Rock Weathering-
Weathering is the process by which exposed rocks are disintegrated and decomposed in their original position I.e in situ.
Factors affecting Weathering-
1.Nature of parent rocks-
- Hard rocks takes less time for weathering as comparison to soft rock.
2.Topography-
- Steep slopes generally encourage rapid soil loss by erosion and allow less rainfall to enter soil before running off.
- Therefore, soil on steep terrain tends to have rather shallow and poorly developed profiles.
3.Climate-
- Climate of any area directly and indirectly affects the weathering process.
- Moist climate have different type of impact than cold climate.
- The plants and bacteria grow more quickly in warm humid climates and they contribute more of carbonic acid and other acids that promote weathering.
4.Geological structures-
- It includes structures like Faults,Folds etc.
- Faults and folds creates some cracks on the rocks which can hold weathering and erosional agents like water ice etc. Which can enhance and affect weathering process.
5.Time-
- The time period to which a rock is exposed to weathering conditions is also very important. Longer the operating time more will be the impact.
6.Chemical composition of soil and rocks
- This is also one of the important factor in weathering.
- For example calceroues rocks goes more under weathering due to water as comparison to other rocks.
- Also types of soil define the types of available microorganisms which are responsible for chemical weathering.
Types of rock Weathering-
There are majorly three types of weathering processes :
1.Physical.
2.Chemical.
3.Biological.
1.Physical-
- Weathering of rocks due to physical factors like temperature,pressure frost etc. Is called as physical weathering.
It can be due to-
- Temperature change.
- Force exerted by water.
- Frost action.
- Force exerted due to change in pressure.
A.Unloading and Expansion
- Due to removal of overlying pressure on the rock there is decrease in the external pressure on the rock ,due to which there is expansion of the rock mass .
Exfoliation -
- It is the physical weathering process in which large flat or curved sheets are detached from the outcrop. These sheets may look like the layers of peeled onion.
B.Temperature and Block Disintegration-
- During the day time the temperature rises and the nights are cold.
- Different rocks expand and contract differently because of varying mineralogical composition which leads to generation of cracks in the rocks.
- Due to repetition of this process the rocks disintegrate into smaller blocks. This process is known as block disintegration.
C.Abrasion-
- Due to action of Water,Winds or ice When rock particles collide with one another or a stable rock mass, it leads to grinding on their surfaces and this process is called as abrasion which further leads to weathering of that rock.
D.Frost action-
Frost wedging : In extremally cold Weather when there is repeated freezing and thawing of water ,then frost wedging takes place.
Frost Heaving is the slipping of the boulders on the sloping surface. During the day water flows below the boulder. In the night it freezes and lifts the boulder a little due to increase of volume of frozen film of water and this process continues and leads to weathering.
E.Hydraulic Action
- It include breaking of rocks due to continues action of water like force due to water waves and removing of outer surface due to small raindrops etc.
F.Gravity
- It includes movement of rocks or soil under the influence of gravity which further causes disintegration of the rocks.
G.Salt Weathering
- There is expansion of Salts in rocks due to thermal action, hydration and crystallisation.
- Many salts like calcium, sodium, magnesium, potassium and barium expands due to increase in temperature and leads to increase in rock cracks.
Salt crystalization-
- It involves cooling salt water to form crystals of pure ice and this process causes disintegration of the rocks.
- When is growth of Salt crystals then chalk breaks down most readily, which is followed by limestone, Shale, sandstone, gneiss and granite etc.
Some of the term related to Physical weathering.
Haloclasty-
- It is weathering due to sals and there crystals.
Slaking -
- It refers to the breakdown of rocks that normally occurs when thoroughly dried clay chunks or lumps immersed in water or alternate wet and drying of rock is known as slaking.
2.Chemical Weathering-
- Chemical change in the rocks through formation of new compounds or formation of new substances is called chemical weathering.
