Ridge Push

Ridge push is the gravitational body force that drives a plate away from an elevated mid-ocean ridge as its lithosphere cools, thickens, and slides off the high, hot axis toward the deeper basin. It arises because the ridge crest stands 2 to 3 km above the old abyssal seafloor, so the cooling slab is pushed laterally by the slope of the lithosphere-asthenosphere boundary. Ridge push is one of the secondary plate-driving forces; most analyses rank it weaker than slab pull, the negative buoyancy of the cold subducting slab, which dominates the motion of plates attached to a trench.