Selina Concise Solutions for ICSE Class 7 Geography Chapter 8 Weathering and Soil

Discuss:

Question : From encycopaedias and the Internet, find out the different types of soil found in India. Discuss the importance of these soils for crops cultivated in our country. You should form groups in class for this activity.
Answer:
Soils of India: Six Different Types of Soils Found in India are as follows:
Soil is our prime natural and economic resource. Soils in India differ in composition and structure.
1. Alluvial Soils : These are formed by the deposition of sediments by rivers. They are rich in humus and very fertile. They are found in Great Northern plain, lower valleys of Narmada and Tapti and Northern Gujarat. These soils are renewed every year.
2. Black Soils : These soils are made up of volcanic rocks and lava-flow. It is concentrated over Deccan Lava Tract which includes parts of Maharashtra, Chhattisgarh, Madhya Pradesh, Gujarat, Andhra Pradesh and Tamil Nadu. It consists of Lime, Iron, Magnesium and also Potash but lacks in Phosphorus, Nitrogen and Organic matter.
3. Red Soils : These are derived from weathering of ancient metamorphic rocks of Deccan Plateau. Its redness is due to iron composition. When iron content is lower it is yellow or brown. They cover almost the whole of Tamil Nadu, Andhra Pradesh, Chhattisgarh, Karnataka, Maharashtra and parts of Orissa.
4. Laterite Soils : These are formed due to in-tense leaching and are well developed on the sum-mits of hills and uplands. They are commonly found in Kerala, Tamil Nadu, Maharashtra, Chhattisgarh and hilly areas of Orissa and Assam.
5. Mountain Soils : These are formed as a result of the accumulation of organic matter derived from forest growth. They are found in Himalayan region and vary in different regions according to altitude. Tea is grown in those areas which receive sufficient rainfall.
6. Desert Soils : In the desert regions of Rajasthan, soils are not well developed. As evaporation is in excess of rainfall, the soil has a high salt content and saline layer forms a hard crust. These soils are gen-erally sandy and deficient in organic matter.
India's diverse geography leads to a variety of soil types that support different agricultural needs across the country. Understanding these soil properties helps farmers choose the right crops to ensure a healthy and plentiful harvest.
Teacher's Tip: To remember Alluvial soil, think of "Alluvium" which means river-deposited material found in the plains.
Exam Tip: Always mention the specific chemical composition (like iron in red soil) when describing the characteristics of Indian soils.

THINK AND ANSWER:

Question : Soil formation is an important benefit of weathering. How is it important for mankind ?
Answer:
Soil formation is an important for mankindas :
1. A habitat for several plants and animals
2. A storage bank for water and nutrients
3. Foundation of the world’s food chain
4. Provides an anchor for plants
Soil provides the essential base for all terrestrial life by supporting plant growth and providing home to billions of organisms. It acts as a natural filter and storage system for our most precious water resources.
Teacher's Tip: Visualize soil as the "skin" of the Earth that protects and feeds everything living on it.
Exam Tip: Use terms like "foundation of the food chain" to emphasize the critical role soil plays in human survival.

VALUES AND LIFE SKILLS:

Question : People have used various farming methods to increase food production. However, in the process, they have stripped soil of nutrients, leading to its degradation. Can you suggest some ways by which we can reduce soil degradation ?
Answer:
We can reduce soil degradation by Contour tilling, terrace farming, strip cropping, contour bunding, afforestation, crop rotation, fallowing and controlled grazing.
These sustainable practices help maintain the structure and chemical balance of the soil while preventing erosion. By implementing these methods, we can protect the land from becoming barren due to over-farming.
Teacher's Tip: Think of "afforestation" as giving the Earth a protective coat of trees to hold the soil in place.
Exam Tip: When listing conservation methods, provide at least four distinct examples to show a broad understanding of the topic.

