Landforms PDF 2024-25

UNIT III LANDFORMS This unit deals with Landforms and their evolution Geomorphic processes — weathering, mass wasting, erosion and deposition; soils — formation 2024-25 ...

UNIT III LANDFORMS This unit deals with Landforms and their evolution Geomorphic processes — weathering, mass wasting, erosion and deposition; soils — formation 2024-25  CHAPTER GEOMORPHIC PROCESSES A fter learning about how the earth was forces continuously elevate or build up parts born, how it evolved its crust and other of the earth’s surface and hence the exogenic inner layers, how its crustal plates processes fail to even out the relief variations moved and are moving, and other information of the surface of the earth. So, variations remain on earthquakes, the forms of volcanism and as long as the opposing actions of exogenic and about the rocks and minerals the crust is endogenic forces continue. In general terms, composed of, it is time to know in detail about the endogenic forces are mainly land building the surface of the earth on which we live. Let forces and the exogenic processes are mainly us start with this question. land wearing forces. The surface of the earth is sensitive. Humans depend on it for their Why is the surface of the earth uneven? sustenance and have been using it extensively and intensively. So, it is essential to understand The earth’s crust is dynamic. You are well its nature in order to use it effectively without aware that it has moved and moves vertically disturbing its balance and diminishing its and horizontally. Of course, it moved a bit faster potential for the future. Almost all organisms in the past than the rate at which it is moving contribute to sustain the earth’s environment. now. The differences in the internal forces However, humans have caused extensive operating from within the earth which built up damage to the environment through over use the crust have been responsible for the of resources. Use we must, but must also leave variations in the outer surface of the crust. The it potential enough to sustain life through the earth’s surface is being continuously subjected future. Most of the surface of the earth had and to external forces induced basically by energy has been shaped over very long periods of time (sunlight). Of course, the internal forces are still (hundreds and thousands of years) and active though with different intensities. That because of its use and misuse by humans its means, the earth’s surface is being potential is being diminished at a fast rate. If continuously subjected to by external forces the processes which shaped and are shaping originating within the earth’s atmosphere and the surface of the earth into varieties of forms by internal forces from within the earth. The (shapes) and the nature of materials of which external forces are known as exogenic forces it is composed of, are understood, precautions and the internal forces are known as endogenic can be taken to minimise the detrimental effects forces. The actions of exogenic forces result in of human use and to preserve it for posterity. wearing down (degradation) of relief/elevations and filling up (aggradation) of basins/ GEOMORPHIC PROCESSES depressions, on the earth’s surface. The You would like to know the meaning of phenomenon of wearing down of relief geomorphic processes. The endogenic and variations of the surface of the earth through exogenic forces causing physical stresses and erosion is known as gradation. The endogenic chemical actions on earth materials and 2024-25 38 FUNDAMENTALS OF PHYSICAL GEOGRAPHY bringing about changes in the configuration ENDOGENIC PROCESSES of the surface of the earth are known as The energy emanating from within the earth is geomorphic processes. Diastrophism and the main force behind endogenic geomorphic volcanism are endogenic geomorphic processes. This energy is mostly generated by processes. These have already been discussed radioactivity, rotational and tidal friction and in brief in the preceding unit. Weathering, mass primordial heat from the origin of the earth. wasting, erosion and deposition are exogenic This energy due to geothermal gradients and geomorphic processes. These exogenic heat flow from within induces diastrophism processes are dealt with in detail in this chapter. and volcanism in the lithosphere. Due to Any exogenic element of nature (like water, variations in geothermal gradients and heat flow ice, wind, etc.,) capable of acquiring and from within, crustal thickness and strength, transporting earth materials can be called a the action of endogenic forces are not uniform geomorphic agent. When these elements of and hence the tectonically controlled original nature become mobile due to gradients, they crustal surface is uneven. remove the materials and transport them over slopes and deposit them at lower level. Diastrophism Geomorphic processes and geomorphic agents All processes that move, elevate or build up especially exogenic, unless stated separately, portions of the earth’s crust come under are one and the same. diastrophism. They include: (i) orogenic A process is a force applied on earth processes involving mountain building materials affecting the same. An agent is a through severe folding and affecting long and mobile medium (like running water, moving ice narrow belts of the earth’s crust; (ii) epeirogenic masses, wind, waves