Sliding on Your Own Home Plate

Like cars in a demolition derby, pieces of Earth’s surface are skidding around, sideswiping and smashing into each other, or ripping apart from each other. All of this movement takes place in slow motion most of the time, so you will not notice it – unless there’s an earthquake.

This exciting feature of our planet is called plate tectonics (tek-TAWN-iks). Earth is the only planet in the solar system that has it.

Plate tectonics causes not only earthquakes, but also volcanoes and tidal waves. It also causes much of the beautiful landscape on Earth, such as mountains.

Plate tectonics occurs because Earth’s outer layer, the crust, is broken into pieces called plates. The plates move. Under the crust is a layer of hot, squishy rock. The plates float around on this less-solid layer. Where the plates meet, several kinds of things can happen.

First, volcanoes occur where hot, liquid rock pushes up through cracks and weak points between the plates. Earthquakes occur when the plates move suddenly, either slipping past each other or diving one under the other. The plates may move only a few inches or feet at a time, but the movement creates a shock wave in the ground that can cause terrible damage and injury to people if their buildings are too flimsy to withstand the shaking.

Mountain ranges form when one plate slides under another pushing land upward, or when two plates push against each other and they both lift up. Plates also pull apart in some places, allowing the soft or liquid rock beneath to rise and form a ridge.

The boundary between two major plates runs right through California. It is called the San Andreas Fault. Los Angeles is on the Pacific Plate, moving toward the northwest. San Francisco is on the North American Plate, moving toward the southeast. In about 20 million years, the two cities, now about 450 miles apart, will slide right past each other.

Learn other fascinating facts about Earth at spaceplace.nasa.gov/en/kids/csearth.shtml.

This article was written by Diane K. Fisher. It was provided by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.