Tsunami
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Twenty-four tsunamis have caused damage in the United States and its
territories 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. As a tsunami
nears the coastline, it may rise to several feet or, in rare cases, tens
of feet, and can cause great loss of life and property damage when it comes
ashore. Tsunamis can travel upstream in coastal estuaries and rivers,
with damaging waves extending farther inland than the immediate coast.
A
tsunami can occur during any season of the year and at any time, day or
night.
What Are Tsunamis, and What Causes Them?
Tsunamis are ocean waves produced by earthquakes or underwater landslides.
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 often incorrectly referred to as tidal waves, but a tsunami
is actually a series of waves that can travel at speeds averaging 450
(and up to 600) miles per hour in the open ocean. In the open ocean,
tsunamis would not be felt by ships because the wavelength would be hundreds
of miles long, with an amplitude of only a few feet. This would also make
them unnoticeable from the air. As the waves approach the coast, their
speed decreases and their amplitude increases. Unusual wave heights
have been known to be over 100 feet high. However, waves that are 10
to 20 feet high can be very destructive and cause many deaths or injuries.
Tsunamis are most often generated by earthquake-induced movement
of the ocean floor. Landslides, volcanic eruptions, and even meteorites
can also generate a tsunami. If a major earthquake is felt, a tsunami could
reach the beach in a few minutes, even before a warning is issued. Areas
at greatest risk are less than 25 feet above sea level and within one mile
of the shoreline. Most deaths caused by a tsunami are because of drowning.
Associated
risks include flooding, contamination of drinking water, fires from ruptured
tanks or gas lines, and the loss of vital community infrastructure (police,
fire, and medical facilities).
From an initial tsunami generating source area, waves travel outward
in all directions much like the ripples caused by throwing a rock into
a pond. As these waves approach coastal areas, the time between successive
wave crests varies from 5 to 90 minutes. The first wave is usually not
the largest in the series of waves, nor is it the most significant. Furthermore,
one coastal community may experience no damaging waves while another, not
that far away, may experience destructive deadly waves. Depending on a
number of factors, some low-lying areas could experience severe inland
inundation of water and debris of more than 1,000 feet.
Learn whether tsunamis have occurred in your area by contacting your
local emergency management office, National Weather Service office, or
American
Red Cross chapter. If you are in a tsunami risk area, learn how
to protect yourself, your family, and your property.
Awareness Information
The West Coast/Alaska Tsunami
Warning Center (WC/ATWC) is responsible for tsunami warnings for
California, Oregon, Washington, British Columbia, and Alaska.
The Pacific Tsunami Warning Center (PTWC) is responsible for
providing warnings to international authorities, Hawaii, and U. S. territories
within the Pacific basin. The two Tsunami Warning Centers coordinate the
information being disseminated.
All tsunamis are potentially dangerous, even though they may not
damage every coastline they strike. 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.
The WC/ATWC and PTWC may issue the following bulletins:
-
WARNING: A tsunami was or may have been generated, which could cause
damage; therefore, people in the warned area are strongly advised to evacuate.
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WATCH: A tsunami was or may have been generated, but is at least
two hours travel time to the area in watch status. Local officials should
prepare for possible evacuation if their area is upgraded to a warning.
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ADVISORY: An earthquake has occurred in the Pacific basin, which
might generate a tsunami. WC/ATWC and PTWC will issue hourly bulletins
advising of the situation.
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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
1992, the Cape Mendocino, California, earthquake produced a tsunami that
reached Eureka in about 20 minutes, and Crescent City in 50 minutes. Although
this tsunami had a wave height of about one foot and was not destructive,
it illustrates how quickly a wave can arrive at nearby coastal communities
and how long the danger can last.
In 1957, a distant-source tsunami generated by an earthquake in
the Aleutian Islands in Alaska struck Hawaii, 2,100 miles away. Hawaii
experienced $5 million in damages from that tsunami.
Plan for a Tsunami
Develop a Family Disaster Plan. Please see the "Family
Disaster Plan" section for general family
planning information. Tsunami-specific planning should include the following:
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Learn about tsunami risk in your community. Contact your local emergency
management office or American
Red Cross chapter. Find out if your home, school, workplace or other
frequently visited locations are in tsunami hazard areas. Know the height
of your street above sea level and the distance of your street from the
coast or other high-risk waters. Evacuation orders may be based on these
numbers.
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If you are visiting an area at risk from tsunamis, check with the hotel,
motel, or campground operators for tsunami evacuation information and how
you would be warned. It is important to know designated escape routes
before a warning is issued.
