Weathering and Denudation

Answer the following questions

Question 1

Define weathering. How does it occur?

Answer

Weathering is a static process and it is defined as disintegration and decomposition of rocks due to several agents like wind, rain, animals, plants etc. It leads to formation of soil.

Weathering occurs because earths surface remains exposed to various elements of weather. These elements of weather like rain, air, heat, frost and cold wear away the rocks.

Question 2

Name the three types of weathering.

Answer

The three types of weathering are:

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

Question 3

What do you understand by denudation?

Answer

Denudation is the long-term effect of processes that cause the wearing away of the earth's surface leading to a reduction in elevation and relief of landforms and landscapes. Denudation is two fold process, i.e. both destructive and constructive. It causes wearing away of rocks and then deposition of the eroded materials forming plains.

Question 4

How does frost cause weathering of rocks?

Answer

When water enters the rocks and turns into ice, its volume increases. During the day, the ice thaws and the water enters deep into rocks. When temperature drops during the night, the water again freezes, widening th cracks. This repeated freezing and thawing results in breaking up of rocks or weathering of rocks.

Question 5

In what ways does atmosphere assist in weathering?

Answer

Atmosphere assists in weathering due to its various elements that participate in disintegration of rocks. The factors of atmosphere that affect weathering are:

1. Temperature - The diurnal and seasonal variation of temperature weakens the rocks and finally leads to their weathering by peeling.
2. Air(wind) - Winds as source of weathering are more effective in arid areas. The sand particles strike the soft rocks and slowly erode them.
3. Rain and flowing water - Water and frost are also important agents of mechanical weathering. The atmosphere contains oxides of sulphur and nitrogen that result in acid rain. Rain water dissolves some of minerals and cause chemical weathering.

Question 6

What is meant by chemical weathering?

Answer

The decomposition of rocks is called chemical weathering. It involves the breaking down of rocks by altering or dissolving the rock minerals due to chemical action or changes. It is more common in hot and humid regions. It is a slow and gradual process which occurs due to exposure to air and water. For example, the iron present in rocks reacts with oxygen and water to form rust.

Question 7

How does biological weathering take place?

Answer

Biological weathering takes place due to biotic factors like plants and animals. It takes place in following ways:

1. The roots of plants grow into cracks and crevices in search of water and nourishment. As they grow, they exert great pressure on the rocks and break them.
2. Sometimes the roots produce carbonic acid which changes the composition of minerals.
3. Animals also loosen and weaken the rocks by burrowing.
4. Human activities such as road construction, mining, farming and deforestation cause weathering and disintegration of rocks.

Question 8

What do you understand by mechanical weathering? How does it take place?

Answer

The breakdown of rocks into smaller fragments by physical processes such as frost wedging is called mechanical weathering or disintegration.

The physical or mechanical weathering occurs due to factors such as the extremes of temperature, nature of rocks, structure of rocks, frost, wind and slope of land. It does not involve any chemical change in the composition of rock. It is more effective in dry regions.

Question 9

How does composition of rock affect mechanical weathering?

Answer

The rocks are of different types. They may be hard or soft, soluble or insoluble. The mechanical weathering takes place in the softer or soluble rocks more easily than in the hard and insoluble rocks. Therefore, composition of rock affects mechanical weathering.

Question 10

Name the factors responsible for chemical weathering.

Answer

The factors responsible for chemical weathering are:

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

Question 11

What is carbonation? Give two examples of the landforms formed by carbonation?

Answer

Carbonation is the reaction of carbonic acid on minerals. Rainwater, when mixed with carbon dioxide in the atmosphere forms a weak solution of carbonic acid. It acts on rocks containing limestone and chalk. The reaction results in calcium bicarbonate which is highly soluble and gets easily washed away in solution as it flows through the rocks or seeps below the surface.

Two examples of the landforms formed by carbonation are stalactites and stalagmites.

Question 12

How does chemical weathering take place?

Answer

The decomposition of rocks is called chemical weathering. It involves the breaking down of rocks by altering or dissolving the rock minerals due to chemical action or changes. It involves processes like oxidation, hydration, carbonation and solution. It is more common in hot and humid regions. It is a slow and gradual process which occurs due to exposure to air and water.

