The Science Behind Tsunamis

On March 10, 2011, many Americans awoke to the shocking news that the east coast of Japan had been rocked by an earthquake with a magnitude of 8.9 – one of the strongest earthquakes ever recorded. Worse yet, a tsunami (a Japanese word meaning “harbor wave”) caused by the earthquake yielded even more devastating destruction, demolishing countless homes, causing a massive explosion in a nuclear power plant, and tossing large sailing vessels inland like toy boats. Those dead and missing are estimated in the tens of thousands, and the effects of this tsunami have been seen as far away as the western coast of North America. 

Most students have heard about the terrible destruction in Japan, but few really understand what a tsunami is or how it occurs.  However, many teachers are using this tragedy as a teachable moment for educating students about the power and devastating effects of these powerful natural disasters. While nothing can be done to eliminate the threat of earthquakes and tsunamis, we can use events like this one to help our students become more scientifically literate citizens. 

To begin, students must understand basic plate tectonics. A quick and easy way to explain this concept to elementary students is to draw a circular diagram of the earth’s layers:  crust, mantle, and core. Explain that the crust is the solid surface of the Earth, while the mantle consists of melted rock. Demonstrate this idea by filling a tub with water (representing the mantle) and placing 8-10 pieces of Styrofoam (representing crustal plates) close together in the middle of the tub. Let go of the Styrofoam, and the pieces should slowly drift apart.  Earth’s crust is made up of “plates” that act just like the Styrofoam, except they move much more slowly (about 1 cm per year). 

Observe the “plates” for awhile, asking students to note how each one behaves. Do all of the pieces move at the same rate? Do bigger pieces move differently than smaller pieces?  Do any of the pieces run into each other? Slide past each other? With intermediate students, you may decide to touch on the different types of faults and fault boundaries. 

Students may be interested to know how scientists made the discovery that crustal plates move, and you might choose to go into greater depth on this topic by using the interdisciplinary lesson plan Scientists Discover Giant Frog Fossil. In this lesson, students examine a world map and read a news article about the discovery of a giant frog fossil. It includes a discussion of continental drift, a vocabulary activity, and information about the supercontinent, Pangaea.

Once students understand the basic idea of plate tectonics, they can learn about earthquakes through hands on lessons such as Earthquake Formation, in which they construct models to explore faults,  and Earthquakes Rock!, in which they learn how earthquakes are measured and investigate which structural designs are most likely to survive an earthquake. 

Finally, a tsunami can be explained as a very large ocean wave caused by an underwater earthquake or volcanic eruption. In the case of this most recent tsunami, the wave was caused by a massive earthquake about 80miles off the east coast of Japan. An excellent lesson for deepening student understanding of this event includes Tsunami Attack, in which students examine how earthquakes, volcanoes, and landslides can trigger tsunami waves using a table-top-sized tsunami generator to observe the formation and devastation of a tsunami. A hands on component allows them to make villages of model houses to test how different material types are impacted by the huge waves.