Slab pull is created by the motion of one tectonic plate as it moves beneath another. When two overlapping plates form a subduction fault, slab pull contributes to the movement of the lower plate as it descends into the mantle.
The tectonic plates that make up the Earth's crust are in constant motion. According to Columbia University, faults where subduction is occurring result in a force known as slab pull. This force is created as the plate begins to sink into the Earth's mantle and serves to pull the lower plate further away from the volcanic ridge where it is formed.