Coastal
areas in the Cascadia Region are at risk for tsunamis - like the tsunami that
devastated communities around the Indian Ocean after a great earthquake on
Dec. 26, 2004.
Tsunamis on Cascadia are not frequent, but could arise either from a large earthquake on the Cascadia
Subduction Zone,
or from a distant earthquake strong enough to send a tsunami across the ocean.
Tsunami
Escape Route signs have been installed on the coasts of Alaska, Hawaii, Washington, Oregon, Alaska and California.
Although tsunamis do not occur frequently, they can cause a
tremendous amount of damage in coastal areas when they do
happen.
To
learn about the physics of tsunamis and why they happen, visit The
Wave the Shook the World - NOVA's reconstruction of the 2004 tsunami, or
the University
of Washington Tsunami site.
Tsunami!,
a 1999 article from "Scientific American" about tsunamis, inundation modeling and warning systems, provides useful background information.
The National Tsunami Mitigation Program provides a coordinated national effort to assess tsunami threat, prepare community
response, issue timely and effective warnings, and mitigate damage. Tsunami Warnings for the Cascadia coast are generated by the Alaska Tsunami Warning Center.
Every
state in the Cascadia Region has issued a brochure warning
people of the danger of tsunamis and what they can do to avoid
being killed by one. These brochures are linked in the mitigation
section of this site. Some useful information about tsunamis
is available from the Oregon
State brochure about tsunamis and is reproduced below.
This information applies to all coastal areas in the Cascadia
Region. Surviving a Tsunami—Lessons from Chile, Hawaii, and Japan is a USGS pamphlet about well-documented tsunami events in several countries.
WHAT
IS A TSUNAMI (SOO-NAHMEE)?
A tsunami is a series of sea waves usually caused by displacement
of the ocean floor by an undersea earthquake. The waves travel
at speeds up to 600 miles per hour, sometimes crossing the
entire Pacific Ocean. As tsunamis enter shallow water near
land, they increase in height and can cause great loss of
life and property damage where they come ashore. Remember,
a tsunami is not one wave but a series of waves. People have
died when they assumed they were safe because they had survived
one large wave, only to be caught by a later arriving, larger
wave.
WHEN
DOES A TSUNAMI OCCUR?
It can occur any time of day or night after an undersea
earthquake. Experts believe that a tsunami caused by an undersea
earthquake near the coast could strike the coast within 5-30
minutes after the earthquake, before official warning is possible.
Undersea earthquakes thousands of miles away can cause smaller
tsunamis on the Oregon coast but will take several hours to
arrive, generally allowing time for official warning.
WHERE
DO TSUNAMIS OCCUR?
Tsunamis are most common in the Pacific Ocean. People on open
beaches, at low-lying areas of the beach, by bay mouths or
bay tidal flats, in low parts of coastal towns and cities,
and near mouths of rivers draining into the ocean are in greatest
danger from tsunamis.
TSUNAMI
FACTS
- Two kinds of
tsunamis could affect the coast:
1.Tsunamis
generated by undersea earthquakes just off the coast
can strike the coast within five to thirty minutes,
possibly disrupting power lines and communications and
leaving little time for an official warning. The actual
ground shaking of the earthquake may be the only warning
you receive.
2. Tsunamis
generated by earthquakes occurring thousands of miles
away will take several hours to reach the coast. There
would be time for official warning, but if you are in
an isolated area, you may not hear the official warning,
you will feel no earthquake, and the only warning you
may have is a sudden unexpected change in sea level.
If the sea level suddenly drops or rises without any
obvious reason, nature may be warning you of impending
danger, and you should move inland or to high ground
immediately.
- Recent research
shows that at any time the Pacific Northwest can experience
large earthquakes and accompanying tsunamis, and that tsunamis
have affected the coast on a regular basis over time. Scientists
have not yet had time to do local studies that will be able
to tell you how high a tsunami may be in any one area and
how far you must run inland or how high you must climb to
escape. The best general advice available today is to (1)
go up to 2 miles inland if you are in a low-lying area or
at least 100 feet above sea level if you can; and (2) go
on foot if at all possible because of traffic jams and earthquake
damage.
