Tsunami that occurred in 2004 in Thailand. The water of the wave can be seen behind the palm trees in the background.

Estimated tsunami travel time forecast map for the 2011 Sendai tsunami, Japan.

A tsunami (from Japanese, meaning “harbor wave”) is a natural disaster, a series of fast-moving waves in the ocean caused by powerful earthquakes, volcanic eruptions, landslides, or a meteor impact in the ocean. A tsunami starts as a small wave and builds up into a larger wave, and starts suddenly. The waves travel at a great speed across an ocean with little energy loss. They can remove sand from beaches, destroy trees, toss and drag vehicles and houses and even destroy whole towns and cities. Tsunamis can even be caused when a meteorite strikes the earth’s surface, though this is very rare. A tsunami normally occurs in the Pacific Ocean, especially in what is called the ring of fire (a volcanically active region around the ocean’s edge), but can occur in any large body of water like lakes and seas. If the coast is not steep, the water may pull back for hundreds of meters before a tsunami hits. People who do not know of the danger of tsunamis often remain at the shore.