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Chapter 9

Weathering

Class 9 - Total Geography Morning Star


Short Answer Questions

Question 1

What is weathering?

Answer

Weathering is the process of breaking down of rocks but not its removal. It is described as disintegration or decomposition of a rock in size by natural agents at or near the surface of the earth.

Question 2

Name three types of weathering.

Answer

Three types of weathering are-

  1. Physical weathering
  2. Chemical weathering
  3. Biological weathering

Question 3

Give two differences between physical and chemical weathering.

Answer

Physical weatheringChemical weathering
It involves rock disintegration without any change in the chemical constituents of the rock.In this weathering, some or all of the minerals in the rocks suffer decay or alteration and transform into different chemical combinations.
Agents of physical weathering include temperature changes, moisture, frost action and wind.Agents of chemical weathering include water, oxygen, carbon or various organic acids.

Question 4

What is known as exfoliation? Name the processes involved in it.

Answer

Sudden temperature changes may cause fissures into which water penetrates which in turn stimulates chemical weathering. Most rocks are not good conductors of heat. The sudden contraction and expansion peels off the outer layer known as exfoliation.

The processes involved are formation of fissures, chemical weathering, contraction and expansion of rocks.

Question 5

Name the four processes involved in chemical weathering.

Answer

The four processes involved in chemical weathering are-

  1. Oxidation
  2. Carbonation
  3. Hydration
  4. Solution

Question 6

What is known as oxidation? What effect does it have on the colour of rocks?

Answer

Oxidation means reaction of minerals in rocks to atmospheric oxygen.

When the atmospheric oxygen comes in contact with iron-compounds in rocks, the iron starts rusting or crumbling. The colour of the rock changes to red, yellow or brown.

Give a technical term for each of the following

Question 1

Disintegration or decomposition of rocks.

Answer

Weathering of rocks

Question 2

Peeling off of the outer layer of rock through contraction and expansion.

Answer

Exfoliation

Question 3

Expansion of minerals in rocks on coming into contact with rainwater.

Answer

Hydration

Distinguish between each of the following

Question 1

Block Disintegration and Exfoliation.

Answer

Block DisintegrationExfoliation
The sudden rise and fall of temperature causes expansion and contraction of rocks. The repeated action leads to tension and splitting of rocks known as block disintegration.Sudden temperature changes may cause fissures into which water penetrates which in turn stimulates chemical weathering. Most rocks are not good conductors of heat. The sudden contraction and expansion peels off the outer layer known as exfoliation.

Question 2

Carbonation and Solution.

Answer

CarbonationSolution
In carbonation, rainwater converts calcium carbonate present in the rocks into calcium bicarbonate which is soluble and is taken away by the ground water.It is the process in which minerals in the rocks dissolve in water.

Structured Questions

Question 1(a)

Define weathering and describe the chief characteristics of weathering.

Answer

Weathering is the process of breaking down of rocks but not its removal. It is described as disintegration or decomposition of a rock in size by natural agents at or near the surface of the earth.

The chief characteristics of weathering are-

  1. It involves disintegration or decay of solid rocks.
  2. It depends on climatic elements and on the characteristics of rocks.
  3. It affects the surface of the earth.
  4. It causes formation of soil.
  5. It involves not one but several processes to cause disintegration of rocks.
  6. It changes hard massive rocks into finer materials.
  7. It prepares rock materials for transportation by agents of gradation.

Question 1(b)

Distinguish between physical and chemical weathering.

Answer

Physical weatheringChemical weathering
It involves rock disintegration without any change in the chemical constituents of the rock.In this weathering, some or all of the minerals in the rocks suffer decay or alteration and transform into different chemical combinations.
Agents of physical weathering include temperature changes, moisture, frost action and wind.Agents of chemical weathering include water, oxygen, carbon or various organic acids.
It is more rapid in desert climates.It occurs in moist and cold climates.
Rocks are affected to great depths.It mostly takes place near the surface of the earth.

Question 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) Physical weathering is also called mechanical weathering as it involves rock disintegration without any change in the chemical constituents of the rock.

(ii) Physical weathering is more rapid in desert climates because temperature changes are sharpest in a desert.

(iii) Chemical weathering occurs in moist and cold climates because such climate has abundant water and oxygen which are the main agents of chemical weathering.

Question 1(d)

Draw a well labelled diagram to show the process of physical weathering.

Answer

Below diagram shows the process of physical weathering:

Draw a well labelled diagram to show the process of physical weathering. Weathering, Total Geography Solutions ICSE Class 9.

Question 2(a)

Describe chemical weathering mentioning the processes involved in it.

Answer

In chemical weathering, some or all of the minerals in the rocks suffer decay or alteration, by such agents as water, oxygen, carbon or various organic acids, and transform into different chemical combinations.

Four main processes involved in chemical weathering are-

  1. Oxidation
  2. Carbonation
  3. Hydration
  4. Solution

Question 2(b)

What is biological weathering? State the main agents of biological weathering.

Answer

Biological weathering involves both physical disintegration and chemical decomposition as all biological matter is made up of oxygen and water.

The main agents of biological weathering are animals, insects, plants and man.

Question 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) Biological weathering is also known as organic weathering because it is the disintegration of rocks as a result of the action by living organisms.

(ii) Vegetation prevents disintegration of rocks because it binds the surface layer and does not allow exposure of rocks beneath to the elements of weathering.

(iii) Chemical and biological weathering is negligible in polar climates because water is in frozen state in the polar regions and most living organisms cannot survive in such cold climatic conditions.

Question 2(d)

Describe the chief characteristics of weathering in different climates.

Answer

The chief characteristics of weathering in different climates are-

  1. In equatorial climates, humidity and temperature are constantly high. Weathering specially chemical weathering is more active in these regions.
  2. In Tropical climates, there is a marked dry season and wet season. Differences in heating leads to consistently high rate of evaporation, During wet season, precipitation of oxides of iron and aluminium takes place from rocks. This promotes formation of laterite soils.
  3. In dry climates or deserts, mechanical weathering is most dominant due to high diurnal range of temperature.
  4. In mid-latitudes or temperate climates, the most powerful agent of weathering is the frost action. In limestone areas, solution or chemical weathering operates on a large scale.
  5. In polar climates, physical weathering due to frost action is most prevalent. Chemical and biological weathering is negligible.
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