- A tsunami wave
increases in height as it approaches shore. Typical wave
heights from tsunamis occurring in the Pacific over the
last 80 years have been between 21 to 45 feet at the shoreline.
A few waves, however, have been much higher- as much as
100 feet or more because of local conditions. Also, tsunamis
may affect local areas differently, causing great damage
and loss of life in one area but little in another.
Past
Tsunami History
On January 26, 1700, a massive earthquake occurred
off the coast of Washington. The earthquake resulted in a
tsunami which hit Japan's coast with waves up to 10 feet high.
Information about the tsunami is available from many sources, including:
- PNSN - The Pacific Northwest Seismic Network
- PGC - The Canadian Pacific Geoscience Centre
-
The Orphan Tsunami - A book on dating the 1700 Cascadia tsunami using Japanese historic archives;
by Brian Atwater et al.
In
1964, an earthquake along the coast of Alaska caused
a tsunami which affected the coast from Alaska to California
and Hawaii. The 1964 Alaskan tsunami
killed 110 people and destroyed property in many areas along
the coast from Alaska to California. In Washington alone,
this tsunami caused $105,000 in damage. It is important to
note that a tsunami can remain deadly for the duration of
the wave activity, and not just at first impact. The first
and second waves from the 1964 Alaska earthquake struck Crescent City, California
at low tide and did little damage. The third and
fourth waves, however, killed 11 people and caused $7.4 million
in damage.
A description
of the 1964 earthquake and tsunami, including runup information, is available from NOAA.
Another
description is on the University of Washington Tsunami
site.
Tsunami
Hazard Information You Should Know
General
Information
The
following information is taken from a publication
from Humboldt State University:
What
Can I Do Ahead of Time to Protect Myself and My Family From
a Tsunami?
- Make disaster
plans beforehand. Talk to the people you live with about
what may happen during a strong earthquake or other disaster.
If you live or work in a low-lying coastal area, know where
to go to survive a tsunami. Hold earthquake/tsunami drills
at home or at work.
- Assemble a portable
disaster supply kit. Have a kit available in your car, at
home and at work. Your kit should include a portable radio
with fresh batteries, water, first aid supplies, flashlight,
and extra clothes or a blanket. Put your kit in a backpack
and leave it in an easy-to-reach place.
- Contact local
emergency officials. Find out what areas are most vulnerable
to tsunami hazards, which areas are safe, and which routes
are best for evacuation.
- Take a first
aid class. Learn survival skills, talk with your family,
friends and neighbors. Knowledge is your greatest defense
against any potential disaster.
IF YOU FEEL
A STRONG EARTHQUAKE WHICH LASTS A LONG TIME WHEN YOU ARE ON
THE COAST:
- Protect yourself
during the earthquake. Duck, cover and hold if inside
and watch for falling objects if outside until the earthquake
is over.
- Move to
higher ground immediately. Gather your family members
and evacuate quickly. Leave everything else behind. A tsunami
may be coming within minutes. Go on foot if at all possible.
If there is no high ground, move inland away from the coastline.
DO NOT WAIT FOR AN OFFICIAL WARNING
- Stay away
from the coast. A later wave may be higher than the
first! Damaging waves may continue to arrive even hours
later.
- Listen to
your radio. Wait until an official all clear signal
has been given before returning to low-lying areas.
- Never go to
the coast to watch for a tsunami if you hear that a warning
has been issued. Tsunamis move faster than a person can
run. Also, incoming traffic hampers safe and timely evacuation
of coastal areas.
- Tsunamis are
not surfable! They are not V-shaped or curling waves. Most
frequently they come onshore as a rapidly-rising turbulent
surge of water choked with debris.
- All tsunamis
- like hurricanes - are potentially dangerous, even though
they may not damage every coastline they strike.
- An earthquake
in your area is a natural tsunami warning. Do not stay in
low-lying coastal areas after a strong earthquake has been
felt.
Damaging tsunamis
are very rare. Our coastlines are vulnerable but tsunamis
are infrequent. Understand the hazard and learn how to protect
yourself, but don't let the threat of tsunamis ruin your enjoyment
of the beach.
General Links for All areas
Information
for British Columbia
Information
for California
Information
for Oregon
Information
for Washington
