"There is a drastic change in the shape of the land," said Anstice Justin, the head of the local unit of the Anthropological Survey of India who was part of the team that went on the reconnaissance mission to North Sentinel island.

"Instead of the lagoon there is a a field of rock. How will they fish there? There are no shallow waters anymore."

The Sentinelese, the most isolated of the five ancient tribes that live in the remote cluster of islands, do not fish in deep seas because unlike the other tribes they have not yet mastered the art of propelling their craft.

They use long poles to negotiate their canoes through shallow waters. Justin said he counted 32 Sentinelese, mostly adult males, a few teenagers and a couple of women, all of them naked, who came to the shore when they saw their speedboat approach.

"They made certain gestures, they were saying something, but it wasn't intelligible to us. But I would assume, like any human being, they would be concerned about what had happened."

Justin said his team left some coconuts in the waters near the island, which the Sentinelese later retrieved.

The government said members of the other primitive tribes -- Jarawas, Great Andamanese, Onge and the Shompen -- all appeared to have largely escaped the tsunami waves because they mostly lived in jungles away from the coast.

But survey teams have not yet visited all the islands or accounted for all the members of these tribes, which have been living in the area for thousands of years.

Many of the tribal people are semi-nomadic and subsist on hunting with spears, bows and arrows, and by fishing and gathering fruit and roots. They still cover themselves with tree bark or leaves.

Justin said the wreckage of two old ships jutted out from one of the washed up beaches of North Sentinel island and a few new breakers had emerged in the waters in another part of the island.

"Everywhere, you could see the earth had erupted, it was as if their land had been invaded."

Unlike the other tribes who have established some kind of contact with the outside world, the Sentinelese, who are drawn from Negrito stock, have been hostile to anyone trying to get anywhere near them.

"Perhaps this change in the topography will induce changes in them, might push them up the evolution chain, if you like.