Tuesday, October 20, 2009

The Tsunami

Tsunami is a set of ocean waves caused by any large, abrupt disturbance of the sea-surface. If the disturbance is close to the coastline, local tsunamis can demolish costal communities within minutes. A very large disturbance can cause local devastation and export tsunami destruction thousands of miles away. The word Tsunami is a Japanese word represented by two characters “Tsu” meaning harbor and “nami” meaning wave. Tsunami rank high on the scale of natural disasters.

Since 1850 alone, Tsunamis have been responsible for the loss of over 420000 lives and billions of dollars of damage to coastal structures and habitats. For e.g. The December 26, 2004 Tsunami killed about 130000 people close to the earthquake and about 58000 people on distant shores. Predicting when and where the next Tsunami will strike is currently impossible.

Tsunamis are most commonly generated by earthquakes in marine and coastal regions. Major Tsunamis are produced by large(greater than 7 on the Richter Scale) shallow focus ( < 30 km depth in the Earth) earthquakes associated with the movement of the sea floor produced a Tsunami in the excess of the 30 meters along the adjacent coastline killing more than 240000 people. From this source the Tsunami radiated outward and within 2 hours had claimed 58000 lives in ThailandSri Lanka and India.

26th December, 2004- Kerala experienced the first ever Tsunami in its recorded history. When the phenomenon occurred; people could not gauge the magnitude of the disaster caused by these monstrous waves. The welling up and retreat of the sea initially attracted the curiosity of people. The scene suddenly changed and high amplitude waves invaded the low-lying coastal tracts of the southern districts of Kerala claiming 175 lives, leaving thousands injured and homeless and causing damage to property worth crores of rupees.

The coastal tracts of Kerala on the South-West of Indian peninsula does not come in the direct face of the wave generated at Banda-Aceh. But these waves reached the coast of Kerala, a far- field destination about 2500 km away. Apart from the long distance from the epicenter, this coast was considered as a shadow zone as far as Tsunami hazards are concerned. The wave orthogonal drawn on the mega ripples generated from the epicenter clearly shows that the Kerala coast is far away from the direct impact of the Tsunami.

The effects of Tsunami were felt all along the coast of Kerala. But the impact was not uniform throughout. The intensity drastically changed even in the main disaster zone. This is mainly due to the variations in the coastal geomorphology and the near shore submarine topology.

Regarding the measures of mitigation, the most important factor to be considered is educating people about Tsunami and the cues that nature provides before a Tsunami hits the coast. More bridges are to be constructed across the backwaters for effective evacuation of the people from the densely populated barrier beaches. Preservation of natural coastal dunes and mangrove forests along with coastal afforestation can reduce the impact of the aggressive waves.


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