It is of following types-
A.Solution-
- In this process some of the rock minerals get dissolved in water. They are therefore removed in solution.
- Soluble rock forming minerals like nitrates, sulphates, and potassium etc. are affected by this process.
- Minerals like calcium carbonate and calcium magnesium bicarbonate present in limestones are soluble in water containing carbonic acid and are removed by this process.
- Rock salt and gypsum are also removed by this process.
B.Carbonation-
- Carbonation is the reaction of carbonate and bicarbonate with minerals which dissolves in water and gets removed.
- Granite,Feldspar etc. Are removed through this way.
- The Feldspar gets converted into Kaolin through this process and it is called as kaolinisation.
C.Hydration-
- This is the process by which water is absorbed by the minerals of the rock.
- Due to the absorption of water by the rock, its volume increases and the grains lose their shape and also gets removed with water.
Example- conversion of anhydrite into gypsum.
E.Oxidation and Reduction-
- Oxidation means a combination of a mineral with oxygen to form oxides or hydroxides.
- Greatest impact of this process is observed on ferrous minerals.
- Red colour of iron upon oxidation turns to brown or yellow.
- Pyrite on oxidation gives rise to limonite and free sulphur.
- When oxidised minerals are placed in an environment where oxygen is absent, reduction takes place.
3.Biological Weathering-
- It is the weathering of rocks due to Biotic agents like plants, animals ,man and microorganisms etc.
It is of following types
- Simple breaking of particles by animals or the pressure from growing roots, known as root wedging.
- Due to living organism like burrowing organisms cause mixing in the soil by their movements (also known as pedoturbation).
- Due to animal respiration or organic decay there is Production of carbon dioxide .
- Quarrying of mining materials and other rocks by Humans for commercial and other uses.
- Disintegration of rocks by Bacteria ,Fungi and Lichen etc.
Products of Weathering-
Weathering leads to generation of soil and related structure on earth and it includes-
Regolith-
- Regolith covers the Solid rocks and this covering or blanket consists of unconsolidated, loose, heterogeneous superficial deposits .
Eluvium -
- Loose weathered material that stays essentially where it formed, without being significantly carried away by wind, water or ice — the residual debris left sitting on or near its parent rock.
Alluvium -
- It is deposit of loose weathered material which has been transported and then deposited by flowing water. Diluvium are masses of waste left after glacial action or fluvio-glacial action and are the deposits of glacial age.
Significance of Weathering-
- It is responsible for formation of soils.
- It is responsible for breaking down the rocks into smaller fragments.
- It helps to break down of minerals which are economically essential.
- It helps in creating various land forms like mountains ,valley etc.
Important one liner on Rock Weathering
What is rock weathering?
Answer: The physical and chemical breakdown of rocks at or near the Earth's surface.
What is mechanical (physical) weathering?
Answer: The breakdown of rocks into smaller pieces through physical forces like freezing, thawing, and abrasion.
What is chemical weathering?
Answer: The breakdown of rocks through chemical reactions with water, oxygen, and other substances.
What is the difference between erosion and weathering?
Answer: Weathering breaks down rocks, while erosion moves the broken-down pieces away.
What is frost wedging?
Answer: A type of mechanical weathering that occurs when water freezes in the cracks of rocks and expands, causing the rock to break apart.
What is oxidation in rock weathering?
Answer: A type of chemical weathering where rocks containing iron react with oxygen to form rust.
What is hydrolysis in rock weathering?
Answer: A type of chemical weathering where water reacts with minerals in rocks to form new compounds.
What is biological weathering?
Answer: The breakdown of rocks by living organisms, such as plant roots and burrowing animals.
What is exfoliation in rock weathering?
Answer: A type of mechanical weathering where the outer layers of rocks peel away due to changes in temperature or pressure.
How does acid rain contribute to rock weathering?
Answer: The acidic rainwater reacts with rocks and minerals, causing them to dissolve or break down more quickly.