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
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
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.
Know Your Tsunami
Familiarize yourself with these terms to help identify a
- Advisory - An earthquake has occurred in the Pacific
basin, which might generate a tsunami.
- Warning - A tsunami was, or may have been generated,
which could cause damage; therefore, people in the warned
area are strongly advised to evacuate.
- Watch - A tsunami was or may have been generated, but
is at least two hours travel time to the area in Watch
What to do Before and During a
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
- Move inland to higher ground immediately and stay
- Stay away from the beach. Never go down to the beach to
watch a tsunami come in. If you can see the wave you are
too close to escape it.
- CAUTION - 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
What to Do After a
The following are guidelines for the period following a
- 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.
- Save yourself - not your possessions
Much of the info on this page was taken from FEMA's web site
which can be referenced at: