Formation of Soil
Hello Friends, Welcome to the Civil Stunner.
As we know we have many type of soil around us. Soil may be
classified in many type. But, today we will see formation of soil.
Soils are formed by weathering of rocks and decomposition of
organic matter. So soils are organic or inorganic depends upon source of
origin.
The weathering of soil occurs with time will decrease
cohesive property of soil within the grain and this results in disintegration
of the big rock masses into small particles. We called this small particles as
soil. Hence the soil formation is the result of weathering action.
Types of Weathering:
Generally, the soils are formed either by,
(1) Mechanical weathering
(2) Chemical weathering
(1) Mechanical weathering:
Mechanical weathering occur due to physical disintegration of
the parent rock. Physical disintegration can occur due to following reasons:
Temperature changes:
All types of
rocks may not have same thermal coefficient. So they behave differently for the
different temperatures values. This will cause the thermal expansion and
contraction with change of the temperature. If this process repeated several
times, its results in disintegration of and soil are formed.
Wedging action of ice:
All rocks are
have some pores that gets filled up with water. During low temperature, this
water freeze and convert into ice and little increase in volume occur. This
volume change will make area expand in rock pores. This result into cracks and
further expansion will propagate the cracks. This will lead to break the rock
and convert as soil.
Spreading of roots of plants:
Sometime there
are trees and shrubs grown near the rocks. The roots of these trees and shrubs
grow inside the rocks and formed cracks in rock mass. The segment of the rock
are forced apart and this action disintegrate the rock and further it will
results in formation of soil.
Abrasion:
Movement of wind, water and glaciers over the
rock surface will result in abrasion and scouring. It result in soil formation.
All this physical disintegration of parent rock won’t bring
any change in chemical composition of rock. The property of soil will be
similar to that of parent rock. The soil formed by physical weathering are
sand, gravel and some other coarse-grained soils.
(2) Chemical
Weathering:
Transformation
of hard rock into soft and erodible material is conducted through process of
chemical weathering. Let’s see some process of chemical weathering:
Hydration:
In this process, water combines with the rock minerals and
results in the change in chemical composition. The chemical reaction causes a
change in volume and decomposition of rock. As example of hydrolysis of SiO2.
Carbonation:
In carbonation, carbon dioxide in the atmosphere combines
with water to form carbonic acid. This carbonic acid reacts chemically with
rock and causes their decomposition. Sedimentary rocks which contains calcium
carbonates are the formed by chemical reaction of rocks by carbonation.
Oxidation:
Oxidation occur due to oxygen ions combine with rock
minerals. Oxidation results in decomposition of parent rock.
Solution:
Some rock minerals make solution with water when they get
dissolved in water. Some chemical reaction takes places in this solution and
because of this soil are formed.
Hydrolysis:
Hydrolysis is chemical process in which water gets
dissociated into H+ and OH-- ions. Hydrogen cation
replace some metallic ions such as sodium, calcium and potassium present in the
rock minerals and this will result into soil formation.
Thanks for reading,
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