Divergent plate boundaries occur where tectonic plates are moving away from each other. There are two main types of tectonic plates - continental plates composed of rocks and minerals, and oceanic plates which are thinner and located under seas. As the plates separate, molten lava rises up between them to form new crust. This divergence is driven by convection currents in the Earth's mantle which push the plates apart. New crust forms underwater as seafloor spreading, and volcanoes and mountains can form on the edges of the separating plates.