RBSE Class 11 Geography Important Questions Chapter 6 Geomorphic Processes

Rajasthan Board RBSE Class 11 Geography Important Questions Chapter 6 Geomorphic Processes Important Questions and Answers. 

RBSE Class 11 Geography Important Questions Chapter 6 Geomorphic Processes

Multiple Choice Questions

1. Which process helps in formation of soil?
(A) Weathering 
(B) Erosion
(C) Transportation 
(D) Deposition.
Answers
(A) Weathering 

2. Which of the most fertile soil of India?
(A) Alluvial 
(B) Black
(C) Red 
(D) Elimate.
Answers
(A) Alluvial 

3. For which crop is black soil suitable?
(A) Wheat 
(B) Rice
(C) Cotton 
(D) Jute.
Answers
(C) Cotton 

4. In which areas saline soils are formed?
(A) Areas with high rainfall
(B) Areas of low rainfall
(C) Torrential rainfall
(D) Deserts.
 Answers
(D) Deserts.

5. Which soil has low pH value?
(A) Peat soils 
(B) Organic soils
(C) Saline soils 
(D) Acidic soils.
Answers
(A) Peat soils 

6. Which action does not have the strength of combination in soil?
(A) Water 
(B) Energy
(C) Air
(D) Erosion.
Answers
(D) Erosion.

7. In which areas is alkaline soil formed?
(A) High rain
(B) Low rainfall
(C) Torrential rain 
(D) In the desert.
Answers
(B) Low rainfall

8. How much expansion in volume takes place when water turns into ice?
(A) l/10th 
(B) l/20th
(C) l/5th 
(D) 1/11th.
Answers
(A) l/10th 

Very Short Answer Type Questions

Question 1. 
Name two processes involved in denudation.
Answer: 
Weathering and Erosion.

Question 2. 
What does the term denude mean?
Answer: 
To lay the rocks bare.

Question 3. 
From which word the term denudation is derived?
Answer: 
Latin word ‘denudare’.

Question 4. 
What is weathering?
Answer: 
Breaking up of rocks by agents related to atmosphere.

Question 5. 
Name three important agents of weathering.
Answer: 
Frost, wind, heat and cold.

Question 6. 
Name the three types of weathering.
Answer: 

• Mechanical (Physical) 
• Chemical 
• Biological.

Question 7. 
State four factors which determine weathering in an area.
Answer: 
Structure of rocks, slope of the land, climate, vegetation.

Question 8. 
What is the main process involved in Mechanical weathering?
Answer: 
Disintegration of rocks.

Question 9. 
What is exfoliation?
Answer: 
Peeling off the outer layers from main rock.

Question 10. 
What term is used for broken fragments by weathering?
Answer: 
Talus or Scree.

Question 11. 
What term is used for disintegration of rocks by frost?
Answer: 
Thaw freeze or Frost shattering.

Question 12. 
In which type of areas, is the frost action found?
Answer: 
In cold areas and in high mountains.

Question 13. 
Name an umbrella shaped rock mass found in India.
Answer: 
Toad rock in Rajasthan.

Question 14. 
What are earth pillars and where these found in India?
Answer: 
The soft rock pillars capped with hard rocks. In Spiti valley (H.P.)

Question 15. 
What are land slides?
Answer: 
When rocks slide down the slopes, under the force of gravity due to increased weight by rain water.
 
Question 16. 
What is bad-land?
Answer: 
An area dissected with gullies and ravines.

Question 17. 
Name a bad-land topography found in India.
Answer:
Chambal valley.

Question 18. 
What does the term ‘in situ’ mean?
Answer: 
When rocks are chemically weathered at the same place.

Question 19. 
Name the gases involved in the process of chemical weathering.
Answer: 
Weak acids, oxygen, carbon dioxide, hydrogen.

Question 20. 
What main process of breaking rocks is involved in chemical weathering?
Answer: 
Decomposition of rocks.

