Well, consider the fact that the vast majority of the earth surface, in fact, almost the entire surface of the earth is entirely volcano-less. Look under your feet -- no volcanoes! Move over a couple of steps and look again -- no volcanoes.
So it is safe to say that a certain thickness of rock would serve enough to prevent volcanoes. You just have to provide enough cooling to ensure a sufficiently thick layer of magma solidifies into solid rock.
So it is safe to say that a certain thickness of rock would serve enough to prevent volcanoes. You just have to provide enough cooling to ensure a sufficiently thick layer of magma solidifies into solid rock.