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A tsunami is one or more water waves caused by a large displacement of water. This is typically in an ocean but the large lakes of the world are big enough to allow a tsunami to form. Tsunamis are usually caused by undersea earthquakes. It is rare, but a tsunami can be cause by an avalanche or landslide that displaces a large volume of water or even an asteroid or comet hitting the ocean.

A tsunami commonly forms when there is a dramatic uplift or fall of the ocean bottom associated with a submarine earthquake. In that case a large volume of water suddenly drops and surrounding water rushes in or a large volume of water is uplifted and water flows away from the area. Tsunami waves are not like normal ocean waves which do not result in a net transport of water. When a tsunami wave forms it is because a large volume of water is entering or leaving an area of the ocean. For this reason the propagation of a tsunami is different and very fast, hundreds of kilometers per hour.

Tsunamis form wherever an undersea earthquake can form, so they are particularly common at the boundary of the Earth's tectonic plates. These plates have areas where they are particularly active, the Pacific "ring of fire" being the most well known.

Typically a tsunami exhibits several waves in succession separated by minutes or hours. This will depend on the character of the original disturbance being fast or slow or limited to a small area or large. When tsunamis propagate across the ocean, they have a small amplitude a few inches (centimeters) high but they extend for hundreds of kilometers. Since there is actual flow of of a large volume of water associated with a tsunami, this height increases as the volume of water approaches the shallower coastal region. At the coast, the height is a fraction of a meter (a few feet) to hundreds of meters.

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12y ago

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