If you are at risk from tsunamis, do the following:
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Plan an evacuation route from your home, school, workplace, or any other
place you'll be where tsunamis present a risk. If possible, pick an
area 100 feet above sea level or go up to two miles inland, away from the
coastline. If you can't get this high or far, go as high as you can. Every
foot inland or upwards may make a difference. You should be able to reach
your safe location on foot within 15 minutes. After a disaster, roads may
become impassable or blocked. Be prepared to evacuate by foot if necessary.
Footpaths normally lead uphill and inland, while many roads parallel coastlines.
Follow posted tsunami evacuation routes; these will lead to safety. Local
emergency management officials can help advise you as to the best route
to safety and likely shelter locations.
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Practice your evacuation route. Familiarity may save your life.
Be able to follow your escape route at night and during inclement weather.
Practicing your plan makes the appropriate response more of a reaction,
requiring less thinking during an actual emergency situation.
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Use a NOAA Weather Radio with a tone-alert feature to keep you informed
of local watches and warnings. The tone alert feature will warn you
of potential danger even if you are not currently listening to local radio
or television stations.
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Talk to your insurance agent. Homeowners' policies do not cover
flooding from a tsunami. Ask about the National Flood Insurance Program.
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Discuss tsunami with your family. Everyone should know what to do
in case all family members are not together. Discussing tsunamis ahead
of time will help reduce fear and anxiety, and let everyone know how to
respond. Review flood safety and preparedness measures with your family.
Assemble a Disaster Supplies Kit
Please see the section "Disaster Supplies Kit"
for general supplies kit information. Tsunami-specific supplies should
include the following:
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Evacuation Supplies Kit in an easy-to-carry contanier (backpack) near
your door.
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Disaster Suplies Kit basics.
How to Protect Your Property
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Avoid building or living in buildings within several hundred feet of
the coastline. These areas are more likely to experience damage from
tsunamis, strong winds, or coastal storms.
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Make a list of items to bring inside in the event of a tsunami.
A list will help you remember anything that can be swept away by tsunami
waters.
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Elevate coastal homes. Most tsunami waves are less than 10 feet.
Elevating your house will help reduce damage to your property from most
tsunamis.
-
Follow flood preparedness precautions.
Tsunamis are large amounts of water that crash onto the coastline, creating
floods.
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Have an engineer check your home and advise about ways to make it more
resistant to tsunami water. There may be ways to divert waves away
from your property. Improperly built walls could make your situation worse.
Consult with a professional for advice.
Media and Community Education Ideas
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If your community is at risk, build and publicize locations of tsunami
evacuation routes. Post signs directing people to higher ground away
from the coast.
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Review land use in tsunami hazard areas so no critical facilities,
such as hospitals and police stations; or high occupancy buildings, such
as auditoriums or schools; or petroleum-storage tank farms are located
where there is a tsunami hazard. Tsunami damage can be minimized through
land use planning, preparation, and evacuation.
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Publish a special section in your local newspaper with emergency information
on tsunamis. Localize the information by printing the phone numbers
of local emergency services offices, the American Red Cross chapter, and
hospitals.
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Periodically inform your community of local public warning systems.
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Work with local emergency services and American Red Cross officials
to prepare special reports for people with mobility impairments on what
to do if an evacuation is ordered, and develop plans to assist them with
evacuation if necessary.
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Interview local officials and insurance companies about the proper
types of insurance to cover a flood-related loss. Include information on
the economic effects of disaster.
What to Do if You Feel a Strong Coastal Earthquake
If you feel an earthquake that lasts 20 seconds or longer when
you are on the coast:
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Drop, cover, and hold on. You should first protect yourself from
the earthquake.
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When the shaking stops, gather your family members and evacuate quickly.
Leave everything else behind. A tsunami may be coming within minutes.
Move
quickly to higher ground away from the coast.
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Be careful to avoid downed power lines and stay away from buildings
and bridges from which heavy objects might fall during an aftershock.
What to Do When a Tsunami WATCH is Issued
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Listen to a NOAA Weather Radio, Coast Guard emergency frequency station,
or other reliable source for updated emergency information. As the
energy of a tsunami is transferred through open water, it is not detectable.
Seismic action may be the only advance warning before the tsunami approaches
the coastline.
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Check your Disaster Supplies Kit. Some supplies may need to be replaced
or restocked.
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Locate family members and review evacuation plans. Make sure everyone
knows there is a potential threat and the best way to safer ground.
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If you have special evacuation needs (small children, elderly people,
or persons with disabilities) consider early evacuation. Evacuation
may take longer, allow extra time.
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If time permits, secure unanchored objects around your home or business.
Tsunami waves can sweep away loose objects. Securing these items or moving
them inside will reduce potential loss or damage.
