Cycle concept in geomorphology has been quite useful and logical despite those who have tried to wriggle out of this reality without much success. Those who believe in geomorphic cycle do not and cannot believe that the evolution of landforms is in a cyclic order in the literal sense or that at the end of one cycle another cycle of the same magnitude starts.

The cycle concept tries to set an ideal framework. The endogenic and exogenic forces and processes are so complex, and relatively varying in intensity, time and space that the literal concept of cycle cannot be adhered to. What is significant is that the cyclic concept emphasizes sequential development of landforms and this is the chief characteristic, merit and reality of the concept.

The sequential development of landscape is too obvious to merit controversy as regards its existence. We can observe what happens to an earthen mound of considerable size. In the initial stages, there will be tiny rills. These will be deepened and enlarged with the passage of time. The height of the mound will gradually decrease. If there were steep slopes on the edges, these will be gradually flattened.

With the passage of time, there will be multiplicity of drainage lines and the surface of the mound will be dissected and lowered. With further advance of time, there will be further vertical wasting of the mound. In the final stages, the rate of reduction will decrease and the mound may persist for a much longer time than what has been taken by the initial and intermediate stages. The last vestiges of the mound may persist for an indefinitely long time. This sequential development of a tiny, simple and familiar case, when examined in detail, is what represents a geomorphic cycle.

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Here the obvious factors are the structure, i.e., the build and composition of the mound, the process, particularly rainfall and stage, i.e., the time factor.

But while it is easy to make an artificial mound the existence of a highland, ab initio, as imagined by W.M. Davis, lacks logic. All uplifts are imperceptibly slow.

The Himalayas are believed to be rising at a rate of 2 mm per year. This is regarded a rather rapid rate of uplift. Now if mountains or plateaus have appeared on the earth with such slow rate it is impossible to imagine that they were allowed to gain great heights, without erosion as imagined by Davis. The plea is that such assumption is for the sake of simplicity but this simplicity is probably based on unreality.

No doubt, high mountains and uplands are there on the surface of the earth but they have risen at an imperceptibly slow rate. But this rate has been too much for the rate of erosion whence the rise overcame erosion. If this be the reality of circumstances, although Davis’s sequential development of landforms in a cycle of erosion is true, the initial conditions were probably what was suggested by Walther Penck—a level surface rising slowly, i.e., the primarrumpf. Whether the surface was emergent from below the sea or whether it was a terrestrial surface, because of the imperceptibly slow uplift the conditions were those of the primarrumpf and erosion started thereupon without waiting for the surface to attain great height.

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Take for instance, the case of the Himalaya. It is a rapidly rising mountain. The uplift is continuing on the basis of different evidences. It has not stopped as was assumed by Davis before the start of his normal cycle. Along with the continued uplift erosion has been apace and the Himalayan landscape is quite frequently one of Maturity’ with inversion of relief, high degree of dissection, immense relief, rounded inter-stream ridges, etc. Thus, the Himalayas do not bear out the cycle of development as pictured by Davis, where the starting point is one of still stand and of maximum altitude without further elevation.

Those who were conscious of the fact of uplift during the cycle of erosion have used the terms ‘cycle of denudation’ or ‘cycle of topographical development’. Probably Davis’s more comprehensive term, ‘cycle of development’ also included all factors and facts during the evolution of landscape.

Wooldridge and Morgan are ardent supporters of Davis’s geomorphic cycle and rightly so but they too like Davis have unjustifiably assumed rapid uplift in the beginning so that there is no scope for “any significant amount of erosion during the process, of elevation. Except for the rapid uplift (approximately instantaneous uplift” according to O.D. von Engeln, 1960, p. 260) assumed for the beginning of the cycle, the cycle concept of Davis is probably still the most suitable and satisfactory framework for explaining landscape evolution. The inferences about what have gone by and what is normally expected in future can be made within this framework.

Hack has challenged Davis’s cyclic concept. He asserts that after equilibrium has been achieved among the various physical factors, e.g., rate of uplift, the type of climate, vegetation, etc. there will be no change in the landscape because uplift and erosion will balance each other. Only when the balance is disturbed by a higher rate of uplift or a change in climate geomorphic change will come into existence. People are trying to verify the cycle or equilibrium concepts in the field. Bretz4 from his field studies in the Ozarks mountains in the U.S.A. confirms the cyclic evolution of landscape.

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Probably Hack’s non-cyclic concept cannot be borne out. The balance or equilibrium, which he imagined, may not be achieved. So many physical factors are involved that it is difficult to imagine that they will so mutually adjust themselves as to create an equilibrium in which landforms will remain constant. Who can any climate be constant and how can tectonic activity be so meticulously responsive to the facts of climate or vegetation? L. Wilson believes in a gradual landscape evolution “perhaps similar to that postulated by Davis.”