Chapter 5 – Weathering | Class 9 School Geography Solution

1. True; Weathering is a slow process.
2. False; Atmospheric carbon dioxide mixes with rain water to form a weak acid called carbonic acid, not oxalic acid.
3. True; Chemical weathering is predominant in humid regions.
4. True; Block disintegration occurs due to temperature variation.
5. True; Degradation and aggradation are integral parts of gradation.

Fill in the blanks with appropriate words

1. ____ slopes aggravate weathering.
2. Erosion involves ____ of weathered materials.
3. Weathering are ot two maintypes _____ weathering and _____ weathering.
4. Hydration is a process in which _____ combines with a mineral.
5. The layer of loose rock material over the primary rock bed produced due to weathering is called _____.

Answer in word or words

Question 4 (a)

What are the rocks or boulders strewn at the foothill region called ?

Answer

The rocks or boulders strewn at the foothill region are called scree.

Question 4 (b)

What type of rock is mostly affected by exfoliation ?

Answer

Granite.

Question 4 (c)

Which process of weathering is responsible for the formation of caves in limestone region ?

Answer

Chemical weathering, specifically carbonation, is responsible for the formation of caves in limestone regions.

Question 4 (d)

Name any one process of weathering that acts due to variation of temperature.

Answer

Block disintegration, also known as thermal expansion and contraction, is a process of weathering that acts due to variation of temperature.

Question 4 (e)

Which process of weathering reduces Felspar to kaolin ?

Answer

Chemical weathering, specifically hydrolysis, reduces feldspar to kaolin.

Correct the following sentences

Question 5 (a)

Checking of soil erosion can be done by deforestation.

Answer

Deforestation can contribute to soil erosion.

Question 5 (b)

Van Mahotsav is celebrated in the first week of August.

Answer

Van Mahotsav is celebrated in the first week of July.

Question 5 (c)

Exfoliation is the process of chemical weathering.

Answer

Exfoliation is a process of physical weathering

Question 5 (d)

Rocks with cracks and joints undergo granular disintegration.

Answer

Rocks with cracks and joints can undergo block disintegration.

Short answer type questions

Question 6 (a)

What is Block disintegration? 

Answer

Block disintegration is a type of physical weathering in which rocks break into large blocks due to repeated cycles of temperature changes. This is a common type of weathering in regions with wide temperature variations, such as desert regions.

Question 6 (b)

What is Exfoliation?

Answer

Exfoliation is a type of physical weathering in which layers of rock peel or flake off due to the release of pressure from overlying rock. This is a common type of weathering in regions with high thermal expansion and contraction, such as mountainous regions.

Question 6 (c)

What is Carbonation?

Answer

Carbonation is a type of chemical weathering in which carbon dioxide reacts with minerals in rocks, forming new compounds such as calcium carbonate. This is a common type of weathering in regions with high concentrations of carbon dioxide in the atmosphere, such as humid regions.

Question 6 (d)

What is Biological weathering?

Answer

Biological weathering is the breakdown of rocks by living organisms such as plants, animals, and microbes. This can occur through physical actions, such as roots penetrating into cracks and crevices in rocks, or through chemical actions, such as the release of acids by lichens and mosses.

Question 6 (e)

What is Oxidation?

Answer

Oxidation is a type of chemical weathering in which oxygen reacts with minerals in rocks, leading to the formation of new compounds such as iron oxide (rust). This is a common type of weathering in regions with high levels of oxygen in the atmosphere, such as humid regions.

Question 6 (g)

What is Soil conservation?

Answer

Soil conservation refers to the practices and methods used to prevent soil erosion and improve soil quality. This can include measures such as planting cover crops, terracing hillsides, and reducing tillage practices.

Question 6 (h)

What are the effects of weathering?

Answer

The effects of weathering can include the breakdown and alteration of minerals in rocks, the formation of new compounds, the shaping of landforms, and the creation of soil. Weathering can also have an impact on human activities, such as by causing soil erosion, contributing to landslides, and affecting the durability of structures made from rocks and minerals.

Answer the following questions

Question 7 (a)

What is weathering? Write the factors that affect weathering.

Answer

Weathering is a process in which huge rocks are broken down or decomposed into fine material. Several forces are responsible for this process. The most common agents of weathering are plants, animals and winds.

