Cycle of Erosion by W.M.Davis
William Morris Davis was born in 12th February, 1850 at Philadelphia, Pennsylvania, into a prominent Quaker family. He was an American Geomorphologist. He had sound knowledge over geography, geology and meteorology, thus called him Father of American Geography. W.M.Davis was professor of Harvard University. From many years he was studying over geomorphic process on earth surface and after fifteen years of hard work he got success to make the model Cycle of erosion.
Concept of Davis: According to Davis “Landscape is the function of structure, process and time”. It means landscape development is dependent on three factors i.e. structure, process and time. These three factors are also called “Trio of Davis”.
Structure: structure means lithological and structural characteristics of rocks like dip, strike, fault and fracture.
Process: process means agent of denudation including weathering and erosion, fluvial action, wind action, sea wave etc.
Time: Required time for landscape evolution. In this context he divided three stages of cycle of erosion, i.e. youth stage, mature stage and old stage.
Basic premises of Davisian Model:
- There is vertical upliftment of landmass.
- There is rapid rate of upliftment of landmass.
- During upliftment no erosion will be started.
- Streams erode their valley rapidly downward until the graded condition is achieved.
Stages of cycle of erosion and their characteristics
Youth stage: Erosion started after completing the upliftment of landmass. Numerous streams are originated with the initiation of upliftment. These streams are called Consequent stream. Many tributaries also developed and when they meet with main stream produce different types of dendritic pattern. In this stage all the rivers are small and widely spaced. All the rivers are engaged in headward erosion and down cutting. Headward erosion caused for stream lengthening. Steep slope and steep channel gradient rivers are actively deepens their valley, thus the valley became very deep and narrow. This process is called valley deepening.
Youthful stage is characterised by rapid downcutting and steep and narrow valley, because steep slope and channel gradient increase the kinetic energy and velocity of river. Thus the carrying capacity of the river is also increased. Big boulders are carried by rivers which help in valley incision through pothole drilling.
Characteristic features of youth stage:
- Very steep and narrow valley. Valley form is gorge and canyon.
- Absolute height remain constant because of very less amount of lateral erosion.
- Relative height is continuously increasing, because of rapid down ward erosion.
- Valleys are of V shape characterised by convex valley side slope.
- Long profile of rivers are characterised by rapids and waterfall.
Mature stage: This stage is characterised by lateral erosion and integrated drainage system. Valley deepening remarkably reduced. Thus both absolute and relative relief decreases. In this stage steep valley slope turns into wide valley due to lateral erosion. The graded conditions spread over larger area and most of the tributaries are graded to base level of erosion.
Old stage: This stage is characterised by almost total absence of downward erosion but lateral erosion is still active. Thus height of water divide decreases rapidly. The entire valley became almost flat with concave valley side slopes. This type of landscape is called as peneplain. Sometimes hard rocks are stand over the peneplain, which resistant to erosion, known as Monadnocks.