What phenomenon is responsible for hot spot volcanism

Mantle plumes is the phenomenon responsible for hot spot volcanism.

Explanation:

Hot spot volcanism is created mainly due to the abnormal hot centres that are known as mantle plumes. A unique Hot spot volcanism will not occur at the tectonic plates of earth boundaries, where all other volcanisms occur.  

Scientific models state these molten rock plumes that are similar to a lava lamp, have rising bulbous head that is fed by a long, narrow tail that originates in the mantle. These features are also called as diapirs.