Chapter 5 Weathering Salient Points – At A Glance
1. The word weathering has been derived from the word weather.
2. The term weathering was first used by geologist G. K. Gilbert.
3. Weathering is a static process, i.e. disintegrated or decomposed rocks do not get removed from their original place.
4. Erosion is a process whereby weathered materials are transported and deposited elsewhere by various exogenetic forces.
5. Denudation is the process in which the lower layers of the rocks are exposed through the removal of the upper layers by weathering and erosion.
Read and Learn Also WBBSE Solutions for Class 9 Geography And Environment
6. Without the effect of external or internal forces, the weathered debris of rocks moves downward along the slope due to the gravitational force and is transported and deposited elsewhere. This process is known as mass wasting.
7. Mechanical weathering occurs in hot desert areas, polar regions, and high mountain regions.
8. Exfoliation occurs in homogeneous rocks like granite.
9. Block disintegration is seen more in basalt.
10. Granular disintegration is prevalent more in heterogeneous rocks, i.e. rocks formed of various minerals.
11. Formation of ice crystals, is observed more along the foothills of the mountains in cold temperate climatic regions.
12. Chemical weathering is more active in equatorial and humid-tropical climatic regions.
13. Water and atmospheric oxygen react with the iron-containing rocks and lead to the formation of rust on them. This process is known as oxidation.
14. The process of solution is more active in rocks like chalk, limestone, dolomite, etc.
15. Biological weathering is caused by various plants and animals.
16. The fragmented rock waste creating a loose covering on the Earth’s surface due to weathering, is called regolith.
17. The process of soil formation from rock debris is called pedogenesis.
18. Smallest particles in the process of soil formation are called the ped.
19. Minerals in the upper layers of the soil mixes with rainwater and move downwards. This is called leaching and the process is called eluviation. The process of accumulation of these particles in the lower layers is called illuviation.
20. Humus is a deep black-colored complex matter, formed due to the decomposition of organic matter. Over a long period of time, soil develops as a result of the mixing of rock wastes, humus, and water.
21. Terrace farming, contour farming, and strip cropping prevent soil erosion on the slopes of the mountains.
22. The process of preventing soil erosion by covering it with a layer of roots of crops, twigs, tendrils, and specks of dust is called mulching.
23. Due to changes in temperature and humidity, increase or decrease of pressure on rocks, etc., surface rocks get disintegrated by mechanical action. This process is called mechanical weathering.
24. Physical change or change of shape in the. rocks are seen in mechanical weathering but there is no change in the chemical composition or character of the rock-forming minerals.
25. The process of granular disintegration causes noises like gunshots.
26. Carbonic acid (H2CO3) plays an important role in the carbonation process,
27. The various methods of soil conservation maintain the quality of soil and prevent soil erosion.
28. Various natural causes of soil erosion are rainfall, winds, sea waves, glacier, etc. and human activities responsible for soil erosion are deforestation, unplanned urbanization, the extension of the transportation network, unscientific settlement, etc.
29. The processes of soil erosion due to stream action are sheet erosion, rill erosion, gully erosion, and ravine erosion.
Chapter 5 Weathering Topic A Weathering And Related Processes Of Weathering Long Answer Type Questions
Question 1 Briefly explains the concepts of erosion and denudation.
Answer:
Erosion: The concept of erosion is discussed below-
1. Definition: When the weathered rocks are transported from their place of origin to some other place by physical agents like rivers, glaciers, winds, etc., the process is called erosion.
2. Process: The main processes of erosion include attrition, friction, plucking, removal of weathered debris, etc.
3. Agent: Agents like flowing water, winds, moving glaciers, etc., transport the weathered material from one place to another.
4. Characteristics:
1. Rocks are removed,
2. underlying layers of rocks are exposed after the upper layers are removed, and
3. erosion is dependent on weathering, it is a fast process.
Example: High-velocity winds in desert areas remove large quantities of sand and small rock fragments (by the process of erosion) to far away places.
Denudation: The concept of denudation is discussed below-
1. Definition: When the lower or underlying layers of the rocks are exposed after the upper layers are removed by weathering and erosion, the process is known as denudation. The term ‘denude’ means ‘to lay bare’.
2. Process: Main processes of denudation are weathering mass wasting and erosion.
3. Characteristics:
1. Weathering and erosion are dependent on mass wasting.
2. This is a slow process.
3. New rocks are exposed to the earth’s surface.
4. Elevation of the land is gradually decreased by the denudation processes and the uneven surface is gradually smoothened and flattened.
5. Nature of rocks, the elevation of land, climate, etc., affect denudation.
4. Regional differences: The rate of denudation is lower in hot dry desert areas than in the high mountainous regions. In humid regions, the rate of denudation is again higher.
5. Importance: Soil is formed as a result of this process and it also plays an important role in the evolution of landforms.
Question 2 Briefly describe the concepts of weathering and mass wasting.
Answer:
Weathering: The concept of weathering Mass Wasting: The process of mass wasting is as follows-
1. Definition: The climatic agents (e.g., temperature, rainfall, etc.) disintegrate and decompose the rocks in their own places (‘in situ’) and this process is called weathering.
2. Nomenclature: As this is an alteration of the physical or chemical characteristics of rocks by various factors of weather/climate, the term weathering is pertinent.
3. Factors: The factors responsible for weathering are temperature and rainfall, plant, man, and other animals, nature of landforms, nature of rocks (lithological characteristics), time, etc.
4. Types: Weathering can mainly be of 3 types-
1. Mechanical (rocks are disintegrated or broken into fragments
2. chemical (rocks . undergo alteration in chemical composition),
3. biological (rocks are altered by the action of plants and animals).
5. Process: Exfoliation, granular disintegration, hydration, oxidation, hydrolysis, etc., are the various processes of weathering.
6. Characteristics:
1. Rocks are disintegrated and decomposed.
2. This is a static process.
3 The weathered materials are not removed or transported. The intensity of weathering depends on the structure and nature of the rocks, climatic factors, etc.
7. Effect: Landforms like rounded or dome-shaped hills, inselbergs, tors, caves, etc., are formed. Weathering also plays a significant role in soil formation.
Mass wasting: The process of mass wasting is discussed below-
1. Definition: When weathered materials like pebbles, boulders, etc., slide down the slopes of mountains due to gravitational pull, the process is known as mass wasting.
2. Nomenclature: As the weathered rock debris is dumped at the lower slopes of the mountains after being carried there, following the natural slope or gradient (by gravitational pull), the term ‘mass’ is thus relevant.
3. Factors: Slope of the land, altitude, shape, size and amount of the weathered materials, presence of vegetation, precipitation, the force of gravity, etc., determine the process of mass wasting.
4. Types: Mass wasting can be of 4 types-
1. Slow flow
2. Rapid flow
3. Landslide
4 . Subsidence.
5. Process: Mudflow, soil flow, solifluction, slump, rock slide, etc., are the various processes of mass wasting.
6. Characteristics:
1. This process is rampant in sloping lands.
2. The debris is removed as a result of gravitational force. It can occur as a slow or rapid process.
3. Physical agents of weathering and erosion (rivers, glaciers, etc.) do not have any role to play in the process of mass wasting.
7. Effect:
1. Landslides occur in mountainous areas as a result of mass wasting.
2. These cause loss of life and property.
3. Steep slopes, erosion on slopes, talus cones, etc., are formed due to mass wasting.
Chapter 5 Weathering Short Explanatory Answer Type Questions
Question 1 What are the controlling factors of weathering?
Answer:
The controlling factors of weathering are as follows-
1. Structure of rocks: The process of weathering is accelerated in soft and jointed (with cracks and fissures) rocks.
2. Relief or topography: Weathering process is more active on steep slopes of hills and plateaus.
3. Climate: The different factors of climate (moisture in the air or humidity, rainfall, temperature) influence weathering to a great extent.
4. Biotic factors: Roots of plants and trees, flowers, fruits, man, and other animals (namely, burrowing animals), are important controlling factors of the weathering process.
Question 2 Write the differences between weathering and mass wasting.
Answer:
The differences between weathering and mass wasting are as follows-
| points of difference | Weathering | Mass wasting |
| 1. Concept | When climatic elements are responsible for the disintegration and decomposition of rocks in their own place, it is called weathering. | When the weathered debris of rocks is carried down slopes due to gravity and is transported and deposited elsewhere, it is known as mass wasting. |
| 2. Characteristics | This is a static process, i.e., the weathered materials are deposited ‘in situ’ or in the same place. | This is a dynamic process, where the weathered materials are transported and deposited elsewhere. |
| 4. Controlling factors | Various climatic elements like air temperature, humidity, rainfall, etc., control the process of weathering. | Mass wasting is mainly controlled by gravitational force. |
| 5. Area of occurrence | Weathering is more or less common all over the world. | Mass wasting only occurs in mountainous areas or on sloping land. |
Question 3 Write the differences between weathering and erosion.
