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.