- a curving chain of active volcanoes formed above a subduction zone and adjacent to a convergent plate boundary.
- A curved chain of volcanoes in the overriding tectonic plate of a subduction zone. Volcanic arcs form as the result of rising magma formed by the melting of the downgoing plate. They are curved because of the curvature of the Earth. The Andes mountains form a volcanic arc. See also island arc.