German scholar, Penck, classified his concept related to erosion into the following stages:
1. First Stage: According to Penck, in this stage, both the processes of upliftment and erosion move together. But the upliftment is more than the erosion.
2. Second stage: In this stage, uplift and erosion remain equally active. As a result, the valleys start to become wide and deep.
3. Third Stage: In this stage, due to competitive rate, the dorsal difference of the upper and lower curves of the uplift and erosion processes remains the same.
4. Fourth Stage: In this stage, the rate of uplift gets inactive and weak, and the erosion is effective at the same rate. As a result, the valleys are deep and move down.
5. Fifth Stage: In this stage, along with the uplift, the rate of erosion also gets inactive and weak. The dorsal difference of both the curves decreases. The concept of Penck related to erosion is being presented by the following diagram.
