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Home , Nilgiri mountains, Shevaroy Hills

UNIT 1 TOPOGRAPHY OF

Structure 1.1 Intrtwiucticm ()b~ecb\eS 1.2 Origin of the Indian Sub-Continent 1 ..7 The Himalayas 1.3 Peninsular Mountains 1.5 Plains I .h Plateaus 1.7 Desert Topography 1.8 Lakes and Swainps 1.9 Coastal Plains 1 .lo 11idian Sea and Islands 1.11 Sulnnlary 1.1 2 Key Words 1.13 Answers toSAQs

1.1 INTRODUCTION

Topography of a country is carved out of the materials composing the earth's crust by nature's sculpturiiig agents. Every topographic feature that exists in India today is, thereftxe, the culnlination of a lengthy succession of geological events spread over a long ti~ile.This unit explains the diverse topographic features existing in relation to water rescxrrce development of our country. Objectives After going through this unit, you should be able to : understand how the Indian sub-continent, its mountains and plains, and the plateaus were formed, identify the topographic features of a given area in the country, appreciate the landscape and enjoy the scenery that meets the eye, with enhanced knowledge of the way in which ithas developed, and appreciate the relevance of tc)pc>graphicfeatures in relation to water resources development.

1.2 ORIGIN OF THE INDIAN SUB-CONTINENT

India was part of Gondwana land, the great southern continent of the world, which broke up after the close of Palaeozoic time period into huge continental blcxks. These crystal slabs gradually drifted apart to form the present day continents of Africa. Australia, Antarctica, India and South America. The Talchir Boulder Bed of glacial origin indicates that during the Pem~o-Carboniferousperiod, India must have been situated far away from the equator. When Gondwana land was fragmented, the Indian continent drifted northwards. This movement caused the Peninsular Indian block to plough into the Mediterranean Sea of Tethys causing the pile of geosynclinal sediments there to Water buckle up. There is evidence to show that the northern borders of the Penisular of l~adia hlock have been overridden by the much younger inountain ranges- the Himalayas. The doubling of the sialic crust is responsible for the formation of the world's most elevated table land in the Tibet, the so called "Rcw,f of the World". The Hilnalayan ranges continued lo be uplifted hy a series of very severe convulsions. These major crust nlovenlents were responsible for the sharply denlarcaled three-fold structural ;u~dphysiographical divisions of India, each wit11 its own characteristic features- the Peinisula, consisting mainly of Precamhrian rocks in a stahle shield area; the Extra-Peninsula, fornled of a system of folded and faulted sedimentary beds which were deposited in a Mediterranean sea; and an intermediate tectonic' rift valley known as the Indo-Gangetic trough which is now filled with a thick deposit of alluvium. Figure 1.1 depicts the main physiographic suh-tlivisic~nsof lntlia

I. ~irnaloyan~igion 2. Indo ~on~rticplains 3. Central ~l'ghlands North Deccan 5. South Deccan 6. Eastern Pattaus 7. 8. East Coact01 plains 9. Wortern Ghats 10. West Coastal plains

Figure 1.1: Phydogrnphic Sub-dMsiom d India (.Tome: Plryskul Geqfjnrphyojlndirr by ('.S.R~%;~muthu,National Book Trust of 1nd1.1) 1.3 THE HIMALAYAS

