The term tsunami comes from the Japanese language meaning harbour ("tsu") and wave ("nami"). Although in Japanese tsunami is used for both the singular and plural, in English tsunamis is well-established as the plural. The term was created by fishermen who returned to port to find the area surrounding the harbour devastated, although they had not been aware of any wave in the open water. A tsunami is not a sub-surface event in the deep ocean; it simply has a much smaller amplitude (wave heights) offshore, and a very long wavelength (often hundreds of kilometres long), which is why they generally pass unnoticed at sea, forming only a passing "hump" in the ocean.
Tsunamis have been historically referred to as tidal waves because as they approach land they take on the characteristics of a violent onrushing tide rather than the sort of cresting waves that are formed by wind action upon the ocean (with which people are more familiar). However, since they are not actually related to tides the term is considered misleading and its usage is discouraged by oceanographers.
CAUSES- EXPLANATION THROUGH DIAGRAM [pic]
Schema of a tsunami
A tsunami can be generated by any disturbance that rapidly displaces a large mass of water, such as an earthquake, volcanic eruption, landslide or meteorite impact. However, the most common cause is an undersea earthquake. An earthquake which is too small to create a tsunami by itself may trigger an undersea landslide quite capable of generating a tsunami.
Tsunamis can be generated when the sea floor abruptly deforms and vertically displaces the overlying water. Such large vertical movements of the earth's crust can occur at plate boundaries. Subduction earthquakes are particularly effective in generating tsunamis, and occur where denser oceanic plates slip under continental plates in a process known as subduction.
Sub-marine landslides; which are sometimes triggered by large earthquakes; as well as collapses of volcanic edifices, may also disturb the overlying water column as sediment and rocks slide downslope and are redistributed across the sea floor. Similarly, a violent submarine volcanic eruption can uplift the water column and generate a tsunami.
Waves are formed as the displaced water mass moves under the influence of gravity to regain its equilibrium and radiates across the ocean like ripples on a pond.
(3)Volcanic Eruption - Although relatively infrequent, violent volcanic eruptions represent also impulsive disturbances, which can displace a great volume of water and generate extremely destructive tsunami waves in the immediate source area .Volcanic disturbances can generate waves by the sudden displacement of water caused by a volcanic explosion, by a volcano's slope failure, or more likely by a phreatomagmatic explosion and collapse and/or engulfment of the volcanic magmatic chambers .The majority of tsunamis that occur in the Pacific Ocean happen around the “Ring of Fire” Area surrounding the Hawaiian Islands .The periphery has also been dubbed the 'Ring of Fire' because of the extraordinarily high number of active volcanoes and seismic activity located in the region .Since 1819, over 40 tsunamis have struck the Hawaiian Islands .One of the largest and most destructive tsunamis ever recorded was generated in August 26, 1883 after the explosion and collapse of the volcano of Krakatoa (Krakatau), in Indonesia. This explosion generated waves that reached 135 feet, destroyed coastal towns and villages along the Sunda Strait in both the islands of Java and Sumatra, killing 36, 417 people .
(4)Extraterrestrial Collision – Tsunamis caused by extraterrestrial collision (i.e. asteroids, meteors) are an extremely rare occurrence. ...