Answer:
The differences between weathering and erosion are as follows-
| points of difference | weathering | Erosion |
| 1. Concept | It is the disintegration and decomposition of rocks ‘in situ’ i.e. in the same place, carried out by climatic factors (temperature, precipitation, etc.). | Erosion is the process of carrying away of rock debris by rivers, winds, etc., (operating on the earth’s surface) from one place to another. |
| 2. Interdependency | It does not depend on erosion. | It depends on weathering. |
| 3. Rate / Pace | It is a very slow process. | It is a relatively faster process. |
| 4. State of weathered materials | Weathered materials lie near or on their parent rocks. | Weathered materials are transported far away from their parent rocks. |
| 5. Elements | Temperature, rainfall, and humidity take an active role in this process. | Rivers, winds, glaciers, sea waves, etc. take a main role in this process. |
| 6. Subsequent process | Erosion occurs rapidly in weathered rocks. | Weathering occurs again on the underlying rocks after the removal of disintegrated materials through erosion. |
Question 4 Write the differences between weathering and denudation.
Answer:
The differences between weathering and denudation are as follows-
| Points of difference | weathering | Denudation |
| 1. Concept | Weathering is the disintegration and decomposition of rocks due to climatic factors (temperature, precipitation, etc.). | Denudation is the process in which the lower layers of the rocks are exposed when the upper layers are removed by weathering and erosion. |
| 2. Interdependency | It does not depend on denudation. | It depends on weathering. |
| 3. Evolution of landforms | It is not directly related to the evolution of landforms. | It has a vital role in the evolution of landforms, which is a long-term process. |
Question 5 Write the differences between erosion and mass wasting.
Answer:
The differences between erosion and mass wasting are as follows-
| Points of difference | Erosion | Mass wasting |
| 1. Concept | It is the process of carrying away of weathered rocks by natural agents from one place to another. | Mass wasting is the movement of rock debris downhill slopes due to gravity. |
| 2. Process | Abrasion, attrition, solution, etc. are the various processes of erosion. | The various processes of mass wasting a/e mudflow, soil flow, slump, etc. |
| 3. Predominance | It is predominant everywhere. | It is predominant in high-relief or sloping areas. |
| 4. Effect of slope | The effect of the slope is less profound in the erosion process. | The effect of the slope is more profound in the mass wasting process because it occurs along a sloping land. |
| 5. Effect of gravitational force | There is no direct relation between erosion and gravitational force. | Mass wasting occurs under the effect of gravity. |
Question 6 ‘Weathering and climate are interrelated.’ Explain.
Answer:
Weathering And Climate Are Interrelated:-
The interrelation between weathering and climate can be discussed if we study the following climatic regions
1. Equatorial climatic region: Temperature and rainfall are intense throughout the year in this region. Along with chemical weathering, mechanical weathering is also rampant here due to excessive heat.
2. Hot and dry desert climatic region: Due to long periods of intense heat and almost negligible rainfall, mechanical weathering is predominant here. For example, exfoliation, granular disintegration, etc. are the prevalent processes.
3. Cold mountainous climatic region /Arctic region: Due to excessive cold, the formation of ice crystals along the cracks of rocks causes mechanical weathering.
4. Tropical monsoon climatic region: Due to the hot and wet climate of tropical monsoon climatic regions, both mechanical and chemical weathering are active here as a result of both heat and rain.
5. Wet-temperate climatic region: In wet-temperate climatic regions, both mechanical and chemical weathering is active, mainly due to the excessive availability of moisture.
Chapter 5 Weathering Short Answer Type Questions
Question 1 What is weathering?
Answer:
Weathering:-
When rocks are broken down in their own places (‘in situ’) either mechanically or chemically due to the action of various elements of weather (namely temperature, rainfall, etc.) the process is known as weathering.
Question 2 What is erosion?
Answer:
Erosion:-
When fragmented rocks are transported from their original place of weathering to some other place by various agents like rivers, glaciers, winds, etc., the process is called erosion.
Question 3 What is denudation?
Answer:
Denudation:-
When the underlying rock layer of the earth’s surface is exposed as a result of the upper layer of rock being weathered and transported to some other place (erosion) by various agents, the process is called denudation (‘denude’ means to ‘lay bare’).
Question 4 What is mass wasting?
Answer:
Mass Wasting:-
When fragmented rocks, pebbles, mud, etc., slide down the slope or gradient of a mountain or a highland (as a result of gravitational force), as a mass of weathered matter, the process is called mass wasting.
Question 5 How can mass wasting be classified?
Answer:
Classification Of Mass Wasting:-
The two main types of mass wasting are- slow movement and rapid movement.
Question 6 Why is weathering also known as the process of disintegration?
Answer:
Weathering Is Also Known As The Process Of Disintegration:-
The rocks on the Earth’s surface are either disintegrated or decomposed as a result of the process of weathering and that is why it is also called a process of disintegration.
Chapter 5 Weathering Multiple Choice Type Questions
Write the correct answer from the given alternatives
1. Transportation of disintegrated rocks is known as—
1. Mechanical Weathering
2. Chemical Weathering
3. Denudation
4. Erosion
Answer: 4. Erosion
2. Movement of weathered rock materials in hilly areas is known as—
1. Mechanical Weathering
2. Chemical Weathering
3. Mass Movement
4. Denudation
Answer: 3. Mass Movement
3. The process in which the rocks of the surface of the Earth gets disintegrated is—
1. Erosion
2. Denudation
3. Disintegration
4. Mass Movement
Answer: 3. Disintegration
4. Weathering, decomposition, and removal of rocks are the combined process of—
1. Disintegration
2. Erosion
3. Denudation
4. Mass Wasting
Answer: 3. Denudation
5. What is the order of relief developed by weathering? –
1. First order
2. Second order
3. Third order
4. Fourth order
Answer: 3. Third order
6. Due to weathering, rocks get—
1. Deformed
2. Loosened
3. Eroded
4. Removed
Answer: 2. Loosened
7. Another name for weathering is—
1. Erosion
2. Denudation
3. Disintegration
4. None Of These
Answer: 3. Disintegration
Chapter 5 Weathering Fill In The Blanks With Suitable Words
1. When the underlying rock layer is exposed to the surface, the process is called denudation
2. Biological weathering is caused by plants.
3. Weathering occurs before the erosion of the rock bed.
4. Weathering and erosion together are called denudation
5. Gravitational force is the cause of mass wasting.
6. Weathering is a Static process.
Chapter 5 Weathering If The statement Is TRUE, Write TRUE And If FALSE, Write ‘FALSE’ Against The Following
1. Disintegration of rocks by weathering is called erosion. False
2. Denudation is a result of weathering and erosion. True
3. Rock bed is rendered bare due to the process of denudation. True
4. The other name weathering is rock disintegration. False
5. Climate has a great influence on the process of erosion. True
6. Climate plays an important role in accelerating the process of weathering. True
7. Weathering is a dynamic process. False
Chapter 5 Weathering Match The Left Column With The Right Column
1.
| Left column | Right column |
| 1. Disintegration of rocks | A. Erosion |
| 2. Decomposition of rocks | B. Mechanical weathering |
| 3. Exposure to rocks | C. Chemical weathering |
| 4. Transportation of rocks | D. Denudation |
Answer: 1-D,2-A,3-B,4-C
2.
| Left column | Right column |
| 1. Disintegration and decomposition of rocks | A. Mass writing |
| 2. Process occurring along slopes | B. Denudation |
| 3. Removal of rocks | C. Weathering |
| 4. Exposition of rocks | D. Erosion |
Answer: 1-B,2-A,3-D,4-C
Chapter 5 Weathering Answer In One Or Two Words
Question 1 Where does mass wasting occur?
Answer: Mountainous area.
Question 2 List two climatic factors responsible for weathering.
Answer: Temperature and rainfall.
Question 3 Who was the first to use the term ‘weathering’?
Answer: G. K. Gilbert.
Question 4 What are weathering and erosion together called?
Answer: Denudation.
Question 5 What is the combined process of disintegration, decomposition and removal called?
Answer: Denudation.
Question 6 What is erosion?
Answer: The removal of weathered and decomposed rock wastes by natural agents is called erosion.
Chapter 5 Weathering Topic B Processes of Weathering Long Answer Type Questions
Question 1 What is meant by mechanical weathering? Describe the main processes involved.
Answer:
Mechanical Weathering:
The process of fragmentation or disintegration of rocks in their own places (‘in situ’) by various agents of climate like temperature, rainfall, snowfall, etc., is called mechanical or physical weathering. The rocks are broken down into smaller fragments, but the chemical compositions are unaltered.
Different processes of mechanical weathering: The various processes of mechanical weathering are-
1. Block disintegration: When the rocks are broken into blocks or boulders, as a result of temperature difference, the process is called block disintegration.
1. Process: When there is differential heating of the outer and inner parts of rocks (the outer parts are more heated than the inner parts), there is a difference in the expansion of the components of those rocks. It is then that the vertical and horizontal cracks are formed within these rocks and they break apart along these cracks into several blocks.
2. Characteristics:
1. Mostly seen in basaltic rocks,
2. Several cracks are formed within the rocks both horizontally and vertically
3. The rocks get broken into square or rectangular shapes,
4. The rocks disintegrate as big chunks or blocks.
3. Occurrence: This process mostly occurs in high-temperature regions.
2. Exfoliation: When the layers of rocks peel off like an onion, this process is called exfoliation.
1. Process: Due to differential heating and cooling of the outer and inner parts of the rocks, the upper layers come off like onion peels and are prone to further weathering.
2. Characteristics:
1. Mostly seen in granitic rocks,
2. Tops of highlands be- come rounded in shape as a result of this type of weathering,
3. This weathering occurs in homogeneous rocks.
3. Occurrence: Exfoliation is most common in hot desert regions like the Sahara and Thar deserts.
3. Granular disintegration: When the rocks expand and contract alternately as a result of differences (hot and cold) in temperature, they break into smaller fragments. This process is called granular disintegration.