Mountains are the spectacular results of deforming forces acting on the earth's crust. A mountain ridge is relatively a long and narrow feature of the raised mass of earth's crust. In fact, a mountain range is a group of ridges and peaks, often in niore or less a parallel arrangement, which are closely associated with each other in age and brigin, such as Himalayas. India has several mountain ranges, chief among them being the Himalayas, the Vindhyas, the Aravalli, the Satpura, the and the Eastern Ghats. The Himalayas (from the Sanskrit words lrimn = snow ,and alaya = abode, meaning the "abode of snow") constitute the highest mountain system of rhe world. They extend for a distance of about 2,500 krn, having a breadth of about 150 to 400 km, and cover an area of about 500,OCK) sq hn. They are typically tectonic in origin, having been uplifted during the Tertiary time period from the bed of the great Mediterranean sea, the Tethys. The Himalayas took probably several million years to attain to their present heights. These uplifting movenlents of these ranges have not ceased yet,li,r this region is still unstable and s'usceptible to earthquakes. During the slow process of mountain formation, by folding and upheaval of the rtxk bcds. the old rivers kept very llluch to their own channels, and hence are seen to cut across these ]nightly ranges. For example, the west-flowing river Sutlej has cut across a b,(N)o 111- high range and runs through a steep-sided valley. The Himalayan chain has an arcual layout with the convex side facing the lndo-~in~eticplain. The southern boundary is clearly demarcated by the 300 m- contour line in the west, and the 150 m-contour line in the east. From the foothills the Himalayas rise rapidly northwards to over 8,000 lii within a short distance. The heights are covered with perpetual snow which feeds the valley glaciers, but the greater ptut of the Hjmalayas lies below the snow-line and is dissected by fluvial erosion. The Himalayan mountains can be divided into three parallel or longitudinal zones, each with definite geographical features - the Great -Himalayas(Himadri) in the oorlh, the Lesser Himalayas (Himuchal) in the ~l;iddle,and the Outer Himalayas (Sl~ivnlik)in thc south. The Himadri The Great Hi~rialayaor the Himadri is a majestic range of mountains which rises above [he lower liniit of perpetual snow. The average elevation of the range is about 6,0()0 111, and some of the highest peaks of Ule Himalayas are situated in this range - Mount Everest (8.848 m);K2 (8.61 1 m); Kanchenjunga (8,598 m); Dhaulagiri (8,172 m): Nanga P.arbat (8.1 26 m); Gasherbrum (8,035 m); Gosainthan (8,013 m); Nan& Devi (7,817 m), and other peaks. This great mountain chain at its western and eastern ends terminates with sharp syntcuial bends. The northern slopes of the Great Himalayan rrulge descend gradually on to some prominent river valleys which run parallel to each other for long distallccs. The Himachal The Lesser Hinlalaya or the Hin~achalis a massive mountainous tract, 75 km wide. Its mounrains and valleys are disposed in all directions, with the lilountains rising to 5,CKK) m and the valleys touching down to 1,000 m of elevation. The suln~nitsare solnewhat of about equal elevation which suggests that this mountain belt is a highly dissected plateau. The Shivalik The Outer Himalaya or the Shivalik forms the fcn>thillsof the Himalayan system, and lies between the Lesser Himalaya and the plains of India. Its width varies from 10to 50 krn, and the average elevation is about 600m. These ranges are co~nposed trf~liainlfrUpper Tertiary sedimentary river deposits. They are folded and faulted Land asd Water II1,m~urws hy earth movements which mark the latest phase of the Himalayan uplift. The td lndiu ranges descend northwards into flat valleys called duns which are intensively cultivated and densely populated.

