WBBSE Solutions For Class 9 Geography And Environment Chapter 5 Weathering

WBBSE Geography Book Class 9 Chapter 5 Weathering Short Questions With Answers :

Question 1. What is Denudation?
Answer:
Denudation :
The laying bare of Seon ae rocks by the process of weathering transport and erosion.

Question 2. What is Disintegration?
Answer:
Disintegration :
It is the process of breaking up or destroy the cohesion of rock particles.

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Question 3. What is Erosion?
Answer:
Erosion :
The removal of part of the land surface by wind, water, gravity or ice.

Question 4. What is Exfoliation?
Answer:
Exfoliation :
It is the process of separation of successive thin shells or spalls from a massive rock such as granite or basalt.

Question 5. What is Hydrolysis?
Answer:
Hydrolysis :
It is chemical reaction during which molecules of water are split into hydrogen (H⁺) and hydroxides (OH^–)

WBBSE Geography Book Class 9

Question 6. What is mass wasting?
Answer:
Mass wasting :
The movement/downslope of rock fragments and soil under the influence of gravity.

Question 7. What is Oxidation?
Answer:
Oxidation :
The absorption of mineral of one or more oxygen ions. It is a major type of chemical weathering, particularly in rocks containing iron.

Question 8. What is Weathering?
Answer:
Weathering :
The breakdown of rocks without its removal, except by gravity is called weathering.

Question 9. What is corrosion?
Answer: Corrasion is the process of mechanical erosion of rock surface by friction of rock materials with the surface.

Question 10. What is Corrasion ?
Answer: Corrosion is the work of wearing away of rock and rock surface by chemical and solvent action.

Question 11. What is Attrision ?
Answer: Attrision is the wear and tear of the transported materials themselves when they collide with each other.

Question 12. From where do the exogenous forces derive their energy?
Answer: From the Sun.

Question 13. Which process levels the land?
Answer: Graduation.

Question 14. Name the processes of gradation.
Answer: Degradation and Aggradation.

Question 15. Name the process by which rocks are broken without any change in their situation.
Answer: Weathering.

Question 16. What is the main cause of exfoliation?
Answer: Insolation.

WBBSE Geography Book Class 9

Question 17. In which type of area the action of frost is more dominant?
Answer: Cold areas where temperature oscillates around freezing point.

Question 18. Which type of weathering is more active in a limestone area?
Answer: Chemical weathering (Carbonation).

School Geography Class 9 Solutions WBBSE Chapter 5 Weathering True Or False:

Question 1. Organic matters are coal and limestone.
Answer: True

Question 2. Important result of weathering is soil formation.
Answer: True

Question 3. Process of weathering is also called geomorphic cycle.
Answer: True

Question 4. Hydration is the chemical union of water with other materials.
Answer: True

Question 5. Frost action is very common in the desert.
Answer: False

Question 6. Quartz and white mica are weather-resistant.
Answer: True

Question 7. Denudation comes before weathering.
Answer: False

School Geography Class 9 Solutions WBBSE

Question 8. Hydration is the chemical union of water with other minerals.
Answer: True

Question 9. Oxidation is a process of mechanical weathering.
Answer: False

Question 10. Carbonation is a process of chemical weathering.
Answer: True

Question 11. The main agent of mechanical weathering is temperature.
Answer: True

Question 12. Gypsum = water + calcium sulphate.
Answer: True

Question 13. Hydrolysis involves chemical changes.
Answer: True

Question14. In differential weathering change is different.
Answer: True

Question15. Slope of land is not a factor of weathering.
Answer: False

School Geography Class 9 Solutions WBBSE Chapter 5 Weathering Fill In The Blanks:

Question 1. Denudation consists of erosion and_______.
Answer: Weathering.

Question 2. _______refers to gradual decomposition of the earth crust.
Answer: Weathering.

Question 3. Frost action is very common in the_________.
Answer: Mountainous area.

Question 4. Chemical union of water with a mineral is called_________.
Answer: Hydration.

Question 5. Fossils are the remains of thing of the _________ plants/animals.
Answer: Living.

Question 6. Chemical weathering is common in the high________ regions.
Answer: Tropical.

Question 7. Mechanical weathering is common in the high
Answer: Mountain.

