GEOMORPHIC PROCESSES

C H A P T E R

After learning about how the earth wasborn, how it evolved its crust and otherinner layers, how its crustal plates

moved and are moving, and other informationon earthquakes, the forms of volcanism andabout the rocks and minerals the crust iscomposed of, it is time to know in detail aboutthe surface of the earth on which we live. Letus start with this question.

Why is the surface of the earth uneven?

The earth’s crust is dynamic. You are wellaware that it has moved and moves verticallyand horizontally. Of course, it moved a bit fasterin the past than the rate at which it is movingnow. The differences in the internal forcesoperating from within the earth which built upthe crust have been responsible for thevariations in the outer surface of the crust. Theearth’s surface is being continuously subjectedto external forces induced basically by energy(sunlight). Of course, the internal forces are stillactive though with different intensities. Thatmeans, the earth’s surface is beingcontinuously subjected to by external forcesoriginating within the earth’s atmosphere andby internal forces from within the earth. Theexternal forces are known as exogenic forcesand the internal forces are known as endogenic

forces. The actions of exogenic forces result inwearing down (degradation) of relief/elevationsand filling up (aggradation) of basins/depressions, on the earth’s surface. Thephenomenon of wearing down of reliefvariations of the surface of the earth througherosion is known as gradation. The endogenic

forces continuously elevate or build up partsof the earth’s surface and hence the exogenicprocesses fail to even out the relief variationsof the surface of the earth. So, variations remainas long as the opposing actions of exogenic andendogenic forces continue. In general terms,the endogenic forces are mainly land buildingforces and the exogenic processes are mainlyland wearing forces. The surface of the earth issensitive. Humans depend on it for theirsustenance and have been using it extensivelyand intensively. So, it is essential to understandits nature in order to use it effectively withoutdisturbing its balance and diminishing itspotential for the future. Almost all organismscontribute to sustain the earth’s environment.However, humans have caused extensivedamage to the environment through over useof resources. Use we must, but must also leaveit potential enough to sustain life through thefuture. Most of the surface of the earth had andhas been shaped over very long periods of time(hundreds and thousands of years) andbecause of its use and misuse by humans itspotential is being diminished at a fast rate. Ifthe processes which shaped and are shapingthe surface of the earth into varieties of forms(shapes) and the nature of materials of whichit is composed of, are understood, precautionscan be taken to minimise the detrimental effectsof human use and to preserve it for posterity.

GEOMORPHIC PROCESSES

You would like to know the meaning ofgeomorphic processes. The endogenic andexogenic forces causing physical stresses andchemical actions on earth materials and

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bringing about changes in the configuration

of the surface of the earth are known asgeomorphic processes. Diastrophism and

volcanism are endogenic geomorphic

processes. These have already been discussed

in brief in the preceding unit. Weathering, masswasting, erosion and deposition are exogenic

geomorphic processes. These exogenic

processes are dealt with in detail in this chapter.

Any exogenic element of nature (like water,ice, wind, etc.,) capable of acquiring and

transporting earth materials can be called a

geomorphic agent. When these elements of

nature become mobile due to gradients, theyremove the materials and transport them over

slopes and deposit them at lower level.

Geomorphic processes and geomorphic agents

especially exogenic, unless stated separately,are one and the same.

A process is a force applied on earth

materials affecting the same. An agent is a

mobile medium (like running water, moving icemasses, wind, waves and currents etc.) which

removes, transports and deposits earth

materials. Running water, groundwater,

glaciers, wind, waves and currents, etc., canbe called geomorphic agents.

Do you think it is essential to distinguish

geomorphic agents and geomorphic

processes?

Gravity besides being a directional forceactivating all downslope movements of matter

also causes stresses on the earth’s materials.Indirect gravitational stresses activate wave andtide induced currents and winds. Without

gravity and gradients there would be nomobility and hence no erosion, transportationand deposition are possible. So, gravitational

stresses are as important as the othergeomorphic processes. Gravity is the force thatis keeping us in contact with the surface and it

is the force that switches on the movement ofall surface material on earth. All the movementseither within the earth or on the surface of the

earth occur due to gradients — from higherlevels to lower levels, from high pressure to lowpressure areas etc.