and currents etc.) which processes involving uplift or warping of large removes, transports and deposits earth parts of the earth’s crust; (iii) earthquakes materials. Running water, groundwater, involving local relatively minor movements; glaciers, wind, waves and currents, etc., can (iv) plate tectonics involving horizontal be called geomorphic agents. movements of crustal plates. In the process of orogeny, the crust is Do you think it is essential to distinguish severely deformed into folds. Due to epeirogeny, geomorphic agents and geomorphic there may be simple deformation. Orogeny is processes? a mountain building process whereas epeirogeny is continental building process. Gravity besides being a directional force Through the processes of orogeny, epeirogeny, activating all downslope movements of matter earthquakes and plate tectonics, there can be also causes stresses on the earth’s materials. faulting and fracturing of the crust. All these Indirect gravitational stresses activate wave and processes cause pressure, volume and tide induced currents and winds. Without temperature (PVT) changes which in turn gravity and gradients there would be no induce metamorphism of rocks. mobility and hence no erosion, transportation and deposition are possible. So, gravitational Epeirogeny and orogeny, cite the stresses are as important as the other differences. geomorphic processes. Gravity is the force that is keeping us in contact with the surface and it is the force that switches on the movement of Volcanism all surface material on earth. All the movements Volcanism includes the movement of molten either within the earth or on the surface of the rock (magma) onto or toward the earth’s earth occur due to gradients — from higher surface and also formation of many intrusive levels to lower levels, from high pressure to low and extrusive volcanic forms. Many aspects of pressure areas etc. volcanism have already been dealt in detail 2024-25 GEOMORPHIC PROCESSES 39 under volcanoes in the Unit II and under driving forces. It should become clear from igneous rocks in the preceding chapter in this this chart that for each process there exists a unit. distinct driving force or energy. As there are different climatic regions owing What do the words volcanism and to variations in thermal gradients created by volcanoes indicate? latitudinal, seasonal, and land and water spread on the surface of the earth, the exogenic geomorphic processes vary from region to EXOGENIC PROCESSES region. The density, type and distribution of The exogenic processes derive their energy vegetation which largely depend upon from atmosphere determined by the ultimate precipitation and temperature also exert energy from the sun and also the gradients created by tectonic factors. Why do you think that the slopes or gradients are created by tectonic factors? Gravitational force acts upon all earth materials having a sloping surface and tend to produce movement of matter in down slope direction. Force applied per unit area is called stress. Stress is produced in a solid Figure 5.1 : Denudational processes and their by pushing or pulling. This induces driving forces deformation. Forces acting along the faces of influence indirectly on exogenic geomorphic earth materials are shear stresses (separating processes. Within different climatic regions forces). It is this stress that breaks rocks and there may be local variations of the effects of other earth materials. The shear stresses different climatic elements due to altitudinal result in angular displacement or slippage. differences, aspect variations and the variation Besides the gravitational stress earth in the amount of insolation received by north materials become subjected to molecular and south facing slopes as compared to east stresses that may be caused by a number of and west facing slopes. Further, due to factors amongst which temperature changes, differences in wind velocities and directions, crystallisation and melting are the most amount and kind of precipitation, its intensity, common. Chemical processes normally lead the relation between precipitation and to loosening of bonds between grains, evaporation, daily range of temperature, dissolving of soluble minerals or cementing freezing and thawing frequency, depth of frost materials. Thus, the basic reason that leads penetration, the geomorphic processes vary to weathering, mass movements, and erosion within any climatic region. is development of stresses in the body of the earth materials. What is the sole driving force behind all Temperature and precipitation are the the exogenic processes? two important climatic elements that control various processes. Climatic factors being equal, the intensity All the exogenic geomorphic processes of action of exogenic geomorphic processes are covered under a general term, depends upon type and structure of rocks. The denudation. The word ‘denude’ means to term structure includes such aspects of rocks strip off or to uncover. Weathering, mass as folds, faults, orientation and inclination of wasting/movements, erosion and beds, presence or absence of joints, bedding transportation are included in denudation. planes, hardness or softness of constituent The flow chart (Figure 5.1) gives the minerals, chemical susceptibility of mineral denudation processes and their respective constituents; the permeability