Question 8. _________ experience Mechanical weathering.
Answer: Deserts.

Question 9. __________ weathering is confined to dry region.

Answer: Mechanical.

School Geography Class 9 Solutions WBBSE

Question 10. _________weathering is confined to wet and rainy areas.
Answer: Chemical.

Question 11. __________ is the chemical union of water with other elements.
Answer: Hydration.

Question 12. Weathering __________ by and__________ is called biological weathering.
Answer: Plants and animals.

Question 13. Weathering depends on _________ of the land.
Answer: Slope.

Geography Class 9 Chapter 5 WBBSE Chapter 5 Weathering 2 Marks Questions And Answers

Question 1. What is Geomorphic cycle?
Answer: The sequence of events, consequent upon the processes of weathering, erosion and deposition, which results in the complete process of landscape change from initial uplift of the land to its final destruction is called the geomorphic cycle or the cycle of erosion.

Question 2. Where is Exfoliation best developed?
Answer: Exfoliation is best seen in rocks of uniform structure. Exfoliation domes are common in the Kalahari, Egyptian and Sinai deserts.

Question 3. Where is frost action very common?
Answer: Frost action is very common in winter in temperate regions and in the snowy mountains all the year.

Question 4. How pediments are formed?
Answer:
Pediments: Weathering contribute in an important way to the recession of cliffs and escarpments. The weathering of scarps has been considered, particularly significant in arid region. The weathering combined with erosion and denudation makes a slow retreat of the edge of upland block. Thereby pediments are formed.

Question 5. What is regolith?
Answer:
Regolith: 90 per cent of the earth’s surface is mantled by regolith. The combined effects of mechanical and chemical weathering cause the breaking up and decomposition of almost all types of rocks on or near the earth’s surface and form a layer of more or less detached rock fragments. This layer of decomposed rock above the bedrock is called Regolith.

Geography Class 9 Chapter 5 WBBSE

Question 6. What are screes?
Answer:
Screes: Screes are masses of debris, comprising loose fragments of rock that cover a steep bare hill slope or are piled up in a conical or fan-shaped mass at its foot. Scree is also called Talus. Screes are among the few landforms which are produced mainly by weathering aided by mass wasting.

Question 7. What do you mean by shattering?
Answer:
Shattering: Shattering is the further disintegration of the products of block disintegration. It is the disintegration of rock along new surfaces of breakage. It produces highly angular pieces with sharp corners and edges.

Question 8. Distinguish between soil and rock.
Answer: The difference between soil and rock can be explained as under :

Soil	Rock
(1)    Soil is formed from rocks.	(1)    Rock is formed from minerals.
(2)    Soil is an organic material which contains humus.	(2)    Rock may be both an organic or an inorganic material.
(3)    Soil is found in the top layer of earth only.	(3)    Rock is found both on the surface of the earth and in the interior of the earth.
(4)    Soil particles are generally fine.	(4)    Rock particles can be fine as well as coarse.

 

Question 9. What is soil conservation?
Answer: Soil conservation methods include protection of forests, afforestation, binding, reclamation of lands, controlling floods, overgrazing, terracing, strip farming, contour ploughing and crop rotation.

Chapter 5 Weathering 2 Marks Questions And Answers (Short Notes)

Question 1. Carbonation.
Answer: Carbonation is the union of carbon dioxide with constituents of a rock. When rainwater falls, the atmospheric carbon dioxide combines with it and turns it into weak acid which is known as carbonic acid (water (H₂O) + carbon dioxide (CO₂) = Carbonic acid). The action of this acid limestone produces a salt, called calcium carbonate) (CaCo₃). This acid water sinks into the ground and forms huge caves by a slow process of carbonation.

Geography Class 9 Chapter 5 WBBSE

Question 2. Exfoliation.
Answer: Exfoliation is also known as onion or spheroidal weathering. Which to peeling off concentric shells of rocks due to combined actions of heat and wind in hot arid and semi-arid regions and monsoon lands. Exfoliation is more common in crystalline rocks. The outer shells of rock become loose due to alternate expansion and contraction due to high temperature during day time and comparatively low temperature during night and these loosened shells are removed by strong winds. Many of the granitic batholiths, which are exposed above the ground surface are being affected by exfoliation weathering. Kanke Dome near Ranchi city exhibits a fine example of such weathering process.