1,4 PENINSULAR MOUNTAINS ------a

In contrast with the Himalayan ranges of tile extra-peninsular region of India, the mountains we find on the Peninsula are not fold mountains. They represent the erosional remnants of former surfaces uplifted and subjecled to more than one cycle of eroion. The drainage of the Peninsula is asymmetrical in respect of practically all its priilcipal rivers having their origin at the western edge almost within sight of the Arabian Sea, and flowing eastwards traversing the full width of the Peninsula. This ren~arkal?ledrainage feature is due to the fact that the present Peninsular feature represents only a part of a lager land mass, the western half of which either drift away or foundered beneath the Arabian sea. The more prominent of the mountain ranges of the Peninsula are : the Aravallis, the Vindhyas, the Satpuras, the Western Ghats, and the somewhat isdated mountain ranges on the east coast collectively known as the Eastern Ghats. Oil The Aravalli mountains cross RajasUun from south-west to north-east, separating the semi-desert of Bikaner, Jodhpur and Jaisalmer area on the west from the more fertile region of Udaipur and Jaipur on the east They are the remnants of ftwlner mountain ranges d tectonic origin. Guru Sikhar (1,722 m) on the Abu hills is the highest peak of the Aravallis. The Vindllya range stretches across nearly the whole width of Peninsular India over a distance of nearly 1,050 km with an average elevation of 300 In. It forms an important watershed and, along with the Satpura range, constitutes the ncmhan boundary of the Deccan. The Satpura range lies south of the Vindhyas and runs more or less paralkl to it. Several of its peaks are over 1,@K) nl high, the highest being Dhupgath (1,350 m) near Pachmari in Madhya Pradesh. The Satpuras consist of a nunher of parallel ranges which enclose between themselves extensive flat-tr~ppecllava plateaus. The Satpas broaden considerably in the central part and have a radial drainage; Uris central part of the range is bordered on the north by the Mahadeo hills ant1 on the south by the Gawilgarh hills. The Western Ghats (Snhyadri) with an average height of 1,21W3 m nln almost parallel to the coast for about 1,680 km along the western bcx-der of the Dwcan eon] the n~outhof the to Kanya Kumari. They are not, strictly speaking, a true mountain range but only the eroded precipitous edge of the from the Tapti upto 16"~latitude; and the ranges are composed of horizontal sheets of basaltic: lava tlows which exhib~ttypical trap features. The Ghats rise almost perpendicularly from the coastal plain upto a height of. 1,000 In at some places. The steep face, thus formed, loc>kslike an ancient sea-cliff. but it is probably a fault scarp the western part of which has drifted away westwards. This special feature of the range accounts for the fact that all the important rivers of Peninsular India, except the Narmada and the Tapti, flow eastwards into the Bay of Bengal, though their sources are on the crest of the Western ~hats'whichare only 50 to 80 km away from the Arabian Sea. The crest line runs in broad curves fonning two re-entrants at Trimhank and Tamhini, carved respectively by the headwaters of the Godavari and Bhima rivers. KalsubJ (1,646 m), (1,567 m), and (1,438 m) are among the highest peaks in this part of the Western Ghats. From 10"~ latiteltie to the Nilgiri mountains, granite and gneiss take thc place of Deccan trap. In this section, thc Ghats run close to the coast until they join the Nilgiri ~nountainsnear Gudalur Thi: P~lphatGap trending east-west lies cross the Ghats. The gap is 24 km wide at its n:ltrowest part ant1 lies at an elevation of 144 m,while the bordering hills rise to a hc~yii~tc!C 1 SO0 111 to 2,000 111. This gap is probal?ly a rift valley caused by the suhs~tienccbetwecn two parallel f~ilults. 171e Wt:btern Ghats conllnue south of the Palghat Gap. And Mudi (2,695 m) is a nodal point fro111 wllich tlarce ranges radiate: the Analmalal to the nortli, the Plani Hills to the nortti-east. and the (Elamalai) to the south. The norththern section oT the Easlertl Ghats lies in Orissa State and , with an average width of 2(X) km in the north and 100 kill in the suuth. (1,501 1111 111 Orissa is ils conspicuous peak above the coastal plain. The general rrcnd (it the ranges is noah-ecut to south-west. The prevailing rock type is kllond(11ilr. In ihc Dcccati. the Eastern Ghats do not form a contindous range except in the C't~cldapahand Kurnool dislricts of Anclhra Pradesh. Between the Pennm and Krjshnki rivcrs, there are parallel ranges and valleys of the Eastern Ghats which trend along north-south direction. Thc most prominent of these ranges is the Nallamula whucbhruns parallel to thc Cloronlondel coast. The cuts Lhs range transversely near Sjvasamudra~~~iu Kmlataka State md later leaps over the Hoeenaka1 tills. Near the southe11 end of the Ghats, the Biligirirangan Hills (highest peak, 1,750 m) fonns a well- def~tledrange. To the cast of r11c Easter]) Ghats, there are two other groups of hills: [he southern group. which 1s tlonlinatttd by the Shevaroy Hills; and the northern group that is cloniinalc.tl by the Javadi IJills. The Nilgirls (or Blue Mountains) a~nstilutethe tllecting ground d IPle Wcstern Ghats ant1 the Eastern Ghats. The Nilgiri mounlains risc abruptly from rhc plains in a stupet~dousprecipice which is probably a lault scarp. The general orictllation of the Nilgi~isis north-east to south-west, wllich co~~espondsto llle orientation of the Eastern C;liats. 'Two of its highest pcaks are Dodda Rella (2,037 nl)and Makurti (2,554 ul). 771e soutb-western part of the mountain orientation known as Kunda, is I~a~~crsctlhy bold ranges and it~tersectcdby decp valleys. Thc surface of the rest of the Nilgiris is extremely undulating with rounded grassy hills and hroad foresl-clad vallcya. " Land and Water Resources of lndia 1.5 PLAINS

