Tsunami: High Risk Regions , Causes & Characteristics

Tsunami is another japanese name for ‘harbor waves’. The Tsunamis are extremely long waves mostly caused due to an earthquake deep below or near the ocean floor. The height of tsunami waves in the deep ocean is usually under 3 feet but it usually travels at a speed of about 800 kms/hour which is equal to the speed of a commercial passenger airplane.

The tsunami waves are highly disastrous and cause much destruction in shallow water and coastal regions. This is because the high speed of tsunami waves gets reduced to about 30-50 km/hour near the on-shore area but a huge amount of water still moves at an extremely high speed.

The deadliest Tsunami was recorded on 26th December 2004 which occurred in the Indian ocean region. It was a result of an undersea earthquake of very high magnitude of about 9.1 to 9.3 in the Indonesian ocean region. It was the area where the Indian tectonic plate subducts below the Burma microplate. As a result, the sudden upliftment of the sea floor displaced a high amount of water and thus the tsunami waves were generated in the Indian ocean. These waves affected around 15 countries including Indonesia, India, Sri Lanka, Thailand, Maldives, and Somalia. The tsunami in 2004 was such a disastrous event that killed more than 2,30,000 people and about 17 Lakhs people were displaced. The Indian regions such as Andaman and Nicobar Islands, Tamil Nadu, Puducherry, Andhra Pradesh and Kerala were seriously affected.

The risk of Tsunami is highest around the active plate boundaries particularly at the subduction zone where most of the earthquakes occur. The ‘Ring of Fire’ in the pacific ocean which includes the countries such as Japan, Indonesia, Philippines, New Zealand, Alaska are the high tsunami prone regions of the world. The low-lying islands, coast with delta, enclosed bay and densely populated settlements face higher inundation risk. In India, Andaman and Nicobar Islands and the eastern coast including Tamil Nadu, Puducherry, Andhra Pradesh and Odisha are relatively more prone to tsunami. Few regions of Kerala and Lakshadweep can be affected by the Indian Ocean tsunami.

A tsunami is a series of ocean or sea waves which have a catastrophic effect on the coastal land region. The tsunami waves have long wavelengths in deep ocean water. They travel at the speed of a jet aircraft and usually have a height of 2 to 3 metres. This small height makes it difficult to get noticed at sea. But when they reach the shallow coastal water, their speed reduces and wave height increases. Water rushes inland in the form of a fast and turbulent surge. The successive waves then arrive in a few minutes to hours.

The inland movement of elephants, birds leaving their nesting sites, and dogs refusing to go outdoors are some of the unusual animal behaviors for sensing tsunamis. The animals can detect some of the environmental changes that human beings cannot easily notice. It includes low frequency sounds and ground vibrations caused due to earthquakes, air pressure changes, and unusual coastal water movement. However, scientific evidence does not rely on animal behaviour as a tsunami warning method.

The tsunami waves cannot be predicted before it gets triggered. However, they can be detected and forecasted after its triggering. The warning centres use the seismographs to locate earthquakes and estimate their depth and magnitude. The sea gauges and deep ocean pressure sensors such as DART buoys often provide the information related to the changes in sea water levels. The computer model compares the information about earthquakes and coastal topography to estimate the arrival time and height of ocean waves. The national warning centres transmit the information to authorities and communities through sirens, mobile phones alerts, radio, and television.