Weathering - Questions & Answers
I. Choose the correct option:1. The process of breaking down of rocks but not their removal:
(a) Weathering
(b) Block Disintegration
(c) Oxidation
(d) Mechanical Weathering
Answer: (a) Weathering
2. Which amongst the following is NOT a characteristic of Weathering?
(a) It affects the surface of the earth
(b) It changes hard massive rocks into finer materials
(c) It causes disintegration of soil
(d) It involves disintegration or decay of solid rocks
Answer: (c) It causes disintegration of soil
3. Rock disintegration without any change in the chemical constituents of the rock:
(a) Block Disintegration
(b) Mechanical Weathering
(c) Carbonation
(d) Organic Weathering
Answer: (b) Mechanical Weathering
4. The sudden contraction and expansion peels off the outer rock layer:
(a) Solution
(b) Exfoliation
(c) Hydration
(d) Oxidation
Answer: (b) Exfoliation
5. Which of the following occurs in moist and cold climates?
(a) Mechanical Weathering
(b) Chemical Weathering
(c) Organic Weathering
(d) Physical Weathering
Answer: (b) Chemical Weathering
6. Weathering due to the action of animals, plants and human beings is also known as:
(a) Mechanical Weathering
(b) Chemical Weathering
(c) Organic Weathering
(d) Physical Weathering
Answer: (c) Organic Weathering
7. Expansion of minerals on coming into contact with rainfall:
(a) Oxidation
(b) Solution
(c) Hydration
(d) Carbonation
Answer: (c) Hydration
8. Which of the following is more rapid in desert climates?
(a) Mechanical Weathering
(b) Chemical Weathering
(c) Organic Weathering
(d) Inorganic Weathering
Answer: (a) Mechanical Weathering
9. In which of the following decomposition of rocks takes place with changes in the chemical constituents of rocks?
(a) Inorganic Weathering
(b) Chemical Weathering
(c) Organic Weathering
(d) Physical Weathering
Answer: (b) Chemical Weathering
10. The internal forces operating in the interior of the earth are called ____________.
(a) Exogenic forces
(b) Endogenic forces
(c) Constructive forces
(d) Weathering forces
Answer: (c) Constructive forces
11. Tension and splitting of rocks is known as ____________.
(a) Hydration
(b) Weathering
(c) Block Disintegration
(d) Solution
Answer: (c) Block Disintegration
12. In which of the following climates physical weathering due to frost action is more prevalent?
(a) Equatorial climates
(b) Polar climates
(c) Tropical climates
(d) Temperate climates
Answer: (b) Polar climates
13. Assertion (A): Weathering is described as disintegration or decomposition of a rock in size by natural agents at or near the surface of the earth.
Reason (R): A rock undergoes disintegration or decomposition only by being exposed.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R does not explain A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (a) Both A and R are true and R is the correct explanation of A.
14. Given below are different climate types with the predominant weathering action. Select which one is incorrect.
(A) Equatorial Climate – Chemical weathering
(B) Tropical Climate – Chemical weathering
(C) Dry Climate – Biological weathering
(D) Temperate Climate – Mechanical weathering
(E) Polar Climate – Mechanical weathering
(a) B (b) C (c) D (d) E
Answer: (b) C
15. Melting of ice in polar regions has increased which type of weathering?
(a) Mechanical
(b) Chemical
(c) Biological
(d) All of them
Answer: (b) Chemical
II. Short Answer Questions
1. What is weathering?
Answer: Weathering is the process of breaking down of rocks but not its removal. It is described as the disintegration or decomposition of a rock in size by natural agents at or near the surface of the earth due to exposure to weather conditions.
2. Name three types of weathering.
Answer: The three types of weathering are Physical (or Mechanical) Weathering, Chemical Weathering, and Biological (or Organic) Weathering.
3. Give two differences between physical and chemical weathering.
Answer:
1. Physical weathering involves the disintegration of rocks without any change in their chemical constituents, whereas chemical weathering involves the decomposition of rocks with changes in their chemical constituents.
2. Factors such as temperature, moisture, frost action, and wind cause physical weathering, while agents like water, oxygen, carbon, and various organic acids cause chemical weathering.
4. What is known as exfoliation?
Answer: Sudden temperature changes cause fissures into which water penetrates, stimulating chemical weathering. Since most rocks are poor conductors of heat, sudden contraction and expansion peels off the outer layer of the rock. This peeling off is known as exfoliation.