ENDOGENIC PROCESSES

The energy emanating from within the earth isthe main force behind endogenic geomorphicprocesses. This energy is mostly generated byradioactivity, rotational and tidal friction andprimordial heat from the origin of the earth.This energy due to geothermal gradients andheat flow from within induces diastrophismand volcanism in the lithosphere. Due tovariations in geothermal gradients and heat flowfrom within, crustal thickness and strength,the action of endogenic forces are not uniformand hence the tectonically controlled originalcrustal surface is uneven.

Diastrophism

All processes that move, elevate or build upportions of the earth’s crust come underdiastrophism. They include: (i) orogenic

processes involving mountain buildingthrough severe folding and affecting long andnarrow belts of the earth’s crust; (ii) epeirogenic

processes involving uplift or warping of largeparts of the earth’s crust; (iii) earthquakesinvolving local relatively minor movements;(iv) plate tectonics involving horizontalmovements of crustal plates.

In the process of orogeny, the crust isseverely deformed into folds. Due to epeirogeny,there may be simple deformation. Orogeny isa mountain building process whereasepeirogeny is continental building process.Through the processes of orogeny, epeirogeny,earthquakes and plate tectonics, there can befaulting and fracturing of the crust. All theseprocesses cause pressure, volume andtemperature (PVT) changes which in turninduce metamorphism of rocks.

Epeirogeny and orogeny, cite the

differences.

Volcanism

Volcanism includes the movement of moltenrock (magma) onto or toward the earth’ssurface and also formation of many intrusiveand extrusive volcanic forms. Many aspects ofvolcanism have already been dealt in detail

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driving forces. It should become clear fromthis chart that for each process there exists adistinct driving force or energy.

As there are different climatic regions owingto variations in thermal gradients created bylatitudinal, seasonal, and land and waterspread on the surface of the earth, the exogenicgeomorphic processes vary from region toregion. The density, type and distribution ofvegetation which largely depend uponprecipitation and temperature also exert

under volcanoes in the Unit II and underigneous rocks in the preceding chapter in thisunit.

What do the words volcanism and

volcanoes indicate?

EXOGENIC PROCESSES

The exogenic processes derive their energyfrom atmosphere determined by the ultimateenergy from the sun and also the gradientscreated by tectonic factors.

Why do you think that the slopes or

gradients are created by tectonic factors?

Gravitational force acts upon all earthmaterials having a sloping surface and tendto produce movement of matter in downslope direction. Force applied per unit areais called stress. Stress is produced in a solidby pushing or pull ing. This inducesdeformation. Forces acting along the faces ofearth materials are shear stresses (separatingforces). It is this stress that breaks rocks andother earth materials. The shear stressesresult in angular displacement or slippage.Besides the gravitational stress earthmaterials become subjected to molecularstresses that may be caused by a number offactors amongst which temperature changes,crystallisation and melting are the mostcommon. Chemical processes normally leadto loosening of bonds between grains,dissolving of soluble minerals or cementingmaterials. Thus, the basic reason that leadsto weathering, mass movements, and erosionis development of stresses in the body of theearth materials.

Temperature and precipitation are thetwo important climatic elements that controlvarious processes.

All the exogenic geomorphic processesare covered under a general term,denudation. The word ‘denude’ means tostrip off or to uncover. Weathering, masswasting/movements, erosion andtransportation are included in denudation.The flow chart (Figure 6.1) gives thedenudation processes and their respective

influence indirectly on exogenic geomorphicprocesses. Within different climatic regionsthere may be local variations of the effects ofdifferent climatic elements due to altitudinaldifferences, aspect variations and the variationin the amount of insolation received by northand south facing slopes as compared to eastand west facing slopes. Further, due todifferences in wind velocities and directions,amount and kind of precipitation, its intensity,the relation between precipitation andevaporation, daily range of temperature,freezing and thawing frequency, depth of frostpenetration, the geomorphic processes varywithin any climatic region.

What is the sole driving force behind all

the exogenic processes?

Climatic factors being equal, the intensityof action of exogenic geomorphic processesdepends upon type and structure of rocks. Theterm structure includes such aspects of rocksas folds, faults, orientation and inclination ofbeds, presence or absence of joints, beddingplanes, hardness or softness of constituentminerals, chemical susceptibility of mineralconstituents; the permeability or impermeability

Figure 6.1 : Denudational processes and theirdriving forces

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etc. Different types of rocks with differencesin their structure offer varying resistances tovarious geomorphic processes. A particularrock may be resistant to one process and non-resistant to another. And, under varyingclimatic conditions, particular rocks mayexhibit different degrees of resistance togeomorphic processes and hence they operateat differential rates and give rise to differencesin topography. The effects of most of theexogenic geomorphic processes are small andslow and may be imperceptible in a short timespan, but will in the long run affect the rocksseverely due to continued fatigue.

