Driving Forces Behind Plate Motion

Most mountain building occurs along convergent boundaries where two plates are moving towards each other.  This convergence is made possible by the movement of those plates. There are three forces believed to drive this plate motion.  The first is ridge push, which results from the upwelling of buoyant mantle beneath the crests of mid ocean ridges, causing the oceanic lithosphere on either side of the ridge axis to then slide under the force of gravity (Image 1). The second force is slab pull, where the older, colder, denser oceanic crust away from the mid ocean ridge sinks into the mantle under its own weight (Image 2). The final force is slab suction, which is a result of convection in the mantle (Image 2).  Of these forces, the one that is currently believed to be the most important is slab pull.