Ch.3: Exogenetic Movements-1
- Arrowmite
- Jun 26
- 10 min read
Exogenetic Movements-1 | Class 9 | Geography | Chapter 3 | Maharashtra State Board
Learn how external forces shape the Earth's surface through mechanical, chemical, and biological weathering, as well as mass movements like landslides and soil creep. Understand natural processes such as exfoliation, oxidation, and block disintegration with real-world examples and illustrations.
Questions & Answers
1. Answer in brief.
(a) What is mechanical weathering?
Ans.
Mechanical weathering is the breaking down of rocks into smaller pieces without changing their chemical composition. It mainly occurs due to factors like temperature changes, freezing of water (frost), crystal growth, release of pressure, and water absorption. This type of weathering is common in dry, arid climates.
(b) What are the main types of chemical weathering?
Ans.
The main types of chemical weathering are:
Carbonation – When carbon dioxide in rainwater forms carbonic acid and dissolves rocks like limestone.
Oxidation – When oxygen reacts with minerals like iron, forming rust.
Solution – When minerals dissolve in water, weakening the rock.
(c) How does biological weathering occur?
Ans.
Biological weathering occurs due to living organisms. For example:
Roots of plants grow into cracks in rocks and break them.
Burrowing animals like ants and rabbits disturb the soil and rocks.
Organisms like algae, moss, and lichens grow on rocks and cause them to decay.
(d) Distinguish between weathering and mass wasting.
Ans.
Weathering | Mass Wasting |
It is the breaking down of rocks into smaller particles due to natural forces. | It is the movement of weathered material down slopes due to gravity. |
It does not involve movement of material. | It involves movement and deposition of materials. |
Happens in place (in situ). | Happens due to gravity pulling the loose materials downhill. |
Caused by atmospheric factors, water, temperature, plants, etc. | Caused mainly by gravity, often triggered by rain, slope angle, or earthquakes. |
2. Write whether the statements are true or false. Correct the incorrect ones.
(a) Climate affects earthquakes.
Ans.
False
Correction: Climate does not affect earthquakes. Earthquakes are caused by internal movements within the Earth's crust, not by climatic conditions.
(b) Mechanical weathering is less effective in humid climates.
Ans.
True
Explanation: In humid climates, chemical weathering is more effective, while mechanical weathering is dominant in arid (dry) climates.
(c) Mechanical weathering happens on a large scale in dry climates.
Ans.
True
Explanation: Dry climates (like deserts) have high diurnal temperature variation, which leads to mechanical weathering processes such as exfoliation and block disintegration.
(d) The breaking down of rocks into smaller particles is called weathering.
Ans.
True
Explanation: Weathering is defined as the natural process of breaking or weakening of rocks into smaller particles.
(e) Lateritic rocks are formed through exfoliation.
Ans.
False
Correction: Lateritic rocks are formed through chemical weathering in tropical regions with heavy rainfall, not by exfoliation (which is a mechanical weathering process).
4. Identify the type of weathering from the given description.
(a) Some animals live inside the grounds by making burrows.
Ans.
Biological weathering
Explanation: Burrowing animals like rats, rabbits, and insects loosen the soil and rock, causing weathering.
(b) The rock rusts.
Ans.
Chemical weathering (Oxidation)
Explanation: When rocks containing iron react with oxygen and water, rust forms — a process known as oxidation.
(c) Water which has accumulated in the crevices of the rocks freezes. Consequently, the rock breaks.
Ans.
Mechanical weathering (Frost action)
Explanation: Water expands on freezing, causing the rock to crack and break apart. This is a common mechanical weathering process in cold regions.
(d) The pipes supplying water in colder regions break.
Ans.
Mechanical weathering (Frost action)
Explanation: Similar to rock crevices, water inside pipes freezes, expands, and causes the pipes to burst — an example of frost weathering.
(e) Sand formation occurs in deserts.
Ans.
Mechanical weathering (Temperature variation / Exfoliation)
Explanation: In deserts, high day-night temperature differences cause rocks to crack and peel, forming sand through exfoliation and granular disintegration.
2. Write whether the statements are true or false. Correct the incorrect ones.
(a) Climate affects earthquakes.
Ans.
False
Correction: Climate does not affect earthquakes. Earthquakes are caused by internal movements within the Earth's crust, not by climatic conditions.
(b) Mechanical weathering is less effective in humid climates.
Ans.
True
Explanation: In humid climates, chemical weathering is more effective, while mechanical weathering is dominant in arid (dry) climates.
(c) Mechanical weathering happens on a large scale in dry climates.
Ans.
True
Explanation: Dry climates (like deserts) have high diurnal temperature variation, which leads to mechanical weathering processes such as exfoliation and block disintegration.
(d) The breaking down of rocks into smaller particles is called weathering.
Ans.
True
Explanation: Weathering is defined as the natural process of breaking or weakening of rocks into smaller particles.
(e) Lateritic rocks are formed through exfoliation.
Ans.
False
Correction: Lateritic rocks are formed through chemical weathering in tropical regions with heavy rainfall, not by exfoliation (which is a mechanical weathering process).
3. Complete the flowchart below.
Ans.