1. Process: Rocks composed of different types of minerals absorb and release heat at varying rates and thereby do not have a uniform rate of expansion and contraction. This results in the granular disintegration of these rocks.
2. Characteristics:
1. This type of weathering is more common in rocks that are heterogeneous in nature.
2. When the rocks burst, sounds similar to gunshots are heard.
3. Formation of sand is an ultimate result of the such weathering process.
3. Occurrence: This type of weathering is more commonly seen in hot desert regions.
4. Work of ice: In cold climatic regions, rocks are broken apart by ice crystals.
1. Process: In the cold Arctic region and other cold mountainous areas, the cracks in the rocks are filled up with ice-melt water in the daytime. This water freezes again at night due to condensation (low temperature) and exerts pressure on either side of the cracks, ultimately breaking them apart.
2. Characteristics:
1. Weathering occurs as a result of the formation of ice crystals.
2. Talus cones are formed on the lower slopes of mountains.
3. Occurrence: This type of weathering occurs mostly in cold climatic regions.
5. Other processes: Other processes of mechanical weathering include the formation of salt crystals, dirt cracking, boulder clearing, hitting by raindrops, etc.
Question 2 What is meant by chemical weathering? Explain the main processes involved in it.
Answer:
Chemical weathering:
The chemical composition of rocks is altered when they react with oxygen, carbon dioxide, water vapor, etc., in their own places. This process is called chemical weathering.
Different processes of chemical weathering: Different processes of chemical weathering are as follows-
1. Oxidation: When the nature of minerals within a rock alters under the influence of atmospheric oxygen and water, the process is called oxidation.
1. Process: In iron-bearing rocks, new minerals are formed and chemical decomposition takes place as a result of the chemical reactions in the presence of oxygen and water.
2. Reaction:
3. Characteristics:
1. This type of weathering takes place due to the action of water.
2. Iron-bearing rocks are subject to rusting as an effect of this.
3. Presence of oxygen is required in this type of weathering.
2. Carbonation: When the nature of rocks is altered as a result of the chemical reaction of water mixed with carbon dioxide, this process is called carbonation.
1. Process: When rainfall mixes with carbon dioxide (C02) in the atmosphere, carbonic acid is formed (C02 + H20—>H2C03). This dissolves limestone (calcium carbonate) by altering it into calcium bicarbonate (due to a chemical reaction).
2 Reaction:
3. Characteristics:
1. This type of weathering occurs mostly due to the action of rainwater.
2. It is more active in limestone rocks.
3. Hydration: When water reacts with the minerals present in the rocks and alters their chemical composition, this process is called hydration.
1. Process: Some minerals present in the rocks have more capacity to absorb water and they expand while undergoing chemical reactions.
2. Reaction:
3 Characteristics:
1. The minerals in the rocks expand.
2. As a result of the absorption of water, the rocks become softer/weaker.
3. This usually occurs in homogeneous rocks.
4. Hydrolysis: When the minerals present in the rocks react with ionized water, and chemical decomposition takes place, the process is known as hydrolysis.
1. Process: When water reacts with the minerals in a rock, new minerals are formed, and the rock is decomposed.
2. Reaction:
3 Characteristics:
1. It occurs in the presence of ionized or charged water.
2. New minerals are formed by this process.
3. Specific temperature is needed for reactions to occur.
Besides, due to the process of solution, gypsum, rock salt, etc., are dissolved in water and the rocks get decomposed.
Question 3 Classify weathering. Explain the role played by man, plants, and other animals in biological weathering.
Answer:
Classification of weathering:
Role of man, plants, and other animals in biological weathering: Man, plants, and animals aid biological weathering both directly and indirectly. The roles played by them are as follows-
1. Role of man: Construction of buildings, roads, etc., lead to the disintegration of rocks. Cultivation of land also leads to mechanical weathering. Mineral exploitation/mining, digging up of ponds and tanks, industrial establishments, etc., directly or indirectly cause weathering.
2. Role of plants: When the roots of plants and trees penetrate into cracks and joints of rocks and soil, the pressure exerted upon them cause the rocks to break apart. Parts of plants (leaves, flowers, fruits, branches, etc.) shed from trees decay and decompose, which aids in the chemical weathering of rocks.
3. Role of other animals: Burrowing animals like rabbits, rats, etc., dig holes in the ground for their survival and at the same time, fragment the rocks. Remains of dead animals react chemically and decompose the rocks.
Question 4 What is biological weathering? State the various processes of biological weathering.
Answer:
Biological Weathering:-
When rocks are disintegrated and decomposed by plants and animals, either directly or indirectly, the process is known as biological weathering. Such type of weathering occurs in almost all climatic regions.
Various processes of biological weathering: The factors of biological weathering (man, animals, and plants) are actually responsible for the two main processes of biological weathering.
1. Bio-mechanical weathering:
1. By animals: Burrowing animals like rats, earthworms, prairie dogs, mice, etc., dig holes in the ground to live and thereby aid in bio-mechanical Termites also help in weathering by bringing the lower layers of the soil to the upper part.
Moreover, the Co2 released by the animals living under- ground brings about changes in the chemical composition of rocks and soil and aids in their weathering. The man also has a vital role in inducing weathering. For example, carrying out mining activities, construction of roads, cultivation of lands, and other unplanned activities.
2. By plants: When the roots of trees and plants penetrate beneath the soil into the underlying rocks, they break the rocks into fragments. Roots can reach up to about 175 feet below the ground and thus aid in mechanical weathering. This is more prominent in areas with dense vegetation. Respiration by the roots of plants, humus, soil moisture carbon dioxide, mild temperature, etc., aids in bio-mechanical weathering of the soil.
2. Bio-chemical weathering: Lichens growing on rocks rot and form humus, which, in turn, is converted to humic acid after mixing with water. This aids in the rapid chemical weathering of rocks. The organisms living in limestone rocks release CO2 with their exhalation, which combines with water to form carbonic acid.
This dissolves the limestone rocks. The acid formed by the rotting of parts of plants like leaves, flowers, fruits, branches, etc., accelerates chemical weathering. During respiration, the tree roots release CO2 which, after combining with water present in the soil, changes into carbonic acid. This eventually dissolves and disintegrates the rocks.
Question 5 Write the differences between mechanical and chemical weathering.
Answer:
Differences between mechanical and chemical weathering: The differences between mechanical and chemical weathering are as follows-
| Points of difference | Mechanical weathering | Chemical weathering |
| 1. Place of occurrence | Rocks get disintegrated in their own places in this type of weathering. | Rocks get decomposed in their own places in this type of weathering. |
| 2. Alteration of minerals | It does not lead to the formation of new minerals. | It leads to the formation of new minerals. |
| 3. Main factors | Temperature, precipitation, etc. are the main factors causing mechanical weathering. | Oj, CO? water, minerals, etc. are the main elements causing chemical weathering. |
| 4. Process | Block disintegration, exfoliation, granular disintegration, etc. are the processes involved in mechanical weathering. | Oxidation, carbonation, hydration, hydrolysis, etc. are the processes involved In chemical weathering. |
| 5. Climate | This process is more predominant in the desert and cold mountainous regions. | This process is more predominant in hot and humid climatic regions. |
| 6. Landforms | Tors, inselbergs. etc., are formed due to mechanical weathering. | Caves, holes, pillars, etc. are formed due to chemical weathering. |
| 7. Identification of rocks | This type of weathering can be identified by the disintegrated rocks. | This type of weathering is Identified by the chemical analysis of rocks. |
| 8. Nature of change In the rocks | Physical changes occur in the rocks in this type of weathering. | Chemical changes occur in the rocks in this type of weathering. |
| 9. Colour | The color of rocks remains unchanged after the effect of mechanical weathering. | The color of rocks may change after the effect of chemical weathering. |
| 10. Sound | Fragmentation of rocks causes sounds. | Chemical changes and reactions in rocks occur silently. |
Question 6 Write the differences between mechanical weathering and biological weathering.
Answer:
Differences between mechanical weathering and biological weathering:
The differences between mechanical weathering and biological weathering are as follows-
| Point of difference | Mechanical weathering | Biological weathering |
| 1. Concept | The disintegration of rocks by various climatic factors is called mechanical weathering. | The disintegration of rocks by various plants and animals (man, bacteria, virus) is called biological weathering. |
| 2. Processes involved | Rocks disintegrate only by mechanical action. | Rocks disintegrated by both mechanical as well as chemical action. |
| 3. Areas of occurrence | This type of weathering is commonly seen in hot desert areas, cold mountainous areas, and cold polar regions. | It is commonly seen in areas where lifeforms are abundant. |
| 4. Identification | The parent rocks in this case can be identified by analyzing the weathered rocks. | It is not easy to identify the original rocks by identifying the weathered rocks. |
| 5. Rate of weathering | This is a slower process than biological weathering. | All animals including man accelerate the weathering process. |
Question 7 Write a comparison between chemical weathering and biological weathering.
