Quakes under Pacific floor reveal unexpected circulat...( Jan. 7 2008Zigzagging some 60000 kil...)

Jan. 7, 2008Zigzagging some 60,000 kilometers across ocean floors, earths system of mid-ocean ridges plays a pivotal role in many workings of the planet, from its plate-tectonic movements to heat flow from the interior, and the chemistry of rock, water and air. It was not until the late 1970s that scientists discovered the existence of vast plumbing systems under the ridges, which pull in cold water, superheat it, then spit it back out from seafloor ventsa process that brings up not only hot water, but dissolved substances taken from rocks below. Unique life forms feed off the vents stew, and valuable minerals including gold may pile up. Now, a team of seismologists working under 2,500 meters of water on the East Pacific Rise, some 565 miles southwest of Acapulco, Mexico, has created the first images of one of these systemsand it does not look the way most scientists had assumed. The resulting study appears in the Jan. 10 issue of the journal Nature.

The hypothetical image of a hydrothermal-vent system shows water forced down by overlying pressure through large faults along ridge flanks. The water is heated by shallow volcanism, then rises toward the ridges middles, where vents (often called black smokers, for the cloud of chemicals they exude) tend to cluster. The new images, from a 4-kilometer-square area show a very different arrangement. The water appears to descend instead through a sort of buried 200-meter-wide chimney atop the ridge, run below the ridge along its axis through a tunnel-like zone just above a magma chamber, and then bubble back up through a series of vents further along the ridge. If you google on images of hydrothermal vents, you come up with cartoons that dont at all match what we see, said lead author Maya Tolstoy, a marine seismologist at Lamont-Doherty Earth Observatory, part of Columbia Universitys Earth Institute.

The images were created using seismometers planted around the ridge t
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