What is tsunami?
Tsunami are large, powerful waves caused by sudden displacement of large quantities of water in the sea / ocean. Common causes for the displacement of large quantities of water are: earth quakes, volcanic activity and landslides.
They can also be caused by detonation of nuclear devices under water, or by the impact of an asteroid.
As the wave of a tsunami moves into shallower water, it gets much higher, so they can be very big and very destructive when they hit coastal areas.
Sometimes (but not always) the water will recede dramatically just before a tsunami strikes a coastal region - if you see the sea suddenly pull back, going further out than a normal low tide in a very short time then you really want to get out of there as quickly as possible and seek safety!
Visit http://en.wikipedia.org/wiki/Tsunami for more information on Tsunami
