Notes

A Tsunami is a series of water waves caused by the displacement of a large volume of a body of water,

typically an ocean or a large lake. It can be generated by earthquakes, volcanic eruptions and other

underwater explosions including denotations of underwater nuclear devices, landslides, glacier

calving, meteorite impqacts and other disturbances above or below water.

The term tsunami comes from japanese ee. It is composed of the two kanji e(tsu) meaning “harbour”

and e (nami), meaning “wave”. It can be put into the plural form by either following ordinary English

practice and add an s, or using an invariable plural as in the japanese.

---------------------------------------------------------------------------------------------------------------------------------------There are only a few other languages that have an equivalent native word. In Acehnese language, the

words are ie beuna or alon buluck (depending on the dialect). In Tamil language, it is aazhi peralai. On

Simeuleu island, off the western coast of Sumatra in Indonesia, in Devayan language, the word is

smong, while in Sigulai language it is emong. In Singkil (in Aceh province) and surroundingb, the

people call tsunamis gloro.
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Tsunamis can be generated when the sea floor abruptly deforms and vertically displaces the

overlying water. A tectonic earthquake is a particular kind of earthquake that is associated with the

Earth’s crustal deformation. When such earthquakes occur beneath the sea, the water above the

deformed area is dicplaced from its equilibrium position. More specifically, a tsunami can be

generated when thrust faults associated with convergent or destructive plate boundaries move

abruptly, resulting in water displacement, as a result of the vertical component of movement involved.

Movement on normal faults will also cause displacement of the seabed, but the size of the largest of

such events is normally too small to give rise to a significant tsunami.

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As the tsunami approaches the coast and the waters become shallow , wave shoaling compresses

the wave and its speed decreases below 80 kilometres per hour (50 mph). Its wavelength diminishes

to less than 20 kilometres (12 mi) and its amplitude grows enormously. Since the wave still has the

same very long duration, the tsunami may take minutes to reach full height. Except for the very

largest tsunamis, the approaching wave does not break, but rather appears like a fast moving tidal

bore. Open bays and coastlines adjacent to very deep water may shape the tsunami further into a

step-like wave with a steep-breaking front.

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When the tsunami’s wave peak reaches the shore, the resulting temporary rise in sea level is termed

run-up. Run-up is measured in metres above a reference sea level. A large tsunami may feature

multiple waves arriving over a period of hours, with significant time between the wave crests. The

first wave to reach the shore may not have the highest run up.