Question 21. 
Which is the gas involved in oxidation?
Answer:
Oxygen.

Question 22. 
Name the four processes of chemical weathering.
Answer: 
Oxidation, Hydration, Carbonation and Solution. 

Question 23. 
What is soil?
Answer: 
The uppermost layer of earth’s crust.

Question 24. 
Name the components of soils.
Answer: 
Minerals, humus, water, organisms.

Question 25. 
Name the different soil horizons.
Answer: 
A-Horizon (Topsoil), B-Horizon (Sub soil), C-Horizon (Mantle).

Question 26. 
Name the dead organic matter found in soils.
Answer: 
Humus.

Question 27. 
Which substance is the most important constituent of soil?
Answer: 
Silica.

Question 28. 
What do you mean by parent material? 
Answer: 
Rocks from which soil is derived.

Question 29. 
In which soil horizon, is humus found? 
Answer: 
Top soil.

Question 30. 
What is soil profile?
Answer: 
A cross-section of soil into layers.

Question 31. 
What is soil erosion?
Answer: 
The removal of topsoil.

Question 32. 
What is deforestation?
Answer: 
Reckless cutting of forests.

Question 33. 
What is afforestation?
Answer: 
Planting of trees in new areas.

Question 34. 
What is terraced agriculture?
Answer: 
Cultivation along terraces on hill slopes.

Question 35. 
What is contour ploughing 
Answer: 
Ploughing at right angles to the slope.

Question 36. 
What is Pedology?
Answer: 
The science that deals with study of soils.

Question 37. 
What is Eutrophication?
Answer: 
Enrichment of water with nutrients causing abundant plant growth.

Short Answer Type Questions

Question 1 
Why is the earth crust unstable? 
Answer: 
The earth crust is dynamic. Continents have been drifting. Drift has occurred horizontally as well as vertically. The internal forces operating from within the earth are also responsible for variation on the outer surface of the earth.

Question 2. 
Name the different external agents.
Answer: 
The following external agents bring changes on the surface of the earth :

• Weathering 
• River 
• Wind 
• Glacier 
• Sea-waves.

Question 3. 
On what factors does the weathering depend?
Answer: 
Weathering depends upon :
(a) structure of rocks 
(b) climate
(c) vegetation
(d) topography and slope of land.

Question 4. 
Name the gases which help in chemical weathering.
Answer: 
The following atmospheric gases help in the process of chemical weathering:

• Oxygen
• Hydrogen 
• Carbon dioxide.

Question 5. 
Name the main processes involved in chemical weathering.
Answer: 
The main processes involved in chemical weathering are:

• Oxidation 
• Carbonation
• Hydration 
• Solution.

Question 6. 
Gravity and Gradient help the movement of all types of materials. How?
Answer: 
Mass movements are aided by gravity and geomorphic agents like running water, glaciers, winds, etc. Without gravity and gradient, mass movement is not possible. Gravity starts the movement on the surface. All movements are caused due to gradient. From higher level to lower one, from high temperature to low temperature, and from high pressure to low pressure areas, movement takes place due to gravity and gradient.

Question 7. 
What is weathering?
Answer: 
The disintegration and decomposition of rocks (chemically and mechanically) by the agent s of weather and climate is called weathering. It is in situ as well as on site.

Question 8. 
What do you mean by enrichment?
Answer: 
When rocks undergo weathering, some materials are removed through chemical or physical leaching by groundwater and thereby the concentration of remaining (valuable) materials increases. Without such a weathering taking place, the concentration of the same valuable material may not be sufficient and economically viable to exploit, process and refine. This is what is called as enrichment.

Question 9. 
Name three types of mass movements.
Answer: 
Mass movements can be grouped into three major types :

1. Slow movement. 
2. Rapid movement.
3. Landslides.

Question 10. 
Explain the significance of weathering.
Answer: 

1. Weathering prepares the way for soil formation.
2. Weathering is responsible for erosion and mass movements.
3. Erosion cannot be significant if nodes are not weathered.
4. Landforms are a consequence of weathering. 
5. Weathering is an important process in the formation of soil.
6. It helps in the enrichment and concentration of valuable ores.

