Vigorous gas expulsion could weaken shelf edge

A team of scientists investigating whether possible cracks along the outer continental shelf off the mid-Atlantic coast might lead to a tsunami-causing landslide has discovered that the entire area is charged with gas.

Based on preliminary results from a just-completed two-week cruise to the area funded by the National Science Foundation (NSF), the scientists say the suspected cracks are a system of large depressions along the shelf edge that appear to have been excavated by gas erupting through the seafloor.

"We don't know the source of the gas," team leader Neal Driscoll of the Woods Hole Oceanographic Institution (WHOI) said. "But it is clear that gas has played an important role in the formation of these features. The gas is trapped under layers of sediment on the shelf edge until some circumstance causes it to escape, blowing holes in the seafloor to form these large pockmark features we thought were cracks."

In a paper published in the journal Geology days before their May 7 departure for the Mid-Atlantic coast, Driscoll and colleagues Jeffrey Weissel of the Lamont-Doherty Earth Observatory of Columbia University and John Goff of the University of Texas Institute for Geophysics, speculated that rising gas might play a part in triggering shelfedge collapse. Even so, they were surprised at the quantity of gas and the apparent vigor of the "blowout" process.

"Our seismic data show that gas is pervasive in and around the blow-outs," Goff said. "Gas has a characteristic signal, which commonly shows up as a bright, high-amplitude reflection that obscures any deeper signals."

"These are exciting findings," said Mike Purdy, director of NSF's division of ocean sciences. "We now know that biological, chemical and physical processes, like those that created the gas reservoirs and gas expulsions described by these investigators, are going on every day in the depth
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Contact: cdybas
cdybas@nsf.gov
703-292-7734
National Science Foundation
29-May-2000