NCERT Class 11 Geography Chapter 6 Geomorphic Processes

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NCERT Class 11 Geography Chapter 6 Geomorphic Processes

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Geomorphic Processes

Chapter: 6

GEOGRAPY [ PART – I ]

SHORT ANSWER TYPE QUESTIONS

Q.1. What are soils?

Ans. Soils are products of a complex mixture of weathered and eroded rock material on the one hand and the organic matters on the other.

Q.2. What is humus?

Ans. The decomposition of plants and microorganisms releases organic chemicals that interact with the loose materials is called humus.

Q.3. Name the primary factors responsible for the development of soils.

Ans. The primary factors responsible for the development of soils are:

1. Parent material.

2. Climate.

3. Biological Activity.

4. Topography.

5. Time.

Q.4. Why earth is uneven?

Ans. Due to internal and external forces earth is changing its surface conditions. The earth crust is always dynamic. It moves vertically and horizontally. The differences in the internal forces making the surface uneven wearing down of relief features is called gradation. The endogenic forces always elevate parts of the earth’s surface and hence the exogenic processes fail to even out of the relief variations of the surface of the earth. The surface of the earth is sensitive. Human being is using the surface intensively and extensively.

Q.5. How is young soil distinguished from mature soil? Explain briefly.

Ans. A soil becomes mature when all soil forming processes act for a sufficiently long time developing a distinctive soil profile.

Soils developing from recently deposited alluvium or glacial actions are young and they exhibit no horizons or only poorly developed horizons.

Q.6. What is the difference between orogeny and epeirogeny?

Ans. 

Orogeny	Epeirogency
1.Crust is severely demaged.	1.Simple deformation.
2. Mountain building process is continue.	2. Continental formation.
3. Folding and Faulting cause tension and compression.	3. Upliftment of landmass.

Q.7. What is chemical weathering?

Ans. The decomposition of rocks by chemical process is called chemical weathering. Chemical weathering results from the action of weak acids and gases like oxygen, carbon dioxide, hydrogen. Chemical weathering produces a chemical change in the minerals of rocks. High temperatures and humidity cause the rocks to decompose.

Q.8. What do you mean by denudation?

Ans. All the exogentic geomorphic process is covered under a general term denudation. The word denudes means to strip off or to uncover weathering mass wasting, erosion and transportation are the types of denudation process.

Q.9. Describe the work of frost in polar areas.

Ans. Frost is an important agent of weathering in cold climates and high maintainous areas. In such areas water enters the rocks through fissure cracks and joints. This water frizzes into ice during the night and the volume increases. 1/11 times. As it expands it exert pressure on the rocks which can 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 than freeze or frost shattering. Finally the rocks are split into blocks. Sharp edged rocks are formed by repetition and long continued action of frost.

Q.10. Name the physical properties of soil.

Ans. The physical properties of soil are:

(i) Texture.

(ii) Structure. and

(iii) Colour.

Q.11. What are the chemical properties of soil?

Ans. (i) Lime content.

(ii) Soluble salts.

(iii) Air in soil.

(iv) Humus.

Q.12. What is weathering?

Ans. Breaking of rocks by agents related to atmosphere is called weathering.

Q.13. Name three types of weathering.

Ans. 1. Mechanical.

2. Chemical.

3. Biological.

Q.14. What is exfoliation?

Ans. Peeling of the outer layers from main rocks.

SHORT ANSWER TYPE QUESTIONS

Q.1. What are the various mobile and mighty exogenic geomorphic agents and what is the prime job they perform?

Ans. The various mobile and mighty geomorphic agents are flowing water, glaciers and wind. Their prime jobs are: 

(i) wearing down the relief.

(ii) transportation. and

(iii) filling up of basins or depressions on the earth’s surface.

Q.2. It is weathering that is responsible for biodiversity on the earth. How?

