1- Volcanos are most commonly found at subduction zone boundaries. This is where the thinner oceanic plates get pulled under the thicker continental plates. As the plates go deeper, they melt and form pockets of magma which can cause mountains to be built and as the hot magma rises, it erupts out of volcanos.
2- Volcanism occurs regularly at two of the three types of plate Boundaries. The most volcanism occurs at diverging plate boundary where plates separate. Volcanoes also form at converging plate boundaries where one plate dives beneath the other at subduction zones.