or impermeability 2024-25 40 FUNDAMENTALS OF PHYSICAL GEOGRAPHY etc. Different types of rocks with differences in their structure offer varying resistances to various geomorphic processes. A particular rock may be resistant to one process and non- resistant to another. And, under varying climatic conditions, particular rocks may exhibit different degrees of resistance to geomorphic processes and hence they operate at differential rates and give rise to differences in topography. The effects of most of the exogenic geomorphic processes are small and slow and may be imperceptible in a short time span, but will in the long run affect the rocks severely due to continued fatigue. Finally, it boils down to one fact that the Figure 5.2 : Climatic regimes and depth of weathering differences on the surface of the earth though mantles (adapted and modified from Strakhov, 1967) originally related to the crustal evolution continue to exist in some form or the other due to differences in the type and structure of earth Activity materials, differences in geomorphic processes Mark the latitude values of different and in their rates of operation. climatic regimes in Figure 6.2 and Some of the exogenic geomorphic processes compare the details. have been dealt in detail here. WEATHERING There are three major groups of weathering processes : (i) chemical; (ii) physical or Weathering is action of elements of weather and mechanical; (iii) biological weathering processes. climate over earth materials. There are a Very rarely does any one of these processes ever number of processes within weathering which operate completely by itself, but quite often a act either individually or together to affect the dominance of one process can be seen. earth materials in order to reduce them to fragmental state. Chemical Weathering Processes Weathering is defined as mechanical A group of weathering processes viz; solution, disintegration and chemical decom- carbonation, hydration, oxidation and position of rocks through the actions of reduction act on the rocks to decompose, various elements of weather and climate. dissolve or reduce them to a fine clastic state through chemical reactions by oxygen, surface As very little or no motion of materials and/or soil water and other acids. Water and takes place in weathering, it is an in-situ or air (oxygen and carbon dioxide) along with heat on-site process. must be present to speed up all chemical reactions. Over and above the carbon dioxide Is this little motion which can occur present in the air, decomposition of plants and sometimes due to weathering synonymous animals increases the quantity of carbon with transportation? If not, why? dioxide underground. These chemical reactions Weathering processes are conditioned by on various minerals are very much similar to many complex geological, climatic, topographic the chemical reactions in a laboratory. and vegetative factors. Climate is of particular importance. Not only weathering processes Physical Weathering Processes differ from climate to climate, but also the depth Physical or mechanical weathering processes of the weathering mantle (Figure 5.2). depend on some applied forces. The applied 2024-25 GEOMORPHIC PROCESSES 41 forces could be: (i) gravitational forces such as overburden pressure, load and shearing stress; (ii) expansion forces due to temperature changes, crystal growth or animal activity; (iii) water pressures controlled by wetting and drying cycles. Many of these forces are applied both at the surface and within different earth materials leading to rock fracture. Most of the physical weathering processes are caused by thermal expansion and pressure release. These processes are small and slow but can cause great damage to the rocks because of continued fatigue the rocks suffer due to Fig.5.3 : Exfoliation (Flacking) and granular repetition of contraction and expansion. disintegration BIOLOGICAL ACTIVITY AND WEATHERING SIGNIFICANCE OF WEATHERING Biological weathering is contribution to or Weathering processes are responsible for removal of minerals and ions from the breaking down the rocks into smaller weathering environment and physical changes fragments and preparing the way for due to growth or movement of organisms. formation of not only regolith and soils, but Burrowing and wedging by organisms like also erosion and mass movements. Biomes earthworms, termites, rodents etc., help in and bio-diversity is basically a result of forests exposing the new surfaces to chemical attack (vegetation) and forests depend upon the and assists in the penetration of moisture and depth of weathering mantles. Erosion cannot air. Human beings by disturbing vegetation, be significant if the rocks are not weathered. ploughing and cultivating soils, also help in That means, weathering aids mass wasting, mixing and creating new contacts between erosion and reduction of relief and changes air, water and minerals in the earth materials. in landforms are a consequence of erosion. Decaying plant and animal matter help in the Weathering of rocks and deposits helps in production of humic, carbonic and other the enrichment and concentrations of certain acids which enhance decay and solubility of valuable ores of iron, manganese, aluminium, some elements. Plant roots exert a tremendous copper etc., which are of great importance pressure on the earth materials mechanically