According to the mantle plume theory what causes hot spots?

According to the mantle plume theory, Plumes are proposed to ascend through the mantle and start to incompletely dissolve on arriving at shallow profundities in the asthenosphere by loose melting.

It leads to enormous volumes of volcanic eruption. The plumes hypothesis suggested that this dissolved magma ascends to the surface and emits to shape "hot spot". the plume head liquefies partially on arriving at shallow profundities, a plume is frequently invoked as the reason for the hotspots at particular region, for example, Hawaii or Iceland.

b.have there own function.