4. Size of Tsunami
Tsunamis have an extremely long
wavelength (wavelength is the distance
between the crest (top) of one wave and the
crest of the next wave) -- up to several
hundred miles long. The period (the time
between two successive waves) is also very
long -- about an hour in deep water.
In the deep sea, a tsunami's height can be
only about 1 m (3 feet) tall. Tsunamis are
often barely visible when they are in the
deep sea. This makes tsunami detection in
the deep sea very difficult.
5. A tsunami can travel at well
over 970 kph (600 mph) in the
open ocean - as fast as a jet flies.
It can take only a few hours for
a tsunami to travel across an
entire ocean. A regular wave
(generated by the wind) travels
at up to about 90 km/hr.
7. •Tsunami is should not be known as tidal
waves. Tsunamis are sometimes incorrectly
called "tidal waves" -- tsunamis are not caused
by the tides (tides are caused by the
gravitational force of the moon on the sea).
Regular waves are caused by the wind.
•If the first part of a tsunami to reach land is a
trough—called a drawback—rather than a
wave crest, the water along the shoreline
recedes dramatically, exposing normally
submerged areas.
8. •Most tsunamis, about 80 percent, happen within the
Pacific Ocean’s “Ring of Fire,” a geologically active
area where tectonic shifts make volcanoes and
earthquakes common.
•A tsunami may be less than a foot (30 centimeters)
in height on the surface of the open ocean, which is
why they are not noticed by sailors. But the
powerful shock wave of energy travels rapidly
through the ocean as fast as a commercial jet. Once a
tsunami reaches shallow water near the coast, it is
slowed down. The top of the wave moves faster than
the bottom, causing the sea to rise dramatically.
9. •Geological features such as reefs, bays, river
entrances, and undersea formations may dissipate
the energy of a tsunami. In some places a tsunami
may cause the sea to rise vertically only a few
inches or feet
•Flooding can extend inland by a thousand feet (300
meters) or more. The enormous energy of a
tsunami can lift giant boulders, flip vehicles, and
demolish houses. Knowledge of the history of
tsunamis in your area is a good indicator of what is
likely to happen in a future tsunami event.
•The 2004 Indian Ocean tsunami could rank as the
most devastating on record. More than 200,000
people lost their lives, many of them washed out to
sea.
11. • An earthquake is a natural tsunami warning. If you feel a strong
quake do not stay in a place where you are exposed to a tsunami. If
you hear of an earthquake be aware of the possibility of a tsunami
and listen to the radio or television for additional information.
Remember that an earthquake can trigger killer waves thousands of
miles across the ocean many hours after the event generated a
tsunami.
•Witnesses have reported that an approaching tsunami is sometimes
preceded by a noticeable fall or rise in the water level. If you see the
ocean receding unusually rapidly or far it's a good sign that a big
wave is on its way. Go to high ground immediately.
•Many people were killed by the Indian Ocean tsunami because they
went down to the beach to view the retreating ocean exposing the
seafloor. Experts believe that a receding ocean may give people as
much as five minutes' warning to evacuate the area.
• Remember that a tsunami is a series of waves and that the first
wave may not be the most dangerous. The danger from a tsunami can
last for several hours after the arrival of the first wave. A tsunami
wave train may come as a series of surges that are five minutes to an
hour apart. The cycle may be marked by a repeated retreat and
advance of the ocean.
12. •Survivors of the Indian Ocean tsunami reported that the
sea surged out as fast and as powerfully as it came ashore.
Many people were seen being swept out to sea when the
ocean retreated.
•A tsunami surge may be small at one point of the shore
and large at another point a short distance away. Do not
assume that because there is minimal sign of a tsunami in
one place it will be like that everywhere else.
• Tsunamis can travel up rivers and streams that lead to
the ocean. Stay away from rivers and streams that lead to
the ocean as you would stay away from the beach and
ocean if there is a tsunami.
• It's always a good idea to keep a store of emergency
supplies that include sufficient medications, water, and
other essentials sufficient for at least 72 hours. Tsunami,
earthquake, hurricane—an emergency can develop with
little or no warning.
13. Plan for a Tsunami
• Develop a Family Disaster Plan
• Learn about tsunami risk in your
community
• If you are visiting an area at risk
from tsunamis, check with the hotel,
motel, or campground operators for
tsunami evacuation information
• Plan an evacuation route from
your home, school, workplace, or
any other place you'll be where
tsunamis present a risk.
14. • Practice your evacuation route
• Use a NOAA Weather Radio with a
tone-alert feature to keep you
informed of local watches and
warnings.
• Discuss tsunami with your family
• Assemble a Disaster Supplies Kit
15. How to Protect Your Property
• 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.
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.
• 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.
• 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.
16. What to Do After a Tsunami
• Continue listening to a NOAA Weather Radio,
Coast Guard emergency frequency station, or
other reliable source for emergency
information
• Help injured or trapped persons
• Use the telephone only for emergency calls
• Stay out of the building if waters remain
around it
• Examine walls, floors, doors, staircases, and
windows to make sure that the building is
not in danger of collapsing.
• Inspect foundations for cracks or other
damage
17. • Look for fire hazards.
• Check for gas leaks
• Look for electrical system damage.
• Check food supplies. Any food that
has come in contact with flood waters
may be contaminated and should be
thrown out.