Answer:
Comparison between chemical weathering and biological weathering:
The differences between chemical and biological weathering are as follows-
| Point of difference | Chemical weathering | Biological weathering |
| 1. Concept | The process of decomposition and disintegration of rocks by the action of acids, C02,02, and water is called chemical weathering. | The process of disintegration of rocks by plants and animals is called biological weathering. |
| 2. Characteristics of rocks | Characteristics of rocks change as a result of changes in their chemical composition in this process. | The physical and chemical characteristics of rocks change in this process. |
| 3. Areas of occurrence | This type of weathering is common in equatorial, tropical, and humid climatic regions. | This type of weathering is common in regions characterized by abundant lifeforms. |
| 4. Identification | If the chemical analysis is not done, the main rocks can not be identified. | It is not easy to identify the main rocks by observing weathered rocks. |
| 5. Rate of weathering | This is a silent weathering process and thus it is not easily perceptible. | It is carried out at a slow rate by life forms, including man. |
Chapter 5 Weathering Short Explanatory Answer Type Questions
Question 1 Why is mechanical weathering pre-dominant in desert areas?
Answer:
Mechanical Weathering Is Pre-Dominant In Desert Areas:-
The factors responsible for the predominance of mechanical weathering in desert areas are as follows-
1. Range or difference of temperature is high: The daily or diurnal range of temperature (difference of temperature between day and night) is high in desert areas. Rocks expand due to heating during the daytime while they contract due to cooling at night. This results in the fragmentation and mechanical disintegration of rocks.
2. Scarcity of rainfall: Chemical weathering rarely takes place due to the scarcity of rainfall in desert areas. Vegetation is also scarce due to lack of water thus, biological weathering is absent. So, only mechanical weathering plays an active part.
3. Excessive denudation: In Desert areas, being more prone to denudation, the upper layers of the rocks are removed by wind action and the rocks underneath are relieved from pressure. The underlying rocks expand consequently and crack form. Subsequently, the rocks disintegrate along these cracks.
Question 2 Rainfall has an impact on mechanical weathering.’ Explain.
Answer:
Rainfall Has An Impact On Mechanical Weathering:-
Rainfall influences mechanical weathering due to the following reasons-
1. Formation of ice: Rainfall is responsible for the formation of ice crystals within the cracks of rocks in colder climatic regions. These crystals subsequently disintegrate the rocks.
2. Raindrops hitting rocks: Raindrops hitting the rock surface over long periods ultimately leads to the fragmentation of the rocks.
3. Expansion of rocks: Rainwater seeping through the rock pores and layers expands the volume of the mineral constituents within them, which, in turn, leads to the breaking apart of the rocks (by mechanical weathering).
Question 3 ‘Exfoliation is predominant in granite. Give reasons.
Answer:
Exfoliation Is Predominant In Granite:-
When the upper layers of the rocks come off from the underlying layers due to differential heating in homogeneous granitic areas, the process is known as exfoliation. Since the upper layers of the rock are more heated than the underlying layers, a thermal gradient is created. The heat-affected upper layers of the rocks expand and come off like the layers of an onion. Exfoliation is thus a common occurrence in granite.
Question 4 The hills formed of granite have rounded or dome-shaped tops. Explain.
Answer:
The Hills Formed Of Granite Have Rounded Or Dome-Shaped Tops:-
The regions having granite rocks that have a high temperature or a dry, and desert type of climate, are found to have hills with rounded tops.
This is because the rocks expand due to heat during the day while they contract at night when the temperature drops. This alternate heating and cooling process affects the upper layers of the rocks. Due to the alternate tension and compression, the upper layers come off from the underlying rock layers like the layers of an onion. This process is called exfoliation. The hills here are thus rendered round in shape.
Question 5 ‘Hot and humid climatic regions are more prone to chemical weathering.’ Why?
Answer:
Hot And Humid Climatic Regions Are More Prone To Chemical Weathering:-
Chemical weathering is predominant in the hot and humid climate of the equatorial and tropical regions, because of the following specific reasons-
1. All the processes of chemical weathering- carbonation, oxidation, hydration, and hydrolysis require high temperatures and rainfall. Both of which are abundant in hot and humid climatic regions. In addition to this, there is also adequate water vapor in the atmosphere of these regions. All of these activities help in the process of chemical weathering.
2. When rainwater falls on the earth’s surface, it mixes with the CO2 present in the atmosphere and forms a mild carbonic acid. When this acid water comes in contact with limestone (calcium carbonate), it changes into calcium bicarbonate, and thus chemical weathering is initiated in the karst topography regions of the equator and tropics.
3. In humid areas, the leaves, flowers, fruits, etc., shed from trees, which, on decaying, form humus and subsequently humic acid. This acid facilitates the chemical decomposition of the rocks.
Question 6 Why is chemical weathering prominent in regions having limestone rocks?
Answer:
Chemical Weathering Prominent In Regions Having Limestone Rocks Because:-
Carbonation is a process that occurs when calcium carbonate (present in limestone) reacts with CO2 in the atmosphere. When rain falls, the CO, in the atmosphere reacts with it and turns it into mild carbonic acid. This carbonic acid reacts with calcium carbonate (limestone) to form calcium bicarbonate and ultimately dissolves the limestone.
In limestone regions, limestone is dissolved by the process of carbonation and creates a host of landform features like stalactites, stalagmites, pillars, etc.
Question 7 Write the differences between exfoliation and frost action.
Answer:
The differences between exfoliation and frost action are as follows-
| Point of Difference | Exfoliation | Frost action |
| 1. Concept | The rock layers peel off and come out like onion peels as a result of the high temperature, in this process. | In cold climatic regions, ice crystals formed within the rock layers aid in disintegrating the rocks. |
| 2. Process | Due to differences in temperature, there is expansion and contraction of the rocks/resulting in their weathering. | The ice crystals formed within the cracks of the rocks exert pressure and thereby break the rocks. |
| 3. Occurrence | It usually occurs in deserts or arid and dry climatic regions. | It usually occurs in cold mountainous regions or polar regions. |
Question 8 Write the differences between exfoliation and granular disintegration.
Answer:
The differences between exfoliation and granular disintegration are as follows-
| Point of difference | Exfoliation | Granular disintegration |
| 1. Nature of rocks | This occurs in homogeneous rocks. | This occurs in heterogeneous rocks. |
| 2. Type of weathering | In this type of weathering, the rock layers come off like onion peels. | Rocks are disintegrated into smaller and minute particles or grains. |
| 3. Shape of relief features | The Landforms formed as a result of this type of weathering are rounded or dome-shaped. | The tops of the hills and mountains become conical as a result of this type of weathering. |
| 4. Sound | The process of exfoliation does not cause any sound. | Gunshot-like noises can be heard in this type of weathering. |
Question 9 Write the differences between oxidation and carbonation.
Answer:
The differences between oxidation and carbonation are as follows-
| Point of difference | Oxidation | Carbonation |
| 1. Concept | Water and oxygen react with the iron content of the rocks and they thus get decomposed. 4FeO + 3H20 + 02 – (Ferrous (Water) (Oxygen) oxide) 2Fe203-3H20 (Hydrated ferric oxide) | Water and C02 react with -the carbonates present in the rocks, and they thus get decomposed. CaC03 + H20 + C02- (Calcium (Water) (Carbon carbonate) dioxide) Ca(HC03)2 (Calcium bicarbonate) |
| 2. Landform | does not lead to the formation of landforms. | It leads to the formation of different features of karst topography (dolines, caves, etc.). |
| 3. Influence | It leads to the formation of rust in iron-containing rocks. | Carbonates are formed in this process. |
Question 10 Write the differences between hydration and hydrolysis.
Answer:
The differences between hydration and hydrolysis are as follows-
| Point of difference | Hydration | Hydrolysis |
| 1. Concept | Hydration is the process of decomposition of rocks when water reacts with the minerals present in them. 4FeO + 3H20— (Ferrous (Water) . oxide) ‘ 1 2Fe203-3H20 (Hydrated ferric oxide) | Hydrolysis is the process of minerals in the rocks reaching ionized water molecules and eventually decomposing the ro KAISI308 + (H+OH-)- (Orthoclase (Ionised feldspar) water) ‘ HAISi308 + K( (Alumino (Po1 silicic acid) hyc |
| 2. Volume | It increases the volume of minerals present in the rocks. | It does not increase the volume of the rocks. |
| 3. New minerals | New minerals are not formed. | New minerals are formed. |
Chapter 5 Weathering Short Answer Type Questions
Question 1 What are the various types of weathering?
Answer:
Various Types Of Weathering:-
Weathering can be of three types-
1. Mechanical,
2 Chemicals,
3. Biological weathering.
Question 2 What is mechanical weathering?
Answer:
Mechanical Weathering:-
When different elements of weather (like temperature, rainfall, etc.) break down the rocks in their own places, this process of rock fragmentation is known as mechanical weathering.
Question 3 Where is mechanical weathering more prevalent on the earth’s surface?
Answer:
Mechanical Weathering More Prevalent On The Earth’s Surface In Mostly Below Areas:-
Mechanical weathering takes place mostly in high mountainous areas and in hot and dry desert regions. For example, the rocks get fragmented as a result of exfoliation, block disintegration, and granular disintegrate- in hot and dry desert regions.
Question 4 Which type of landforms result from mechanical weathering?
Answer:
Types Of Landforms Result From Mechanical Weathering:-
1. A soft layer of soil called regolith is formed due to mechanical weathering.
2. Due to exfoliation, rounded hills (especially in granite-gneiss rocks) are formed. For example, the Ranchi dome near Ranchi lake in Jharkhand.
3. In cold climatic regions, angular rock fragments are formed as a result of weathering by ice and these accumulate in a cone-shaped manner in the foothill zones and are called talus or scree.
