sign in sign up
<<
Home , Aravalli Range

Space Relationship of with Neighbouring Countries

GUIDANCE IAS IAS

GUIDANCE Structure and relief

Before moving ahead it is necessary to understand the terms- Structure & Relief.

Structure Relief It refers to rocks of an It is the difference area. In particular the between highest point composition (what they and lowest point of the are made of), the area. arrangement of rocks and the (faulted For example- On or folded etc). Earth, the highest point is Mt Everest For example - (8848 mts) and the lowest point is Challenger Deep of AS composition - Mariana TrenchI Metamorphic Rocks (10,034 mts). Hence the relief of Earth is Nature - Folded 18,882 mts. Mountains ThereCE are 5 orders of Nrelief. For the sake of simplicity, structure and relief of India can be studied as- Four Groups or Four Physiographic Regions (i) Indian Peninsula - with Coastal (ii) Himalayas - Started - Mesaziac (iii) Indo-Gangetic Plains (iv) Island GroupsGUIDA

(1) IAS

GUIDANCE

2 IAS

GUIDANCE

3 IAS

GUIDANCE

4 IAS

GUIDANCE

5 IAS

GUIDANCE

5 IAS

GUIDANCE

7 IAS

GUIDANCE

8 IAS

GUIDANCE

9 IAS

GUIDANCE

10 IAS

GUIDANCE

11 Broad Division of Peninsula: 1) Central Highlands: a) : • Semi-arid to arid landscape covered with Aeolian deposits (sedimentary). • Origin started with formation of Aravalli in purana period when there was development of sedimentary platforms of Aravalli. During marine transgression of tertiary period, further sedimentation continued under marine conditions. • Final stage of evolution corresponded with quaternary period when rejuvenation of Aravalli led to dismemberment & disappearance of rivers making them dry. Since then, dominant Aeolian processes have re-distributed sediments. It has 2 parts:  Great Indian Desert – represents true desert whereby absence of relief causes very low precipitation. Eastern part of it is rocky desert while western part is sandy desert & is covered with shifting sand dunes. Streams are small & seasonal.  Bagar – semi-arid region representing tropical steppe (short grassland). Some agriculture is undertaken.  Northern part – dry belt & channels of ghaggar & mythical are found.  Southern part – Luni & and its tributaries are present. IAS Diagram: b) Aravalli Range: • Represents an old fold mountain which is nearing its peneplain stage of development. • Represent the oldest of earth, formed in 2 stages –

1. Early – 2.1 billion years ago. 2. Late Proterozoic – 700 million years ago. (Also called as .) In quaternary they also experienced rejuvenation related with faulting. • Its structure represent fan-folding with presence of anti & synclinorium. • Types of rocks – Igneous & metamorphic rocks forms core of Aravalli (i.e. & ) representing a batholith & related metamorphosis. Also presence of limestone which have experienced e.g. Abu hill is an exposedGUIDANCE batholith. • They can also be called as relict mountains. • Structure: towards southern part, they are broader & higher due to which they even intercept greater precipitation & are also forested (elevation > 1000m). As one moves north, their altitude declines & they also become narrow. Further north they are divided into fan-shaped ridges which break the monotonousity of Indus-ganga plains & give impression of actual extension of Aravalli’s. • Average relief is 400-600m, highest peak: gurushikar. c) plateau/uplands: • Origin – formed at the closing of along with formation of Maharashtra plateau from re-union hotspot volcanism. The emplaced during the period was very hot & fluid due to which it travelled far north leading to its formation. • General slopes – slopes towards north, average elevation in south is 600m & in north it is 400m. • River – Chambal & its tributaries. It is dissected by them and has led to formation of Badland topography – presence of gullies & ravines. has a rolling topography. • Badland topography — Too many valleys, steeper valleys & many of them are dry. This is related to rejuvenation suffered in region during late tertiary & quaternary probably due to Himalayan orogeny.

