Tsunami
• Tsunamis (Japanese for ‘harbor wave’), also known as a seismic sea wave, are a series of very large waves with extremely long wavelengths, in the deep ocean, the length from crest to crest may be 100 km and more.
• It is usually generated by sudden displacements in the sea floor caused by earthquake, landslides, or volcanic activity.
• Most tsunamis, including the most destructive ones, are generated by large and shallow earthquakes which usually occur near geological plate boundaries, or fault- lines, where geological plates collide.
• When the seafloor abruptly deforms the sudden vertical displacements over large areas disturb the ocean’s surface, displace water, and generate tsunami waves.
• Since the wave height in the deep ocean will be only a few decimetres or less (i.e., a few inches), tsunamis are not usually felt aboard ships. Nor are they visible from the air in the open ocean. The waves could travel away from the triggering source with speeds exceeding 800 km/h over very long distances.
• They could be extremely dangerous and damaging when they reach the coast, because when the tsunami enters shallow water in coastal areas, the wave velocity will decrease accompanied by an increase in wave height.
• In shallow waters, tsunami wave heights can increase rapidly by several meters, sometimes exceeding 30 meters, leading to massive destruction within a short span.
• Example: The earthquake in the Indian Ocean on December 24, 2004, triggered a devastating tsunami that severely impacted India, particularly the southern coastline and the Andaman and Nicobar Islands.
• MeteoTsunamis: These are usually less destructive caused by weather systems, much smaller and focused along smaller regions of the oceans or even Great Lakes. These are often caused by fast moving storm systems reaching over 6 feet (2 meters) high, mostly seen at the east coast of the U.S.
Map: Tsunami affected area in 2004
Not following the coastal zone development regulations within 500 metres of the coast is a challenge. Development projects (residential, commercial, recreational, etc.) are still carried out making the local population more vulnerable.
• Mining of sand and other minerals from the sea makes the concerned area highly vulnerable to tsunamis.
• There is an urgent need to check unwanted construction and mining in ecologically sensitive coastal areas.
• Destruction of various coastal natural vegetation like Mangroves etc. has enormously exposed human habitations to the problems of storm surges and tsunami waves.
• Excessively wide area of Tsunami Risk makes it difficult to cover remote coastal areas, and need higher funding for disaster resilient preparation.