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.