Flash floods create slot canyons. These narrow canyons are gashed into eroding plateaus and are not very wide, but usually fall to depths of hundreds of feet. Powerful and fast-moving flash floods can create slot canyons because there is little vegetation or substantial soil to slow the water. Each time a flash flood courses over a plateau it finds the depression made by the last flood and cuts deeper.
Plateau canyons begin with fast-moving rivers that cut deep into the river bottom over time. The water that forms them is powerful, but does not come and go quickly like flash floods. Instead, the river -- through its normal cycles -- cuts into the rock, wearing it down deeper and deeper. The harder the rock, the steeper the canyon. Softer rock results in walls that erode more quickly, creating a wider canyon that can be deep but not steep.
The ocean has its own canyons. Submarine canyons are not unlike canyons on land, but they are cut into the ocean floor by currents. Some of these begin at a shore where a canyon river runs into the sea. The river continues to cut its canyon when it reaches into the ocean. Other submarine canyons are cut by particle-filled currents that plunge to the ocean floor.