Finally, it boils down to one fact that thedifferences on the surface of the earth thoughoriginally related to the crustal evolutioncontinue to exist in some form or the other dueto differences in the type and structure of earthmaterials, differences in geomorphic processesand in their rates of operation.

Some of the exogenic geomorphic processeshave been dealt in detail here.

WEATHERING

Weathering is action of elements of weather andclimate over earth materials. There are anumber of processes within weathering whichact either individually or together to affect theearth materials in order to reduce them tofragmental state.

Weathering is defined as mechanical

disintegration and chemical decom-

position of rocks through the actions of

various elements of weather and climate.

As very little or no motion of materialstakes place in weathering, it is an in-situ oron-site process.

Is this little motion which can occur

sometimes due to weathering synonymous

with transportation? If not, why?

Weathering processes are conditioned bymany complex geological, climatic, topographicand vegetative factors. Climate is of particularimportance. Not only weathering processesdiffer from climate to climate, but also the depthof the weathering mantle (Figure 6.2).

Figure 6.2 : Climatic regimes and depth of weatheringmantles (adapted and modified from Strakhov, 1967)

Activity

Mark the latitude values of differentclimatic regimes in Figure 6.2 and

compare the details.

There are three major groups of weatheringprocesses : (i) chemical; (ii) physical ormechanical; (iii) biological weathering processes.Very rarely does any one of these processes everoperate completely by itself, but quite often adominance of one process can be seen.

Chemical Weathering Processes

A group of weathering processes viz; solution,carbonation, hydration, oxidation andreduction act on the rocks to decompose,dissolve or reduce them to a fine clastic statethrough chemical reactions by oxygen, surfaceand/or soil water and other acids. Water andair (oxygen and carbon dioxide) along with heatmust be present to speed up all chemicalreactions. Over and above the carbon dioxidepresent in the air, decomposition of plants andanimals increases the quantity of carbondioxide underground. These chemical reactionson various minerals are very much similar tothe chemical reactions in a laboratory.

Physical Weathering Processes

Physical or mechanical weathering processesdepend on some applied forces. The applied

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forces could be: (i) gravitational forces suchas overburden pressure, load and shearingstress; (ii) expansion forces due to temperaturechanges, crystal growth or animal activity;(iii) water pressures controlled by wetting anddrying cycles. Many of these forces are appliedboth at the surface and within different earthmaterials leading to rock fracture. Most ofthe physical weathering processes are causedby thermal expansion and pressure release.These processes are small and slow but cancause great damage to the rocks because ofcontinued fatigue the rocks suffer due torepetition of contraction and expansion.

BIOLOGICAL ACTIVITY AND WEATHERING

Biological weathering is contribution to orremoval of minerals and ions from theweathering environment and physical changesdue to growth or movement of organisms.Burrowing and wedging by organisms likeearthworms, termites, rodents etc., help inexposing the new surfaces to chemical attackand assists in the penetration of moisture andair. Human beings by disturbing vegetation,ploughing and cultivating soils, also help inmixing and creating new contacts betweenair, water and minerals in the earth materials.Decaying plant and animal matter help in theproduction of humic, carbonic and otheracids which enhance decay and solubility ofsome elements. Plant roots exert a tremendouspressure on the earth materials mechanicallybreaking them apart.

SPECIAL EFFECTS OF WEATHERING

Exfoliation

This has already been explained underphysical weathering processes of unloading,thermal contraction and expansion and saltweathering. Exfoliation is a result but not aprocess. Flaking off of more or less curvedsheets of shells from over rocks or bedrockresults in smooth and rounded surfaces(Figures 6.3; 6.4). Exfoliation can occur dueto expansion and contraction induced bytemperature changes. Exfoliation domes andtors result due to unloading and thermalexpansion respectively.

SIGNIFICANCE OF WEATHERING

Weathering processes are responsible forbreaking down the rocks into smallerfragments and preparing the way forformation of not only regolith and soils, butalso erosion and mass movements. Biomesand bio-diversity is basically a result of forests(vegetation) and forests depend upon thedepth of weathering mantles. Erosion cannotbe significant if the rocks are not weathered.That means, weathering aids mass wasting,erosion and reduction of relief and changesin landforms are a consequence of erosion.Weathering of rocks and deposits helps inthe enrichment and concentrations of certainvaluable ores of iron, manganese, aluminium,copper etc., which are of great importancefor the national economy. Weathering is animportant process in the formation of soils.

