Date Source Location Estimated
Lives Lost
29 Nov 1975 Hawaii, USA 2
17 Aug 1976 Philippines *8,000
19 Aug 1977 Indonesia 189
18 Jul 1979 Indonesia 540
12 Sep 1979 New Guinea 100
12 Dec 1979 Colombia 500
26 May 1983 Sea of Japan 100
2 Sep 1992 Nicaragua 168
12 Dec 1992 Flores Is., Indonesia 1,000
12 Jul 1993 Okushiri Is., Japan 230
3 Jun 1994 Java, Indonesia 222
4 Oct 1994 Shikotan Is., Russia 11
14 Nov 1994 Philippines 74
9 Oct 1995 Manzanillo, Mexico 1
1 Jan 1996 Sulawesi, Indonesia 9
17 Feb 1996 Irian Jaya, Indonesia 110
23 Feb 1996 Peru 12
17 July 1998 Papua New Guinea 2,500
* May include earthquake casualties

Characteristics of the Tsunami Phenomena
A tsunami travels outward from the source region as
a series of waves. Its speed depends upon the depth
of the water, and consequently the waves undergo
accelerations or decelerations in passing respectively
over an ocean bottom of increasing or decreasing
depth. By this process the direction of wave propagation
also changes, and the wave energy can become
focused or defocused. In the deep ocean, tsunami
waves can travel at speeds of 500 to 1,000 kilometers
per hour. Near shore, however, a tsunami slows down
to just a few tens of kilometers per hour. The height
of a tsunami also depends upon the water depth. A
tsunami that is just a meter in height in the deep
ocean can grow to tens of meters at the shoreline.
Unlike familiar wind-driven ocean waves that are
only a disturbance of the sea surface, the tsunami
wave energy extends to the ocean bottom. Near
shore, this energy is concentrated in the vertical direction
by the reduction in water depth, and in the
horizontal direction by a shortening of the wavelength
due to the wave slowing down.
Tsunamis have periods (the time for a single wave
cycle) that may range from just a few minutes to as
much as an hour or exceptionally more. At the shore,
a tsunami can have a wide variety of expressions depending
on the size and period of the waves, the
near-shore bathymetry and shape of the coastline, the
state of the tide, and other factors. In some cases a
tsunami may only induce a relatively benign flooding
of low-lying coastal areas, coming onshore similar to
a rapidly rising tide. In other cases it can come onshore
as a bore - a vertical wall of turbulent water that
can be very destructive. In most cases there is also a
drawdown of sea level preceding crests of the tsunami
waves that results in a receding of the shoreline, sometimes
by a kilometer or more. Strong and unusual ocean
currents may also accompany even small tsunamis.
Destruction from tsunamis is the direct result of three factors:
inundation, wave impact on structures, and erosion.
Strong tsunami-induced currents have led to the erosion
of foundations and the collapse of bridges and seawalls.
Flotation and drag forces have moved houses and overturned
railroad cars. Tsunami associated wave forces
have demolished frame buildings and other structures.
Considerable damage also is caused by the resultant
floating debris, including boats and cars that become dangerous
projectiles that may crash into buildings, piers,
and other vehicles. Ships and port facilities have been
damaged by surge action caused by even weak tsunamis.
Fires resulting from oil spills or combustion from damaged
ships in port, or from ruptured coastal oil storage
and refinery facilities, can cause damage greater than that
inflicted directly by the tsunami. Other secondary damage
can result from sewage and chemical pollution following
the destruction. Damage of intake, discharge, and
storage facilities also can present dangerous problems. Of
increasing concern is the potential effect of tsunami
drawdown, when receding waters uncover cooling water
intakes associated with nuclear plants.
air-coupled tsunami Synonym for atmospheric tsunami.
atmospheric tsunami Tsunami-like waves generated by
a rapidly moving atmospheric pressure front moving
over a shallow sea at about the same speed as the
waves, allowing them to couple.
internal tsunami Tsunami wave manifested as an internal
wave and traveling along a thermocline.
local tsunami A tsunami which its destructive effects
are confined to coasts within a hundred km, of the
source, usually an earthquake and sometimes a landslide.
microtsunami A tsunami of such small amplitude that it
must be observed instrumentally and is not easily detected
visually.
near-field or local tsunami A tsunami from a nearby
source, generally less than 200 km away. A local tsunami
is generated by a small earthquake, a landslide
or a pyroclastic flow.
Numerical Modeling: snapshots of the water surfaces 10 minutes after
the initiation of the submarine landslide of the pyroclastic flow
(on the South-East part of Monserrat Island)
Pacific-wide tsunami A tsunami capable of widespread
destruction, not only in the immediate region of its generation, but across the entire Pacific Ocean
paleotsunami Research on paleotsunamis, events occurring
prior to the historical record, has recently been
taking place in a few regions around the Pacific. This
work is based primarily on the collection and analysis
of tsunami deposits found in coastal areas, and other
evidence related to the uplift or subsidence associated
with nearby earthquakes. In one instance, the research
has led to a new concern for the possible future occurrence
of great earthquakes and tsunamis along the
northwest coast of North America. In another instance,
the record of tsunamis in the Kuril-Kamchatka region
is being extended much further back in time. As work
in this field continues it may provide a significant
amount of new information about past tsunamis to aid
in the assessment of the tsunami hazard.
regional tsunami A tsunami capable of destruction in a
particular geographic region, generally within about
1000 km of its source. Regional tsunamis also occasionally
have very limited and localized effects outside
the region.
Most destructive tsunami can be classified as local or
regional, meaning their destructive effects are confined
to coasts within a hundred km, or up to a thousand
km, respectively, of the source -- usually an
earthquake. It follows that the majority of tsunami related
casualties and property damage also come from
local tsunami. Between 1975 and 1998 there have
been at least eighteen in the Pacific and its adjacent
seas resulting in significant casualties and/or property
damage.