Question 3. Block disintegration.
Answer: The disintegration of surface rocks is caused by their exposure to the extreme range of temperature. Under perfect dry condition in cloudless regions, diurnal range of temperature becomes high due to intense heat of the blazing sun by day and rapid long waves radiation by night. The rocks successfully expand and contract and the stresses so developed may ultimately fracture fresh, massive rocks into small blocks. Such a process is known as Block disintegration.

Question 4. Oxidation.
Answer: Itis a process in chemical weathering when oxygen combines with minerals of a rock (particularly the rock having iron compound), it decays and the rock gets rusted. The colour is changed into red, brown or yellow and rocks are powdered in brown.

Question 5. Biological weathering.
Answer: This kind of weathering is caused by animals, plants, human beings. Seeds of various plants and fruits are sometimes scattered by animals, birds and human being. These seeds take the shape of plants whose roots penetrate in the holes of the rocks. The holes become widened by expansion and contraction, resulting in the disintegration of rocks.

Question 6. Granular Disintegration.
Answer: Different minerals present in the rocks may have different rates of expansion and contraction. For example, dark coloured minerals will absorb more heat and expand to a greater extent than light coloured minerals. Such alternating expansion and contraction between day and night leads to a break up into rock into small fragments. This is called granular disintegration.

Geography Class 9 Chapter 5 WBBSE

Question 7. Hydrolysis.
Answer: When water combines itself with certain mineral compounds, there is true chemical change. The process, called hydrolysis this produces a new and different compound. During hydrolysis, the hydronium ions from water combine with minerals and change them completely. When feldspar is completely hydrolyzed clay minerals and quartz are produced. Elements like potassium, calcium, sodium, magnesium are released.

N₄CL +H₂O → NH₄OH & H⁺ & CL^–

Besides the above-mentioned processes of chemical weathering, some minerals are removed in solution from the rocks. Rocks are then decayed. Regions, where chemical weathering is most effective, are the equatorial climatic region and Tropical humid regions.

Question 8. Mass Wasting.
Answer: Mass wasting also known as slope movement or mass movement is the geomorphic process by which soil, sand, rocks etc. move down slope as a mass under the force of gravity. Types of mass wasting includes, creep, slides, flows, topples and falls each with its own characteristic features. Mass wasting may occur at a very slow rate in areas that are dry or that receives sufficient rainfall. Sometimes they may occur at very high speed, such as landslides, with disastrous effects. Mass wasting is triggered by weathering and erosion of the surface of the land.

WBBSE Solutions For Class 9 Geography And Environment Chapter 5 Weathering 3 Marks Questions And Answers

Question 1. Differentiate between Mechanical and Chemical weathering.
Answer:
Mechanical Weathering Chemical Weathering

Mechanical Weathering	Chemical Weathering
1.    It leads to disintegration of rocks.	1.    It leads to decomposition of rocks.
2.    It is done by agents of weather like temperature, humidity, rainfall, etc.	2.    It is done by atmospheric elements like gases, etc.
3.    It is more common in hot, cold, dry and arid regions.	3.    It is more common in hot and humid regions.
4.    It is a comparatively slow process.	4.    It is a comparatively fast process.
5.    It only leads to disintegration and no change in minerals	5.    It leads to the complete change in the mineral constituents of rocks.
6.    It is done by processes like crystal growth, thermal tension, pressure release and by biological means.	6.    It is done by processes like solution, carbonation, hydration, hydrolysis, oxidation, reduction and bio-chemical weathering.

 

Question 2. What is differential weathering?
Answer: Different rocks and even different parts of the same rock weather at different rates even under the same general conditions. Therefore, after prolonged weathering, some parts of a rock may be greatly changed, but other parts are so little changed that they stand out in bold relief after the weathered material is removed. Such features are said to be the result of differential weathering.

Class 9 Geography Chapter 5 Questions And Answers WBBSE

Question 3. Under which type of climatic condition, chemical weathering is most effective?
Answer: In chemical weathering, rainfall and humidity play the most vital part. For this reason, it is most effective in hot and humid regions. In the equatorial climatic regions and in tropical humid regions chemical weathering is very much active.