EXERCISES

A. Match the column

Answer:
1. Granular disintegration - (ii) is common in deserts
2. Oxidation - (v) results in the rusting of iron
3. Carbonation - (iv) mainly affects limestone regions
4. Hydration - (i) causes feldspar to become a powdery mass
5. Solution - (iii) is the simplest form of chemical weathering
Matching different types of weathering with their effects helps identify the chemical and physical changes occurring in various environments. This understanding allows us to predict how different landscapes will change over time.
Teacher's Tip: Connect "Oxidation" with "rust" and "Carbonation" with "limestone" to remember these chemical processes easily.
Exam Tip: In matching questions, double-check that every item in column A has a unique and logical partner in column B.

B. Distinguish between each of the following pairs:

Question 1: Degradation and aggradation
Answer:
Degradation : The process by which rock materials from the earth’s surface are removed resulting in general lowering of land surfaces.
Aggradation : The process by which the rock material removed from the earth’s surface and then deposited in depressions such as valleys, lakes and sea beds. The depression fills
While degradation wears down the high parts of our landscape, aggradation builds up the low-lying areas. Together, these two processes work to level out the Earth's surface over millions of years.
Teacher's Tip: Think of "De-" as "down" (wearing down) and "Ag-" as "adding" (building up).
Exam Tip: Use the word "deposition" when defining aggradation to accurately describe the build-up process.

Question 2: Weathering and erosion
Answer:
Weathering : It is the process by which rocks on the land surface break down or crumble because of the action of the elements of weather such as rain, frost and temperature changes.
Erosion : It is the process by which the weathered materials are transported elsewhere by agents such as running water, moving ice waves, and winds.
Weathering is the "breaking" of the rock in its original place, whereas erosion is the "moving" of those broken pieces to a new location. Without weathering, erosion would have much less loose material to transport.
Teacher's Tip: Weathering is static (staying in place), while erosion is dynamic (involving movement).
Exam Tip: Be sure to list the agents of erosion, such as wind and water, to provide a complete answer.

Question 3: Granular disintegration and exfoliation
Answer:
Granular disintegration : A form of weathering where the grains of a rock become loosened and fall out to leave a pitted and uneven surface.
Exfoliation : When the surface layers of rounded and boulders gradually peel off in layers due to expansion of the outer layer during the day and the contraction of the same layer during night, the process is called exfoliation.
Granular disintegration happens at a microscopic level as individual crystals pull apart, while exfoliation involves large sheets of rock peeling away like an onion. Both are caused by temperature changes that make different parts of the rock expand at different rates.
Teacher's Tip: Think of exfoliation as a rock "shedding its skin" in large layers.
Exam Tip: Mention the role of "expansion and contraction" when explaining the cause of exfoliation.

Question 4: Hydration and solution
Answer:
Hydration : This occurs when water itself chemically combines with some minerals present in rocks. Thus, crystalline minerals, such as feldspar and potash, absorb water and become a powdery mass due to the process of hydration, resulting in their erosion.
Solution : This is the simplest form of chemical weathering by which some minerals dissolve in water when rainwater falls on rocks or when river water flows over rocks. The soluble minerals dissolve and are removed, . resulting in the breakup of the rocks.
Hydration involves a chemical change where water enters the mineral structure, whereas solution is simply minerals disappearing into the water like sugar. Both processes weaken the rock and lead to its eventual breakdown.
Teacher's Tip: In solution, minerals "vanish" into the water, but in hydration, they "swell up" and turn to powder.
Exam Tip: Identify that these are both forms of "chemical weathering" to categorize them correctly.

Question 5: Soil erosion and soil conservation
Answer:
Soil erosion : It refers to the washing away or removal of the layers of soil by various agents like running water and wind.
Soil conservation : It refers to the protection of soil against erosion and exhaustion because of deforestation, excessive grazing, running
Soil erosion is a destructive process that removes the fertile topsoil necessary for farming. Soil conservation includes all the active steps humans take to stop this loss and keep the land healthy.
Teacher's Tip: Conservation is the "shield" we build to protect the soil from the "attack" of erosion.
Exam Tip: Mention human activities like "deforestation" when describing what we are conserving the soil against.

