Question

how does the process of accretion create deep trenches on the earths surface?)

Explanation:

Accretion in the context of plate tectonics (when one tectonic plate is subducted under another) leads to deep trenches. Oceanic plates, being denser, subduct beneath continental or other oceanic plates. As the subducting plate moves down into the mantle, the overriding plate's edge and the subducting plate's descent create a depression (trench) at the boundary. The accumulation (accretion) of material from the subducting plate onto the overriding plate, along with the downward pull of the subducting plate, deepens this trench over geological time.

Answer:

Accretion (via tectonic plate subduction: denser oceanic plate subducts under another plate; the subducting plate’s descent and material transfer to the overriding plate create a deep trench as the overriding plate’s edge and subducting plate’s pull form a depression, deepening over time).