NCERT Solutions for Class 11 Geography Chapter 5 - Geomorphic Processes

93. Multiple choice questions.

(i) Which one of the following processes is a gradational process?

(a) Deposition

(b) Diastrophism

(c) Volcanism

(d) Erosion

Ans. (d) Erosion

(ii) Which one of the following materials is affected by hydration process?

(a) Granite

(b) Clay

(c) Quartz

(d) Salts

Ans. (b) Clay

(iii) Debris avalanche can be included in the category of:

(a) Landslides

(b) Slow flow mass movements

(c) Rapid flow mass movements

(d) Subsidence

Ans. (c) Rapid flow mass movements

94. Answers the following questions in about 30 words.

(i) It is weathering that is responsible for biodiversity on the earth. How?

Ans. Yes, the earth’s biodiversity can be attributed to weathering. The causes are:

(a) Biomes and biodiversity are primarily a result of forests, which depend on the depth of weathering mantles; erosion cannot be significant if the rocks are not weathered; weathering processes are responsible for breaking down the rocks into smaller fragments and preparing the way for formation of not only regolith and soils but also erosion and mass movement.

(b) This indicates that weathering promotes mass wasting, erosion causes a decrease in relief, and erosion-related changes to landforms.

(c) The weathering of rocks and deposits aids in the enrichment and concentration of a  number of precious ores, including those for iron, manganese, aluminium, copper, and other elements that are crucial to the country’s economy.

(d) Weathering is an important process in the formation of soils.

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

Ans. The movements that transfer the mass of rock debris down the slopes under the direct influence of gravity are called mass movements.

Air, water or ice do not carry debris with them from place to place but the debris may carry with it air, water or ice. Mass movements occur on steep slopes in humid areas.

Various mass movements that are really rapid and perceptible are:

(a) Earthflow: Movement of water saturated clayey or silty earth materials down low angle terraces or hill sides.

(b) Mudflow: In the absence of vegetation cover and with heavy rainfall, thick layers of weathered materials get saturated with water and either slowly or rapidly flow down along definite channels.

(c) Debris avalanche is characteristic of humid regions with or without vegetation cover and occurs in narrow tracks on steep slopes.

(iii) 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 river, glaciers and wind.

Their prime jobs are:

(a) Eroding down the relief or weathering,

(b) Transportation,

(c) Depositing of basins or depressions on the earth surface.

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

Ans. Yes, weathering is a necessary condition for the formation of soils. The primary factor influencing how soil forms is the depth of the weathering material. First, bacteria and other inferior plant bodies like mosses and lichens, colonise the weathered material or transported deposits. The decayed remnants of animals and plants aid in the buildup of humus. Minor grasses and ferns might emerge; subsequently, bushes and trees will begin to sprout from seeds carried by the wind and birds. As material mass becomes porous and sponge-like with the ability to retain water and permit air passage, plant roots penetrate it, burrowing animals bring up particles, and eventually mature soil, a complex mixture of minerals and organic material, forms.

95. Answer the following questions in about 150 words:

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

Ans. Our earth is a playfield for two opposing groups of geomorphic processes. These are Exogenetic and Endogenetic forces.

(a) The earth’s surface is being continuously subjected to by the external forces originating within the earth’s atmosphere known as Exogenetic forces and by the internal forces from within the earth known as Endogenetic forces.

(b) The actions of exogenetic forces result in degradation of relief/elevations and aggradation of basins/depressions, on the earth’s surface.The phenomenon of wearing down of relief variations of the surface of the earth through erosion is called Gradation.

(c) The endogenetic forces continuously elevate or build up parts of the earth’s surface and hence the exogenetic processes fail to even out the relief variations of the surface of the earth.

(d) As a result, variations remain as long as the opposing actions of exogenetic and endogenetic forces continue.

(e) The building up and wearing down of the earth’s surface by endogenetic and exogenic forces are going on from the time of the earth crust was developed and undeveloped by atmosphere.

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

Ans. The atmosphere, which is governed by the sun’s primary energy as well as the gradients produced by tectonic causes, provides energy for exogenic processes. Different rock minerals have different maximum and minimum expansion and contraction rates. Every mineral expands and pushes against its neighbour as the temperature rises, and every mineral contracts in response to a drop in temperature. The splitting of individual grains within rocks, which eventually fall off, is caused by diurnal fluctuations. Granular foliation or granular disintegration may come from this process of individual grains dropping off. The technique of salt crystallisation is the most efficient salt weathering method. Salt crystal formation is encouraged in regions with alternating wet and dry conditions, pushing out neighbouring grains in the process. Gypsum and  sodium chloride crystals heave up the materials beneath them in desert regions, and as a result, polygonal cracks appear all over the surface. Chalk is the rock that dissolves the most easily when salt crystals grow, followed by limestone, sandstone, shale, gneiss, granite, etc.

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

Ans. No, physical and chemical weathering are not independent of each other. Despite their differences, they remain interconnected. Weathering processes can be mechanical or physical and are influenced by external influences.

There are several types of forces that can be applied, including:

(a) Gravity forces such overburden pressure, load, and shearing stress.

(b) Expansion forces brought on by temperature changes, crystal development, or animal activity.

(c) Water pressures regulated by wetting and drying cycles.

In the following way physical and chemical weathering are interdependent:

(a) The minerals on the rocks have not yet been subjected to chemical reactions, in some circumstances chemical weathering or breakdown of large rocks cannot begin on the unweathered rock.

(b) After rocks break down or when the physical weathering process causes fissures to appear on the rock, chemical weathering begins.

(c) Similar to how chemically weathered materials speed up, physical weathering does too.

(d) In actuality, physical or chemical weathering occurs concurrently or simultaneously and  is interconnected rather than in a sequential or independent manner.

(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?

Ans. Soil formation process is step by step procedure in which soil comes into existence. It can be studied under following heads:

Process of Soil Formation

Soil formation depends on weathering. It is this weathering which is 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. 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. It increases the capacity to retain water and to permit the passage of air. Finally, a mature soil which is a complex mixture of mineral and organic products forms.

Soil-forming Factors

Five basic factors control the formation of soils are:

(a) Parent material

(b) Topography

(c) Climate

(d) Biological activity

(e) Time.

Soil forming factors act in union and affect the action of one another.

Climatic and biological activity play an important role in soil formation. Moisture and temperature are two important features of climatic condition for the development of soil profile. Precipitation provides water. Without water, it is unable to proceed chemical and biological activities. Extreme 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.

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