C. Give geographical reasons:

Question 1: Temperature changes result in physical weathering.
Answer:
Temperature changes result in expansion and contraction of rocks during day and night resulting in degradation of rocks. In the temperate latitudes the frost shatters the rocks.
Constant heating and cooling causes internal stress in the rock, leading it to crack and break apart physically without changing its chemistry. This is particularly effective in environments with extreme day and night temperature differences.
Teacher's Tip: Think of a glass cracking if you pour boiling water into it; rocks crack similarly due to heat stress.
Exam Tip: Use the specific terms "expansion" and "contraction" to explain the mechanism behind the weathering.

Question 2: Gases in the atmosphere affect weathering.
Answer:
The minerals contained in the rocks react with the gases and moisture in the air like oxygen reacts with iron and causes the rocks to rust and get eroded.
Atmospheric gases like O₂ and O₂ combine with rainwater to create chemical reactions that eat away at rock minerals. This process turns hard rock into soft, easily eroded material over time.
Teacher's Tip: Oxygen is the gas that makes iron turn into crumbly red rust.
Exam Tip: Mention "moisture" as a necessary ingredient for these atmospheric gases to react with rocks.

Question 3: Human activities affect weathering.
Answer:
Human activities like mining, quarrying deforestation, tunnelling, road construction and farming affect the weathering.
By breaking deep rocks and exposing them to the air, humans accelerate the natural process of weathering. Activities like road building physically crush rocks, making them more vulnerable to chemical decay.
Teacher's Tip: We are like "artificial weathering agents" because we break rocks much faster than nature does.
Exam Tip: List at least three specific human activities, like "mining" or "quarrying," to provide a strong answer.

Question 4: Soil is a very important resource.
Answer:
Soil is an important resource as human beings depend on it for their basic needs of food, shelter and clothing. It takes thousands of years for a thin layer of soil to form.
Almost everything we use, from the cotton in our clothes to the wood in our homes, starts with the nutrients provided by soil. Because it takes so long to form, we must treat it as a non-renewable resource that needs protection.
Teacher's Tip: No soil means no plants, and no plants means no life on land.
Exam Tip: Emphasize the "time factor" (thousands of years) to explain why soil is a precious and limited resource.

Question 5: There is a need for soil conservation.
Answer:
Soil should be conserved as humans depend directly or indirectly on soil for their basic needs of food, shelter and clothing.
Without active conservation, fertile topsoil can be lost forever, making it impossible to grow food for our growing population. Conservation ensures that the environment remains stable and the ecosystem stays in balance.
Teacher's Tip: Conservation is "earth-insurance" for the future of human food security.
Exam Tip: Link the "need" for conservation back to the human dependency on soil for "food, shelter and clothing."

D. Answer the following questions in brief:

Question 1: Name any four agents of erosion.
Answer:
Soil erosion also refers to the loss of fertility of soil, which makes the soil infertile and exhausted. Cutting down of trees and forests, overgrazing by animals, floods, and improper farming practices are some of the main causes of soil erosion.
Natural agents that move soil include running water, wind, glaciers, and waves. Human actions like cutting trees also leave the soil vulnerable to these natural forces.
Teacher's Tip: Remember the big four movers: Water, Wind, Ice, and Gravity.
Exam Tip: Be careful to distinguish between the "agents" (the movers) and the "causes" (the human activities).

Question 2: List any three factors that affect weathering.
Answer:
Factors that affect weathering are :
1. Local climate
2. Mineral composition
3. Structure of rock
4. Human activities
5. Amount of exposed or bare rocks surface, and human activities.
Weathering happens differently depending on if a rock is in a wet rainforest or a dry desert. Harder minerals and solid rock structures also resist breaking down longer than soft or cracked rocks.
Teacher's Tip: Think of how climate (weather) is the most obvious factor in "weather-ing."
Exam Tip: Clearly number your factors to make the list easy for the examiner to read.

