Cycle of Erosion.pptx

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1. Cycle of Erosion

2. Cycle of erosion is also called as G eomorphic cycle G eographic cycle T heory of the evolution of landforms

3. Definitions It is  an idealized model that explains the development of relief in landscapes .   It is a model for stream erosion and landscape development. It is a cyclic process through which various endogenic and exogenic forces take part to the chronological development and evolution of landforms in a sequential manner.

4. Assumptions The lithology of the whole area must be homogeneous in type. Upliftment of land occurs rapidly/There is a short-period rapid rate of upliftment in land mass.  E rosion process does not take place until the completion of the upliftment process.  The evolution of landforms takes place in an orderly manner in such a way that a systematic sequence of landforms is developed through time in response to an environmental change .   Rivers/Streams erode their valleys rapidly down­ward until the graded condition is achieved.

5. Each landform in the world undergoes a series of denudation processes over time. Initially, before the start of erosional activities, the terrain consists of a flat surface. Due to the activation of endogenous forces, there is a sudden uplift of the land. There is no denudation process during the process of land upliftment . After the upliftment of land, the sequence of denudation process or landform development process starts. The uplifted land goes through youth, maturity, and old age, all these changes happen in sequential order over time. In old age, the final landform of the land is the peneplain . The development of landforms occurs in form of  "slope decline".

6.  William Morris Davis first formulated the concept of geomorphic cycle in 1889, entitled as  ‘Theory of Cycle of Erosion’ . Davis studied the Appalachian Mountains of North America, which is a humid climatic region, and based on the study, he proposed the cycle of erosion.   ”Geographical cycle is a period of time during which an uplifted landmass undergoes its transformation by the process of land sculpture ending into low featureless plain called peneplain or peneplane ... Three factors viz., structure, process, and stage play important role in the origin and development of landforms of a particular place .”

7. William Morris Davis, an American geomorphologist, was the first geomorphologist to present a general theory of landform development . Various models were developed on the basis of this reference system e.g., normal cycle of erosion, arid cycle of erosion, glacial cycle of erosion, marine cycle of erosion etc. Thus, ‘geographical cycle’ is one of the several possible models based on Davis’ reference system of landform development According to Davis, there are three major factors ( i.e structure, process, and time) that play important role in the cycle of erosion and landform development. These three factors of landform transformation are basically known as  ‘Trio of Davis’ . Landforms were assumed to change through time from “youth” to “maturity” to “old age,” each stage having specific characteristics.

8. The three factors of landform transformation/Trio of Davison Structure/ Structure of Landmass: The structure of the landmass is the first factor in the Davisian erosion cycle. The cycle of erosion depends on the composition of the terrain. Some terrain is made up of hard rocks which slow down the process of erosion, and formations made of soft rocks have a faster process of erosion.  The structure of rocks such as faults, foldings , and fractures also determines the intensity of the erosion process, the slope replacement process, and the landform development process.

9. Process Process means a geomorphic process which refers to the types of geomorphic agents that determine erosion, transport, and deposition activities. Flowing water, winds, glaciers, groundwater, waves, etc. are the major geomorphic agents. Flowing water agents are active in the humid region while winds are active in the desert region.

10. Time Davis' model is based on the evolution of landforms over time, passing through youth, mature, and old stages

11. Youthful stage Erosion starts after the com­pletion of the upliftment of the landmass Water-divider is one of the most prominent features in this stage . Upper curve (UC) representing summits of water divides is not affected by erosion. River meander is a rare feature that develops based on the primary ridges and slopes. Bottom erosion of river is the main erosional process in the youth stage .   Bottom erosion/Vertical erosion/Valley deepening is greater than lateral erosion in the valley . The gap between the summit and the valley increases. Deep valleys are formed in this phase . The valleys have a steep slope.

12. The gap between the summit and the valley increases. Deep valleys are formed in this phase. The valleys have a steep slope. The gap between the summit and the valley increases. Deep valleys are formed in this phase. The valleys have a steep slope. Small rivers and short tributaries are engaged in head-ward erosion due to which they extend their lengths. The process is called stream lengthening (increase in the lengths of the rivers ). Erosion starts after the com­pletion of the upliftment of the landmass  Increased channel gradient and flow velocity increases the transporting capacity of the rivers.

13. Mature stage Various drainage patterns become prominent in this stage. Lateral/side erosion by river majorly takes part rather than the vertical/bottom. (Vertical erosion or valley deep­ening is remarkably reduced .) Water-dividers become less prominent. ( The summits of water divides are also eroded.) The gradient of the slope is reduced. "V" shaped valley is transformed into a "U" shaped valley . There is well integrated drainage network.

14. Old stage T he river valley floor becomes extremely wide and develops almost a plain land, which Davis identified as  ‘ Peneplain ’ .   Vertical erosion of the valley stops as it reaches the base level of erosion . Formation of peneplain (base level plain, no further erosion) takes place . Two most important and prominent features of old stage of erosion are  ‘ Monadnock ’  and  ‘Oxbow Lake’ . Monadnock are the remaining part of the eroded water-dividers, and in the other side, oxbow lake develops when a river intersects its well-formed curves and flows in a straight line . Formation of peneplain (base level plain, no further erosion) takes place.

15. Old stage is characterized by almost total absence of valley incision but lateral erosion and valley widening is still active process.  Relative or available relief also de­creases sharply because of active lateral erosion but no vertical erosion .

16. Monadnocks

17. Positive aspects of the theory It is simple and logical. The theory laid the foundation for other theories on evolution of landforms. The theory was based on careful field observations.

18. Negative aspects of the theory/demerits/criticisms/drawbacks/shortcomings Irrelevant co-relation of time between land upliftment and erosion: Davis stated that land uplifts rapidly and erosion does not take place until its completion. It is quite baseless . There is no assurance about this assumption. Landscape may uplift during the erosion process and both of upliftment and erosion can take part in the evolution of landforms at the same time. Over-emphasized the role of  the stages or time:  Davis relatively ignored the importance of structure [role of rock types]  and process [ role of geomorphic agents such as running water, groundwater, winds, wave, glaciers, etc ] which are important controlling factors of landform development. The role of stages [ i.s youth, mature, and old) or time are overemphasized. He also ignored the role of climate in landform development.

19. Overemphasized of erosion process: Davis ignored the role of deposition and weathering in landform development and overemphasized the erosion factor. C ompletion of the erosion cycle: According to Davis, the erosion cycle is completed after the formation of the peneplain or reaching the old stage, but in reality, landform development is a never-ending process . Over generalization of the concept: Too much of generalization in the Davisian cycle presents an inadequate framework for landforms interpretation.

20. The geographical cycle proposed by Davis is backward looking as it considers complete suspension of the uplift after the erosion has set in. There are no logical grounds for the assumption that flat slopes arer old and steep slopes are young. Other variables controlling the slope are nature of soil material and the bedrock, climate, vegetation and the downslope factors acting at the slope foot. There is little evidence to prove that landforms actually evolve to an end product or peneplane .

21. Terms to know Geomorphology Geomorphology is the development and evolution of physical features or landforms on the Earth’s surface. Lithology It is the study of rocks. Valley incision V alley deepening through vertical erosion.

22. References https://www.studyprobe.in/2020/05/cycle-of-erosion-theory-by-davis.html https://www.onlyiasexam.com/2019/10/davis-cycle-of-erosion-geography-upsc.html

23. Questions to explore "Landscape is a function of structure, process, and stage." Critique the statement. Discuss the Davisian concept of the cycle of erosion and show how it explains the evolution of landforms.