- The river erodes vertically by hydraulic action. The valley is deepened by vertical erosion.
- As the river cuts down, the steep sides are attacked by weathering. This breaks up and loosens the soil and rock.
- The loosened material slowly creeps down the slope because of gravity or is washed into the river by rainwater. The river carries it away.
- The end result is a steep sided valley that has the shape of the letter V.