Volcanic Mountains. As the name suggests, volcanic mountains are formed by volcanoes. Volcanic Mountains are formed when molten rock (magma) deep within the earth, erupts, and piles upon the surface. Magna is called lava when it breaks through the earth's crust.When the ash and lava cools, it builds a cone of rock.olcanic Mountains are formed when molten rock (magma) deep within the earth, erupts, and piles upon the surface. Magna is called lava when it breaks through the earth's crust. When the ash and lava cools, it builds a cone of rock.