Fiction: Tsunamis are giant walls of water.
Facts: Tsunamis normally have the appearance of a fast-rising and fast-receding flood. They
can be similar to a tide cycle occurring over 10 to 60 minutes instead of 12 hours. Occasionally,
tsunamis can form walls of water, known as tsunami bores, when the waves are high enough
and the shoreline configuration is appropriate.
Fiction: A tsunami is a single wave.
Facts: A tsunami is a series of waves. Often the initial wave is not the largest. The largest wave
may occur several hours after the initial activity starts at a coastal location. There may also be
more than one series of tsunami waves if a very large earthquake triggers local landslides. In
1964, the town of Seward, Alaska, was devastated first by local tsunamis caused by submarine
landslides resulting from the earthquake and then by the earthquake’s main tsunami. The local
tsunamis began even as people were still experiencing the shaking. The main tsunami,
triggered at the site of the earthquake, did not arrive for several hours.
Fiction: Boats should move to the protection of a bay or harbor during a tsunami.
Facts: Tsunamis are often most destructive in bays and harbors, not just because of the waves
but because of the violent currents they

• If your community is at risk, build tsunami evacuation routes and publicize their
locations. Post signs directing people to higher ground away from the coast.
• Review land use in tsunami hazard areas so no new critical facilities, such as hospitals
and police stations; high-occupancy buildings, such as auditoriums or schools; or
petroleum-storage tank farms are built where there is a tsunami hazard. Consider
relocating existing critical facilities outside the tsunami hazard area when opportunities
arise, or at least explore ways to reinforce facilities and structures, such as critical
bridges needed for evacuation. Tsunami damage can be minimized through land use
planning, preparation, and evacuation.
• Ask your local newspaper or radio or television station to:
-Do a series on the dangers of tsunamis and floods.
-Do a story featuring interviews with local officials about land use
management and building codes in floodplains.
-Highlight the importance of staying informed about local
conditions.
-Run public service ads about how to protect lives and property in
a tsunami.
Help the reporters to localize the information by providing them with the local emergency
telephone number for the fire, police, and emergency medical services departments
(usually 9-1-1) and emergency numbers for the local utilities and hospitals. Also provide
the business telephone numbers for the local emergency management office, local
American Red Cross chapter, and state geological survey or department of natural
resources.
• Work with officials of the local fire, police, and emergency medical services departments;
utilities; hospitals; emergency management office; and American Red Cross chapter to
prepare and disseminate guidelines for people with mobility impairments about what to
do if they have to evacuate.
• Periodically inform your community about local public warning systems.
• Interview local officials and insurance companies about the types of insurance that cover
flood-related losses. Include information on the economic effects of disaster.

