A tsunami, a Japanese word that translates as "harbor wave," is usually caused by a sudden rise or fall of part of the earth's crust under or near the ocean.

It is not a single wave, but a series of waves that can travel across the ocean at speeds of more than 500 miles an hour. As the tsunami enters the shallows of coastlines in its path, its velocity slows but its height increases.

A tsunami that is just a few centimeters or meters high from trough to crest can rear up to heights of 100 to 150 feet as it hits the shore, striking with devastating force.

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Major Tsunami in History

1. Papua New Guinea:  In July 1998, southern Pacific island nation Papua New Guinea had an earthquake at 7.0 Richter Scale. More than 1,000 people died and 2000 were missing and 6,000 more were homeless.
   
2. Japan 1993: In July 1993, Japan's Hokkaido island had an earthquake at 7.8 Richter Scale in its south-western sea area. The tsunami caused by the quake generated 30.5-meter-high wave. 146 people died and 117 were missing.
   
3. Bangladesh 1991: In April 1991, the coastal area of Bangladesh was hit by strong typhoon, storm rain, and tsunami, flooding 16 counties and affecting 10 million people. 138,000 people died and the country's economic loss was 3 billion US dollars.
   
4. 11 Disasterous Tsunamis:In December 1988, Bangladesh was struck by strong wind and tsunami. At least 15,000 spotted deer, 2,000 wild pigs, baboons, monkeys and Bangladesh tigers were killed.
   In April 1991, the coastal area of Bangladesh was hit by strong typhoon, storm rain, and tsunami, flooding 16 counties and affecting 10 million people. 138,000 people died and the country's economic loss was 3 billion US dollars.
   In September 1992, Nicaragua had an earthquake at 7.0 Richter Scale, which had destroyed most production and life facilities in its coastal region along the Pacific. 268 people died, 153 were missing and 800 homes collapsed.
   In December 1992, eastern Indonesia had an earthquake at 7.0 Richter Scale, causing a tsunami that claimed 2,500 lives.
   In July 1993, Japan's Hokkaido island had an earthquake at 7.8 Richter Scale in its south-western sea area. The tsunami caused by the quake generated 30.5-meter-high wave. 146 people died and 117 were missing.
   In June 1994, Indonesia's eastern Java region had an earthquake at 5.9 Richter Scale. 128 people died.
   In November 1994, northern Philippine had an earthquake at 6.7 Richter Scale. The following tsunami killed at least 33 people and injured 70 others.
   In February 1996, eastern Indonesia had an earthquake at 7.0 Richter Scale. The following tsunami destroyed 75% of the building in its Biak County.
   In July 1998, southern Pacific island nation Papua New Guinea had an earthquake at 7.0 Richter Scale. More than 1,000 people died and 2000 were missing and 6,000 more were homeless.
   In November 1999, the southern Pacific island country Vanuatu had an earthquake at 7.1 Richter Scale. The tsunami killed 6 people.
   In December 26 2004, sea area around Indonesia's Sumatra Island had an earthquake at 8.9 Richter Scale. The following tsunami hit the neighboring countries. At the moment, it has killed at least 12,600 people. Sri Lanka is the worst hit country. At least 4,500 were killed in the tsunami.