Geomorphic cycle, also called geographic cycle, or cycle of erosion, theory of the evolution of landforms. In this theory, first set forth by William M. Davis between 1884 and 1934, landforms were assumed to change through time from “youth” to “maturity” to “old age,” each stage having specific characteristics. The initial, or youthful, stage of landform development began with uplift that produced fold or block mountains. Upon dissection by streams, the area would reach maturity and, ultimately, would be reduced to an old-age surface called a peneplain, with an elevation near sea level. The cycle could be interrupted by uplift during any period of the life cycle and thus returned to the youthful stage; this return is called rejuvenation. The geomorphic cycle could be applied to all landforms such as hillslopes, valleys, mountains, and river drainage systems. It was assumed that, if the stage of a landform was known, its history followed directly according to a predetermined framework.

What are the Similarities Between Davis and Penck Cycle of Erosion?

• Davis and Penck cycle of erosion are two models that explain the development of relief in landscapes.
• Both are geographic models.

What is the Difference Between Davis and Penck Cycle of Erosion?

Davis cycle of erosion is the geographic cycle model explained by William Morris Davis in 1899. In contrast, the Penck cycle of erosion is the geographic cycle model explained by Walter Penck in 1924. The key difference between Davis and Penck cycle of erosion is that Davis cycle of erosion is time-dependent and monocyclic while Penck cycle of erosion is not time-dependent and it is polycyclic. Moreover, there are three factors in Davis cycle of erosion as structure, process and stages, while there are five factors in Penck cycle of erosion as Primarumpf, Aufsteigende, Gleichforminge, Absteigende and Endrumpf. Also, according to the Davis cycle of erosion, the cycle starts only when uplift is stopped. In contrast, according to the Penck cycle of erosion, erosion does not remain suspended till the uplift is complete.

What is Davis Cycle of Erosion?

The American geographer William Morris Davis described the Davis cycle of erosion in 1899. He explained the cycle based on the erosion pattern of American mountainous valleys. He paid more attention to endogenic force. Davis cycle of erosion is time-dependent. There are three factors in Davis cycle of erosion. They are structure, process and time (stages). As per Davis, the cycle of erosion occurs as a function of the above three factors.

Figure 01: Possible Evolution of the Cape Town Landscape by Erosion of the Cape Fold Belt Mountains

There is a major assumption in Davis cycle of erosion. He assumed that erosion starts only when the uplift is stopped. During landform development, uplifted landmasses undergo three stages in sequence: youth, maturity, and old stage. Therefore, landforms change from youth stage to maturity stage to old stage in Davis cycle of erosion. At the final stage, landscape relief reduces to its minimum level. Therefore, according to the Davis cycle of erosion, the altitude of the main valley floor decreases with time.

What is Penck Cycle of Erosion?

German geographer Walter Penck introduced the Penck cycle of erosion, which is another geographic model that explains the development of landforms. He studied the Davis cycle of erosion and agreed with most of Davis’s thoughts. However, he disagreed with certain things. The stages component in Davis cycle of erosion is not included in the Penck cycle of erosion. He rejected the idea that the stages are sequential and explained that there might be interruptions of the sequence due to rejuvenation. Furthermore, the Penck cycle of erosion is not time-dependent.

Penck also theorized that the erosion cycle is a never-ending process, meaning that the Penck cycle of erosion is polycyclic. Another important facet of the Penck cycle of erosion is that it says the erosion does not remain suspended till the uplift is complete. Therefore, both upliftment and erosional acts take place simultaneously. Unlike in the Davis cycle of erosion, both endogenic and exogenic forces equally affect the landform formation in the Penck cycle of erosion. There are five stages in Penck cycle of erosion: Primarumpf, Aufsteigende, Gleichforminge, Absteigende and Endrumpf.