The factors that affect weathering are

1. Local Climate: Weathering rates can vary significantly depending on the local climate. In areas with high temperatures and abundant moisture, chemical weathering processes tend to be more active. In contrast, cold and dry climates can lead to physical weathering through processes like freeze-thaw cycles.
2. Mineral Composition: The type of minerals present in a rock can greatly influence its susceptibility to weathering. Some minerals are more resistant to weathering than others. For example, quartz is relatively resistant, while minerals like feldspar are more susceptible to chemical weathering.
3. Structure of Rock: The physical structure of the rock can impact weathering. Rocks with cracks, joints, or other weaknesses are more vulnerable to weathering as water and other agents can penetrate these openings and break down the rock more easily.
4. Biological Activity: The presence of plants, microorganisms, and animals can contribute to weathering. Plant roots can penetrate rocks and create openings for chemical weathering to occur. Burrowing animals can also disrupt rock surfaces.
5. Human Activity: Human activities, such as mining, construction, and pollution, can accelerate weathering processes. Pollution, in particular, can introduce acidic substances into the environment, leading to more rapid chemical weathering.

Question 7 (b)

How is erosion different form weathering ? – Explain.

Answer

Aspect	Erosion	Weathering
Definition	The process of transporting and removing weathered rock and soil particles from their original location by natural agents like wind, water, ice, or gravity.	The process of breaking down rocks and minerals in situ (in place) without the removal of material.
Location	Occurs during the movement of material from one place to another.	Occurs where rocks and minerals are located, without significant movement.
Processes	Physical transportation and removal of weathered material. Common agents include wind, water, ice, and gravity.	Physical or chemical breakdown of rocks and minerals. Includes mechanical (physical) and chemical processes.
Outcome	Results in the relocation and deposition of weathered material in new locations.	Transforms the composition and physical characteristics of rocks over time.
Agents	Natural agents such as rivers, glaciers, wind, ocean waves, and gravity play a significant role in erosion.	Agents include physical forces (e.g., freeze-thaw cycles, abrasion) and chemical reactions (e.g., dissolution, oxidation).
Transported Material	Involves the movement of weathered rock and soil particles, such as sediment, sand, or pebbles.	Does not involve the movement of material; weathered rocks remain in place.
Resulting Landforms	Creates landforms such as river valleys, canyons, deltas, sand dunes, and sediment deposits.	Alters the composition and physical properties of rocks, potentially making them more susceptible to erosion.

Question 7 (c)

Where on earth physical or mechanical weathering predominate? Why ?

Answer

Physical or mechanical weathering predominates in regions with wide temperature variations, such as desert regions, as well as in regions with high thermal expansion and contraction, such as mountainous regions. This is because physical weathering is caused by physical factors such as temperature and pressure, rather than chemical or biological factors.

Question 7 (d)

What is mass wasting ?

Answer

Mass wasting, also known as landslides, is the downslope movement of rock, soil, and other materials under the influence of gravity. This can occur due to factors such as slope angle, soil and rock properties, and the presence of water.

Question 7 (e)

Write three causes of soil erosion.

Answer

The three causes of soil erosion

1. Overgrazing: Grazing livestock can cause soil erosion as their hooves compact the soil and their feeding habits can remove vegetation cover, which is essential for protecting the soil from erosion.
2. Improper land use and management practices: Improper land use and management practices such as removing vegetation cover, intensive plowing, and not using proper soil conservation techniques can all contribute to soil erosion.
3. Water runoff: Heavy rainfall and melting snow can cause water runoff, which can lead to soil erosion. The faster the water moves, the more soil it can carry with it, leading to more erosion.

Question 7 (f)

Write three measures that can be taken for soil conservation.

Answer

The three measures that can be taken for soil conservation are

1. Planting cover crops: Cover crops can help to protect soil from erosion by providing a barrier against wind and water, and also adding organic matter to the soil.
2. Reducing tillage practices: Reducing tillage practices can help to improve soil structure and reduce erosion by leaving plant residues on the soil surface, which helps to protect the soil from erosion.
3. Terracing hillsides: Terracing hillsides can help to slow down the movement of water and soil down steep slopes, reducing erosion. It also allows for more efficient use of water and nutrients in agricultural practices.

Cross-Word

Question 8

Clues

Across-

(1) Onion peeling method of mechanical weathering.

(2) Weathered material that accumulates at the foot of a mountain.

Down-

(1) Process of breaking down of rocks that involves transportation.

(3) The predominant element responsible for weathering in cold regions.

(4) In this process oxygen combines with water to cause chemical weathering.

Answer

Across:

Exfoliation

Talus

Down:

Erosion

Frost

Oxidation

Identify the processes of Mechanical weathering and chemical weathering from the given list and write them in the following chart

Question 9

Long answer type or Essay type questions

Question 10 (a)

What is mechanical weathering? Describe the processes of mechanical weathering, with diagrams.