Plains are relatively low lands mcxlerately mlling or flat. Plains occurrin~on continental borders are known as coastal plains. Interior plains are those which are situated in the interior of a continent. The plains of India are of great impc>rtancefrom historical point of view. as they have been the craddles of ancient cultures. Almost all the different typcs of plains are found in the vast Indian subcontinent, whch are briefly describccl as li>llows : Alluvial Plains An outstanding example of this category is thc Tndo-Gangetic plain which lies immediately south of the Himalayas, stretching froill the arid and seiiii-arid plains of Raiasthan in the west to the Ganga delta in the east. The northern boundary of this plain is well-defined, but the southern boundary is a wavy irregular line along the northern edge of Peninsular India. The Indo-Gangetic plain is a fore-deep fonned either by downwarp or as a rift- valley. It is at present an alluviuul-filled trough. The total area of the plain is 652,0(k) sq kni: ot which one-third lies in the arid region of western Rajasthan. Tfie thickness of the alluvium is maxir~lumin the Ganga plains, theminimum in the western plains. The surface of this plain is ,at the leveld the tide near the mouth of the Ganga, but in the Pun.jab it is over 2()O in above sea level. The Indus and the Ganga have a nuinber of large trihut:ules which \ flow parallel amongst the~ilselvesfor long distances. The drier parts of the plain in the Punjab extend south-wards and gradually ruerge with the arid plains of Raiasthan which is known as the Thar Desert. Tt~ouphthls region is geographically a part of the Indo-Gangetic alluvial plain, yet it is ditlcrent in that the action of wind is predominant over that of flowing surface water. MOSI of this arid plain was under the sea from the Permo-Carboniferous period until it was uplifted during the Pleistocene period. The existence of several dry beds of rivers indicates that the region was once a fertile tract. At present the Luni (or Salt River) is the only flowing river in the region; its water is sweet in its upper reaches, but hence onwards turning brackish, and is quite saltish by the time it enters the sea. There are several saline lakes in this arid region of whch the S:~nlbhuLake is the largest. To the north of Jaisalmer a number of playa lakes known :IS Rums occur in the basins rinin~edby low scarps. Though fed by centripetal drainage, these lakes are generally dry for greater part of the year. The sand-dunes :\re usually of the harchan type, which in the Barinst region are as much as 50 to lo() 111 high. The Gangs plain occupies about 357,oNl sq hn and is spread over puts of Uttar Pradesh, Bihar and . The Yamuna flows near the western hounc1;iry of the plain for 8(X) knl and joins the Gmga at Allahahad. Further east is the- Bihar plain which is a land of rivers; the Ganga flows along its southern border, receiving on its left bank three large tributaries, namely, the Ghaghara, the Gandak. and the Kosi. These streanls are responsible for tilling up a 2,000 metre-deep rrough, with alluvial deposits at the foot of the Nepal Himalayas. The plains in north Bengal extend from the ftn>tof the Eastern Himalayas to tht' northern liillit of the Bengal basin. Its eastern part is drained by the rlvcrs joirlinp the Brahmaputra, and he western part by the tributaries of the Guqa. Further south lies the Barind plain which is the older delta of the Ganga fornletl tluriilf the Peleistocene period and later uplifted and eroded into terraces. The Beng:~lbas111 is nlaiilly conlposed of the Ganga delta. It is a low tlat country which would be completely submerged if the sea-level rose e,vell by about 6 ni. The alluvial plun is almost at the base level of erosion in the Sunderbans and is traversed hy a network of estuaries and channels. (The alluvial plains d Peilinsular India will be dcscribed while dealing with the east and west coasts of India.) Terrated Plains Most rivers in tile Himalayan region have built their respective plains at high dtitudes' anti later dissected then1 into terraces. The lndus in Kashmir Himalayas, the Sutlei i11 the Punjab Himalayas, and the Ganga in the Kunlaon HimalayBs, have left behind such terraced plains at many places. ku.usrririe plains are common on the Himalayas and other mountains. The Vale of Kashnur and the llllphal basin are excellent cxaniples of ancient lakes which have been filled up uid later uplifted to their present position. The Kashmir valley, which is one of the most beautiful atid picturesque spots in India, is 150 hi1 long Src>mnorth- west to south-east, with a width of 80 knl, and an avcrage elevation of 1,70?i) 111. Thc valley is enclosed by a ring of tnountdns, the Pir Panjal in the south, and a northerly branch of the Great Hinialayas in the north. River Jhelu~ntlows across the valley from south to noxth.

I11 the central pan of Mmipur lulls lies the luge Iniphal basin wtuch is SO h11 long anti 30 k'ln broad. surrounded on all sides by high nlountains. This plain which is the hai of un old lake has ;I centripetal drainage. Gliicial Plains

Thc Ladakh pl;\in, it1 the ncxth-eastern part of thc Kashnlir Hilllalayas. lies lo the east of the Shyok riva and north of the Cha~igCllennlo river. In this llal vitlley there is nhuntlanl evitlencc of li,rnier glacialicm. Typical cx;~mplcsof /)ierlr~ronlplaitis ;we fc~utidat the fool of the Hi~ualayas.The piedmonl pli~insin the Puli.jah are clissected into terraces hy strcalils which remain dry during niost of the year. Arid plaitis wluch ;Ire generally rocky are present west of the Aravallis, especially near .laisalrner lown. Ltrvn plains occur on the coast it] wcstern India. Pt~(li/~l(ii~~,s.causal hy[lie recession of hills, are common in South Inclia. Cloaslal j)lains ol' the cnlerpenl lype will) logtx,ns arid backwalers are li,unci on the coasls of I'eninsular India. I'o~~c~/~l~~irt,sfor~uedin carlier geological apes and Inter upliSied are seen on solne hilltops such us thosc 011 the Nilgiris and the Shillong hills.