Ans. Weathering processes are responsible for the biodiversity on the earth. Biomes or biodiversity is basically a result of forests and forests depend upon depth of weathering mantles. Barrowing and wedging by organism like earthworms, termites rodents etc. help in exposing the surface to chemical attack and assists in the penetration of moisture and air. Men by disturbing vegetation ploughing and cultivating soils also helps in mixing and creating new contracts between air water and minerals in the earth materials. Decaying plant and minerals matter help in the production of carbonic and other acids which enhance decay and solubility of some elements.

Q.3. What are mass movements that are real rapid and perceptible? List.

Ans. Mass movements are those movements involving transfer of mass of rock debris down the slopes under the direct influence of gravity without assistance of kinetic energy of any geomorphic agent. Some of the mass movements that are real rapid and perceptible are:

(i) Earth flow.

(ii) Mud flow.

(iii) Avalanche.

Q.4. What do you mean by Regolith?

Ans. The world’s different landscapes have been made mainly by the action of weather on rocks. Regolith is a term that can be used broadly to refer to any layer of relatively loose or soft material lying on the bed rock. When regolith is formed by decomposition and disintegration of the bed rock that lays directly beneath it, it is called residual regolith. The regolith transported by streams ice wind and deposited else where is called transported regolith.

Q.5. Distinguish between:

(i) Soil and Rock.

Ans. 

Soil	Rock
1. Soil is formed due to erosion and weathering of rocks. Hence, it is an unconsolidated rock material.	1. A rock is naturally occurring mass of solid materials. It is composed of inorganic or organic material.
2. Soil has layers which have different physical, chemical and biological properties.	2. Rock does not have layers.
3. Soils are the sources of food and moisture for plants.	3. It is not the source of food and moisture for plants.

(ii) Eluviation and Illuviation.

Ans. 

Eluviation	Illuviation
It is the mechanical translocation of clay or other fine particles down the soil profile.	It is the accumulation of the washed down (eluviated) material in the lower horizons of the soil profile.

(iii) Cheluviation and Leaching.

Ans. 

Cheluviation	Leaching
It is the downward movement of material similar to the leaching but under the influence of organic complex compounds.	It is the removal and downward movement of material from a horizon in a solution.

(iv) Earth flow and Mud flow.

Ans. 

Earth flow	Mud flow
In hilly and mountainous regions of humid climates, water saturated soil and regolith rich in clay matters takes the form of an earth flow. Earth flow 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 earth flow in the treeless tundra.	Mass wasting takes the form of mud flow if proportion of water to mineral matter is large. It travels fast down the channels of stream. Mud flow also originate high in mountains where melting winter snows pick up weathered rocks rich in clay.

Q.6. Distinguish between Mechanical and Chemical Weathering.

Ans.

Mechanical Weathering	Chemical Weathering
1. It is also called physical weathering.	1. Chemical weathering includes the processes that cause rock to rot or decay due to the action of air and water on the minerals present in the rock.
2. It is responsible for the disintegration of rocks without changing their chemical compositions.	2. High temperature and humidity caused the rock to decompose.
3. It is caused about mainly by changes in temperature and the pressing action of water.	3. Chemical weathering results from the action of weak acids and gases like oxygen, carbon dioxide and hydrogen.
4. It is physical break up of rocks owing to internal and external stresses caused by weathering agents.	4. It is the process which leads to the decomposition or decay of solid rocks by means of chemical reactions.

Q.7. Without gravity and gradient there will be no erosion. Discuss.

Ans. Gravity besides being a directional force activating all down slopes movements of matter also causes stresses on the earth materials. Indirect gravitational stresses activate wave and tide induced currents and winds. Without gravity and gradation there would be no mobility and hence no erosion, transportation and deposition are possible. So gravitational stresses are as important as the other geomorphic processes. Gravity is the force that is keeping us in contact with the surface and it is the force that switches on the movement of all surface earth materials. All movements either within the earth or on the earth’s surface occur due to gradients from higher levels to lower levels, from higher temperature zones to lower temperature zones from high pressure to low pressure areas etc.

Q.8. What is oxidation?

Ans. Oxidation: The atmospheric oxygen combines with the minerals of rocks especially iron compounds to form oxides. With the result rocks get rusted as iron is rusted dur to presence of air and water. The original colour of rocks changes into red, yellow or brown. The rocks begins to decay and crumble to a powered mass of brown dust. This process is known as oxidation.

