Chapter 13 — 5.2 Physiography of India

Physiography means the description of the physical features of the earth's surface, its relief, or the arrangement of highlands and lowlands. India's relief is the product of a long geological history. About 200 million years ago the peninsula was part of the ancient southern continent of Gondwanaland, along with Africa, Australia and Antarctica. When Gondwanaland broke up, the Indian plate drifted north-east across the Tethys Sea and, about 50 million years ago, collided with the Eurasian plate. The sediments of the Tethys were crushed, folded and lifted into the Himalaya, and the trough that formed in front of the rising mountains was filled by the rivers to make the Northern Plain. The peninsula itself, a hard, stable block of ancient rocks, was pushed up and tilted but not folded.

On this basis India is divided into six or seven physiographic divisions, which every student should be able to draw on an outline map:

• The Northern Mountains, the Himalaya with the Trans-Himalaya behind it and the Purvanchal hills continuing it to the east: young fold mountains, about 2,400 km long and 150 to 400 km wide.
• The Great Northern Plain, the plains of the Indus, Ganga and Brahmaputra, about 2,400 km long and 150 to 300 km wide, of deep alluvium.
• The Peninsular Plateau, the triangular tableland south of the plains, of ancient crystalline rocks, with the Central Highlands north of the Narmada and the Deccan Plateau south of it.
• The Thar or Great Indian Desert in the north-west, between the Aravalli and the Indus.
• The Coastal Plains, the narrow western coastal plain between the Western Ghats and the Arabian Sea and the wider eastern coastal plain between the Eastern Ghats and the Bay of Bengal.
• The Islands, the Andaman and Nicobar Islands in the Bay of Bengal and the Lakshadweep Islands in the Arabian Sea.

The three great divisions differ in age and character. The peninsula is the oldest land, worn down over hundreds of millions of years into a rolling plateau with old rounded hills; the Himalaya is the youngest and still rising, with sharp peaks, deep gorges and frequent earthquakes; the plain is the newest of all, still being built by the rivers. Together they give India a mountain wall that guards it, a plain that feeds it and a plateau that holds its minerals, and the sections that follow take each in order from north to south.

The Himalaya, the abode of snow, is the highest and youngest mountain system in the world, a great arc about 2,400 kilometres long from the Indus gorge near Nanga Parbat in the west to the Brahmaputra gorge near Namcha Barwa in the east, and 150 to 400 kilometres wide, narrowing eastward. It is a range of young fold mountains, formed when the northward-moving Indian plate collided with the Eurasian plate and the sediments of the Tethys Sea between them were squeezed into folds and thrust upward; the process began about 50 million years ago and is still going on, so that the peaks rise a little every year and the region is shaken by earthquakes. Fossils of sea creatures found near Everest are the proof that the summit of the world was once the floor of a sea. The Himalaya is convex to the south and bends sharply at both ends, at Nanga Parbat in the west and Namcha Barwa in the east, the two syntaxial bends.

From north to south the Himalaya consists of three parallel ranges.

The Himadri or Greater Himalaya is the northernmost and highest, a continuous range with an average height of about 6,000 metres, its crest covered with permanent snow and glaciers. It holds the highest peaks of the world: Everest, 8,849 metres, on the Nepal-China border, called Sagarmatha in Nepal and Chomolungma in Tibet; Kangchenjunga, 8,586 metres, the highest peak in India, on the Sikkim-Nepal border; Makalu, Dhaulagiri, Annapurna and Nanga Parbat, 8,126 metres, and Nanda Devi, 7,817 metres, the highest peak wholly within India before the inclusion of Kangchenjunga. The core is of granite and crystalline rocks. The great rivers, the Indus, Sutlej and Brahmaputra, rise beyond it and cut through it in deep gorges.

