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Summary
Our Earth’s surface is like a place where two different natural powers are always working. One set of powers, from inside the Earth, pushes land up and makes it uneven. Another set of powers, from outside, like flowing water, wind, and glaciers, works to wear down these raised parts and make the surface level. These outside powers change the Earth’s relief through weathering and erosion. The whole process of wearing away rocks and leveling the land is called denudation. This happens in two main ways: weathering and erosion.
Weathering is when rocks break down into smaller pieces or change their composition right where they are, on or near the Earth’s surface. It doesn’t involve moving the broken material far away. Think of it as rocks getting old and crumbly due to natural agents. This process turns hard, solid rock into finer material. Weathering is like the first step in changing the land, as it prepares rock bits for other forces to carry away. It’s a still process, meaning the rock breaks down in its place.
Erosion is the carrying away of these weathered rock materials from one spot to another. Agents like running water, ice, wind, or ocean waves pick up and move the broken rock. So, erosion is a moving process. Erosion depends on weathering because there needs to be broken material for erosion to act upon. Weathering is the start of denudation, while erosion is a later stage.
Mass wasting is when gravity pulls rock and soil down a slope. This happens when bedrock is broken by weathering. These broken pieces, called rockwastes, move downhill. Sometimes, large piles of this debris, called scree or talus, gather at the bottom of hills. Denudation, then, is the combined effect of weathering, erosion, and mass wasting, all working together to strip the land bare. Gradation is a related idea, where erosion, transport, and then the dropping of rock bits (deposition) work to bring land surfaces to a common level. This can involve lowering high areas (degradation) or building up low areas (aggradation).
Weathering can happen in different ways. Mechanical or physical weathering breaks rocks into smaller pieces without changing what they are made of. This can be caused by changes in temperature, where rocks expand when hot and shrink when cold, eventually cracking. This is common in deserts. Block disintegration is when rocks break into block-like pieces. Exfoliation is like an onion peeling, where outer layers of rock flake off. Granular disintegration happens when different minerals in a rock expand and contract at different rates, causing the rock to crumble into grains. Frost action occurs when water gets into cracks, freezes, expands, and wedges the rock apart.
Chemical weathering changes the chemical makeup of rocks, causing them to decompose. Oxidation is when minerals react with oxygen, like iron rusting. Carbonation happens when carbon dioxide dissolved in water forms a weak acid that reacts with rocks like limestone, creating features like caves and sinkholes. Hydration is when minerals absorb water and expand. Hydrolysis is a chemical reaction between water and minerals. Climate affects these processes; mechanical weathering is more common in very cold or very dry places, while chemical weathering is more common in hot and wet places.
Biological weathering involves living things. Plant roots can grow into cracks and split rocks. Burrowing animals can loosen rock and soil. Decomposing plants and animals can produce acids that chemically weather rocks.
Weathering has several effects. It helps create soil, which is vital for plants. It can expose useful minerals. However, it can also lead to soil erosion if the loose material is washed or blown away. Soil forms when weathering breaks down rock into small particles, and then organic matter from plants and animals mixes in over a long time. This process is called soil genesis.
Soil erosion is the wearing away of the top layer of soil. This can be caused by heavy rain, strong winds, steep slopes, or when land is left bare without plants. To protect soil, we can plant trees (afforestation), prevent too much animal grazing, and use farming methods like terracing on slopes. Keeping soil fertile is also important, by adding manure or rotating crops.
Textual Questions, Answers (Oriental)
Multiple Choice Questions
[a] Which one of the following is an example of physical weathering?
A. solution
B. frost action
C. carbonation
Answer: B. frost action
[b] Which one of the following is an example of chemical weathering
A. block disintegration
B. exfoliation
C. oxidation
Answer: C. oxidation
[c] The most important factor of soil formation is-
A. weathering
B. folding
C. tectonic movement
Answer: A. weathering
[d] Granular disintegration is caused by-
A. release of pressure on rockbeds
B. thermal change
C. crystal growth
Answer: B. thermal change
[e] The principal natural agent of mechanical weathering is-
A. sun
B. rain
C. wind
Answer: A. sun
[f] The type of weathering which is predominant in the hot desert is-
A. biological weathering
B. chemical weathering
C. mechanical weathering
Answer: C. mechanical weathering
[g] Rock gets rusted as iron oxide due to the process of-
A. carbonation
B. oxidation
C. hydration
Answer: B. oxidation
[h] Limestones deposit which grow upward from the floor of the cave are called-
A. stalactites
B. stalagmites
C. column
Answer: B. stalagmites
True or false
(a) Chemical weathering is the process of mechanically disintegration or break-up of rocks
Answer: False
Explanation: Chemical weathering involves the decomposition of rocks through chemical reactions, whereas mechanical disintegration refers to physical weathering without any change in chemical composition.