Q.9. Is weathering essential as a prerequisite in the formation of soils? Why?

Ans. Weathering plays an important role in the formation of soils. Rock debris is generated out of the weathering process. It is the weathering mantle which is the basic input for the soils to form.

Q.10. What is carbonation?

Ans. Carbonation: Rain water mixed with carbon dioxide is slightly acidic. It dissolves limestone chalkened marble rock. In limestone areas this acid water sinks into the ground and forms huge caves by a slow process of carbonation.

LONG ANSWER TYPE QUESTIONS

Q.1. “Our earth is a playfield for two opposing groups of geomorphic processes.” Discuss.

Ans. It is correct to say that our earth is a playfield for two opposing groups of geomorphic processes. We know that the earth’s crust is dynamic and it moves vertically and horizontally. The internal forces of the earth operating within the earth which build up the crust have also been responsible for the variation in the outer surface of the crust. The external forces are involved to degrade the landforms built up by the internal forces. The action of the exogenic forces result in wearing down of relief of elevation and filling up of basins on the earth’s surface.

The endogenic forces continuously elevate or build up parts of the earth’s surface and hence the exogenic processes fail to even out the relief variations of the surface of the earth. Thus variation remains as long as the opposing actions of exogenic and endogenic forces continue. So in this way our earth is a playfield for two opposing groups of processes.

Q.2. Are physical and chemical weathering processes independent of each other? If not, why? Explain with examples.

Ans. No, physical and chemical weathering processes are not independent of each other. Physical or mechanical weathering processes depend on some applied forces leading to rock stress or fracture, while in chemical weathering, processes like carbonation, hydration, oxidation, solution and reduction act on the rocks to decompose, dissolve or reduce them to a fine classic states. No chemical weathering takes place without the production of physical stresses and no disintegration of rocks by thermal expansion probably occurs in the absence of the chemical process associated with the presence of water.

Q.3. Discuss the factors responsible for soil formation and also the process involved.

Ans. The following factors are responsible for the soil formation:

(i) Parent Material: The parent material is derived from the rocks. The chemical and mechanical weathering, weather the rock and produce the parent material. It is incorporated by biological remains. As the rocks are comprised of various minerals, the mineral contents are present in the parent rock. Calcium, phosphorus, nitrogen, potassium and sodium contents are found in the soil. These mineral contents and the biological remains determine the properties of the soil.

(ii) Climate: Climate plays an important role in the soil formation. It acts directly or indirectly. Weathering is the direct action of climate in soil formation. It depends upon the rain water and temperature. The biological action is the indirect action of climate in soil formation. It depends upon the temperature. The biological activities are limited in cold climates and intensive in humid, tropical and subtropical climate areas.

Besides, a long period action of climate reduces the differences caused by parents materials. Where there is short period action of the climate, the properties of parent material reflect the soil. Hence the same parent material may produce two types of soil in two climatic regions and two different parent materials may produce a single type of soil in a particular climate region.

For example, the sandy soils of the desert are derived from sandstone and granite rock as well. These soils are formed under the hot desert climatic conditions. On the other hand, crystalline granite rocks produce laterites in the moist climate conditions of Rajmahal hills and the dry chilka soil in the drier regions of Andhra Pradesh.

(iii) Biological Activity: Biological organisms also play an important role in the soil formation. Plant life consists of trees, shrubs, grasses, bacteria and fungi. Dead plants provide humus to the soil. Humus maintains the fertility of the soil.

The climatic conditions determine the activities of the living organisms (bacteria and fungi). These organisms are more active in humid tropical and sub-tropical climatic regions and their activities are limited in cold climatic areas. Hence, they consume humus and make the soil poor in tropical and sub-tropical regions and rich in cold climatic areas because of the limited activities of living organisms. Thus the soils of humid tropical and sub-tropical climatic regions are poor and the soils of cold climatic regions are rich.