After a tsunami, you should:
• Continue using a NOAA Weather Radio or staying tuned to a Coast Guard
emergency frequency station or a local radio or television station for updated
emergency information. The tsunami may have damaged roads, bridges, or other
places that may be unsafe.
• Check yourself for injuries and get first aid if necessary before helping injured or
trapped persons.
CORE ACTION MESSAGES
• Stay informed.
• Climb to higher ground.
If you cannot escape a wave, climb onto a roof or
up a tree, or grab a floating object and hang on until
help arrives. Some people have survived tsunami
waves by using these last-resort methods.
CORE ACTION MESSAGES
• Stay informed.
• Take care of yourself and help others.
• Watch for hazards.
Tsunamis
July 2004
Talking About Disaster: Guide for Standard Messages
Produced by the National Disaster Education Coalition, Washington, D. C.
TN-7
• If someone needs to be rescued, call professionals with the right equipment to
help. Many people have been killed or injured trying to rescue others in flooded areas.
• Help people who require special assistance—infants, elderly people, those without
transportation, large families who may need additional help in an emergency situation,
people with disabilities, and the people who care for them.
• Avoid disaster areas. Your presence might hamper rescue and other emergency
operations and put you at further risk from the residual effects of floods, such as
contaminated water, crumbled roads, landslides, mudflows, and other hazards.
• 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.
• Stay out of a building if water remains around it. Tsunami water, like floodwater, can
undermine foundations, causing buildings to sink, floors to crack, or walls to collapse.
• When re-entering buildings or homes, use extreme caution. Tsunami-driven
floodwater may have damaged buildings where you least expect it. Carefully watch
every step you take.
• Wear long pants, a long-sleeved shirt, and sturdy shoes. The most common injury
following a disaster is cut feet.
• Use battery-powered lanterns or flashlights when examining buildings. Batterypowered
lighting is the safest and easiest to use, and it does not present a fire hazard
for the user, occupants, or building. DO NOT USE CANDLES.
• 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. Cracks and damage to a foundation
can render a building uninhabitable.
• 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 have come from upstream. Fire is the most frequent hazard following
floods.
• Check for gas leaks. If you smell gas or hear a blowing or hissing noise, open a
window and get everyone outside quickly. 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.
• 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.
• Check for damage to sewage and water lines. 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 that were made before the tsunami
hit. Turn off the main water valve before draining water from these sources. Use tap
water only if local health officials advise it is safe.

Why talk about tsunamis?
All tsunamis are potentially, if rarely, dangerous. Twenty-four tsunamis have caused damage in
the United States and its territories in the past 200 years. Since 1946, six tsunamis have killed
more than 350 people and caused significant property damage in Hawaii, Alaska, and along the
West Coast. Tsunamis have also occurred in Puerto Rico and the Virgin Islands. When a
tsunami comes ashore, it can cause great loss of life and property damage. 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?
Tsunamis are large ocean waves generated by major earthquakes beneath the ocean floor or
major landslides into the ocean. Tsunamis caused by nearby earthquakes may reach the coast
within minutes. When the waves enter shallow water, they may rise to several feet or, in rare
cases, tens of feet, striking the coast with devastating force. People on the beach or in low
coastal areas need to be aware that a tsunami could arrive within minutes after a severe
earthquake. The tsunami danger period can continue for many hours after a major earthquake.
Tsunamis also may be generated by very large earthquakes far away in other areas of the
ocean. Waves caused by these earthquakes travel at hundreds of miles per hour, reaching the
coast several hours after the earthquake. The International Tsunami Warning System monitors
ocean waves after any Pacific earthquake with a magnitude greater than 6.5. If waves are
detected, warnings are issued to local authorities who can order the evacuation of low-lying
areas if necessary.
How can I protect myself from a tsunami?
If you are in a coastal community and feel the shaking of a strong earthquake, you may have
only minutes until a tsunami arrives. Do not wait for an official warning. Instead, let the strong
shaking be your warning, and, after protecting yourself from falling objects, quickly move away
from the water and to higher ground. If the surrounding area is flat, move inland. Once away
from the water, listen to a local radio or television station or NOAA Weather Radio for
information from the Tsunami Warning Centers about further action you should take.
Even if you do not feel shaking, if you learn that an area has experienced a large earthquake
that could send a tsunami in your direction, listen to a local radio or television station or NOAA
Weather Radio for information from the Tsunami Warning Centers about action you should take.
Depending on the location of the earthquake, you may have a number of hours in which to take
appropriate action.