(b) Exfoliation occurs in the rock consisting of homogeneous minerals.
Answer: True
Explanation: Exfoliation happens when rocks with homogeneous minerals, such as granite, expand during the day and contract at night, causing surface layers to peel off like onion skins.
(c) Rusting on rocks is caused by carbonation.
Answer: False
Explanation: Rusting is caused by oxidation, a chemical reaction between minerals (especially iron) and oxygen, not by carbonation, which involves carbon dioxide and water reacting with minerals like limestone.
(d) Carbonation takes place in limestone region.
Answer: True
Explanation: Carbonation is most active in limestone regions where carbonic acid (formed from carbon dioxide and water) reacts with calcium carbonate in rocks to form soluble calcium bicarbonate.
(e) Mechanical weathering is very favourable in the desert region.
Answer: True
Explanation: Deserts experience extreme temperature fluctuations, which lead to repeated expansion and contraction of rocks, making mechanical weathering highly effective.
Answer in very short
1. (a) What is weathering?
Answer: Weathering refers to the process by which rocks get broken down to small fragments when they are exposed on the surface of the land; it is the disintegration and decomposition of rocks in situ. According to B. Sparks, “Weathering is the mechanical fracturing and chemical decomposition of rocks, in situ, by natural agents at the surface of the earth.”
1. (b) What are the two main types of weathering?
Answer: Weathering is mainly of two types: Mechanical or Physical Weathering and Chemical Weathering. There is also a Biological Process.
1. (c) Describe the different processes involved in mechanical weathering.
Answer: Mechanical weathering processes include:
- Block Disintegration: Rocks in arid regions develop joints and cracks from successive expansion and contraction, breaking into smaller blocks, also aided by pressure release. Shattering is the further disintegration into angular pieces.
- Exfoliation (Onion Peeling): Thin surface layers of homogeneous rocks peel off due to differential expansion and contraction between the surface and inner layers.
- Granular Disintegration: Rocks break into small fragments as different minerals within them expand and contract at different rates.
- Frost Action: Water in rock cracks freezes, expands, widens cracks, and breaks the rock, common in cool, temperate, or high-altitude regions.
2. What is chemical weathering? Describe the different processes of chemical weathering. In which climatic zone does such weathering predominate?
Answer: Chemical weathering is the decomposition and disintegration of rocks due to chemical reactions. According to Arther Holmes, it is “The alternation and solution of rock material by chemical processes.”
The main processes are:
- Oxidation: Minerals in freshly exposed rocks take up additional oxygen, forming oxides or hydroxides, like iron rusting.
- Carbonation: Atmospheric carbon dioxide mixed with water forms carbonic acid, which reacts with minerals, especially calcium carbonate in limestone, forming soluble bicarbonates.
- Hydration: Minerals absorb water and expand, causing stress and disintegration, like feldspar converting to kaolinite.
- Hydrolysis: A chemical reaction between mineral ions and water ions (H⁺ or OH⁻) breaks down rocks, often forming clay.
Chemical weathering is important in:
I. Equatorial regions: High temperature and rainfall make chemical weathering most favourable.
II. Tropical Regions: Humid and dry conditions invite chemical weathering, especially during rainy seasons. It is also most active in limestone rocks.
3. (a) Describe the processes of mechanical weathering in brief.
Answer: The processes of mechanical weathering involve:
(a) Temperature changes causing rocks to expand and contract, leading to breakage.
(b) Block Disintegration, where rocks break into smaller blocks due to temperature changes and pressure release.
(c) Exfoliation, the peeling off of surface layers of rocks.
(d) Granular Disintegration, where rocks break into fragments due to differential mineral expansion.
(e) Frost Action, where freezing water expands in rock cracks, breaking them apart.
3. (b) Which type of weathering is dominant in humid tropics? Classify intrusive rocks with examples.
Answer: In humid tropics, characterized by high temperature and rainfall, chemical weathering is most favourable and its rate is highest.