Question 11. 
Define soil.
Answer: 
The uppermost layer of the earth’s crust is called soil. It consists of a thin layer of loose material of rock waste. The soil consists of mineral particles, organic matter (humus), water, air and living organisms (bacteria).

Question 12. 
What is humus? How is it formed? What is its significance in soil formation?
Answer: Humus. Humus is a dark substance formed in soils. It is a dead organic matter formed by decay of animals and plants. Trees, shrubs, grass and bacteria help in the formation of humus. In warmer climates, humus is destroyed by countless bacteria. In colder areas soils are rich in humus and it is collected in the soil. Tropical humid soils are poor in humus because it is consumed by bacteria. Humus is vital to the fertility of soils. It provides nitrogen, phosphorus and calcium to the soils. It sustains other forms of life. It helps the weathering of minerals to add to fertility of soils. It increases water holding capacity of soils.

Question 13. 
Describe the work of frost in polar areas.
Answer: 
Frost. Frost is an important agent of weathering in cold climates and high mountainous areas. In such areas water enters the rocks through fissures cracks and joints. This water freezes into ice during the night and its volume increases 1/11 times. As it expands, it exerts pressure on the rocks which causes a widening of the cracks. There is repeatedly melting and freezing of water. It makes the cracks wider still. The action is similar to a wedge and is known as thaw freeze or Frost shattering. Finally, the rocks are split into blocks. Sharp- edged rocks are formed by repetition and long continued action of frost.

Question 14. 
How are earth pillars formed?
Answer: 
Earth pillars. Rain washes away soft material in clay regions. The boulders or hard rocks like a cap protect the underlying rocks with the result, earth pillars are formed. When the cap rocks fall, the earth pillars are destroyed. The examples of earth pillars are found in Bolzano (Italy) and Spiti valley (Himalayas).

Question 15. 
What is oxidation and carbonation?
Answer: 
Oxidation. The atmospheric oxygen combines with minerals of rocks especially iron compounds to form oxides. With the result, rocks get rusted as iron is rusted due to presence of air and water. The original colour of the rocks changes into red, yellow or brown. The rocks begin to decay and crumble to a powdered mass of brown dust. This process is known as oxidation. Carbonation. Rain water mixed with carbon dioxide is slightly acidic. It dissolves limestone, chalk and marble rack. In limestone areas, this acid water sinks into the ground and forms huge caves by a slow process of carbonation.

Question 16. 
Describe the importance of soils.
Answer: 
Soil is a valuable natural resource. Mankind has lived and continues to live on the soils. Many human and economic activities depend upon soils. All our food comes directly or indirectly from soils. Livestock farming depends upon raising of grass on different soils. Soils form an important element for all living things. Soils have affected the march of civilizations. Ancient civilizations developed in fertile river valleys. Fertile soils attract human settlements.

Question 17. 
What are the functions of soil for which it needs to be preserved?
Answer: 
Soil has a great significance for mankind as a basic natural resource. It occupies a significant place in the biosphere. Good soils lay the basis of a flourishing agriculture and human habitation. Due to soil erosion, productivity is reduced. Soils are the basis for providing food stuffs and agricultural raw materials for industries. Therefore, all measures are adopted to preserve soils.

Question 18. 
Distinguish between Geomorphic agent and Geomorphic process.
Answer: 
Any exogenetic element of nature (like water, ice, wind, etc.) capable of acquiring and transporting earth materials can be called a geomorphic agent. When these elements of nature become mobile due to gradients, they remove the materials and transport them over slopes. That means, immobile they affect the materials and mobile they remove, transport and deposit the same.

