Cycle of Erosion

Cycle of Erosion/ Geomorphic Cycle:

Cycle of Erosion, which is also called geographic or geomorphic cycle is an idealized model that explains the development of relief in landscapes. The model starts with the erosion that follows uplift of land above a base level and ends, if conditions allow, in the formation of a peneplain (a more or less level land surface produced by erosion over a long period, undisturbed by crustal movement). Landscapes that show evidence of more than one cycle of erosion are termed “polycyclical”. The cycle of erosion and some of its associated concepts have, despite its popularity, been a subject of much criticism. To understand the cycle of evolution of landscape, let us start with a relatively flat upland area in a humid region.

1. During the youth stage, the area remains more or less flat. The stream valleys are generally narrow.
2. In mature stage, the relief of the land increases and the landscape is changed into one consisting of hills and valleys. The “relief” of an area may be defined as the maximum difference in the elevation.
3. In old stage, the streams will approach base level and the land will be reduced to a peneplain. The peneplain is an undulating plain which lies nearly at base level. Some mounds or hillocks of hard rocks still persist. These hillocks are called “monadnocks”.

Origin of the concept of cycle of Erosion:

The originator of the erosion cycle model, William Morris Davis, divided it into stages. The transition of these stages is gradual.

Youthful Stage: The beginning of the model starts from an uplifted landscape. The very first stage of the erosion is its youth stage, where river incision is the dominant process shaping the landscape. During the youthful stage the difference between ups and downs, and heights and valley bottoms increases rapidly.

Mature Stage: With the rapid change in the level of landscape the youthful stage enters into a mature stage in which the height differences between valley bottoms and uplands are at their greatest level. In this stage, slope decline becomes a more important phenomenon, and uplands lose height more rapidly than the rivers incising stage, effectively diminishing relief.

Old stage: The last stage is known is Old stage. In this stage, erosion has acted so long that the landscape, despite its original height, is reduced into a rolling lowland. That landscape of low relief is called a peneplain and may contain residual heights standing out from the general level. The peneplain can be uplifted, which starts a second erosion cycle.

Davis acknowledged that a full cycle was a special case and that initial uplift was not necessarily rapid or followed by a prolonged period of quiescence. However, as Walther Penck pointed out, Davis and his followers usually used a rapid uplift and quiescence approach to explain landscapes. This means that the model, as understood by most, assumes rapid and episodic tectonic uplift. Another characteristic of the model is that slopes evolve by decline, with initially-steep slopes worn out by erosion forming successively-gentler slopes. Weaknesses of the model are that it is mostly theoretical and deductive in nature and it does not take into account the complexity of tectonic movements or climate change. The nature of surface processes is also poorly represented by the model. The model in its original form is intended to explain relief development in temperate landscapes in which erosion by running water is assumed to be of prime importance. Nevertheless, the cycle of erosion has been extended, with modifications, into arid, glacial, coastal, karst and periglacial areas.

VARIANTS OF CYCLE OF EROSION ON VARIOUS TYPES OF LANDSCAPE