What is the process by which one tectonic plate slides beneath another?

The process by which one tectonic plate slides beneath another is subduction. It occurs at a convergent plate boundary, where two plates move toward each other and the denser plate sinks into the Earth's mantle beneath the other. In most cases, the descending plate is cold oceanic lithosphere, which is denser than the underlying asthenosphere.

Subduction zones commonly produce deep ocean trenches, powerful earthquakes, volcanic arcs, and mountain belts. As the descending slab carries water-rich minerals into the mantle, released water can help generate magma in the overriding plate. That magma may rise to form volcanoes, as seen around the Pacific Ring of Fire. The process also recycles oceanic crust back into Earth's interior.

Subduction is not the same as obduction. Obduction occurs when a slice of oceanic crust is pushed onto continental crust instead of sinking beneath it. Convection describes heat-driven movement within Earth's mantle, while accretion refers to material being added to a plate or continent. Subduction usually proceeds at only a few centimeters per year, but its effects accumulate over millions of years and help drive the global plate-tectonic system.