Question 3: In which regions of the world is ‘frost action’ the common form of weathering?
Answer:
In temperate latitudes frost action is common form of weathering.
This happens because water enters rock cracks and freezes, expanding by 9% and exerting enough pressure to shatter the rock. These regions experience the necessary freeze-thaw cycles that drive this physical process.
Teacher's Tip: Frost action is like a rock "wedging" its way apart using ice.
Exam Tip: Specifically mention "temperate latitudes" or "mountainous regions" to pinpoint the correct location.

Question 4: Which is the most important effect of weathering?
Answer:
Landslides and soil erosion are two major effects of weathering.
Weathering turns solid mountain faces into loose rubble that can suddenly slide down as a landslide. It also creates the fine particles that are eventually carried away as eroded soil.
Teacher's Tip: Weathering "prepares" the rock for its final movement via landslides or erosion.
Exam Tip: List both landslides and erosion to show you understand how weathering impacts both steep and flat land.

Question 5: What are the components of topsoil?
Answer:
The topmost layer is the topsoil (Layer D) which consists of clay, silt, sand and humus.
Topsoil is the most fertile layer because it contains "humus," which is decayed organic matter. The mixture of clay, silt, and sand determines how well the soil can hold water and air for plants.
Teacher's Tip: Think of topsoil as a "super-smoothie" of minerals and decayed plants.
Exam Tip: Make sure to include "humus" as it is the most vital component for fertility.

Question 6: Name the various methods of conserving soil.
Answer:
The various methods of conserving soil are :
Contour tilling, terrace farming, strip cropping, contour bunding, afforestation, crop rotation, fallowing and controlled grazing.
Each of these techniques is designed to either hold the soil in place or maintain its nutrient levels. Using a combination of these methods is the most effective way to protect farmland.
Teacher's Tip: These methods act as "earth-saving tools" that every farmer should know.
Exam Tip: Provide a diverse list including both structural methods (terracing) and biological ones (afforestation).

Question 7: Distinguish between contour tilling and contour bunding.
Answer:
Contour Tilling - In this method the farmer tills or ploughs the fields along the contours of the land rather than tilling up and down the slope. Contour tilling is practised in hilly areas rather than the plains. It prevents the soil from being washed away by water or by surface run-off as the contour acts like a bund. The contour also facilitates the percolation of water into the soil.
Contour Bunding - Soil is conserved by making bunds or walls or embankments made of mud along contour lines to prevent water from draining out of the cultivated field, thereby preventing erosion.
Tilling is about the "direction" of the ploughing, while bunding is about "building" physical walls. Both use the natural shape (contours) of the hill to trap water and soil before they can escape.
Teacher's Tip: Tilling is the "active work," while bunding is the "protective wall."
Exam Tip: Mention "hilly areas" when describing contour tilling to provide geographical context.

Question 8: What do you understand by controlled grazing ?
Answer:
Controlled grazing is a simple method of soil conservation, It is to restrict the grazing of cattle, sheep and goats on grasslands and within forests. When cattle graze on fields, grass and smaller plants get tom from their roots, leaving the soil loose and exposed to wind and water erosion. Moreover, the pressure of the animals hooves on the soil makes it lose its cohesion and structure, exposing it to the forces of wind and water. Land meant for grazing of cattle should be specially selected and fenced off.
By rotating animals between different fields, the grass has time to grow back and hold the soil together. This prevents the ground from being trampled into dust by too many hooves at once.
Teacher's Tip: Controlled grazing gives the land a "rest" so the grass can protect the soil again.
Exam Tip: Mention how animal "hooves" damage the soil structure to add scientific depth to your answer.

