01 March 2005

Quake reformed Indian islands' geography

The earthquake that triggered Asia's tsunami has moved, twisted and tilted India's Andaman and Nicobar Islands, raising some out of sea and sinking large parts of others.

Shifts in tectonic plates have submerged India's southernmost point, split one island in two, destroyed beaches and villages, fuelled social pressures and even threatened the habitat of an ancient and isolated tribe of hunter-gatherers.

India's government says more than 7 000 people lost their lives when the tsunami struck the remote island chain on the morning of December 26, although independent experts on the archipelago put the figure significantly higher, at between 10 000 and 12 000 deaths.

The earthquake, at 9.0 on the Richter scale the world's biggest in decades, came after the India tectonic plate collided with and was forced underneath the Burma plate.

Scientists in Port Blair said the archipelago lies on the Burma plate, but a crack had developed in the plate between the northern Andaman Islands and the southern Nicobar Islands.

The navy's chief hydrographer, Rear Admiral BR Rao, said land from the islands' capital Port Blair to the north had gone up, whereas land to the south had sunk.

"Because of the earthquake, the movement of the plates, the topography and the coastline has changed," he said. "There has been a northwest-southeast tilt."

Rao said Indira Point, where a lighthouse marked India's southernmost limit on Great Nicobar island, had sunk by between 1,4 and 1,5m and is now under water.

The northernmost inhabited island of Diglipur has risen by between 0,5 and 0,8m.

Worst affected has been the island of Katchal in the southern Nicobars, where more than 4 600 people died in the tsunami. The entire coastal belt of the island and most of its villages are now under water.

As a result, the island's Nicobarese tribal people, pig and coconut farmers who live close to the sea, are now outnumbered by more recent settlers. Within a week of the tsunami, tribal leaders wrote to the authorities demanding illegal settlers be thrown out of their tribal land.

The nearby island of Trinket has split in two, one of six islands which have been evacuated.

In the northern Andaman group, North Sentinel island has risen out of the water, its beautiful lagoons replaced on three sides by foul-smelling mudflats.

Anthropologists are worried the Sentinelese, an ancient and endangered tribe of hunter-gatherers living in near total isolation on the island, will struggle to fish in the rougher, deeper waters which now surround most of their territory.

"The Sentinelese use feeble outrigger canoes," said Anstice Justin of the Anthropological Survey of India. "They use neither oars nor paddles but a long pole, which means they are confined to fishing close to the shore."

In the end, the Sentinelese will probably survive by carrying their canoes to the one lagoon which has survived, experts say.

Such were the forces unleashed on December 26 that the islands have not just titled but also moved between one and four metres, said Surveyor-General of India Dr Prithvish Nag.

He said his team had taken readings from 22 control points around the islands in April 2004, and repeated the exercise at 12 of the points which remained visible and above sea-level after the earthquake.

"Generally we found that there has been a shift, but it has been an erratic one," he said. "But there is an indication of an anti-clockwise twist as well around Port Blair."

The Andaman and Nicobar islands have experienced almost 10 000 aftershocks since December 26, more than 200 of them registering as "moderate" earthquakes at 5.0 or above on the Richter scale.

While seismologists say this is a normal pattern after a major earthquake, Nag says he will wait for things to settle down before completely remapping the islands.


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