In plate tectonics, a subduction zone is a region of the Earth's crust where one tectonic plate moves under another tectonic plate and sinks into the Earth's mantle. Subduction zones are some of the most geologically active regions on Earth and are often associated with earthquakes, volcanoes, and tsunamis.

Subduction zones form when two oceanic plates or an oceanic plate and a continental plate collide. The denser plate is forced beneath the less dense plate and sinks into the Earth's mantle. As the descending plate moves deeper into the mantle, it heats up and releases water and other volatiles. These volatiles cause the overlying mantle rock to melt, forming magma that can erupt onto the Earth's surface as volcanoes.

Subduction zones are also responsible for the creation of mountain ranges. As the descending plate moves beneath the overriding plate, it creates a zone of weakness in the crust. This zone of weakness can lead to the formation of folds, faults, and thrust faults, all of which can contribute to the formation of mountain ranges.

Some of the most well-known subduction zones include the San Andreas Fault in California, the Cascadia Subduction Zone off the coast of the Pacific Northwest, and the Japan Trench.