5. Name the four processes involved in chemical weathering.
Answer: The four main processes involved in chemical weathering are Oxidation, Carbonation, Hydration, and Solution.
6. What is known as oxidation? What effect does it have on the colour of rocks?
Answer: Oxidation is the reaction of minerals in rocks to atmospheric oxygen (often contained in rainwater). When iron compounds in rocks come in contact with oxygen, they start rusting or crumbling. This process changes the colour of the rock to red, yellow, or brown.
III. Distinguish between each of the following:
1. Block Disintegration and Exfoliation.
Answer: Block Disintegration: It occurs when a sudden rise and fall of temperature causes repeated expansion and contraction of rocks. This leads to tension and the splitting of rocks into blocks.
Exfoliation: It occurs when sudden temperature changes cause only the outer layer of rocks (which are poor conductors of heat) to expand and contract, leading the outer layer to peel off like an onion.
2. Carbonation and Solution.
Answer: Carbonation: It is a chemical reaction where rainwater absorbs carbon dioxide to produce a weak acidic effect, dissolving calcareous rocks (like gypsum, marble, and limestone) by converting calcium carbonate into soluble calcium bicarbonate.
Solution: It is the direct process in which minerals in the rocks dissolve in water. Rock minerals such as salts are highly soluble in water and disintegrate directly upon contact with rain or water.
IV. Structured Questions
1. (a) Define weathering and describe the chief characteristics of weathering.
Answer: Definition: Weathering is the basic process of breaking down rocks but not its removal, functioning as a static process of rock disintegration and decay by natural agents.
Chief Characteristics:
1. It involves disintegration or decay of solid rocks.
2. It depends on climatic elements and rock characteristics (chemical composition, hardness, texture, permeability).
3. It affects the surface of the earth.
4. It causes the formation of soil.
5. It involves several processes to cause the disintegration of rocks.
6. It changes hard massive rocks into finer materials.
7. It prepares rock materials for transportation by agents of gradation.
1. (b) Distinguish between physical and chemical weathering.
Answer:
- Disintegration vs Decomposition: Physical weathering breaks rocks without changing chemical constituents. Chemical weathering decomposes rocks by changing their chemical makeup.
- Agents: Physical weathering is driven by temperature changes, moisture, frost action, and wind. Chemical weathering is driven by water, oxygen, carbon, and organic acids.
- Results: Physical weathering increases the surface area making rocks vulnerable to chemical weathering. Chemical weathering results in new minerals being formed or existing ones dissolving, leading to softer, weaker rocks.
1. (c) Give a geographical reason for each of the following:
(i) Physical weathering is also called mechanical weathering.
(ii) Physical weathering is more rapid in desert climates.
(iii) Chemical weathering occurs in moist and cold climates.
Answer:
(i) It is called mechanical weathering because the disintegration of rocks happens through purely mechanical/physical forces (like pressure, expansion, and contraction) without altering the chemical chemistry of the rock.
(ii) Desert climates experience an extreme diurnal (daily) range of temperature. The sudden rise in temperature during the day and sharp fall at night causes rapid expansion and contraction, accelerating processes like block and granular disintegration.
(iii) Recent studies show that melting water in polar/cold regions contains more carbonic acid because carbon dioxide is more soluble at low temperatures than at high temperatures. Therefore, moist conditions combined with higher carbon dioxide solubility allow chemical weathering to occur even in cold climates.
1. (d) Draw a well labelled diagram to show the process of physical weathering.
Answer: [Teacher's Note: Students should draw a diagram illustrating the three types of mechanical weathering as outlined in the chapter text: (a) Block disintegration showing rocks splitting into large cubes/blocks, (b) Granular disintegration showing rocks crumbling into small grainy fragments, and (c) Exfoliation showing the outer layer of a rock peeling off.]
2. (a) Describe chemical weathering mentioning the processes involved in it.
Answer: Chemical weathering is the decay or alteration of rock minerals by agents such as water, oxygen, carbon, or organic acids. This process transforms original minerals into different chemical combinations. The four main processes involved are:
1. Oxidation: Reaction of atmospheric oxygen with rock minerals, causing iron compounds to rust.
2. Carbonation: Carbon dioxide in rainwater produces a weak acid that dissolves calcareous rocks like limestone.
3. Hydration: Rock minerals absorb water, expand, become heavy, and disintegrate (e.g., feldspar converts to kaolin).
4. Solution: Direct dissolving of rock minerals (like rock-salt) into water.
2. (b) What is biological weathering? State the main agents of biological weathering.
