His Geographical cycle of erosion is basically not a cycle as believed by many Geographers. It can be defined as The process of landform development passing through the Youth to Mature and then Old Stage, which is directed towards are well defined end-product i.e. 'Peneplain' (Davis called it 'Peneplane'), a featureless undulating landform feature.
Also Read : Penck's Model of Erosion
According to Davis Landform development is a function of :-
- Structure - Type of rocks from which mountains are formed and various other structural features such as faulting, folding, etc.
- Process - It means the denudation process/weathering and erosion.
- Time - It was not used only inn Temporal meaning but 'time' in his Model is used as a process itself.
Assumptions
- Landform development is a result of interaction of Endogenetic and Exogenetic forces.
- Landform development takes place an orderly manner in a Systematic Sequence through time according to environmental changes.
- Rivers erode their valley downward rapidly until the graded condition is not achieved.
- The upliftment takes place rapidly not slowly as described in Plate Tectonics Theory.
- Upliftment and erosion does not go hand in hand i.e. erosion starts only after the upliftment completes. This assumption became the focal point of severe attacks by the critics of the cyclic concept of Cycle of Erosion.
The Theory
Davis Model of Cycle of Erosion(Graphical representation)
UC - Upper Curve (represents highest altitude of divide summits).
LC - Lower curve (represents valley floor).
ADG - Base Level/Sea level
AC - Absolute Maximum Relief
BC - Relative Relief from valley at B.
NOTE:- No river can erode it's valley floor beyond the base level (Sea Level). Thus base level indicates maximum possible vertical Erosion (valley deepening) by the rivers.
The whole land form development goes through three stages -
1. Youth Stage
Since in this stage there is high gradient slopes is present, which leads to high velocity and high Kinetic Energy (K.E.) of Streams consequently high carrying capacity of streams which results into flow of big rock boulders in streams which results in to excessive vertical incision of the valley floor. All these into:-
- Absolute relief remains almost constant (CF is parallel to horizontal axis) because of insignificant lateral erosion.
- UC is not affected by erosion.
- LC is declined sharply due to high down-cutting and hence valley deepening.
- Relative relief increases because low lateral erosion and high vertical erosion.
- Valley sides form Gorges and Canyons.
- Valleys are of V shaped and characterized by convex valley side slopes.
- This phase is characterized by many rapids and waterfalls, which decline with end of this stage.
2. Mature Stage
In this stage gradient becomes lesser which results into decrease in vertical erosion and increase in lateral erosion.
- UC falls sharply and LC also falls but not as in the previous phase.
- There is a marked fall of relative relief, Absolute relief also decreases.
- Marked decrease in valley deepening.
- Time period of this phase is more than Youth stage.
3. Old Stage
Gradient reduces extremely, which result into minimum Kinetic Energy (K.E.) hence no valley incision but lateral erosion and valley widening is still active.
- UC falls more rapidly and becomes almost parallel with the LC, which is reduced to almost Base Level.
- Water divides are reduced in dimension by both down-wasting and back-wasting.
- Absolute relief as well as relative relief decreases rapidly.
- The valley becomes almost flat with concave valley side slopes having extensive flood plains.
- In this stage streams tends to form meanders and other features like Ox-Bow Lakes, residual convexo-concave Monadnocks and extensive undulating plain of low relief are formed.
- In the end the entire landscape is transformed into featureless 'Peneplain' (Davis called it 'Peneplane').
- Time Period of this Phase is longest of all the phases.
Positive Aspects fo the Model
- The Model is very simple and present in simple and lucid language but very well communicated.
- Based his model on careful field observation.
- It is able to predict the future and Historical description of landform development.
- It came after a very long gap after Hutton's Model on Geographical History.
Criticism of the Model
- The Model prescribes rapid upliftment of landforms but this is evident that it is very much slower according to Plate Tectonics Theory.
- He described that upliftment and erosion can't go hand in hand but this is heavily criticized by many geographers because erosion will not wait for completion of upliftment. Davis however said that he deliberately done it for two reasons: - (I). For simplicity of the Model and (II). The erosion during upliftment is negligible.
3. Davisian Model requires large period of stable land mass but this is also wrong as we know from Plate Tectonics Theory that the plates are continuously moving.
Conclusion
Although many parts of his theory was rejected but still his Theory holds significance as it provided the basis of the future Model of Penck.
Also Read: Koeppen's Classification of Climate