Monday, May 10, 2010

First tsunami in the world!

A meteor impact created the Chicxulub Crater about 65 million years ago. This impact may also have caused the Cretaceous-Tertiary extinction event. There is clear evidence for a tsunami more than one kilometre high. The tsunami disturbed and transported sediments over huge distance.

On Wednesday, November 29, 1975, the largest, local earthquake to strike the Hawaiian Islands since 1868, subsequently designated as the Kalapana Earthquake of 1975, generated the most destructive local tsunami in Hawaii in the 20th Century. Actually, two earthquakes occurred. The first earthquake, a foreshock, occurred earlier at 13:35 GMT (3:35 a.m local time). It had a magnitude of 5.7 and its epicenter was near Lae'apuki on Kilauea's south coast on the island of Hawaii.

The second and larger earthquake occurred a little over an hour later at 14:48 GMT (4:48 a.m. local time). This second earthquake was considerably larger with a magnitude of 7.2. Its epicenter was offshore at 19.3° N, 155.0° W, near Kamoamoa, just a few miles east but closer to the shoreline than the earlier foreshock. Its focal depth was only 8 km below the surface, near the magmatic chambers of the Puna Volcanic rift zone. The earthquake was induced by magmatic movements. At the time the first earthquake struck, there were thirty-two (32) people camping for the night at the Halape beach park near the base of a cliff. According to campers' accounts, trembling of the earth and sounds of rocks falling from the cliff, awakened them. A few of the campers moved to the coconut grove adjacent to the beach, believing it was safer from falling rocks.

The second earthquake, a little over an hour later, caused larger boulders to start falling down the cliff, thus forcing the rest of the remaining campers to flee toward the sea. Subsequently, these same campers were forced back to the cliffs when campers at the coconut grove were seen fleeing the rising ocean.

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