Answer: Biological weathering is the disintegration and decomposition of rocks caused by living organisms. It involves both physical breakdown and chemical decay. Its main agents are humans, plants, animals, and insects.
2. (c) Give a geographical reason for each of the following:
(i) Biological weathering is also known as organic weathering.
(ii) Vegetation prevents disintegration of rocks.
(iii) Chemical and biological weathering is negligible in polar climates.
Answer:
(i) It is known as organic weathering because all biological matter is made up of organic compounds. When organisms die and decay, they release organic acids which react chemically with minerals in the rocks.
(ii) Vegetation prevents rock disintegration because extensive root systems bind the surface soil layer together securely, preventing the underlying rocks from being exposed to direct elements of physical and chemical weathering.
(iii) In polar climates, biological weathering is negligible because the extreme cold does not support abundant plant or animal life. Historically, chemical weathering was also considered negligible because low temperatures restrict chemical reactions, making frost action (physical weathering) overwhelmingly dominant.
2. (d) Describe the chief characteristics of weathering in different climates.
Answer:
- Equatorial climates: Due to constantly high humidity and temperature, chemical weathering is most active.
- Tropical climates: Marked by distinct wet and dry seasons. High evaporation in dry seasons and precipitation of iron/aluminum oxides in wet seasons promotes the formation of laterite soils.
- Dry climates or deserts: Mechanical weathering is completely dominant due to the high diurnal range of temperature.
- Mid-latitudes or Temperate Climates: Frost action is the most powerful weathering agent. Chemical weathering (solution) operates on a massive scale in limestone areas.
- Polar climates: Physical weathering due to frost action is most prevalent. However, higher solubility of carbon dioxide in cold meltwater indicates that some chemical weathering does occur.
V. Thinking Skills
1. Weathering is a natural process, but human activities can speed it up. Do you agree with this statement? Give reasons to support your answer.
Answer: Yes, I agree with this statement. Humans are active agents of weathering. Activities such as large-scale mining, excavations, construction of roads and buildings, and agriculture physically break and crush solid rocks. Additionally, humans dump chemicals and industrial wastes underground, which provides organic and inorganic acids that rapidly accelerate the chemical decomposition of rocks.
2. It is weathering that is responsible for bio-diversity on the earth. Justify this statement giving examples.
Answer: Weathering breaks down hard, massive rocks into finer and finer materials, which is the foundational step in the formation of soil. Soil is absolutely essential for the growth of plants (flora). In turn, these plants provide habitat and food for animals and insects (fauna). By producing the soil needed to sustain the base of the food chain, weathering is directly responsible for making bio-diversity on Earth possible.
3. You went to the Rann of Kutch for the Rann Utsav, which is celebrated annually in Gujarat. On your way, which kind of weathering did you notice? What could be its cause/causes?
Answer: In a dry and highly saline region like the Rann of Kutch, one would primarily notice Mechanical Weathering (such as block and granular disintegration) and Chemical Weathering (specifically, Solution). The causes include the severe diurnal (day-to-night) range of temperature typical of arid landscapes, which forces rocks to rapidly expand and contract. Additionally, the region is rich in soluble rock-salts, which rapidly dissolve upon coming into contact with whatever limited moisture or rainwater is available.
VI. Practical Work
1. Collect rock samples. Perform experiments to study physical and chemical weathering. Write down your report.
Answer: [Teacher's Note: For this practical exercise, collect varied rock pieces. You can test chemical weathering (carbonation) by placing a piece of limestone or chalk in vinegar and observing it fizz and dissolve. To study physical weathering, observe how porous rocks left in a freezer with water might crack due to frost action. Document your methodology and findings in a report.]
2. Observe the process of weathering active in your surroundings. State its chief characteristics. Draw, paint or take pictures.
Answer: [Teacher's Note: Look for local examples such as tree roots widening cracks in pavements (biological weathering), the outer layers of boulders peeling off (exfoliation), or iron gates and iron-rich stones turning reddish-brown (oxidation). The chief characteristic you should document is that the solid rocks or materials are decaying or breaking apart in place (in situ) without being transported. Capture these observations through photographs or sketches.]