Geomorphic Cycle: Devis & Penck – UGC NET Geography – Detailed Notes

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.

Though Davis acknowledged that rock type, structure, and the processes of erosion play a part in landform determination, he emphasized that time was the primary factor. It is now believed that time is no more important in landform development than the other factors. The cycle-of-erosion theory has long been accepted in the face of accumulating quantitative data that refutes it. It is generally held now that the initial conditions-or uplift-in a region do not necessarily predetermine the end products. Rather, there tends to be an eventual attainment of dynamic equilibrium between landforms and the processes that act upon them. When this happens, the physiographic history of a region is “erased.” 

Davis Cycle

After the upliftment of landmass by the tectonic forces the process of denudation is started. The rivers, valleys and associated landforms passes through distinctive stages, provided that there has been no significant interference by earth movements or by changes of sea-level or climate. This idealized concept of landscape evolution was introduced to geomorphology more than sixty years ago by W.M. Davis, who referred to the whole sequence of stage as a Cycle of Erosion.

The basic goal of Davisian model of geographical cycle and general theory of landform development was to provide basis for a systematic descriptions and genetic classification of landforms. According to this concept a landscape has a definite life history, and as the processes of land structure operate on it the surface features are marked by several changes in its life time. Thus, the evolution of landscape passes through a cycle, and cycle follows a definite sequence of development.

The successive stage of developmental sequences can be divided into three parts and may be identified as youth, maturity and old age. Davis presentation of scheme was both vigorous and vivid and his colourful analogy of the human life and landscapes both passing through the stages of youth, maturity and old age caught the imagination of scientific world.

Youth

The uplift is complete and has stopped. Immediately erosion of the uplifted block sets in. The streams follow initial irregularities available without adjusting to the structure. These are consequent streams. The floors of the valley suffer down cutting while the summits remain almost unaffected. Increased relief heralds the beginning of mature age, indicated by widening of the gap between lines ‘A’ and ‘B’.

Maturity

At this stage, the vertical erosion slows down and the horizontal action increases. A characteristic feature is the erosion of mountain tops at a faster rate than lowering of the valley floor. The coming closer of lines ‘A’ and ‘B’ indicates emergence of a gentle slope. The subsequent streams gain importance now.