Final answer:
A trench is formed when two oceanic plates converge and one is subducted beneath the other.
Step-by-step explanation:
When two oceanic plates converge and one is subducted beneath the other, a trench is formed. A trench is a long, narrow depression in the ocean floor that is the deepest part of the ocean. It is a result of the intense pressure and friction caused by the collision of the plates. The subducted plate gets pushed under the other plate and into the mantle, creating a trench.
Learn more about Plate Tectonics