Answer

Mechanical weathering is the physical breakdown of rocks into smaller pieces without a change in their chemical composition. It is caused by physical forces such as temperature changes, pressure, and the actions of wind, water, and ice. The processes of mechanical weathering include:

1. Exfoliation: This is a process in which the outer layers of a rock are stripped away due to the release of pressure. This can occur in rocks that were once buried deep beneath the earth’s surface and have since been exposed through uplift and erosion. The pressure release causes the outer layers of the rock to expand and flake off, resulting in a rounded rock surface.
   
2. Frost weathering: This is a process in which water seeps into the cracks and crevices in rocks and freezes, expanding and pushing the rock apart. When the ice melts, the water drains away, leaving the rock weakened and susceptible to further weathering. This process is common in regions with freeze-thaw cycles, such as mountainous regions.
   
3. Granular disintegration: This is a process in which rocks break down into smaller pieces due to the actions of wind and water. Over time, wind-blown sand and dust can erode rocks, causing them to break down into smaller pieces. Similarly, water can cause rocks to break down due to the abrasive action of waterborne sediments.
   

Question 10 (b)

What is chemical weathering? Describe the processes of chemical weathering.

Answer

Chemical weathering is the breakdown of rocks and minerals through chemical reactions that alter their composition. It occurs when minerals react with water, oxygen, carbon dioxide, and other substances in the environment. The processes of chemical weathering include:

1. Hydrolysis: This is a process in which water reacts with minerals in rocks, causing them to break down. The water molecules split apart the mineral molecules, creating new compounds such as clay minerals. This process is common in regions with high levels of rainfall and humidity.
2. Oxidation: This is a process in which minerals react with oxygen in the air, causing them to break down and form new compounds. For example, iron in rocks can react with oxygen to form iron oxide (rust). This process is common in regions with high levels of oxygen in the air.
3. Carbonation: This is a process in which carbon dioxide in the atmosphere dissolves in water to form carbonic acid. The carbonic acid then reacts with minerals in rocks, causing them to break down and form new compounds. This process is common in regions with high levels of carbon dioxide in the atmosphere.

Question 10 (c)

How does Biological weathering take place ?

Answer

Biological weathering is the breakdown of rocks and minerals by living organisms such as plants, animals, and microbes. It occurs through physical and chemical actions of living organisms. The processes of biological weathering include:

1. Root wedging: This is a process in which plant roots grow into cracks and crevices in rocks, exerting pressure and causing the rock to break apart. This process is common in regions with high vegetation cover.
2. Biodegradation: This is a process in which microbes break down organic matter in rocks, releasing organic acids that can dissolve minerals in the rock. This process can lead to the formation of new compounds such as iron oxide.
3. Burrowing and boring: This is a process in which animals burrow into rocks and soil, causing physical disruption and exposing the rock to weathering agents. This process is common in regions with high animal activity, such as riverbanks and coastlines.

Question 10 (d)

How is soil formed ? What are the causes of soil erosion?

Answer

Soil is formed over long periods of time by the breakdown of rocks and minerals through weathering, and the accumulation of organic matter. The process of soil formation involves the following factors:

1. Climate: The type and intensity of weathering is largely determined by climate. In regions with high rainfall and humidity, chemical weathering is more prevalent, while in dry regions, physical weathering is more common.
2. Parent material: The type of rock and minerals from which the soil is formed also affects its properties, such as nutrient content and pH.
3. Topography: The slope and shape of the land affect the amount of water and sunlight that reaches the soil, which in turn affects the type of vegetation and organisms that inhabit it.
4. Time: Soil formation is a slow process that takes thousands of years. The longer a soil profile has been developing, the deeper and more complex it becomes.

Soil erosion is the loss of soil due to the actions of natural agents such as water, wind, and ice, and human activities such as agriculture, deforestation, and construction. The causes of soil erosion include:

1. The character of soil: Some soils are more susceptible to erosion than others due to their texture, structure, and nutrient content. For example, sandy soils are more easily eroded than clay soils.
2. The character of land slope: The slope of the land affects the amount of water and sunlight that reaches the soil, which in turn affects the type of vegetation and organisms that inhabit it. Steep slopes are more prone to erosion than gentle slopes.
3. Bare land: When land is left bare without any vegetation cover, it is more susceptible to erosion due to the lack of protection from wind and water. This can occur after land is cleared for agriculture, grazing, or construction.

Question 10 (e)

How can soil be conserved ?

Answer

The soil be conserved by

1. Planting cover crops and trees to reduce erosion.
2. Reducing tillage to maintain soil structure.
3. Implementing erosion control measures such as terracing and contour ploughing.
4. Reducing overgrazing by limiting the number of livestock on grazing lands.
5. Using conservation tillage practices such as no-till and reduced tillage.