Tsunami is a japanese word, meaning harbour wave and is used as the scientific term for a seismic sea wave. Generated by an undersea earthquake or possibly an landslide or volcanic eruption. When the ocean floor is titled or offset during an earthquake, a set of waves is created similar to the concentric waves are generated by an object dropped into the water. Most tsunamis originate along the ring of fire, a zone of volcanoes and seismic activity 32,500 km long, that encircles the pacific ocean. Since 1819 about 40 tsunamis have struck the Hawaiian islands.
A tsunami can have wave length or width 100 to 200 km, and may travel hundreds of kilometers acroos the deep ocean, reaching speeds about 725 to 800 km/h. upon entering shallow coastal waters, the out at sea, suddenly grows rapidly. When half a meter high may be 15 m high or more. When the wave reaches the shore it because of the great volume of water affected. They are capable of obliterating coastal settlements.
Tsunami should not be confused with storm surges, which are domes of water that rise underneath hurricanes or cyclones and cause extensives coastal flooding when the storms reach land. Storms surges are particularly devastating if they occur at the high tide. A cyclone and accompanying storm suge killed an estimated 500,000 people in Bangladesh in 1970.