What Drives Plate Motions? Convection (hot rocks rise and cold rocks sink) is the ultimate driver of plate tectonics A. Forces that Drive Plate Motion The mantle consists of almost entirely solid rock, but is hot and weak enough to act like a viscous, fluid-like convective flow. The simplest type of convection is like heating a pot of water. The base, which has been heated up, becomes less dense and rises in thin sheets/blobs that spread out to the surface. As the surface cools, it densifies and the cooler water sinks back to the bottom, where it reheats, etc. This is like mantle convection. Slab pull happens when cold, dense oceanic lithosphere sinks through the less dense underlying warm asthenosphere (sink down like a rock pulled into mantle by gravity).