(12)

• Rock – Basalt, which is susceptible to erosion & the process, has been further accelerated by man-made factors – extensive grazing & clearing of vegetation. Despite these problems it represents an important area of human’s agglomeration as it is sandwiched between hard terrains of Aravalli (west) & Bundelkhand (east). d) Bundelkhand: • Represent a formed during period and since then it has suffered denudation and represents an erosion surface/peneplain. • Hard & crystalline structure made up of granite & gneisses, height 300-600m, slopes northwards towards basin. • Latosol/red soils, absence of minerals of metallic nature. e) Vindhyas escarpment: • Origin – rocks forming this were deposited in purana basin during Proterozoic period. However, region experienced upwarping related with emplacement of batholith during tertiary period. In quaternary period, rejuvenation of Narmada has created escarpment structure. Thus, they look tall due to presence of Narmada fault in south. General elevation is in between 600-700m although at some places they can reach 900m. • Arc shaped, primarily sedimentary rocks which have been metamorphosed e.g. sandstones (used in red fort) & (metamorphosed limestones). • Gently slopes towards north. Its southern slope is a scarp (steep). Diagram: IAS

2) : a) : • Old fold mountains, formed in early Proterozoic = (2-1.9 billion years ago). • Present Mountain like feature is related to it being a black mountain situated between valley (north) & Tapi river valley (south). • Average elevation = (900m – 1000m). • Dhupgarh is highest peak (1350m) on mahadeo hills. Structure – crystalline rocks primarily granite & gneisses, also presence of sedimentary rocks like – limestone & . Western part is covered with basaltic lava. Slope – althoughGUIDANCE highest peak is on east, but general elevation decrease from west to east. Diagram: b) Deccan Basalt/Maharashtra plateau: • Origin – formed at the closing of Mesozoic from re-union hotspot volcanism. Fissures are located on northern- . Outlier of this is Kathiawar peninsula. • Basaltic plateau, presence of ridge and valley topography. • Residual hills are formed by differential erosion of Maharashtra plateau. • It is also known as Deccan traps. Its relief gently declines towards east in a step like manner which represents flow of lava sheets one after the other. • Kathiawar represents an outlier of this whereby intervening rocks have been removed by faulting & erosion by rivers like Sabarmati & Mahi. Diagram:

(13)

c) Karnataka plateau: • It represents one of the oldest shields of India-Dharwar Shield formed in Archean period. Thus, it represents old erosion surface/peneplains. • Although it has experienced rejuvenation so it reflected upward peneplains which has an elevation of 600-900m height. • Malnad – series of crystalline ridges is present, hills & valleys, receives greater precipitation & is more forested. Maidan – average altitude 600m, densely populated. Difference is more perceptible in human geography of region- Maidan is more populated. • Granite & gneisses – highly metamorphed. Diagram: d) Telangana & Rayalseema: • Old shield & like Karnataka plateau, part of Dharwar shield rocks made of granite & gneisses, they are old erosion surfaces. • In cudappah basin – sedimentary metamorphosed rocks are formed. • Average elevation 500-600m, lies in the of eastern & western ghats. Dry deciduous vegetation is formed. Diagram: IAS

3) Western Ghats: • Represent an escarpment, continuous from north to south & act as water divide. Have passes. • Present height is reached as a result of tectonic rejuvenation of quaternary period, presence of several north-south fault zone which represents recent rejuvenation & many of these fault lines are still active. Diagram:

• Altitude – Diagram: Southern hill complex:GUIDANCE due to rise and rejuvenation of southern granulite province in quaternary (which is separated from rest of Western Ghats by east-west fault-lines manifested in Palakkad/palghat gap), highest peak is found in southern most part of Western Ghats. • Parallel to western coast & forms an almost complete water divide. • Meet at Nilgiri range/hills. • They represent crystalline structure (made up of granite & gneisses) although in north they are covered with basaltic lava. • Four passes: 1) Bhorghat (connects Mumbai & Pune) 2) Thalghat gap (connects Mumbai & Nasik) 3) Palghat (Chennai & Kochi) 4) Shenkottah (Madurai to Kottayam city of Kerala). Diagram:

(14)

4) Eastern Ghats: i. Eastern Ghats represents old fold mountain formed between (1.7-1.6 billion years ago). ii. Eastern Ghats represents a true mountainous character only in north in form of northern circars, south of which it is divided into several isolated hills which are even transverse to coast. This is because of flow of rivers which broke them into discontinuous hills. iii. Altitude continuously declines from north to south. iv. Structure – crystalline made of granite.

