NCERT Solutions for Class 11 Geography Chapter 8 - Geomorphic Processes

Question 1:

Which one of the following processes is a gradational process?

  1. Deposition
  2. Diastrophism
  3. Volcanism
  4. Erosion

(d). Erosion

Question 2:

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

  1. Granite
  2. Clay
  3. Quartz
  4. Salts

(d). Salts

Question 3:

Debris avalanche can be included in the category of:

  1. Landslides
  2. Slow flow mass movements
  3. Rapid flow mass movements
  4. Subsidence

(b). Slow flow mass movements

Question 4:

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


Biological Activity and Weathering. Biological weathering is contribution to or removal of minerals and ions from the weathering environment and physical changes due to growth or movement of organisms. Burrowing and wedging by organisms like earthworms, termites, rodents etc., help in exposing the new surfaces to chemical attack and assists in the penetration of moisture and air. Man by disturbing vegetation, ploughing and cultivating soils, also helps in mixing and creating new contacts between air, water and minerals in the earth materials. Algae utilise mineral nutrients for growth and help in concentration of iron and manganese oxides as desert varnishes on thesurfaces. Plant roots exert a tremendous pressure on the earth materials mechancially breaking them apart.

Question 5:

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


Mass movements occur on steep slopes in humid areas :
(a) Soil flow occurs along hill rocks due to flow of clay soils.
(b) Mud flow occurs fast down the channels along volcanic slopes.
(c) Debris avalanche occurs along humid slopes.

Question 6:

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


River, glacier, wind and sea waves are the mobile and mighty exogenic geomorphic agents. These perform the work of eroding the features of earth, transporting and depositing this material. These disintegrate the landforms.

Question 7:

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


Formation of soils depends upon weathering. Weathering prepare rocks for soils formation by breaking material into small pieces. It helps in erosion, transportation and deposition of load help in formation of soils.

Question 8:

'Our earth is a playfield for two opposing groups of geomorphic processes.’ Discuss.


The earth’s surface is being continuously subjected to by the external forces originating within the earth’s atmosphere and by the internal forces from within the earth, and it is ever changing. The external forces are known as exogenetic forces and the internal forces are known as endogenetic forces. The actions of exogenetic forces result in wearing down (degradation) of relief/elevations and filling up (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 known as gradation. 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. So, variations remain as long as the opposing actions of exogenetic and endogenetic forces continue. In general terms, the endogenetic forces are mainly land building forces and the exogenetic processes are mainly land wearing forces. The building up and wearing down of the earth’s surface by endogenetic and exogenetic forces respectively are going on from the time the earth’s crust was developed and enveloped by atmosphere.

Question 9:

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


The exogenic processes vary from region to region due to different climatic regions in different latitudes. This is due to thermal variation in different regions. This results in variation in amount of insolation. The exogenic geomorphic processes derive their ultimate energy from insolation.

Question 10:

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


Physical and chemical weathering work together. Sometimes one process is domainant, at other times the second process dominates. Both processes include disintegration and decomposition. In both processes water, pressure and gases help.

Question 11:

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


All soil forming processes involve weathering. There are, however, several other factors that influence the end product of weathering. Five of them are primary factors. They singly or jointly are responsible for the development of various types of soils. These factors are :
(1) Parent Material. Soils from weakly cemented sandstone will be sandy and soils from shales will be shallow and fine-textured. Similarly clay formation is favoured more by a high percentage of decomposable dark minerals and less by quartz. The parent material, thus, influences the soil formation by their different rates of weathering.
(2) Climate. Acidic soils are formed in humid areas due to intense weathering and leaching. Alkaline soils are formed in areas of low rainfall due to the accumulation or retention of lime. The climate is an increasingly dominant factor in forming varied type of soils especially because of the effects of temperature and precipitation. It also plays an indirect role in the formation of soil by way of its influence on vegetation.
(3) Biota. The decomposition of organic wastes and residues and the activities of living plants and animals have marked influence on the soil development. Burrowing animals, such as moles, prairie dogs, earthworms, ants and termites help soil development slowly by decomposing organic matters and forming weak acids that dissolve mineral faster. The roots of living plants and decomposed plant materials release weak organic acids that help in weathering and soil development.
(4) Topography. Steep hillsides have thin soil cover because of surface runoff that results in the erosion of surface. On the other hand, gentle hillsides preserve appreciable soil cover due to the luxuriant vegetation and sufficient water passing in vertically to deeper levels. The topography influences the soil formation through its relationship with water and temperature.
(5) Time. Under ideal conditions, a recognisable soil profile may develop in 200 years and under less favourable circumstances, it may extend to several thousand years. The rate of soil development is determined by the effects of time and other distinct factors-climate, parent material, topography and biota.
Soil Forming Processes
Several processes are involved in soil formation and may, to some extent, affect the soil profile. The processes are :
(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 (eluviated) material in the lower horizons of the soil profile.
(3) Cheluviation. It is the downward movement of material, similar to leaching but under the influence of organic complex compounds.
(4) Leaching. It is the removal and downward movement of material from a horizon in solution.