Geomorphic processes and geomorphic agents especially exogenetic, unless stated separately, are one and the same. A process is a force applied on earth materials affecting the same. An agent is a mobile medium (like running water, moving ice masses, wind etc.) which removes, transports and deposits earth materials. Running water, groundwater, glaciers, wind, waves and currents, etc., can be called geomorphic agents.

Question 19. 
Describe the various factors helping mass movements.
Answer: 
Several activating or initiating causes precede mass movements. They are 

1. removal of support from below to materials above through natural or artificial means
2. increase in gradient and height of slopes, 
3. overloading through addition of materials naturally or by artificial filling, 
4. overloading due to heavy rainfall, saturation and lubrication of slope materials
5. removal of material or load from over the original slope surfaces
6. occurrence of earthquakes, explosions or machinery vibrations
7. excessive natural seepage
8. heavy drawdown of water from lakes, reservoirs and rivers leading to slow outflow of water from under the slopes or river banks
9. indiscriminate removal of natural vegetation. Heave (heaving up of soils due to frost growth and other causes), slide and flow are the three forms of movements.

Question 20. 
What do you mean by Diastrophism? Which processes are included in it?
Answer: 
Diastrophism. All processes that move, elevate or build up portions of the earth’s crust come under diastrophism. 

They include : 

1. orogenic processes involving mountain building through severe folding and affecting long and narrow belts of earth’s crust
2. repair- ogenic processes involving uplift or warping of large parts of the earth’s crust
3. earthquakes involving local, relatively minor movements
4. plate tectonics, involving horizontal movements of the crustal plates.

In the process of orogeny, the crust is severely deformed into folds. Due to epeirogeny, there may be simple deformation. Orogeny is a mountain building process whereas epeirogeny is a continental building process. Through the processes of orogeny, epeirogeny, earthquakes and plate tectonics, there can be faulting and fracturing of the crust. All these processes cause pressure,volume and temperature (PVT) changes which in turn induce metamorphism of rocks.

Question 21. 
On what forces does the physical weathering depend?
Answer: 
Physical weathering is also called mechanical weathering. The applied forces can be :

1. Gravitational forces such as over burden pressure, load and shearing stress, 
2. Expansion forces due to temperature changes, crystal growth or animal activity. 
3. Water pressure controlled by wetting and drying cycles.

These forces lead to rock failure or fracture. Most of the physical weathering processes are caused by thermal expansion and pressure release. 

Comparison Questions

Question 1. 
Distinguish between the following pairs :
Rock and Soil.
Answer: 
Rock and Soil. Any natural solid inorganic or organic material out of which the crust of the earth is formed is called a rock. But the soil is uppermost covering of the rocks. These rocks break up and rock particles are formed. These particles constitute soils. Rocks are aggregate of minerals. These minerals of the parent rock form the inorganic matter in soils. Soils are limited in depth. These are found upto a depth of 2 to 3 metres, but rocks have a greater depth. Rocks are found in the interior parts, while soil is found only on the outer surface of the earth.

Question 2. 
Distinguish between the following pairs :
Decomposition and Disintegration of Rocks.
Answer: 
Decomposition. The decay of rocks by chemical means or process is called decomposition. It produces a chemical change in minerals at their original places. It results from the action of atmospheric gases. It does not involve any motion of minerals of rocks. Rocks are weakened and crumbled to a powdered mass. Disintegration. It means the breaking of rocks into loose fragments without changing their mineral composition. It is the work of mechanical weathering done by insolation, frost, rainfall, wind, etc. A series of joints or cracks develop into rocks. Rocks split and are broken into pieces. Disintegration occurs at rock places. It is important in dry areas.

Question 3. 
What do you mean by Regolith?
Answer: 
The world’s different landscapes have been made mainly by the action of weather on rocks. The term rock weathering is used to describe chemical decomposition and physical disintegration of rocks. Lying above the bedrock may be a layer of loose material, the regolith (rego-blanket, lith-rock). Regolith is a term that can be used broadly to refer to any layer of relatively loose or soft material lying on the bedrock. When regolith is formed by decomposition and disintegration of the bedrock that lies directly beneath it, it is called residual regolith. The regolith transported by streams, ice, wind and deposited elsewhere is called transported regolith.