The Himachal or Lesser Himalaya lies south of the Himadri, 60 to 80 kilometres wide and 3,700 to 4,500 metres high, made of compressed and altered rocks. Its ranges include the Pir Panjal in Kashmir, the longest, the Dhauladhar in Himachal Pradesh and the Mahabharat in Nepal. Between it and the Himadri lie the famous valleys of Kashmir, Kangra and Kullu, and on its slopes stand the hill stations of Shimla, Mussoorie, Nainital, Darjeeling and Dalhousie. Its high grassy meadows, called margs in Kashmir, such as Gulmarg and Sonamarg, and bugyals in Uttarakhand, are summer pastures.

The Shiwalik or Outer Himalaya is the southernmost and lowest range, 10 to 50 kilometres wide and 900 to 1,100 metres high, made of loose sediments, gravel and boulders brought down by the rivers from the higher ranges and folded only recently; it is discontinuous, and in the east it is called the Churia hills in Nepal and the Duars near Bhutan. Between the Shiwalik and the Himachal lie long flat valleys called duns, such as Dehra Dun, Kotli Dun and Patli Dun, fertile and well settled. The Shiwalik is easily eroded and its streams, choked with boulders, spread destructive floods on the plain below.

North of the Himadri, and separated from it by the valley of the Indus, lie the ranges of the Trans-Himalaya or Tibetan Himalaya, which are older than the Himalaya proper and lie mostly in Ladakh and Tibet. They are the Karakoram, the Ladakh range, the Zaskar range and the Kailash range in Tibet. The Karakoram, the backbone of high Asia, holds K2 or Godwin Austen, 8,611 metres, the second highest peak in the world and the highest in the territory claimed by India, and the great glaciers of Siachen, 76 kilometres long, the longest outside the polar regions, Baltoro and Biafo. These ranges are dry, cold and bare, because the Himalaya to the south cuts off the monsoon, and Ladakh behind them is a cold desert where Leh, at 3,500 metres, receives less than 10 centimetres of rain a year. The passes across them, Karakoram Pass and Khardung La, are among the highest in the world.

From west to east the Himalaya is divided, by the gorges of the great rivers, into four regional sections.

• The Punjab or Kashmir Himalaya, about 560 km between the Indus and the Sutlej, in Jammu and Kashmir, Ladakh and Himachal Pradesh. It contains the Kashmir valley, a former lake bed at 1,600 metres between the Pir Panjal and the Himadri, the Zoji La and Banihal passes, the Pir Panjal range and the Kangra and Kullu valleys; Nanga Parbat stands at its western end.
• The Kumaon Himalaya, about 320 km between the Sutlej and the Kali, in Uttarakhand. Its peaks include Nanda Devi, 7,817 m, Kamet, Trisul and Badrinath, and it holds the sources of the Ganga and Yamuna at the Gangotri and Yamunotri glaciers, the pilgrim towns of Badrinath and Kedarnath, the Mana and Niti passes into Tibet, the hill stations of Mussoorie and Nainital, and the Valley of Flowers.
• The Nepal or Central Himalaya, about 800 km between the Kali and the Tista, mostly in Nepal, with Sikkim and Darjeeling at its eastern end. It is the highest section, with Everest, Kangchenjunga, Makalu, Dhaulagiri and Annapurna, eight of the world's fourteen peaks above 8,000 metres. In India this section includes the Darjeeling Himalaya of West Bengal, whose highest point is Sandakphu, 3,636 metres, and the Sikkim Himalaya with Kangchenjunga and the Nathu La and Jelep La passes into Tibet.
• The Assam or Eastern Himalaya, about 720 km between the Tista and the Brahmaputra, through Bhutan and Arunachal Pradesh. Its peaks are lower, Namcha Barwa 7,756 m, Kangto and Chomolhari in Bhutan; it is wetter, forested and less known, and the Bomdila and Se La passes lead into Tibet. At its eastern end the Brahmaputra, called the Tsangpo in Tibet, breaks through the range in the deepest gorge on earth and turns south into Assam.

The Himalaya thus becomes lower, narrower and wetter from west to east: the snow line, which is at 5,000 metres in Kashmir, falls to 4,000 metres in Sikkim because the eastern ranges receive far more snow from the monsoon.

