Twenty-four tsunamis have caused damage in the United States and its territories alone
during the last 204 years.
Just since 1946, six tsunamis have killed more than 350 people and caused
a half billion dollars of property damage in Hawaii, Alaska, and the West Coast.
Tsunamis (pronounced soo-ná-mees) are also known as seismic sea waves.
The word is Japanese and means "Harbor Wave" because of the devastating effects
these waves have had on low lying Japanese coastal communities.
Tsunamis are mistakenly called "tidal waves".
Tsunamis are a series of enormous waves created by an underwater disturbance
such as an earthquake, landslide, meteorite or volcanic eruption.
The waves can travel at speeds averaging 450 miles per hour but can reach speeds
up to 600 miles per hour.
In the open ocean, tsunamis are not felt by ships because the wave lengths are
hundreds of miles long, with an amplitude of only a few hundred feet.
As the waves approach land, their speeds decrease and their amplitudes increase.
The topography of the coastline and the ocean floor will influence the size of the wave.
Waves can reach 100 feet high, however waves that are 10 to 20 feet high
can be very destructive and cause many deaths and injuries.
There may be more than one wave and the succeeding wave may be larger than the one before it.
A small tsunami at one beach can be a giant wave a few miles away.
If a major earthquake is felt, a tsunami could reach land in a few minutes,
even before a warning is issued.
All tsunamis are potentially dangerous.
Even though they may not damage every coastline they strike.
A tsunami can strike anywhere along most of the United States coastline.
The most devastating tsunamis have occurred along the coasts of Alaska,
Washington, Oregon, California and Hawaii.
Areas at greatest risk are less than 25 feet above sea level and within one mile of the shoreline.
A tsunami can travel upstream in coastal estuaries and rivers, with damaging waves
extending farther inland than the immediate coast.
Tsunamis can occur during any season of the year, and at any time of the day or night.
Most deaths caused by a tsunami are due to drowning.
Other risks include flooding, contamination of the drinking water supplies and fires
from ruptured tank and gas lines.