Tsunami risk reduction requires a comprehensive approach
consisting of warning guidance, risk assessment, and
preparedness and education. An effective tsunami warning
system requires activities in all components. ITIC’s mitigation
program is directed towards coastal residents, their national
and local officials, school teachers, mass media, policy makers,
and the general public. It includes training classes, lectures,
community briefings, and media broadcasts. ITIC materials
include informational booklets, textbooks, lecture materials,
audio-visual aids, posters, photographs, television and radio
materials, and other publications. A prepared and aware
public will know immediately how to respond when a tsunami
emergency is declared. ITIC works with governments and
civil society organizations to implement community-based
mitigation programmes that will reduce tsunami impacts
and save lives.
Under ITIC's ITP-Hawaii Programme on tsunami warning
and mitigation systems, scientists, engineers, and tsunami
programme officials can spend up to three weeks in Hawaii
at ITIC, PTWC, and with local civil defense agencies
learning about tsunamis,operations of tsunami warning
systems, risk assessment, and education and preparedness
programmes. ITIC also conducts the ITP-International
Programme, which annually visits Member States to
provide in-country capacity assessments, and
tsunami awareness and technology training

Recently, numerous congressional inquiries have asked about the possibility of
tsunamis occurring in U.S. coastal areas; the extent to which these areas are currently
monitored; how tsunamis can be detected; and whether there is a national capacity
to issue evacuation warnings for tsunamis. These concerns stem from the December
26, 2004, tsunami triggered by an underwater earthquake off the west coast of
northern Sumatra in Indonesia. That earthquake was measured at Mw 9.0.1 The
ensuing tsunami devastated many coastal areas around the northern Indian Ocean,
and caused loss of life and damages in other areas. International disaster agencies
currently estimate that at least 150,000 people lost their lives to the tsunami.
The National Oceanic and Atmospheric Administration (NOAA) of the
Department of Commerce and various international science agencies have indicated
that there were few, if any, tsunami early warning systems monitoring the Indian
Ocean on December 26, 2004. However, nations bounded also by the Pacific Ocean,
including Australia and Indonesia, had tsunami early warning systems monitoring the
Pacific shores where they perceived a threat.2 Because of the lack of infrastructure
to receive tsunami warnings rapidly, some have pointed out that for people on
Indonesia’s Indian Ocean shores, emergency communications were useless in many
cases.
Although most deadly tsunamis have occurred historically in the western Pacific
Ocean, there are examples of recoded events in the Atlantic. In 1692, a tsunami
generated by massive landslides in the Atlantic Puerto Rican Trench reached
Jamaica’s coast, causing an estimated 2,000 deaths. In 1775, a tsunami struck in the
eastern Atlantic Ocean on the coast of Portugal, killing an estimated 60,000 people.
More recently, in 1929, a tsunami generated in the Grand Banks region of Canada hit
Nova Scotia, killing 51.
On January 5, 2005, the House Science Committee, House Coastal Caucus, and
House Oceans Caucus co-sponsored a briefing organized by the U.S. Geological
Survey (USGS) of the Department of the Interior. One purpose of the briefing was
to consider the possible implications of the Indian Ocean tsunami for the United
States. Experts from USGS and NOAA delivered presentations on the circumstances
surrounding that tsunami disaster, and discussed current capabilities for monitoring,
detection, and early warning around the globe.4

