At divergent plate boundaries, two tectonic plates move apart from each other. As the plates move apart, new crust is formed as magma rises from the Earth's mantle and fills the gap between the plates. This process is called seafloor spreading.
At convergent plate boundaries, two tectonic plates collide with each other. When two oceanic plates collide, one plate is usually subducted beneath the other. The subducted plate melts and forms magma, which can rise to the surface and create new crust. However, when two continental plates collide, they are usually too buoyant to be subducted. Instead, they collide head-on and form mountains. The collision of two continental plates can also cause the destruction of crust as the plates are compressed and thickened.