for the national economy. Weathering is an breaking them apart. important process in the formation of soils. When rocks undergo weathering, some SPECIAL EFFECTS OF WEATHERING materials are removed through chemical Exfoliation or physical leaching by groundwater and thereby the concentration of remaining This has already been explained under (valuable) materials increases. Without physical weathering processes of unloading, such a weathering taking place, the thermal contraction and expansion and salt concentration of the same valuable weathering. Exfoliation is a result but not a material may not be sufficient and process. Flaking off of more or less curved economically viable to exploit, process and sheets of shells from over rocks or bedrock refine. This is what is called enrichment. results in smooth and rounded surfaces (Figure 5.3). Exfoliation can occur due to MASS MOVEMENTS expansion and contraction induced by temperature changes. Exfoliation domes and These movements transfer the mass of rock tors result due to unloading and thermal debris down the slopes under the direct expansion respectively. influence of gravity. That means, air, water or 2024-25 42 FUNDAMENTALS OF PHYSICAL GEOGRAPHY ice do not carry debris with them from place to the relationships among different types of mass place but on the other hand the debris may movements, their relative rates of movement carry with it air, water or ice. The movements and moisture limits. of mass may range from slow to rapid, affecting shallow to deep columns of materials Landslides and include creep, flow, slide and fall. Gravity These are relatively rapid and perceptible exerts its force on all matter, both bedrock and movements. The materials involved are relatively the products of weathering. So, weathering is dry. The size and shape of the detached mass not a pre-requisite for mass movement though depends on the nature of discontinuities in the it aids mass movements. Mass movements are rock, the degree of weathering and the steepness very active over weathered slopes rather than of the slope. Depending upon the type of movement of materials several types are over unweathered materials. identified in this category. Mass movements are aided by gravity and Slump is slipping of one or several units of no geomorphic agent like running water, rock debris with a backward rotation with glaciers, wind, waves and currents participate respect to the slope over which the movement in the process of mass movements. That means takes place (Figure 5.4). Rapid rolling or sliding mass movements do not come under erosion though there is a shift (aided by gravity) of materials from one place to another. Materials over the slopes have their own resistance to disturbing forces and will yield only when force is greater than the shearing resistance of the materials. Weak unconsolidated materials, thinly bedded rocks, faults, steeply dipping beds, vertical cliffs or steep slopes, abundant Figure 5.4 : Slumping of debris with backward rotation precipitation and torrential rains and scarcity of vegetation etc., favour mass movements. of earth debris without backward rotation of Several activating causes precede mass mass is known as debris slide. Debris fall is movements. They are : (i) removal of support nearly a free fall of earth debris from a vertical or from below to materials above through natural overhanging face. Sliding of individual rock masses down bedding, joint or fault surfaces or artificial means; (ii) increase in gradient and is rockslide. Over steep slopes, rock sliding is height of slopes; (iii) overloading through very fast and destructive. Figure 5.5 shows addition of materials naturally or by artificial landslide scars over steep slopes. Slides occur filling; (iv) overloading due to heavy rainfall, as planar failures along discontinuities like saturation and lubrication of slope materials; (v) removal of material or load from over the original slope surfaces; (vi) occurrence of earthquakes, explosions or machinery; (vii) excessive natural seepage; (viii) heavy drawdown of water from lakes, reservoirs and rivers leading to slow outflow of water from under the slopes or river banks; (ix) indis- criminate removal of natural vegetation. Heave (heaving up of soils due to frost growth and other causes), flow and slide are Figure 5.5 : Landslide scars in Shiwalik Himalayan ranges near the three forms of movements. Figure 5.5 shows river Sarada at India-Nepal border, Uttar Pradesh 2024-25 GEOMORPHIC PROCESSES 43 bedding planes that dip steeply. Rock fall is free by rock debris carried by these geomorphic falling of rock blocks over any steep slope agents also aids greatly in erosion. By erosion, keeping itself away from the slope. Rock falls relief degrades, i.e., the landscape is worn occur from the superficial layers of the rock face, down. That means, though weathering aids an occurrence that distinguishes it from erosion it is not a pre-condition for erosion to rockslide which affects materials up to a take place. Weathering, mass-wasting and substantial depth. erosion are degradational processes. It is erosion that is largely responsible for Between mass wasting and mass continuous changes that the earth’s surface movements, which term do you feel is is undergoing. As indicated in Figure 6.1, most appropriate? Why? Can solifluction denudational processes like