AP
 
New York, Oct 30: The tsunami that killed 230,000 people in 2004 was the biggest in the Indian Ocean in some 600 years, two new geological studies suggest. 

That long gap might explain how enough geological stress built up to power the huge undersea earthquake that launched the killer waves four years ago, researchers said.

The work appears in Thursday's issue of the journal Nature. Two research teams report that by digging pits and taking core samples in Thailand and northern Sumatra, they found evidence that the last comparably large tsunami struck between the years 1300 and 1400.

The researchers found deposits of sand that were apparently left by the waves, and estimated their age with carbon dating of associated plant debris.

The December 2004 disaster killed people in 14 countries. Waves more than 100 feet high struck northern Sumatra and deposited sand more than a mile inland, researchers said. In Thailand, the waves also ran more than a mile inland, leaving deposits of sand some 2 inches to 8 inches (5 centimetres to 20 centimetres) thick.