The ridge of a trench is the parapet.
It could be called a trench, crevice, ocean ridge, or abyss.
Ridge
Trench
The opposite of a trench would be an embankment, berm, or dike.(the opposite of a marine trench is a seamount or ridge)
A ridge, specifically the Mid-Atlantic Ridge.
Trenches are formed by divergent plates, Whereas Ridges are formed by plate in collision.
a trench.
Deep Trench in the ocean floor. It can sometimes be mistaken for a mid-ocean ridge.
Both in the ocean
hard to say
usually a rift or trench