When rocks undergo weathering, somematerials are removed through chemicalor physical leaching by groundwater andthereby the concentration of remaining(valuable) materials increases. Withoutsuch a weathering taking place, theconcentration of the same valuablematerial may not be sufficient andeconomically viable to exploit, process and

refine. This is what is called enrichment.

MASS MOVEMENTS

These movements transfer the mass of rockdebris down the slopes under the directinfluence of gravity. That means, air, water or

Fig.6.4 : Exfoliation (Flacking) and granulardisintegration

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ice do not carry debris with them from placeto place but on the other hand the debrismay carry with it air, water or ice. Themovements of mass may range from slow torapid, affecting shallow to deep columns ofmaterials and include creep, flow, slide andfall. Gravity exerts its force on all matter,both bedrock and the products of weathering.So, weathering is not a pre-requisite for massmovement though it aids mass movements.Mass movements are very active overweathered slopes rather than overunweathered materials.

Mass movements are aided by gravity andno geomorphic agent like running water,glaciers, wind, waves and currents participatein the process of mass movements. That meansmass movements do not come under erosionthough there is a shift (aided by gravity) ofmaterials from one place to another. Materialsover the slopes have their own resistance todisturbing forces and will yield only when forceis greater than the shearing resistance of thematerials. Weak unconsolidated materials,thinly bedded rocks, faults, steeply dippingbeds, vertical cliffs or steep slopes, abundantprecipitation and torrential rains and scarcityof vegetation etc., favour mass movements.

Several activating causes precede massmovements. They are : (i) removal of supportfrom below to materials above throughnatural or artificial means; (ii) increase ingradient and height of slopes; (iii) overloadingthrough addition of materials naturally or byartificial filling; (iv) overloading due to heavyrainfall, saturation and lubrication of slopematerials; (v) removal of material or load fromover the original slope surfaces; (vi) occurrenceof earthquakes, explosions or machinery;(vii) excessive natural seepage; (viii) heavydrawdown of water from lakes, reservoirs andrivers leading to slow outflow of water fromunder the slopes or river banks; (ix) indis-criminate removal of natural vegetation.

Heave (heaving up of soils due to frostgrowth and other causes), flow and slide arethe three forms of movements. Figure 6.5shows the relationships among different typesof mass movements, their relative rates ofmovement and moisture limits.

Landslides

These are relatively rapid and perceptiblemovements. The materials involved arerelatively dry. The size and shape of thedetached mass depends on the nature ofdiscontinuities in the rock, the degree ofweathering and the steepness of the slope.Depending upon the type of movement ofmaterials several types are identified in thiscategory.

Slump is slipping of one or several units ofrock debris with a backward rotation withrespect to the slope over which the movementtakes place (Figure 6.6). Rapid rolling or sliding

Figure 6.6 : Slumping of debris with backward rotation

Figure 6.7 : Landslide scars in Shiwalik Himalayan rangesnear river Sarada at India-Nepal border, Uttar Pradesh

of earth debris without backward rotation ofmass is known as debris slide. Debris fall isnearly a free fall of earth debris from a verticalor overhanging face. Sliding of individual rockmasses down bedding, joint or fault surfacesis rockslide. Over steep slopes, rock sliding isvery fast and destructive. Figure 6.7 showslandslide scars over steep slopes. Slides occuras planar failures along discontinuities like

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bedding planes that dip steeply. Rock fall isfree falling of rock blocks over any steep slopekeeping itself away from the slope. Rock fallsoccur from the superficial layers of the rockface, an occurrence that distinguishes it fromrockslide which affects materials up to asubstantial depth.

Between mass wasting and mass

movements, which term do you feel is

most appropriate? Why? Can solifluction

be included under rapid flow movements?

Why it can be and can’t be?

In our country, debris avalanches and

landslides occur very frequently in the

Himalayas. There are many reasons for

this. One, the Himalayas are tectonically

active. They are mostly made up of

sedimentary rocks and unconsolidated

and semi-consolidated deposits. The

slopes are very steep. Compared to the

Himalayas, the Nilgiris bordering

Tamilnadu, Karnataka, Kerala and the

Western Ghats along the west coast are

relatively tectonically stable and are

mostly made up of very hard rocks; but,

still, debris avalanches and landslides

occur though not as frequently as in the

Himalayas, in these hills. Why? Many

slopes are steeper with almost vertical

cliffs and escarpments in the Western

Ghats and Nilgiris. Mechanical weathering

due to temperature changes and ranges

is pronounced. They receive heavy

amounts of rainfall over short periods.