GRAND CHALLENGE #1: Provide hazard and
disaster information where and when it is needed.
Improve tsunami and seismic sensor data and
infrastructure for better tsunami detection;
Enhance tsunami forecast capability along our
coastlines (Pacifi c, Atlantic, Caribbean, and Gulf of
Mexico) by increasing the number of Deep-ocean
Assessment and Report of Tsunamis (DART) buoys,
tide gauges, and seismic sensors feeding real-time
data into on-line forecast models;
Develop standardized and coordinated tsunami
hazard and risk assessments for all coastal regions
of the United States and its territories;
Encourage data exchange and interoperability
among all regional tsunami and all-hazard warning
systems, coordinated by the Intergovernmental
Oceanographic Commission’s sub-Commission for
the Caribbean.
GRAND CHALLENGE #2: Understand the natural
processes that produce hazards.
Develop improved and sustained monitoring and
research of both the generating mechanisms and
the physical characteristics of the tsunami and
more accurate description of the sites at risk;
Research and better understand the protective role
coastal marshes, coral reefs, barrier islands, and
other coastal features play during a tsunami;
Conduct an annual review of the status of tsunami
research and develop a strategic plan for tsunami
research in the United States.
GRAND CHALLENGE #3: Develop hazard mitigation
strategies and technologies.
Develop engineering advancements for sea walls
and energy dissipaters that will minimize impact;
Develop coastal management plans that will
protect coastal features that act as natural energy
dissipaters to minimize the tsunami impact;
Promote development of model mitigation
measures and encourage communities to adopt
construction, critical facilities protection, and landuse
planning practices to reduce the impact of
future tsunamis.
GRAND CHALLENGE #4: Reduce the vulnerability
of infrastructure.
Develop risk assessments and inundation models to
inform the location of lifelines, hospitals, schools,
power plants and utilities, fi re and police stations,
and equipment away from the risk area or harden
those structures for adequate protection from the
assessed tsunami risk.
GRAND CHALLENGE #5: Assess disaster resilience.
Develop improved and standardized assessments
of societal, economic, and environmental
vulnerability to, impacts of, and a more robust
response and recovery capacity related to tsunami;
Develop effective land use plans based on risk
assessments and better topographic and
bathymetric maps to predict inundation levels
and possible effects;
Improve use of risk assessment tools, mitigation
practices, evacuation plans, and timely and
accurate warnings to promote risk-wise behavior by
decision makers and individuals.
GRAND CHALLENGE #6: Promote risk-wise behavior.
Increase outreach to all communities at risk to raise
awareness, improve preparedness, and encourage
the development of tsunami response plans;
Ensure interoperability between the United States’
national system and other regional tsunami
warnings systems;
Provide technical expertise and assistance, as
appropriate, to facilitate the development and
enhancement of the international tsunami and
all-hazard warning systems, including for the
Indian Ocean;
Employ geographically specifi c communication and
dissemination strategies for extended warnings and
probabilistic forecasts based on improved social
science research into individual response;
Increase the effectiveness of warnings and
evacuations through informed community
planning and annual drills.

While tsunamis usually occur in the Pacifi c Ocean, all low-lying coastal areas can be struck by
tsunamis. In North America, higher risk areas have warning systems in place, and clearly marked
evacuation routes.
The best advice for surviving a tsunami is to get as far away from its destructive force as possible.
• If you are caught on land near the coast during an earthquake, move as quickly as possible away
from the water and, if possible, up higher ground.
• If you are on open water in a boat, move as quickly as possible to deeper water.
Most buildings will not provide a great deal of protection from tsunamis. Some may collapse, others may fl ood
trapping you inside.
This basic knowledge passed down from generation to generation
saved whole villages of the Moken people during the
recent Indian Ocean tsunami. Moken Elders tell stories of the
Laboon, the wave that eats people. They say that before the
wave arrives, the earth shakes, birds and bugs fall silent, water
animals move deep into the ocean and land animals move to
higher ground, then the water recedes. As the story goes, when
these signs occur all the people must abandon their homes
and move to higher ground as quickly as possible, because
the water will return quickly in quantities bigger than can be
imagined. As far as any one can tell, only one Moken died in
the recent tsunami.
What is lifesaving knowledge in your community?