Intrusive igneous rocks (also called plutonic rocks) are formed when magma cools and solidifies beneath the Earth’s surface. They are classified based on their texture (crystal size) and mineral composition.
Classification by Mineral Composition (simplified):
- Felsic Rocks: Rich in feldspar and silica (quartz). Generally light-colored. Example: Granite (coarse-grained, composed mainly of quartz, feldspar, and mica).
- Intermediate Rocks: Composition between felsic and mafic. Example: Diorite (coarse-grained, composed mainly of plagioclase feldspar, amphibole, and pyroxene; less quartz than granite).
- Mafic Rocks: Rich in magnesium and iron (ferromagnesian minerals). Generally dark-colored. Example: Gabbro (coarse-grained, composed mainly of pyroxene and plagioclase feldspar).
- Ultramafic Rocks: Very rich in magnesium and iron, low silica content. Very dark-colored. Example: Peridotite (coarse-grained, composed mainly of olivine and pyroxene).
Classification by Texture (related to cooling rate):
Intrusive rocks are generally coarse-grained (phaneritic texture) because the magma cools slowly underground, allowing large crystals to form. The examples above (Granite, Diorite, Gabbro, Peridotite) all typically exhibit this coarse-grained texture.
Answer in short questions
1. Differentiate between weathering and erosion.
Answer: The distinction between weathering and erosion is as follows:
| Weathering | Erosion |
| 1. It is the decay or disintegration of rocks on the surface of the earth. | 1. Removing or wearing away of disintegrated rocks. |
| 2. Main agents of weathering are temperature, humidity and precipitation. | 2. Main agents of erosion are river, glacier, wind and waves. |
| 3. Weathering is a static process. | 3. Erosion is a dynamic process. |
| 4. Weathering is independent. It does not depend on erosion. | 4. Erosion depends on weathering. |
| 5. Weathering is the initial stage of denudation. | 5. Erosion is the last stage of denudation. |
| 6. It is not involved with transportation of weathered products except gravity. | 6. Erosion includes removal or transportation of the weathered rock material from one place to another. |
2. What is Mechanical weathering?
Answer: When disintegration of rocks takes place without any change in chemical composition of minerals, it is called Mechanical or Physical weathering. This is a physical process in which the rock is broken into smaller pieces, each retaining the characteristic of the original rock. The end result is many small pieces from a single large one. The chemical nature and composition of the rock remains the same. According to C. D. Ollier (1969), “Weathering is the breakdown and alternation of minerals near the earth’s surface to products that are more in equillibrium with newly imposed physio-chemical conditions.” According to W. D. Thornbury, “Weathering may be defined as the disintegration or decomposition of rock in place.”
3. Under what type of climatic condition, mechanical weathering is most effective?
Answer: Mechanical weathering is predominant in hot and cold deserts, cool climate and dry temperature regions, polar and tundra region, taiga regions etc. Mechanical or physical weathering is important in Polar regions, where weathering is mainly due to freeze-thaw. Most of the regions are snow covered, and mechanical weathering, particularly frost action, plays the vital role. Chemical actions become weak due to low temperature. Thus, in cold areas like Arctic, physical weathering is dominant. In dry deserts, physical weathering is considered to be dominant due to wide ranges of temperature. Dearth of water in dry and desert regions offers there little scope for chemical weathering. Rocks get cracks and fractures very easily for heavy compression and tension and it shatters bare rocks into pieces.
4. In which type of climate mechanical weathering is more prevalent? State with reasons.
Answer: Mechanical weathering is largely found in hot desert regions, glaciated high mountainous regions and frozen cold temperate regions.
In Polar regions, weathering is mainly due to freeze-thaw. Most of the regions are snow covered, and mechanical weathering, particularly frost action, plays the vital role. Chemical actions become weak due to low temperature. Thus, in cold areas like Arctic, physical weathering is dominant.
In dry deserts, physical weathering is considered to be dominant due to wide ranges of temperature. Dearth of water in dry and desert regions offers there little scope for chemical weathering. Rocks get cracks and fractures very easily for heavy compression and tension and it shatters bare rocks into pieces.
