Major Undersea Volcano Chain Sighted
Every wrinkle of the Earth's mountain ranges is know to mapmakers by now. But much of the ocean floor, 71% of the Earth's surface, is still terraincongnita. In late March, an international team of scientists returned from a 2-month cruise in the South Pacific with a major piece of that murky picture: confirmation of the existence of a 2000-kilometer-long chain of undersea volcanoes southwest of Easter Island.
The chain - known as the Foundation Seamounts - is "one of the largest structures on the sea floor yet to be discovered," says Jacqueline Mammerickx, emeritus scientist at teh Scripps Institution of Oceanography in California. Her analysis of radar scanning data from U.S. Navy satellities a few years ago produced the first solid hints of the volcanoes' existence. Variation in the height of ocean surfaces indicate gravitational anomalies caused by undersea structures. But a vist to the site was needed to see if they were really there, say Roger Hekinian of the French ocean research agency IFREMER, who co-led the expedition aboard the German oceanographic ship SONNE. Using underwater cameras and sampling equipment, the scientists identified some 37 volcanoes, ranging as high as 4000 meters. What's more, they found evidence that the volcanoes were formed by a "hot spot" - a plume of magma originating 100 or more kilometers beneath the ocean floor. Most undersea volcanoes are formed from shallower magma in the ridges between spreading continental plates, but this chain extends well into the Pacific plate. Because magma from the hot spot probably comes from very deep in Earth's mantle, Hekinian sys analysis of samples - if the team can pinpoint the hot spot when they return next winter - should provide valuable information about the interior of the planet.
taken from:
"Major Undersea Volcano Chain Sighted." SCIENCE, v.268, 12 May 1995, p.809.