Question 4. Define weathering. Or, What do you mean by weathering?
Answer: By the term ‘weathering’ we mean the decaying or wearing away of the rock of the earth’s crust by the action of weather condition. In fact, the term ‘weathering’ comes from the word ‘weather’. The decaying or breaking down of rock-bed by the action of weather elements such as, the sun, the heat of the sun, rain, wind, moisture, humidity, frost, etc., is called weathering. It is the natural process of decaying rocks.

Question 5. Write about Biological weathering.
Answer: The weathering which is caused living organism is known as biological weathering. Biological weathering is carried out through plants, animals and human beings.

(1) Plants:
The roots of the plants seeking water and nutrients penetrate deeply through cracks and joints causing widening of the cracks. Finally, the rocks are split apart.

(2) Animals:
Burrowing by earthworms, ants, rats, etc. also disintegrates the rocks. They loosen and weaken the rock and soil making it easy for other agents to remove them.

(3) Humans:
Human activities such as mining, quarrying, deforestation, construction of roads in hilly areas, etc., disturb and put pressure on the rock strata.

Question 6. Describe in brief the factors affecting weathering.
Answer: Factors affecting weathering :

(1) Structure of rocks :
It includes minerals, nature of rocks and their hardness. Joints permit water to enter rocks and help weathering. Hard rocks are resistant, while soft rocks are easily broken.

Class 9 Geography Chapter 5 Questions And Answers WBBSE

(2) Slope of the land :
Weathering is subjected to the slope of land.

(3) Climate :
Mechanical weathering predominate in dry areas while chemical weathering operate in wet climate.

(4) Vegetation :
Bare surfaces are weathered to a greater extent. Vegetation cover protects the surface from weathering.

(5) Presence of Joints :
Joints permit water to enter the rocks help weathering.

Question 7. Differentiate between weathering and erosion. (S.Question)
Answer:

Weathering	Erosion
1. Disintegration of rocks occurs at the same place.	1. Disintegrated or broken rocks blown and flown forward.
2. It is static.	2. It is mobile.
3. Mainly it is done by the agents of weathering.	3. It is done by the action of wind, river or glacier.
4. In this process, there is no transportation of materials.	4. In this process, transportation of materials takes place.
5. It is a slow process.	5. It is a fast process.
6. Weathering is an independent process.	6. Erosion is dependent on weathering.

 

Question 8. In which climatic regions do the mechanical and chemical weathering dominate respectively? (S.Question)
Answer: The mechanical weathering is dominant in the
(1) Hot and desert region,
(2) Cold and dry region and
(3) Dry temperature region.
The chemical weathering is dominant in the hot- humid regions, i.e.
(1) Equatorial and
(2) Tropical monsoon regions. It is also active in the moist temperate regions.

Class 9 Geography Chapter 5 Questions And Answers WBBSE

Question 9. What are the effects of weathering?
Answer:
1. Weathering causes the rock layers to be broken. This influence the formation of landforms.

2. The layers of broken rocks caused by weathering which lie on the earth’s crust, form an important layer on the earth’s crust called Regolith.

3. In wet tropical region the chemical reactions occurring in rocks in contact with some minerals causes the formation of important minerals like bauxite and laterite.

4. Chemical weathering results in the segregation of some minerals from the rocks which are left behind, and add fertility to the soil, which is necessary for plant life.

5. Weathering helps in soil formation indirectly.

6. Weathering leaves behind large amounts of undissolved silica or sand, as remnants.

Class 9 Geography Chapter 5 Questions And Answers WBBSE

Question 11. Write a note on denudation.
Answer:
Denudation :
Denudation means laying bare. The word ‘denudation’ comes from the Latin word denudare which means to ‘strip bore’. Denudation is the wearing away of rocks so that the underlying rock are laid bare. It is slow but continuous process. Actually, denudation is the combined action of weathering process and erosional process and it also includes mass wasting. Thus denudation is a group of processes which act collectively to wearing away of rocks or surface whereby the underlying rocks are laid bare. Thus, Denudation = Weathering + Erosion + Mass wasting.