Moreover, the acidity formed by humus is also limited in the soils of humid tropical regions. Hence, a high proportion of mineral contents are found in the soils of these regions. These mineral contents also make the soils poor. Bacteria also change the gaseous nitrogen of the air into chemical form which can be consumed by plants.

(iv) Topography: Like parent materials, topography of a region is a passive control factor in the soil formation. The topography determines the amount of exposure of a surface covered by the parent materials to sunlight and the amount of surface and subsurface drainage over and through the parent materials. Soils will be thin on steep slopes and thick over flat upland areas. Soil formation is particularly favourable on gentle slopes where erosion is slow and percolation of water is good. Accumulation of organic matter giving the soil dark colour, with thick layers, is observed over flat areas. In mid-latitudes, the south facing slopes exposed to sunlight have different conditions of vegetation and soils and the north facing slopes with cool, moist conditions have some other soils and vegetation.

(v) Time: It is the most important factor in the soil formation. The length of time the soil forming processes operate, determines maturation of soils and profile development. When the soil-forming processes act for a sufficiently long time, developing a distinctive soil profile, the soil becomes mature. Soil developing from recently deposited alluvium or glacial till are considered young and they exhibit no horizons or only poorly developed horizons. There is no specific time frame of the maturation for the soils.

Q.4. Which are the physical attributes of soils?

Ans. The physical attributes of the soil are -texture, structure, colour and capacity to hold water.

Soil Texture: It refers to the particle sizes comprising the soil. The particles are classified as gravel, sand, silt and clay in decreasing order of size. Four texture types are recognised. These are:

(i) sand.

(ii) sand-loam.

(iii) loam and

(iv) clay.

All the texture types are combinations of different sizes of particles. Soil texture determines the water carrying capacity of the soils.

Soil Structure: It refers to the arrangement in which soil grains are grouped together into large pieces. Major types of structures are -bulky, granular, columnar, prismatic, crumb and platy. Soil structure influences the absorption of water by the soil, its erodibility and ploughing.

Soil Colour: It indicates the origin and composition of the soil. Increasing quantities of humus produce a range from white, brown to black. The presence of iron oxides and hydroxides gives it red and yellow colours.

Water Carrying Capacity: It refers to the capacity of the soil to absorb water from rain as well as from air and its capacity, to hold it.

Q.5. Discuss in what different ways weathering takes place.

Ans. Weathering refers to the disintegration or decomposition of rocks in-situ or on-site. Weathering is the process by which the rocks exposed on the surface get broken up into smaller particles. It is different from agents of erosion in the way that weathering takes place in-situ i.e.; rocks break down at the place where they occur.

The chief agents of weathering are temperature, frost, air and rain. Weathering helps erosion but it is not a part of erosion. There can be weathering without erosion and erosion too without weathering.

There are three main types of weathering:

1. Physical or Mechanical.

2. Chemical. and

3. Biological.

Physical or mechanical weathering is responsible for disintegration of rocks or development of stresses in them. It is brought about mainly by changes in temperature and freezing action of water.

Chemical weathering is the process that causes rocks to rot or decay due to the action of air and water on the minerals present in the rocks.

Biological weathering takes place by plants and animals. Grazing by large animals uncovers the soil, thus increasing surface run off and soil erosion. Cracks may be caused and widened by root pressure of plants.

Q.6. How mechanical weathering takes place in cold and hot regions?

Ans. Mechanical weathering, which is responsible for the disintegration of rocks without changing their chemical composition is brought about by the changes in temperature in hot regions and freezing action by water in cold regions.

Weathering in Cold Regions: Weathering in the cold regions take place due to the action of freezing water. In these regions, water in the cracks or joints in rocks freezes and it increases its volume and the rock requires more space which causes progressive widening of the cracks in rock and the rock is ultimately split into pieces or blocks. It is also known as frost weathering.

Weathering in Hot Regions: Weathering in hot regions, particularly in deserts take place due to temperature changes. In these regions, the bare rocks are heated and get expanded. Different minerals which constitute the rock react to the heat differentially. The rate of expansion and contraction of these minerals differs. As a result, cracks and joints develop in the rock layers which ultimately split it up into angular blocks of fragments or grains.