So, there is almost direct rock fall quite

frequently in these places along with

landslides and debris avalanches.

EROSION AND DEPOSITION

Erosion involves acquisition and transportationof rock debris. When massive rocks breakinto smaller fragments through weatheringand any other process, erosional geomorphicagents like running water, groundwater,glaciers, wind and waves remove andtransport it to other places depending uponthe dynamics of each of these agents. Abrasion

by rock debris carried by these geomorphicagents also aids greatly in erosion. By erosion,relief degrades, i.e., the landscape is worndown. That means, though weathering aidserosion it is not a pre-condition for erosion totake place. Weathering, mass-wasting anderosion are degradational processes. It iserosion that is largely responsible forcontinuous changes that the earth’s surfaceis undergoing. As indicated in Figure 6.1,denudational processes like erosion andtransportation are controlled by kinetic energy.The erosion and transportation of earthmaterials is brought about by wind, runningwater, glaciers, waves and ground water. Ofthese the first three agents are controlled byclimatic conditions. They represent three statesof matter —gaseous (wind), liquid (runningwater) and solid (glacier) respectively.

Can you compare the three climatically

controlled agents?

The work of the other two agents oferosion-waves and ground water is notcontrolled by climate. In case of waves it isthe location along the interface of litho andhydro sphere — coastal region — that willdetermine the work of waves, whereas thework of ground water is determined more bythe lithological character of the region. If therocks are permeable and soluble and wateris available only then karst topographydevelops. In the next chapter we shall bedealing with the landforms produced by eachof these agents of erosion.

Deposition is a consequence of erosion.The erosional agents loose their velocity andhence energy on gentler slopes and thematerials carried by them start to settlethemselves. In other words, deposition is notactually the work of any agent. The coarsermaterials get deposited first and finer oneslater. By deposition depressions get filled up.The same erosional agents viz., running water,glaciers, wind, waves and groundwater actas aggradational or depositional agents also.

What happens to the surface of the earthdue to erosion and deposition is elaborated

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Is weathering solely responsible for soil

formation? If not, why?

Pedology is soil science. A pedologist is a

soil-scientist.

Soil-forming Factors

Five basic factors control the formation of soils:(i) parent material; (ii) topography; (iii) climate;(iv) biological activity; (v) time. In fact soilforming factors act in union and affect theaction of one another.

Parent Material

Parent material is a passive control factor insoil formation. Parent materials can be anyin-situ or on-site weathered rock debris(residual soils) or transported deposits(transported soils). Soil formation dependsupon the texture (sizes of debris) and structure(disposition of individual grains/particles ofdebris) as well as the mineral and chemicalcomposition of the rock debris/deposits.

Nature and rate of weathering and depth ofweathering mantle are important considerationsunder parent materials. There may bedifferences in soil over similar bedrock anddissimilar bedrocks may have similar soilsabove them. But when soils are very youngand have not matured these show strong linkswith the type of parent rock. Also, in case ofsome limestone areas, where the weatheringprocesses are specific and peculiar, soils willshow clear relation with the parent rock.

Topography

Topography like parent materials is anotherpassive control factor. The influence oftopography is felt through the amount ofexposure of a surface covered by parent

materials to sunlight and the amount ofsurface and sub-surface drainage over andthrough the parent materials. Soils will be thin

on steep slopes and thick over flat uplandareas. Over gentle slopes where erosion is slowand percolation of water is good, soil formation

in the next chapter on landforms and theirevolution.

There is a shift of materials in massmovements as well as in erosion from oneplace to the other. So, why can’t both betreated as one and the same? Can therebe appreciable erosion without rocksundergoing weathering?

SOIL FORMATION

You see plants growing in soils. You play inthe ground and come into contact with soil.You touch and feel soil and soil your clotheswhile playing. Can you describe it?

Soil is a dynamic medium in whichmany chemical, physical and biologicalactivities go on constantly. Soil is a resultof decay, it is also the medium for growth.It is a changing and developing body. It hasmany characteristics that fluctuate with theseasons. It may be alternatively cold andwarm or dry and moist. Biological activityis slowed or stopped if the soil becomes toocold or too dry. Organic matter increaseswhen leaves fall or grasses die.

