Tsunami: So rare that India did not bother to monitor it

The tidal waves occurred because the massive earthquake heaved the ocean floors off the Indonesian coast. ‘‘The undulation of the ocean floor triggered the tsunami,’’ says Shetye. ‘‘Once that happens, a tsunami propagates at the speed of 750-800 km/hr. The waves would have travelled at the speed of a jet engine to hit Sri Lanka and India within just over two hours after the quake.’’

From the sky or coastline, the open sea would still appear unsuspectingly calm. As the waves approached the southern and eastern coastline of India, they slowed down but rose in height. In the shallow coastal waters the waves morphed into a wall of water almost 10 m high, swallowing everything in its way.

While the US and 26 nations share data through a Pacific Tsunami Warning Centre, the calamity was unexpected along the nation’s 7,000-km coastline that is typically prepared for warnings of storm surges or cyclones. ‘‘In India such an event is so rare that we never felt a need for it,’’ says Shetye. ‘‘The economics of such a system would have to be considered.’’

The NIO team will soon analyse the tide gauge data of the affected ports to analyse the sequence of events, a beginning to a study of the phenomenon.

Scientists have, in the recent past, discussed rough estimates that global warming would increase sea levels by 2020, with the potential to affect metros like Mumbai, Kolkata or Chennai but nobody was prepared for a tidal wave.

‘‘In winter, oceans are usually calm,’’ says G B Pant, director Indian Institute of Tropical Meteorology in Pune. ‘‘So more people and tourists would be near the coastline or at sea, thus increasing level of destruction and lives lost.’’

In Hawaii, tidal wave warnings are flashed over televisions and through the civil defense sirens. Pant says the setting up of a tsunami warning system in India would be ‘‘administratively difficult’’ since it is a rare phenomenon scattered over open seas.

Destructive tsunamis have occurred in the last decade in Japan, Indonesia, Philippines, Peru and Mexico.

Shetye says: ‘‘The quake occurred in the subduction zone of the Indian subcontinent at about 33 km under the seabed. It occurred due to the Indian plate subducting (going under with extreme force) under the Burmese place. The entire area, as a result of this, is a seismic hotspot that witnesses regular seismic activity.’’

Dr K S Krishna, another scientist at the centre, says normally Tsunamis occur at depths of between 75 and 100 km under the sea-bed. ‘‘This time, however, the quake occurred only 33 km under the seabed and hence this Tsunami was more intense,’’ he says.

What made the situation worse was the fact that the Tsunami hit the eastern coast just an hour after the high tide time, 8 am. But had it hit the coast at the peak of the high tide, the damage would have been much severe.

What is important from the subcontinent’s point of view, is the fact that India had a window of two-and-a-half hours before the tidal wave crashed into the east coast. ‘‘Right now, we know how a Tsunami is created and how it works, but as far as predicting Tsunamis go, we have a long way to go,’’ Shetye says. ‘‘After all, this was the first recorded Tsunami to have hit India.’’