Essay Type Questions

Question 1. 
Define weathering. Explain the work of weathering by different agents.
Answer: 
Weathering. Weathering involves breaking up of rocks by process of disintegration and decomposition. This results from the work of natural agents related to atmosphere. The rocks are broken into fragments by integration through external agents. The rocks are decayed due to chemical changes and the process is called decomposition. Weathering occurs where rocks are situated. Weathering helps erosion by exposing rocks to break.

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.
2. Slope of the land. Weathering is active on steep slopes.
3. Climate. Mechanical weathering predominates in dry areas, while chemical weathering operates 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 and help weathering.

Types of Weathering. There are two main types of weathering:

1. Physical or Mechanical weathering.
2. Chemical weathering.

(A) Physical weathering: 
It is also known as Mechanical weathering. It includes the disintegration of rocks without changing their mineral composition. This type of weathering results from the action of temperature changes, frost, wind and rainfall.
It is an in-situ or on site process. The physical weathering depends upon:

• Gravitational forces
• Shear stress
• Expansion due to temperature changes.
• Wet and dry cycles.
• Thermal exhaustion and pressure release.

1. Temperature changes. There is a great daily range of temperature in deserts. During the day time, rocks are heated greatly and expand. But at night, temperatures fall and these rocks begin to contract. There is rapid expansion and contraction of rocks everyday. With the result, a series of cracks of joints develop in the rocks. Rocks split and are broken with a sound like the shot of a gun. Rocks are split by granular or block disintegration. These broken fragments are called Talus or Scree. In homogeneous rocks, weathering takes the form of exfoliation. Due to the alternate expansion and contraction of rocks, the outer layers peel off from the main mass. The process of removal of thin shells of rocks is known as exfoliation.

2. Frost. Frost is an important agent of weathering in cold climates and high mountainous areas. In such area, water enters the rocks through fissures, cracks and joints. This water freezes into ice during the night and its volume increases 1/11 times. As it expands, it exerts pressure on the rocks which causes a widening of the cracks. There is repeated melting and freezing of water. It makes the cracks wider still. The action is similar to a wedge and is known as thaw freeze or Frost shattering. Finally the rocks are split into blocks. Sharp-edged rocks are formed by repetition and long continued action of frost. This process is known as freezing, thawing and Frost wedging.

3. Rainfall. Rainwater takes the form of running water and affects weathering in the following ways :
(a) Soil erosion. Running water scoops out gullies along the slopes and washes away fine soil to create a serious problem of soil erosion.

(b) Bad land. Running water forms a highly dissected land surface with gullies and ravines. Such an area is called bad land such as in Chambal valley.

(c) Earth pillars. Rain washes away soft material in clay regions. The boulders or hard rocks like a cap protect the underlying rocks. As a result, earth pillars are formed. When the cap rocks fall, the earth pillars are destroyed. The examples of earth pillars are found in Bolzano (Italy) and Spiti valley (Himalayas).

(d) Landslides. Rainwater increases the weight of the rocks which hold it. With the result, rocks slide down the slopes under the force of gravity.

4. Wind. Wind’s mechanical weathering is important in deserts and arid areas. The dust-laden wind acts as a sand blast and produces fantastic weathering results.
(a) The trains passing through deserts are to be repainted very frequently due to effect of weathering.
(b) Telegraph wires are eroded by wind action.
(c) The windows facing seashore are weathered so that plain glasses look like frosted glasses.
(d) Rocks are fantastically weathered such as Toad Rock in Rajasthan. Umbrella like rocks are formed due to undercutting.

