rift valley remains one of geology's great mysteries. According to Geologist Wilfred Bryan of the Woods Hole (Mass.) Oceanographic Institution, the submarine explorers found indications that contrary to some theories, the continents are not forced apart by powerful lava flows at the site of the rift valley. If massive eruptions of lava were forcing the continents apart, Bryan says, the crews of the subs would have seen giant volcanoes like those in Hawaii. But they spotted only small mountains--a sign of minor uplifting by forces beneath the earth's crust. The new observations, he explained, suggest that the continents are being pulled apart and hauled along by semimolten rock moving like two giant conveyor belts in opposite directions.

The lava flows that the deep divers found in the rift valley were hardened into all sorts of bizarre configurations:

5-ft.-high stumps with protrusions that extended like arms, curving formations that looked like the neck and head of a swan, and linked tubes that resembled a string of sausages in a butcher's shop. But the size and shape of these flows indicated that the molten rock had not been forced out under tremendous pressure. On the contrary, it seemed to have simply peaked from the interior of the earth through cracks created as the earth's surface was stretched. Explained Bryan: "Like a cobblestone street, the earth's crust can be pulled apart very easily. And it is the rift valley where this fracturing is occurring."

During this process, the scientists found, mineral deposits such as iron, manganese and copper accumulate in the rift valley as lava-heated water circulates through cracks in the sea-floor rocks. But the depths at which these minerals are located would probably make them too costly to mine, at least for the moment.

Although the scientists were somewhat disappointed by their failure to see an actual undersea eruption of lava, the expedition was not without its excitement--or perils. Frequent landslides along the walls of the valley were a constant threat to the three ships; if their shells had been ruptured by tumbling rock, the crushing pressure of the water (two tons a square inch) would have meant quick death for the crews. All three submersibles were also bothered by minor mechanical difficulties; Alvin's final two dives had to be scrubbed because of an electrical problem. Even so, the performance of the little subs and their crews more than met the expectations of the Project FAMOUS planners.

Besides accumulating vast amounts of data, photographs and actual samples of the sea floor, the mission left no doubt that in the depths of the sea, as in space, men are still better explorers than machines alone.

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