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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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