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Tsunami ('soo-nar-me') is a Japanese word; 'tsu' meaning harbor and 'nami' meaning wave.
A tsunami is a huge volume of moving seawater that has nothing to do with tides although it is sometimes mistakenly called a tidal wave. Imagine a train of giant waves that can travel for thousands of miles across the sea at speeds as fast as a passenger jet - almost 500 mph.
The most frequent cause of a tsunami is the buckling of the seafloor caused by an undersea earthquake.
Tsunami waves move outwards, away from their source. If you throw a stone in a pond it will create a series of ripples. A tsunami is just like those ripples but the disturbance that sets them moving is much greater than a small stone. One or more waves can be created per event. Successive peaks can be anywhere from five to ninety minutes apart.
As a tsunami reaches the shore it gradually slows down and increases in height. The highest tsunami occur if they encounter a long and gradual shallowing of the water.
When the tsunami reaches land it destroys everything in its path including buildings, trees, wildlife and people.
For additional information visit the following links provided by FEMA and the National Weather Service:
More Tsunami Links