Define the following terms

Question 1

Oxidation

Answer

The process by which oxygen present in air and water react with minerals in the rock is called oxidation. For example, most rocks contain a certain amount of iron. Oxygen and water react with iron to form iron oxide which easily erodes in comparison to iron. As it is removed the rocks are weakened and thus decomposed.

Question 2

Solution

Answer

The process by which the rainwater reacts with minerals present in the rock and dissolves them causing decomposition of rock is called solution. For example, rock salt dissolves in water.

Question 3

Exfoliation

Answer

Exfoliation is the weathering process by which concentric shells, slabs, sheets, or flakes are successively broken loose and stripped away from a rock mass.

Question 4

Weathering

Answer

Weathering is defined as disintegration and decomposition of rocks due to several agents like wind, rain, animals and plants. It leads to formation of soil.

Question 5

Denudation

Answer

All processes that cause degradation of landscape, weathering mass movement, erosion and deposition of eroded material are called denudation.

Distinguish between the following pairs

Question 1

Chemical and Mechanical Weathering

Answer

Question 2

Weathering and Denudation

Answer

Give a reason for the following statements

Question 1

Wind is the main agent of gradation in the arid & semi arid regions.

Answer

Due to the absence of vegetation the soil is loose & exposed to the action of winds & scanty rainfall.

Question 2

Erosion is the main work of river in the upper course.

Answer

In the upper course of the river the gradient of the slope is high, therefore, the velocity of the river is also high. So the main action of the river is erosion.

Question 3

Weathering is a static phenomenon.

Answer

As there is no involvement in the movement of disintegrated rock fragments in weathering process.

Question 4

Deposition is the main work of river in the lower course.

Answer

As the river approaches the sea or ocean, its gradient decreases, resulting in a reduction of the river's velocity. It's volume also increases due to addition of tributaries along the way. Due to this, it cannot carry the sand particles any more and deposits all the sediments at its mouth. Hence, deposition is the main work of river in the lower course.

Question 5

Chemical weathering may affect the farming activities.

Answer

Chemical weathering may dissolve the soluble components of the soils. This may cause the soils to become infertile and may affect farming activities.

Choose the correct option

Question 1

Which of following work is active in the lower course of a river?

1. Erosion
2. Deposition
3. Both erosion & deposition
4. Transportation

Answer

Deposition

Question 2

Identify the landform by studying the image.

1. Deflation Hollow
2. Seif dune
3. Barchans
4. Sand Hill

Answer

Barchans

Question 3

Through which of the following chemical weathering Feldsper is converted to Keolin?

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

Answer

Hydration

Question 4

Which of the following weathering is also known as Onion Peeling?

1. Block disintegration
2. Exfoliation
3. Granular disintegration
4. None of the above

Answer

Exfoliation

Question 5

Which of the following weathering is also known as Mechanical weathering?

1. Chemical weathering
2. Physical weathering
3. Biological weathering
4. None of the above

Answer

Physical weathering

Question 6

Which of the following landforms is formed in the lower course of the river?

1. V-shaped valley
2. Meander
3. Delta
4. Waterfall

Answer

Delta

Question 7

Which of the following is the erosional landform of wind?

1. Barchans
2. Seifs
3. Deflation Hollows
4. Delta

Answer

Deflation Hollows

Question 8

In which course of the river the river erosion is more lateral than vertical?

1. Upper course
2. Middle course
3. Lower course
4. All the above

Answer

Middle course

Question 9

The limestone topography is affected through which of the following weathering process?

1. Physical weathering
2. Biological weathering
3. Oxidation
4. Carbonation

Answer

Carbonation

Question 10

Which of the following features is observed in this image?

1. Delta
2. Meander
3. V shaped valley
4. Rapids

Answer

Meander

Question 11

Waterfall is formed due to the erosion by which of the following agent?

1. Wind
2. Underground Water
3. River
4. Glacier

Answer

River

Question 12

Which of the following is a static process?

1. Erosion
2. Weathering
3. Denudation
4. Solution

Answer

Weathering