What best describes an oceanic-continental boundary?

• A. A boundary where two continental plates collide.
• B. A boundary where an oceanic plate collides with a continental plate, resulting in subduction zones and volcanic activity.
• C. A boundary where plates move apart.
• D. A boundary where two oceanic plates slide past each other.

Answer: (B)

An oceanic-continental boundary is a convergent boundary where the denser oceanic plate sinks beneath the lighter continental plate in a process called subduction. As the oceanic plate descends, it melts and releases fluids into the overlying mantle, which generates magma that rises to form volcanoes along the continental margin. The downward-moving slab also creates a deep trench at the edge of the continent and is the source of strong earthquakes in the region.

This setup explains why you get volcanic activity and a trench at the margin, along with relative uplift and mountain building inland over time as the continental crust is affected by the subduction zone. Other boundary types produce different features: two continental plates colliding build tall mountain ranges with little long-lived volcanism; plates pulling apart form new seafloor and mid-ocean ridges; and plates sliding past each other cause earthquakes with little volcanism.