--PA 1.6.+-- PLATEAUS ----

~lateiausare Iugh lalltls with large sunln~itareas consisting of broad Ilattisli surfaces. Usually Ihere is an ahrupt risc or Pall from the surt'i~ceof a plateau to thc itdjacent lu~tl.The tcrm "lugh lanti" is entirely relative in its purport. tor Illally plateaus are situated at a higher elevation than somi mountains, whilc Inany plains are tugher than some plqteaus. The surl'accs of plareaus may he like rhosc of plains ve~rytliil, rolling or hilli. They are often so dissected hy streanls that it is difliculr to recogtuse their origihal plateau characteristics. Volcanic Plateaus -1 hue of the Iiugest plateaus are built up by rhc successive outpourings of lava fvni eruptions coliutig out of fissures. Such plateau lavas are usually made of bas* t. A good illustration of this type is the plateau formed hy the Deccan traps. SmaHi r degraded plateaus are ftxmed by resistant lava caps that pmtecr the land from. erosion and maintain its high elevation after the surrounding laid has'heetl worn away. Plateaus, like mountains, are affected by weathering and may he found in all stages ot'dissection by streams and other erosive agents. When not much dissecteti, their flal surfaces look like plains in surface topography. If they are highly dissected, ae chariicteristic plateau surfaces are largely removed, and instead, nan-ow ridges, deep canyons, and even hills and valleys are left in their place. With continued erosion, plateaus become less rugged in relief, and they are finally worn down to peneplains. Land and Water Resources Peninsular India, except for its coastal plains, can be considered to be-a vast of India plateau. The main features of a plateau landscape are: extensive flat or rtJllitlg plains dotted with conical or rounded hills, situated at an elevation ranging tion1 300 m to 900 m, and bordered by scarps. The Malwa Plateau, in Madhya Pradesh, lies to the north of the Vindhyas and is composed of extensive lava flows. There now exist rolling plains separated by flat-topped forested hill ranges. The Vindhya Plateau is situated south of the Malwa plateau, and is composed mainly of fluvio-marine deposits of probably the Cambrian age, which has uplifted and peneplaned several times since then. In structure it is a flat-topped syncline with very striking east-west erosional scarps forn~edof resistant quartzites. The Chhota Nagpur Plateau lies to the west of the Bengal basin, the largest and the most typical part of which is the Ranchi Plateau, the average elevation of its upper part being 700 m. Monadnocks (hills left as a residual of erosion) of rounded massive granite, and sonlewhat elevated terraces of older flood plains are characteristic of this peneplain. The plateau is deeply dissected along its borders giving rise to steep escarpments. In the western part of this region, there are mesa-like plateaus which are remnants of an older extensive peneblain. South of the Narmada river there are several high plateaus. Mention nlay be made of the Betul Plateau and the central lava plateau in the Satpuras rising to a height of 1,200 m. The Deccan Plateau is the Largest Plateau in India. It covers an area of 700,000 sq krn, and slopes eastwards and also northwards. The northern-cum-em boundary may be defined by the 300 metre-contc~urline; and the Westeni Ghats form its western boundary. The part of the Deccan plateau in Maharashma State is fonned of plateau basalt. The valleys of the Godavari, Bhilna and Krishna rivers (within the plateau) are flanked by flat-topped steep-sided hills. In Andhra Pradesh, the plateau is fonned mainly on Precambrian Gneissw. Thc topography of Deccan plateau is characterised by rounded hills and rolling plains. The 600-meler contour line may be taken a$ the bc~undaryof plateau which is a well-marked featurc of the topography of India. This plateau abuts against the Western Ghats and 1s bounded on the east by the Eastern Ghats. The Nilgiri is situatcd along its southen1 boundary. B.L.Rice ( refer Mysore Gazetteer, 1897) has given a graphic description in this regard : "From the gigantic head and shoulders, as it were, ol the Nilgiri group, whjch commands the soutllcrn irontier, are stretched forth like two arms in north-west and north-east direct~ons, tes~~ectively,the Western and Eastern Ghat ranges, llolding within their mightly embrace the mountain locked plateau of Mysore". Physiogtaphically, the Karnatnkn plateau cmi he divided into two clitities the Malnad ant1 lhe Maidan. Malnucl is the llilly arca bordering ~hcWestern Gl~atsanti has an average width of 35 klil and a mean elevation of 1,000 m. It is erotled infosleep hills and decp valleys, and is covercd with dense itw-ests. The Maidan 1s loinled of rolling plains with low grtrrtitic., ~~zc~issicand schixt hills.