5) Eastern Plateau: a) Bastar and Dandakaranaya uplands: • Represent old shield formed in Archean period. Thus, they represent old erosion surface having rolling topography. This rolling topography is broken by presence of hills & valleys at some places. • Made up of granite & gneisses, crystalline. • 600-900m height. b) Chhattisgarh Basin: • Fort like basin surrounded on all sides by high mountains & plateaus. It was formed during upper purana and represents a basin platform. Another important event was during Gondwana when rifting led to formation of Mahanadi valley. IAS • Coal deposits (Korba is a Thermal power plant) are found here. • North-west & north – presence of baghel khand and ramgarh hills. Eastern – Northern circars. Western – Amarkantak. Southern – it gradually raises towards Dandakaranaya & Bastar uplands. • Rivers – Mahanadi and Indravati, fertile zone, in the past – was known as rice bowl of India. c) Baghelkhand plateau: • It is an old peneplain surface. Towards north it is bounded by son & in south there is presence of ridges and valleys made up of sandstone and limestone. • Uneven relief surface (relief range = 150m-1200m). • Behaves like a water divide between son and Mahanadi. Structure – the features reveal close similarity with vindhyan uplands. Although it seems that they got separated during Gondwana by son rift valley. d) Chota NagpurGUIDANCE Plateau (C.N.P): • Oldest shield of Indian peninsula formed in Archean period (3.56 billion years ago) and has been affected by various tectonic events. Last such event was during Himalayan orogeny which caused their rejuvenation. Thus, they represent uplifted peneplains (of Davis). • It has 3 parts: i. Hazaribagh plateau – smaller but higher (900-1000m), flat-topped hills are found which are known as pat lands (laterite soil). ii. Ranchi plateau – larger but lower (600m). iii. Rajmahal hills – basaltic. Diagram: e) Meghalaya plateau: Diagram: • Continuation of Eastern Ghats: Thus, represents part of Indian peninsula. It got separated from main peninsula during tertiary period owing to Himalayan orogeny collisions which led to formation of Garo-Rajmahal gap. • Crystalline structure, granitic & gneisses rocks which have been strongly metamorphosed. • Average relief = 1200m – 1500m, no. of ranges – Garo, khasi, Jaintia, mikhir rengma & barail.

(15)

• Southern slopes are steep while northern slope is gently sloping. Structurally it represents a cuesta. Diagram: • Some outliers of Meghalaya plateau (isolated hill blocks) are formed to its north which has probably separated by river erosion. • Forms a water divide between Brahmaputra & meghna basin.

Coastal plains: Daigram: Characteristics: 1) Eastern coast – emergent coastline. (Smooth due to delta formation.). Western coast – submergent coastlines. (Indented due to estuaries.) • Origin: Besides difference in other characteristics of eastern and western coastlines their time of origin also seems to be different. It seems that it was east coast which evolved first as India broke away from, Australia and Antarctica (140-120 million years ago). During later part of this period part of western coast also seems to have originated. • As India started its Northward journey breaking away from Gondwanaland these parts of coast seems to have formed. However, during earlier part of northward journey Madagascar remained attached to India. It only got separated around 85 million years ago in cretaceous period when rest of western coastIAS seems to have evolved. • Next important event occurred during tertiary period when formation of Rajmahal-Garo gap reduced the length of east coast. Before it, it extended upto shillong. During the tertiary period marine transgression also had impact on part of western coast whereby the Kutch region, cambay Basin & parts of Malabar Coast were formed. • Another major event occurred in quaternary whereby faulting and rejuvenation led to shortening of west coast. Thus, it seems that west coast acquired its final outline during this faulting event and is thus representative of submergent coastline. On the other hand, east coast is representative of emergent coastline whose evolution along deltas is still very active.

2) General characteristics: Since mode of origin of coastline is different, there are several differences in characteristics: i. Width – west coast is narrower than eastern coast. ii. Coastline:GUIDANCE • West coast – indented coastline which is result of presence of estuaries and its cliffy nature. Has greater number of natural harbours. • East coast – smooth coastline and is a result of its emergent nature and presence of deltas, absence of natural harbours and thus ports have to be maintained at high cost. iii. Eastern coast has greater depositional features viz., sand dunes, good & wide beaches, mud flats, spits and bars. • Western coast – fewer beaches and general lack of depositional features. Infact along them few quaternary deposits are found which also reflects that faulting which led to its formation may be still active. iv. East coast – Large Rivers deposit sediments & presence of deltas cause reverse dendritic pattern. • Western coast – parallel drainage pattern, small space to meander, rivers directly drain into sea. v. West coast – influenced more by south-west monsoon winds & receives greater precipitation during summer monsoons. • East coast – particularly is more influenced by north-east monsoon winds, receives greater precipitation during winter monsoons. vi. East coast is more hazardous as there is greater probability of tropical cyclones as well as tsunami. 2004 tsunami had large impact on east coast line. Western coast has lesser probability of such hazards. (16)

