Wednesday, January 4, 2012

Earth's deepest spot spanned by bridges

From Earth's deepest spot spanned by bridges
DURHAM, N.H., Dec. 29 (UPI) -- U.S. researchers say they've discovered seafloor "bridges" spanning the Mariana Trench, the deepest point on the planet's surface at 6.8 miles below sea level.

Marine geophysicists recently mapped a set of seafloor features, finding as least four underwater "bridges" across the depths of the trench where the Pacific Plate dives under the Philippine Plate off the eastern coast of the Philippines, reported Thursday.

"It wasn't common knowledge that these bridges occurred at all," James Gardner, a marine geophysicist at the University of New Hampshire who discovered the structures, said. "This is really the first time they've been mapped in any detail."

As the Pacific and Philippine tectonic plates converge, they carry underwater seamounts and other underwater features that plow into other structures on the opposite side of the trench in a sort of slow-motion underwater collision, creating structures spanning the depths of the trench.

"As the Pacific Plate gets thrust down underneath the Philippine Plate, it wouldn't be totally unexpected that you'd find these things bridging across the trench and being accreted to the inner wall," Gardner said.

What the underwater bridges mean for the marine life in the area is unknown, he said.

"I would certainly expect [them] to have different fauna and flora than the trench floor, because they stand about 2 kilometers [1.2 miles] higher," Gardner said. "But the extreme depth would make it hard to monitor the biology or seafloor currents in the area."

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