Atlantic gas-venting cracks could indicate future landslides

Jul 31, 2000 02:00 AM

American scientists have found gas-venting cracks in the floor of the Atlantic Ocean which could lead to undersea landslides that would trigger tsunamis along the East Coast of the United States. But don't rush out and buy those swim fins just yet.
"It's a real slim possibility," says John Goff, research scientist at the Institute for Geophysics at the University of Texas at Austin. "There is a real threat but the chances of it happening anytime within our lifetime have to be very remote. But we don't know that for sure until we really look at these things a lot closer."
"It is worth noting," adds Jeffrey Weissel, senior research scientist at the Lamont-Doherty Earth Observatory of Columbia University. "We felt compelled to construct a tsunami scenario based upon our discovery of these cracks, which look like they might indicate a future large-scale landslide."
Goff, Weissel and Neal Driscoll of the Woods Hole Oceanographic Institution found the cracks by examining data collected by theNational Oceanic & Atmospheric Administration (NOAA). That initial research was published in a recent of the journal Geology.

The scientists weren't certain what caused the cracks. They conducted a two-week research voyage in May to gather more information and found the cracks were caused by the venting of natural gas. The system of cracks stretches along a 25-mile section of the outer continental shelf off southern Virginia and North Carolina, north of Cape Hatteras.
They're in a water depth of 300-600 feet between the Norfolk Canyon and the Albemarle-Currituck submarine slide, which occurred about 18,000 years ago. "There was a very large slide in that region tens of thousands of years ago that almost certainly created a large tsunami. It's all very speculative at this point but we think that major slide was probably related to gas and so it requires further investigation," Goff says.
"It's a two-edged sword," Weissel adds. "You could say the gas under pressure is being vented so things should besafer now. That's one side of the sword. The other side is the expulsion of the gas has pushed the shelf edge into a mechanically unstable situation and might in fact exacerbate the prospects of future large scale slope failure."

A tsunami created by such a landslide could result in waves up to several metres above normal along the Virginia-North Carolina coastline and lower Chesapeake Bay. Tsunamis can be devastating on populated coastlines. A tsunami that struck northern Papua, New Guinea in July 1998 killed about 2,000 people. A 1929 tsunami resulting from an earthquake-induced landslide on the Grand Banks killed 51 people along the south coast of Newfoundland.
Besides assessing any potential danger from the cracks, the scientists say their research will uncover other information. That includes whether the natural gas offers any economic opportunities. The cracks might also prove interesting to biologists.
"Often when we have seeps of different kinds on the sea floor, these are associated with exotic ecosystems," Weissel says. "There's a possibility that living off the East Coast is an exotic community of fairly unusual plants and animals," he adds.

Source: HealthSCOUT
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