Recall that the home planet coalesced from a hot cloud of gas and dust 4.5 billion years ago. The surface could radiate its heat to space, so it cooled pretty quickly, but the high-temperature rock on the inside could not, and in fact has generated more heat from radioactive decay and gravitational energy. We're sitting on a big ball of fiery rock wrapped by a dozen or two kilometers of relatively cool rock. It's not a pile of cold rock . So all that magma is looking for a way to escape up through the crust.
Some people even think volcanoes have changed climate over the millennia.
Details, please The biggest clue to the origin of volcanoes is their peculiar distribution. Most above-water volcanoes are on the Ring of Fire, which marks the intersection between tectonic plates surrounding the Pacific Ocean. The Ring, and other areas with similar crustal action, are called subduction zones. The upper mantle is thought to be the source of magma columns that feed volcanoes. Rising magma gathers in the magma chamber a few kilometers below the vent.