Plate Boundaries

There are about a dozen major tectonic plates, shown in Figure 29 on page 682. Most major plates contain both continental and oceanic crust. The edges of plates meet at plate boundaries. There are three types of plate boundaries: divergent boundaries, convergent boundaries, and transform boundaries. At each type of boundary, plates move in a different way. As the plates move apart, collide, or slide past each other, they cause changes in Earth's surface.

The motions of Earth's plates have been measured directly using global positioning system (GPS) sensors. The plates move very slowly, about 0.1 to 10 centimeters per year. This speed is similar to the rate at which your fingernails grow—about 4 centimeters per year.

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