5. Salt Weathering. Salts in rocks expand due to thermal action hyderation and recrystalisation. High temperatures (30°C - 50°C) in deserts favour such exhausion. In such areas, chalk breaks down most readily.
(B) Chemical weathering. The decomposition of rocks by chemical processes is called chemical weathering. Chemical weathering results from the action of weak acids, and gases like oxygen, carbon dioxide and hydrogen. Chemical weathering produces a chemical change in the minerals of rocks. High temperatures and humidity cause the rocks to decompose. Chemical weathering is done through following four processes :

(a) Oxidation. The atmospheric oxygen combines with minerals of rocks especially iron compounds to form oxides. With the result, rocks get rusted as iron is rusted due to presence of air and water. The original colour of the rocks change into red, yellow or brown. The rock begins to decay and crumbles to a powdered mass of brown dust. This process is known as oxidation.

(b) Hydration. The chemical union of water with a mineral is called hydration. When rain water enters the rocks it increases the volume of rocks. As a result, the pressure reduces the minerals to powder. Felpar is reduced to Kaolin due to hydration.

(c) Carbonation. Rain water mixed with carbon dioxide is slightly acidic. It dissolves limestone, chalk and marble rocks. In limestone areas, this acid water sinks into the ground and forms huge caves by a slow process of carbonation.

(d) Solution. Some of the minerals like rock salt and gypsum are dissolved in water. These minerals are removed in solution from the rocks. This process is known as solution.

Question 2. 
Describe a typical soil profile.
Answer: 
Three well-marked layers of soil are found above the bedrock. These horizontal layers are called soil horizons. The order of these layers over the bedrocks is called soil profile. Three layers, well-marked in a soil profile are as under : 1. A-Horizon. This is the uppermost layer of the soil profile. It contains organic matter. It has a fine soil rich in humus. This is also called Top Soil. Bacteria and earthworms live in the lower part of this horizon. This is also called a zone of eluviation because the mineral solution is carried downwards by leaching of soil.

2. B-Horizon. This is called sub-soil also. It is a zone of accumulation where the leached material from A-Horizon is retained. It is also known as a zone of alluviation. This layer is compact and contains sand, silt and clay. 

3. C-Horizon. This layer contains weathered rock material. C-Horizon is often known as mantle. Below this is underline bedrock, known as D-Horizon.

Question 3. 
Explain various forms of mass wasting.
Answer: 
MASS WASTING:
The force of gravity acts constantly upon all soil, regolith and bedrock. Wherever the ground surface is sloping, force of gravity is directed downslope parallel with the surface. Every particle has at least some tendency to roll or slide downhill and will do so whenever the downslope force exceeds. The material sliding downslope is called mass wasting.

Forms of mass wasting : 
The forms of mass wasting range from the land catastrophic slides to the small flows of water saturated soil. Its forms are :

• Falls 
• Topples 
• Slides 
• Flows.

(1) Soil creep: Careful inspection of hillside often discloses evidence that the soil has been very slowly moving downslope rather steadily over a long period of time. This phenomenon is called soil creep. It is the result of shear distributed along countless joint fractures and bedding or cleavage surface in the rock.

(2) Earth flow: In hilly and mountain-ous regions of humid climate, water-saturated soil and regolith rich in clay minerals take the form of an earthflow. Earthflow is a form of mass wasting in which behaviour of the earth material is that of a plastic solid. Solifluction is an arctic variety of earthflow in the treeless tundra.

(3) Mudflow : Mass wasting takes the form of mudflow if proportion of water to mineral matter is large. It travels fast down the channels of streams. Mudflows also originate high in mountains where melting winter snow picks up weathered rocks rich in clay.

(4) Landslides: Along vertical rock cliff, the process of physical weathering loosens the rocks. When the force of gravity brings them down they are described as rockfalls. The falling rock masses break into smaller fragments to form a slope of loose materials called talus. Sliding of a single block on its lower surface is called rockslide. When a block slips on curved fracture plane rotating backward upon a horizontal axis, it is known as slump.

