Tsunamis

A tsunami is a series of massives waves that occur in the worlds oceans when the water is rapidly displaced on a massive scale. Such phenomena like earthquakes, mass movements (both above and below the water), landslides, volcanic eruptions (or other underwater explosions) or large meteorite impacts have the potential to cause such tragic events. After effects of tsunamis can range anywhere from unnoticeable to devastating. A tsunami usually has a very small amplitude offshore but a vey large wavelength, which is why one can vertually pass unnoticeable in the open sea. A tsunami is usually much larger then a regular tidal wave, but they pass through and around any obsticle that comes in their way. The most damage that occurs is usually by the huge mass of water behind the initial wave front. Tsunamis contain immense amounts of energy, can propagate at high speeds and travel far distances, which means they can cause damage several kilometers away from their place of origin. The height of a tsunami wave in open water is only about 1m, very unnoticeable to seaman in a boat, but they travel at speeds somewheres between 400-500 mph due to the deepness of the ocean water. When a tsunami begins to reach land, the sea begins to get shallower and the tsunami slows down. As it slows down it begins to 'pile-up'. The waves become steeper and taller and the distance bewteen sucsessive crests is shorter. A stunami wave can reach heights of 6 stories or more as in gets cloder to the coastline and compresses. Unfortunately, there are no signs or warnings of tsunamis, but if an earthquake is felt near a body of water that could be considered a sign of one in the making.

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~http://en.wikipedia.org/wiki/Tsunami