4. Identify the type of weathering from the given description.
(a) Some animals live inside the grounds by making burrows.
Ans.
Biological weathering
Explanation: Burrowing animals like rats, rabbits, and insects loosen the soil and rock, causing weathering.
(b) The rock rusts.
Ans.
Chemical weathering (Oxidation)
Explanation: When rocks containing iron react with oxygen and water, rust forms — a process known as oxidation.
(c) Water which has accumulated in the crevices of the rocks freezes. Consequently, the rock breaks.
Ans.
Mechanical weathering (Frost action)
Explanation: Water expands on freezing, causing the rock to crack and break apart. This is a common mechanical weathering process in cold regions.
(d) The pipes supplying water in colder regions break.
Ans.
Mechanical weathering (Frost action)
Explanation: Similar to rock crevices, water inside pipes freezes, expands, and causes the pipes to burst — an example of frost weathering.
(e) Sand formation occurs in deserts.
Ans.
Mechanical weathering (Temperature variation / Exfoliation)
Explanation: In deserts, high day-night temperature differences cause rocks to crack and peel, forming sand through exfoliation and granular disintegration.
E X T R A
Class 9 Geography Chapter 3 Exogenetic Movements Part 1 Intext Questions and Answers
1. Complete the statements choosing the correct option from the bracket:
1. .…………………… is formed due to chemical precipitation between water and alkalis.
(a) Limestone
(b) Sandstone
(c) Coal
(d) Iron
Ans.
(a) Limestone
2.…………………… process occurs in rocks which have iron present in them.
(a) Shattering
(b) Oxidation
(c) Carbonation
(d) Granular
Ans.
(b) Oxidation
3. Sometimes the weathered materials do not move downward but sink ‘in situ’. This is called ………………….. .
(a) carbonation
(b) exfoliation
(c) precipitation
(d) slumping
Ans.
(d) slumping
4. periglacial regions along the slopes, small layers of soil accumulate because of the movement of soil. This is called ………………….. .
(a) soil erosion
(b) solifluction
(c) shattering
(d) block disintegration
Ans.
(b) solifluction
5. Biological weathering occurs because of ………………….. .
(a) high temperatures
(b) frost
(c) crystal growth
(d) living organisms
Ans.
(d) living organisms
6. come minerals in the rock get dissolved in the water and undergo chemical weathering. This process is called ………………….. .
(a) solution
(b) carbonation
(c) exfoliation
(d) precipitation
Ans.
(a) solution
7. When dilute carbonic acids reacts with the minerals in the rocks the process is called as ………………….. .
(a) carbonation
(b) exfoliation
(c) precipitation
(d) slumping
Ans.
(a) carbonation
8. When the outer layers of the rock fall apart from the main rock due to difference in temperatures, the process is called ………………….. .
(a) shattering
(b) oxidation
(c) exfoliation
(d) carbonation
Ans.
(c) exfoliation
9. .…………………… is a universal solvent.
(a) Soil
(b) Water
(c) Carbon
(d) Oxygen
Ans.
(b) Water
10. Alkalis in the rock dissolve because of the solution and make them ………………….. .
(a) even
(b) sturdy
(c) brittle
(d) crusty
Ans.
(c) brittle
2. Answer in one sentence each.
1. What are the Exogenetic processes?
Ans.
Exogenetic processes are external processes like weathering, erosion, transportation, and deposition that shape the Earth's surface.
2. Explain the Process of weathering.
Ans.
Weathering is the natural breaking down or weakening of rocks into smaller particles due to atmospheric and biological factors.
3. What is Mechanical Weathering?
Ans.
Mechanical weathering is the physical breakdown of rocks into smaller fragments without changing their chemical composition.
4. What is Chemical Weathering (Salt Weathering)?
Ans.
Chemical weathering, such as salt weathering, occurs when minerals in rocks dissolve or react chemically with water, forming new substances and weakening the rock.
5. What do you mean by Biological Weathering?
Ans.
Biological weathering is the breakdown of rocks due to the actions of living organisms like plant roots, animals, and microbes.
6. What is Slumping?
Ans.
Slumping is a type of mass movement where weathered materials sink or collapse in their original place without moving downhill.
7. What is Solifluction?
Ans.
Solifluction is the slow downward movement of water-saturated soil or rock debris along gentle slopes in periglacial regions.
8. Explain Granular Weathering.
Ans.
Granular weathering occurs when water seeps into porous rocks like sandstone and causes the grains to loosen and fall apart.
9. What is Block Disintegration?
Ans.
Block disintegration is the breaking of rocks into large blocks due to the widening of cracks caused by temperature changes and water.
10. What is Exfoliation?
Ans.
Exfoliation is the peeling off of outer layers of rock due to temperature variation between the surface and inner parts of the rock.
11. What does the term ‘diurnal Range’ mean?
Ans.
Diurnal range refers to the difference between the maximum and minimum temperature within a single day.
12. What is Solution?
Ans.
Solution is a chemical weathering process where minerals in rocks dissolve in water, weakening the rock structure.
13. Name the two types of mass movements.
Ans.
