How an underwater earthquake causes a tsunami
Tsunami is a Japanese word in which tsu means harbor and nami means wave. Thus the word means harbor wave.
A tsunami is a series of waves of extremely long wavelength that are usually caused by a strong disturbance of the water, such as an underwater earthquake, landslide, or volcanic eruption; a meteorite can also cause a tsunami.
The waves travel outward in all directions from the disturbance, similar to what you would see if you threw a rock in a pond.
The average wave speed is 450 miles per hour.
Tsunami waves differ dramatically from traditional waves in that the tsunami waves have great depth, extending from the ocean floor the to waters surface. The height above the water may be only a few inches, but the huge wave is actually hidden in the water below.
Traditional surface waves, such as those you would see at an ocean coastline, are shallow waves; they are caused by the gravitational pull of the moon, sun, and planets, or by wind.
Because of the great depth of the tsunami waves, when they hit the coastline their height may increase from a few inches to tens of feet. And the tremendous speed of the waves (about 500 miles per hour) can carry the tsunamis a great distance onto land, flooding areas, destroying structures, and injuring or killing people.
The sequence above illustrates how an underwater earthquake disturbs the water and causes a tsunami.
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