What best describes a continental-continental boundary?

• A. A boundary where two continental plates collide, leading to mountain ranges.
• B. A boundary where one oceanic plate subducts beneath a continental plate.
• C. A boundary where two oceanic plates separate.
• D. A boundary where plates slide horizontally past one another.

Answer: (A)

When two continental plates collide, you get a continental-continental boundary. Because continental crust is buoyant, it doesn’t sink into the mantle, so there isn’t subduction. Instead, the collision crumples and thickens the crust, lifting it into massive mountain belts. This process involves intense compression, metamorphism of rocks, and shallow to intermediate earthquakes, and it tends to produce high, expansive mountain ranges like the Himalayas rather than volcanic arcs. The key idea is that mountain building results from the collision and stacking of buoyant crust, not from one plate sinking beneath another or magma rising to the surface.