Wednesday, 17 Sep, 2008 Environment
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Mega-Tsunami Deposited Massive Coral Boulders on Tonga Island?

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Scientist managed to discover signs of ancient devastation on an isolated tropical island located in the South Pacific Ocean. Seven huge boulders made of coral were found on the flat island of Tongatapu, the main island of Tonga. These stones have the same composition as the reefs that line the coast and geologists consider these are the largest boulders ever dumped by a mega-tsunami, a large wall of water that is 130 feet high and which stormed onto the island thousands of years ago.

The stones were discovered by a team of scientists from the University of Texas, Austin, headed by Matthew Hornbach. They were puzzled by how the rocks might have gotten on the island.

"Tongatapu is flat as a pancake, and here are seven boulders from bus-sized to house-sized sitting hundreds of meters inland and 10 to 20 meters [33 to 66 feet] above sea level. I mean, you can see these things on Google Earth, from space," said Hornbach.

The researcher performed a number of computer simulations of the type of tsunami, which could have deposited such huge boulders. It is worth mentioning that massive tsunamis can be formed by landslides and powerful earthquakes.

"But the estimated wave energy generated by the landslides we modeled was too low by an order of magnitude," said the researcher. The models of the earthquake produced widespread tsunamis that would be evident throughout the area and not only on the western part of the island. The researchers required a more powerful source.

In 2007 they found an unnamed underwater volcano, located 22 miles west of the island. After analyzing the sides of the volcano, researchers discovered that a three-mile-long section of its edge probably collapsed, generating a wave 130 feet high that stormed ashore.

The geologists consider that the wave had almost the same size as the Krakatau's wave, produced by a powerful eruption that occurred in 1883 and left the islands of Java and Sumatra under water. However, the stones found along Tongatapu are larger than deposits produced by the Krakatau's tsunami. Researchers estimated that one of such stones weights about 1,600 tons.

"Look, we can't discount that something else may be going on here. A hypercane or some extremely powerful storm could have done it. But to my knowledge no storm has ever deposited anything bigger than car-sized boulders," Hornbach said.

According to Jose Borrerros of ASR Research, a marine consulting company based in Raglan, New Zealand, the giant-ness of the wave that might have deposited the massive boulders has never been seen in human time.

Source: Discovery

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