A tsunami (?? ?)(pronounced /(t)su?'n??mi/) is a series of waves that is created when a large volume of a body of water, such as an ocean, is rapidly displaced. The Japanese term is literally translated into "(great) harbor wave."
Earthquakes, volcanic eruptions and other underwater explosions (detonations of nuclear devices at sea), landslides, bolide impacts, and other mass movements above or below water all have the potential to generate a tsunami. Due to the immense volumes of water and energy involved, the effects of tsunamis can be devastating.
The Greek historian Thucydides was the first to relate tsunami to submarine quakes,[1][2] but understanding of the nature of tsunami remained slim until the 20th century and is the subject of ongoing research.
Many early geological, geographical, and oceanographic texts refer to tsunamis as "seismic sea waves."
Some meteorological storm conditions such as 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, they may resemble (though are not) tsunamis, inundating vast areas of land. Such a storm surge inundated Burma (Myanmar) in May 2008.
The term tsunami comes from the Japanese, meaning "harbor" (tsu, ?) and "wave" (nami, ?). (For the plural, one can either follow ordinary English practice and add an s, or use an invariable plural as in the Japanese.[3]) Tsunami are common throughout Japanese history; approximately 195 events in Japan have been recorded.[citation needed]
Tsunami are sometimes referred to as tidal waves. In recent years, this term has fallen out of favor, especially in the scientific community, because tsunami actually have nothing to do with tides. The once-popular term derives from their most common appearance, which is that of an extraordinarily high tidal bore. Tsunami and tides both produce waves of water that move inland, but in the case of tsunami the inland movement of water is much greater and lasts for a longer period, giving the impression of an incredibly high tide. Although the meanings of "tidal" include "resembling"[4] or "having the form or character of"[5] the tides, and the term tsunami is no more accurate because tsunami are not limited to harbours, use of the term tidal wave is discouraged by geologists and oceanographers.
There are only a few other languages that have a native word for this disastrous wave. In the Tamil language, the word is aazhi peralai. The South Eastern coasts of India had experienced these kind of waves some 700 years before, and they were a regular event by that time, as the stone carvings (scriptures in stone) show. In the Acehnese language, it is ië beuna or alôn buluëk [6] (Depending on the dialect. Note that in the fellow Austronesian language of Tagalog, a major language in the Philippines, alon means "wave".) On Simeulue island, off the western coast of Sumatra in Indonesia, in the Defayan language the word is semong, while in the Sigulai language it is emong [7].
Causes
Causes
A tsunami can be generated when converging or destructive plate boundaries abruptly move and vertically displace the overlying water. It is very unlikely that they can form at divergent (constructive) or conservative plate boundaries. This is because constructive or conservative boundaries do not generally disturb the vertical displacement of the water column. Subduction zone related earthquakes generate the majority of all tsunamis.
Tsunamis have a small amplitude (wave height) offshore, and a very long wavelength (often hundreds of kilometers long), which is why they generally pass unnoticed at sea, forming only a slight swell usually about 300 mm above the normal sea surface. They grow in height when they reach shallower water, in a "shoaling" process described below. A tsunami can occur at any state of the tide and even at low tide will still inundate coastal areas if the incoming waves surge high enough.
On April 1, 1946 a Magnitude 7.8 (Richter Scale) earthquake occurred near the Aleutian Islands, Alaska. It generated a tsunami which inundated Hilo on the island of Hawai'i with a 14 m high surge. The area where the earthquake occurred is where the Pacific Ocean floor is subducting (or being pushed downwards) under Alaska.
