After learning about how the earth was born, how it evolved its crust and other inner layers, how its crustal plates moved and are moving, and other information on earthquakes, the forms of volcanism and about the rocks and minerals the crust is composed of, it is time to know in detail about the surface of the earth on which we live. Let us start with this question. Why is the surface of the earth uneven? First of all, the earth’s crust is dynamic. You are well aware that it has moved and moves vertically and horizontally. Of course, it moved a bit faster in the past than the rate at which it is moving now. 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). Of course, 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 (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 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 orces and the exogenic processes are mainly land wearing forces. The surface of the earth is sensitive. Humans depend on it for their sustenance and have been using it extensively and intensively. So, it is essential to understand its nature in order to use it effectively without disturbing its balance and diminishing its potential for the future. Almost all organisms
contribute to sustain the earth’s environment. However, humans have caused over use of resources. Use we must, but must also leave it potential enough to sustain life through the future.
Most of the surface of the earth had and has been shaped over very long periods of time (hundreds and thousands of years) and because of its use and misuse by humans its potential is being diminished at a fast rate. If
the processes which shaped and are shaping the surface of the earth into varieties of forms (shapes) and the nature of materials of which it is composed of, are understood, precautions can be taken to minimise the detrimental effects of human use and to preserve it for posterity.
GEOMORPHIC PROCESSES
You would like to know the meaning of geomorphic processes. The endogenic and exogenic forces causing physical stresses and chemical actions on earth materials and bringing about changes in the configuration of the surface of the earth are known as geomorphic processes. Diastrophism and volcanism are endogenic geomorphic processes. These have already been discussed in brief in the preceding unit. Weathering, mass wasting, erosion and deposition are exogenic geomorphic processes. These exogenic processes are dealt with in detail in this chapter.
Excercise
1. Multiple choice questions.
(i) Which one of the following processes is a gradational process?
(a) Deposition (c) Volcanism
(b) Diastrophism (d) Erosion
(ii) Which one of the following materials is affected by hydration process?
(a) Granite (c) Quartz
(b) Clay (d) Salts
(iii) Debris avalanche can be included in the category of:
(a) Landslides (c) Rapid flow mass movements
(b) Slow flow mass movements (d) Subsidence
2. Answer the following questions in about 30 words.
(i) It is weathering that is responsible for bio-diversity on the earth. How?
(ii) What are mass movements that are real rapid and perceptible? List.
(iii) What are the various mobile and mighty exogenic geomorphic agents and what is the prime job they perform?
(iv) Is weathering essential as a pre-requisite in the formation of soils? Why?
3. Answer the following questions in about 150 words.
(i) “Our earth is a playfield for two opposing groups of geomorphic processes.”
Discuss.
(ii) Exogenic geomorphic processes derive their ultimate energy from the sun’s heat. Explain.
(iii) Are physical and chemical weathering processes independent of each other? If not, why? Explain with examples.
(iv) How do you distinguish between the process of soil formation and soilforming factors? What is the role of climate and biological activity as two important control factors in the formation of soils?
Please refer to attached file for NCERT Class 11 Geography Geomorphic Processes