Question 5 Where does mechanical weathering occur due to frost or ice?
Answer:
Mechanical Weathering Occurs Due To Frost Or Ice:-
In the high mountainous areas and Arctic regions, frost or ice plays a major role in mechanical weathering. The ice in the cracks of the rocks exerts pressure on either side and eventually breaks the rocks
Question 6. What is block disintegration?
Answer:
Block Disintegration:-
Block disintegration is a type of mechanical weathering. When the cracks in the rocks expand and contract due to differential heating (i.e., hot during the daytime and cool at night), they get weakened and eventually break apart in the form of blocks. This is called block disintegration.
Question 7 Why is granular disintegration more prevalent in hot desert areas?
Answer:
Granular Disintegration More Prevalent In Hot Desert Areas:-
Granular disintegration is a type of mechanical weathering found in hot and arid desert regions. Due to differential heating, the various minerals present in the rocks expand and contract alternately and these rates of expansion and contraction differ in the case of different minerals. As a result, the rocks get broken down into small fragments.
Question 8 What is exfoliation?
Answer:
Exfoliation:-
When the intensity of temperature is high, there is a difference in temperature in the outer and inner layers of the rocks. As a result, the outer layers of the rocks come off from the underlying layers (like onion peels). This is called exfoliation. The surface of the rock assumes a rounded shape as a result of this. Exfoliation is a common occurrence in the granite-gneiss rocks of the Chota Nagpur Plateau (near Ranchi) in India.
Question 9 Why people residing in desert areas can hear sounds similar to gunshots?
Answer:
People Residing In Desert Areas Can Hear Sounds Similar To Gunshots:-
The temperature is very high in desert areas and the rocks are heated over a long period of time during the day. However, since different minerals in the rocks have different capacities of absorbing and releasing heat, this unequal expansion and compression within the rocks exert great pressure on them, and subsequently, they burst, making a loud noise, that is similar to the sound of gunshots.
Question 10 What is chemical weathering?
Answer:
Chemical Weathering:-
When rocks are subject to decomposition due to a reaction with oxygen, carbon dioxide, water vapor, etc., present in the atmosphere or water, the process is known as chemical weathering.
Question 11 In which climatic region is chemical weathering prevalent?
Answer:
Due to high temperatures and heavy rainfall, the equatorial regions are more prone to chemical weathering (as a result of hydrolysis, hydration, etc.).
Question 12 Why is chemical weathering more common in equatorial regions?
Answer:
Chemical Weathering More Common In Equatorial Regions:-
The equatorial regions experience chemical weathering because- equatorial regions have high temperatures and receive rainfall throughout the year, the leaves of the forests in this region fall on the ground and form humic acid, which facilitates the chemical decomposition of the rocks.
Question 13 What is oxidation?
Answer:
Oxidation:-
Chemical reaction occurs in the rocks as a result of water (in the presence of oxygen) reacting especially with iron present in the rocks. It forms oxides and hydroxides and eventually weakens and dissolves the rocks. Brownish/yellowish stains are seen on the rocks as a result of rust formation.
Reaction:
Question 14 What is carbonation?
Answer:
Carbonation:
When water mixes with carbon dioxide, carbonic acid forms and it chemically reacts with calcium carbonate present in the rocks and then dissolves the rocks. This process is known as carbonation. This is how limestones are dissolved and karst landforms are formed. For example, Borra caves near Vishakhapatnam in Andhra Pradesh.
Example:
Question 15 What is hydration?
Answer:
Hydration:-
When the minerals present in the rocks mix with water and alter their chemical process composition. This is called hydration. This is an important process of chemical weathering. Hydration actually causes granular disintegration and makes the rocks further susceptible to chemical weathering, especially by oxidation and carbonation. For example, the process of hydration changes feldspar into kaolinite clay and the process is known as kaolinization.
Question 16 What is hydrolysis?
Answer:
Hydrolysis:-
The chemical combination of minerals with ionized water to form new minerals, decomposing the rock is called hydrolysis. For example, clay and silicon are by-products of such a chemical reaction of granite.
Question 17 Why is carbonation more predominant in limestone regions?
Answer:
Carbonation More Predominant In Limestone Regions:-
The process of carbonation is predominant in limestone regions because when carbon dioxide mixes with water it forms carbonic acid, and when this reacts with limestone (calcium carbonate), it forms calcium bicarbonate and dissolves the limestone.
Question 18 What is biological weathering?
Answer:
Biological Weathering:-
Rocks are sometimes broken down by plants and animals. Again, humic acid from decaying plants and animals results in the breaking down of rocks. When the rocks are subject to change as a result of the decaying of plants and animals, the process is known as biological weathering.
Question 19 What are the different types of biological weathering?
Answer:
Different Types Of Biological Weathering:-
Biological weathering is of two types- bio-mechanical weathering, and bio-chemical weathering.
Question 20 What is the role of plants in biological weathering?
Answer:
Role Of Plants In Biological Weathering:-
When the roots of plants grow and exert pressure on the cracks in the rocks, the rocks disintegrate. The rotten plant remains (namely, leaves, stems/trunks, etc.) result in the formation of humic acid, which eventually dissolves the rocks.
Question 21 What is the role of human beings in biological weathering?
Answer:
Role Of Human Beings In Biological Weathering:-
Rocks are broken down into fragments as a result of agricultural practices, mining activities, etc. 2 Rocks are disintegrated and dissolved as a result of the construction of houses, roads, excavation of canals, etc.
Question 22 What is colloid plucking?
Answer:
Colloid Plucking:-
The wet soil particles or colloids that form on the rocks, dry up eventually and exert pressure on the minerals present in the rocks. This results in weathering of rocks and this process are called colloid plucking.
Question 23 Why does rust form on rocks?
Answer:
Rust Form On Rocks Because:-
The iron-bearing minerals present in certain rocks are prone to the formation of rust. The process of oxidation converts the ferrous oxide present in the rocks into ferric acid, which results in the formation of light brown and yellow colored rust.
Question 24 What is desert varnish?
Answer:
Desert Varnish
In desert areas, the orangish-yellow-colored coating that forms on the rock layers is called desert varnish. It is composed of clay, iron, and manganese oxide. They are found mostly in basalt and quartzite rocks.
Question 25 What is slaking?
Answer:
Slaking:-
Slaking is the process of alternate wetting and drying of rocks. In coastal regions rocks gradually get wet and dry twice a day due to tide action. Consequent expansion and contraction of rock shells result in the disintegration of rocks. Slaking is common in clayey alluvial soil.
Question 26 What is chelation?
Answer:
Chelation:-
Chelation is the process where organic acid reacts with an insoluble mineral and transforms it into a soluble mineral. Podsol soil is formed by the chelation process in the coniferous forest regions.
Question 27 What is sheeting?
Answer:
Sheeting:-
Sheeting is a process in which cracks and fractures develop parallel to the ground surface in massive rocks such as granites, quartzites, etc. The main cause of sheeting is the removal of superincumbent load that results in a reduction of pressure off the rock layers.
Question 28 What is spalling?
Answer:
Spalling:-
Spalling is a common mechanism of rock weathering. In this process cracks and fractures develop and lozenge or irregular platy rock fragments form. The main causes of spalling are the unloading of superincumbent load, freezing and thawing, and thermal expansion.