Question 12. Discuss briefly Salt Weathering.
Answer: Salt Weathering: Salt weathering is another type of mechanical weathering by crystal growth. Salts are abundant in the rocks of dry lands since scanty rainfall does not remove all solubles. Aerosolic atmospheric salts formed by evaporation of wave spray in distant oceans is washed down in the ground or on rocks during occasional rains. Salts in solution on rocks crystallize when rock moisture evaporates. The growing crystensile strengths. They wedge rock granules out of their sockets. Salt weathering through crystal growth is common in arid and coastal areas where salt is comparetively abundant in rocks.

Question 13. Discuss the process of weathering by frost action.
Answer:
Definition :
In humid, cool temperate region or in high altitude, water is – collected in cracks and pores of rocket daytime and freezes at night. We know, ice expands \begin{equation}\frac{1}{10} \text { th }\end{equation}of the volume of water it freezes. Thus the frozen water exerts enormous pressure on walls of cracks. As a result the cracks are widened and ultimately the rock breaks into pieces. This is called Frost Action.

Mechanism :
Disintegration of rocks into large-size blocks due to freeze and thaw of water is of common occurrence in temperature and. cold climatic
regions. Frost action weakens the rocks in two ways.
Examples:
(1) Due to freeze and thaw of water between the particles of the rocks and
(2) Due to freeze and thaw of water in the crevices and pore spaces. The diurnal freeze and thaw cycle causes alternate expansion and contraction which introduce tension and stresses due to which rocks are disintegrated into small particles.

Question 14. State some measures to conserve soil fertility.
Answer:
(1) Soil fertility should be maintained by supplying adequate manure and water to the soil.
(2) Soil should be used according to soil character. Care should be taken to preserve its fertility and productivity. The cultivation of soil-exhausting plants and crops should be avoided or proper precautions should be taken.
(3) Crop rotation should be introduced to regenerate the fertility of the soil; sometimes green manure revives the productivity.
(4) Care should be taken to convert the infertile soil into fertile ones by applying chemical fertilizers.
(5) Agricultural researches can bring about new thoughts on soil character, new method for its preservation and new ideas to increase its productivity.

Question 15. Explain the process involved in soil formation.
Answer: Several processes are involved in soil formation and may, to some extent, affect the soil profile. These processes are :

(1) Eluviation :
It is the mechanical translocation of clay or other fine particles down the profile.

(2) Iuviation :
It is the accumulation of the washed down (eluviated) material in the lower. horizons of the soil profole..

(3) Cheluviation :
It is the downward movement of material, similar to leaching but under the influence of organic complex compounds.

(4) Leaching :
It is the removal and downward movement of material from a horizon in solution.

Class Ix Geography Book WBBSE Chapter 5 Weathering 5 Marks Questions And Answers

Question 1. Define chemical weathering and describe the process involving in it.
Answer: Decomposition of bedrock by alternating and dissolving the component rock minerals is known as chemical weathering. This weathering includes various chemical process which are as follows –

(1) Solution:
It is the process is which the soluble minerals are dissolved by water entering into rocks through crevices. Thus rainwater causes chemical disintegration of rock salt and gypsum. It is known as solution process. Landform resulting from underground drainage in Erosion by water action limestone region in limestone region.

 

(2) Oxidation:
The process of oxidation takes place when the oxygen of the atmosphere combines with same other element,
Example: when iron combines with oxygen ferric oxide is formed. The oxidized rocks generally break into brown, yellow or red powdery mass.

(3) Carbonation:
The process of carbonation is the union of carbon-di-oxide from the atmosphere with rock minerals and some of the minerals that are otherwise not soluble can be removed easily through this process.
Example: Limestone is especially susceptible to this process.

(4) Hydration:
Hydration occurs when the water itself combines chemically with same element or mineral potash feldspar turns to a clay mineral known as kaolin because of hydration.

(5) Reduction:
Whenever there is loss of oxygen from anything the process is called reduction. It is not a common process of chemical weathering. When the partial decay of vegetation occurs in water to produce organic matter, it can change the ferric compounds in the ferrous compounds.

Question 2. Discuss the factors influencing mechanical weathering.
Answer: The word weathering means ‘Disintegration And Decomposition of rocks’. Mechanical weathering means disintegration of rocks by mechanical means. In this process, chemical composition is not changed. As the disintegration of rocks is done physically, it is also known as Physical Weathering.

