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In this article we are discussing the various types of Physical & Biological weathering processes.
Physical Weathering Process:
a) Physical or mechanical weathering processes depend on applied forces, which include:
i) Gravitational forces such as overburden pressure, load & shearing stress.
ii) Expansion forces due to temperature changes, crystal growth or animal activity.
iii) Water pressures controlled by wetting & drying cycles.
b) These forces are applied at the surface and within the different Earth materials leading to rock fracture.
c) The physical weathering processes caused by thermal expansion & pressure are small & slow. They cause great damage due to continuous fatigue. In this process rocks suffer due to constant contraction & expansion.
d) These are few types of physical weathering.
Unloading and Expansion:
a) There is a vertical pressure release by removal of overlaying rock by erosion. This process lets the upper layers of rocks to expand, thereby causing rock masses to disintegrate.
b) Fractures that develop are roughly parallel to the ground. In case of a curved ground surface, arched fractures are produced. This type of fractures produce massive sheets or exfoliated slabs of rock.
c) These rock slabs are hundreds or thousands of metres in length. This process may create large & smooth-rounded domes called exfoliation domes.
Temperature changes & expansion:
a) Due to rise or fall in temperature, every mineral expands or contracts, respectively.
b) Constant temperature change during daytime result in regular internal movement in the mineral grains in rock’s layers. This process is drastic in dry climates.
c) Due to these movements, rocks become weak due to continuous fatigue. This eventually causes stress resulting rock fractures parallel to the surface.
d) Due to all the processes mentioned above, the rocks surfaces appear smooth. In rocks, like granite, smooth-surfaced & rounded rocks are formed due to this exfoliation are called as tors.
Freezing, Thawing & Frost Wedging:
a) Due to growth of ice within the pores & cracks of rocks, frost weathering occurs. Ice in the rocks goes through repeated cycles of freezing & thawing.
b) In Glacial areas, the process of frost wedging is common. In this process, the rapid freezing of water causes sudden expansion and high pressure.
c) These expansion makes the fractures & the cracks in the rocks wider till the rock breaks apart.
Salt weathering:
a) Salts present in rocks like calcium, sodium, potassium etc. expand due to thermal action, hydration & crystallisation.
b) This expansion is dependent on the atmospheric temperature & thermal property of the minerals.
c) The process of salt expansion usually occurs in desert & arid areas. Salt crystals in rock pores cause individual grains to split. This leads to the granular disintegration or granular foliation in rocks.
d) In areas with alternative wetting & drying conditions, salt crystals expand and push the neighbouring rock grains aside.
e) This will eventually cause the splitting & breaking in rocks.
Biological agents of weathering
a) It is the process wherein the living organisms directly or indirectly contribute to the process of decomposition of rocks. Plants and trees that grow between the rocks penetrate the crevices of rocks and exert pressure which brings about mechanical disruption of the rocks.
b) Burrowing animals also dig the ground and also weaken the soil and break the soft rocks.
c) Decaying plants and animals accelerate the process of weathering by the production of carbonic acid and humic acid. Certain groups of bacteria, algae and mosses breakdown the rock-forming silicates and use it as a nutrient for their growth thus weakening the rocks.
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