The two types of mass movements are rapid mass movements (e.g., landslides) and slower mass movements (e.g., solifluction).
14. What are the types of Mechanical weathering?
Ans.
The types of mechanical weathering are temperature change, frost action, crystal growth, release of pressure, and water.
15. Types of chemical weathering.
Ans.
Types of chemical weathering include oxidation, solution, and carbonation.
16. Where does Mechanical weathering occur?
Ans.
Mechanical weathering mainly occurs in dry or arid regions like deserts with high temperature variation.
17. Chemical weathering can be seen in which climates?
Ans.
Chemical weathering is commonly seen in humid and tropical climates with heavy rainfall.
3. Write whether the statements are TRUE or FALSE. Correct the incorrect statements.
1. Soil creep is uncommon in areas with dry climates and gentle slopes.
Ans.
False
Correction: Soil creep is common in areas with dry climates and gentle slopes, where mass movement occurs slowly.
2. Shattering is a type of mechanical weathering.
Ans.
True
Explanation: Shattering is caused by temperature changes and is a form of mechanical weathering where rocks break into sharp fragments.
3. Granular weathering occurs in areas of heavy rainfall.
Ans.
True
Explanation: Granular weathering happens when water penetrates porous rocks like sandstone in high rainfall areas, loosening the grains.
4. Distinguish between:
1. Mechanical Weathering and Chemical Weathering.
Ans.
Point of Difference | Mechanical Weathering | Chemical Weathering |
1. Definition | The physical breakdown of rocks without changing their composition. | The breakdown of rocks by chemical reactions that change their composition. |
2. Causes | Caused by temperature changes, frost, pressure release, etc. | Caused by water, oxygen, carbon dioxide, and chemical reactions. |
3. Common in | Dry and arid climates (e.g., deserts). | Humid and tropical climates with high rainfall. |
4. Change in composition | No chemical change in the rock composition. | Involves chemical change of minerals in the rock. |
5. Examples | Exfoliation, frost action, block disintegration. | Oxidation, solution, carbonation. |
5. Give geographical reasons:
1. Oxidation process occurs in heavy rainfall areas.
Ans.
Because oxidation requires moisture, and in areas with heavy rainfall, rocks containing iron come in contact with water and oxygen, leading to the formation of rust (a reddish layer), which weakens the rocks.
2. Chemical weathering occurs in areas of heavy rainfall.
Ans.
Because rainwater acts as a solvent and reacts with minerals in rocks, and the abundance of water in high rainfall areas accelerates chemical reactions like carbonation, solution, and oxidation.
3. Mechanical weathering takes place in the cold regions.
Ans.
Because in cold regions, water in the cracks of rocks freezes and expands, causing the rock to break apart — a process called frost action or frost weathering.
4. Rapid mass movements occur along the steep slopes.
Ans.
Because gravity acts more strongly on steep slopes, and during rainfall, the water-soaked weathered material becomes heavy and moves quickly down the slope, causing landslides and rockfalls.
5. Mechanical weathering is seen in areas where the diurnal range of temperature is high. OR Change in temperature leads to Mechanical weathering.
Ans.
Because the repeated expansion and contraction of minerals due to day-night temperature variation causes stress in the rocks, leading to cracking and peeling, known as exfoliation.
6. Water plays an important role in chemical weathering.
Ans.
Because water dissolves minerals in rocks and forms weak acids like carbonic acid, which chemically react with rock components and lead to their breakdown.
7. Frost leads to mechanical weathering.
Ans.
Because when water trapped in rock cracks freezes, it expands in volume, exerting pressure on the rock and eventually causing it to shatter.
6. Answer in brief:
1. What is a mass movement? What are the types of mass movements?
Ans.
Mass movement is the downward movement of weathered rock material under the influence of gravity.There are two types:
Rapid mass movements (e.g., landslides, rockfalls)
Slower mass movements (e.g., soil creep, solifluction).
2. How does external processes occur?
Ans.
External processes occur due to forces acting on the Earth’s surface such as solar energy, gravity, and kinetic energy of wind, water, and ice, which lead to weathering, erosion, transportation, and deposition.
3. What is exfoliation?
Ans.
Exfoliation is a mechanical weathering process in which the outer layers of a rock peel off due to heating and cooling, especially in areas with high temperature variation.
4. Explain the process of oxidation.
Ans.
Oxidation is a chemical weathering process where iron in rocks reacts with oxygen and water to form rust, creating a reddish layer and weakening the rock, especially in humid regions.
7. Explain:
1. Block Disintegration
Ans.
Block disintegration is a type of mechanical weathering where due to temperature changes and the accumulation of water in joints or cracks, large blocks of rock separate and break off from the main rock body.
2. Carbonation
Ans.
Carbonation is a chemical weathering process where rainwater absorbs carbon dioxide from the atmosphere to form weak carbonic acid, which dissolves rocks like limestone and leads to their breakdown.
Example: Water (H₂O) + Carbon dioxide (CO₂) → Carbonic acid (H₂CO₃)
3. Solution
Ans.
Solution is a type of chemical weathering where minerals in rocks dissolve directly in water, especially in rocks like limestone and salts, weakening the rock structure.
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