Chapter 5 Weathering Multiple Choice Type Questions
1. The main process of mechanical weathering in a warm desert is—
1. Saline Crystal Formation
2. Frost Action
3. Granular Disintegration
4. Block disintegration
Answer: 3. Granular Disintegration
2. Which component plays an important role in the oxidation process of the weathering of rocks?
1. H2
2. 02
3. N2
4. C02
Answer: 2. 02
3. The main component of chemical weathering is—
1. Water
2. Sunlight
3. Air Stream
4. Flora
Answer: 1. Water
4. Chemical formula of humic acid is—
1. c187c186c89c9c1
2. C10H20°10
3. C12H10O10
4. C5h607
Answer: 1. c187c186c89c9c1
5. Limestone-clad areas are prone to—
1. Carbonation
1. Hydration
3. Hydrolysis
3. Oxidation
Answer: 1. Hydration
6. Snowfall-prone areas experience—
1. Mechanical Weathering
2. Chemical Weathering
3. Biological Weathering
4. Mechanical And Chemical Weathering
Answer: 1. Mechanical Weathering
7. Which of the following is visible in homogeneous rocks?
1. Block Disintegration
2. Exfoliation
3. Granular Disintegration
4. Biological Weathering
Answer: 2. Exfoliation
8. Rusting of rocks due to chemical weathering is known as—
1. Oxidation
2. Carbonation
3. Solution
4. Hydrolysis
Answer: 1. Oxidation
9. Areas that are prone to chemical weathering are—
1. Tundra Areas
2. Cool Temperate Areas
3. Equatorial Areas
4. Semi-Arid Areas
Answer: 3. Equatorial Areas
10. Exfoliation occurs in—
1. Basalt
2. Granite
3. Sandstone
4. All Types Of rocks
Answer: 2. Granite
11. The process of mechanical weathering which is most effective in high altitude areas or cold areas is—
1. Colloid Plucking
2. Bolder Cleaving
3. Frost Action
4. Sheeting
Answer: 3. Frost Action
12. The kind of weathering that takes place in heterogeneous rocks is—
1. Disintegration
2. Boulder Cleaving
3. Exfoliation
4. Granular Disintegration
Answer: 4. Granular Disintegration
13. When water freezes into ice, its volume—
1. Decreases By 8%
2. Increases By 9%
3. Increases By 10%
4. Decreases By 11%
Answer: 2. Increases By 9%
14. Heavy rainfall-prone tropical areas witness—
1. Mechanical Weathering
2. Chemical Weathering
3. Biological Weathering
4. None of the above
Answer: 2. Chemical Weathering
15. Result of mechanical weathering in rocks is—
1. Physical Change
2. Chemical Change
3. Both Physical And Chemical Change
4. No Changes Occur
Answer: 1. Physical Change
16. The process in which calcium carbonate transforms into calcium bicarbonate is—
1. Oxidation
2. Carbonation
3. Hydrolysis
4. Solution
Answer: 2. Carbonation
17. Both mechanical and chemical weathering occur more in—
1. Cool Temperate Areas
2. Warm Temperate Areas
3. Equatorial Regions
4. Desert Regions
Answer: 2. Warm Temperate Areas
18. A major factor of mechanical weathering is—
1. Gravitational Force
2. Oxygen
3. Hardness Of Rocks
4. Heat
Answer: 4. Heat
19. Cold regions experience—
1. Mechanical weathering
2. Chemical weathering
3. Biological weathering
4. Bio-Mechanical weathering
Answer: 1. Mechanical weathering
20. The kind of weathering which changes the shape of a rock is known as—
1. Biological Weathering
2. Mechanical Weathering
3. Bio-Mechanical Weathering
4. Chemical Weathering
Answer: 2. Mechanical Weathering
21. Gunshot-like noises occur in—
1. Exfoliation Process
2. Frost Weathering
3. Granular Disintegration
4. Block Disintegration
Answer: 3. Granular Disintegration
22. The process of weathering in granite is—
1. Exfoliation
2. Dirt Cracking
3. Boulder Cleaving
4. Oxidation
Answer: 1. Exfoliation
23. One of the main causes of exfoliation is—
1. Humidity
2. Solar Energy
3. Decrease In Pressure
4. Rainfall
Answer: 2. Solar Energy
24. Exfoliation is common in—
1. Desert Region
2. Polar Region
3. Humid Region
4. Coastal Region
Answer: 1. Desert Region
25. The weathering process that forms a rounded hill is—
1. Frost Action
3. Granular Disintegration
3. Exfoliation
3. Boulder Cleaving
Answer: 3. Exfoliation
26. Due to excessive temperature variation, the bedded rock peels off like an onion, which is called—
1. Block Disintegration
2. Granular Disintegration
3. Exfoliation
4. Shattering
Answer: 3. Exfoliation
27. When carbon dioxide dissolves in water is formed.
1. Carbonic Acid
2. Calcium Bicarbonate
3. Organic Acid
4. None Of These
Answer: 1. Carbonic Acid
28. Exfoliation is a type of—
1. Mechanical Weathering
2. Chemical Weathering
3. Biological Weathering
4. None Of These
Answer: 1. Mechanical Weathering
29. Block disintegration is common in—
1. Granite
2. Gabbro
3. Basalt
4. Sandstone
Answer: 3. Basalt
30. The process of formation of humus through the decomposition of dead plants or animals is known as—
1. Eluviation
2. Podsolization
3. Humification
4. Illuviation
Answer: 3. Humification
Chapter 5 Weathering Fill In The Suitable Words
1. Rock disintegration takes place in Mechanical type of weathering.
2. Oxidation is a type of Chemical weathering.
3. Decomposition occurs in Chemical weathering.
4. Exfoliation is commonly found in desert areas.
5. Limestone gets dissolved as a result of carbonation
6. Rocks containing iron forms rust as a result of oxidation
7. In areas of snowfall, mechanical weathering largely occurs.
8. In tropical regions, chemical weathering is largely seen.
9. Carbon dioxide mixed with water forms carbonic acid.
10. The constituents of rocks are not altered in case of mechanical weathering.
11. In cold climatic regions, the first action is the process of mechanical weathering.
12. In heterogeneous rocks, granular disintegration takes place.
13. Rocks change only in shape in case of mechanical weathering.
14. Weathering does not occur in permafrost areas.
15. In limestone regions, the process of solution creates permafrost topography.
16. Mechanical weathering due to salt crystals occurs largely in sandstone
17. Humans cause biotic weathering through agriculture.
18. Granular disintegration occurs in Heterogeneous rocks.
19. When water changes into ice, Increases its volume
20. Weathering is a slow process.
21. Due to the process of hydration hematite transforms into Limonite
22. Granular disintegration is an example of mechanical weathering.
23. The chemical weathering that occurs due to the reaction of carbon dioxide is called Carbonation
Chapter 5 Weathering If The Statement Is True, Write TRUE And If False, Write ‘FALSE’ Against The Following Write The Correct Answer From The Given Alternatives
1. Mechanical weathering is dominant in a tropical climate. False
2. Carbonic acid helps in oxidation. False
3. Chelation is a type of biochemical weathering. True
4. Solution is a process of mechanical weathering. False
5. Rocks become smooth and circular as a result of exfoliation. False
6. Rusting of rocks occurs due to the process of carbonation. False
7. The characteristics of rock remain unchanged in chemical weathering. False
8. Atmosphere is the main component of weathering. False
9. Rainfall during monsoon helps in mechanical weathering. True
10. Granular disintegration occurs silently. False
11. Chemical weathering is dominant in desert climates. False
12. Mechanical weathering changes the mineral composition of the original rocks. False
13. Burrowing animals like rats, rabbits, earthworms, etc. cause mechanical weathering. False
Chapter 5 Weathering Match the left column with the right column
1.
| Left column | Right column |
| 1. Exfoliation | A. Cold mountain region |
| 2. Frost action | B. Tropical region |
| 3. Hydrolysis | C. Limestone region |
| 4. carbonation | D. Hot desert area |
Answer: 1-D,2-A,3-B,4-C
2.
| Left column | Right column |
| 1. Mineral of the tropical region | A. Oxidation |
| 2. Rusting of rocks | B. Bauxite |
| 3. Plants and minerals | C. Mass wasting |
| 4. Gravitational force | D. Biological weathering |
Answer: 1-B,2-A,3-D,4-C
Chapter 5 Weathering Answer In One Or Two Words
Question 1 Where does granular disintegration take place?
Answer: Desert area.
Question 2 Which gaseous component is needed in oxidation?
Answer: Oxygen.
Question 3 What is the process of combination of rock minerals with water called?
Answer: Hydration.
Question 4 Which type of weathering results in rusting of rocks?
Answer: Oxidation.
Question 5 Name a burrowing animal.
Answer: Rat.
Question 6 Exfoliation occurs in which rock?
Answer: Granite.
Question 7 Which type of weathering occurs due to the construction of houses and roads?
Answer: Mechanical weathering.
Question 8 Ice disintegration occurs in which climatic region?
Answer: Tundra.
Question 9 Which type of weathering causes changes in the structural composition of rocks?
Answer: Chemical weathering.
Question 10 Which type of weathering is hydrolysis?
Answer: Chemical weathering.
Question 11 Name the cone-shaped depositional feature formed as a result of mechanical weathe¬ring on hill slopes.
Answer: Screen or Talus.
Question 12 Which acid is formed due to the decomposition of organic matter?
Answer: Humic acid.
Question 13 Give an example of an easily soluble rock.
Answer: Limestone.
Question 14 In which climatic regions is mechanical weathering predominant?
Answer: Arid and semi-arid regions.
Question 15 Which type of weathering is prevalent in homogeneous rocks?
Answer: Exfoliation.
Question 16 Which type of weathering occurs in limestone areas?
Answer: Carbonation.
Question 17 Which type of weathering is prevalent in rainy tropical regions?
Answer: Chemical weathering.
Question 13 What type of chemical weathering occurs due to the reaction of iron with oxygen?
Answer: Oxidation.
Question 19 What is the process known whereby small-grained rocks are further fragmented in the coastal areas?
Answer: Slaking.
Question 20 Which process causes the disintegration of rocks as a result of a decrease in the pressure of the superincumbent rock layers (due to mechanical weathering)?
Answer: Spalling.
Question 21 What is formed as a result of the decomposition of branches, leaves, flowers, and fruits of trees after they fall to the ground?
Answer: Humus.
Question 22 The process whereby rocks are broken apart is an example of which type of weathering?
Answer: Mechanical weathering.
Question 23 What happens when rocks get heated during the daytime?
Answer: They increase in volume.
Question 24 Which type of weathering causes rocks to get fragmented in a square shape?
Answer: Block disintegration.
Question 25. Which type of weathering causes rock layers to come off like the peels of an onion?
Answer: Exfoliation.
Question 26 Which type of weathering is predominant in the Thar Desert?
Answer: Granular disintegration.
Question 27 In which type of weathering does gunshot-like noises occur?
Answer: Granular disintegration.
Question 23 In which type of weathering do both physical and chemical changes occur in rocks?
Answer: Chemical weathering.
Question 29 Which type of weathering helps to form laterite soil in the tropical climate?
Answer: Oxidation.
Question 30 In which rock is exfoliation maximum?
Answer: On the granites in the warm desert climate.
Question 31 Which regions are prone to mechanical weathering?
Answer: Hot deserts, tundra region, polar region, and high mountainous region.
