The submarine never saw it coming. In 2005, the nuclear-powered USS San Francisco crashed into an undersea extinct volcano, known as a seamount, in the western Pacific Ocean, killing one crew member and crippling the vessel. Although the sub returned to dock in Guam and a larger disaster was averted, the accident underscores one of marine geologists' biggest complaints: Earth's oceans are still mostly aqua incognita. With only about 10% of the sea floor mapped with high-resolution sonar from ships, scientists assembling global maps have to rely on an indirect method: using orbiting radar satellites to trace subtle bumps and depressions in the water surface, which mirror the shape of the sea floor. Even the most advanced map, published in Science last October (Science, 3 October 2014, p. 65), has trouble identifying and locating seamounts less than 2 kilometers tall. But now, a new study demonstrates how a French radar instrument on an Indian satellite could greatly enhance seamount maps, putting submariners on safer courses while helping with climate science, fisheries science, and tsunami forecasts.
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