Long wavelength seismic sea waves generated by
the sudden displacement of the seafloor. The name is of
Japanese origin, meaning “harbor wave.” Tsunami are also
commonly called tidal waves, although this is improper
because they have nothing to do with tides. Tsunami may rise
unexpectedly out of the ocean and sweep over coastal communities,
killing hundreds of people and causing millions of
dollars in damage. Such events occurred in 1946, 1960,
1964, 1992, 1993, and 1998 in coastal Pacific areas. In 1998
a catastrophic 50-foot (15-m) high wave unexpectedly struck
Papua New Guinea, killing more than 2,000 people and leaving
more than 10,000 homeless. The December 2004 Indian
Ocean tsunami killed approximately 300,000 people, making
it the most destructive tsunami known in history.
Tsunami are generated most often by thrust earthquakes
along deep-ocean trenches and convergent plate
boundaries. Tsunami therefore occur most frequently along
the margins of the Pacific Ocean, a region characterized by
numerous thrust-type earthquakes. About 80 percent of all
tsunami strike circum-Pacific shorelines, with the most
being generated in and striking southern Alaska. Volcanic
eruptions, giant submarine landslides, and the sudden
release of gases from sediments on the seafloor may also
generate tsunami. Tsunami are not rare on Pacific islands
including Hawaii and Japan, which now have extensive
warning systems in place to alert residents when they are
likely to occur. Before these warning systems were in place,
residents would have no warning when the tsunami, in
some cases reaching 50 feet or more in height. would occasionally
strike coastal areas.
Some historical tsunami have been absolutely devastating
to coastal communities, wiping out entire populations
with little warning. One of the most devastating tsunami in
recent history was generated by the eruption of the Indonesian
volcano Krakatau in 1883. When Krakatau erupted, it
blasted a large part of the center of the volcano out, and seawater
rushed in to fill the hole. This seawater was immediately
heated and it exploded outward in a steam eruption and a
huge wave of hot water. The tsunami generated by this eruption
reached more than 120 feet (37 m) in height and killed
more than 36,500 people in nearby coastal regions. Another
famous tsunami was also generated by a volcanic eruption of
Santorin (now called Thira) on the Mediterranean island of
Crete. In 1600 B.C.E., this volcano was the site of the most
powerful eruption in recorded history, and it generated a
tsunami that destroyed many Mediterranean coastal areas
and probably led to the eventual downfall of the Minoan civilization
on Crete. The tsunami deposited volcanic debris at
elevations of up to 800 feet (245 m) above the mean ocean
level on the nearby island of Anaphi, and the wave was still
more than 20 feet (6 m) high when it ran up the shorelines on
the far side of the Mediterranean in Israel.
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