Weathering : Types

Weathering is often divided into the processes of mechanical weathering and chemical weathering. Biological weathering, in which living or once-living organisms contribute to weathering, can be a part of both processes.

Types of Weathering :

1. Physical Weathering Processes

Physical weathering involves mechanical disintegration of rocks due to temperature changes, freeze-thaw cycles, wet-dry cycles, crystallisation of salts, animal and plant activity, etc.
Various mechanisms of physical weathering are explained below.

(a) Exfoliation due to pressure release or unloading

Intrusive igneous rocks formed deep beneath the Earth’s surface are under tremendous pressure due to overlying load.
Removal of the overlying load because of continued erosion causes vertical pressure release with the result that the upper layers of the rock expand and fracture parallel to the surface.
Over time, sheets of rock break away from the exposed rocks along the fractures, a process known as exfoliation.
Exfoliation due to pressure release is also known as “sheeting“.

(b) Exfoliation due to thermal stress weathering

Thermal stress weathering results from the subsequent expansion and contraction of rocks caused by diurnal and seasonal variations in the temperatures.
This process is most effective in dry climates and high elevations where diurnal temperature changes are drastic.

(c) Salt Weathering

Salt weathering occurs when saline solutions seep into cracks and joints in the rocks and evaporate, leaving salt crystals behind.
Strong heating in arid climates typically causes strong evaporation and crystallization, which is normally associated with salt weathering.

2. Chemical Weathering

Chemical weathering involves chemical decomposition of rocks and soil.
Chemical weathering processes include dissolution, solution, carbonation, hydration, oxidation and reduction that act on the rocks to decompose, dissolve or reduce them to a fine state.
These weathering processes are interrelated and go hand in hand and hasten the weathering process.
Acids produced by microbial and plant-root metabolism, water and air (oxygen and carbon dioxide) along with heat speed up all chemical reactions.

(a) Carbonations:

The reaction of carbonate minerals and CO2 from air and soils forms carbonic acid.
Carbonic acids dissolve calcium carbonate and magnesium carbonate, resulting in cave formation.

(b) Hydration:

Hydration is the chemical addition of water.
When rock takes up water, it expands when temperature increase; as a results volume increase. This process gets reversed when the temperature cools. Continued replication of this process causes fatigue in rocks and leads to disintegration.

(c) Oxidation:

The breaking of rocks occurred due to disturbances caused by the addition of oxygen. The minerals involved in the oxidation process are iron, magnesia, and sulfate.
Over time, the red color of oxides iron turns to yellow color. When placed below water where oxygen is absent, oxide iron turns into a greenish and blushing color.

3. Biological weathering

Weakening and breaking of an object into the smaller object by plants, animals, and microbes.
The growth or movement of an organism leads to the removal of minerals and ions from the environment. Organisms like earthworms, termites, and rodents help in exposing new surfaces to chemical attacks and assist in the penetration of moisture and air.
Decaying plants and animals helps to produce humid, carbonic, and other acids that enhance chemical weathering.
Vegetables release acids that enhance the chemical weathering because of bacterial activities enhanced.
Algae extract the mineral from rocks.

Significance of weathering:

Weathering is responsible for soil formation.

Forest gets minerals from weathered materials.
Erosion only starts after weathering.
Weathering helps the extraction of valuable ore like iron, and magnesium which helps to increase the economy.

Weathering : Types,Weathering : Types,Weathering : Types