Institute of Lifelong Learning, University of Delhi The above lesson has been checked for plagiarism by the s/w used by the ILLL technical team Discipline course -1 Semester -1 Paper – Geomorphology Lesson- Mass Wasting Lesson Developer: Dr.Prabuddh Kr. Mishra College /Department: Bhim Rao Ambedkar College University of Delhi
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Discipline course -1 Paper Lesson Developer: … The movement of weathered material under the influence of gravity and ... wasting is the downslope movement of soil or rock material
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Institute of Lifelong Learning, University of Delhi
The above lesson has been checked for plagiarism by the s/w used by the ILLL technical
team
Discipline course -1 Semester -1
Paper – Geomorphology Lesson- Mass Wasting
Lesson Developer:
Dr.Prabuddh Kr. Mishra
College /Department: Bhim Rao Ambedkar College University of Delhi
Institute of Lifelong Learning, University of Delhi
The above lesson has been checked for plagiarism by the s/w used by the ILLL technical
team
Table of Contents
3. Geomorphic Process
3.2 Mass Wasting
1.1 Meaning and concept
1.2 Factors affecting mass waiting
1.3 Classification of Mass movement
Summery
Exercise
References
Institute of Lifelong Learning, University of Delhi
The above lesson has been checked for plagiarism by the s/w used by the ILLL technical
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Mass Wasting
1.1 Meaning and concept
The movement of weathered material under the influence of gravity and with or without
the influence of rainwater is called as mass movement or wasting. In other words, mass
wasting is the downslope movement of soil or rock material under the influence or gravity
without the direct aid of other medium such as water, air or ice, water and ice, however, are
frequently involved in mass wasting by reducing the strength of rock of soil and by
contributing to plastic and fluid behaviour of soil. Mass movements include both
detachment of rock materials and their down slope transport. The collective term for
gravitation or downslope movements of weathered rock debris is mass wasting.
R.J. Chorley has remarked that, "the relation between mass wasting and tectonics is a
relatively clear one. Where rocks are shattered, reliefs are high, this is where mass
movement is common and in fact, the denudation of high mountains may be the result of
mass wasting rather than fluvial or glacial process.”
Mass movement is a common phenomenon in all high and steep hill country and it can also
occur on very low-angle slopes. Very large land slides are most common in the technically
and seismically active belts of rising mountains chains where steep slopes, rapidly incising
rivers and glaciers in valley floors, jointed and fractured rock masses on slopes, severe
physical weathering, fluctuations in groundwater pressure, and many joints dipping steeply
out of the slopes, all contribute to instability.
1.2 Factors which results in mass wasting
1. Weathering reduces the shearing strength of materials by physical and chemical
changes through granular disintegration, hydration and expansion, saturation and
loss of compactness, drying and cracking etc. Original rocks materials may be
subject to mass wasting because of their composition. For example, rocks and
materials like schist, sand, gravel shale, soil etc. are easily sheared permitting fall,
slide, flow, creep or subsidence.
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2. The texture and structure of materials may also be conducive to mass wasting
because of their roundness or compaction.
3. Movements may takes place along the places of structural weakness such as
bedding planes, foliation, cleavage, fractures and Joints and faults.
4. Changes in environmental conditions including climatic factors and vegetational
cover may result in mass-wasting, (less vegetation cover, more lose will be the soil
and hence mass wasting also will be more).
5. Slope gradient is, always an important factor. Thus, a complex of factors in usually
involved in mass wasting, resulting in a variety of mass movement.
The role of water in the reduction of shearing strength is particularly important. This is often
referred to as lubrication of rock on weathered rocks debris. This really achieved through
the introduction of inter-granular forces by pore water pressure and the buoyant effect of
water. However, rapid mass wasting frequently takes place after heavy rains or rapid
melting of snow cover and does emphasize the effect of water on gravity movements (Fig.
4).
To watch video on mass wasting click on following web link: https://www.youtube.com/watch?v=yXaUbzVh4bI
1.3 Classification of Mass movement
Shapre (1938) made one of the first attempts at classification of the various types of mass
wasting and though several others have been proposed since then, his classifications are still
widely used. He recognized four major types of mass wasting which he called slow flowage,
rapid flowage, landslides and subsidence.
