Question

which statement describes one event that happens at deep ocean trenches?
crust is formed.
mountains are formed.
seafloor spreading occurs.
denser plates slide under lighter plates.

Explanation:

Deep - ocean trenches are formed at subduction zones. In a subduction zone, the denser oceanic plate (due to its higher density from being cooled and having more mafic composition) slides under the less - dense continental plate or another less - dense oceanic plate.

• Crust is not formed at deep - ocean trenches. New crust is formed at mid - ocean ridges (where seafloor spreading occurs).
• Mountains are formed at convergent boundaries where two continental plates collide (e.g., the Himalayas) or at volcanic arcs (which are associated with subduction zones but not the same as the trench itself).
• Seafloor spreading occurs at mid - ocean ridges, not at deep - ocean trenches.

Answer:

D. Denser plates slide under lighter plates.