Process of Soil Formation

Soil formation or pedogenesis depends firston weathering. It is this weathering mantle(depth of the weathered material) which isthe basic input for soil to form. First, theweathered material or transported depositsare colonised by bacteria and other inferiorplant bodies like mosses and lichens. Also,several minor organisms may take shelterwithin the mantle and deposits. The deadremains of organisms and plants help inhumus accumulation. Minor grasses andferns may grow; later, bushes and trees willstart growing through seeds brought in bybirds and wind. Plant roots penetrate down,burrowing animals bring up particles, massof material becomes porous and sponge-likewith a capacity to retain water and to permitthe passage of air and finally a mature soil, acomplex mixture of mineral and organicproducts forms.

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is very favourable. Soils over flat areas maydevelop a thick layer of clay with goodaccumulation of organic matter giving the soildark colour.

Climate

Climate is an important active factor in soilformation. The climatic elements involved insoil development are : (i) moisture in terms ofits intensity, frequency and duration ofprecipitation - evaporation and humidity;(ii) temperature in terms of seasonal anddiurnal variations.

Precipitation gives soil its moisture contentwhich makes the chemical and biologicalactivities possible. Excess of water helps in thedownward transportation of soil componentsthrough the soil (eluviation) and deposits thesame down below (illuviation). In climates likewet equatorial rainy areas with high rainfall,not only calcium, sodium, magnesium,potassium etc. but also a major part of silica isremoved from the soil. Removal of silica fromthe soil is known as desilication. In dry climates,because of high temperature, evaporationexceeds precipitation and hence ground wateris brought up to the surface by capillary actionand in the process the water evaporates leavingbehind salts in the soil. Such salts form into acrust in the soil known as hardpans. In tropicalclimates and in areas with intermediateprecipitation conditions, calcium carbonatenodules (kanker) are formed.

Temperature acts in two ways — increasingor reducing chemical and biological activity.Chemical activity is increased in highertemperatures, reduced in cooler temperatures(with an exception of carbonation) and stopsin freezing conditions. That is why, tropical soilswith higher temperatures show deeper profilesand in the frozen tundra regions soils containlargely mechanically broken materials.

Biological Activity

The vegetative cover and organisms that occupythe parent materials from the beginning and alsoat later stages help in adding organic matter,moisture retention, nitrogen etc. Dead plantsprovide humus, the finely divided organic matter

of the soil. Some organic acids which formduring humification aid in decomposing theminerals of the soil parent materials.

Intensity of bacterial activity shows updifferences between soils of cold and warmclimates. Humus accumulates in cold climatesas bacterial growth is slow. Withundecomposed organic matter because of lowbacterial activity, layers of peat develop in sub-arctic and tundra climates. In humid tropicaland equatorial climates, bacterial growth andaction is intense and dead vegetation is rapidlyoxidised leaving very low humus content inthe soil. Further, bacteria and other soilorganisms take gaseous nitrogen from the airand convert it into a chemical form that canbe used by plants. This process is known asnitrogen fixation. Rhizobium, a type ofbacteria, lives in the root nodules of leguminousplants and fixes nitrogen beneficial to the hostplant. The influence of large animals like ants,termites, earthworms, rodents etc., ismechanical, but, it is nevertheless importantin soil formation as they rework the soil upand down. In case of earthworms, as theyfeed on soil, the texture and chemistry of thesoil that comes out of their body changes.

Time

Time is the third important controlling factor

in soil formation. The length of time the soilforming processes operate, determinesmaturation of soils and profile development. A

soil becomes mature when all soil-formingprocesses act for a sufficiently long timedeveloping a profile. Soils developing from

recently deposited alluvium or glacial till areconsidered young and they exhibit no horizonsor only poorly developed horizons. No specific

length of time in absolute terms can be fixedfor soils to develop and mature.

Is it necessary to separate the process of

soil formation and the soil forming

control factors?

Why are time, topography and parent

material considered as passive control

factors in soil formation?

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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 andwhat 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’sheat. Explain.

(iii) Are physical and chemical weathering processes independent of eachother? 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 twoimportant control factors in the formation of soils?

Project Work

Depending upon the topography and materials around you, observe and recordclimate, possible weathering process and soil contents and characteristics.

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