The Natural Destructive Forces of Tsunami

Other things which contribute to the size of a tsunami are: shoreline and bathymeteric configuration, the velocity of the seafloor deformation, the water depth near the earthquake source, and the efficiency at which energy is transferred from the earth"s crust to the water column.

             Submarine landslides, which often accompany large earthquakes, as well as collapses of volcanic edifices, can also disturb the overlying water column, as sediment and rock slide downward and are redistributed across the sea floor. Similarly, a violent submarine volcanic eruption can create an impulsive force that uplifts the water column and generates a tsunami. Conversely, supermarine landslides and cosmic-body impacts disturb the water from above, as momentum from falling debris is transferred to the water. Generally speaking, tsunami generated from these mechanisms, unlike the Pacific-wide tsunami caused by some earthquakes, dissipate quickly and rarely affect coastlines distant from the source area.

             Tsunami differ from wind-generated waves, which can be observed on a local lake or at a coastal beach, in that they are characterized as shallow-water waves with long periods and wavelengths. The wind-generated swells that can be observed at any California beach might have a period of about 10 seconds and a wavelength of 150 m. A tsunami, on the other hand, can have a wavelength in excess of 100 km and period on the order of one hour. As the tsunami crosses the deep ocean its height from crest to trough will only be a few feet or less. They can not be felt aboard ships nor can they be seen from the air in the open ocean.

             As a result of their extremely long wavelengths, tsunami behave like shallow-water waves. A wave becomes a shallow-water wave when the ratio between the water depth and its wavelength gets very small. Shallow-water waves move at a speed that is equal to the square root of the product of the acceleration of gravity (9.

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