5. Why is the chemical weathering most active in limestone or chalk area?
Answer: Chemical weathering, especially the carbonation process is most active in limestone rocks (CaCO₃). When rain water (H₂O) falls, sometimes the atmospheric carbon dioxide (CO₂) combines with it and turns it into weak acid which is known as carbonic acid (H₂CO₃) [water (H₂O) + carbon dioxide (CO₂) = carbonic acid (H₂CO₃)]. The chemical reaction of this acid (H₂CO₃) on limestone or calcium carbonate (CaCO₃) produces a component, called calcium bi-carbonate [CaCO₃ + H₂CO₃ = Ca(HCO₃)₂]. In limestone regions, the carbonic acid (H₂CO₃) forms varieties type of landforms. When this carbonic acid fed rain water falls on limestone rocks (CaCO₃), the calcium carbonate present in the rock absorbs carbon dioxide from rain water and becomes calcium bicarbonate. Calcium bicarbonate is more easily soluble and is removed as the water flows on the rock or seeps below the surface.
6. What is soil erosion?
Answer: Soil erosion means the wearing away of the upper part of the soil. It sometimes, happens where bare soil is left exposed on the ground. Rain water, running water and wind carry away the loose particles of soil. It is a great problem, particularly to agriculture and landuse.
Write short notes
(i) Solution
Answer: The process of carbonation is known as ‘solution’ wherein atmospheric carbon dioxide after mixing with water forms carbonic acid (CO₂ + H₂O = H₂CO₃). When this carbonic acid fed rain water falls on limestone rocks (CaCO₃), the calcium carbonate present in the rock absorbs carbon dioxide from rain water and becomes calcium bicarbonate. Calcium bicarbonate is more easily soluble and is removed as the water flows on the rock or seeps below the surface. The solution process is accelerated when water (H₂O) falls over limestone rocks, leading to the formation of long furrows with vertical walls, known as Karren or Clint. Deep narrow grooves between clint are called grikes.
(ii) Hydration
Answer: When minerals form new compounds by chemically reacting with water, the process is called Hydration. Thus, Hydration is a process by which certain types of mineral expand as they take up water, causing additional stresses in the rock. Many of the decomposition products of rockforming minerals are subject to hydration, thereby accelerating the disintegration of the rock in itself. Hydration is a mechanical effect, but it occurs intimately with hydrolysis in such a manner that it is difficult to draw any hard and fast line between mechanical and chemical weathering. When carbon dioxide is dissolved in water, the chemical action takes place at a fast rate. For example, Feldspar mineral through hydration is converted into Keolinite, a process known as ‘Kaolinization’. An example of hydration is: 2 Fe₂O₃ (Hematite) + H₂O (water) = 2 Fe₂O₃. 3H₂O (Limonite).
(iii) Exfoliation
Answer: When a rock consists of homogeneous minerals like granite, the thin surface layer of rocks absorbs heat during the day and expands. During the night, this surface layer contracts more than the inner ones and is peeled off one after another like an onion. This is known as Exfoliation or Onion Peeling.
Rocks are bad conductors of heat. When the rock consists of homogeneous minerals, it expands due to high temperature at daytime and contracts at night when the temperature falls to near freezing point. Thus, a rock layer close to the surface is subject to repeated alternate expansion and contraction, but rocks below it do not take part in it. As a result, the surface layer is pulled apart and peels off like layers of onion. This process is called exfoliation. N. H. Horrocks comments, “Exfoliation is partly produced by frost action, even in hot deserts where freezing of dew at night can produce frost heaving.”
Many granitic batholiths exposed above the ground surface are continuously affected by exfoliation weathering. For instance, Kanke Dam near Ranchi city exhibits a fine example of such weathering. The effect of this process is that a round shaped hill top is formed.
(iv) Block disintegration
Answer: In arid regions, rocks develop joints and cracks through successive processes of expansion and contraction and ultimately break down into smaller blocks. This type of landform is known as block disintegration.
This process occurs due to temperature change: in desert areas, bare rock surfaces are highly heated during the day, and the outer layers expand considerably. During the night, the temperature often falls close to freezing point, resulting in contraction. The alternate expansion and contraction develop a series of joints both parallel and perpendicular to the exposed surface, and the rock tends to break into blocks. This is appropriately termed Block Disintegration. It should also be pointed out that block disintegration should not be considered the result of only temperature changes; rather, unloading of superincumbent load or release of confining pressure also helps in this process.