4. What is disintegration? What are its types?
Answer: 
Weathering includes decomposition and disintegration of rocks. Regolith (Rego = Blanket lith = Rock) is the layer of loose material broken like residual regolith, transported regolith. Disintegration is due to mechanical weathering by different agents.
(1) Frost action: In middle and high latitude climates and at high altitudes alternate freezing and melting of water called frost action provides powerful mechanism for breaking up of rocks.

(2) Salts: In the dry climates of low and middle latitudes, an important agent of rock disintegration is salt. The dry climates have long droughts in which evaporation can occur continuously causing water deep in the rock to be drawn surfaceward by capillary force. Near the rock surface, this moisture steadily evaporates permitting dissolved salts to be deposited in openings of the rock. Although minute in size and appearing fragile, the growing salt crystals are capable of exerting powerful stresses.

(3) Temperature changes: Temperature changes are also a factor in the disintegration of rocks. Daily temperature changes may not cause rock disintegration, but repeated expansion and contraction assist in breaking up of rocks already affected by other stresses and by chemical decay.

(4) The action of the roots of growing plant :
These exert pressure upon the confining walls of regohth or rock is yet another kind of mechanical weathering. This process is especially important in the breakup of rock already weakened by other physical and chemical means Rock first of all breaks into block called block disintegration, then into grains called granular disintegration. Some rocks disintegrate like skins of onions, which are called spheroidal weathering or exfoliation

Question 5. 
Describe the different processes of physical weathering.
Answer: 
Physical Weathering Processes. Physical or mechanical weathering processes depend on some applied forces. The applied forces could be : 
(i) gravitational forces such as overburden pressure, load and shearing stress, 

(ii) expansion forces due to temperature changes, crystal growth or animal activity, 

(iii) water pressures controlled by wetting and drying cycles. Most of the physical weathering processes are caused by thermal expansion and pressure release. These processes are small and slow but can cause great damage to the rocks because of continued fatigue the rocks suffer due to repetition of contraction and expansion umpteen times.

(1) Unloading and Expansion : Removal of overlying rock load because of continued erosion causes vertical pressure release and with the result the upper layers of rock expand producing failure and consequently disintegration of rock masses. Fractures will develop roughly parallel to the ground surface. In areas of curved ground surface, arched fractures tend to produce massive sheets or exfoliation slabs of rock. Deep seated igneous rocks under as much as 25,000 or more pounds of pressure per square inch expand due to erosion of overlying rocks and consequent reduction of pressure. Exfoliation sheets resulting from expansion due to unloading and pressure release may measure hundreds or even thousands of feet in horizontal extent. Large, smooth rounded domes called exfoliation domes result due to this process.

(2) Temperature Changes and Expansion :
Various minerals in rocks possess their own limits of expansion and contraction. With rise in temperature every mineral expands and crowds against its neighbour and as temperature falls, a corresponding contraction takes place. Because of diurnal changes in the temperatures, this internal movement among the mineral grains of the superficial layers of rocks takes place regularly. This process is most effective in dry climates and high elevations where diurnal temperature changes are drastic. As has been mentioned earlier though these movements are very small they make the rocks weak due to continued fatigue. 

The surface layers of the rocks tend to expand more than the rocks at depth and this leads to the formation of stress within the rock resulting in heaving and fracturing parallel to the surface. Due to differential heating and resulting expansion and contraction of surface layers and their subsequent fall-off as flakes (exfoliation) from the surface results in smooth rounded surfaces in rocks. In rocks like granites, smooth surfaced and rounded, small to big boulders called tors form due to such flaking or exfoliation.

(3) Freezing, Thawing and Frost Wedging: Frost weathering occurs due to growth of ice within pores and cracks of rocks during repeated cycles of freezing and thawing (melting). This process is most effective at high elevations in mid-latitudes where freezing and thawing is repeated often. Glacial areas are subject to frost wedging daily. The pressure exerted by frozen water is about 2000 pounds per square inch. In this process, rate of freezing is important. Rapid freezing of water causes its sudden expansion and high pressure. The resulting expansion affects joints, cracks and small inter-granular fractures to become wider and wider till rock breaks apart. Heaving and thrusting due to ice crystal growth in pore spaces of soils is quite significant.

