The Earth's crust is divided into plates that move against each other. The motion of sections of the Earth's crust is called Plate Tectonics. Plate tectonics can cause earthquakes and volcanoes.
Image: The boundaries of the tectonic plates.
Types of boundaries between plates:
Areas where tectonic plates collide. One plate lowers underneath the other plate in a process called subduction.
Areas where tectonic plates move away from each other. Divergent boundaries between tectonic plates form trenches
Areas where tectonic plates slide against one another. Energy built up from tension in transform boundaries can cause earthquakes.