Atmosphere And Weather

Causes of Tsunamis



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The largest earthquake ever recorded struck Chile in 1960, measuring 9.5 on the Richter scale. Approximately 1,655 people died in the monstrous quake. Besides the devastation in Chile, about 140 people died in Japan, 61 in Hawaii, and 32 in the Philippines. A tsunami took their lives, a train of huge waves that traveled far from the earthquake that began it, to carry destruction across the widest ocean on earth.

Tsunamis are caused by events that create an abrupt change in the water level of a particular area of the ocean. The tsunami spreads out from this point, the way ripples spread in a lake when a stone is dropped in it. Where the plates that make up the earth’s surface come together there are often earthquakes, which may lift the seabed or lower it, displacing water and sometimes causing a tsunami.

Earthquakes are not the only events that can cause tsunamis, however. Undersea landslides or volcanic eruptions can also cause them, as can landslides into water or even the impact of huge meteorites.

Once a tsunami is set in motion, it can travel at up to 450 miles per hour as a long wave or as a series called a wave train in the open ocean. It may pass right under a ship in deep water without disturbing its voyage. However, once the wave reaches shallower water near land, it can tower up to 100 feet high. In the 1960 tsunami, waves 38 feet tall inundated Hilo Hawaii and waves 18 feet tall struck Honshu Japan.

Near shore, coastal topography and the shape of the sea floor govern the speed, height, and destructive power of a tsunami. Some landforms concentrate the destructive power of these waves by focusing their force. This is one reason why some areas of the world are susceptible to repeated tsunamis.

However, a tsunami can theoretically hit any coast. Anyone living at an elevation of less than 25 feet and within one mile of the coastline is conceivably at risk, though tsunamis are probably most common near the Pacific and Indian Oceans.

In the United States, the state of Hawaii has experienced the largest number of tsunamis. For this reason, it has the best-developed warning system, using sirens, television, radio, and the internet to alert its population. A system of emergency workers and trained Civil Defense volunteers are prepared to lead people to safety.

Other states that have experienced tsunamis in recorded history are Alaska, California, Oregon, and Washington.

Tsunamis cause immeasurable death and destruction. Modern early warning systems, however, help evacuate hazardous areas near shore and can save many lives. Large tsunamis are reasonably rare, fortunately, and the damage they do can be greatly reduced with warning systems, zoning, and building codes.



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