island arc

(geography) A group of volcanic islands, usually situated in a curving arch-like pattern that is convex toward the open ocean, having a deep trench or trough on the convex side and usually enclosing a deep basin on the concave side; formed by volcanic activity associated with oceanic plate subduction at convergent plate margins. Also known as volcanic arc.

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An island chain, mostly of volcanic origin, in the form of an arc. According to plate tectonic theory, the arc is formed when oceanic crust plunges into the mantle where it undergoes subduction. The magma thus formed creates a chain of submarine volcanoes which are eventually built up into islands.