Tsunami Origins
Objectives
Students will be able to:
- Explain why tsunamis originate on tectonic plate boundaries
Materials
Computers with Internet access
Copies of the Student Worksheet
Copies of the tectonic plate map
World map created in previous lesson
Background
A tsunami can be generated by any disturbance that rapidly displaces a large mass of water, such as an earthquake, volcano, landslide or a meteorite. However, the most common cause is an undersea earthquake. An earthquake which is too small to create a tsunami by itself may trigger an undersea landslide quite capable of generating a tsunami.
Tsunamis can be generated when the sea floor abruptly deforms and vertically displaces the overlying water. Such large vertical movements of the earth's crust can occur at plate boundaries. Subduction earthquakes are particularly effective in generating tsunamis, and occur where denser oceanic plates slip under continental plates in a process known as subduction.
Sub-marine landslides; which are sometimes triggered by large earthquakes; as well as collapses of volcanic edifices, may also disturb the overlying water column as sediment and rocks slide downslope and are redistributed across the sea floor. Similarly, a violent submarine volcanic eruption can uplift the water column and generate a tsunami.
Waves are formed as the displaced water mass moves under the influence of gravity to regain its equilibrium and radiates across the ocean like ripples on a pond. (Wikipedia)
Procedure
Part 1
How many earthquakes do you think occurred in the world today? How many volcanoes? And what does that have to do with tsunamis?
1. Visit the USGS Earthquake Hazards Program - Earthquake Bulletin site and answer the questions on the Student Worksheet.
2. Obtain a copy of the tectonic plate map. Do the boundaries of the plates match up with the locations of the earthquakes on the USGS site?
Part 2
3. Visit Volcano World's Current Volcanic Activity site and answer the questions on the Student Worksheet. (it might be helpful to use the world map created in the last lesson)
4. Refer to the tectonic plate map. Do the boundaries of the plates match up with the locations of the active volcanoes on the Volcano World site?
5. Click on the BBC's Tsunami Animated Guide and view the 9 slides explaining how the Asian tsunami happened.
Assessment
If you were a scientist in charge of predicting tsunamis, what type of information would you think would be helpful to gather? Explain.
If you had a limited amount of sensors or buoys to put into the water to help detect a tsunami, where in the world would you put them? Explain.
How would you compare or combine the data about earthquakes, volcanoes and the water to help predict a tsunami?