Following physical forces effect the mechanical weathering:—

Class Ix Geography Book WBBSE

(1) Temperature:-
Mostly in the desert areas the diurnal range of temperature is great. In the daytime, due to high temperature, rocks expand while at night due to low temperature they contract. This rapid expansion and contraction leads to the formation of cracks and joints in the rocks. Again rocks split along cracks and joints the disintegration of rocks takes place. The expansion and contraction of different kinds of minerals take place differently and the rocks break into angular fragments. The loose fragments at the foot hills are known as Scree or Talus.

Due to successive processes of expansion and contraction the hard rocks disintegrate into blocks which is known as Block disintegration. Again more expansion and contraction takes place on the outer layer of a rock than on the inner layer and in the long run the outer layer detach itself from the inner and layer peels off in layers. This is shelling process and is known as exfoliation and generally occurs
in the rocks of uniform structure.

(2) Wind :-
In the arid regions and deserts winds laden with sandblast the front part of the rocks resulting in disintegration.

(3) Frost :-
In the cold regions during day time water enters the joints and crevaces of the rocks. After a considerable fall in temperature, particularly at night, this water freezes and expands in volume. The result is that the joints and cracks widen and in due course the rocks break into small fragments.

(4) Plants and animals :-
Sometimes animals bring seeds of plants and drop them in the cracks. The plants grow and the roots expand resulting in the breaking of rocks. Burrowing animals and human activity also cause mechanical weathering.

Question 3. Discuss in brief the mechanical wealthering caused by biological agents.
Answer:

(1)Root Tension Weathering :
Tree roots growing in crevices (narrow openings in a rock) exert a wedge-like force that causes to pry apart masses of rocks. Roots of plants and trees grow into cracks in the rocks in search of water and other food for living. They expose rock even for chemical weathering. They facilitate the percolation of water and air, the ultimate effect of which is the breaking down of the rocks. They help to decompose the rock through the acid secretions by which they obtain minerals.

Class Ix Geography Book WBBSE

(2)Burrowing Animals Weathering :
Rodents (rat, rabbit, squirrel, etc.) and termites, insect and worm lossen particles in rocks and aid to expose the rock surface to chemical weathering also. The acids formed when animal matter decays play a part in chemical weathering.

 

(3)Differential Weathering :
When a landscape is associated with a number of different rock types, some may become comparatively strong or resistant to weathering and other may be weak or easily weathered. The action of weathering processes at different rate on different rock types in a landscape is known as Differential Weathering. Some geographer hold the opinion that differential weathering may contribute towards the origin of landforms. It is weathering that breaks up rocks at different rates and itis erosion that removes weathered particles and produces the landforms.

Question 4. Why does the carbonation process or chemical weathering most active in limestone rocks?
Answer: Chemical weathering, especially the carbonation process is most active in limestone rocks (Caco₃). When rainwater ( H₂o ) falls, sometimes the atmospheric carbon dioxide (Co₂) combines with it and turns it into weak acid which is known as carbonic acid (H₂co₃) [water ( H₂o ) + carbon dioxide (Co₂= carbonic acid (H₂co₃). The chemical reaction of this acid (H₂co₃) on limestone or calcium carbonate (Caco₃) produces a component, called ee bi-carbonate [Caco₃+ H₂co₃ = Ca(HCO₃)₂.] In limestone regions,.the carbonic acid (H₂co₃) form various ae of Eaaiacns. Given here a short description of some of es landforms—

(1) Karren/Lapies/Clint :
Solution process is accelerated when water (H₂o) falls over limestone rocks. Thus long furrows formed which have verical walls. These are known as Karren or Clint. Deep narrow grooves between clint called grikes.

(2) Caverns :
Underground caves are formed by various methods in’a limestone area. These are known as caverns.

(3) Sink Holes :
There are hundreds of small holes in limestone. These holes are called sinkholes.

(4) Stalactite, Stalagmite and Pillar :
Inside the caverns water containing limestone in solution drips through joints in the ceiling of the cave. As the interior of the cave is warm, water evaporates readily leaving a deposit of dissolved limestone hanging from the ceiling. This deposit is called stalactite. When water drips from the ceiling, it may form a deposit on the floor of the cave as well. Such deposits grow upwards from the floor. These are called stalagmite. In some places, stalactites and stalagmites may join together to form a column or pillar.