Name of coastal units. Type of coast Other features. 1) Kutch Submergent Sandstones & Presence of large saline marshes, limestones of ter ary cliffs, beaches, mangroves. period 2) Kathiawar/Saurashtra Submergent Deccan Basal c rocks Estuaries, cliffs, beaches, mud fats, raised marine benches. 3) Submergent Deccan traps with Estuaries, cliffs, wave cut pla orms, some lateri c beaches & sand dunes. for ma o n + som e quaternary sediment. 4) Goa – Canara coast Submergent Peninsular genesis, Highly clify where cliff of western crystalline rocks + Ghats almost reach near coast, very lateri c forma on n a r row, wav e - c u t p l a o rm s, beaches, sand-dunes. 5) Malabar coast Submergent coastline Strongly metamorphic Broadest part of western coast but with signs of based rocks: line & has greater depositional emergence i.e. greater charnockites are found features + Estuaries & lagoons & deposi onal features backwaters (Kavals), fine beaches, are found. Strongly coastal sand-dunes at some places metamorphic based it becomes cliffy. rocks: charnockites are found 6) Coromandel coast Primarily represents Lithology is grani c & Large deltas, long beaches, spits & emergent coast line gneissic primarily but sand-dunes, coral reefs. but in its southern in extreme south, parts signs of charnockites are found submergence are present a er point Calimere. 7) Andhra coast Represents emergent Lithology is grani c & Large deltas, absence of coral reefs. coast line. gneissic Kolleru lake earlier was a lagoon later became inland lake due to deposi on. 8) Utkal coast Emergent coast line Grani c, gneissic + Large delta of Mahanadi, dense l a t e r i c r o c k s , mangrove forests, several deltaic between Mahanadi & islands, beaches & sand dunes. Krishna-Godavari delta coast becomes narrower due to presence of northern GUIDANCEcircars 9) Emergent coast line Quaternary L a rg e del ta w i t h v e r y d e n s e sedimentary rocks mangroves. Several dal inlets, deltaic islands, very fine beaches & sand-dunes.

(17)

HIMALAYAS • Himalayan mountain ranges present an example of Continent-Continent Collision. Such a collision started around 55m.y.a between Asia/Tibet and Indian Peninsula and has continued since then. Evidences suggest that the process is still active which is also evident in active seismicity in the region. • Indian Peninsula was formed as a part of Gondwana land which was formed by the end of Pre-Cambrian period. It was sandwiched between Africa & Madagascar on the north & North-west and Australia & Antarctica in South-east and south. In permean period (276-260 MYA) a series of continental fragments consisting of Turkey, Iran & Tibet drifted away from Gondwana land, thus opening neo-Tethys ocean on their trails. • Thus, with the opening of this ocean, the first stage of formation of Himalaya’s i.e. geosynclinal stage began. This stage has continued upto final closing of Tethys around 42 m.y.a. Thus, geosynclinal stage represents the largest stage in the formation of Himalayas. • More concretely, beginning of formation of Himalayas started about 135 m.y.a as Indian Peninsula broke away from Australia & Antarctica & started to move north across neo-Tethys ocean along with Madagascar with a velocity of about 11cm/year. At about 85 m.y.a, a further split occurs between Indian Peninsula & Madagascar. Diagram: • Around 65 m.y.a, there is evidence that at cretaceous stage Kohistan would have risen above sea level & would have collided with Asia. This would have led to emergence of trans-Himalayan ranges. Trans- Himalayan ranges were formed earlier than other Himalayan ranges are also proved by presence of Antecedent Rivers like Indus, Satluj, Kali, Gandak, Ghaghara, Kosi & Brahmaputra. These IAS rivers originate from southern boundary of Tibet (in trans-Himalayan ranges) & cut deep gorges in Himalayan ranges furnishing evidences of their antecedent nature. • Next stage in Himalayan formation was continent-continent collision, which started as north-western tip of peninsula crashed into Tibet leading to rise of Potwar plateau (55 m.y.a). This collision led to beginning of formation of western Himalayan ranges. • In next 10-13 million years, peninsula took a full anticlockwise turn and like a door slamming shut led to full closing of Tethys Sea. This led to beginning of emergence of eastern Himalayan ranges. Thus, it is clear that Himalayas represent Diachronous i.e. broadly speaking they were formed in 2 stages – western Himalayas formed earlier than eastern Himalayas. • With full consumption of Tethys sea floor northward journey of Indian Peninsula slowed to about 4-5 cm/year. Thus, in other words northward movement continued & continued collision between Indian Peninsula & Tibet led to formation of present physiography of Himalayas. HimalayanGUIDANCE ranges are represented by presence of several parallel mountain ranges each of which were formed in different stages. 5 stages are as follows –

