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What is Weathering and its types?

*Exogenic Movements:-These movements are basically the movements that affect the outer surface of the earth.The wearing down of rocks and formation of the soil is included in these types of precesses.Denudation is a term that is used for all types of exogenic processes like Weathering ,Erosion ,Deposition and Mass wasting .These Exogenic forces derive their energy from sun's insolation and forces by tectonic plates .These tectonic plates apply force and that produces stress in the rocks by pushing and pulling of the rocks . Because of the stress , deformation of rocks take place in the earth's crust.


    Source:-Weathering of rocks

   (1).Weathering :-  It is defined as mechanical disintegration and chemical decomposition of the crust's rocks and material by the actions of various elements of weather and climate.As we see the diversity of earth's surface like deserts ,plains , mountains ,hills ,rain forests , savannah ,glaciers ,rivers ,oceans , etc.All these landscapes are influenced by weathering.

*Classification of weathering :-
   (A).Physical Weathering
   (B).Chemical Weathering
   (C).Biological Weathering

    (A).Physical Weathering :- It is also known as mechanical weathering.It depends on various forces or factors like :-
 (1).Gravitational forces
 (2).Expansion forces due to temperature changes
 (3).Induced pressure due to wetting and drying of water.

        (a).Temperature changes and expansion :- When temperature rises so the material expands and with lowering the temperature the material contracts.Due to this differential heating and their subsequent exfoliation from the surface results in smooth rounded surfaces in rocks.

       (b).Salt weathering :- There are various types of salts like sodium , calcium ,magnesium ,potassium etc.All these sslts have a tendency to expand with varying temperatures.Wetting and drying of salts also results in weathering of rocks.

       (c).Unloading and expansion :- When there is removal of upper or overlying layer because of erosion and other factors, causes vertical pressure release.Thus due to this release of load,upper layer of remaining rock expand to produce disintegration of rock masses.Due to this process, cracks or fracture develops and this finally results in formation of massive sheets.


    Source :-Monument Valley Utah(USA)

     (B).Chemical Weathering :- There are many processes by which this type of weathering happens like carbonation, solution, hydration, oxidation and reduction.

         (a).Carbonation :- It is the process in which carbon dioxide from air and water reacts with each other at the presence of some catalyst and forms carbon acids.These are weak acids with low pH scale.When this type of acids reacts with calcium and magnesium ,then hydrogen is replaced by these minerals and calcium and magnesium carbonates are formed.In this process, calcium and magnesium are eroded in the form of chemiChe weathering.

         (b).Solution :- Solute is dissolved in Solvent completely ,then Solution is prepared.Solute should be in less quantity whereas Solvent should be in more quantity.Solvent is always in liquid form but solute may be solid or liquid.The term Hydration  indicates when something is dissolved in water.Soluble rock forming minerals like common salt, nitrates, sulphates, potassium, etc. are easily dissolved in the water.When coming contact with water, many minerals disintegrate and mix up as a suspension in the water or solvent.

         (c).Hydration :- When water molecule is chemically integrate with another mineral or molecule,then this process is called hydration.Generally the minerals which integrate with water, expands and due to this expansion in size, may result in development of cracks and fractures.Thid process cannot be reversed.
     
        #Hydration processes :-

CaSO4-----------hydration-----------CaSO4·2H2O
CaSO4·2H2O<-heat->CaSO4·​12H2O+32H2O

            (d).Oxidation (rusting) and reduction :- When any mineral reacts with oxygen to form oxides or hydroxides, then this chemical reaction is called Oxidation. Iron(Fe) is rusted by this process of oxidation.
           When there is absence of oxygen then reduction takes place ,it is completely reverse process of oxidation.


   Source:-Bioweathering
    
  (C).Biological Weathering :- This type of weathering is caused by the growth of bacteria or fungi.They uses the rock mineral for their survival.In the Himalayan region,there are certain types of bacteria which only live on bare rocks.They extracts minerals from it.

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