------.----L---p.-.---p-- - - ~..~ . . 1.7 DESERT TOPOGRAPHY

The tlry plains of the Punjab extend soulhwards and merge gradually into the arlti plains of R+jasthan. This arid region is bounded on the east hy the Aravalli ranpe. The general elevation of this part of the country varies between 150 kuld 300 1n The mode of evolution of the landscape of this deserl region is different limn that ol herest of the Indo-Gangetic plain, because wind has taken il prominent put. compared to running water, in shaping the landscape. It is a region of deficient rainfall and shifting sandy. The presence of dry beds of former rivers incl~catethe gradual desiccation of this region. The Luni (or Salt River) - referred to earlier - is the only flowing river in these arid plains, and even this carries a mere trickle of water in years of deficient rainfall. The ground water in the greater part of this arid land is impregnated with salt. ' There cue a number of salt lakes in this arid region of which the Sambhar is the largest. 1f3&60 lull west of Jaipur town, and covers an area of24 sq km during the rainy season. In the dry months its surface is encrusted with bright white saline soils. Salt is manufactured from the brine of this lake. I A100 km-wide strip along the western border of Rajasthan, between the parallels 26" Nand 29'' N, includes morc than tlu-ee-fourths of the sandy desert. Here the annual rainfall is very low- about 15 cm per year. There are numerous sand dunes, west of Shahgarh, which run in chains of a complex pattern, the longitudinal type predollzi nating. South of 2h"~latitude, the dunes continue to dot the landscape, hut are generally of the bunJim or transverse type. In the Bariner region the barchans are 5 to 100 m high. A helt of steppe country strelches westwards from the li~tof the Aravalli range and merges gradually into the desert region. There are fewer dunes in this region whlch is drained by numerous short, ephemeral streams. The highest group of hills in western Ra-jasthan lies here in this region. Parts of the hilly tract are buried under sand, and this area represents fluvial landscape carvad out by earlier powerful rivers, modified later on by wind erosion. The Thar Desert of Rajasthan, to the scwth of the Himalayan chain, and the vast Taklarnakan desert, to the north, form part of the large desert helt of Central Asia which is continuous with the Sahara. The aridity of this region appears to have been caused only in geologically very recent times, since all along this vast expanse fhere are remains of flourishing human settlements, with forests and other evidences of a humid climate. The'continental desiccation has been caused by the deflection of moisture-bearing winds from the Indian Ocean with consequent disruption of the drainage pattern of the country. Because of the metetxological influence of'the Himalayas on the atmospheric circulation, the Thar area of Rajasthan has"not felt the full i~npact of this desiccation. On account of its altitude, and its location being directly in the path of the monsoons, the Himalayan mountain system precipitates much of the moisture of the monsoons either as rain or snow, which feed a number of rivers flowing down to the southern plains. In this way, the Himalayas have protected th~sarea fronl the desiccation which has taken over Central Asia. On the other hand, the interception of the monsoon-wind circulation from the ocean, by the Himalayan chain, has gradually desiccated parts of Tibet and the Tarim basin lying to its north-west; all these areas fall within some of the most desolate regions of the earth today because the river systems there have withered away, giving rise to the growing volume of sands. 1.8 LAKES AND SWAMPS

A lake is ui inland hody of standing water which may be fresh, brackish (tw sialtiah. Lakes are anlong the most widely distributed of all topographic features for they are found at all latitudes and altitudes. Lake basins originate in Inmy ways such as cluc lo c~ustalmovements, lava dalns, blockade of valley by glaciers, due to strean action and so on. The Rain of Kutch is almost a lake which has coriginatedjartly by subsidence resulting fro~ilseismic phenomena which accompanied the earthquake ot 18 15 in that region. Thc Wular, the largest lake in the Kashmir valley, (l(I0 scl k111 in area) which greatly influences die flow of the Jheluni and other rivers, occupies i\ structural depression having occurred there. Ncar Nainital, in the Kumilon Himalaya, there is a scrics of lakes which lies on a line formed by fi~ulling. 11 liiay be mentioned that if part of a river valley is warped upwarcls due to geological upheavals, it will act as a tiluii and cause pounding of water. giving rise to a lake.