1) Trans-Himalayas Uplift: (55mya-35mya): • Formation of trans-Himalayan ranges () began as Indian Peninsula collided into Asia in west. It continued from west to east as rest of Indian Peninsula collided with Asia. Trans-Himalayan ranges are made up of volcanic and metamorphic rocks which reveal that melting of Tethys sea floor had an important role in their formation. Although, they are also covered with some sedimentary outliers. 2) Eo-Himalayas/Tethyan Himalayan ranges (45-35 m.y.a): • The full collision between Indian Peninsula & Tibet is represented along a suture zone formed by the island arc represented by Ladakh-Kohistan ranges. They are present along I.T.S.Z which represents boundary between 2 plates. South of suture zoned lie the Tethyan Himalayan ranges. Tethyan-Himalayan ranges represent the accretionary wedge formed on the Tethys floor. Thus, they are primarily sedimentary in nature and their formation was simultaneous with Trans –Himalayan ranges between 45-35 m.y.a. Interestingly, Tethyan Himalayan ranges have escaped metamorphism despite being strongly folded & Faulted. Thus, marine fossils still remain preserved in these rocks. Diagram: (18)

3) Neo- Himalayan phase/ Great Himalayan uplift (24-17 m.y.a): • As process of convergence and collision continued, deformation and folding of rocks of Indian Peninsula led to formation of Great Himalayan ranges during early Miocene. As the collision continued, great Himalayan rocks were strongly deformed and even thrust faulting occurred. This led to formation of the thrust fault zone known as MCT. Along this thrust zone some nappe’s belonging to main Himalayas moved south and even today formed many of the peaks of middle Himalayas. 4) Lesser Himalayan Uplift (11-7 m.y.a) or middle Himalaya’s uplift: • As the process of convergence continued another set of parallel ranges representing middle Himalayas emerged south of MCT. Their formation is similar to that of great-Himalayan ranges i.e. also formed due to folding of rocks of peninsular crust. This phase is believed to be one of strongest phase of evolution which is reflected in the complexity of folding found in region. Moreover, discontinuity of mid-Himalayas also testifies to such assertion. • Similar to great-Himalayas, continued collision led to formation of series of thrust faults south of mid-Himalayas. Together these are called main boundary thrust (M.B.T). Diagram: 5) Neo Tectonic/quaternary phase: (2.6 m.y.a-end of Pleistocene): • With formation of mid-Himalayan ranges, extensive loading occurred leading to creation of sagging or downward flexure in the Indian Peninsular platform. Such a flexure created a linear depression south of lesser Himalayas. This depression is known as Himalayan foredeep. With formation of Himalayan foredeepIAS marine transgressions occurred which led to debouching of river from newly created Himalayas and peninsula in the foredeep. Thus, over a period of time there was accumulation of large amounts of sediments in Himalayan foredeep. • Initially Himalayan foredeep had marine environment but continued deposition & infilling converted it to sub-aerial fluvial & marshy environment. This led to formation of extensive Great Plains. As convergence continued between 2 plates, fracture zones developed in the foredeep whereby the northern part began to get deformed. The deformation of these sediments led to formation of 3rd set of parallel ranges called – Shiwalik. These are separated from lesser Himalayas by MBT. • On south, they are separated from Indus-Ganga plains by partially formed thrust faults represented by Himalayan front fault or Himalayan front thrust (HFF/HFT). • The upliftment of Himalayas still continues in Holocene. Such an upliftment is partly on account of collision which still continues and partly by Isostatic upliftment which Himalayan zone experienced on account of unloading related to erosion and valley formation as well as recession of glaciers following the end of last ice age. GUIDANCE ii) Structure and Relief: 1) Trans-Himalayan ranges: • Average relief – 4500m, present in a zone which is 35-40 km wide. Continuous from Pakistan to Arunachal Pradesh. Structure: • Volcanic rocks (mostly granite) and strongly metamorphosed into gneisses. Contain many important peaks (e.g. K2). These peaks represent batholiths which were emplaced. • Lie in higher latitude and hence covered with extensive glaciers. Outside polar zones largest glaciers are found here. • Indus Tsangpo-suture zone: represents boundary zone between Indian Peninsula and Tibet. Here suturing between 2 plates has occurred & is represented in presence of strongly metamorphosed volcanic rocks which represent island arc formed due to sinking of Tethys floor. Along with presence of & Gneisses, phyllite is present that represents strong metamorphism due to pressure. 2) Tethyan Himalayas: • Average relief-4300m; Average width is about 40kms. Primarily made up of sedimentary rocks which escaped metamorphism & hence marine fossils are found in rocks. Limestone, sandstone and rocks are found.

