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December 27, 2004

How the shape of ocean floors can affect speed and height of tsunami

Topics: General Science

-TimesOnline.co.uk Dec 27.

THE long arch of Sumatra and Java, sweeping like a crescent across the north of the Indian Ocean, is one of the most active geological regions in the world.

Close by, in the Sundra Strait between Sumatra and Java, is Krakatoa, the scene in 1883 of one of the world's most catastrophic volcanic eruptions, when an entire island virtually disappeared.

Yesterday the region was the setting for an earthquake and tsunami more frightening than anything dreamed up for a Hollywood disaster movie.

The cause lies deep beneath the ocean, where two of the great tectonic plates that carry the continents around the Earth collide. The Indian-Australian plate slides under the Philippine plate in a "subduction zone" 750 miles long and more than 300 miles wide.

The movement is jerky, as the submerging plate tends to drag the upper plate down with it. But as pressure builds, the upper plate breaks free, springing back to its original position. Yesterday's movement was just 16½ yards at a depth six miles below the seabed, but it was more than enough.
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Posted by Hyscience at December 27, 2004 4:55 AM


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