《Erik Bender-Tsunami !》.pptVIP

Tsunami ! A tsunami (sue-naa-me) is scientifically described as a series of very long wavelength ocean waves caused by the sudden displacement of water by earthquakes, landslides, or submarine slumps and are mostly caused by earthquakes of magnitude 7.5 or greater. Undersea landslides and volcanic eruptions can also cause tsunamis. They travel in the open ocean at speeds of 600-800 kilometers per hour, but with wave heights of just a few centimeters. As they approach shallow water they begin to slow down and their wave heights may increase by several meters. Though devastating, this kind of a tsunami is very rare. Much more common are tsunamis that strike in the form of a steadily rising high tide. There are no towering wave and the water rises rapidly, flooding low-lying areas, then receding. Often wrongly referred to as Tidal Waves they have nothing to do with tides!  The largest know tsunami in recent times occurred in the Pacific Ocean in 1960 and was spawned by an MW9.5 earthquake in Southern Chile. It caused damage and casualties in many countries along the Pacific Rim, as far as Japan. The eruption of Krakatau in 1883 caused a great tsunami in the Indian Ocean which killed 35,000 people. It affected harbors at Chennai and Colombo and as far as the Cape of Good Hope. In the Alaskan Earthquake of 1964 a section of seafloor more than four hundred miles long and one hundred miles across suddenly arched upward, forcing the overlying water upward and outward as if the seafloor were a giant paddle. Although this happened almost instantaneously, it was not the speed of the uplift but the sheer volume of water displaced that produced the powerful tsunami. A tsunami generated by a sudden change in the deep ocean floor is a wave that extends from the sea surface to the bottom, miles below. The wave travels at great speed, 500 miles an hour or faster, depending on the depth of water. The waves traveling down the coast are slower than those in the open sea, so that t