(19)

• Also represent strongly folded zone. However there is no clear cut boundary between them & great Himalayas and they look like almost attached to great Himalayas. 3) Great Himalayas/main Himalayas: • Average altitude – 6000m, width – 25km, remarkable continuity from Pakistan to Arunachal Pradesh. • Lithology – crystalline mountain ranges made of granite and Genesis & ’s, absence of fossils. The crystalline cover is overlained by a thin sedimentary cover. • Tallest peaks found (, Kanchenjunga etc.). • Main central Thrust –represents a thrust zone of reverse faulting made up of schist’s, gneisses and phyllites. 4) Lesser Himalayas/Middle Himalayas: • Altitude = 3600m-4200m, width about 80 kms in west & it narrows down in the east. • Very similar to main Himalayas, Un-fossiliferous metamorphosed crystalline rocks with presence of metamorphosed sedimentary rocks. • Many of their peaks represent nappies whose root zone lies in the great Himalayas.They are discontinuous. • Main boundary thrust – Thrust zone of reverse faulting made up of strongly metamorphosed rocks – schist, gneisses and phyllites. Diagram: 5) Sub-Himalayan zone/Shiwalik: • Average altitude – 1300m, average width – 45km is west, 8km is east. IAS • Made of sedimentary formation which are fossilised and contain fossils of both marine and fresh water origin. • Remarkably continuous from west to east, continuity seems to be broken only along Teesta river valley (80km) in east. • They are separated from mid Himalayas by Tectonic valleys which are locally referred to as duns. • To their south they are separated from I-G plain by a transition zone called Bhabar zone. Although here also tectonic convergence has led to formation of thrust zone of reverse faulting called HFF. HFF are present in eastern part where convergence today is strong e.g. Darbhanga fault line is part of HFF.

Peculiar Characteristics of Himalayas: i) Shape and presence of Syntaxial bends: Diagram • Arc shapedGUIDANCE with presence of hair pin like bends/Syntaxial bends. This is related with presence of rigid outliers of Indian Peninsula in form of Aravalli’s in west and Eastern Ghats in east. • During collision these outliers penetrated much into Asia compared to the central portion made up of comparatively less rigid rocks. Thus, this has led to such a structure. ii) Western Himalayas vs Eastern Himalayas: • Western Himalayas are broader and less tall with relief increasing gradually towards north in a step like manner. • Eastern Himalayas are narrower and taller and also their height increases suddenly as one move from plains to Himalayas. They represent almost wall like structure. Reason: • Himalayan ranges are Diachronous i.e. western ranges formed first and eastern ranges later, thus former are older and more denuded, and thus lower (relativity). Eastern ranges are younger, less denuded & hence relatively higher. • Difference in characteristics is also related to anti-clockwise movement of Indian Peninsula. Such an anti-clockwise door slamming shut movement, created greater convergence forces in east and same type of tensional forces in west imparting such characteristics. iii) Tallest Mountain of the world:

(20)

• The Unusual height of Himalaya’s is alien to other mountain ranges of world. It is probably related to support provided by median mass of Tibetan plateau (4000-5000m).