Geography Class 9 West Bengal Board

Example :
CaCO, + H,CO, = Ca (HCO,),
[Limestone + carbonic acid = calcium bi-carbonate.]

Question 5. Discuss the influence of climate on weathering.
Answer: Influence of climate on weathering: Climate has a close relation with weathering. The process of weathering differs from one climatic region to another. Such as-

(1) Mechanical weathering :
Mechanical or physical weathering is important in-

Polar regions :
Weathering in polar regions is mainly due to freeze-thaw. Most of the regions are snow-covered, Mechanical weathering, particularly, frost
action, plays the vital role Chemical actions become weak due to low temperature. Thus, in cold areas like Arctic, physical weathering is dominant.

Dry and desert regions :
In dry and deserts, physical weathering is considered to be dominant due to wide ranges of temperature. Dearth of water in dry and desert regions offers there little scope for chemical weathering.

(2) Chemical weathering :
Chemical weathering is important in—

Equatorial regions :
In equatorial region here is high temperature as well as high rainfall throughout the year. In hot and humid climatic condition, chemical
weathering is definitely most favourable in this region. CO, of air, humic acid from vegetation and nitric acid from thunder of clouds help in the chemical weathering in rocks. The rate of chemical weathering is the highest for certain
rocks in this region.

Tropical Region :
Here the range of temperature is wide in between summer and winter. This region experiences humid as well as dry weather condition. All
these invite physical and chemical weathering to act upon. During rainy season, chemical weathering comes in action.

(3) Dual Action :
In humid temperate region, both physical and chemical weathering work together.

Question 6. What are the effects of weathering?
Answer: The processes involved in weathering are very much slow, but they play vital role in sculpturing landforms.

The following are some of the effects of weathering :

(1) Mass Wasting :
The term mass wasting is associated with the process whereby materials (such as soil, rock) are transported naturally, from the surface of the Earth, down a slope by the force of gravity. Mechanical and chemical weathering sometimes act together to weather away land and to loosen rock structure over a vast area. It is known as mass wasting. It decomposes and weakens the upper layers so severely that the whole region undergoes decay. The mass wasting makes a vast wasteland which is very difficult to use.

Geography Class 9 West Bengal Board

(2) Outcroppings of rock :
Weathering wears away the top-covering and then underlying rock crops up and is exposed to view.

(3) Talus or Scree :
Talus or Scree is a feature which includes a mass of boulders and broken rocks of all sizes. They accumulate at the foot of a mountain. They are the weathered rocks and roll down under the action of gravity.

(4) Formation of ores :
Weathering helps to produce mineral ores of tin, aluminium, manganese and uranium. Chemical weathering in Tropical region is responsible for the formation of laterite.

(5) Regolith :
Disintegration by weathering produces a layer of loose rock

(6) Differential weathering produce different landforms :
Weathering on granite weathering produces limestone cavern with stalactite stalagmite, pillars etc.

(7) Increased soil fertility :
Weathering makes the soil fragile and porous. It becomes airy and favours plant growth. Thus weathering adds fertility to the soil.

Question 7. Discuss the agents of soil erosion.
Answer:

Agents of Soil Erosion :
The agents of soil erosion are powerful agents of soil and transport it. Generally, there are four types of soil erosion—
(1) Sheet erosion,
(2) Slip erosion,
(3) Rill erosion and
(4) Gully erosion.

(1) Sheet Erosion :
When a layer of soil on surface, is removed over a large area by running water, it is called sheet erosion.

(2) Slip Erosion :
A slip is a landside in which rocks-filled water move down in one mass. This slip is due to the pressure of water absorbed by soil during heavy rain. When it is unable to percolate down a greater mass of overlying soil on steep land slips down.

(3) Rill Erosion :
It is the removal of loose surface soil by small rill channel which may progressively join up to form gullies. In this stage, the small streams which are formed by joining the water channels, start downward cutting of soil leaving behind finger like rills over the surface.

Geography Class 9 West Bengal Board

(4) Gully Erosion :
When soil is removed by water flowing along definite paths down the’slope in channels, it is called gully erosion.

