Tsunamis
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.
Terms to help identify a Tsunami hazard
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 status.
Information
A message with information about an earthquake that is not expected to generate a tsunami.
Usually only one bulletin is issued.
Be familiar with the tsunami warning signs.
A strong earthquake lasting 20 seconds or more near the coast may generate a tsunami.
A noticeable rapid rise or fall in coastal waters is also a sign that a tsunami is approaching.
Tsunamis most frequently come onshore as a rapidly rising turbulent surge of water
choked with debris.
They are not V-shaped or rolling waves and are not "surfable."
Tsunamis may be locally generated or from a distant source.
In 2011, a 9.3 earthquake occurred of the coast of Japan.
The tsunamis triggered from the quake and the thousands of aftershocks
killed thousands in Japan when entire towns were devastated.
The tsunamis hit Hawaii and continued to the coasts of North and South America
(from Alaska to Chile).
Chile's Pacific coast, one of the furthest areas from Japan (11,000 miles),
was struck by waves 6.6 foot high, compared with an estimated wave height
of 128 feet at Omoe peninsula, Miyako city, Japan.
In 2004, a 9.3 earthquake occurred off the coat of the Indonesian island of Sumatra.
A series of tsunamis was triggered which killed 225, 000 people in 11 countries.
In 1992, the Cape Mendocino, California, a 7.1 earthquake produced a tsunami
that reached Eureka in about 20 minutes (a distance of 38 miles), and Crescent City
in 50 minutes (a distance of 84 miles).
This illustrates how quickly a wave can arrive at nearby coastal communities
and how long the danger can last.
Damages were recorded to be $48.3 million.
In 1957, a distant-source tsunami generated by an earthquake in the Aleutian Islands in Alaska struck Hawaii, 2,100 miles away.
Hawaii suffered $5 million in damages.