Natural Devastation
Natural Devastation The largest earthquake in 40 years shifted huge geological plates beneath the Indian Ocean on Dec. 26, 2004, causing a immense and abrupt displacement of millions of tons of water. Indonesia villages closest to the epicenter were swamped within minutes, while elsewhere the waves radiated outward, making landfall at speeds topping 500 mph (www.cbsnews.com). The phenomenon we call tsunami is a series of large waves of extremely long wavelength and period usually generated by a violent, impulsive undersea disturbance or activity near the coast or in the ocean. When a sudden displacement of a large volume of water occurs, or if the sea floor is suddenly raised or dropped by an earthquake, big tsunami waves can be formed by forces of gravity. The waves travel out of the area of origin and can be extremely unsafe and destructive when they reach the shore. Often the term, "seismic or tidal sea wave" is used to describe the same phenomenon; however the terms are misleading, because tsunami waves can be generated by other, non seismic disturbances such as volcanic eruptions or underwater landslides, and have physical characteristics different of tidal waves. The tsunami waves are completely unrelated to the astronomical tides - which are caused by the extraterrestrial, gravitational influences of the moon, sun, and the planets. Thus, the Japanese word "tsunami", meaning "harbor wave" is the correct, official and all-inclusive term. It has been internationally adopted because it covers all forms of impulsive wave generation. By far, the most destructive tsunamis are generated from large, shallow earthquakes with an epicenter or fault line near or on the ocean floor. These usually occur in regions of the earth characterized by tectonic subduction along tectonic plate boundaries. The high seismicity of such regions is caused by the collision of tectonic plates. When these plates move past each other, they cause large earthquakes, which
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