Gradation, Aggradation, Degradation, Difference between aggradation and degradation

 

Gradation:

                 The word ‘Gradation’ comes from the word ‘Grade’, the word ‘Grade’ first used by G.K. Gilbert,1876, he used the word for explaining the concept of ‘graded river’ where the author discussed the concept of equilibrium of landforms. W.M.Davis, J.E.Keseli, J.H.Mckin have also used the word Grade.

                The term ‘Gradation’ was originally used by Chamberlin and Salisbury in 1904. According to them “all those processes which tend to bring the surface of the lithosphere to a common level”

Definition:

            Equilibrium of landforms by the erosion, transportation and deposition by all exogenous forces called gradation.

Process:  

Gradation= Erosion + Transportation + deposition

Erosion- Wearing down the uplands
Transportation- Transporting the eroded materials
Deposition-Filling up low lands

Classification:

      The gradation process belongs to two categories –

               i) Degradation ii) Aggradation

Degradation:

      It is a process of lowering the surface of the earth by exogenous forces like weathering, erosion, mass wasting and ultimately surface meets the base level.

Characteristics:

i) Very slow process.

ii) Among all the exogenous agents' rivers takes an important role to lower the land surface by abrasion, solution, hydraulic force and attrition.
iii) Denudation occurs and the new surface of landforms is exposed.
iv)  Original height and dimension of landforms reduce.
v) Resultant landforms are Canyon, Inselberg, Monadnock, Butte, Mesa etc.

Effects: 

i) Regolith originated on the earth's surface-basic material for soil formation.

ii) Mountains become plateaus and plateaus become planes.
iii) Backward movement of hill slope is progressed.
iv) Erosional landforms occur.

Process:  

                 Erosion, mass wasting, transportation

  Erosion- Wearing down of uplands
  Transportation- Eroded rock transports from one place to another
  Mass wasting- Erosion by gravitation

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Aggradation:

                    It is a process of increasing the height of the landforms by filling up lowlands and depressions (like basins) with eroded materials which originated from the exogenous processes, which is called aggradation.

Characteristics: 

i) Very slow process.

ii) Deposition of eroded materials in low lands and increasing the height of the lowlands results in levelling the earth's surface.

iii) Deposition by dynamic natural forces like river, glacier, wind, sea waves etc.

iv) Weathering helps aggradation indirectly through the disintegration of the rock masses

v) Resultant landforms are loess, alluvial fans, delta, flood plains etc.

Effects: 

 i) Different types of depositional landforms occur.

ii) Reduces the slope of the land.

iii) Flat surfaces occur.

Process: 

                    Deposition by river, glacier, wind, sea waves, humans and animals etc.

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Difference between Aggradation and Degradation

Subject	Degradation	Aggradation
Definition	In a process  where the height  of the landforms reduces by the removal of earth materials called  degradation.	In a process where increasing the height of original landforms occurs due to the deposition of  eroded materials in lowlands called   aggradation
Influencing factors	Dynamic natural forces like rivers, glacier, wind etc. and their erosional activity.	Weathering, erosion and mass wasting and depositional action of river, glacier and wind etc.
Height	The height of the landforms reduce	Height of the landforms increase
Nature	Destructive process	Constructive process
Effects	Created new landforms but didn’t make any sculptures on the land surface.	Creating sculpture and landforms.

Relationship with aggradation, degradation and gradation -

 Gradation, aggregation and degradation are interrelated. If degradation occurs due to weathering and mass wasting process then loosen materials are transported by weathering agents at last eroded materials are deposited in lowlands making the land rise up which is called aggregation and when both processes are active in a region or land surface then gradation occurs.