CONCEPT OF CYCLE OF
EROSION
(Geographical Cycle of Davis)
In the US of 1889, the famous geologist William Moris Davis first introduced the concept of Geographical Cycle or Cycle of Erosion. After this, he confirmed his idea on the basis of special study in 1894, 1899 and 1902. According to Davis sir, "The erosion cycle or geographic cycle is the period of time under which a raised landmass becomes undamaged by the process of erosion and transforms into a shapeless plain plain." (The cycle of erosion is a period of time during which an uplifted landmass undergoes its transformation by the process of sculpture mining in low featureless plain.- w.M.Davis). Like other scholars, Worcester has also recognized Davis' geographical history. But Barcester considers it more appropriate to call the erosion cycle rather than calling it a geographical cycle. They have also considered erosion cycle as a period under which the factors of erosion in different stages transform the elevated land area into low level land. (The cycle of erosion is the time required for streams to reduce a newly formed landmass to base level). The base level is the floor beyond which erosion is not possible. The sea level is the best example of base level, thus Davis observed the cyclic pattern in the development of site forms in a historical setting. The use of the cyclic method in the development of site forms is an important part of Davis's concept. He informed that the construction and development of site forms is influenced by the structure, process and condition. In Davis' words, "Landscape is a function of structure, process and stage" (Landscape is a function of structure, process and stage). These three factors (structure, process and condition) are known as 'Trio of Davis'. A brief description of these three factors is given below:
1. Structure - The structure includes characteristics such as the texture, properties and nature of rocks. Broadly, the study of the folds, faults, joints, dips, strike, mineral composition, porosity, permeability and relative hardness, etc. are studied under it. The structure is gradually formed over a long period by diastrophism. According to WD Thornbury, "Geological structure is the main factor controlling the development of site forms. Every site form has a glimpse of its structure."Structure, in fact, is the foundation for the formation of any topography, that is, first the structure of rocks is developed, then later on they develop various
geomorphic forms. Is older than.Regardless of what we see, the structure has its function and effects.
2. Process - The processes or factors that create and disturb topography on the ground are called processes. These processes that bring about changes on the ground floor can also be endogenetic and exogenetic can also include erosion of volcanoes and earthquakes in endogenous factors and weathering of exogenous factors as well as impermeable of river, glacial, ground water, wind and sea waves. And depositional functions are included. Every Topography is the result of a particular process . The exogenous process has its own specific domain. In which it develops a community of specific landforms. For example, flowing water (river) is a major factor in erosion and deposition in tropical regions which creates landforms like falls, garages, alluvial fins, floodplains, Gokhur lakes and deltas. The work of wind would have been predominant in dry and hot deserts. From which land forms such as Chhatrak, Jugen, Yardang and Barkhan are developed. Similarly, in glaciated areas, the work of glacial, lime rocks in underground water and sea waves and currents in coastal areas is seen more. According to Thornbury, each factor of the gradient equilibrium acts at a different speed — hence causing a higher relief on the ground.
3. Stage - Stage refers to the extent to which an instrument of denudation has pruned a plot. According to von Angilan, "state refers to the specific development during the changes brought about by processes over a landmass." Like human life, the development of landmass takes place in some gradual stages, which Davis has called Young Stage, Mature Stage and Old Stage. It is not necessary that different stages arrive at a given time at a given time, as processes are controlled by structure. Landfields with soft rocks soon pass through all stages of development, while hard rock landmarks pass through each stage late.
On this basis, WM Davis said that, "Landscapes are the result of structure, process and condition".
Pre-Assumptions of Davisian Cycle of Erosion
(1) The beginning of erosion or geographic cycle is considered on a surface whose rise from the sea is short term completed it at a more rapid pace. Special circumstances in this rise can also occur at slow speed.
(ii) The speed of rise above the surface is faster than its weathering.
(iii) The erosion does not begin until the uplift is over, that is, the uplift and erosion do not work together.
(iv) Erosion cycle is mainly accomplished by air, glacier, river and ground water.
(v) The erosion cycle in a terrain depends on the height, width, texture, structure, properties of rivers, distance from the sea and the amount of rainfall, etc. on that surface.
(vi) The erosion cycle on the ground is completed in a gradual manner ie first the youth-age, then the aging and finally the old-age patterns develop.
(vii) It is a never ending process. The ground that is decaying can rise up and down below the earth's internal movements. As a result, the phase of erosion can be forward or backward respectively.
(vii) All the land forms of the world are the result of the interaction of endogenous and exogenous forces.
