CHAPTER 6: Geomorphic Processes NCERT SOLUTION CLASS 11TH GEOGRAPHY| EDUGROWN NOTES

Q1.It is weathering that is responsible for bio-diversity on the earth. How?
Answer
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.

Q2.What are mass movements that are real rapid and perceptible? List.

Answer

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
Q3.What are the various mobile and mighty exogenic geomorphic agents and what is the prime job they perform?

Answer

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.

Q4. Is weathering essential as a pre-requisite in the formation of soils? Why?

Answer

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.

Q5.“Our earth is a playfield for two opposing groups of geomorphic processes.” Discuss.

Answer

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.
Q6. Exogenic geomorphic processes derive their ultimate energy from the sun’s heat. Explain.

Answer

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 arecovered 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.
Q7.Are physical and chemical weathering processes independent of each other? If not, why? Explain with examples.

Answer

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.

Q8.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?

Answer

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.

Long Answer Type Questions:

Q1.What are different types of mass movements?
Answer:
There are three types of mass movements: Slow Movements: Creep is one type under this category which can occur on moderately steep, soil covered slopes. Movement of materials is extremely slow and imperceptible except through extended observation. Materials involved can be soil or rock debris. Soil creep, talus creep, rock creep, rock- glacier creep etc can be identified. It also includes solifluction which involves slow downslope flowing soil mass or fine grained rock debris saturated or lubricated with water. This process is quite common in moist temperate areas where surface melting of deeply frozen ground and long continued rain respectively, occur frequently. When the upper portions get saturated and when the lower parts are impervious to water percolation, flowing occurs in the upper parts.

Rapid Movements: These movements are mostly prevalent in humid climate regions and occur over gentle to steep slopes. Movements of water- saturated clayey or silty earth materials down low angle terraces or hill slides is known as earth flow. When slopes are steeper ever the bedrock especially of soft sedimentary rocks like shale or deeply weathering igneous rock may slide downslope. With heavy rainfall, thick layers of weathered
materials get saturated with water and either slowly or rapidly flow down along definite channels. It looks like a stream of mud within a valley.

Landslides: The types of landslides.

• Slumps: The slipping of one or several units of rock debris with a backward rotation with respect to the slope over which the movement takes place.
• Debris slide: rapid rolling or sliding of earth debris without backward rotation of mass is known as Debris slide.
• Rockslide: Sliding of individual rock masses down bedding, joint or fault surface is rockslide.
• Rock fall: Rock fall is free falling of rock blocks over any steep slope keeping itself away from the slope. Rock falls occurs from the superficial layers of the rock face.

Q2.Explain different types of chemical weathering.
Answer:
Different types of chemical weathering includes:

1. Oxidation and Reduction: Oxidation is the effect of oxygen in air and water on the rocks. The atmospheric oxygen in rainwater unites with minerals in rocks specially with iron compounds. When oxidised minerals are placed in an environment where oxygen is absent, reduction takes place. It exists normally below water table, in area of stagnant water in more hot and humid climates.

2. Carbonation: When the carbon dioxide in atmosphere dissolves in water it form carbonic acid that affects the rocks, it is carbonation. It has acidic affect and dissolves calcium carbonates and magnesium carbonates such as gypsum, marble, limestone.

3.  Hydration: When the hydrogen of water dissolves in rocks hydration occurs. Certain minerals in rocks increase their volume and become heavy when observe water contains hydrogen. They break due to its increased pressure and the colour also changes.

4. Solution: Rainwater is able to dissolve certain minerals and leaching of the soil occurs. Normally solids are also removed during leaching. For e.g.: gypsum, rock salt, etc. undergo solution.

Q3.Explain different types of physical weathering.
Answer:
Different types of physical weathering includes:

• Exfoliation: Due to differential heating and resulting expansion and contraction of surface layers and their subsequent 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 exfoliation.
• Frost: It is an active agent in cold climatic regions in high altitudes and the cracks are filled with water during the day time, this water is frozen at night when temperature falls below freezing point.
• Pressure: Many igneous and metamorphic rocks crystallize deep in the interior under the combine influence of high pressure and temperature. The salt near surface pores cause splitting of the grains within the rocks which eventually falls off, this result into granules disintegration.

Q4.Explain about erosion and deposition.
Answer:
Erosion involves acquisition and transportation of rock debris. When massive rocks break into smaller fragments through weathering and any other process, erosional geomorphic agents like running water, groundwater, glaciers, wind and waves remove and transport it to other places depending upon the dynamics of each of these agents. Abrasion by rock debris carried by these geomorphic agents also aids greatly in erosion. By erosion, relief degrades, i.e., the landscape is worn down. Weathering aids erosion it is not a pre-condition for erosion to take place. Weathering, mass-wasting and erosion are degradational processes. It erosion that is largely responsible for continuous changes that the earth’s surface is undergoing. The erosion and transportation of earth materials is brought about by wind, running water, glaciers, waves and ground water.

Deposition is a consequence of erosion. The erosional agents loose their velocity and hence energy on gentler slopes and the materials carried by them start to settle themselves. In other words, deposition is not actually the work of any agent. The coarser materials get deposited first and finer ones later. By deposition depressions get filled up. The same erosional agents viz., running water, glaciers, wind, waves and groundwater act as aggradational or depositional agents also. What happens to the surface of the earth due to erosion and deposition is elaborated in the next chapter on landforms and their evolution. There is a shift of materials in mass movements as well as in erosion from one place to the other.