At the Brahmaputra gorge the Himalaya bends sharply southward at the eastern syntaxis of Namcha Barwa and continues, much lower, along the border of India and Myanmar as a series of ranges running north to south. These are the Purvanchal or Eastern Hills, sometimes called the Eastern Highlands, and geologically they are part of the same fold system as the Himalaya, made of the same young sedimentary rocks, sandstone and shale, folded in the same collision but with their axis turned through a right angle by the pressure of the Indian plate against the Burmese plate. They form a crescent 1,000 kilometres long from Arunachal Pradesh to Mizoram, convex to the west, with an average height of 1,500 to 2,000 metres, and they are the watershed between the Brahmaputra and the Irrawaddy and Chindwin of Myanmar.

From north to south the ranges are: the Patkai Bum along the Arunachal-Myanmar border, through which the Pangsau Pass carries the old Stilwell Road to Myanmar; the Naga Hills in Nagaland, whose highest peak is Saramati, 3,826 metres, the highest point of the Purvanchal; the Manipur Hills surrounding the oval Imphal valley, a former lake basin at 800 metres with Loktak Lake, the largest fresh-water lake of the north-east; the Mizo Hills or Lushai Hills in Mizoram, a series of parallel north-south ridges with the Blue Mountain, Phawngpui, 2,157 metres; and the Tripura Hills, low ridges running into Bangladesh. The Barail range branches westward from the Naga Hills into Assam, and the Mikir or Karbi Anglong hills stand as an isolated block in the Assam valley. Across the Brahmaputra, the Meghalaya plateau with the Garo, Khasi and Jaintia hills is not part of the Purvanchal at all but a detached piece of the ancient peninsular block, an outlier of the Chota Nagpur plateau separated from it by the alluvium of the Bengal basin and the Rajmahal gap; but it stands in the same region and receives the world's heaviest rain at Mawsynram and Cherrapunji on its southern scarp.

The Purvanchal is a region of heavy rainfall, over 200 centimetres, dense evergreen forest, shifting cultivation called jhum, and tribal peoples, the Nagas, Mizos, Kukis and Meiteis, who make up the population of the four hill states. Communications are difficult, the hills are prone to landslides in the monsoon, and the whole region is within the highest zone of earthquake risk; the Assam earthquakes of 1897 and 1950 were among the greatest ever recorded. Its passes, few and high, have nevertheless been routes of migration and invasion, and in 1944 the Japanese army was stopped at Kohima and Imphal in these hills.

Between the Himalaya and the Peninsular Plateau lies the Great Northern Plain, also called the Indo-Gangetic Plain, one of the largest and most fertile alluvial plains on earth. It stretches about 2,400 kilometres from the mouths of the Indus in the west to the mouths of the Ganga and Brahmaputra in the east, and is 150 to 300 kilometres wide, broadest in the west and narrowing eastward towards Assam; its area is about 7 lakh square kilometres, and it holds about 40 per cent of India's people.

Origin. When the Himalaya rose, the crust in front of it sagged into a long, deep trough or foredeep between the mountains and the peninsular block. For millions of years the Indus, Ganga, Brahmaputra and their hundreds of tributaries, cutting into the fresh, soft rocks of the rising mountains, have poured their silt into this trough and filled it. The alluvium is 1,000 to 2,000 metres deep in places, and beneath it the old peninsular rocks continue northward under the plain. The plain is therefore not eroded flat but built up flat, a depositional plain, and it is still growing: the delta of the Ganga advances into the Bay of Bengal every year. Its surface is almost level, sloping from about 300 metres above sea level near Delhi to sea level at the coast, a gradient of only 20 centimetres a kilometre, so that the rivers wander in wide meanders and shift their courses.

