Rock slide under the waves.
The bathymetric survey reveals a large scar on the side of the mid-Atlantic ridge at 26.5 [degrees] N latitude, about 3,000 meters below the surface of the ocean. The mountainside, apparently gave way and slid downhill at tremendous speed, running up and over a smaller ridge farther down the slope in a matter of minutes, suggests Brian E. Tucholke, who reports the finding in the February Geology. This is the first evidence of a rock slide ever found in the rift valley of the mid-ocean ridge.
The avalanche carried about 19 cubic kilometers of rock, Tucholke estimates. By comparison, less than 3 cubic kilometers of rock moved in the landslide that sparked the 1980 eruption of Mount St. Helens.
Tucholke says the mid-Atlantic slide must have occurred sometime in the last 450,000 years. If it happened quickly, the avalanche could have spawned a wave 700 meters high. But by the time the wave reached the North American or African coastline, it would have dwindled to less than a meter in height.
In the past few years, oceanographers have found underwater rock slides far larger even than the example in the mid-Atlantic. An ancient slide discovered along the flank of a Hawaiian volcano measures approximately 5,000 cubic kilometers in size.
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|Title Annotation:||underwater avalanche in the Atlantic basin|
|Date:||Mar 14, 1992|
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