Volcanoes are most commonly found at the edges of the Earth's moving tectonic plates because in these there's cracks in the crust and the crust is not a solid continuing mass. Because the crust is cracked in here the enormous pressure and temperature from the mantle layer manages to push up through the cracks between the plates and in that way to create volcanoes, usually chain of volcanoes located on the edges of the tectonic plates. Depends on the type of boundary between the plates, are they colliding, submerging, or moving away from each other to what extent there will be a volcanic activity, and also from the location of the plate boundaries depends are there going to be volcanoes below the surface of the water or above the surface.
