When there's a volcanic activity in certain area, very often it happens that there's magma that intrudes into the cold rock in the surrounding area. The intrusion of the hot magma into the cold rock layers causes big changes into the structure of the rocks. The high temperature and high pressure manage to influence the structure of the preexisting rocks, mostly on the places where the magma touches the cold rocks, leading to the formation of metamorphic rocks. This type of metamorphism is known as contact metamorphism.