E. Answer the following questions in one or two paragraphs:

Question 1: What is gradation? Describe the two processes involved in gradation.
Answer:
Gradation is the process of levelling the land by means of moving agents like rivers, or wearing away and lowlands are raised by adding the eroded material by the process of deposition. This is because there is constant earth movement which raises mountains and winds, seas and waves. The highlands are made low by erosion and this process is called degradation and materials are deposited elsewhere in depressions like valleys, lakes, etc. and these lowlands are raised by the process called aggradation.
Gradation is the Earth's way of trying to make everything flat by moving material from high spots to low spots. It is a constant battle between forces that lift the land up and forces that wear it down.
Teacher's Tip: Imagine gradation as a giant sandpaper that smooths out the Earth's surface over time.
Exam Tip: Be very clear in defining both "degradation" (wearing down) and "aggradation" (filling up).

Question 2: Describe the process that leads to exfoliation.
Answer:
When the surface layers of rounded rocks and boulders gradually peel off in layers is called exfoliation. This occurs due to expansion of the outer layer during the day and the contraction of the same layer during the night, repeatedly over a period of time.
Since rocks are poor conductors of heat, only the outer shell gets hot and expands, while the inside stays cool. This creates a "shell" that eventually snaps and flakes off, much like the layers of an onion.
Teacher's Tip: Think of "onion skin weathering" to remember the look of exfoliation.
Exam Tip: Use the term "mechanical weathering" to describe the category that exfoliation falls into.

Question 3: Discuss the role of water in the process of chemical weathering.
Answer:
Water plays an important role in chemical weathering. The carbon dioxide in atmosphere dissolves in rainwater and form carbonic acid and reacts with minerals in the rocks. The soluble minerals dissolve in water such as feedspar and potash absorb water and become a powdery mass. Similarily soluble minerals dissolve and are removed, resulting in the breakup of the rocks. Rock salt, gypsum, and silica are examples of minerals that are highly soluble and when rainfall falls they decompose.
Water acts as a "universal solvent" that carries acids and reactive chemicals deep into the rock. Without water, most chemical reactions that break down rock minerals simply wouldn't happen.
Teacher's Tip: Water is the "delivery truck" that brings chemicals into the rock to dissolve it.
Exam Tip: Mention the formation of "H₂CO₃" (carbonic acid) when explaining the chemical role of rainwater.

Question 4: How do animals and plants assist in weathering?
Answer:
The decaying remains of dead plants in soil tend to form organic acid which when dissolved in water cause chemical weathering. Ants, earthworms and burrowing animals such as rats and rabbits loosen soil and make tunnels causing weathering.
Living things act as "biological weathering agents" by physically breaking rocks with roots or burrowing. Even after death, they continue to break down rocks through the chemical acids released during decay.
Teacher's Tip: Even a tiny ant or a slow tree root can eventually break a massive boulder.
Exam Tip: Distinguish between "biological physical" (burrowing) and "biological chemical" (organic acids) weathering.

Question 5: What is meant by the terms ‘soil erosion’ and ‘soil conservation’?
Answer:
Soil erosion refers to washing away or removal of the layer of soil by various agents like running water and wind. Sheet erosion and gully erosion are the two most common ways by which soil gets eroded. When there is heavy rainfall, the top layer of soil over large areas gets washed away. This is known as sheet erosion. When rainwater in region flows down the slopes making deep and narrow furrows, it is called gully erosion. Soil erosion also refers to the loss of fertility of soil, which makes the soil infertile and exhausted. Cutting down the trees and forests, overgrazing by animals, floods, and improper farming practices are some of the main causes of soil erosion.
Soil conservation is the protecting of soil against erosion and exhaustion by planting trees, shrubs and grass on hill slopes. Soil can be conserved by controlling grazing of cattle and use of proper farming methods such as the levelling of fields, terracing of hill slopes, construction of mud walls or bunds and ploughing fields in circles.
Erosion is the natural or human-caused loss of our valuable topsoil, which destroys land productivity. Conservation is the scientific effort to stop this loss using engineered structures and smart planting.
Teacher's Tip: Sheet erosion is like losing a whole "sheet" of paper; gully erosion is like carving deep "scars" in the ground.
Exam Tip: Differentiate between "sheet" and "gully" erosion as they are frequently asked as short notes.

