Subduction

Subduction is a geological process in which one tectonic plate moves beneath another and sinks into the mantle. It occurs at convergent plate boundaries, where an oceanic plate, typically denser and thinner, collides with either another oceanic plate or a continental plate. The denser plate is forced downward, forming a deep trench at the surface and a descending slab that can extend several hundred kilometers into the mantle.

The descending slab drives the recycling of lithospheric material, transporting water-rich minerals and sediments into deeper Earth layers. As the slab descends, increasing pressure and temperature cause metamorphic reactions that release fluids, which lower the melting point of the overlying mantle wedge. This partial melting generates magmas that rise to form volcanic arcs, such as the Andes or the Japanese Islands. Subduction zones are also associated with intense seismic activity, including megathrust earthquakes that can generate tsunamis.

Subduction plays a central role in the long‑term evolution of the planet. It regulates the composition of the crust by reworking oceanic lithosphere, contributes to the growth of continental crust, and drives plate motions through slab pull, the force exerted by the sinking plate. The rate of subduction varies globally, typically ranging from a few centimeters to over ten centimeters per year, influencing the geomorphology and tectonic activity of affected regions.