Since predicting earthquakes is so hard, tsunami protection relies
on warning systems. These warning systems combine seismographs
with water-based sea level gauges, sea fl oor pressure
sensors and satellite communications, so that when a tsunami
causing earthquake occurs warnings can be provided to coastal
areas as quickly as possible.
How fast can a tsunami reach land?
Courtesy National Oceanic and Atmospheric Agency (NOAA)
This map, from the Pacifi c Tsunami Warning Systen,
shows approximate travel times for a tsunami
generated by an earthquake near Hawaii.
Not all countries are served by warning systems, and even those that are often have trouble getting warnings out to
small or remote communities. In addition, while warnings help save lives, they do not protect land, buildings and
vegetation from the power of massive waves. So, in some places people have taken actions to develop some protection
from the force of the sea. Sea walls, are usually built to prevent coastal erosion, however they might in some
instances help dissipate energy in tsunami waves so that less destruction occurs on land. Natural barriers to water
also help. In the December 2004 tsunami, communities protected by mangrove forest suffered less damage than
those completely exposed to the wave.
The Huu-Ay-Aht people remember the stories the Elders tell about the great wave that nearly wiped them out 300
years ago. They also remeber the tsunami of 1964; their community wasn’t built then, but the nearby town of Bamfi
eld suffered a lot of damage. They are taking steps to protect both themselves and their homes. They have been
negotiating with the Government of British Columbia to move their entire community further away from shore and
onto higher ground. While an agreement hasn’t been reached yet, the Boxing Day tragedy in Asia has reenergized
their efforts.
On April 1, 1946, a magnitude 7.4 earthquake occured off the southern coast of the Aleutian
Islands (just west of Alaska). Although the earthquake was relatively small, it lifted a huge part
of the sea bed and generated a massive tsunami. A 30m wave hit Scotch Gap on Unimak Island
within 45 minutes of the quake, completely destroying a 30m, reinforced concrete lighthouse
located well above sea level. Five hours later, the wave hit Hawaii killing 159 people. It was still
over 15m high when it ran aground in Hilo on the Big Island (shown above). This tsunami was
the impetus for what is now the Pacifi c Tsunami Warning System.

When a tsunami hits shallow water close to shore, it begins to
interact with the land. Part of the wave is refl ected back offshore,
like a ball hitting a wall. Turbulence and friction slow down the
part that is not refl ected, but because the wave has so much energy
to begin with none of these processes signifi cantly decrease its
overall energy.
When a tsunami slows down but doesn’t lose a lot of energy,
what do you think happens to the wave physically?
Tsunami 5
Physics tells us that when the energy in a system remains constant, but velocity decreases, the mass in the system
must increase. A slower moving tsunami, is a physically higher tsunami; all the water in the wave “scrunches together
like the ribs of an accordian and heaves upward” (Waves of destruction).
In other words, when the front part of the wave starts to slow down, all the mass at the back of the wave catches up
with it, and creates a MUCH bigger wave. As they reach land, very large tsunamis have been known to reach heights
of 30 meters. This measure is known as the run up height.
When a tsunami enters
shallow water it loses
velocity, but gains height.
Coming ashore
How a tsunami comes ashore really depends on how it begins and
how the land is shaped. In some cases, water will actually withdraw
from sheltered harbours, leaving boats stranded, shells exposed,
and fi sh gasping for breath on the exposed ground. In other cases,
the ocean just rises and rises without warning and a wall of water
fl oods onto shore.
The force with which the waves hit lands is tremendous. It is enough
to wipe away beaches, knock down trees and crush structures. The
water will continue inland for hundreds of meters, pushed along by
the huge mass of water behind it. To make matters worse, the wave
can be just as destructive as it withdraws, smashing together objects
caught in its wake, and dragging debris far out to sea.
In 1964, a magnitude 9.2 earthquake off the
coast of Alaska spawned a tsunami which
did extensive damage to many coastal
towns including Kodiak, AK (above) and
Port Alberni, BC.
Photo courtesy NOAA.
http://www.photolib.noaa.gov/historic/c&gs/theb1341.htm
Predicting tsunamis
Since most tsunamis are caused by earthquakes, being able to predict tsunamis means being able to predict earthquakes.
Unfortunately, predicting earthquakes is extremely diffi cult. As much as we do know about the Earth, there are too
many variables that contribute to earthquakes to know with any certainty when one will occur. The best scientists
can do is provide probabilities that tell us how often, on average, earthquakes of various sizes will occur.
For instance, the most geologically active region of Canada (and the continental United States) lies along the west
coast. In this region there are about 1000 small earthquakes each year, most so small that no one feels them. There
have been about 100 earthquakes of magnitude 5 or more in the last 70 years. Once every 10 years or so, there is an
earthquake of magnitude 7 or bigger – these are called crust damaging quakes. Big megathrust quakes (magnitude
9 or greater) occur only once every 300-500 years.
If we can’t know for sure when an earthquake and
tsunami will occur, how do probabilities help?

