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Tsunami,Killer Wave!

Tsunami waves are very different from other ocean waves. Ordinary waves, which are in fact caused by the wind blowing over the water, affect only the surface of the ocean. Water movement due to these wind-generated waves rarely extends below a depth of 500 feet even in large storms. Ordinary wind-generated waves never travel at more than 60 miles per hour and are usually much slower. Tsunami waves, on the other hand, could easily keep pace with a Boeing 747 with speeds that can exceed 700 kilometers per hour (500 miles per hour or more) in the deep ocean. Yet the incredibly fast waves may be only a foot or two high in deep water.
Tsunami waves also have much greater wavelengths. Wind waves are rarely longer than 1,000 feet from crest to crest, but tsunami waves are often an incredibly long 100 miles between crests. With a height of 2 or 3 feet spread out over 1,000 feet miles, the slope of even the most powerful tsunami would be impossible to see from a ship or airplane, passing unnoticed in deep water.
A popular misconception is that there is only one giant wave in a tsunami. On the contrary, a tsunami may consist of 10 or more waves forming what is called a “tsunami wave train”. The individual waves follow one behind the other, anywhere from 5 to 90 minutes apart.

Tsunamis evolve through three overlapping but quite distinct physical processes: generation by any force that disturbs the water column, propagation from deeper water near the source to shallow coastal areas and, finally, inundation of dry land.

Generation is the process by which a sea floor disturbance, such as movement along the fault reshapes the sea surface into a tsunami.

Propagation of the tsunami transports seismic energy away from the earthquake site through undulations of the water. At this point, the wave is so small compared with both the wavelength and the water depth that researchers apply linear wave theory, which assumes that the height itself does not affect the wave’s behavior. The theory predicts that the deeper the water and the longer the wave, the faster the tsunami.

As a tsunami approaches shore, it begins to slow and grow in height. Just like other water waves, tsunamis begin to lose energy as they rush onshore, but despite these losses, tsunamis still reach the coast with tremendous amount of energy. Tsunamis have great erosion potential. Capable of inundating, or flooding, hundreds of meters inland, the fast-moving water associated with the inundating tsunami can crush homes and other coastal structures. Tsunamis may reach a maximum vertical height onshore above sea level, often called run-up height, of 10, 20, and even 30 meters.


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