erosion and be included under rapid flow movements? transportation are controlled by kinetic energy. Why it can be and can’t be? The erosion and transportation of earth materials is brought about by wind, running water, glaciers, waves and ground water. Of In our country, debris avalanches and these the first three agents are controlled by landslides occur very frequently in the climatic conditions. They represent three states Himalayas. There are many reasons for this. One, the Himalayas are tectonically of matter — gaseous (wind), liquid (running active. They are mostly made up of water) and solid (glacier) respectively. sedimentary rocks and unconsolidated and semi-consolidated deposits. The Can you compare the three climatically slopes are very steep. Compared to the controlled agents? Himalayas, the Nilgiris bordering Tamilnadu, Karnataka, Kerala and the The work of the other two agents of Western Ghats along the west coast are erosion-waves and ground water is not relatively tectonically stable and are controlled by climate. In case of waves it is mostly made up of very hard rocks; but, the location along the interface of litho and still, debris avalanches and landslides occur though not as frequently as in the hydro sphere — coastal region — that will Himalayas, in these hills. Why? Many determine the work of waves, whereas the slopes are steeper with almost vertical work of ground water is determined more by cliffs and escarpments in the Western the lithological character of the region. If the Ghats and Nilgiris. Mechanical weathering rocks are permeable and soluble and water due to temperature changes and ranges is available only then karst topography is pronounced. They receive heavy develops. In the next chapter we shall be amounts of rainfall over short periods. dealing with the landforms produced by each So, there is almost direct rock fall quite of these agents of erosion. frequently in these places along with Deposition is a consequence of erosion. landslides and debris avalanches. The erosional agents loose their velocity and hence energy on gentler slopes and the materials carried by them start to settle EROSION AND DEPOSITION themselves. In other words, deposition is not Erosion involves acquisition and transportation actually the work of any agent. The coarser of rock debris. When massive rocks break materials get deposited first and finer ones into smaller fragments through weathering later. By deposition depressions get filled up. and any other process, erosional geomorphic The same erosional agents viz., running water, agents like running water, groundwater, glaciers, wind, waves and groundwater act as glaciers, wind and waves remove and aggradational or depositional agents also. transport it to other places depending upon What happens to the surface of the earth the dynamics of each of these agents. Abrasion due to erosion and deposition is elaborated 2024-25 44 FUNDAMENTALS OF PHYSICAL GEOGRAPHY in the next chapter on landforms and their Is weathering solely responsible for soil evolution. formation? If not, why? There is a shift of materials in mass movements as well as in erosion from one Pedology is soil science. A pedologist is a place to the other. So, why can’t both be soil-scientist. treated as one and the same? Can there be appreciable erosion without rocks undergoing weathering? Soil-forming Factors Five basic factors control the formation of soils: SOIL FORMATION (i) parent material; (ii) topography; (iii) climate; (iv) biological activity; (v) time. In fact soil You see plants growing in soils. You play in forming factors act in union and affect the the ground and come into contact with soil. action of one another. You touch and feel soil and soil your clothes while playing. Can you describe it? Parent Material Soil is a dynamic medium in which many chemical, physical and biological Parent material is a passive control factor in activities go on constantly. Soil is a result soil formation. Parent materials can be any of decay, it is also the medium for growth. in-situ or on-site weathered rock debris It is a changing and developing body. It has (residual soils) or transported deposits many characteristics that fluctuate with the (transported soils). Soil formation depends seasons. It may be alternatively cold and upon the texture (sizes of debris) and structure warm or dry and moist. Biological activity (disposition of individual grains/particles of is slowed or stopped if the soil becomes too debris) as well as the mineral and chemical cold or too dry. Organic matter increases composition of the rock debris/deposits. when leaves fall or grasses die. Nature and rate of weathering and depth of weathering mantle are important considerations Process of Soil Formation under parent materials. There may be differences in soil over similar bedrock and Soil formation or pedogenesis depends first dissimilar bedrocks may have similar soils on weathering. It is this weathering mantle above them. But when soils are very young (depth of the weathered material) which is and have not matured these show strong links the basic input for soil to form. First, the with the type of parent rock. Also, in case of weathered material or transported deposits some limestone areas, where the weathering are colonised by bacteria and other inferior processes are specific and peculiar, soils will plant bodies