The alternate expansion and contraction of outer rock layers is more than the inner layers. The outer layers are peeled off from the main mass of the rock in the form of concentrate slide. This kind of weathering is call exfoliation.

Q.7. Explain various forms of Mass wasting.

Ans. Mass wasting: The force of gravity acts constantly upon soil regolith and bed rock. Wherever the ground surface is sloping, force of gravity is directed downslopes. The material sliding downslope is called mass wasting. The following are the forms of mass wasting:

(i) Soil creep: Often on the slopes of mountain the soil has been very slowly moving downslopes rather steadily over a long period of time. This phenomenon is called soil creep.

(ii) Earth Flow: In hilly and mountainous regions of humid climate water saturated soil and regolith take the form of earth flow. Earth flow is a form of mass wasting in which behaviour of earth material is that of plastic solid. Solidification is an arctic variety of earth flow in the treeless Tundra.

(iii) Mudflow: Mass wasting taking the form of mud flow if proportion of water to mineral matter is large. It travels fast down the channels of streams. Mud flow also originate high in mountains where melting winter snow picks up weathering rocks in day.

(iv) Landslides: A long vertical rockcliff the process of physical weathering loose the rocks. When the force of gravity bring from down they are described rock falls. 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 to rotating backward upon a horizontal axis it is known as slump.

Q.8. How do you distinguish between the process of soil formation and soil-forming factors? What is the role of climate and biological activity as two important control factors in the formation of soils?

Ans. The soil forming processes are given as under:

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

2. Illuviation: It is the accumulation of the washed down material in the lower horizon of the soil profile.

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

4. Leaching: It is the removal and down- ward movement of material from a horizon in solution and depends on several sets of factors including climate, rock forming materials and organisms present.

Soil forming factors are:

(i) climate.

(ii) parent material.

(iii) topography.

(iv) biological activity. and

(v) time.

The role of climate and biological activity is important. The climatic elements involved in soil development are moisture and temperature. Precipitation gives water. Without water, chemical and biological activities are not possible. Excess of water helps in the downward transportation of soil components through the soil and deposits the same down below.

Temperature acts in two ways-increasing or reducing the biological activity. Biological activity increases in warmer temperatures. In humid tropical and equatorial climates, bacterial growth and action is intense and dead vegetation is rapidly oxidized leaving very low humus content in the soil.

Q.9. Exogenic geomorphic processes derive their ultimate energy from the sun’s heat. Explain.

Ans. The configuration of the surface of the earth is changed through geomorphic processes. Weathering, mass wasting and erosion and deposition are the examples of exogenic geomorphic processes. An element of nature (like water, ice, wind etc.) becomes mobile due to gradients and removes the materials and transports them over slopes and deposits them at lower levels bringing about the change in the configuration of the earth. For accomplishing this task or to become mobile, the geomorphic agent needs energy. Let us consider some of the exogenic processes.

Weathering: Weathering is action of elements of weather and climate over the earth materials. The main elements of weather and climate are temperature, pressure, winds, humidity, clouds and precipitation. All these elements are directly or indirectly the results of the solar energy.

Mass Movement or Mass Wasting: These movements transfer the mass of rock debris down the slopes under the direct influence of gravity. Although weathering is not a pre- requisite for mass movements, it aids mass movements. The weathering depends upon the solar energy.

Erosion and Deposition: Erosion involves acquisition and transportation of rock debris and deposition is a consequence of erosion. The erosion and transportation of earth materials is brought about by wind, running water, glaciers, waves and groundwater. Of these, wind, running water and glaciers are controlled by climatic conditions and the climate is determined by the sun’s energy.

Thus, we can say that the exogenic geomorphic processes derive their ultimate energy from the sun’s heat.

Q.10. Explain the significance of weathering.

Ans. (i) Weathering process the way for soil formation.

(ii) Weathering is responsible for erosion and mass movements.

(iii) Erosion cannot be significant if nodes are not weathered.

(iv) Landforms are a consequence of weathering.

(v) Weathering is an important process in the formation of soil.

(vi) It helps in the enrichment and concentration of valuable ores.