At a convergent boundary, the denser plate – usually the oceanic plate, is subducted under the less dense plate- usually the continental plate. Due to stress of the subduction, the two plates press against each other as they collide and begin to bend forming a deep trench at the boundary. At the boundary, as the subducted plate dives into the mantle it melts and the magma rises and erupts through the fissures within the boundary forming mountain ranges. Whenever there are mountains there are valleys too.
