Easy Over: What Happens when Layers of Rock are Squeezed Together?

Problem

What happens when layers of rock are squeezed together?

Materials

• 4 hand towels

Procedure

1. Stack the outstretched towels on a table.
2. Place your hands on opposite ends of the towels.
3. Slowly push the ends of the towels about 4 inches (10 cm) toward the center.
4. Observe the shape of the towels.

Results

The towels form folds.

Why?

Pushing from opposite directions causes the towels to be squeezed into shapes called folds. The result is a surface with a wavelike appearance. Forces pushing toward each other from opposite directions are called compression forces. Such forces within the Earth can crush rocks like a mighty nutcracker, and can slowly squeeze rock layers into folds like those of the stack of towels. If the compression force is applied quickly, the rocks break, producing earthquakes (violent shaking of the Earth caused by a sudden movement of rock beneath its surface).

Let's Explore

Science Fair Hint: Photographs of the covered papers before and after compression can be displayed. Indicate which type of material would most likely break under pressure and thus produce earthquakes.

1. Does the amount of force affect the results? Repeat the experiment twice, first pushing your hands less than 4 inches (10 cm) toward the center, and then pushing them more than 4 inches (10 cm) toward the center. Science Fair Hint: Photographs and/or diagrams showing the difference in the results can be used as part of a project display.
2. Would the type of material being compressed affect the possibility of causing an earthquake? Repeat the original experiment, replacing the towels with materials such as the following:
   • A sheet of newspaper covered with a thin layer of sand
   • A sheet of newspaper covered with a thin layer of modeling clay

Show Time!

1. Demonstrate how compression force crushes different materials. Cover a table with a sheet of newspaper. Place a testing material between the palms of your hands. Hold your hands over the newspaper so that any falling particles land on it. Push your hands together as hard and as fast as possible, making an effort to crush the material. Observe each material tested and describe the results. Test these items:
   • A slice of bread
   • A cracker
   • A cookie
   • An empty ice cream cone
2. Demonstrate how compression forces create folds by pushing on both ends of a large sponge. Use this as part of an oral demonstration. Diagrams of the results can be displayed.

Check It Out!

A mountain is a rock mass rising more than 2,000 feet (610 m) above the surrounding land. The Appalachians, the Rockies, the Himalayas, and the Alps are all examples of folded mountain ranges that were formed by compression forces. Read about folded mountain ranges, including any evidence of earthquakes in these regions.

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