Magma flows up from underground caverns and erupts along a chain of volcanoes

This is called subduction,and it diffuses water into the magma-filled mantle.That lowers the magma's melting point and makes it rise into the overlying North American plate. From a subterranean chamber, the magma travels upwards and erupts along a chain of volcanos.Magma still deep underground slowly cools, crystallizing to form solid rock, including the granite now found in Yosemite National Park and the Sierra Nevada Mountains. We'll come back to that later.