The mantle is a highly viscous layer between the crust and the outer core. Earth's mantle is an approximately 2,970 km thick (~1,800 mi) rocky shell that constitutes approximately 84 percent of Earth'
s volume. [Wikipedia]
A mantle plume is an upwelling of abnormally hot rock within the Earth's mantle. As the heads of mantle plumes can partly melt when they reach shallow depths, they are thought to be the cause of volca
nic centers known as hotspots and probably also to have caused flood basalts. [Wikipedia]