The block disintegration process mainly acts on Basalt type of rocks. Results include: (i) Steps like stairs formed by this process; Deceantrans are formed by this mechanical process. (ii) Flat shaped hill tops are formed by this type of mechanical process. Shattering is the further disintegration of the products of block disintegration, involving the disintegration of rock along new surfaces of breakage, producing highly angular pieces with sharp corners and edges.
(v) Oxidation
Answer: The process of oxidation occurs when minerals in freshly exposed rocks take up additional oxygen. Deep-buried clays are often blue or grey in colour as long as air is excluded from them, but on exposure, they are oxidised and turn red or brown as ferric compounds are formed.
The chemical process of oxidation simply means a reaction of atmospheric oxygen to form oxides. When water is mixed with oxygen, its reaction with the minerals of the rocks forms hydroxide. The process of oxidation occurs when minerals in freshly exposed rocks take up additional oxygen. The chemicals break down rocks as they react with oxygen. For example, iron contained in rocks is rusted in the presence of oxygen. The rust expands, breaking up the iron-bearing rocks. An example is: 4 FeO + O₂ + 3H₂O → 2Fe₂O₃H₂O (Ferrous oxide + Oxygen + Water → Hydrous oxide [Limonite]).
(vi) Biological weathering
Answer: Biological weathering, or Organic weathering, refers to the disintegration, break up, and decomposition of rock masses by plants, animals, and activities of man. This type of weathering includes both (a) Mechanical disintegration and (b) Chemical decomposition.
(a) Mechanical disintegration includes:
(i) Plant-roots: The roots of trees and plants enter the cracks, joints, and hollows and loosen the rocks from inside.
(ii) Animals: Burrowing of animals such as rodents, insects, and worms loosen particles in rocks. Charles Darwin had calculated that insects in the British gardens upturn 254 kg of soil per hectare per year.
(iii) Man: Many activities of man, such as mining, quarrying, and agricultural practices, add to the weathering of rocks.
(b) Chemical decomposition includes:
(i) Plants: Decomposed leaves, stems, flowers, etc., form humus which, mixed with water, forms acid to react with the rock and leads to chemical weathering.
(ii) Animals: Decomposition of animals results in the formation of organic acids which may react with minerals present in rocks, leading to chemical weathering.
(vii) Soil conservation
Answer: Conservation of soil means protection for soil from erosion and preservation of soil fertility. Soil is a natural resource, so it should be conserved. The conservation of soil can be done in two ways: (1) By checking soil erosion and (2) By increasing the fertility of the soil.
Measures to Check Soil Erosion include:
(a) Preservation of soil erosion by afforestation: New plants should be planted in regions where soil has become exposed, in order to check rain wash and surface run off. Around agricultural land, trees should be planted to control soil erosion.
(b) Restriction of Overgrazing: Overgrazing should be avoided so that new plants can grow there. If vegetative cover on land is saved, soil erosion can be checked naturally.
(c) Introduction of contour cultivation/terraced cultivation: On mountain slopes, running water rushes down turbulently and carries away mud, silt, and clay. To check the force of running water and rain wash, a series of steps or terraces can be made on the land. This will check soil erosion.
(d) Prohibition of Jhum Cultivation: In ‘Jhum’ cultivation (also known as ‘shifting cultivation’), forested lands are first destroyed by fire to clear the forest, and cultivation is introduced. After a few years, when soil fertility decreases, the land is discarded, and a new plot is taken for cultivation. The abandoned land remains bare and open, becoming an arena of soil erosion. This type of cultivation should be prohibited to check soil erosion.
Measures to Conserve Soil fertility include:
(i) Soil fertility should be maintained by supplying adequate manure and water to the soil.
(ii) Soil should be used according to soil character. Care should be taken to preserve its fertility and productivity. The cultivation of soil-exhausting plants and crops should be avoided or proper precautions should be taken.
(iii) Crop rotation should be introduced to regenerate the fertility of the soil; sometimes green manure revives productivity.
(iv) Care should be taken to convert infertile soil into fertile ones by applying chemical fertilizers.
(v) Agricultural research can bring about new thoughts on soil character, new methods for its preservation, and new ideas to increase its productivity.
Answer the following questions briefly
(I) Describe how does the Mechanical weathering take place.
Answer: Mechanical weathering takes place through various processes:
Temperature changes: In very hot and dry regions like deserts, extreme temperature differences cause rocks to break. During the day, rocks, especially on the surface, get very hot and expand. At night, rapid cooling takes place causing the rocks to contract. This continuous expansion and contraction causes rocks to crack and eventually break up.
