In this article we will discuss about the concept of ‘cycle of erosion’.
Cyclic concept was probably postulated first in geology by Scottish geologist James Hutton in 1785 when he propounded the concept of ‘cyclic nature of the earth history’ and the dictum of ‘no vestige of a beginning; no prospect of an end’ and ‘present is key to the past’.
The concept of cyclic nature of the earth history was later on transformed into the concept of ‘uniformitarianism’ which states that ‘the same physical processes and laws that operate today, operated throughout geologic time, although not necessarily always with the same intensity as now.’
Probably based on this inheritance of Hutton’s concept of the cyclic nature of the earth history and the evolutionary concepts of Charles Darwin (Origin of Species through natural selection) William Morris Davis (1850-1934 A.D.) presented his concept of cycle of erosion under the title of geographical cycle of erosion in the year 1899 though the concept of ‘complete cycle of river life’ was already propounded in the year 1889. The Davis’ model of geographical cycle of erosion was based on the basic concept of ‘sequential change in landforms through time like the evolution of an organic life.’
According to Davis landforms undergo sequential changes through time (passing through three stages of youth, mature and old).
The earth’s surface is affected by two types of forces viz.,:
(i) endogenetic forces and
(ii) exogenetic forces wherein endogenetic forces create vertical irregularities on the earth’s surface by forming several types of relief features of different dimensions whereas exogenetic processes originating from the atmoshpere (rivers, wind, glaciers, seawaves, groundwater, periglacial processes etc.) try to remove the vertical irregularities created by the endogenetic forces and ultimately become successful in bringing down the reliefs to low featureless plain called as a peneplain.
The whole period of the creation of relief features by endogenetic processes and their destruction by exogenetic processes is called cycle of erosion which Davis defined as follows: “geographical cycle is the period of time during which an uplifted landmass undergoes its transformation by the process of land sculpture ending into a low featureless plain-a peneplane.”
The concept of ‘geographical cycle’ of Davis was severely criticised by German geographers and the term ‘cycle’ was described as confusing and hence untenable. Walther Penck though accepted the basic concept of cycle of erosion but rejected the Davisian model of geographical cycle and propounded his own model of cycle of erosion.
Inspite of severe criticism in Germany the Davisian model of geographical cycle of erosion was adopted by most of the contemporary and subsequent geomorphologists all over the world. It may be safely argued that Davisian model of cycle of erosion, say the first general theory of landform development, dominated the entire field of geomorphology and geomorphological investigations right from its inception in 1899 to 1950 throughout the world.
His ‘cycle of erosion’ was basically concerned with the evolution of landforms in humid temperatle areas but the cyclic concept was later on applied to almost all the geomorphic processes e.g. arid cycle of erosion, glacial cycle of erosion, marine cycle of erosion, karst cycle of erosion, periglacial cycle of erosion etc.
C. H. Crickmay suggested modifications in Davisian model of ‘geographical cycle’ in 1933 and described the process of panplanation to be more powerful and effective than Davis’ process of peneplanation in the evolution of landforms. According to Crickmay the end product of the cycle of erosion would be panplain and not the peneplain. L.C. King proposed a new cycle of erosion named as ‘the cycle of pediplanation’ to explain the characteristics and evolution of landforms of arid and savanna regions of Africa as he found Davisian model of geographical cycle unfit to explain the landforms of the aforesaid regions. J.C. Pugh (1966) and M.F.
Thomas (1966) propounded the concept of savanna cycle of erosion to account for the development of landforms of semi-arid savanna regions of Africa. A.N. Strahler (1950), J.T. Hack (1960) and R.J. Chorley (1962) rejected the evolutionary concept of landform development as advanced by W.M. Davis and his followers and pleaded for the concept of ‘time—independent landforms’ instead of Davisian concept of ‘time-dependent landforms’ and advanced the concept of ‘dynamic equilibrium model’ of landform development.
Recently, ‘tectonogeomorphic model’ of Marie Morisawa (1975, 1980), ‘episodic erosion theory’ of S.A. Schumm and R.W. Lichty (1965) etc. have been suggested to explain the landform development. These models are, in fact, modified forms of Davisian model of landform development.