A tsunami ( ) is a series of waves created when a body of water, such as an ocean, is rapidly displaced. Earthquakes, mass movements above or below water, some volcanic eruptions and other underwater explosions, landslides, underwater earthquakes, large asteroid impacts and testing with nuclear weapons at sea all have the potential to generate a tsunami. The effects of a tsunami can be devastating due to the immense volumes of water and energy involved. Since meteorites are small, they will not generate a tsunami.

The Greek historian Thucydides was the first to relate tsunamis to submarine quakes, but understanding of the nature of tsunamis remained slim until the 20th century and is the subject of ongoing research.

Many early geological, geographic, oceanographic etc., texts refer to "Seismic sea waves"—these are now referred to as "tsunami".

Some meteorological storm conditions—deep depressions causing cyclones, hurricanes—can generate a storm surge which can be several metres above normal tide levels. This is due to the low atmospheric pressure within the centre of the depression. As these storm surges come ashore the surge can resemble a tsunami, inundating vast areas of land. These are not tsunami. Such a storm surge inundated Burma (Myanmar) in May 2008.

Terminology

The term tsunami comes from the Japanese meaning harbor ("tsu", 津) and wave ("nami", 波). Jap. tsunami, tunami, f. tsu harbour + nami waves.—Oxford English Dictionary. For the plural, one can either follow ordinary English practice and add an s, or use an invariable plural as in Japanese. Tsunamis are common throughout Japanese history; approximately 195 events in Japan have been recorded.

Tsunamis are often referred to popularly as tidal waves. In fact, tsunamis have nothing to do with tides; however, the popular term derives from their most common appearance, which is that of an extraordinarily high incoming tide. Tsunamis and tides both produce waves of water that move inland, but in the case of tsunamis the inland movement of water is much greater and lasts for a longer period, giving the impression of an incredibly high tide. Use of the term tidal wave is discouraged by geologists and oceanographers, but it is worth noting that the term tsunami is no more accurate because tsumanis are not limited to harbours.

The only other language than Japanese that has a word for this disastrous wave is Tamil language and the word is "Aazhi Peralai". South Eastern coasts of India have experienced these waves some 700 years before and was a regular event by that time as per the stone carvings (scriptures in stone) read.