Weathering

Types of Weathering

Physical Weathering

A change in the shape and size of the rock as it is reduced to soil. 

Chemical Weathering

Components of the rocks are being affected as a result of its exposure. The minerals that make up the rocks are altered causing a change in colour and texture. 

Biological/Organic Weathering

Can be physical or chemical or combination of both.

Physical weathering usually dominate in areas of extreme temperatures for example in cold deserts (Antarctica) and hot deserts (Sahara)

Physical Weathering

A change in the shape and size of the rock as it is reduced to soil.

Chemical Weathering

Components of the rocks are being affected as a result of its exposure

Biological/Organic Weathering

Can be physical or chemical or combination of both.

Physical weathering usually dominate in areas of extreme temperatures for example in cold deserts (Antarctica) and hot deserts (Sahara)

Chemical weathering usually dominates warm, moist places for example forests (Amazon)  

Physical Weathering

Thermal Expansion

Rocks are forces to expand drastically when exposed to high temperature during the day. Then at night-time, they are forced to contract when the temperature falls at night. The constant expansion and contraction, causes the rocks to undergo stress and they eventually begin to break up.

Some of the rocks may break up grain by grain; this process is called ‘granular disintegration’

Some of the rocks break up in complete layers; this process is called ‘exfoliation’

Freeze-Thaw Action

The cracks and joints of rocks in areas of high altitude are filled with water during the day. This water freezes at nigh to form ice. When ice freezes, it expands thus needing more space. As this cycle continues, the wedge of ice forces the rocks to split or break down. This process usually occurs in areas where the rock type is limestone. Freeze-thaw is also termed as frost shattering or frost action.

Salt Weathering /Haloclasty

This type of weathering usually occurs in coastal areas and deserts. Salt crystals are formed in the cracks and joints of rocks from water that was evaporated during the day. As the salt crystals become larger, they put pressure on the rocks. If this process continues, they rocks begin to break through granular disintegration.

Pressure Release/Dilation

When soil and other materials such as ice cover rocks, they exert (place) pressure on the rocks. If the overload is suddenly removed, the rock expands and in so doing begins to break up or flake off (exfoliation).  

Physical (Biological) Weathering

Plants: The roots of plants tend to split up rocks and even concrete structures as they grow and travel to search for food.

Animals: Large animals such as elephants and hippos crush rocks as they move about in their (habitat) natural environment. Also small rodents that tunnel through the soil contribute to the breakdown of rocks while making their homes.

Chemical Weathering

When water comes in contact with rocks, the chemistry of the rocks is altered. This chemical change is what is described as chemical weathering. The changes occur through reaction with rainwater, gasses and minerals. Chemical weathering usually occur in tropical regions that are dominated by high rainfall totals. Chemical weathering may cause minerals to dissolve or cause them to turn into weak and easily eroded clay.

Carbonation

As carbon dioxide dissolves in water, a weak carbonic acid is formed. The solution dissolves the mineral and the rocks begin to ‘melt’ and loose its shape and size. Limestone surfaces are predominantly affected by carbonation

A number of limestone features are formed such as limestone pavements, swallow holes, clints and grimes.

Hydration/Hydrolysis

Hydration takes place when rocks absorb water and the minerals begin to expand. As the expansion takes place pressure is placed on the rocks and it begins to weaken. Hydration stimulates exfoliation; as a result the layers of the rocks will begin to peel off.

Hydrolysis occurs when water creates larger minerals in rocks that are exposed. These larger minerals exert great stress on the rocks and force them to decomposed.

Solution

Rocks usually contain different minerals, which have different solubility in water especially if the water is slightly acidic. Some of the minerals dissolve faster than others, which leave hollows within the rock structure leaving the structure weaker and prone to other agents of weathering.

Biotic Weathering

Biotic weathering involves both physical and chemical processes. It involves weathering of the Earth’s surface by plants and animals. Plant roots grow into cracks and joints in the rocks and widen and deepen them as they grow. Some smaller plants extract iron from rocks thus weakening the structure. These processes enable other forms of chemical and physical weathering to work on the newly exposed surfaces.

Burrowing animals such as rabbits, insects and other animals including earthworms can loosen pieces of rock only to a limited extent. A layer of soil, keeping rain and frost out, usually protects rocks. Animals and insects removes this layer exposing the rocks in the soil to weathering agents that attack the rocks directly and break them down further.

Dead and decaying animals produce humic acid found in soil water. It is found mainly in tropical areas and weathers rocks quickly. This is a form of chemical biotic weathering.