<P> A mantle plume is an upwelling of abnormally hot rock within the Earth's mantle, first proposed by J. Tuzo Wilson in 1963 . As the heads of mantle plumes can partly melt when they reach shallow depths, they are often invoked as the cause of volcanic hotspots, such as Hawaii or Iceland, and flood basalts such as the Deccan and Siberian traps . Some such volcanic regions lie far from tectonic plate boundaries, while others represent unusually large - volume volcanism near plate boundaries or in large igneous provinces . </P> <P> A mantle plume is posited to exist where hot rock nucleates at the core - mantle boundary and rises through the Earth's mantle becoming a diapir in the Earth's crust . The currently active volcanic centers are known as hotspots . In particular, the concept that mantle plumes are fixed relative to one another, and anchored at the core - mantle boundary, would provide a natural explanation for the time - progressive chains of older volcanoes seen extending out from some such hot spots, such as the Hawaiian--Emperor seamount chain . </P> <P> The hypothesis of mantle plumes from depth is not universally accepted as explaining all such volcanism . It has required progressive hypothesis - elaboration leading to variant propositions such as mini-plumes and pulsing plumes . Another hypothesis for unusual volcanic regions is the "Plate model". This proposes shallower, passive leakage of magma from the mantle onto the Earth's surface where extension of the lithosphere permits it, attributing most volcanism to plate tectonic processes, with volcanoes far from plate boundaries resulting from intraplate extension . </P> <P> In 1971, geophysicist W. Jason Morgan further developed the hypothesis of mantle plumes . In this hypothesis, convection in the mantle transports heat from the core to the Earth's surface in thermal diapirs . In this concept, two largely independent convective processes occur in the mantle: the broad convective flow associated with plate tectonics, which is driven primarily by the sinking of cold plates of lithosphere back into the mantle asthenosphere, and mantle plumes, which carry heat upward in narrow, rising columns, driven by heat exchange across the core - mantle boundary . The latter type of convection is postulated to be independent of plate motions . </P>

A mantle plume that starts beneath the ocean results in