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Tsunamis (pronounced soo-ná-mees),
also known as seismic sea waves (mistakenly
called “tidal waves”), are
a series of enormous waves created by an
underwater disturbance such as an earthquake,
landslide, volcanic eruption, or meteorite.
A tsunami can move hundreds of miles per
hour in the open ocean and smash into land
with waves as high as 100 feet or more.
From
the area where the tsunami originates,
waves travel outward in all directions.
Once the wave approaches the shore, it
builds in height. The topography of the
coastline and the ocean floor will influence
the size of the wave. There may be more
than one wave and the succeeding one may
be larger than the one before. That is
why a small tsunami at one beach can be
a giant wave a few miles away. All tsunamis
are potentially dangerous, even though
they may not damage every coastline they
strike. A tsunami can strike anywhere along
most of the U.S. coastline. The most destructive
tsunamis have occurred along the coasts
of California, Oregon, Washington, Alaska,
and Hawaii.
Earthquake-induced
movement of the ocean floor most often
generates tsunamis. If a major earthquake
or landslide occurs close to shore, the
first wave in a series could reach the
beach in a few minutes, even before a warning
is issued. Areas are at greater risk if
they are less than 25 feet above sea level
and within a mile of the shoreline. Drowning
is the most common cause of death associated
with a tsunami. Tsunami
waves and the receding water are very destructive
to structures in the run-up zone. Other
hazards include flooding, contamination
of drinking water,
and fires from gas lines or ruptured tanks.
Familiarize yourself with these terms to
help identify a tsunami hazard:
- Advisory -
An earthquake has occurred in the Pacific
basin, which might generate
a tsunami.
- Watch -
A tsunami was or may have been generated,
but is at least two hours travel time
to the area in Watch status.
- Warning -
A tsunami was, or may have been generated,
which could cause damage; therefore,
people in the warned area are strongly
advised to evacuate.
During a Tsunami
The following are guidelines for what you
should do if a tsunami is likely in your
area:
- Turn on your radio to learn
if there is a tsunami warning if an earthquake
occurs and you are in a coastal area.
- Move inland to higher ground immediately
and stay there.
If there is noticeable recession in water
away from the
shoreline this is nature’s tsunami
warning and it should
be heeded. You should move away immediately.
After
a Tsunami
The following are guidelines for the
period following a tsunami:
- Stay away from flooded and damaged
areas until officials say it is
safe to return.
- Stay away from debris in the water;
it may pose a safety hazard to
boats and people.
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