Mantle convection. 3-D computer model showing the movement of magma which rises as hot plumes (light purple) heated by the Earth's core (orange). The plumes reach the outer layer of the upper mantle and fan out before finally sinking as cooler magma. Convective currents in the mantle drive plate tectonics and forms volcanoes on the Earth's crust. Image created by Shuxia Zhang and Shuo Wang at the University of Minnesota Supercomputing Institute.