Chapter 5 Weathering TOPIC C Effect of Weathering and Soil Erosion Long Answer Type Questions
Question 1 State the effects of weathering. Explain how soil is formed as a result of weathering.
Answer:
Effects of weathering:
The effects of weathering are-
1. Formation of landforms: Landforms like tors and rounded hills in the humid tropical regions, inselbergs in the hot dry desert regions, caves, stalactites, and stalagmites in limestone areas, etc., are all formed as a result of weathering.
2. Formation of minerals: New minerals are formed as a result of chemical reactions. For example, bauxite is formed in humid tropical countries.
3. Facilitates agriculture: Due to the disintegration of rocks by weathering, the porosity of soil increases, which facilitates air and water circulation and hence aids in agricultural practices.
4. Formation of regolith: Due to the disintegration and decomposition of rocks, regolith is formed, which plays a major role in soil formation later on.
Soil Formation: The soil-forming process, as a result of weathering, may be explained by the following stages-
1. First stage: Various processes of mechanical, chemical, and biological weathering, break down rocks into smaller fragments and decompose them further. This loose layer of fragmented rocks on the top is called regolith, which is the first step of soil formation.
2. Second stage: Rainwater and air seep through the various layers of the rocks through this regolith layer which facilitates chemical weathering of the fragmented rocks. Biological weathering is also initiated by the microorganisms and the dead remains of plants and animals present in the top layer. As a result a black-colored substance called humus forms through the process of humification.
3. Third stage: Humus and other weathered particles oxidize in the presence of oxygen and form new minerals. This process is called mineralization. During the process of soil formation iron, aluminum, and other minerals are transported from the top layer to the lower layers of the soil. This process is called eluviation. These minerals get accumulated in the lower layers and this process is called illuviation.
Thus, with the passage of time, the components in the soil-forming process change their physical and chemical characteristics to form a soft layer called soil on the surface of the Earth, with organic matter and minerals as their constituents.
Question 2 Briefly explain the concept of soil erosion.
Answer:
Concept of soil erosion:
The concept of soil erosion is-
Definition: The process in which soil particles are removed from the top layer by natural or man-made factors, is called soil erosion.
Factors: The following equation explains the process-
e = g(cl, v, t, s, h)
where, e = soil erosion, g = effectiveness, cl= climate, v = vegetative cover, t = landform or relief, s = type of soil, h = role of man or human interference.
Causes of soil erosion: They may be classified as-natural and man-made causes.
Natural causes:
1. Rainfall: In regions with high rainfall, the raindrops loosen the soil particles from the rock layer and wash them away.
Wind: Winds blow with high velocity in open desert areas and coastal tracts (receiving no obstacles) and lead to soil erosion.
Flowing water: Currents of river water and sea waves over the adjacent land areas cause soil erosion.
2. Man-made causes:
Deforestation: In deforested areas, the bare land is more prone to soil erosion. The roots of the trees bind the soil together. When the trees are cut down, the region becomes prone to soil erosion and is thus rendered infertile.
Overgrazing: Excessive grazing by cattle, goats, and sheep in grassland areas results in the baring of the ground, leading to soil erosion.
Unscientific methods of cultivation: In areas where shifting or ‘jhum’ cultivation is practiced, the forest is cleared by burning it down (which is unscientific), and this leads to soil erosion.
Process of soil erosion: Soil erosion is mainly caused by flowing water and wind.
By work of flowing water:
1. Sheet erosion: When rainfall or flowing water removes the soil layer by layer, it is known as sheet erosion.
2. Rill erosion: When rainwater or a river (in its youth stage), flows along the slopes of a mountain as narrow channels or rills, soil erosion occurs.
2. Gully erosion: These rills become wider and deeper due to more soil erosion, and this is known as gully erosion.
4. Ravine erosion: When the gullies become further deepened and widened, the topography is converted to a ‘badland’, where cultivation is not possible and the area becomes inaccessible too.
2. By work of wind: In desert areas, winds carry sand from one area to other distant areas, leading to erosion of the top layer.
Effects of soil erosion:
1. Effects on the physical environment:
1. As a result of soil erosion, the groundwater level decreases,
2. hydrological cycle is affected,
3. food chain is disturbed as habitats of the decomposers (like bacteria, fungi, etc.) present in the soil are destroyed,
4. the navigability of rivers and other waterbodies decrease (due to aggradation by soil deposits or siltation), and the areas become more prone to floods.
2. Effects on the human environment:
1. Fertility of soil decreases, crop productivity gets reduced,
2. decrease in the navigability of rivers hampers trade and water transport,
3. ecosystem of wetlands is damaged as they get filled up with soil deposits.
Areas prone to soil erosion: Continuous flat areas, plateaus devoid of vegetation, desert areas, coastal areas, riverine tracts, etc., are more prone to soil erosion.
Question 3 Briefly discuss the methods of soil conservation. Or, Discuss the preventive measures for soil erosion.
Answer:
Different methods of soil conservation:
The various measures adopted for preventing soil erosion and increasing the fertility of the soil are known as soil conservation measures.
1. Agricultural methods
1. Afforestation: If trees are planted along the slopes of mountains, on infertile and barren lands, soil erosion can be prevented. This is because the roots of the trees bind the soil together.
2. Restriction on overgrazing: If overgrazing can be controlled in grassland areas, soil erosion can be prevented.
3. Ban on shifting or ‘jhum’ cultivation: When the forests are burnt down for clear land, the trees are destroyed and soil erosion also increases. This can only be prevented by banning such a practice.
4. Step/Terrace farming: The slopes of the mountains are carved into steps or terraces to retain rainwater on each step (to be used by the cultivated crops). Soil erosion can be prevented by practicing such type of farming.
5. Creation of forest line/boundary: If forest boundaries are created (by planting trees) on all sides of agricultural fields, coastal regions (especially in the direction of the winds), etc., then soil erosion can be reduced.
6. Crop rotation: If any land is cultivated throughout the year with different types of crops (not allowing it to lay bare), then the land is not exposed to soil erosion.
7. Contour farming: Bunds are constructed along the contour of the land (horizontally along the slopes of mountains), to prevent water from washing down and hence it prevents soil erosion.
8. Strip cropping: When crops are cultivated in long strips prepared along the slopes, they prevent soil from being carried away by flowing water along the slopes.
9. Land cover: If the unused parts of the crops like stems, hay, etc., are spread over any bare land, soil erosion can be prevented, especially in muddy areas.
2. Infrastructural methods:
1. Construction of artificial walls: If walls are constructed on seashores and along river banks, soil erosion by flowing water can be prevented.
2. Digging of canals: If canals are dug to facilitate drainage and several waterbodies are constructed especially in desert areas, soil erosion can be prevented.
3 Other methods: More advanced research on preventing soil erosion and increasing soil fertility, spreading awareness among the people, can help in soil conservation.
Chapter 5 Weathering Short Explanatory Answer Type Questions
Question 1 What is the role of man in soil erosion?
Answer:
Role Of Man In Soil Erosion:-
The activities carried out by human beings that lead to soil erosion, are as follows-
1. Deforestation: Due to the cutting down of trees, the soil is exposed to weathering. Thus rainwater washes away the fertile topsoil.
2. Unscientific methods of cultivation: Shifting cultivation, intensive cultivation, etc., reduce soil fertility and increase soil erosion.
3. Increased grazing: Excessive grazing practiced on the thin soil along the mountain slopes, leads to exposure of the soil to weathering and erosion.
Question 2 How does terrace farming help in conserving soil?
Answer:
Terrace Farming Help In Conserving Soil As Follows:-
The rate of flow of water along the slopes of hills and mountains can be controlled. In such areas, farming is done on steps cut along the slopes at different heights. Each step or terrace is bordered by slightly elevated mud bunds which prevent the washing away of water down the slope and thus store water on these terraces. Thus, runoff is reduced and infiltration of water underground is increased. These terraces are of three types-
1. Bench-like steps: The lower part of these steps are flat and on the outer sides, low bunds are constructed.
2. Successive steps: A series of steps or terraces at different altitudes (like a staircase), prevents water from washing down and thus conserves soil.
3. Plain or flat steps: The lower part of these steps are flat and different crops are cultivated here. Thus, water seeps underground and soil erosion is prevented because run-off is controlled.
Question 3 How does weathering help in increasing soil fertility?
Answer:
Weathering Helps In Increasing The Soil Fertility:-
The role of weathering in increasing soil fertility is discussed as follows-
1. A soft layer called regolith is formed on the upper surface of the Earth as a result of weathering. The minerals present in this regolith seep underground (in solution with water) and supply essential nutrients to the plants.
2. The roots of trees cause the rocks to break apart (biotic or biological weathering). Besides, burrowing animals like rabbits, rats, etc., loosen up the soil by digging into it and thereby allowing air circulation in the soil, which is beneficial to the plants.
3. Humus is formed as a result of the decaying of leaves, flowers, etc., that are shed from the trees. When humus mixes with the oxygen present in the atmosphere, it enriches the various minerals found in the soil, which, in turn, increases the fertility of the soil.
Question 4 What are the landforms developed due to weathering?
Answer:
Landforms Developed Due To Weathering Process:-
Weathering is a process in which surface rocks are disintegrated or decomposed and remain in their original place or ‘in situ’. Weathered materials are transported through the process of erosion.
