Which description best defines subduction?

• A. The flow of magma beneath plates
• B. A process where continents split apart
• C. The process in which a continental plate and an oceanic plate collide, forcing the oceanic plate down into the mantle
• D. The collision of two continental plates causing mountain building

Answer: (C)

Subduction is the sinking of one tectonic plate into the mantle at a convergent boundary, driven by density differences—usually the oceanic plate sliding beneath a less dense continental or another oceanic plate. This descent creates a subduction zone, deep ocean trenches, volcanic activity, and earthquakes as the slab melts and interacts with mantle rocks.

The description fits this idea because it specifies a collision between a continental plate and an oceanic plate, with the oceanic plate being forced down into the mantle.

Why the other ideas don’t fit: flow of magma beneath plates describes general magma movement rather than the entire process of one plate descending; continents splitting apart refers to rifting and continental drift in a distinct boundary type; and the collision of two continental plates leads to mountain building without subduction of oceanic crust, since there isn’t a dense oceanic slab to sink.