Plate Tectonics - Magma Plumes

Volcanic activity is also evident away from the plate margins and it is the locations of magma plumes which can cause this.

Magma plumes are areas of hot, upwelling mantle.

A hot spot develops above the plume in the crust. Magma generated by the hot spot rises through the rigid plates of the lithosphere and produces active low viscosity volcanoes at the Earth's surface. As oceanic volcanoes move away from the hot spot with the migration of their tectonic plate, they cool and subside, producing older island chains.

The Hawaiian Island chain is being constructed in this way. As continental volcanoes move away from the hot spot, they cool, subside, and become extinct.