Slab suction forces are one of the major plate tectonic driving forces. Slab suction occurs when a subducting slab drives flow in the nearby mantle. This flow then exerts shear tractions on nearby plates. This driving force is important when the slabs (or portions thereof) are not strongly attached to the rest of their respective tectonic plate. They cause both the subducting and overriding plate to move in the direction of the subduction zone. Slab suction is the weakest of the three major forces involved in plate motion, the others being slab pull, the strongest, and ridge push.