Tsunami formation is quite complex. The size and energy of the
wave are related to the earthquake’s magnitude and depth, water
depth where the quake occurs, the amount of vertical motion of the
sea fl oor, the velocity of that motion, and the effi ciency with which
energy is transferred from the earth’s crust to ocean water.
What is the diff erence between velocity and speed?
Do you know what engineers mean by effi ciency?
When an earthquake happens under water, the ocean fl oor can
drop (or rise) very suddenly. In a megathrust earthquake, the displacement
can be extremely large and occur over the entire length
(sometimes more than 1000km) and width of a fault. Energy is
transferred to the water both from the shaking of the earth and the
sudden rise or fall of the sea fl oor.
Why would a drop or rise in the sea fl oor
transfer energy to water?
The December 26, 2004 earthquake in the Indian Ocean dropped millions, possibly billions, of cubic meters of water
by about 15 m. In other words, in a very short period of time, the water went from having billions and billions of
joules of potential energy, to having billions and billions of joules of kinetic energy. This energy is what spreads out
from the source and across the ocean to form the tsunami wave.
What is the diff erence between potential and kinetic energy?
Even though tsunamis are big waves, in deep water their size is
hidden in the ocean depths. Crests may be a meter high or smaller
and separated by 100 kilometers or more, but they are also moving
extremely fast, sometimes more than 500 kilometers per hour. as
fast as a transcontinental airplane. Tsunamis don’t get large until
they get close to shore.

What happens to waves in a really strong wind or hurricane?
Every wave can be described by its amplitude, wavelength and period.
So, as devastating as tsunamis are for both people and property,
their formation and actions are governed by physics.
The amount of energy carried by a wave is related to its amplitude.
High energy waves have large amplitudes and low energy waves
have smaller amplitudes. In other words, bigger waves have way
more energy than smaller waves – and tsunamis are BIG waves.
The energy (E) in a wave is actually proportional (α) to the square
of its amplitude (A).
E α A2
This means that every time the amplitude of a wave doubles, the
energy it contains actually increases 4 times.
So while an every day 1m wave has 1 unit, a large tsunami of 32m
has over 1000 times more energy. The largest tsunamis are about
30 meters high when they hit land.

Amplitude, wavelength and period
To help measure the amount of energy in a wave, scientists make different measurements, which are shown in the
diagram. If you think of the diagram as a picture of waves on the water, the straight horizontal line represents the
water when it is perfectly still.
Peaks (or crests) are the highest points above the fl at water line.
Troughs are the lowest points below the fl at water line.
The amplitude of the wave is how high it is above the fl at water
line (or how low it is below the fl at water line).
The wavelength is the distance from peak to peak, or trough to
trough.
The period of the wave is the length of time from when one peak
passes a point to when another peak passes the same point.

