Unit 4: Earthquakes and Volcanoes

Over millions of years, ocean basins open and close, continents move and change shape, and mountains are pushed up and eroded away. Such dynamic processes continually reshape the surface of the Earth. The movement of rigid plates on the Earth’s surface, known as plate tectonics, is the cause of these changes. Volcanic eruptions and earthquakes are dramatic hints of the great movements that take place over the vastness of geological time.