Belts from north to south. At the foot of the Shiwalik, where the mountain streams leave the hills, they drop their coarsest load of boulders and pebbles in a belt 8 to 16 kilometres wide called the Bhabar. The gravel is so porous that the streams sink into it and disappear. South of the Bhabar the streams re-emerge in a belt 15 to 30 kilometres wide of springs, marsh and thick forest, the Terai, once malarial jungle, now largely cleared for farming and the home of national parks such as Dudhwa, Jim Corbett and Jaldapara. The Terai of West Bengal in Jalpaiguri and the Duars is the tea and forest belt of the north. South of the Terai is the alluvial plain proper, which has two levels: the Bangar, the older alluvium of the higher ground between the rivers, above the reach of floods, with a slightly leached, sometimes calcareous soil containing nodules of lime called kankar; and the Khadar, the newer alluvium of the flood plains along the rivers, renewed by fresh silt every monsoon and therefore the most fertile land in India. In the delta the plain ends in the tidal marshes, swamps and islands of the Sundarbans.

The plain is dotted with features of river deposition: ox-bow lakes and abandoned channels, called bils in Bengal and tals elsewhere; the badlands of ravines along the Chambal; and in Punjab the interfluves between rivers called doabs, of which the Ganga-Yamuna Doab is the most famous.

The Northern Plain is divided from west to east by its rivers into three regional plains, and each has a character of its own.

The Punjab-Haryana Plain in the west, about 640 kilometres long and 300 wide, was built by the Indus and its five tributaries, the Jhelum, Chenab, Ravi, Beas and Sutlej, from which Punjab takes its name, the land of five rivers. Only the part east of the Ravi lies in India after 1947. Its surface is a series of doabs, the tongues of land between two rivers: the Bist Doab between the Beas and Sutlej, the Bari Doab between the Beas and Ravi, and so on. The rivers here flow in shallow valleys with bluffs called dhayas and old flood plains called bets, and the plain rises gently to the Delhi ridge in the south-east, a spur of the Aravalli. With canal irrigation this dry plain has become the granary of India and its most prosperous farmland.

The Ganga Plain is the largest, about 1,400 kilometres from the Yamuna in the west to the Bangladesh border in the east and 300 kilometres wide, covering Uttar Pradesh, Bihar and West Bengal. It is itself divided into the Upper Ganga Plain of western Uttar Pradesh, including the Ganga-Yamuna Doab and the Rohilkhand plain, drier and higher; the Middle Ganga Plain of eastern Uttar Pradesh and Bihar, wetter and lower, crossed by the Ghaghara, Gandak, Kosi and Son and subject to the terrible floods of the Kosi, the sorrow of Bihar; and the Lower Ganga Plain of West Bengal, where the river splits into the Bhagirathi-Hooghly and the Padma and builds the largest delta in the world. The Ganga plain is the most densely populated region of India, with over 900 persons per square kilometre in parts of Bihar and Bengal.

The Brahmaputra Plain in the east, the valley of Assam, is about 720 kilometres long and only 60 to 100 kilometres wide, shut in by the Himalaya on the north and the Purvanchal and Meghalaya hills on the south and reached from the rest of India only through the narrow Siliguri corridor. The Brahmaputra, up to 10 kilometres wide, wanders across it in braided channels between sandbanks and islands, of which Majuli is the largest river island in the world; the plain is subject to annual floods and earthquakes and is bordered by the tea gardens of the Terai-like foothills, the Duars, and by the swamps and grasslands of Kaziranga, home of the one-horned rhinoceros.

The three plains are linked by the continuous alluvium beneath them and by the great rivers that join them: a grain of silt from the Kumaon Himalaya may travel down the Ganga through all three and come to rest on a Sundarbans island. Their differences are of rainfall, which increases from 50 centimetres in Punjab to over 200 centimetres in Assam, and this difference decides their crops: wheat in the west, rice and jute in the east.

