Tsunami is a special type of wave that greatly affects distant coastlines. A large undersea disturbance such as undersea or coastal seismic activity produces a single wave of great wavelength.

The wavelength of a tsunami is in excess of 100 km, but its height is about a meter or so. In Deep Ocean water these waves travel at great speeds.

Their velocities are commonly 600- 800 km per hour. However, in open sea they are seldom noticed because of great length which makes the slow rise and fall of water difficult to observe.

As a tsunami approaches a coast, with shallow water, its wavelength gets shortened with the result that the wave height may increase up to 15 m or more.


Such a gigantic wave is capable of coastal devastation which results in huge losses of property and human lives. In fact, such a killer wave is the result of an earthquake along an offshore subduction zone.

Since velocity of tsunami is very great and it is impossible to detect them in the open ocean, so their accurate forecasts are difficult and occurrences are often unexpectedly sudden.

Keeping in view the vast damage and destruction done by them, a warning system is in operation for those nations which surround the Pacific Ocean where a large number of tsunami occur.

Warning should always be taken with all seriousness, even though sometimes there may be false alarms. The reason is that the causes for the generation of tsunami lie beneath the ocean and, therefore they are difficult to monitor in any consistent manner.


The world’s fifth-largest quake in a century hit Southern Asia on Sunday, 26 December, 2004, triggering a speeding killer tsunami that crashed into Sri Lanka and India drowning hundreds and swamped tourist islands in Thailand and the Maldives.

A wall of water upto 10 meters high set off by the 8.9 magnitude undersea earthquake swept into Indonesia, over the coast of Sri Lanka and along the Southern Thai tourist island of Phuket.

The death toll is estimated to be more than 4500. The undersea earthquake was of the magnitude of 8.9 as measured by the U.S. Geological survey. It first struck at 7.59 a.m. (00.59 GMT) off the coast of the northern Indonesia island of Sumatra and swung north with multiple tremors into the Andaman, islands.

This earthquake disaster was the worlds biggest since 1964. Some say that it was the biggest one since 1900.


In Sumatra alone about 30,000 persons lost their lives and lacs of people were rendered homeless. According to seismologists this havoc was caused due to the subduction of Indian plate beneath the Bermese plate.

It is not the proper place to discuss the huge loss of life and property which occurred due to tsunami which visited various countries and islands of South Asia.

It is, however, clear that tsunami is the most terrible sea wave which affects the coastline and coastal zone. Newspapers reported “thousands drown as tsunami levels coastlines across South Asia”.