Lake basills may tccur behind danis fonned by lava; they 111ay cccur on the irregular surfaces of a lava flow; or they liray be situated in the cratcrs or r.trltlor 1r.j ol'exli~iclvolcanoes. The cauldron-like hollow rimmed by block of basalt. 111 ahich lic the waters of the Lonar Lake, is considered to be an "explosion crirter" anti therefore classed as a crates lake. It is almost circular in outline wit11 21 tl~:lnlcle~of 70() Ill. Glacial Lake Rasins Deposidon of moraines oilen obstruct the drainage of valleys and proclu)sl%~kes. Lakes crf this type urc usually s~nalland are asstxiated with somc cMc(vesent day tiiliialayan glaciers, as in the case of Chonibu Glacier in Sikkim. Glaciers niaq blockade valleys and thus cause ptwnding of waters. The passage ol' ;I gliaier traiisvcrsely across a valley, as in the case of the Chong Kumdan ~lauiel,&he Shyok, a tributary oS the Indus, produces a temporary lake. Such a !Me. okviouhly, causes disastrous tlotxls when the ice-dani bursts. A large number of glacial laktb basins have been eroded or excavated by the direct action of moving njasses of Ice. Lakes Formed by Stream Action In graded and nearly graded rivers, a dharacteristic of mature and old lopograpl~y. the shallow basins, in abandoned ~iieanderson tlcxxl plains, fonn oxl)ol islakcs. (111 many tlood plains small, shallow dcpressicons are left due tco irregular tiepos~tionof alluvium. After floods or heavy rains, these basins fomi lakes without natu~;~l outlets. As a result of uneven deposition of sediment by the network of distributaries on a delta, some shallow basins are colnpletely surrcmnded by the deposits and converted into what are known as delta lakes. Such lakes iW dso feormed by the enclcxing of ahollow between two deltas, as in the case ot near Eluru in Andhra Ptadesh due to the growth of the Gcxlavari and Krislina deltas. If IWO SUC~IIISon opposite sides of a valley discharge their alluvium on the valley floor. (he I'ans iiiay co~uplelelydam the vallcy and form a lake h:~.iu. Basins are also fornied in several other ways. The Clhilka Lake of Orissa and the Pulical Lake ol' Nellore are exaniples of lagoons clcveloped hy cleposits of sand carrieci up tlie coast by sea currents in Ihe Bay of Bellgal. In thesc cases, hars or s1)it.s of sand have been tleposited across the nlouths of snlnll bays or inlels. The back-wnlers or krn.trl,s of Slarc have also occurred due to similar causes. At the fqot ol'greal walerlhlls pol-holes arc of coniinon c~currcnce.Such plrrr~,qc) basins g~.atiuallyincrease in size and linally heconle large enough to he called lakes. A~olitirrhc~.sirr.s ;~rc s~~lall and teniporary hollows lying anlong wiild hlown sand heaps ant1 dunes. Exalilples of such lakes are sccrl in western Raiaslhan. La~idsl~dt.~solnetinles cause large Inasses 01' rocks to fall across slreani courses. In sonle cases. pcrnianenl lakes are thus lor~ned.Thc Gohna Lake ol Garhwal was fonned hy a huge lantlslide across a lrihutary ol'lllc Gangs: anti s~llalllakes of Bulrtiel khanct are also exa~iiplesin point. Salt Lakes Salt lakes lar 1\111 less comnion llia~ifresh water lakes, and cxisl ~iiai~ilyin arid regions. Sollie ol the lakes of Latiakh and Rupshu in Ja~n~nuand Kash~riirSlate. such as Salt Lake, the Pangong Lake ant1 the Tso Morari, ;we conlinually shrinking and hecoming ruore and more saline. These lakes afford clear evidences of desiccation taking place. The Pangong Lakc, on its hanks, has terraces or beach-n~arksat various levcls, the highest being 40111 ahove the surtacc of thc present lake. The Tso Mo~ixihas 1en:lccs a1 a heighl ot 15 nl ahovc tlie presenl level of its waters. Western R;,iasthan has niany playi~lakes, thal is. interior hasins wilh a centripela1 drainage. The most important of thesc. ;IS nlcntionctl earlier, is lhc salt lake ol' Sanlhhar which has iun area 01'24 sq knl when full during the nionsoon. at which period {hedepth of water is a little Inore Illan olre nlctre. During the rest of the year it is dry. the surl'i~ccheing encrusted with a sally silt. Sall lakes [nay also he lhrnled hy the isolalion of amis of the sea hy clioslr-oyllisnl or tleposition of sediment. Swamps Swamps are hasins tilled, or partially filled. with a mixture of watcr, fresh or decayed vegetation and soil. M(1rs11,/)(\5' and r~~or~i.s,sCOIIIC under this category. Swarnps are very abuudanl in humid regions of coastal pl aijis and on tlotxl plains anci deltas where abandoned river channcls are tilled with vegetation. Swamps occur wherever the waters of zone ol' perlnancnt saturation (of top soil) rise ahove ground level. Conversely, swamps more or less dry up atter long perituis of dry weather when the water table is lowered below ils usual level. The coastal r~larshesof Bengal and Kerala are swainps which contain a luxuriant growth ot' I he mangrove plants. Year which is an early stage in the fi,niiation of coal accumulates in hogs. The lignite deposits in Kerala and Madras States must have originated koni such peat bogs.

1.9 COASTAL PLAINS

The plains on the West Coast of India are confined to a narrow helt about 10 to 25 hn wide stretching between the sea and the Western Ghats, and extending from Surat in the north to Kanya Kuniari in the sou+. At the northern end of the helt lie Land Water W-ourr.e' Kutch and Kathiawar peninsulas, and one vast plain which reaches to the fii14hes1 d India limits of . Further south lic the coastal plains proper, which coulti I)e subdividecl regionally into the Konkan cost, Karnataka coast, and Keralu coasl their limits corresponding to . Karnataka and Kesala Stales. respectively A characteristic feature of ttc west coasi plains is the occurrcnc.c of several hcautiful coastal lakes connected by canals.

