Subduction
Subduction recycles lithosphere into the mantle, driving plate tectonics.
Subduction is a geological process that takes place where tectonic plates converge. At these boundaries, the heavier plate—usually oceanic lithosphere, though some continental lithosphere can also be involved—dives beneath the other and sinks into the mantle. This recycling of lithosphere into Earth’s interior is what drives plate tectonics; without it, plate tectonics would not happen. Subduction zones are Earth’s most significant tectonic features, and so far, Earth is the only planet where subduction has been observed.
The process works because cold, rigid oceanic lithosphere is slightly denser than the hot, ductile asthenosphere beneath it. Once subduction starts, it is mostly sustained by the negative buoyancy of the dense sinking slab, which descends largely under its own weight. Subduction rates are typically measured in centimeters per year, with convergence speeds reaching up to 11 cm per year. The sinking slab usually angles between 25 and 75 degrees relative to Earth’s surface.
Subduction zones are marked on the surface by arc-trench complexes. On the ocean side, the approaching plate often shows a slight shallowing—an outer trench high or swell—before plunging into an oceanic trench, the deepest parts of the seafloor. Beyond the trench lies the forearc region of the overriding plate. Depending on how much sediment is available, this area may include an accretionary wedge of material scraped off the descending slab. Not all subduction zones have such a wedge; accretionary arcs have a well-developed forearc basin behind it, while non-accretionary arcs do not. Farther inland, volcanoes form long chains called volcanic arcs.
Earthquakes are common along subduction zones. Fluids released from the subducting plate trigger volcanism in the overriding plate. When the slab sinks at a shallow angle, the overriding plate develops a belt of deformation marked by crustal thickening, mountain building, and metamorphism. A steeper subduction angle, by contrast, leads to the formation of back-arc basins.
Subduction is part of the larger system of plate tectonics. Earth’s lithosphere—its rigid outer shell—is broken into sixteen large plates and several smaller ones. These plates move slowly, driven mostly by the pull of sinking lithosphere at subduction zones. The sinking slab is part of convection cells in the ductile mantle, which help release heat from rad
- process
- Subduction
- field
- Geology / Plate Tectonics
- key_measurement
- Rates of convergence as high as 11 cm/year
- typical_subduction_angle
- Between 25 and 75 degrees
- total_length_of_oceanic_subduction_zones
- 55,000 km (34,000 mi)
- known_on
- Earth only
Lore & Background
The surface expression of subduction zones is an arc-trench complex, which includes an oceanic trench, a forearc region, a volcanic arc, and a back-arc region. Earthquakes are common along subduction zones, and fluids released by the subducting plate trigger volcanism in the overriding plate. Subduction zone earthquakes occur at greater depths (up to 600 km) than elsewhere on Earth. The subducting basalt and sediment are rich in hydrous minerals; during subduction, these break down, producing supercritical water that rises into the overlying mantle, generating magma via flux melting. Arc volcanoes tend to produce dangerous eruptions because they are rich in water and tend to be extremely explosive.
Reader's Guide
Subduction is the fundamental process that drives plate tectonics, recycling oceanic lithosphere into the mantle and creating most of Earth's continental crust. It shapes the planet's surface through the formation of oceanic trenches, volcanic arcs, and mountain belts. The process also controls the global water cycle by transporting water into the deep mantle via hydrous minerals, which is later released through volcanism. Subduction zones are responsible for the deepest parts of the ocean floor and the most powerful earthquakes and volcanic eruptions on Earth. Understanding subduction is essential for assessing natural hazards such as earthquakes, tsunamis, and volcanic eruptions, as well as for interpreting the geological evolution of the planet. The study of subduction zones also provides insights into the composition and dynamics of Earth's deep interior, as seismic tomography shows that some slabs can penetrate the lower mantle and sink to the core–mantle boundary.
Did You Know?
- Subduction rates of convergence can be as high as 11 cm per year.
- Subduction zone earthquakes can occur at depths up to 600 km (370 mi), far deeper than typical earthquakes.
- Arc volcanoes such as Krakatoa, Nevado del Ruiz, and Mount Vesuvius are examples of subduction-related volcanoes.
- Oceanic subduction zones are located along 55,000 km (34,000 mi) of convergent plate margins.
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