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What is a Tsunami

What is a Tsunami?
Tsunamis are large, often destructive sea waves, which are usually caused by earthquakes below the ocean, volcanic eruptions, or
underwater landslides. From the Japanese phrase meaning, "harbor wave," tsunamis can devastate the infrastructure of coastal cities and can be very deadly. Though tsunamis are often misleadingly called tidal waves for their resemblance to a rising tide, tsunamis are unrelated to the tides, but are caused by movements in the earth, usually far below the ocean. Landslides in the ocean have caused some of the largest tsunamis in history, known as megatsunamis.

Tsunami waves have a much longer wavelength than normal waves, reaching hundreds of kilometers in length, while the height (amplitude) of the waves remains just above normal, slowly building until it reaches the shallow waters along the coast. Just before the large wave hits the coast, the water drastically recedes in what is called a drawback. The giant wall of water then travels at high speeds toward land, crashing and destroying everything in its path. The tsunami then recedes back to the ocean, pulling with it much of the debris of the structures it has destroyed.

The slow build-up of the waves is one factor that makes tsunamis difficult to predict. Earthquakes, considered the main cause of tsunamis, are also not absolute predictors of a tsunami, because some large earthquakes do not result in a tsunami, and some small earthquakes do. Most tsunamis occur around the Pacific Ocean because of the high level of seismic activity in this Pacific Ring of Fire.

Major Historic Tsunamis
March 11, 2011, Japan - After the 9.0 magnitude earthquake in Japan, the country was hit with tsunamis 33 feet high to as tall as 97 feet tall, killing about 20,000 people.

December 26, 2004, Indonesia - The most destructive tsunami in recorded history, the Asian tsunami of 2004 devastated eleven countries, killing 230,000 people around the Indian Ocean and reaching about 98 feet in height.

July 9, 1958, Lituya Bay Alaska - The Lituya Bay megatsunami is the tallest recorded tsunami in history, reaching heights of 1,720 feet.

August 26, 1883, Indonesia - The eruption and collapse of Krakatoa volcano in Indonesia caused a series of tsunamis, reaching 135 feet and killing over 36,000 people.