Slab pull

The gravitational force on a cold, dense subducting slab as it sinks into the mantle; the dominant driver of plate tectonic motion.

Negative buoyancy: The downward gravitational pull on material denser than its surroundings. Slab pull exists because cooled oceanic lithosphere is denser than the mantle beneath it.
Plate velocity correlations: The observed link between plate speed and the length of attached subducting slab edge. The clearest evidence that slab pull, not mantle drag, sets plate speeds.
Ridge push: Driving force from the elevation and gravitational slide of lithosphere away from mid-ocean ridges. The classic alternative force, now considered secondary to slab pull.
Pacific plate: The largest oceanic plate, moving about 7-10 cm per year, ringed by subduction zones. Its long attached slabs make it the fastest major plate on Earth.
Oceanic lithosphere: The rigid outer layer of ocean basins, cooling and thickening as it ages away from ridges. Its cooling history is what generates the density excess that makes slabs pull.
Basalt to eclogite transition: Metamorphic transformation of oceanic crust to denser eclogite at roughly 50 km depth. This density jump sharply increases the slab's negative buoyancy as it descends.
Fast-moving plates: Plates such as the Pacific moving over 7 cm per year, driven by long attached slabs. The Pacific's ring of subduction zones explains its speed as a plate.
Mantle drag: The traction exerted by mantle flow on a plate's base, once proposed as the main driver. The abandoned early hypothesis that plates were dragged by underlying convection cells.
Farallon plate: A vanished oceanic plate that subducted beneath western North America for over 100 million years. Imaged slab remnants beneath North America record its slow sinking and fate.
Seafloor spreading: The creation of oceanic lithosphere at mid-ocean ridges as plates diverge. Supplies the young, buoyant lithosphere that ages and densifies into sinking slabs.

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