Block Disintegration: In arid regions, rocks develop joints and cracks through successive expansion and contraction and ultimately breakdown into smaller blocks. This occurs due to temperature changes where bare rock surfaces are highly heated during the day causing outer layers to expand, and at night, temperatures fall causing contraction. Alternate expansion and contraction develop joints, and the rock breaks into blocks. Unloading of superincumbent load or release of confining pressure also helps in this process.
Exfoliation or Onion Peeling: When a rock consists of homogeneous minerals like granite, the thin surface layer absorbs heat during the day and expands. During the night, this surface layer contracts more than the inner ones and peels off like an onion. This is because rocks are bad conductors of heat, and the surface layer is subject to repeated alternate expansion and contraction while rocks below are not.
Granular Disintegration: Different minerals present in rocks have different rates of expansion and contraction. Dark coloured minerals absorb more heat and expand more than light coloured minerals. This alternating expansion and contraction between day and night leads to the break up of rock into small fragments.
Frost Action: In humid, cool temperate regions or high altitudes, water collected in cracks and pores of rocks at daytime freezes at night. Ice expands by about 1/10th of its volume when it freezes, exerting enormous pressure on the walls of cracks. As a result, cracks are widened, and the rock breaks into pieces. This disintegration occurs due to freeze and thaw of water between rock particles and in crevices and pore spaces.
(2) Describe the various processes of Chemical weathering.
Answer: The most important processes of chemical weathering are:
- Oxidation: This process occurs when minerals in freshly exposed rocks take up additional oxygen. It is a reaction of atmospheric oxygen to form oxides. When water is mixed with oxygen, its reaction with rock minerals forms hydroxide. For example, iron in rocks rusts in the presence of oxygen, and the rust expands, breaking up the iron-bearing rocks.
- Carbonation: This refers to the absorption of carbon dioxide from the atmosphere by minerals present in the rocks. It is also known as ‘solution’. Atmospheric carbon dioxide mixes with water to form carbonic acid (CO₂ + H₂O = H₂CO₃). When this carbonic acid rain falls on limestone rocks (CaCO₃), the calcium carbonate absorbs carbon dioxide from rainwater and becomes calcium bicarbonate, which is more easily soluble and is removed by water.
- Hydration: This is a process by which certain types of mineral expand as they take up water, causing additional stresses in the rock. Minerals form new compounds by chemically reacting with water. Many decomposition products of rock-forming minerals are subject to hydration, thereby accelerating rock disintegration. For example, feldspar mineral through hydration is converted into Keolinite (‘Kaolinization’).
- Hydrolysis: This is a chemical reaction between mineral and water, specifically between hydrogen ions or hydroxyl (OH) ions, and the ions of the mineral. It is the chemical breakdown of rocks as they react with water. Some rock minerals react with water to form clay, weakening the rock’s structure. Silicate minerals are most affected by hydrolysis.
(3) Distinguish between Mechanical and Chemical weathering.
Answer: The distinction between Mechanical Weathering and Chemical Weathering is as follows:
Mechanical Weathering
(i) It is a physical process in which the rock is broken into smaller pieces.
(ii) There is no change in the composition of minerals present in the rocks.
(iii) Physical weathering takes place in all regions where there are wide changes in temperature.
(iv) Disintegration of rock is associated with the mechanical weathering.
(v) Block disintegration, exfoliation, granular disintegration, shattering etc. are the important processes of mechanical weathering.
(vi) Mechanical weathering largely found in hot desert regions, glaciated high mountainous regions and frozen cold temperate regions.
Chemical Weathering
(i) The weathering of rock begins through chemical process.
(ii) Chemical weathering results in changing composition of minerals present in the rocks.
(iii) Chemical weathering takes place in all regions where there is rain.
(iv) Decomposition of rock is associated with the chemical weathering.
(v) Carbonation, oxidation, hydration, hydrolysis, solution etc. are the important processes of chemical weathering.
(vi) Chemical weathering largely occurr in equatorial humid regions, tropical wet regions, and limestone regions.
(4) What measures should be adopted for the conservation of soil?
Answer: The conservation of soil can be done in two ways: (1) By checking soil erosion and (2) By increasing the fertility of the soil.
