Tsunamis

• Tsunami comes from the Japanese word meaning "harbour wave". They are often incorrectly referred to as tidal waves, they are not caused by the tides, as tides are caused by the earth's gravitational pull and regular waves are caused by the wind.


• A tsunami is a series of waves generated by underwater earthquakes, submarine rock slides or a volcanic eruptions and in rare cases a asteroids or meteoroids crashing into in the water from space. An earthquake has to be over magnitude 6.75 to cause a tsunami. They are very destructive and cause loss of life when they strike a coast.


• A tsunami starts when a huge volume of water is quickly shifted. This rapid movement can happen as the result of an underwater earthquake (when the sea floor quickly moves up or down), a rock slide, a volcanic eruption, or another high-energy event.


• After the huge volume of water has moved, the resulting wave is very long (the distance from crest to crest can be hundred of miles long) but not very tall (roughly 3 feet tall). The wave propagates (spreads) across the sea in all directions; it can travel great distances from the source at tremendous speeds.


• Tsunamis can be up to several miles long.


• In the deep sea, a tsunami's height can be only about 1 m (3 feet) tall. Tsunamis are often barely visible when they are in the deep sea. This makes tsunami detection in the deep sea very difficult


• A tsunami can travel at well over 970 kph (600 mph) in the open ocean - as fast as a jet flies. It can take only a few hours for a tsunami to travel across an entire ocean. A regular wave travels at up to about 90 km/hr.


• Tsunamis are very rare. There are roughly six major tsunamis each century.