Wave That Shook the World
calculate approximate speeds and travel times for sample tsunamis.
- copy of the "Tracking Tsunamis" student handout
- copy of the "Tsunami Scenarios" student handout
- copy of the "World Map" student handout
- calculator with square root function
- drawing compass
Review subduction zones and how earthquakes occur in these zones. (See Activity
Answer for more information.) Draw a subduction zone on the board and
review with students how the December 26, 2004, earthquake off of the Sumatran
coast created a tsunami: A massive displacement of water from its equilibrium
position caused the tsunami. Gravity worked to restore the water to its
equilibrium position. The waves traveled from their place of origin in all
directions and energy from the quake was transferred by the water.
Tsunamis, because of their long wavelengths, lose little energy as they
travel. (The rate at which a wave loses energy is inversely proportional to its
wavelength.) Inform students that there is a formula that can be used to
estimate the speed of the wave created from this energy. The formula is used to
measure the speed of ocean waves, like tsunamis, that have very long
wavelengths relative to the depth of the water. Tsunamis can have wavelengths
greater than 700 kilometers (the average ocean depth is 3-4 kilometers). The
formula estimates the tsunami's speed while it is in deeper waters (as it
approaches shallower coastal waters, the tsunami slows down, its wavelength
shortens, and its height increases).
Brainstorm with students some factors that may play a role in the speed of a
tsunami. (Student responses may include the magnitude of an earthquake, the
amount of displaced water, and the depth of the water.) Tell students that the
formula to approximate tsunami speed considers the depth of the water and the
acceleration due to gravity. The formula is:
where speed (meters/second) = square root of g (acceleration due to
gravity, which is 9.81 meters/second2) x d (water depth in
Have students work with a partner. Provide each team with a copy of the
handouts and other materials. Review the handouts with them. Tell students that
they will use the speed formula to calculate tsunami speed and determine the
time each tsunami takes to travel to specific locations in each of the
scenarios presented. Students can check their distance estimates at
Students will need to convert their answers, which will be in meters/second,
to kilometers/hour. Help students think how they might move the decimal point
to accomplish the last step in this conversion.
To conclude, hold a class discussion about the order in which the tsunami
will strike each location (1st, 2nd, or 3rd).
Have teams share some ways people at each location might prepare for the
approaching tsunami. (Some considerations are evacuating people to high ground,
alerting hospitals, deciding whether there is time for help from outside the
country, or sending people away by boat.)
As an extension, ask students to research why and how the Pacific Tsunami
Warning Center was developed and what future plans are being formulated for a
worldwide tsunami warning system.
tsunami is a series of waves created in a body of water by a disturbance that
vertically displaces the water column. Tsunamis are not tidal waves (they are
not caused by the forces that create tides). An epicenter is the point on
Earth's surface straight above where an earthquake originates.
Water waves are grouped by the forces that cause or generate them (generating
forces) and those that restore equilibrium (restoring forces). The generating
forces are different for tsunamis and wind-driven waves, but the restoring
force for both is gravity.
Wave Comparison Chart
or distant winds that blow across the ocean's surface
100 m to 200 m
s to 20 s
40 to 90 km/h (40 km/h, the speed of a moped, is most common)
earthquakes (most tsunamis); also created by volcanic eruptions, landslides,
underwater explosions, and meteor impacts
100 m to >500 km; are at least three times the ocean depth at which the wave
min to 2 h
up to 1,000 km/h (the speed of a jet plane)
Most tsunamis are created by sub-marine earthquakes that occur at subduction
zones. At these zones, one tectonic plate is moving or subducting beneath its
neighboring plate. Many things can happen at these sites to trigger a tsunami.
At Sumatra, stick-slip friction occurred. The upper plate dragged downward with
the lower plate and then the upper plate became deformed, built up strain
energy, and then snapped up. The magnitude of an earthquake determines how much
energy is released and then transferred by the water. The earthquake's
magnitude also plays a role in how high above sea level the water level rises.
Magnitude does not play a large role in the tsunami's speed.
Several factors affect the height of a tsunami wave and the damage it can cause
as it approaches and reaches the shore—the energy the wave carries; the
tides, whether high or low; and the land formation and features.