(4) Salt Weathering : Salts in rocks expand due to thermal action, hydration and crystallisation. Many salts like calcium, sodium, magnesium, potassium and barium have high coefficients of volumetric expansion. Expansion of these salts depends on temperature and their thermal properties. High temperature ranges between 30° and 50°C and up to 80°C of surface temperatures in deserts favour such salt expansion. Salt crystals in near-surface pores cause splitting of individual grains within rocks, which eventually fall off. This process of falling off of individual grains may result in granular disintegration or granular foliation. Under chemical weathering processes, hydration and dehydration of salts results in volume changes and cause expansion.

Source Based Questions

1. Read the following paragraph and answer the questions given below:
In our country where we live, debris avalanches and also landslides occur very frequently in the Himalayas.There are several reasons for this. Such as Himalayas are technically active. These areas mostly made up of sedimentary rocks and unconsolidated and semi- consolidated deposits. These slopes are very steep compared to the Himalayas. Nilgiris bordering T.N, Karnataka, Kerala and the western ghats along with west coast are mainly tectonically stable and mainly made up of very hard rocks. Still, debris avalanches or landslides occur not as fast as in the hilly areas of Himalayas. Several slopes are steeper with almost vertical cliffs and escarpment in the western ghats and Nilgiris.

(i) Where debris avalanches and landslides occur?
(a) Plains 
(b) Plateaus
(c) Mountains 
(d) Himalayas
Answer: 
(d) Himalayas

(ii) Which of the following is a reason of landslides?
(a) Tectonically active
(b) Mostly made of sedimentary rocks
(c) Unconsolidated deposits
(d) All of these
Answer: 
(d) All of these

(iii) Which of the following areas are relatively tectonically stable?
(a) Tamil Nadu 
(b) Karnataka
(c) Kerala 
(d) All of these
Answer: 
(d) All of these
 
2. Read the following paragraph and answer the questions given below:
There are several factors that control the soil formation. These are parent material, topography, climate, biological activity and time. These are the basic factors that control the soil formation. A passive control factor in soil formation is parent material. This can be any in situ or on situ weathered rock debris, like parent material topography is another passive control factor. Climate is a significant factor in soil formation. The climatic elements such as moisture, temperature etc. involved in soil development. Precipitation gives soil its moisture content, which makes the chemical and biological activities.
(i) How many basic factors are there for soil formation?
(a) 4
(b) 5
(c) 6
(d) 7
Answer:
(b) 5

(ii) Which of the following a passive control factor in soil formation?
(a) Parent material 
(b) Climate
(c) Moisture 
(d) Temperature
Answer: 
(a) Parent material

(iii) Which of the following is an element involved in soil development?
(a) Moisture 
(b) Precipitation
(c) Temperature 
(d) All of these
Answer: 
(d) All of these 
  
HOTS QUESTIONS 

Question 1
Which forces are generated due to Gravity? 
Answer: 
Gravitational force acts upon all earth materials having a sloping surface and tends to produce movement of matter in down slope direction. Force applied per unit area is called stress. A stress is  produced in a solid by pushing or pulling. This induces deformation. Forces acting along the faces of earth materials are shear stresses (separating forces). It is this stress that breaks rocks and other earth materials. The shear stresses result in angular displacement or slippage. 

SELF EVALUATION TEST 

1. Name the two types of agents of change. 
2. What does the term denude mean? 
3. Name two agents of weathering. 
4. What is bad land? 
5. What are landslides? 
6. What are earth pillars? 
7. Name the different soil horizons. 
8. What is soil erosion? 
9. State four factors determining weathering in an area. 
10. Explain the significance of weathering.