Volcanic arc

A curved chain of volcanoes that forms above a subduction zone, where one tectonic plate sinks beneath another and generates magma.

Subduction: The process by which one tectonic plate descends beneath another into the mantle. The descending plate supplies the setting and materials that generate arc magma.
Convergent boundary: A boundary where two tectonic plates move toward each other. Volcanic arcs form at convergent boundaries where one plate subducts.
Andes: A mountain range along western South America, including a long continental volcanic arc. The Andes display arc volcanism above the Nazca Plate's subduction beneath South America.
Hotspot volcanism: Volcanism associated with localized mantle upwelling, commonly forming chains as a plate moves over a hotspot. Hotspot chains can curve too, but they do not require a subduction zone.
Flux melting: Partial melting caused when added volatile substances lower a rock's melting temperature. Water released from the descending slab promotes melting in the mantle above it.
Oceanic trench: A long, deep depression in the seafloor formed where a plate bends into a subduction zone. The trench marks the surface edge of the subduction system that feeds an arc.
Cascade Range: A mountain range in western North America that includes volcanoes of the Cascades volcanic arc. Its volcanoes form above the Juan de Fuca Plate's subduction beneath North America.
Mid-ocean ridge: An underwater mountain chain formed where tectonic plates move apart and new oceanic crust forms. Ridge volcanism occurs at divergent boundaries rather than above sinking plates.
Mantle wedge: The wedge-shaped mantle region between a subducting plate and the overriding plate. This mantle region melts and feeds many arc volcanoes.
Island arc: A curved chain of volcanic islands formed above oceanic subduction. It is the oceanic expression of a volcanic arc.

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