Sediments travel, make waves in gravel.
Now, the Grand Banks slope has produced another scientific first. Over the last two years, a team of Canadian and U.S. researchers has been using the Sea MARC I (sidescan sonar) and a submersible to survey the underwater effects of the 1929 quake. They have discovered a field of "gravel dunes"--2-to 3-meter-high ridges 50 to 100 m apart, standing below 1,500 to 4,500 m of water. "this is a new type of bedform which we associated with quite fast flows of the  turbidity current," says Alexander Shor at Lamont-Doherty Geological Observatory (LDGO) in Palisades, N.Y., who has coauthored a paper with David Piper at the Geological Survey of Canada in Dartmouth, Nova Scotia, and John Hughes Clark at Dalhousie University in Halifax, Nova Scotia.
According to Shor, "smaller bedforms develop from fast tidal currents in shallow water, but normally the flows in deep water aren't strong or persistent enough to form [such large features in gravel]." But as more surveys are conducted with sonar systems along coastlines where strong turbidity currents might have flowed, it's likely that more gravel dunes will turn up. Already Albert to Malinverno at LDGO and co-workers report finding similar beforms off the coast of Nice, France.
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|Title Annotation:||effects of turbidity current in 1929 Grand Banks earthquake|
|Date:||Nov 23, 1985|
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