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		Tsunamis are disasters that can be generated in all of the world's oceans and inland seas. They can cause huge devastation to property and human life over a wide area.	Key Points Tsunami is derived from the Japanese words meaning 'harbour wave'. A tsunami is not a single wave but a series of waves (a wave train) An earthquake can generate a tsunami if it is of sufficient force causing sudden displacement of massive amounts of water. Tsunami waves can cross entire oceans without great loss of energy. Also in this Series Tsunami Disasters Also in the BBC BBC News: Tsunami Disaster The science of tsunamis External Web Links National Geophysical Data Centre NOAA's National Weather Service NOAA's Pacific Tsunami Warning Center (PTWC) Disclaimer The BBC is not responsible for the content of external websites.

	Tsunamis are a natural hazard that can cause great destruction and loss of life not only to shores near their source, but sometimes to shores across an entire ocean basin. Tsunamis have been reported since ancient times and have been extensively documented. Although tsunamis are infrequent, their history can educate and inform us about their characteristics and help in the development of more effective warning programs. What is a tsunami? A tsunami is a series of large waves generated by an impulsive disturbance that displaces the water. Earthquakes, landslides, volcanic eruptions, explosions can all cause disturbance to the sea floor, which causes a large volume of water to be suddenly displaced, forming tsunami waves. Tsunamis are often incorrectly referred to as tidal waves’. The word ‘tsunami’ is derived from the Japanese words meaning ‘harbour wave’. Often tsunamis are referred to by the more common name of ‘tidal waves’; however, this usage is considered incorrect by oceanographers since no tides are actually involved in their creation. What causes a tsunami? Tsunamis are often referred to as seismic sea waves as they are usually the result of a sudden rise or fall of a section of the earth’s crust. They are generally caused by earthquakes and less commonly by submarine landslides, submarine volcanic eruptions and meteorites. To initiate a tsunami, earthquakes must occur underneath or near the ocean and create movements in the oceans floor. This seismic disturbance can vertically displace the water column, creating fluctuations in the level of the ocean. Displaced water mass causes tsunamis waves. As the displaced water mass attempts to find its equilibrium, tsunami waves are formed. The tsunamis waves move outwards, away from their source and in deep waters can travel unnoticed on the surface at speeds up to 590 mph, crossing an entire ocean in a day or less. The speed of the tsunami depends on the depth of the ocean basin and as the tsunami waves reach the shallower water, the front of the wave slows down. Then, as the tsunami approaches shore, the waves pile up to create a wave that can rise up to 30 feet before hitting the shore. Effects of tsunami With wavelengths of up to and in excess of 60 miles, these seismic surges can assault coastlines, carrying rocks weighing as much as 20 tonnes 180 metres inland. The enormous energy of a tsunami can demolish houses, flip large vehicles and move heavy boulders. Tsunamis are a threat to life and property to anyone living near the ocean. Where are tsunamis generated? Tsunamis can be generated in all of the world's oceans and each region of the world appears to have its own patterns and cycle of frequency in generating tsunamis. Tsunamis have been recorded in all major oceans of the world. While tsunamis have been recorded in all major oceans of the world, they are most common around the edge of the Pacific because of the many large earthquakes along the margins of the Pacific Ocean. According to the National Geophysical Data Centre (NGDC), the first recorded tsunami occurred off the coast of Syria in 2000 BC. Since 1900, most tsunamis have been generated in Japan, Peru, Chile, New Guinea and the Solomon Islands. Regions that have generated tsunamis affecting the entire Pacific Basin include Kamchatka Peninsula, the Gulf of Alaska, South American coast and the Aleutian Islands. Hawaii, in the centre of the Pacific Basin, has experienced tsunamis generated in all parts of the Pacific. The Mediterranean and Caribbean Seas both have histories of locally destructive tsunamis, however, only a few tsunamis have been generated in the Atlantic and Indian Oceans. Tsunami prediction The United States Coast and Geodetic Survey established the tsunami warning system. A tsunami warning system was established by the United States Coast and Geodetic Survey as a result of the loss of life and damage caused by tsunamis in the Pacific. Pacific Tsunami Warning Centre (PTWC) became operational in 1948 and now links to over 30 seismological stations throughout the Pacific Basin. It provides data on earthquakes in the Pacific which may be capable of causing tsunamis and issues a ‘tsunami watch’ to all receiving stations. Unfortunately, there was no warning system in places for the Indian Ocean prior to the December 2004 tsunami, which caused huge devastation. Arrangements are now being made to implement a hi-tech network of ocean monitoring technology and a community response drill, which will take an emergency warning to every beach. As it is not possible to predict tsunamis, numerical models and historical records can help scientists to determine where tsunamis are likely to be generated, so preparation can be made for these natural hazards.
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Tsunamis