South of the Northern Plain lies the Peninsular Plateau, a great triangular tableland of about 16 lakh square kilometres, the largest physiographic division of India, with its base along the plain and its apex at Kanyakumari. It is the oldest part of the country, a fragment of Gondwanaland made of hard crystalline rocks, granite, gneiss and schist, more than 2,500 million years old, that have never been folded since and have been worn down by erosion into an undulating surface of rolling uplands, broad shallow valleys and isolated rounded hills. It is a stable block, rarely shaken by earthquakes, and it is India's storehouse of minerals, iron, manganese, coal, bauxite and mica. Its general height is 600 to 900 metres, and it is tilted so that it is higher in the west and slopes down to the east, which is why nearly all its rivers, the Mahanadi, Godavari, Krishna and Kaveri, flow eastward to the Bay of Bengal. The Narmada valley, a rift or fault trough, divides the plateau into two parts.

North of the Narmada lie the Central Highlands, an irregular belt between the plain and the Vindhya-Satpura ranges. Their parts are:

• The Aravalli Range on the north-west, running about 800 kilometres from Delhi to Gujarat through Rajasthan, the oldest fold mountains in India and among the oldest on earth, now worn to broken ridges of 300 to 900 metres, with the highest point at Guru Shikhar, 1,722 metres, on Mount Abu. It is the divide between the desert to its west and the Malwa plateau to its east.
• The Malwa Plateau in Madhya Pradesh, between the Aravalli and the Vindhya, of black volcanic soil, drained northward by the Chambal and the Betwa, which have cut deep ravines into it near the Yamuna.
• The Bundelkhand and Baghelkhand uplands east of Malwa, of old granite and gneiss, rocky and poor, between the Yamuna and the Vindhya.
• The Vindhya Range, a long escarpment of sandstone running from Gujarat east through Madhya Pradesh to Sasaram in Bihar, 450 to 1,100 metres, forming the northern wall of the Narmada valley and the traditional boundary between north and south India.
• The Satpura Range south of the Narmada, between it and the Tapi, a block mountain of about 900 kilometres from Rajpipla in Gujarat through the Mahadeo Hills, with Dhupgarh at Pachmarhi, 1,350 metres, and the Maikal range with Amarkantak, the source of the Narmada and the Son, in the east.
• The Chota Nagpur Plateau in the north-east, covering Jharkhand, the Purulia district of West Bengal and parts of Chhattisgarh and Odisha, a series of steps at 300 to 1,100 metres of granite and gneiss, drained by the Damodar, Subarnarekha and their tributaries, with the Ranchi and Hazaribagh plateaus, the Rajmahal hills of basalt in the east, and Parasnath, 1,366 metres, its highest point. It is the richest mineral region of India, with the coal of Jharia and Raniganj, the iron of Singhbhum and the mica of Koderma, and is called the Ruhr of India.

The Meghalaya plateau of the Garo, Khasi and Jaintia hills is a detached eastern fragment of the same block, separated from Chota Nagpur by the Rajmahal-Garo gap filled with Ganga alluvium.

South of the Narmada and the Satpura lies the Deccan Plateau, the largest part of the peninsular block, a triangle of about 5 lakh square kilometres bounded by the Satpura on the north, the Western Ghats on the west and the Eastern Ghats on the east. Its height is 500 to 1,000 metres, higher in the west and south, sloping to the east. Its north-western part, covering Maharashtra and parts of Gujarat, Madhya Pradesh and Karnataka, is the Deccan Trap, where about 65 million years ago enormous outpourings of lava through fissures spread in sheet upon sheet, 2,000 metres thick in places, to make flat-topped hills and step-like slopes and, on weathering, the black cotton soil or regur. South of the Trap the plateau is of the older granite and gneiss, in the Karnataka plateau with its Malnad hill country and Maidan plains and the Telangana plateau with its rocky knolls. The plateau is drained eastward by the Godavari, Krishna and Kaveri. Its edges are the two Ghats.

