Explosives volcanoes are most likely to be found on subduction plate boundaries where one plate subducts (goes under) another plate. The subducting plate is usually a plate made of denser oceanic crust and the upper plate usually consists of less dense continental crust. Because of the composition of the magma and the high silica content found in the continental crust, these eruptions are much more explosive than the gentler basaltic flows characteristics of oceanic hotspot eruptions or undersea divergent plate boundaries.
Most explosive eruptions occur in volcanoes above subduction zones, where one tectonic plate dives beneath the other. Eighty to 120 kilometers below the surface, magma forms when the rocks of the mantle melt just above the subducting plate.
