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USGS CMG InfoBank: Tsunami

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Comment: 05:49 - 06:54 (01:05)
Source: Annenberg/CPB Resources - Earth Revealed 24, Waves, Beaches and Coasts
Keywords: "James Sadd", ocean, wave, "seismic sea wave", tsunami, coast, "wave height", "geologic hazard", earthquake, "sea floor", wavelength, "circular orbit", "wave velocity", sediment

Our transcription: Perhaps the ultimate ocean wave is the "seismic sea wave," otherwise known as the "tsunami."
Tsunamis can strike coasts without warning.
With wave heights sometimes exceeding 30 meters.
These waves have a potential for death and destruction that makes them the subject of legend throughout the world.
Unlike ordinary wind-generated waves, tsunamis are caused by a much more powerful force -- earthquakes.
Undersea and coastal earthquakes can cause the ocean floor to shift suddenly.
This movement of the ocean floor displaces a vast volume of the overlying water creating these unusual waves.
Tsunamis are tremendously fast moving, some traveling in excess of 800 kilometers per hour.
The wavelength of a tsunami may be 150 kilometers, and so the movement of the orbiting water particles within the wave will stir up deep sea sediments even in the mid-ocean.
Remarkably, however, such a tsunami may measure only a meter, or so, high in the open ocean.
But as tsunamis approach the coast, they bunch up and rise monster-like from the sea.
In a few minutes a tsunamis can completely devastate a coastal community.

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