The Western Ghats or Sahyadri run unbroken for about 1,600 kilometres along the western edge of the plateau from the Tapi valley to Kanyakumari, at an average height of 900 to 1,200 metres, rising steeply from the coastal plain as an escarpment, an edge of the tilted block, and sloping gently eastward. They are continuous except for gaps: the Thal Ghat and Bhor Ghat near Mumbai, through which the railways climb to Nashik and Pune, and the wide Palghat gap, 30 kilometres, in Kerala, through which the railway from Chennai reaches Kochi and the monsoon reaches Coimbatore. Their peaks rise southward: Kalsubai, 1,646 metres, in Maharashtra; Kudremukh in Karnataka; and in the south, where the Nilgiri hills join the Ghats, Doda Betta, 2,637 metres, and, in the Anaimalai hills south of the Palghat gap, Anaimudi, 2,695 metres, the highest peak of peninsular India. The Cardamom hills continue to the cape. The Ghats face the south-west monsoon and receive over 250 centimetres of rain on their western slopes, so that their forests are dense and the great rivers of the peninsula rise within a few kilometres of the Arabian Sea and flow east.

The Eastern Ghats are a broken chain of hills along the eastern edge of the plateau from the Mahanadi in Odisha to the Nilgiri in Tamil Nadu, about 1,300 kilometres, lower, 600 metres on average, older and worn, cut into separate blocks by the Mahanadi, Godavari, Krishna and Kaveri, which pass through them to the coast. Their parts are the hills of Odisha and the Visakhapatnam region, where Mahendragiri, 1,501 metres, and the Arma Konda are the highest, the Nallamala, Palkonda and Velikonda hills of Andhra Pradesh, the Javadi and Shevaroy hills of Tamil Nadu. They receive less rain and are less forested than the Western Ghats. The two Ghats meet at the Nilgiri hills, the Blue Mountains, a knot of highland at 2,000 metres with the hill station of Udagamandalam or Ooty.

The Deccan is the land of the Marathas and the Vijayanagar kingdom, of black-soil cotton and of the industrial cities of Pune, Hyderabad and Bengaluru; the rain-shadow east of the Ghats is its chronic drought zone.

West of the Aravalli range, between it and the Indus valley of Pakistan, lies the Thar or Great Indian Desert, the largest desert of India and, at about 2 lakh square kilometres, one of the most populous deserts in the world. It covers the western half of Rajasthan, the districts of Jaisalmer, Barmer, Bikaner and Jodhpur, and extends into Haryana, Punjab and northern Gujarat, and across the border into Sindh. It is bounded on the east by the Aravalli, on the south by the Rann of Kutch and on the west by the Indus plain.

The Thar is a desert because it lies in the belt of the sub-tropical high pressure, because the south-west monsoon winds from the Arabian Sea blow parallel to the Aravalli instead of across it and pass over without rising, and because the Bay of Bengal branch has spent its moisture before it arrives. Rainfall is under 25 centimetres, less than 10 at Jaisalmer, and erratic; the summer temperature exceeds 45 degrees and the winter nights fall near freezing. The land is a plain of ancient rock covered by sand, with three kinds of surface: the sandy desert of shifting sand dunes, barchans and longitudinal dunes up to 150 metres high in the west; the stony desert of bare rock and gravel, called bagar, nearer the Aravalli; and the salt lakes, of which Sambhar near Jaipur is the largest and the source of salt. Only one river of any size crosses it, the Luni, which rises in the Aravalli near Ajmer and dies in the salt marsh of the Rann of Kutch without reaching the sea; every other stream is a dry bed that flows for a few hours after a storm. The dry valley of the ancient Saraswati or Ghaggar, once a great river, runs along its northern edge. Vegetation is thorny scrub, the khejri tree and grass after rain, and the animals are the camel, the chinkara, the desert fox and the great Indian bustard.