(ix) Rivers continue to deepen their valley till they become prone.
Graphic Representation of Cycle of Erosion
Davis prepared a graph to explain his model of geographical cycle of erosion (Fig)
(Geographical Cycle of Davis)
In the US of 1889, the famous geologist William Moris Davis first introduced the concept of Geographical Cycle or Cycle of Erosion. After this, he confirmed his idea on the basis of special study in 1894, 1899 and 1902. According to Davis sir, "The erosion cycle or geographic cycle is the period of time under which a raised landmass becomes undamaged by the process of erosion and transforms into a shapeless plain plain." (The cycle of erosion is a period of time during which an uplifted landmass undergoes its transformation by the process of sculpture mining in low featureless plain.- w.M.Davis). Like other scholars, Worcester has also recognized Davis' geographical history. But Barcester considers it more appropriate to call the erosion cycle rather than calling it a geographical cycle. They have also considered erosion cycle as a period under which the factors of erosion in different stages transform the elevated land area into low level land. (The cycle of erosion is the time required for streams to reduce a newly formed landmass to base level). The base level is the floor beyond which erosion is not possible. The sea level is the best example of base level, thus Davis observed the cyclic pattern in the development of site forms in a historical setting. The use of the cyclic method in the development of site forms is an important part of Davis's concept. He informed that the construction and development of site forms is influenced by the structure, process and condition. In Davis' words, "Landscape is a function of structure, process and stage" (Landscape is a function of structure, process and stage). These three factors (structure, process and condition) are known as 'Trio of Davis'. A brief description of these three factors is given below:
1. Structure - The structure includes characteristics such as the texture, properties and nature of rocks. Broadly, the study of the folds, faults, joints, dips, strike, mineral composition, porosity, permeability and relative hardness, etc. are studied under it. The structure is gradually formed over a long period by diastrophism. According to WD Thornbury, "Geological structure is the main factor controlling the development of site forms. Every site form has a glimpse of its structure."Structure, in fact, is the foundation for the formation of any topography, that is, first the structure of rocks is developed, then later on they develop various
geomorphic forms. Is older than.Regardless of what we see, the structure has its function and effects.
2. Process - The processes or factors that create and disturb topography on the ground are called processes. These processes that bring about changes on the ground floor can also be endogenetic and exogenetic can also include erosion of volcanoes and earthquakes in endogenous factors and weathering of exogenous factors as well as impermeable of river, glacial, ground water, wind and sea waves. And depositional functions are included. Every Topography is the result of a particular process . The exogenous process has its own specific domain. In which it develops a community of specific landforms. For example, flowing water (river) is a major factor in erosion and deposition in tropical regions which creates landforms like falls, garages, alluvial fins, floodplains, Gokhur lakes and deltas. The work of wind would have been predominant in dry and hot deserts. From which land forms such as Chhatrak, Jugen, Yardang and Barkhan are developed. Similarly, in glaciated areas, the work of glacial, lime rocks in underground water and sea waves and currents in coastal areas is seen more. According to Thornbury, each factor of the gradient equilibrium acts at a different speed — hence causing a higher relief on the ground.
3. Stage - Stage refers to the extent to which an instrument of denudation has pruned a plot. According to von Angilan, "state refers to the specific development during the changes brought about by processes over a landmass." Like human life, the development of landmass takes place in some gradual stages, which Davis has called Young Stage, Mature Stage and Old Stage. It is not necessary that different stages arrive at a given time at a given time, as processes are controlled by structure. Landfields with soft rocks soon pass through all stages of development, while hard rock landmarks pass through each stage late.
On this basis, WM Davis said that, "Landscapes are the result of structure, process and condition".
Pre-Assumptions of Davisian Cycle of Erosion
(1) The beginning of erosion or geographic cycle is considered on a surface whose rise from the sea is short term completed it at a more rapid pace. Special circumstances in this rise can also occur at slow speed.
(ii) The speed of rise above the surface is faster than its weathering.
(iii) The erosion does not begin until the uplift is over, that is, the uplift and erosion do not work together.
(iv) Erosion cycle is mainly accomplished by air, glacier, river and ground water.
(v) The erosion cycle in a terrain depends on the height, width, texture, structure, properties of rivers, distance from the sea and the amount of rainfall, etc. on that surface.
(vi) The erosion cycle on the ground is completed in a gradual manner ie first the youth-age, then the aging and finally the old-age patterns develop.
(vii) It is a never ending process. The ground that is decaying can rise up and down below the earth's internal movements. As a result, the phase of erosion can be forward or backward respectively.
