NCERT Solutions for Class 11th: Ch 6 Geomorphic Processes


Page No: 44

1. Multiple choice questions.

(i) Which one of the following processes is a gradational process?
(a) Deposition
(b) Diastrophism 
(c) Volcanism
(d) Erosion
► (d) Erosion

(ii) Which one of the following materials is affected by hydration process?
(a) Granite 
(b) Clay
(c) Quartz
(d) Salts
► (d) Salts

(iii) Debris avalanche can be included in the category of:
(a) Landslides 
(b) Slow flow mass movements
(c) Rapid flow mass movements
(d) Subsidence
► (c) Rapid flow mass movements

2. Answer the following questions in about 30 words.

(i) It is weathering that is responsible for bio-diversity on the earth. How?


Weathering processes are responsible for the bio-diversity on the earth. Biomes and biodiversity
is basically a result of forests or vegetation. The forests depend upon the depth of weathering mantles.

(ii) What are mass movements that are real rapid and perceptible? List.


Mass movements transfer the mass of rock debris down the slopes under the direct influence of gravity. No geomorphic agent like running water, glaciers, wind, waves and currents participate
in the process of mass movements.
The mass movements that are real rapid and perceptible are:
• Earth flow
• Mud flow
• Landslide

(iii) What are the various mobile and mighty exogenic geomorphic agents and what is the prime job they perform?


Weathring, mass movements, erosion, transportation and deposition are the various mobile and mighty exogenic geomorphic agents. These agents bring the geomorphic changes on the surface of the earth.

(iv) Is weathering essential as a pre-requisite in the formation of soils? Why?


Yes, weathering is an essential as a pre-requisite in the formation of soils. Weathering processes are responsible for breaking down the rocks into smaller fragments and prepare the for formation of soils.

3. Answer the following questions in about 150 words.

(i) “Our earth is a playfield for two opposing groups of geomorphic processes.” Discuss.


It is right to say that our earth is a playfield for two opposing groups of geomorphic processes. The earth’s crust is dynamic, it has moved and moves vertically and horizontally. The differences in the internal forces operating from within the earth which built up the crust have been responsible for the variations in the outer surface of the crust. The earth’s surface is being continuously subjected to external forces induced basically by energy (sunlight). Also, the internal forces are still active though with different intensities. That means, the earth’s surface is being continuously subjected to by external forces originating within the earth’s atmosphere and by internal forces from within the earth. The external forces are known as exogenic forces and the internal forces are known as endogenic forces.
The actions of exogenic forces result in wearing down of relief or elevations and filling up of basins/depressions, 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. So, variations remain as long as the opposing actions of exogenic and
endogenic forces continue.
In general terms, the endogenic forces are mainly land building forces and the exogenic processes are mainly land wearing forces.

(ii) Exogenic geomorphic processes derive their ultimate energy from the sun’s heat. Explain.


The exogenic processes derive their energy from atmosphere determined by the ultimate energy from the sun and also the gradients created by tectonic factors. All the exogenic geomorphic processes are
covered under a general term, denudation. Weathering, mass movements, erosion and transportation are included in denudation.

• Weathering: It is action of elements of weather and climate over earth materials. The components of of weather and climate are temperature, pressure, winds, humidity and precipitation. All these components directly or indirectly derive their energy from the sun.

• Mass Movement: These movements transfer the mass of rock debris down the slopes under the direct influence of gravity. Weathering is not a pre-requisite for a mass movement. However, weathering aids in mass movement.

• Erosion and deposition: Erosion involves acquisition and transportation of rock debris. The erosion and transportation of earth materials are brought about by the wind, running water, glaciers, waves and ground water. Of these, the first three agents are controlled by climatic conditions while climate is decided by the energy of the sun.

Thus, All exogenic geomorphic processes derive their ultimate energy from the sun’s heat. However, the gravitational force of earth aids in all exogenic geomorphic processes because gravity makes mobility possible.

(iii) Are physical and chemical weathering processes independent of each other? If not, why? Explain with examples.


Physical and chemical weathering processes are not independent of each other. Physical weathering processes depend on some applied forces. The applied forces could be gravitational forces such as overburden pressure, load and shearing stress; expansion forces due to temperature changes, crystal growth or animal activity;  water pressures controlled by wetting and drying cycles. While in chemical weathering processes such as solution, carbonation, hydration, oxidation and reduction act on the rocks to decompose, dissolve or reduce them to a fine clastic state through chemical reactions by oxygen, surface and/or soil water and other acids.

Chemical Weathering process depends on the work of physical weathering process. The agents of physical weathering such as temperature change and freezing break the rocks and provide easy passage to chemical weathering process to work on. The chemical weathering processes make rocks decayed and decomposed which can be easily broken down by the physical weathring processes.

(iv) 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?


The process of soil formation starts with weathring. The weathring mantle provide the basic input for soil to form. First, the weathered material or transported deposits are colonised by bacteria and other inferior plant bodies like mosses and lichens. Also, several minor organisms may take shelter within the mantle and deposits. The dead remains of organisms and plants help in humus accumulation. Minor grasses and ferns may grow; later, bushes and trees will start growing through seeds brought in by birds and wind. Plant roots penetrate down, burrowing animals bring up particles, mass of material becomes porous and sponge like with a capacity to retain water and to permit the passage of air and finally a mature soil, a complex mixture of mineral and organic products forms.

Soil formaing factors control the formation of soils. These are five in number: (i) parent material; (ii) topography; (iii) climate; (iv) biological activity; (v) time. Soil forming factors act in union and affect the action of one another.

The climate and biological activity play very important role. The climatic elements involved in soil
development are moisture and temperature. Precipitation gives soil its moisture content which makes the chemical and biological activities possible. Excess of water helps in the downward transportation of soil components through the soil (eluviation) and deposits the same down below (illuviation). Temperature acts in two ways — increasing or reducing chemical and biological activity. Chemical activity is increased in higher temperatures, reduced in cooler temperatures (with an exception of carbonation) and stops in freezing conditions.

Biological Activity includes the effects of vegetative cover, organisms and bacteria. The vegetative cover and organisms help in adding organic matter, moisture retention, nitrogen etc. Dead plants provide humus, the finely divided organic matter of the soil.  With the increase in temorature, biological activity increases. In humid tropical and equatorial climates, bacterial growth and action is intense.

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