The Seward, Alaska, tsunami created at an ocean depth of 4,000 m is calculated
to travel at 713 km/h. The travel times to each location are:
Kodiak, Alaska: about 32 minutes
Kauai Island, Hawaii: about 6 hours
Kwajalein, Marshall Islands: about 9 hours 26 minutes
The Ka Lae, Hawaii, tsunami created at an ocean depth of 4,500 m is calculated
to travel at 756 km/h. The travel times to each location are:
Dutch Harbor, Alaska: about 5 hours 6 minutes
Kwajalein, Marshall Islands: about 5 hours 30 minutes
Samoa: about 5 hours 30 minutes
The Gran Canaria, Canary Islands, tsunami created at an ocean depth of 3,500 m
is calculated to travel at 667 km/h. The travel times to each location are:
Terceira, Azores: about 2 hours 21 minutes
Safi, Morocco: about 1 hour 5 minutes
St. Johns, Newfoundland: about 5 hours 44 minutes
Web Site—Wave That Shook the World
In this companion Web site to the program, find out about how well officials
can prepare for the next big tsunami, read an Ask the Expert feature, see how
the Indonesian event unfolded, and delve into the global history of these
seismic sea waves.
Calculating the Threat of Tsunami
Defines the term tsunami and includes information about wave energy.
Earthquakes and Society
Includes charts and information about earthquakes at subduction zones.
The Great Sumatra Earthquake and Tsunami of December 2004
Provides a five-part high-school level earth science lesson plan that explores
the geologic processes involved with the Indonesian tsunami. Includes analysis
of actual seismograms from which students plot the earthquake's epicenter.
Includes graphics of subduction zones and describes how tsunamis travel.
International Tsunami Information Center
Answers frequently asked questions about tsunamis and lists the largest
Life of a Tsunami
Explains tsunami speed and amplification.
Contains a map of locations for 13 tsunamis.
Physics of Tsunamis
Characterizes tsunamis and considers how they travel in different water
Describes the physical characteristics of tsunamis and includes definitions of
wavelength, wave height, wave amplitude, wave frequency, and wave velocity.
Includes formulas for calculating velocity.
Tsunami: Frequently Asked Questions
Answers questions about causes of tsunamis and how they differ from other
Tsunami—Seismic Sea Wave
Describes seismic sea waves and discusses four damaging tsunamis.
U.S. Search and Rescue Task Force: Tsunamis
Provides basic information about tsunamis, features 10 destructive tsunamis,
and presents tsunami safety rules.
Distinguishes between deep-water waves and shallow-water waves and provides an
example of a tsunami velocity calculation.
What is a Wave?
Defines a wave and illustrates examples of different waves.
Maps latitude and longitude for cities, towns, and villages.
Brent A. and Sean P. Smith. Physical Oceanography. Arlington, VA: NSTA Press, 2000.
Includes background information, lessons, and activities related to water,
waves, and the ocean.
Macquitty, Miranda and Frank Greenaway. Eyewitness: Ocean. New York, NY: DK
Publishing, Inc., 1995.
Focuses on Earth's ocean environments and includes a section on waves and
Van Rose, Susanna. Eyewitness: Earth. New York, NY: DK Publishing, Inc., 1994.
Discusses Earth and highlights modern oceanography, plate tectonics, and the
formation of the ocean floor.
The "Tracking Tsunamis" activity aligns with the following National Science
Education Standards and Principles and Standards for School Mathematics.
Science Standard B:
Transfer of energy
Energy is a property of many substances and is associated with heat,
light, electricity, mechanical motion, sound, nuclei, and the nature of a
chemical. Energy is transferred in many ways.
Science Standard D:
Earth and Space Science
Structure of the Earth system
Lithospheric plates on the scales of continents and oceans constantly move
at rates of centimeters per year in response to movements in the mantle. Major
geological events, such as earthquakes, volcanic eruptions, and mountain
building, result from these plate motions.
Number and Operations
Science Standard B:
Motions and forces
Conservation of energy and the increase in disorder
The total energy of the universe is constant. Energy can be transferred
by collisions in chemical and nuclear reactions, by light waves and other
radiations, and in many other ways. However, it can never be destroyed. As
these transfers occur, the matter involved becomes steadily less ordered.
Interactions of energy and matter
Waves, including sound and seismic waves, waves on water, and light
waves, have energy and can transfer energy when they interact with matter.
Classroom Activity Author
by WGBH Educational Outreach staff.