Hilly relief Etched hilly relief Rhodes Fairbridge and Charles Finkl argue that peneplains are often of mixed origin polygenetic as they may have been shaped by etchplanation during periods of humid climate and pediplanation during periods of arid and semi-arid climate. The long time spans under which some peneplains evolve ensures varied climatic influences. King wrote: [12] A peneplain in the Davisian sense, resulting from slope reduction and downwearing, does not exist in nature. It should be redefined as "an imaginary landform.

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He explained the evolution of south African landscape through a cycle of erosion. He stared his study over the arid, semi arid and savana region of south Africa. This region is characterised by extensive plain area along with some uplifted landscape, scarp and eroded place, which he has given name as Pediplanation. Pediplanation refers to the remarkable surfaces of planation, surrounded by isolated hills and piles of boulders.

Thus, L. King proposed an entirely new theory as cyclic model of pediplanation in the year of Rock pediments, flanking river valley and having concave slope with varying angle from 1. Scarps having steep slope of varying angle from 15 degree to 30 degree. The steep sided residual hills known as Inselberge or bornhardts with varying shape and size.

The cycle of pediplanation of L. King performed by twin processes i. The cycle of pediplanation passes through three stages — youth, mature and old stage. Youth stage: This stage is characterised by upliftment of the landscape. Thus, the river started rapid down cutting that also given birth lots of gorge and canyons. Knick point is another remarkable sfeature in this stage cause by changes of slope gradient. But with the march of time down cutting goes slow down and small pediments will begin to appear at the bottom of the valley.

Mature stage: This stage is characterised by active lateral erosion, downcutting or vertical erosion totally stop. Due to lateral erosion the interfluve area become narrowed down, after some time it turn into a steep sided rounded top like feature, called as Inselberge. Active lateral erosion is also cause for valley retreating. Thus, valley sides are distanced from the channel, but significant change in slope can not found.

Many of inselberges are losing its height due to lateral erosion and weathering, thus it turns into castle koppies. After sometime these castle koppies also started to disappear due to extension of pediment. These pediments also coalesce with othe pediments to form extensive flat plain, called as pediplain. These pediplain is charactyerised by undulated surface with low relief, concave slope and few remnants of inselberge and castle koppies.

Old stage: This stage is characterised by disappearance of residual hills. The entire landscape became a flat extensive low angled pediments. Another reason was, at that time most of the geomorphologists were least interested about geomorphic theories as they were busy in quantifying landforms, data obtained through field instruments, laboratory experiments which take vary short time and smaller spatial scales.



Etchplanation involves 2 processes namely deep weathering followed by exhumation. Deep weathering refers to rapid chemical weathering and this causes rock paricles to further disintegrate into even smaller particles. This occurs when rainwater enters cracks and crevices in rocks thus exposing the rock to greater surface area of weathering. This process of deep weathering occurs during the warm pliocene period and results in a deep layer of weather materials. Exhumation or removal of weathered materials happens during periglacial times due to flash floods or solifluction. Hence, this can expose the basal surface of weathering the limit to weathering- from completely weathered rocks in the upper layers to unjointed basal suface. Outcrop in the basal surface that is exposed in the surface is formed as inselberg.


7 Major Geomorphic Theories of Landform Development

Davisian Theory: The most popular theory of landform development was given by American geomorphologist William Morris Davis. His concept of geographical cycle or commonly known as cycle of erosion provided a genetic classification and systematic description of landforms. However, Prof. The main premises of Penckian model of landscape development are the following: 1. On the basis of morphological characteristics tectonic movements can be explained and their causal factors ascertained. Development of landscape is not time- dependent. The shape of the hillslope depends on the relative rates of valley incision by rivers and removal of debris from the hill-slope.



Charles Musarurwa 7 Theories of Inselberg formation: can their differences be explained by equifinality? Because they are found in different environments, theories concerning their formation have remained controversial and hence many explanations have been advanced. In this paper only two schools of thought will be reviewed and these are: the one represented by Lester King and that by C. Twidale and colleagues. The last part of the paper assesses whether it is appropriate to have a variety of theories to explain the same phenomenon, that is; is equifinality applicable to inselberg development? This paper confines the comparison of the work done by King and Twidale to the tropical regions since both worked in tropical environments.

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