(vii) All the land forms of the world are the result of the interaction of endogenous and exogenous forces.
(ix) Rivers continue to deepen their valley till they become prone.
Graphic Representation of Cycle of Erosion
Davis prepared a graph to explain his model of geographical cycle of erosion (Fig)
The beginning of the cycle of erosion is marked by the rapid and short lived upliftment of landmass of homogeneous structure. The initial phase of rapid and short lived period is not included in the cycle time as
this represents the preparatory stage of the cycle of erosion. In Fig. , the horizontal line, i.e., X-axis represents time whereas vertical line, i.e., Y-axis represents attitude. The upper curve shows the hill tops or crests of water divides, i.e., absolute relief above the base level, i.e., mean sea level represented by the line ADG. Similarly, lower curve shows valley floors, i.e., lowest relief above the base level, i.e., mean sea level. AC shows maximum absolute relief whereas BC represents initial average relief. The difference between the upper curve and the lower curve of a landmass is known as initial relief. The base level represented by the line ADG determines the maximum limit of vertical erosion because no river is ever able to erode its valley below the base level. At the point C, rapid upliftment of landmass stops and erosion starts. This marks the beginning of the cycle of erosion.
The whole cycle of erosion passes through three stages, viz., (i) Youthful stage, (ii) Mature stage, and (iii) Old stage.
(i) Youth Stage. Youth stage commences when the process of erosion starts after rapid and short lived upliftment is complete. Following are the main characteristics of this stage.
1. In the beginning the rivers are small and widely spaced. There may be a few consequent trunk streams but few large tributaries.
2. Erosion starts in the river valley but there is no erosion on the top surface or summits of water divides.
3. The length of streams and their tributaries increases due to headward erosion (erosion towards the source of stream) which is prominent form of erosion in this stage. This process is known as stream lengthening.
4. Due to steep slope and steep channel gradient, the rivers are actively involved in vertical (down) erosion as a result of which the depth of valleys increases. This is known as valley deepening,
5. The cross profile of the valleys is V-shaped,
characterised by convex valley side slopes. The
valleys are deep due to steep gradient of channel, high
velocity of river flow, increased erosion, and enhanced transport capacity.
6. The overall valley form is gorge or canyon. 7. Because of increased downcutting and valley deepening, the lower curve representing valley floor
7. Long profiles of the rivers are characterised by the formation of waterfalls, cataracts and rapids where steam courses cross beds of resistant rocks. These features are most typical of early youth. They gradually diminish as the time passes and almost completely disappear by the end of youthful stage, i.e., before maturity starts.
8. As the rivers carry their load, their capacity to erode is reduced due to transfer of energy in transporting the load, and consequently deposition starts.
9.By the end of the youthful stage, a balance is reached between erosion and deposition and velocity of water is just enough to transport the sediment load supplied from the drainage basin and neither erosion nor deposition takes place. In this position, the river is said to be graded which is represented by smooth unbroken long profile of the river. The duration of youth stage is short.
(ii) Mature Stage. Mature stage commences after the river has crossed its youthful stage and is characterised by the following features.
(1) In mature stage the main function of the river becomes Lateral Erosion in which the river gives its valley Keeps widening continuously.
(2) Erosion of peaks of hills and water separators begins. This causes the upper curve (UC) to decline, ie both absolute and relative reliefs tend to decrease.
The mature stage is marked by maximum level of relief as the distance between lower curve and upper curve is maximum
(3) Most of the slopes become prone to erosion. Down-cutting of the valley is greatly reduced and Lateral Erosion intensifies.
(4) In the old age, due to slow slope of the valley, the flow velocity of rivers and their transport capacity are reduced. Therefore, equilibrium starts to be established in erosion and deposition actions.
(5)Important topography associated with this stage are the erosion, the Gokhur Lake, the natural embankment, the flood plain and the cave river, etc.
Old Stage -
(i) In erosion, the vertical erosion of rivers stops completely, but the work of lateral erosion and art of the valley still continues. Of tributaries The number is reduced or expired.
(ii) The upper curve begins to decline rapidly. That is, the absolute relief seems to decrease rapidly1.
(iii) Finally, both the curves are close to each other. The relief is almost exhausted and the terrain is its own. The base reaches the bottom. The rivers form the wide plains of the bar forming the meander. This flat ground has been called by Pennyplane * (common ground).
(iv) Scattered residual hills of low altitude with convex-concave gradient composed of resistant rocks are found somewhere in the Peniplane. Davis has described them as Monadnocks.
