The Cascade Volcanoes in the Pacific Northwest formed due to which type of plate interaction?

• A. Ocean-Continent Convergence
• B. Ocean-Ocean Convergence
• C. Continent-Continent Convergence
• D. Divergent boundary activity

Answer: (A)

The key idea is subduction at a convergent boundary. The Cascade Volcanoes form because an oceanic plate (the Juan de Fuca plate) is sinking beneath the continental North American plate. As the oceanic plate dives down, fluids released from the subducting slab cause melting in the overlying mantle, producing magma that rises to form a chain of explosive stratovolcanoes inland from the coast. This is classic ocean-continental convergence.

Other boundary types don’t fit the Cascade setting: ocean-ocean convergence creates island arcs, continent-continent convergence builds high mountain belts with little volcanism, and divergent boundaries produce spreading ridges with different volcanic activity.