Oceanic trenches are underwater chasms that can reach 2-4 km or 1.9-2.5 miles below the surrounding seafloor. These can be the deepest areas of an ocean. Such trenches are formed by colliding tectonic plates – the trench is formed where one plate sinks below the edge of another plate. Volcanoes may be generated in the upper plate along the interaction boundary, creating volcano island chains on or near one side of the oceanic trench.
In fictional worlds, oceanic trenches can be eerie and remote locations that hide the darkest secrets of the ocean. There may be submarine caves near these regions, and they may be home to massive leviathans or underwater civilizations. There may be long lost shipwrecks within them or perilously perched on the edge of the trench.
How deep are the ocean trenches of your world and what lays at their bottom?