Island arcs are formed by which tectonic process?

• A. Subduction of two ocean plates, where one is subducted beneath the other
• B. Divergence of continental plates
• C. Erosion forming curved coastlines
• D. Formation of large volcanic plateaus

Answer: (A)

Island arcs form at convergent boundaries when one oceanic plate is forced beneath another. As the subducting slab sinks, it releases fluids into the overlying mantle, lowering melting temperatures and triggering magma generation. This magma rises to the surface to feed a chain of explosive volcanoes that sit above the subduction zone, creating a curved sequence of islands parallel to the deep-sea trench. The arc’s curved shape reflects the geometry of the bending subduction boundary. This differs from divergence of continental plates, which creates rift zones and new ocean basins; erosion alone cannot produce volcanic island chains; and large volcanic plateaus arise from flood basalts, not subduction-related island arcs.