Volcanoes

[DBusby]

Why are their volcanoes at constructive plate boundaries, destructive plate boundaries and hot spots?

[incitatus]

Because at these points the disturbance in the earths crust is enough to melt rock. At constructive and destructive boundaries the frictional forces provide the energy. at hotspots it is much more to do with bouyancy- a plume of hot molten rock rises through the substrate because it is less dense. Think of a lava lamp.