Measures to Check Soil Erosion:
(a) Preservation of soil erosion by afforestation: New plants should be planted in regions where soil has become exposed, in order to check rain wash and surface run off. Around the agricultural land, trees should be planted to control soil erosion.
(b) Restriction of Overgrazing: Overgrazing should be avoided so that new plant can grow there. If vegetative cover on land is saved soil erosion can be checked naturally.
(c) Introduction of contour cultivation/ terraced cultivation: On mountain slopes, running water rushes down turbulently and carries away mud, silt and clay. To check the force of running water and rain wash a series of steps or terraces can be made on the land. This will check soil erosion.
(d) Prohibition of Jhum Cultivation: In ‘Jhum’ cultivation (shifting cultivation), forested lands are destroyed by fire, and cultivation is introduced. After a few years, when soil fertility declines, the land is discarded, becoming bare and prone to erosion. This type of cultivation should be prohibited.
Measures to Conserve Soil fertility:
(i) Soil fertility should be maintained by supplying adequate manure and water to the soil.
(ii) Soil should be used according to soil character. Care should be taken to preserve its fertility and productivity. The cultivation of soil-exhausting plants and crops should be avoided or proper precautions should be taken.
(iii) Crop rotation should be introduced to regenerate the fertility of the soil ; sometimes green manure revives the productivity.
(iv) Care should be taken to convert the infertile soil into fertile ones by applying chemical fertilizers.
(v) Agricultural researches can bring about new thoughts on soil character, new method for its preservation and new ideas to increase its productivity.
Extras
Additional MCQs
1. What are the two opposing forces responsible for shaping the earth’s surface?
A. Volcanic and tectonic forces
B. Erosion and precipitation
C. Endogenetic and exogenetic forces
D. Temperature and wind
Answer: C. Endogenetic and exogenetic forces
40. What soil conservation technique involves planting trees around fields?
A. Shelter belt
B. Terrace farming
C. Crop rotation
D. Strip farming
Answer: A. Shelter belt
Additional Questions, Answers
1. What is weathering?
Answer: Weathering refers to the process by which rocks get broken down to small fragments when they are exposed on the surface of the land. It may be described as the disintegration or decomposition of rocks in situ by natural agents at or near the surface of the earth. According to B. Sparks, weathering is the mechanical fracturing and chemical decomposition of rocks, in situ, by natural agents at the surface of the earth. According to W. D. Thornbury, weathering may be defined as the disintegration or decomposition of rock in place.
63. Explain the importance of soil as a dynamic entity and describe the process of soil genesis.
Answer: Soil is the upper weathered layer of the earth’s crust. It is not a lifeless matter but is considered to be a link between the living and non-living. Soil is a dynamic entity which is always undergoing physical, chemical, and biological changes. According to F. J. Monkhouse, “Soil is the thin surface-layer on the earth, comprising mineral particles formed by the break-down of rocks, decayed organic material, living Organism, soil water and soil atmosphere”. According to Dokuchaiev, “Soil is an independent, subaerial, evolutionary natural body on the earth’s surface occurring at dynamic equilibrium with environment”.
Soil development, called Soil genesis, is the final product of weathering and soil development processes occurring simultaneously.
During weathering, rocks are broken down into smaller particles. This weathered material undergoes further changes through pedogenesis or soil development, which is largely a biological phenomenon. Living organisms (algae, fungi, bacteria etc.) secrete organic acids, produce CO₂, and add organic matter after death. These geochemical, biochemical, and biophysical processes convert weathered rock debris into true soils, consisting of a complex mineral matrix associated with organic compounds and a rich micro-organism population. Dead organic matter is mineralized, and these minerals are gradually added to different layers (horizons) of the developing soil, forming a soil profile.
The stages in Soil Formation are:
(i) Stage-1: Bare rock begins to break up near the surface as a result of weathering. The softened and loose rock mixture formed on the bedrock is called Regolith.
(ii) Stage-2: The organic layer develops. Bacteria and other micro-organisms act on the remains of plants and organic material, forming humus and releasing minerals vital to plant growth.
(iii) Stage-3: Water percolating through the material, distributes minerals, creating soil.
Ron’e Dutta is a journalist, teacher, aspiring novelist, and blogger who manages Online Free Notes. An avid reader of Victorian literature, his favourite book is Wuthering Heights by Emily Brontë. He dreams of travelling the world. You can connect with him on social media. He does personal writing on ronism.
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