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Elephants on the coast of Thailand are acting strange.They stamp their feet and motion toward the hills.The sea draws back from the beaches.Fish fall heavily in the mud.Suddenly,a huge wave appears.This is no ordinary wave.It is tsunami!
Tsunami waves are larger and faster than normal surface waves.A tsunami wave can travel as fast as a jet plane and can be as tall as a ten-story building.Imagine dropping a stone into a pond.The water on the surface ripples（起涟漪）.A tsunami is like a very powerful ripple.Tsunamis begin when the ocean rises or falls very suddenly.Large amounts of seawater are displaced.This movement caused huge waves.
For a tsunami to occur,there must be some kind of force that causes the ocean water to become displaced.Most tsunamis are caused by underwater earthquakes.However,volcanoes ,landslides（塌方）,large icebergs,and even meteorites（陨石）are capable of causing one of these mighty waves.
Tsunamis are extremely powerful.Ordinary waves lose power when they break.Tsunami waves can remain powerful for several days.Because tsunami waves are so strong,they can kill people,damage property,and completely ruin an ecosystem in just one hour.
Scientists have no way of predicting when a tsunami will hit.However,if a powerful enough earthquake occurs, scientists can send out a warning or a watch.A warning means that a tsunami will very likely hit soon.A watch means that conditions are favorable for a tsunami.When people are informed of a watch or a warning,they have more time to prepare.It is best not to get caught unaware when a tsunami is on the way.