INDO-GANGETIC PLAINS/NORTH-INDIAN PLAINS: Origin: • Indo-Gangetic plains evolved as a consequence of filling of Himalayan fore deep basin which was formed in front of rising Himalayas. As lesser Himalayas were formed flexuring of peninsular crust led to formation of a linear depression at their foot. Such an isostatic flexure was result of loading of crust following the formation of Himalayas. This flexure/depression has been called as Himalayan fore deep. • Once Himalayan fore deep was formed, infilling of Himalayan fore deep by sediments brought by newly emerged Himalayan rivers & as well as peninsular rivers took place. Over a period of time it led to large deposition extending a depth of 2-7 kms and width of 250-450kms occurred. Such an extensive sedimentation occurred in 2 phases. Initially it occurred in marine environment which later gave way to sub-aerial fluvial environment. • In Pliocene period, the fore deep plains began to break into 2 unequal parts along Himalaya’s frontal faults. The process continues in Pleistocene leading to conversion of northern part into Shiwaliks while southern part ranging between 200-450km wide became the subsiding basin. The subsiding basin was filled up by river borne sediments brought from both Himalayan & peninsula rivers. Eventually it got transformed into Indo-Gangetic plains. Thus, I-G plains are result of crustal sagging and sinking which was followed by sediments deposition brought by rivers. Although their formation started with formation of Himalayan fore deep, presentIAS plan was finally achieved in Pleistocene. Structure and Relief: I) Classification on the basis of relief: A) Bhabar: Diagram: • It is formed by merger or coalescence of alluvial fans formed by Himalayan Rivers. As these rivers came out of higher reaches their velocity is drastically reduced. This results in lesser capacity of rivers to carry load resulting in deposition of coarser load leading to formation of alluvial fans. Over a period of time, these fans have expanded & merged to form Bhabar zone. • Bhabar is a 7-15km wide linear zone lying adjacent to foothills of Shiwalik. It is primarily made of cobbles & Pebbles including some boulders due to which it is characterised by higher porosity & permeability. This is so high that most of theGUIDANCE streams disappear because they begin to flow underground. These zones are famously called as Duars/Dwar (meaning – door) as rivers enter into plains from these regions. B) Tarai: • As rivers come out of Bhabar zone, they enter into an area of low relief with defective drainage. This to the spreading of waters laterally leading to creation of a marshy zone whose width ranges from 15-30km. this zone is characterised by excessive dampness and humidity. Tarai is found to be more developed in its eastern section as eastern part receives greater precipitation.

Economic significance: Bhabar: 1) Land under non-agricultural land use. Hence, most suitable for forestry. It should be preserved as an ecological zone. Vegetation ranges from tropical to sub-tropical forests. 2) Location of national parks & wildlife sanctuaries – tourist spot. 3) Ecosystem services. 4) Important transportation cities (Haridwar etc.) are located. As they are located between mountain & plains they act as Nodes/terminals in transportation route.

(21)

5) They can also be developed as industrial areas (fresh-water availability) e.g. Haridwar – pharmaceutical, precision industry; electronic & paper, forest based industries, educational centres can be developed. • Conclusion: - Can be related with Draft national land use policy – need to promote environment friendly industries, foot-loose industries. Tarai: Economic significance: 1) Agriculture – highly nitrogen rich soil, fertility is very high, availability of water is more than Bhabar. 2) Marshy & flood & disease prone zone – need to demarcate area into 2 zones viz., ecological & agriculture. 3) Dense forests are found – moist deciduous & wildlife: presence of elephant, antelopes, rhinos & carnivores. 4) Tourism circuits can be developed. 5) Sugarcane cultivation & sugar industries are located here. 6) Rice is also cultivated.

C) Bhangar and Khadar: • Rest of I-G plains are primarily made up of flood plains of rivers. The flood plains on basis of relief & other characteristics can be divided into Bhangar & Khadar. • Bhangar – old flood plains of rivers represented in form of alluvial terraces. It is made up of older alluvium due to which they are also dark in colour. It is filled with kankars which are aggregatesIAS of calcareous deposits. They represent dry points in the Indo-Gangetic flood plains due to which they are inhabited by rural settlements formed in Pleistocene. • Khadar – lying at lower level as it represents present flood plains of rivers. Colour of alluvium is light. Lesser concretisation of deposits/kankars is found. It is annually affected by floods due to which its fertility is renewed annually. This area is agriculturally significant part of India.

Regional Classification: 1) Punjab Plains: Primarily made of (area between 2 rivers) of rivers. refers to flood plains which lie between river & its tributaries. • Beas + Satluj – Bhist; Beas + Ravi – Bari; Ravi + Chenab = Rechna; Chenab + Jhelum = Chuj; Chenab + Jhelum + Indus – Sind-sagar. • Flood plain is divided into Bhangar and khadar. Bhangar is called bet land. In northern Punjab, high velocities of rivers comingGUIDANCE from Himalayas have caused extensive erosion & gullies. Gullies are locally called Chos. • In south it extends to Thar (drier part of thar & semi-arid called as Bagar land (several dry beds of ghaggar). 2) Gangetic Plains: Divided from Punjab plains by water divide of Aravalli. There is not a clear cut demarcation in eastern part as merger of flood plains of 2 rivers takes place. It is having the following divisions: i) Upper Gangetic plains – it has following sub-parts: • Ganga-Yamuna Doab – Lie in semi-arid & sub-humid region. Prominent Bhangar terraces are found. Over these Aeolian sandy ridges are deposited & are called as ‘Bhur’. • Rohilkhand: Large parts are made up of Bhabar & Tarai. • Avadh plains: Presence of extensive Khadar. ii) Middle Gangetic plains: • Although not separated on surface from Upper Gangetic plains, these are demarcated from them on basement by Faizabad ridge. Present in Eastern U.P. and Bihar, rivers – Ganga, Gandak, Kosi, Ghaghara, and son. • Presence of extensive Khadar land & are very flat, high meandering occurs – oxbow lakes (e.g. Tal). High tendency of rivers to shifts courses & hence area is severely affected by floods. iii) Lower Gangetic plains:

