King’s Model of Slope Development

L . C. Kings proposed several theories on slopes as a part of the broad scheme of landscape evolution. He proposed several sets of cycles like the river cycle, the hill slope cycle, the landscape cycle etc.

King’s work on the cycle of erosion is based on his observation of the African landscape. He held that subtropical and semi-humid climates should be regarded as ‘normal’ instead of humid temperate, on which much of the discussion of slope evolution is based. His river cycle bears close similarity with Davis’ cycle of slope evolution.

King made a closer examination of the African landscape and stated that it comprises two important elements: the gentle concave slope found in the valley bottoms and borders of the streams or old water course. They are Pediments which, over a period of time, slowly extend their area and see the adjoining uplands retreat.

Pediments, according to King (1953), are normally covered with detritus, but pediments themselves are essentially cut rock surfaces. The pediment is the fundamental landform to which epigene landscapes tend to be reduced. He termed the entire process of pediment formation as pedimentation.

The second element is the steep slopes that bound upland blocks. He called it ‘scarps’. The scarps here have originated by the process of erosion only and maintain steep slopes of 15 to 30 degrees. There is no reduction in their steepness when they are wasted back by weathering or rainwash. This is the process of Parallel Retreat, which King called ‘scarp retreat’.

King’s Cycle of Pediplanation

King’s landscape cycle discusses the process of pediplanation which shapes the erosion surface. Different stages of his cycle are discussed below.

Youth Stage

The cycle of pediplanation begins with the upliftment of an earlier-formed pediplain. The streams carry out a rapid downward erosion. As the cycle draws near the end of youth, the earlier fast down-cutting slows down and witnesses the emergence of pediments in the valley bottoms. These pediments become wider because of the reduction of upland areas by scarp retreat.

In the late youthful stage, most interfluves will be converted into inselbergs, and many will be rounded off like domes.

Maturity Stage

In the mature stage, the process of weathering causes a reduction in the number of Inselbergs. There will be a widening of pediments of adjoining valleys, which would eventually coalesce. The few remaining inselbergs preserve the vestiges of the former pediplain (Small,1978).

The relief which during the youth saw an increase will now show a decline or may remain constant in maturity

Old Age Stage

The old age will see very few residual hills as a relief has mostly been destroyed. The whole landscape will now be dominated by gently sloping pediments; the ‘multi-concave’ surface is the ultimate form of the cycle (Small,1978).

King did not restrict the application of his concept to the African landscape only but he extended this to other non-arid climates of the world to explain the process of landform evolution operating under most climatic conditions.

Thus, the King’s landscape cycle involves two processes ‘pedimentation’ and ‘scarp retreat’. The operation of these two processes leads to the formation of erosion surface.

King’s View on Slope Elements

Hillslope evolution is a function of denudation that involves two phases- The production of land waste and the removal of land waste. He underlined two principal agents responsible for denudation (a) Flowing Water and (b) Mass Movement.

King accepted the hillslope elements suggested by Wood (1942). He further stated that these elements are the product of hillslope evolution. The element is four in number- the waxing slope, the free face, the debris or talus slope (constant) and the pediment.

King (1957) believed that each element has a semi-independent evolution. They also react to each other in varying degrees. His definition of the elements are given below:

1. The waxing slope is the convex crest of a hill or scarp
2. The Free face is the outcrop of bare bedrock exposed on the upper part of the hillside. It is the most active element in the back wearing of the slope as a whole.
3. The debris slope: consists of detritus slipped or fallen from the face and resting at its angle of repose against the lower part of the free scarp face.
4. Pediment: A pediment is a broad concave ramp extending from the base of the other slope elements down to the bank or alluvial plain of the adjacent stream.

King argued, ‘these four slope elements are to be found in hillslopes all over the world in all climatic environments; though locally one or more of the elements may be suppressed, such departures afford no contradiction of the normality of full development’.

The following figure illustrates clearly different elements of the slopes and their relative positions (fig).

As stated earlier, he accepted all four elements of wood that appear in a fully developed slope. But full development of slopes with all four elements also depends on other factors, like a strong bedrock and adequate relief ‘failing these, the free face tends first to disappear, followed by necessity by the debris slope. A decadent convexo-concave hillslope results’ (King, 1957).

Disagreeing with Davis regarding the ‘normal’ type of landscape, he holds the semi-arid type as normal landscape, and pediplain is the ultimate cyclic landform formed by coalescing pediments. A pediplain is multi-concave upward (1953, King).

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