Weathering and Its Type

 

Weathering and Its Type

 

Weathering, erosion, and deposition are processes that act together to wear down and build up the Earth's surface.  These processes have occurred over billions of years.

Weathering is breaking down rocks, soil, and minerals by contacting the atmosphere, water, and biological organisms of the Earth and  takes place in situ, i.e. in the same place, with little or no movement.

The weathering of rocks occurs through both physical and chemical processes. Chemical weathering is decomposition of rock caused by chemical reactions resulting in formation of new compound. Whereas Mechanical (physical) weathering is the breakdown of rock into smaller pieces. 

TYPES OF WEATHERING

 

 

 

 

 

Physical Weathering

Physical weathering, also called mechanical weathering, is a process that causes the disintegration of rocks, mineral, and soils without chemical change. The primary process in physical weathering is abrasion (the process by which clasts and other particles are reduced in size). Physical weathering can occur due to temperature, pressure, frost, root action, and burrowing animals. For example, cracks exploited by physical weathering will increase the surface area exposed to chemical action, thus amplifying the rate of disintegration.

Abrasion by water, ice, and wind processes loaded with sediment can have tremendous cutting power to forms gorges, ravines, and valleys around the world. In glacial areas, huge moving ice masses embedded with soil and rock fragments grind down rocks in their path and carry away large volumes of materials.

Where does it occur?

Physical weathering happens especially in places places where there is little soil and few plants grow, such as in mountain regions and hot deserts.

 

How does it occur?

Either through repeated melting and freezing of water (mountains and tundra) or through expansion and contraction of the surface layer of rocks that are baked by the sun (hot deserts).

 

DIFFERENT TYPE OF PHYSICAL WEATHERING

EXFOLIATION

Exfoliation occurs as cracks develop parallel to the land surface a consequence of the reduction in pressure during uplift and erosion.Typically in upland areas where there are exposures of uniform coarsely crystalline igneous rocks.

How does it occur?

The rock mass at depth is under high pressure from underlying rocks. It tends to be uniform and lack fractures.

As progressive erosion occurs, the rock mass is subjected to progressively lower pressure of overlying rocks which leads to tension in directions at right angles to the land surface.

 This tension is relieved by formation of cracks which follow the land surface - they are relatively flat on plateaus, but can be steep on the flanks of mountains which are called exfoliation domes.

Once the cracks develop, water enters and causes chemical weathering leading to the formation of new low-density minerals. This enhances the cracks and encourages slabs of rock to detach from the surface.

 

Block Distingation

Block disintegration occurs due to repeated expansion and contraction of rocks during day and night, causing stress on the joints of the rocks, which eventually splits the rocks into blocks. It occurs in the area where the diurnal range of temperature is very high.

Granular disintegration

A form of weathering where the grains of rock become loosened and fall out is called Granular disintegration. It takes place in crystalline rocks, which becomes rough on disintegration. Temperature and frost plays a vital role in granular disintegration.

 

CHEMICAL WEATHERING

Chemical weathering is predominantly high in the hot and humid regions such as the equatorial, tropical and subtropical zones; because rainwater reacts with the mineral grains in rocks to produce new minerals (clays) and soluble salts. These reactions occur mainly when the water is slightly acidic.Chemical weathering takes place through one of the following processes of oxidation, carbonation, solution, and hydration. Oxygen, Carbon-dioxide, Hydrogen and water are the agents of Chemical weathering.

Oxidation

Oxidation is the reaction of oxygen in air or water with minerals present in the rock. Most of the rocks contain iron in it, which when comes in contact with air changes to iron oxide, familiar brownish crust or rust. Iron oxide crumbles easily and is far more easily eroded than the original iron. Thus, it weakens the overall structure and strength of the rock.

Carbonation

Carbonic acid is the main agent when it comes to the carbonation type of chemical weathering. As rain droplets pass through the air, it grabs carbon dioxide, forming carbonic acid. This weak acid reacts with the calcium carbonate in stones when it seeps into the cracks. Carbonation is significant in the formation of caves in the limestone region.

Solution

Many minerals are dissolved by water, especially when the rain-water contains enough carbon dioxide to make it a weak acid. These dissolved minerals, when swept away, leave the remaining particles loose. This breaks down the rocks.

Hydration

Certain chemicals in the rock expands on the absorption of water in humid conditions. These minerals swell and cause cracks and wearing of the rocks. This type of weathering is called hydration.

DIFFERENT BETWEEN PHYSICAL WEATHERING AND CHEMICAL WEATHERING 

 

Biological Weathering

Biological weathering is the weakening and subsequent breakdown by plants, animals and microbes of rock.

 

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