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Be ready to evacuate. Being prepared will help you to move more
quickly if a tsunami warning is issued.
What to Do When a Tsunami WARNING is Issued
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Listen to a NOAA Weather Radio, Coast Guard emergency frequency station,
or other reliable source for updated emergency information. Authorities
will issue a warning only if they believe there is a real threat from tsunami.
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Follow instructions issued by local authorities. Recommended evacuation
routes may be different from the one you use, or you may be advised to
climb higher.
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If you are in a tsunami risk area, do the following:
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If you hear an official tsunami warning or detect signs of a tsunami,
evacuate at once. A tsunami warning is issued when authorities are
certain that a tsunami threat exists, and there may be little time to get
out.
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Take your Disaster Supplies Kit. Having supplies will make you more
comfortable during the evacuation.
-
Get to higher ground as far inland as possible. Officials cannot
reliably predict either the height or local effects of tsunamis. Watching
a tsunami from the beach or cliffs could put you in grave danger. If you
can see the wave, you are too close to escape it.
Return home only after local officials tell you it is safe. A tsunami
is a series of waves that may continue for hours. Do not assume that
after one wave the danger is over. The next wave may be larger than
the first one.
What to Do After a Tsunami
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Continue listening to a NOAA
Weather Radio, Coast Guard emergency frequency station, or other reliable
source for emergency information. The tsunami may have damaged roads,
bridges, or other places that may be unsafe.
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Help injured or trapped persons. Give first aid where appropriate.
Call for help. Do not move seriously injured persons unless they are in
immediate danger of further injury.
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Help a neighbor who may require special assistance - infants, elderly
people, and people with disabilities. Elderly people and people with
disabilities may require additional assistance. People who care for them
or who have large families may need additional assistance in emergency
situations.
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Use the telephone only for emergency calls. Telephone lines are
frequently overwhelmed in disaster situations. They need to be clear for
emergency calls to get through.
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Stay out of the building if waters remain around it. Tsunami waters,
like flood waters, can undermine foundations, causing buildings to sink,
floors to crack, or walls to collapse.
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When re-entering buildings or homes, use extreme caution. Tsunami-driven
flood waters may have damaged buildings where you least expect it. Carefully
watch every step you take.
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Wear sturdy shoes. The most common injury following a disaster is
cut feet.
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Use battery-powered lanterns or flashlights when examining buildings.
Battery-powered lighting is the safest and easiest, preventing fire hazard
for the user, occupants, and building.
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Examine walls, floors, doors, staircases, and windows to make sure that
the building is not in danger of collapsing.
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Inspect foundations for cracks or other damage. Cracks and damage
to a foundation can render a building uninhabitable.
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Look for fire hazards. There may be broken or leaking gas lines,
flooded electrical circuits, or submerged furnaces or electrical appliances.
Flammable or explosive materials may come from upstream. Fire is the most
frequent hazard following floods.
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Check for gas leaks. If you smell gas or hear a blowing or hissing
noise, open a window and quickly leave the building. Turn off the gas using
the outside main valve if you can, and call the gas company from a neighbor's
home. If you turn off the gas for any reason, it must be turned back on
by a professional.
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Look for electrical system damage. If you see sparks or broken or
frayed wires, or if you smell burning insulation, turn off the electricity
at the main fuse box or circuit breaker. If you have to step in water to
get to the fuse box or circuit breaker, call an electrician first for advice.
Electrical equipment should be checked and dried before being returned
to service.
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Check for sewage and water line damage. If you suspect sewage lines
are damaged, avoid using the toilets and call a plumber. If water pipes
are damaged, contact the water company and avoid using water from the tap.
You can obtain safe water from undamaged water heaters or by melting ice
cubes.
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Use tap water if local health officials advise it is safe.
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Watch out for animals, especially poisonous snakes, that may have come
into buildings with the water. Use a stick to poke through debris.
Tsunami flood waters flush snakes and animals out of their homes.
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Watch for loose plaster, drywall, and ceilings that could fall.
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Take pictures of the damage, both of the building and its contents,
for insurance claims.
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Open the windows and doors to help dry the building.
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Shovel mud while it is still moist to give walls and floors an opportunity
to dry.
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Check food supplies. Any food that has come in contact with flood
waters may be contaminated and should be thrown out.
Produced by the National Disaster Education Coalition:
American
Red Cross, FEMA,
IAEM,
IBHS,
NFPA,
NWS,
USDA/CSREES,
and USGS. HTML formating By the
Disaster Center
From: Talking About Disaster: Guide for Standard Messages. Produced
by the National Disaster Education Coalition, Washington, D.C., 1999.