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Tsunami reformed shape, depth of coastal lands

WANDOOR, India—The earthquake that triggered the catastrophic Dec. 26 tsunami was so violent that it transformed much of the coastal landscape from western Indonesia to India's Andaman and Nicobar islands.

The coastline sank 3 feet in some places, submerging fishing villages. Elsewhere, the coast rose out of the sea, exposing coral reefs to certain death. Some islands tilted, one side rising up and the other falling.

The seismic shifts will alter lives for generations. The land may revert to its original level, but not for more than 100 years.

In the meantime, entire villages will have to relocate to higher land. An endangered sea turtle will have to find a new beach to lay its eggs. For fishermen, coral reefs that once teemed with fish have gone barren.

"The reefs have broken up," said Pralad Mondal, 48, who netted a meager 45 pounds of fish on a two-day expedition from the port of Wandoor on South Andaman island. "Some have gone up and some have gone down. There's not as much fish."

The affected area stretches north from Indonesia's hard-hit Aceh province on the northern tip of Sumatra several hundred miles to the Andaman and Nicobar archipelago.

For more than a century, pressure built along an undersea fault where the oceanic Indian plate runs into the Burma sub-plate, the continental plate on which Sumatra, Andaman and Nicobar rest.

The two plates move toward each other at a rate of about half an inch a year, putting greater and greater stress on the rock where they meet, said Eric Geist, a tsunami expert at the U.S. Geological Survey in Menlo Park, Calif.

The rock gave way on Dec. 26 at 7:59 a.m., unleashing an earthquake that measured 9.0 on the Richter scale, the world's fourth-largest since 1900.

The rupture, which started 22 miles beneath the seabed, allowed the two plates to thrust forward suddenly and dramatically.

Land connected to the Burma plate shifted westward by as much as 6 to 10 feet, according to computer modeling estimates. The end of the Burma plate rose, pushing the seabed up 16 feet. The ocean water rose with it, then rolled down toward distant shores as tidal waves.

Closer to the Sumatra shore, the Burma plate sank, pulling the coastline under water. The west coast of Sumatra dropped by an estimated 3 feet. In Nicobar, one island was split in two, and the land in between is now under water.

At the southernmost tip of the Nicobars, a beach that was a nesting spot for the endangered leatherback turtle has submerged, said Manish Chandi of the Andaman & Nicobar Environmental Team.

The tsunami killed a researcher who was observing the nesting of the leatherback, the largest living turtle, with a 5-foot long shell and a weight of 400 to 1,500 pounds. Another researcher was missing for two weeks before he found his way back through the jungle to a village.

The northwestern coast of Simeulue, a small Indonesian island near the epicenter of the quake, rose 5 feet, estimates geologist Kerry Sieh, who in mid-January set down in a helicopter on a newly exposed reef on Simeulue's shore.

"We were astonished to find ourselves walking through a pristine marine ecosystem, missing only its multitude of colors, its fish and its water," Sieh wrote in a travelogue posted on the Internet.

"Corals of every shape and size rested lifeless on the reef platform: branching corals, massive corals, staghorn corals, fire corals, brain corals, whorls, fans. And here and there a poor crab."

On the southern end of the same island, the coast appeared to have sunk nearly a foot.

Island tilting is nothing new. By studying ancient corals off Sumatra, Sieh's team at the California Institute of Technology in Pasadena had determined that islands tilted during major earthquakes there in 1797, 1833 and 1935.

The offshore Indonesian islands sink into the sea over time, though generally by less than half an inch a year, Sieh said. At that rate, it would take 150 years for the uplifted coast of Simeulue to return to its pre-earthquake level. By then, the underwater fault may be preparing to rupture once again.


(c) 2005, Knight Ridder/Tribune Information Services.

GRAPHIC (from KRT Graphics, 202-383-6064): 20050315 TSUNAMI.

ARCHIVE PHOTOS on KRT Direct (from KRT Photo Service, 202-383-6099): India+tsunami

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