M A S T E R P A G E
The depth of the ocean water also controls the speed of seismic sea waves. As the depth changes, the wave’s
speed and direction change, resulting in the phenomenon we call refraction—the change in direction of a wave as
it moves from one medium to another.
Extensive international cooperation has developed a tsunami early warning system for the Pacific Islands. A
system for the U.S. Pacific Coast is being developed. The older system is centered at the Pacific Tsunami
Warning Center in Honolulu, where data are collected from seismic observatories across the globe. The Center
evaluates the potential of a tsunami and institutes special observations at various tsunami watch stations. All these
data are verified and emergency preparation procedures are put into effect when necessary.
Causes Other Than Earthquakes
Not all destructive sea waves are caused by earthquakes. Some are caused by landslides and volcanic eruptions
and some are artificially created by events like underwater nuclear explosions. In 1883, the Krakatoa Island
volcano erupted, blowing the island away down to a depth of about 43 m below sea level. This event caused giant
waves that killed some 36,000 people in Java and Sumatra.
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