Which process forms ocean trenches?

• A. Subduction of one plate beneath another
• B. Divergent spreading
• C. Transform faulting
• D. Isostatic rebound

Answer: (A)

Ocean trenches form where one tectonic plate subducts, or sinks, beneath another. At convergent boundaries, the dense oceanic plate dives into the mantle beneath either another oceanic plate or a continental plate, pulling the plate boundary down and creating a deep, narrow trench. This subduction process also often leads to magma generation and volcanic arcs on the overriding plate, along with strong earthquakes.

Divergent spreading creates new crust at mid-ocean ridges, not trenches. Transform faulting moves plates side by side with little vertical change, so trenches don’t form there. Isostatic rebound is crustal adjustment to loading or unloading rather than trench formation. Therefore, the feature formed by this process is ocean trenches through subduction.