Origin Of Soil | 3 phases or cycle | (Erosion, Physical & Chemical weathering)

 Origin Of Soil

As we all know soil is composed by the disintegration or decomposition of rocks. This process is continuously occurring from millions of years of geological time.

We can define this cycle/process in 3 phases, 

    1) Erosion.

    2) Transportation & deposition

    3) Earth Movement.

Let’s discuss this phases in detail:-

1)   Erosion.

Scientists says that the cycle starts with the erosional phase in which there is degradation of exposed rock by weathering process.

This weathering process again divided into two parts.

a)    Physical weathering.

b)    Chemical weathering.

Physical Weathering

          Physical weathering is due to erosion of rocks caused by the action of wind, water, glaciers, also by the disintegration caused by alternate freezing and thawing in cracks in the rock.

This results that the newly formed soil particles retains the same composition as like the parent rock. The shape can be angular, rounded, flat & elongated. Examples of physical weathering are gravel and sand.

 

Chemical Weathering

          Chemical weathering results in changes in the mineral form of parent rock due to the action of acids or alkalies, oxygen & CO2 in water.

This weathering forms a group of crystalline particles of colloidal size less than 2 micro, it also known as clay mineral. The shape of the most clay particles have plat-like form (high specific surface area to mass ratio) with the result that their structure is influenced significantly by surface forces. If products of rock weathering are still located at the place where they originated, they are known as residual soil. They contain angular rock fragments of varying sizes. Residual soils have better engineering properties than parent one. 

  

    

Transportation & Deposition

          In this phase the fragmented or disintegrated material is transported by agents such as wind, water or ice to other locations. Simply we can say that soil which is transported from the origin by wind, water, ice or any other agency and has been deposited is known as Transported soil. This soil may contain large amount of pores and small in size.

The characteristics are influenced by the agency of transportation. According to mode of transport they are classified as:-

Alluvial Deposit  =Deposited by river water.

Marine Deposit   =deposited by sea water.

Lacustrine Deposit=deposited by still water like lakes.

Aeolian deposit  =transported by wind.

Glacial Deposit =transported by ice

 

You can see Transportation of soil in detailed in next page…..