The Earthâs outer crust (the lithosphere) is composed of a series of tectonic plates. These plates move on a hot flowing mantle layer called the asthenosphere. Heat within the asthenosphere creates convection currents that cause tectonic plates to move several centimeters per year relative to each other. When two tectonic plates meet, we get a âplate boundary.â There are three major types of plate boundaries. If two tectonic plates collide, they form a convergent plate boundary. Usually, one of the converging plates will move beneath the other, which is known as subduction.