Waves are a topic of particular interest in physics because many
natural phenomena – light, sound, and yes, water waves - occur
as waves.
Th ink about waves you seen on the water.
What do you know about waves?
In physics, a wave is a disturbance which moves through a medium
(water, air, a slinky) from one point to another. The key point is that
it is the disturbance that moves, not the medium. The disturbance
is caused by energy transferring from one particle to another, so
waves are sometimes called energy transfer phenomenon.
Have you ever been in a boat?
What happens to the boat when the water is wavy?
Waves of energy can pass back and forth
through the metal coils of a Slinky while
the Slinky as a whole never moves.
Tsunami 3
Amplitude and energy: Why size matters
What happens to waves in a really strong wind or hurricane?
Every wave can be described by its amplitude, wavelength and period.
So, as devastating as tsunamis are for both people and property,
their formation and actions are governed by physics.
The amount of energy carried by a wave is related to its amplitude.
High energy waves have large amplitudes and low energy waves
have smaller amplitudes. In other words, bigger waves have way
more energy than smaller waves – and tsunamis are BIG waves.
The energy (E) in a wave is actually proportional (α) to the square
of its amplitude (A).
E α A2
This means that every time the amplitude of a wave doubles, the
energy it contains actually increases 4 times.
So while an every day 1m wave has 1 unit, a large tsunami of 32m
has over 1000 times more energy. The largest tsunamis are about
30 meters high when they hit land.
Waves on water are usually caused by the wind. Individual molecules
of air traveling over the water’s surface crash into individual
molecules of water, and in doing so transfer energy to them. The
water particles then transfer energy to other nearby particles of
water and so on. We see this energy transfer as a ripple on the water,
or in heavier winds (which transfer more energy), waves. This
process keeps on going from one set of molecules to the next until
the waves reaches the shore.
All waves are energy transfer
phenomena.

Within hours killer waves radiating from the epicenter slammed into the coastline of 11 Indian Ocean countries, snatching people out to sea, drowning others in their homes or on beaches, and demolishing property from Africa to Thailand.

Tsunamis have been relatively rare in the Indian Ocean. They are most prevalent in the Pacific. But every ocean has generated the scourges. Many countries are at risk.

In the wake of the Christmas weekend tsunami in the Indian Ocean, one of the worst disasters in history, National Geographic News examines the killer waves' causes and warning signs—information that can be a lifesaver in a tsunami zone.

• A tsunami is a series of great sea waves caused by an underwater earthquake, landslide, or volcanic eruption. More rarely, a tsunami can be generated by a giant meteor impact with the ocean.

Scientists have found traces of an asteroid-collision event that they say would have created a giant tsunami that swept around the Earth several times, inundating everything except the mountains 3.5 billion years ago. The coastline of the continents was changed drastically and almost all life on land was exterminated.

Giant forces that had been building up deep in the Earth for hundreds of years were released suddenly on December 26, shaking the ground violently and unleashing a series of killer waves that sped across the Indian Ocean at the speed of a jet airliner.

By the end of the day more than 150,000 people were dead or missing and millions more were homeless in 11 countries, making it perhaps the most destructive tsunami in history.

The epicenter of the 9.0 magnitude quake was under the Indian Ocean near the west coast of the Indonesian island of Sumatra, according to the USGS, which monitors earthquakes worldwide. The violent movement of sections of the Earth's crust, known as tectonic plates, displaced an enormous amount of water, sending powerful shock waves in every direction.

The earthquake was the result of the sliding of the portion of the Earth's crust known as the India plate under the section called the Burma plate. The process has been going on for millennia, one plate pushing against the other until something has to give. The result on December 26 was a rupture the USGS estimates was more than 600 miles (1,000 kilometers) long, displacing the seafloor above the rupture by perhaps 10 yards (about 10 meters) horizontally and several yards vertically. That doesn't sound like much, but the trillions of tons of rock that were moved along hundreds of miles caused the planet to shudder with the largest magnitude earthquake in 40 years.

Above the disturbed seafloor the great volume of the ocean was displaced along the line of the rupture, creating one of nature's most deadly phenomena: a tsunami. Within hours killer waves radiating from the earthquake zone slammed into the coastline of 11 Indian Ocean countries, snatching people out to sea, drowning others in their homes or on beaches, and demolishing property from Africa to Thailand.