The delta is the most important shape formed in the last phase of the erosion cycle.
Davis presented his model of cycle of erosion in very simple and highly applicable style. He achieved this simplicity by eliminating supposedly irrelevant information and adopting restrictive assumptions.
Davis was the first geomorphologists to propound the idea of 'geographical cycle' or 'cycle of erosion'. Thus he gave a new direction to research and teaching in geomorphology.
Although Davis's model of 'geographical cycle" enjoyed wide popularity immediately after its publication in 1899, this model has been criticises on several counts by outstanding geomorphologists all over the world.
The whole cycle of erosion passes through three stages, viz., (i) Youthful stage, (ii) Mature stage, and (iii) Old stage.
(i) Youth Stage. Youth stage commences when the process of erosion starts after rapid and short lived upliftment is complete. Following are the main characteristics of this stage.
1. In the beginning the rivers are small and widely spaced. There may be a few consequent trunk streams but few large tributaries.
2. Erosion starts in the river valley but there is no erosion on the top surface or summits of water divides.
3. The length of streams and their tributaries increases due to headward erosion (erosion towards the source of stream) which is prominent form of erosion in this stage. This process is known as stream lengthening.
4. Due to steep slope and steep channel gradient, the rivers are actively involved in vertical (down) erosion as a result of which the depth of valleys increases. This is known as valley deepening,
5. The cross profile of the valleys is V-shaped,
characterised by convex valley side slopes. The
valleys are deep due to steep gradient of channel, high
velocity of river flow, increased erosion, and enhanced transport capacity.
6. The overall valley form is gorge or canyon. 7. Because of increased downcutting and valley deepening, the lower curve representing valley floor
7. Long profiles of the rivers are characterised by the formation of waterfalls, cataracts and rapids where steam courses cross beds of resistant rocks. These features are most typical of early youth. They gradually diminish as the time passes and almost completely disappear by the end of youthful stage, i.e., before maturity starts.
8. As the rivers carry their load, their capacity to erode is reduced due to transfer of energy in transporting the load, and consequently deposition starts.
9.By the end of the youthful stage, a balance is reached between erosion and deposition and velocity of water is just enough to transport the sediment load supplied from the drainage basin and neither erosion nor deposition takes place. In this position, the river is said to be graded which is represented by smooth unbroken long profile of the river. The duration of youth stage is short.
(ii) Mature Stage. Mature stage commences after the river has crossed its youthful stage and is characterised by the following features.
(1) In mature stage the main function of the river becomes Lateral Erosion in which the river gives its valley Keeps widening continuously.
(2) Erosion of peaks of hills and water separators begins. This causes the upper curve (UC) to decline, ie both absolute and relative reliefs tend to decrease.
The mature stage is marked by maximum level of relief as the distance between lower curve and upper curve is maximum
(3) Most of the slopes become prone to erosion. Down-cutting of the valley is greatly reduced and Lateral Erosion intensifies.
(4) In the old age, due to slow slope of the valley, the flow velocity of rivers and their transport capacity are reduced. Therefore, equilibrium starts to be established in erosion and deposition actions.
(5)Important topography associated with this stage are the erosion, the Gokhur Lake, the natural embankment, the flood plain and the cave river, etc.
Old Stage -
(i) In erosion, the vertical erosion of rivers stops completely, but the work of lateral erosion and art of the valley still continues. Of tributaries The number is reduced or expired.
(ii) The upper curve begins to decline rapidly. That is, the absolute relief seems to decrease rapidly1.
(iii) Finally, both the curves are close to each other. The relief is almost exhausted and the terrain is its own. The base reaches the bottom. The rivers form the wide plains of the bar forming the meander. This flat ground has been called by Pennyplane * (common ground).
(iv) Scattered residual hills of low altitude with convex-concave gradient composed of resistant rocks are found somewhere in the Peniplane. Davis has described them as Monadnocks.
The delta is the most important shape formed in the last phase of the erosion cycle.
Davis presented his model of cycle of erosion in very simple and highly applicable style. He achieved this simplicity by eliminating supposedly irrelevant information and adopting restrictive assumptions.
Davis was the first geomorphologists to propound the idea of 'geographical cycle' or 'cycle of erosion'. Thus he gave a new direction to research and teaching in geomorphology.
Although Davis's model of 'geographical cycle" enjoyed wide popularity immediately after its publication in 1899, this model has been criticises on several counts by outstanding geomorphologists all over the world.
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