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 Wave That Shook the World Classroom Activity

Objective
To calculate approximate speeds and travel times for sample tsunamis.

• copy of the "Tracking Tsunamis" student handout (PDF or HTML)
• copy of the "Tsunami Scenarios" student handout (PDF or HTML)
• copy of the "World Map" student handout (PDF or HTML)
• calculator with square root function
• drawing compass
• ruler
• world atlases

1. 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.

2. 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).

3. 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 meters)

4. 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

5. 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.

6. 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.)

7. 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.

A 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

 Kind of Wave Mode of Generation Range of Wavelength Wave Frequency (Period) Wave Speed wind-driven local or distant winds that blow across the ocean's surface about 100 m to 200 m 5 s to 20 s about 40 to 90 km/h (40 km/h, the speed of a moped, is most common) seismic-sea wave (tsunami) sub-marine earthquakes (most tsunamis); also created by volcanic eruptions, landslides, underwater explosions, and meteor impacts from 100 m to >500 km; are at least three times the ocean depth at which the wave was generated 10 min to 2 h variable, 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.

Scenario A
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:

Kauai Island, Hawaii: about 6 hours

Kwajalein, Marshall Islands: about 9 hours 26 minutes

Scenario B
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:

Kwajalein, Marshall Islands: about 5 hours 30 minutes

Samoa: about 5 hours 30 minutes

Scenario C
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 Sites

NOVA Web Site—Wave That Shook the World
www.pbs.org/nova/tsunami/
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
www.science.org.au/nova/045/045key.htm
Defines the term tsunami and includes information about wave energy.

Earthquakes and Society
www.umich.edu/~gs265/society/earthquakes.htm
Includes charts and information about earthquakes at subduction zones.

The Great Sumatra Earthquake and Tsunami of December 2004
www.wilson.wnyric.org/t/drobison/regents/WellOrganized/tsunami.htm
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.

HyperPhysics: Tsunami
hyperphysics.phy-astr.gsu.edu/hbase/waves/tsunami.html
Includes graphics of subduction zones and describes how tsunamis travel.

International Tsunami Information Center

Life of a Tsunami
walrus.wr.usgs.gov/tsunami/basics.html
Explains tsunami speed and amplification.

Oceanography: Waves
www.poemsinc.org/oceano/waves.htm
Contains a map of locations for 13 tsunamis.

Physics of Tsunamis
wcatwc.arh.noaa.gov/physics.htm
Characterizes tsunamis and considers how they travel in different water depths.

Tsunami
www.tulane.edu/~sanelson/geol204/tsunami.htm
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.

www.pmel.noaa.gov/tsunami_faqs.htm
Answers questions about causes of tsunamis and how they differ from other waves.

Tsunami—Seismic Sea Wave
vulcan.wr.usgs.gov/Glossary/Tsunami/description_tsunami.html
Describes seismic sea waves and discusses four damaging tsunamis.

U.S. Search and Rescue Task Force: Tsunamis
www.ussartf.org/tsunamis.htm
Provides basic information about tsunamis, features 10 destructive tsunamis, and presents tsunami safety rules.

Water Waves
electron4.phys.utk.edu/141/dec8/December%208.htm
Distinguishes between deep-water waves and shallow-water waves and provides an example of a tsunami velocity calculation.

What is a Wave?
www.gmi.edu/~drussell/Demos/waves-intro/waves-intro.html
Defines a wave and illustrates examples of different waves.

WorldAtlas.com
worldatlas.com/aatlas/imageg.htm
Maps latitude and longitude for cities, towns, and villages.

Books

Ford, 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 weather.

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:Physical Science

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.

Mathematics Standard
Number and Operations

 Science Standard B:Physical Science

Motions and forces

• Gravitation is a universal force that each mass exerts on any other mass. The strength of the gravitational attractive force between two masses is proportional to the masses and inversely proportional to the square of the distance between them.

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.

Mathematics Standard
Algebra

Classroom Activity Author

Developed by WGBH Educational Outreach staff.

 Wave That Shook the World Original broadcast:March 29, 2005

 Major funding for NOVA is provided by Google and BP. Additional funding is provided by the Howard Hughes Medical Institute, the Corporation for Public Broadcasting, and public television viewers.