@oceanswimmer: A slot canyon is made of narrow corridors that are sliced into eroding plateaus by bursts of rushing water. Many of them measure less than a few feet across but can drop several hundred feet to the floor.
There are also box canyons. Box canyons form as sections of the wall collapse further back into the land. The heads of box canyons are marked by cliffs on at least three sides.
Another canyon is a submarine canyon. They are similar to canyons that are on land as far as their form and shape but they are cut by currents on the ocean floor. Many of them are extensions of river canyons as they dump into the ocean. Others are gouged from the turbid currents that often plunge to the ocean floor.