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What is a tsunami anyway?

Mechele R. Dillard's picture

The current weather situation, from Japan to Oregon, has many people asking, "What is a tsunami, anyway?"

A tsunami is devastating Japan, and other areas, including areas of the U.S., are expected to be hit, as well. But, many people may be asking, “What is a tsunami, exactly?”

“Tsunami” is a Japanese word, combining two meanings: “tsu,” or “harbor,” and “nami,” or “wave.” Since 1850, it is estimated that at least 420,000 people have been killed by tsunamis, with damage estimates to be in the billions. The tsunami itself is a set of ocean waves that are generated by a large, abrupt disturbance of the sea surface, such as the 8.9 earthquake seen in Japan overnight. Major tsunamis typically are produced by earthquakes greater than 7 on the Richer scale. Unfortunately, with current technology, predicting tsunamis is not possible, although tsunami arrival and impact can be projected by modern modeling and measurement technologies once it has been generated.

The Pacific is often a source of tsunami activity, because dense oceanic plates slide under lighter continental plates. When the plates fracture, the movement occurring on the seafloor produces a quick transfer of energy from the earth to the ocean. Underwater landslides sometimes associated with smaller earthquakes can also result in a tsunami. Additionally, volcano action an asteroid impacts can produce a tsunami. Any action resulting in vertical movement of the seafloor changes the sea surface, and the resulting tsunami forms as wavelengths which correspond to the movement of the earth, and wave heights which are formed based on the vertical displacement. The direction of the waves is created according to the corresponding coastline formation. Because the properties of each tsunami is so unique, predicting paths of and following tsunamis as they develop is difficult.

Tsunami warning systems were created in 1946 in the pacific basin. These systems monitor earthquake activities, as well as the passage of tsunami waves at tide gauges. Earthquake monitoring does allow for a reasonable estimate of the potential generation of a tsunami, but does not produce direct information about the tsunami, and this system still does not allow accurate prediction of impact. There are many factors that can change the direction and impact of a tsunami, including local area land features and harbors, limiting their overall effectiveness. However, modern, real-time, deep ocean tsunami detectors do provide information to make tsunami forecasts, and were first put to the test on Nov. 17, 2003, at Rat Islands, Alaska. It was the first time model predictions were obtained as the tsunami developed, before the waves hit coastlines. Ongoing development of these real-time detectors allow for better lead time, potentially giving residents time for evacuation.

For more information on tsunamis, visit the National Oceanic and Atmospheric Administration.

Read more about the ongoing tsunamis in the Pacific on
Tsunami fears increase as police evacuate coastal residents in Oregon
Tsunami will hit the West coast, thousands fleeing to higher ground
Earthquake in Japan being felt in Oregon, Tsunami warnings
Guam, Philippines issue tsunami alerts following earthquake in Japan
8.9 Earthquake Off Japan Triggers Tsunami, Causing Major Damage

Image: Wikimedia Commons

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