Question 6: Why is soil conservation important ? Give three reasons.
Answer:
Soil conservation is very important because soil consists of mineral particles, moisture, living organisms like bacteria and earthworms, and decayed organic matter. It is one of the most important resources as human beings-depend on it, both directly and indirectly, for their basic needs of food, shelter, and clothing. It takes thousands of years for even a thin layer of soil to form.
Conserving soil ensures that we can continue to feed a growing human population for many generations. It also protects the billions of micro-organisms that live in the soil and keep our ecosystem healthy.
Teacher's Tip: Soil is a "life-support system" that we simply cannot live without.
Exam Tip: Focus on the "thousands of years" it takes to form soil to emphasize why its conservation is so urgent.

Question 7: Explain any two methods of soil conservation briefly.
Answer:
1. Contour Tilling - In this method the farmer tills or ploughs the fields along the contours of the land rather than tilling up and down the slope. Contour tilling is practised in hilly areas rather than the plains. It prevents the soil from being washed away by water or by surface run-off as the contour acts like a bund. The contour also facilitates the percolation of water into the soil.
2. Terrace Farming - Terrace farming involves making terraces or steps on a hill or mountain by cutting into the side of the hill or mountain. Since the land is made flat, it reduces surface run-off, thereby preventing erosion. It also facilitates the absorption of water into the soil. Terrace cultivation is common on mountain slopes all over the world.
3. Contour Bunding - Soil is conserved by making bunds or walls or embankments made of mud along contour lines to prevent water from draining out of the cultivated field, thereby preventing erosion.
Terrace farming physically creates flat land out of steep hills, making it safe for farming without losing soil. Contour methods use the natural curves of the Earth to trap and save every drop of water and inch of soil.
Teacher's Tip: Terrace farming looks like a giant "staircase" carved into a mountain side.
Exam Tip: When explaining terrace farming, mention that it specifically reduces "surface run-off" to stop erosion.

F. Make a chart for your classroom showing the causes of different types of weathering.
Answer:
Do it yourself.
A good chart should include physical, chemical, and biological weathering with pictures of each. Showing the "cause" (like frost or acid) next to the "effect" (like shattered rock) makes it much easier to learn.
Teacher's Tip: Use bright colors to separate the three categories of weathering on your chart.
Exam Tip: Practicing this chart is a great way to memorize all the sub-types of weathering for your test.

G. Form pairs or groups of three or four students and discuss, with examples, how we depend directly and indirectly on soil.
Answer:
Do it Yourself with the help of teacher.
Discussing this helps us realize that even things like milk (indirectly from grass) and houses (directly from clay bricks) come from the soil. It makes us more aware of why we should care for our environment.
Teacher's Tip: Try to list 10 items in your room and trace each one back to the soil!
Exam Tip: Use a real-life example like "cotton for clothing" to illustrate direct dependency in your answers.

H. Picture Study:
Question 1: What is this farming method called ?
Answer:
Terrace farming.
This method transforms steep, useless slopes into productive agricultural land by creating flat steps. It is a traditional and highly effective way to manage farming in mountainous regions.
Teacher's Tip: Think of "Terrace" like a "T" for "Tiered" or layered steps.
Exam Tip: Identifying this method from a picture is a common exam question; look for the "step" appearance on a hill.

Question 2: Mention any two other methods that help in controlling soil erosion.
Answer:
Construction of mud walls, ploughing fields in circles, levelling of fields can also prevent soil erosion.
Planting shelterbelts of trees acts as a windbreak, while cover cropping ensures the soil is never left naked to the rain. These varied methods work together to keep the Earth's fertile skin safe.
Teacher's Tip: "Cover crops" are like a living blanket that keeps the soil warm and protected.
Exam Tip: Mentioning "afforestation" is usually the easiest and most important second method to remember.