So, the process of weathering and erosion together develop various types of landforms, namely- Round shaped topography develops over granite by the process of exfoliation; flattened topography develops on basalt by the process of block disintegration; residual hills like inselbergs form in the hot deserts
Sometimes, these are transformed in mesas, and buttes due to excessive weathering and erosion; in humid tropical climates, tors develop; in limestone regions, caves, stalactites, stalagmites, etc. form due to carbonation and solution processes.
Sometimes, rivers that flow over a karst region may disappear and enters underground through shallow holes or sink holes which develop blind or dry valleys on the surface. Felsenmeer forms through the deposition of talus or scree along the foothills.
Question 5 Write the differences between regolith and humus.
Answer:
The differences between regolith and humus are as follows-
| Point of difference | Regolith | Humus |
| 1. Concept | The layer formed of disintegrated and decomposed rock particles lying on the top layer of the Earth’s surface is called regolith. | Humus is a black or deep brown colored material that is formed by the decomposition of various organic materials. |
| 2. Nature | Regolith is formed by the disintegration of rocks, so, these are solid materials. | Humus is a semi-solid matter that is formed through the decomposition of organic matter. |
| 3. Origin | Regolith is formed from fragmented rocks. | Humus is formed through the decomposition of plant, animal, and organic matter. |
Question 6 What are the differences between eluviation and illuviation?
Answer:
The differences between eluviation and illuviation are as follows-
| points of difference | eluviation | illuviation |
| 1. Work process | It is a process of transportation. | It is a process of deposition |
| 2. Place | This process occurs on the upper layer of the soil i.e, surface | This process occurs beneath the soil surface |
| 3. Presence of minerals | Minerals are removed from the upper layer of soil. | Minerals are deposited below the soil surface. |
| 4. Dependency | The process of eluviation depends on the amount of rainfall received. | The process of illuviation depends on the nature of the eluviation process. |
| 5. Colour of the soil layer | The upper layer of soil is light in color due to the removal of minerals. | Sub-surface soil is deep in color due to the deposition of minerals. |
Chapter 5 Weathering Short Answer Type Questions
Question 1 What is soil erosion?
Answer:
Soil Erosion:-
When soil particles from the top layer are separated and transported elsewhere due to natural or man-made factors, it is called soil erosion. For example, soil erosion occurs as a result of surface run-off due to heavy rainfall (the topsoil is washed off and transported elsewhere).
Question 2 Where is terrace farming practiced?
Answer:
Terrace Farming:-
Terrace farming (or step farming) is usually practiced along the slopes of mountains. For example, it is common in the hill slopes of Darjeeling.
Question 3 What is talus?
Answer:
Talus:-
The action of ice and snow in the cold mountainous regions, widens the cracks in the rocks and eventually breaks the rocks into angular fragments. These fragments are deposited at the foothill zones in a cone-like formation known as a talus or scree. These features are commonly seen in the Ladakh region. They are also known as Blackspade or Felsenmeer.
Question 4 What is humification?
Answer:
Humification:-
The process by which the organic matter present in the soil is decomposed by micro-organisms and turned into a black-colored semi-solid substance, is called humification.
Question 5 What is eluviation and illuviation?
Answer:
Eluviation And Illuviation:-
The process by which the dissolved minerals in the upper layers of the soil are transferred to the lower layers is called eluviation. The process in which the minerals present in the soil are deposited in the lower layers of the soil/rocks is known as illuviation.
Question 6 What is terra rosa?
Answer:
Terra Rosa:-
In the karst region, the dissolved limestone gets removed and accumulated in the upper layers of the soil as a result of the process of carbonation. This red-colored layer of soil deposited on the earth’s surface is called terra rosa (‘terra’ meaning soil and ‘rosa’ meaning red).
Question 7 What is regolith?
Answer:
Regolith:-
The layer formed of disintegrated and decomposed rock particles lying on the upper layers of the earth’s surface is called regolith. The soil-forming process starts from the formation of regolith (a slow process).
Question 8 What is solum?
Answer:
Solum:-
The humus-rich layer formed in the process of soil formation lying on the parent rock is called solum. The term ‘soil’ is derived from the Latin word ‘solum’.
Question 9 What are tors?
Answer:
Tors:-
Due to differential weathering, the hard inner layers of the rocks are exposed to the surface when the surrounding soft regolith gets removed. Sometimes the rocks that have broken apart along the points or cracks may tumble down the slope of hills. The remaining upright hard rocks situated on the slopes or in the foothills of gently sloping hills are called tors.
Question 10 What is humus?
Answer:
Humus:-
Dead plants, animal remains, fallen leaves, flowers, fruits, etc. get deposited on the regolith layer as raw organic matter. The organic matter is decomposed by micro-organisms and turned into deep brown or black-colored complex matter.
This complex matter is known as humus. The soil that is rich in humus is fertile in nature. The water-holding capacity of humus-rich soil is greater. The dead remains of plants and animals decompose in rainwater to form humic acid (C187H186 Og NGS,) which accelerates the process of chemical weathering in rocks containing magnesium, feldspar, and sulfur.
Chapter 5 Weathering Multiple Choice Type Questions
Write the correct answer from the given alternatives
1. The first stage of soil formation is—
1. Solum
2. Regolith
3. Batholith
4. Monolith
Answer: 2. Regolith
2. Conical rocks formed due to frost action—
1. Talus or Scree
2. Erg
3. Pediment
4. Bajada
Answer: 1. Talus or Scree
3. Terrace farming is prevalent in—
1. Hilly Areas
2. Deserts
3. Plain Areas
4. Coastal Areas
Answer: 1. Hilly Areas
4. Soil erosion in desert areas takes place—
1. Due To River Action
2. Due To Glacial Action
3. Due To Wind Action
4. Due To Human Beings
Answer: 3. Due To Wind Action
5. Layer of soil formed due to weathering in limestone regions is called—
1. Terra Rosa
2. Talus
3. Blocksped
4. Pediment
Answer: 1. Terra Rosa
6. The process of humus formation is called—
1. Regolith
2. Humification
3. Mineralisation
4. Alluviation
Answer: 2. Humification
7. Which process of weathering leads to the formation of karst landforms?
1. Oxidation
2. Carbonation
3. Hydrolysis
4. Block Disintegration
Answer: 2. Carbonation
8. One of the man-made reasons for soil erosion is—
1. Water Flow
2. Farming
3. Extension Of Root
4. Digging Holes In Soil
Answer: 2. Farming
9. The process of weathering that forms inselbergs is known as—
1. Exfoliation
2. Carbonation
3. Hydrolysis
4. Oxidation
Answer: 1. Exfoliation
10. The layer of disintegrated rock particles that are formed due to weathering is known as—
1. Hardpan
2. Batholith
3. Regolith
4 Lopolith
Answer: 3. Regolith
11. Covering the land with straw, roots of the crops, etc. is a process of soil conservation, which is called—
1. Mulching
2. Terracing
3. Strip Cropping
4. Contour cropping
Answer: 1. Mulching
12. The process that results in the removal of minerals from the upper layer of soil, is—
1. Humification
2. Mineralisation
3. Calcification
4. Eluviation
Answer: 4. Eluviation
13. Forms due to weathering.
1. Mountain
2. Plateau
3. Soil
4. Desert
Answer: 3. Soil
14. Maximum eluviation occurs in—
1. Desert areas
2. Cold areas
3. Rainy areas
4. Temperate areas
Answer: 3. Rainy areas
Chapter 5 Weathering Fill In The Suitable Words
1. The layer of loose and unconsolidated materials lying over the bedrock is called Regolith
2. The most important effect of weathering is the formation of soil
3. Step cultivation should be practiced on hill slopes in order to prevent soil erosion.
4. Deposition of groundwater helps in the weathering of rock beds.
5. The erosion of soil by raindrops is a Natural cause
Chapter 5 Weathering If The Statement Is True, Write TRUE And If False, Write ‘FALSE’ Against The Following
Write The Correct Answer From The Given Alternatives
1. Weathering helps in the storage of groundwater in the rock beds. True
2. The disintegrated layer of the rocks as a result of weathering is called regolith. True
3. Rock particles formed by the disintegration due to ice crystals are called boulders. False
4. Regolith is formed in the last stage of soil formation. False
5. An important influence of weathering is the formation of soil. True
6. Afforestation controls soil erosion. True
7. Weathering helps in increasing soil fertility. True
8. Soil erosion increases due to excessive grazing. True
Chapter 5 Match The Left Column With The Right Column
| Left column | Right column |
| 1. Primary stage for the formation of soil | A.Eluviation |
| 2. Minerals removal process | B.illuviation |
| 3. Mineral dispositional process | C. Mulching |
| 4. Soil conversation process | D.Regolith |
Answer: 1-D,2-A,3-B,4-C
Chapter 5 Weathering Answer In One Or Two Words
Question 1 What is the loose and thin layer of finely fragmented rocks due to weathering known as?
Answer: Regolith.
Question 2 In the process of soil formation, when the minerals present in the regolith are removed from the upper to lower layers, what is this process known as?
Answer: Eluviation.
Question 3 What is the process called by which the humus is formed?
Answer: Humification.
Question 4 When weathering occurs as a natural process, what is it called?
Answer: Geomorphic weathering.
Question 5 What is the process called by which the depth of gullies increases due to erosion?
Answer: Gully erosion.
Question 6 How can the soil on the slopes of mountains be conserved?
Answer: By terrace farming.
Question 7 What is the process of conserving soil by covering it with a layer of organic material called?
Answer: Mulching.