Hutchinson proposed a classification of mass movement on slopes based on mechanisms of
movement, morphology of the mass and the rate of movement and has identified as four
major types: creep, freeze, thaw movements, landslides mass movement involving sinking.
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Summary
Denudation refers to weathering, mass wasting, erosion, and transportation.
Mass wasting refers to the movement of large quantities of weathered materials down
the slopes.
Mass wasting involves the processes of creeping, sliding slumping, flowing and falling.
Slopes are either straight or concave or convex.
Mass wasting on slopes can be triggered by earthquake, undercutting by streams,
heavy or prolonged rains, or volcanic eruption.
Types of downslopes movement are flows, if they move as viscous fluid: slides, if they
move over the ground: falls, if they travel in the air is free fall.
Creep is the slow downslope movement of overburden and, in some cases, bedrock.
Landslides are sometimes called as avalanches, that term is best reserved for
snowslides. Slides involving overburden are called debris sliders.
Sheet flow refers to refers to the movement of individual particles downslope. Strictly,
this is not an aspect of mass movement.
Rain action produces gullies and earth pillars when condition are favourable, e.g.,
gullies form on sloping land free of vegetation when rainfall is fairly heavy; earth’s pillar
forms on slopes composed of clay and boulder where there is little or no vegetation.
The end product of weathering is called as regolith.
Water in regolith moves upward by capillary action and downward by infiltration.
Exercises
State the meaning of mass wasting. Name the three features that it can produce.
Illustrate with relevant diagrams.
Explain the factors which results in mass wasting.
Name the types of slumps and explain each in detail.
Differentiate between fall and flow.
Briefly explain the geomorphic importance of mass wasting.
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Briefly explain what could happen to the surfaces of steep slopes :
a) When belts of trees are cut down
b) After a prolonged period of frosty weather
c) When cutting is made for a road.
References
Birkeland P.W. 1984. Soils and Geomorphology. New York, Oxford University Press.
Robinson D.A., and Williams R.B.G., 1994. Rock Weathering and Landform Evolution. John Wiley & Sons, Inc., New York
Berner, E. B., and R. A. Berner. 1996. Global Environment: Water, Air, and Geochemical Cycles. Upper Saddle River, N.J.: Prentice Hall. Bland, W., and D. Rolls. 1998. Weathering : An Introduction to the Scientific Principles . New York: Arnold.
Colman, S. M., and D. P. Dethier. 1986. Rates of Chemical Weathering of Rocks and Minerals. New York: Academic Press.
Ollier, C.and Pain, C. 2000. The Origin of Mountains ,Routledge.
S. Singh. 1998. Geomorphology, Prayag Pustak Bhawan, Allahabad.
Dayal, P. 1976. A Text Book of Geomorphology, Shukla Book Dept, Patna.
A.N. Strahler & A.R. Strahler 1978. Modern Physical Geography, John Wiley.
J.A. Steers, 1961. The Unstable Earth, Lyell Book Dept, Ludhiana.
Kale V. and Gupta, A. 2001. Elements of Geomorphology. Oxford University Press, Calcutta.
Bharatdwaj, K. 2006 Physical Geography: Introduction to Earth.Discovery Publishing House,Delhi.
Leong G.C. 2006 Certificate Physical and Human Geography, Oxford India.
Bunnett, R.B. 1965. Physical Geography in Diagrams, Pearson Education, India.
Bloom, Arthur L., (2003) Geomorphology: A Systematic Analysis of Late Cenozoic Landforms.
First Indian Reprint. Delhi: Pearson Education (Singapore) Pvt. Ltd.
Institute of Lifelong Learning, University of Delhi
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Chorley, Richard J., Schumm, Stanley A. and Sugden, David E., (1984) Geomorphology.
London: Methuen & Co. Ltd.
Engeln, O. D. von, Geomorphology. (1960) New York: The Macmillan Company.
Suggested Readings
Thornbury, W. D. (2004) Principles of Geomorphology, CBS Publishers, Delhi.
Strahler, A. and Strahler, A. (2002) Physical Geography: Science and Systems of the Human Environment, John Wiley and sons, New York.