Kid's Activity: Understanding Tsunamis

by Robert Krampf

How do earthquakes cause devastation? Why do some earthquakes produce a tsunami while most do not? This experiment a bit to help you understand more about earthquakes.

You will need:

• Wooden pencil
• Large, zipperlock, plastic bag
• Water

Several people wanted to know why this earthquake produced a tsunami when most earthquakes do not. To understand that, we need to know about faults. Before you start listing all my faults, such as forgetting to include parts of the experiment, I am talking about geologic faults. Imagine the rocks in the Earth as a wooden pencil. If you hold the ends of the pencil and push upwards on the center with your thumbs, the pencil will bend slightly and then suddenly break. When pressure causes the same thing to happen in the Earth's crust, the break is called a fault.

There are different kinds of faults, depending on the direction of the pressure. Hold your hands in front of you, side by side, with the palms up. Imagine them as the rocks on either side of the fault. If you move one of your hands away from you, you can simulate a strike slip fault. This is a very common type of fault. A good example is the San Andreas Fault in California.

Because the sides of the fault move horizontally, this type of fault often results in fences and roads that are broken, with one side shifted several feet to the right or left of the other.

While strike slip faults are common, there are other ways that the rocks can move. If the pressure of the sides is towards each other, then one side is forced upwards, causing a thrust fault. If the pressure is away from each other, then one side can move downwards, forming a gravity or normal fault.

The kind of fault has a big impact on the formation of a tsunami. Fill a large zipperlock bag half-full of water. Seal it well, and work over the sink, just in case. Hold your hands in front of you as you did before, with the bag of water laying on your palms. Watch what happens to the water when you slide one hand away from you, simulating a strike slip fault. You should not see much movement of the water. Next, move one hand upwards quickly to simulate a thrust fault. You get a lot more movement as the water rushes from the lifted hand to the lower hand. You get the same sort of rush if you lower one hand, as in a gravity fault.

The recent earthquake was produced by a thrust fault, which caused a similar surge in the water of the ocean. That surge produced the waves that caused the destruction. Be sure to do the experiment over the sink. I carried mine into the den to show my Mom how it works. The zipper was not completely sealed, and I produced a tsunami on the floor.

I hope that this will help you understand some of the science behind this event. My thoughts are with all those that lost loved ones in this disaster.

Have a wonder filled week.

Since 1987, the goal of Robert Krampf's Science Education Company has been to make science fun and understandable. Based in St. Augustine, Florida, Mr. Krampf presents his amazing science shows at educational institutions across the country. He also offers a variety of consulting services, to help educators bring science to life in their programs. His free Experiment of the Week e-mail list distributes fun, hands-on science experiments to over 180,000 people each week.

Copyright © Robert Krampf. Permission to republish granted to Pregnancy.org, LLC.