The Kutch peninsula was once an island surrounded by sea uid lagtw)ns i~lltilthc Great and Little Rums of Kutch got silted up. Lack of rainfall in this region has given rise to arid and semi-arid landscapes; and hence, coastal sand dunes, sandy plains, and bare rocky hills are the charactcr~sticphysiographic fealures of the Kutch pe~linsula.The Great Ran11 is a broad plain for~nedof dark silt with salt encrustation, the plain nsing only a few meters above the sea-level; a1 sonlc pliices it is actually below the sea level. Patches of high ground, sonlc rcxky uad soale saidy and covered with grass, rise like islands above the general level of the barren plains. The Rann gets llocxled every year partly by river waters and partly by the rise of the sea. The Katlliawar peninsula lies to thc sour11 ot Kulch. The two Ranns. the Lit?le Kann of Kutch and the Rann of Cambay. along with the Nal lake, nearly encircle the peninsula fro111 east and north-east. There is a central table-land from wluch all the rivers of this peninsula rise and radiate outwards. in the scwthkrn part tllere are some high hills (Mt Girnas, 1,l 17 111). The Gir Range with its dense forests is fu~lousas the home of the 111dianlion. Many ol'the hills in this regiun are volcanic in origin and xeot thc crlrsta type, thc seaward slope being steeper than the inland side slope. The Gujarat plait~slie lo the east of Kathiawar and stretch towards the interior highland5. Wind-blown loess covcrs the greater part of the country neareithe coaq, which hy weathering has given rise to a semi-arid type of landscape. The Konkan coast, cl~xacteriscdby cliffs of hasaltic trap rtxks, stretches from north of to Danan, a dislancc of 500 kni. There are submerged foresls war the city of Bombay, as well as raised terraces formed of coral reefs or of loosely cemented fragmentary skell-limc~stonrrocks. South of Bombay city, the rocky coast has a series of small bays and coves lying between jutting headlands and containing beautiful beaches fonned of bright white sands.

The Karlaataka coast 11.~3several rtxky cliffs. The chief river in this region is the Sharavathi which, before entering the plains, plunges down a cliff 275 111 height at the Gersopp or . The plains are nowhere more than 24 lan wide anti ae often only 8 km wide. The Kerala plains are con~parativelymuch wider and less hilly. A nurrlbcr of lakes or backwaters (kayals) lie along the coast, the largest of which is the Ve~i~anad kayal which stretches for more than 80 km in length. The Tanlil Nadu and Andhra Pradesh coasts (East Coast) extencis norl hwards from Kanya Kumari upto the Krishna and Godavari deltas for 1,100 km with an average width of' 120 km. Further north, the hills almost approach the sea. The coastal plains again widen north of Berhampur and extend to the Chilka lake, the Mahnadi delta, and the Balasore coastal plain, where they merge into the deltaic plains of the Ganga. On the coast, the Kaveri delta is the most important physiographic feature. The Andhra plains 'stretch from near Berhampur to the Pulicat lake, 50 km north of Madras (Che~ai)city. Two of the biggest rivers of the Deccan, the Krishna and the Godavari, flow in this region and form their deltas. Between the two deltas lies the Kolleru lake which affords evidence of the coastal plain rising towards th6 sea. The Krishna after phsing through a deep gorge and cutting into khond(1litr rocks, enters the coastal plains at Vijaywada and flows for 90 km before it reaches the sea. The Gorlavd emerges on the plains from a gorge at Polavarun and soon divides itself into two distributaries between which the tnain delta lies. The Orissa plains include the delta with Cuttack at its head. Thc seaward margin ol dus cielra is straighter than that elf the Ganga delta ant1 is Mngai with sand ciunes. The 111ost imp)rtant physiographic feature south ofthe Mahanadi delta is the Chilka lake which is a pear-shaped expanse {af waler, 70 kni kag. Its birth is due to the formation of a bar at the rnouth of the bay. Two srrealris drain into the lake which contains a nu~nberof nxky islands and is bcxdered by hills on the south and the west .

-pa 1.10 INDIAN SEA AND ISLANDS

Indian Sea The bottom of the sea is generally smother than the surface of the dry land, though there are high ridges, plateaus, submarine volcancxs, and valleys present on the sea tied. The continenlal shelf is that portion yf the continental platform that llies beneath the ocean (Figure 1.2).

1 . fntrrior plain 6. Epieontintntal Sea 2. Plotrau . I. ~ontintntalShrW 3. ~ountain 8; ~dqt,ot continental ftattorm b. Coast plain 9. Conttntntal Slope 5. Edge of ~bntinent 10 occan qasin

Flgure 1.2 :~lypsogrophic Curve Co~ltinentalshelves extend to varying clistances tiem the respective continents, depending upon their slope, until their general surface is about 75 fathoms c)r 1135 m below the sea level. From the outer limits of the continental shelves the descent to the floor of the cxean basiris is generally sleep. The slopes, whether gradual or steep, which connect the continental platforms and wean basins, are known as contircurttal slopes (Figure 1.2). Structurally, the real wean basin must be regarded as comniencing not at the visible shcxelines, but at the edge of the continental shelf. The two Indian seas, the Arabian Sea and the Bay of Bengal, which are the northward extensions of the Indian Ocean, originated hy the breaking up of the Gondwana continent during the late Cruutat*eousor early Tertiury times, There is no well-defined continental shelf in these seas, and the 200 m-depth line upto which the shelf extends runs roughly parallel to the amt. The width up to 100 m represents the major part of the continental shelf. This zone is about 350 km wide south of Kathiawar, and 220 la11 wide south ofthe delta of Ganga, but in general, its width ranges kern 50 km on the east coast to 100 lull on the west coast of the Peninsula.