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Seabed of jet hunt zone mostly flat with 1 trench

Wednesday - 4/2/2014, 9:08pm  ET

Australian Defense ship Ocean Shield is docked at naval base HMAS Stirling while being fitted with an autonomous underwater vehicle (AUV) and towed pinger locator to aid in the search for missing Malaysia Airlines Flight MH370, Sunday, March 30, 2014, in Perth, Australia. It will still take three to four days for the ship to reach the search zone — an area roughly the size of Poland about 1,850 kilometers (1,150 miles) to the west of Australia (AP Photo/Rob Griffith)

JUSTIN PRITCHARD
Associated Press

WELLINGTON, New Zealand (AP) -- Two miles beneath the sea surface where satellites and planes are looking for debris from the missing Malaysian jet, the ocean floor is cold, dark, covered in a squishy muck of dead plankton and -- in a potential break for the search -- mostly flat. The troubling exception is a steep, rocky drop ending in a deep trench.

The seafloor in this swath of the Indian Ocean is dominated by a substantial underwater plateau known as Broken Ridge, where the geography would probably not hinder efforts to find the main body of the jet that disappeared with 239 people on board three weeks ago, according to seabed experts who have studied the area.

Australian officials on Friday moved the search to an area 1,100 kilometers (680 miles) to the northeast of a previous zone as the mystery of Malaysia Airlines Flight 370 continued to confound. There is no guarantee that the jet crashed into the new search area. Planes that have searched it for two days have spotted objects of various colors and sizes, but none of the items scooped by ships has been confirmed to be related to the plane.

The zone is huge: about 319,000 square kilometers (123,000 square miles), roughly the size of Poland or New Mexico. But it is closer to land than the previous search zone, its weather is much more hospitable -- and Broken Ridge sounds a lot craggier than it really is.

And the deepest part is believed to be 5,800 meters (19,000 feet), within the range of American black box ping locators on an Australian ship leaving Sunday for the area and expected to arrive in three or four days.

Formed about 100 million years ago by volcanic activity, the ridge was once above water. Pulled under by the spreading of the ocean floor, now it is more like a large underwater plain, gently sloping from as shallow as about 800 meters (2,625 feet) to about 3,000 meters (9,843 feet) deep. It got its name because long ago the movement of the Earth's tectonic plates separated it from another plateau, which now sits about 2,500 kilometers (1,550 miles) to the southwest.

Much of Broken Ridge is covered in a sediment called foraminiferal ooze, made of plankton that died, settled and was compacted by the tremendous pressure from the water above.

"Think like it's been snowing there for tens of millions of years," said William Sager, a professor of marine geophysics at the University of Houston in Texas.

Like snow, the layer of microscopic plankton shells tends to smooth out any rises or falls in the underlying rock. In places, the layer is up to 1 kilometer (half a mile) deep.

But if the fuselage of the Boeing 777 did fall on to Broken Ridge, it would not sink much into the muck.

"The surface would be soft, it would squeeze between your toes, but it's not so soft that you would disappear like snow," Sager said. "Something big like pieces of an airplane, it's going to be sitting on the surface."

Searchers will be hoping that if the latest area turns out to be where the plane crashed -- and that remains educated guesswork until searchers can put their hands on aerial debris sightings and check what it is -- the fuselage did not go down on the southern edge of Broken Ridge.

That's where the ocean floor drops precipitously -- more than 4 kilometers (2 1/2 miles) in places, according to Robin Beaman, a marine geologist at Australia's James Cook University. It's not a sheer cliff, more like a very steep hill that a car would struggle to drive up. At the bottom of this escarpment is the narrow Diamantina trench, which measurements put as deep at 5,800 meters (19,000 feet), though no one is sure of its greatest depth because it has never been precisely mapped.

"Let's hope the wreck debris has not landed over this escarpment -- it's a long way to the bottom," Beaman said.

The Diamantina trench, named after an Australian navy vessel, is one of the deeper sections of the parts of the oceans that surround Antarctica, according to Mike Coffin, the executive director of the Institute for Marine and Antarctic Studies at Australia's University of Tasmania.

The trench's rocky crags and crannies would make it difficult for ships using instruments like side-scanning sonar or multi-beam echo sounders to distinguish any debris from the crevices.

Searchers will especially be hoping to locate the jet's two "black boxes," which recorded sounds in the cockpit and data on the plane's performance and flight path that could help reconstruct why it diverted sharply west from its overnight flight from Kuala Lumpur, Malaysia, to Beijing on March 8. The black boxes were designed to emit locator pings for at least 30 days, and are projected to lose battery power -- and thus their pings -- by mid-April.

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