like mosses and lichens. Also, show clear relation with the parent rock. several minor organisms may take shelter within the mantle and deposits. The dead Topography remains of organisms and plants help in humus accumulation. Minor grasses and Topography like parent materials is another ferns may grow; later, bushes and trees will passive control factor. The influence of start growing through seeds brought in by topography is felt through the amount of birds and wind. Plant roots penetrate down, exposure of a surface covered by parent burrowing animals bring up particles, mass materials to sunlight and the amount of of material becomes porous and sponge-like surface and sub-surface drainage over and with a capacity to retain water and to permit through the parent materials. Soils will be thin on the passage of air and finally a mature soil, a steep slopes and thick over flat upland areas. complex mixture of mineral and organic Over gentle slopes where erosion is slow and products forms. percolation of water is good, soil formation is 2024-25 GEOMORPHIC PROCESSES 45 very favourable. Soils over flat areas may of the soil. Some organic acids which form develop a thick layer of clay with good during humification aid in decomposing the accumulation of organic matter giving the soil minerals of the soil parent materials. dark colour. Intensity of bacterial activity shows up differences between soils of cold and warm Climate climates. Humus accumulates in cold climates Climate is an important active factor in soil as bacterial growth is slow. With formation. The climatic elements involved in undecomposed organic matter because of low soil development are : (i) moisture in terms of bacterial activity, layers of peat develop in sub- its intensity, frequency and duration of arctic and tundra climates. In humid tropical precipitation - evaporation and humidity; and equatorial climates, bacterial growth and (ii) temperature in terms of seasonal and action is intense and dead vegetation is rapidly diurnal variations. oxidised leaving very low humus content in Precipitation gives soil its moisture content the soil. Further, bacteria and other soil which makes the chemical and biological organisms take gaseous nitrogen from the air activities possible. Excess of water helps in the and convert it into a chemical form that can downward transportation of soil components be used by plants. This process is known as through the soil (eluviation) and deposits the nitrogen fixation. Rhizobium, a type of same down below (illuviation). In climates like bacteria, lives in the root nodules of leguminous wet equatorial rainy areas with high rainfall, plants and fixes nitrogen beneficial to the host not only calcium, sodium, magnesium, plant. The influence of large animals like ants, potassium etc. but also a major part of silica is termites, earthworms, rodents etc., is removed from the soil. Removal of silica from mechanical, but, it is nevertheless important the soil is known as desilication. In dry climates, in soil formation as they rework the soil up because of high temperature, evaporation and down. In case of earthworms, as they exceeds precipitation and hence ground water feed on soil, the texture and chemistry of the is brought up to the surface by capillary action soil that comes out of their body changes. and in the process the water evaporates leaving behind salts in the soil. Such salts form into a Time crust in the soil known as hardpans. In tropical Time is the third important controlling factor climates and in areas with intermediate precipitation conditions, calcium carbonate in soil formation. The length of time the soil nodules (kanker) are formed. forming processes operate, determines Temperature acts in two ways — increasing maturation of soils and profile development. A or reducing chemical and biological activity. soil becomes mature when all soil-forming Chemical activity is increased in higher processes act for a sufficiently long time temperatures, reduced in cooler temperatures developing a profile. Soils developing from (with an exception of carbonation) and stops recently deposited alluvium or glacial till are in freezing conditions. That is why, tropical soils considered young and they exhibit no horizons with higher temperatures show deeper profiles or only poorly developed horizons. No specific and in the frozen tundra regions soils contain length of time in absolute terms can be fixed largely mechanically broken materials. for soils to develop and mature. Biological Activity Is it necessary to separate the process of The vegetative cover and organisms that occupy soil formation and the soil forming the parent materials from the beginning and also control factors? at later stages help in adding organic matter, Why are time, topography and parent moisture retention, nitrogen etc. Dead plants material considered as passive control provide humus, the finely divided organic matter factors in soil formation? 2024-25 46 FUNDAMENTALS OF PHYSICAL GEOGRAPHY EXERCISES 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 soil- forming factors? What is the role of climate and biological activity as two important control factors in the formation of soils? Project Work Depending upon the topography and materials around you, observe and record climate, possible weathering process and soil contents and characteristics. 2024-25