Question 8. What are the causes of soil erosion?
Answer: Causes of Soil Erosion: Soil erosion takes place when soil is removed faster than it is formed. The major causes of soil erosion can be summed up in the following ways.

(1) Character of the soil :
The loose and fragile soil easily wear away by the action of rainwater, running water and wing. Thus the erosion of soil caused.

(2) Character of the land slope :
The slope of the land determines the force of action. The erosional agents act upon soil vigorously on the steep slope of the land where as they are less destructive on the flat land.

(3) Bare Land :
The roots of the plants find the soil. The bare lands easily wear away by the action of rain water and running water. The vegetation cover always fights against soil erosion.

(4) Unwise and uncontrolled use :
(1) Removal of vegetation cover has aggravated the loosening of the soil which is later washed away by rain water.
(2) Overgrazing by animals is also responsible for soil erosion.
(3) Faulty method of cultivation is also responsible for soil erosion.

Question 9. State the measures to check soil erosion.
Answer: Measures to Check Soil Erosion: Soil can be conserved in many ways—

(1) Preservation of soil erosion by afforestation :
New plants should be planted in regions where soil has become exposed, in order to check rain wash and surface runoff. Around the agricultural land, trees should be planted to control soil erosion.

(2) Restriction of Overgrazing :
Overgrazing should be avoided so that new plant can grow there. If vegetative cover on land is saved soil erosion can be checked naturally.

(3) Introduction of contour cultivation/terraced cultivation :
On mountain slopes running water rushes down turbulently and carries away mud, silt and clay. To check the force of running water and rain wash a series of steps or terraces can be made on the land. Thus will check soil erosion.

(4) Prohibition of Jhum Cultivation :
In Shum cultivation (which is also known as ‘shifting cultivation’) at first forested lands are destroyed by making fire to clear out the forest, and the cultivation is introduced on it. After a few years of cultivation, when the fertility of soil goes down, the land is left and another new plot of land is so taken for cultivation. The land which is left, remains there bare open and the abandoned land becomes the arena of soil erosion. This type of cultivation should be prohibited to check soil erosion.

Question 10. Discuss the process of formation of soil.
Answer: Just like air, Water and sunlight, soil is a prime source for sustenance of plant life which inter alia supports the animal life on the Earth. All soils initially come from organic substances, rocks and minerals on the Earth surface, which are termed as “parent materials”. Soil is considered as the ‘skin of the Earth’. The formation of the soil as a combination of weathering of parent materials, its deposition in layers and transportation by weathering agents like rain, wind etc. over a long period of time. Soil, in course of time gets enriched by humus as a result of decaying of organic substances. Soils are usually formed from rocks through the intermediate stage of formation of Regolith which results due to weathering of rocks.

Fragmented rock materials undergo further decay from fine grains of sand, sand particles, clay, etc. The natural agents of soil formation of this stage are running water, wind, glacier, plants and other organisms. Remains of dead animals and plants decompose and mix with the sand and clay and undergo changes to make the organic matter humus in the upper layer of the soil. Thus from the loose, uncompacted dust and rocks found on top of bedrock, soil is formed. It is rich in organic matter and mineral that can support plant life.

Geography Class 9 West Bengal Board

Question 11. What are the factors which determine the speed and type of weathering?
Answer: The speed of weathering and the type of weathering are determined by several factors. They are
(1) The Nature of the Rock,
(2) Topographic Conditions,
(3) Climate and
(4) The Vegetative Cover.

(1) The Nature of the Rock :
The composition of the rock is an important factor for weathering. Chemical weathering is active in igneous rocks. Among the sedimentary rocks, limestone is affected mainly by carbonation and by water. Rock which are joined and fissured are more susceptible to weathering than rocks which contain few cracks.

(2) Topographic Conditions :
Weathering varies with altitude, slope of land, etc. Altitudes and steep slopes quicken the removal of rock debris so that new surfaces are quickly exposed to the process of weathering.

(3) Climate :
Disintegration of rocks are rampant on steep mountain slopes and cliffs, in frost-ridden areas and in desert region. Under humid condition in low-relief tropical region decomposition and solution are powerful enough. In the temperate zones, the weather is widely variable. There leading process of weathering vary from season to season.

(4) The Vegetative Cover :
Weathering is more intensive on bare rocks than on rocks with vegetative cover.