(22)

It has 2 parts – • Northern part – primarily made of Bhabar (Duars), extensive Tarai is present. • Southern part – Delta region, this area is made up of distribution of Ganga and is muddy (fine sediments of silt & clay). Here some areas are located at higher levels & appear like islands Known as ‘Chars’. iii) Brahmaputra plains: • Narrower (In north – Himalayas, south – Shillong plateau). • Brahmaputra is highly braided river here and large part of area suffers from floods. Its northern part is made up of Bhabar and Tarai & is narrower while its southern part is wider and continuity is broken by outliers of shillong plateau. • Presence of riverine islands e.g. Majuli Island.

ISLANDS OF INDIA: There are mainly 3 groups of island in India: 1) Andaman and Nicobar Islands: Diagram: Origin: • Andaman and Nicobar islands represents an 850km long chain of islands which represent an extension of Arkanyoma Mountains of Myanmar. They have been formed as a result of ocean- oceanIAS collision occurred between Indian and . • Andaman and Nicobar island arc comprises two nearly parallel arcuate belts. The western arc is represented by more than 300 islands belonging to Andaman and Nicobar group. It primarily represents an accretionary wedge which is resting over ophiolites which are basic to ultrabasic. The eastern arc is primarily representing sea mounts and some dormant and active volcanoes. At 2 places, this raises over sea level i.e. Narcondam and Barren islands. Structure: • These primarily represent a mountainous topography. Western arc is sedimentary in nature – sandstones, limestone and shale, while the eastern arc is primarily made up of igneous rocks – Andesitic to basaltic composition.

Arrangement: • Islands are characterised by hilly and steep slopes, coastal plains are very narrow particularly along western sea board. WesternGUIDANCE coast is very narrow & cliffy where ridges of sandstone and limestone directly overlook the sea. There is more presence of coral (fringing) reefs on western side. In eastern sea board, main cities are found as coast is broader than west and natural harbours are found there e.g. Ritchie archipelago. • Rivers are found but with short & swift courses. General relief = 200-500m, highest peak – saddle peak (730m) in north Andaman.

2) : • 2 groups – Amindivi and Cannanore Island. It is a group of 23 islands and represents coral atolls which have been formed on laccadive – Chagos ridge. Diagram:

• Lagoon is located towards windward side (western sea board. Hence, western sea board has gentle slope & eastern sea board has steep slopes. • Average relief – 5m above sea level, made up of calcium carbonate and sandstone, rougher topography. Differences:

(23)

1) Andaman & Nicobar receives more rainfall (250 cm) than Lakshadweep (100cm) due to low relief in latter. 2) Vegetation – Lakshadweep: absence of soil, coconut plantation while the Andaman & Nicobar: Equatorial forests/vegetation. 3) Other islands: a) Eastern coastal Islands: • New-Moore Island, Sagar Island, north of Mahanadi, Krishna-Godavari delta region. • These are sedimentary islands & have been formed by deposition of sediments by river & redistribution by action of waves & tides. • These islands represent sand bars and barriers islands which have risen above sea level. • Low altitude, average altitude is 5m above sea level. With development of vegetation they have stabilised, primarily made up of sandstones & shale. • Disasters can cause significant alteration in these islands. b) West coast islands: Features: • These are continental islands, formed by subduction of inter-connecting continental land expect St. Mary island which is a result of hotspot volcanism. (3rd phase of H.S volcanism) • Rest all have lithology similar to that of coast: (Diu – Basaltic, Mumbai – Basaltic, Pigeon Cock – Granitic to Gneissic). IAS Represent hilly and undulating terrain. c) Riverine Island: • On large rivers – Ganga & Brahmaputra which became braided in mid & lower reaches. Ex – ‘Chars’, Majuli. • Southern River – Srirangapatna Island (on Kaveri River). • These islands represent point bars, primarily formed of sandstones, most of them are unconsolidated and hence nature changes over time. Some have acquired permanency due to vegetation. GUIDANCE

(24)