The desert is not empty. Its people are the Rajputs and the pastoral communities who herd camels, sheep and goats, and its cities, Jaisalmer, Bikaner and Jodhpur, grew on the caravan routes. Since 1958 the Indira Gandhi Canal, 650 kilometres long, has brought the water of the Sutlej and Beas from Harike in Punjab across the desert as far as Jaisalmer, turning the sand of Ganganagar and Hanumangarh into wheat and cotton fields and pushing the frontier of cultivation westward, though it has also brought waterlogging and salinity. The Thar has India's largest deposits of gypsum and lignite, a new field of oil and gas at Barmer, and the great wind and solar power stations of Jaisalmer and Bhadla. On its edge stands Pokhran, the site of the nuclear tests of 1974 and 1998.

The Rann of Kutch to the south, a vast salt marsh flooded by the sea in the monsoon and a white crust of salt in the dry season, is a related landscape, once an arm of the sea silted by the Indus.

The Peninsular Plateau is fringed by two narrow strips of lowland between the Ghats and the sea, the coastal plains, which differ so much from each other that the examination regularly asks for a comparison.

The Western Coastal Plain runs about 1,500 kilometres from the Rann of Kutch to Kanyakumari between the Western Ghats and the Arabian Sea, and is narrow, only 10 to 25 kilometres and never more than 80, because the Ghats rise steeply close to the shore. It is a coast of submergence, drowned by a rise of sea level, so it has drowned river mouths or estuaries, natural harbours such as Mumbai, Mormugao and Kochi, and no deltas. Its rivers are short and swift. From north to south it has four parts: the Gujarat plain including Kathiawar and Kutch, wider and formed by the Sabarmati, Mahi, Narmada and Tapi; the Konkan coast from Daman to Goa, rocky with small bays and creeks; the Kanara or Karnataka coast from Goa to Mangaluru, the narrowest; and the Malabar coast of Kerala, distinguished by its long backwaters or kayals, lagoons behind sand bars connected to the sea, such as Vembanad and Ashtamudi, on which Kochi and Alappuzha stand and which serve as waterways. The plain is wet, over 250 centimetres of rain, and grows rice, coconut, spices and rubber.

The Eastern Coastal Plain runs about 1,100 kilometres from the mouth of the Ganga to Kanyakumari between the Eastern Ghats and the Bay of Bengal and is much wider, 80 to 120 kilometres, because the Ghats are low and far from the shore and the great rivers have built it outward. It is a coast of emergence, raised relative to the sea, so it is straight and smooth, with sand bars, lagoons and few harbours, and its ports such as Chennai and Visakhapatnam are artificial or built in rare natural bays. Its rivers, the Mahanadi, Godavari, Krishna and Kaveri, have built the great fertile deltas that make it the rice bowl of the east. Its parts are the Utkal coast of Odisha with the Mahanadi delta and Chilika lake, the largest brackish lagoon in Asia; the Northern Circars of Andhra Pradesh between the Mahanadi and Krishna with the Godavari and Krishna deltas and Kolleru lake; and the Coromandel coast of Tamil Nadu from the Krishna to the cape with the Kaveri delta and Pulicat lake. Rainfall is lower, 100 centimetres, and comes largely from the retreating monsoon in winter.

The West Bengal coast, a short stretch from the Subarnarekha to the Sundarbans, belongs to the Ganga delta rather than to either plain and is described with the physiography of the state.

India has two groups of islands far from the mainland, very different in origin, and a number of small islands near the coast.

The Andaman and Nicobar Islands lie in the Bay of Bengal between 6 and 14 degrees north, about 1,200 kilometres from Kolkata and Chennai and only 150 kilometres from Sumatra. They are a chain of about 572 islands, islets and rocks running north to south for 800 kilometres, with a total area of 8,249 square kilometres, of which about 37 are inhabited. They are the summits of a submerged mountain range, the continuation of the Arakan Yoma of Myanmar, made of sandstone, limestone and volcanic rock, and they are therefore hilly, rising to Saddle Peak, 732 metres, on North Andaman. The Andaman group in the north, with North, Middle and South Andaman and Little Andaman, is separated from the Nicobar group in the south by the Ten Degree Channel; the Nicobars end at Great Nicobar, where Indira Point is the southernmost land of India. Barren Island, east of the Andamans, has the only active volcano in India, which erupted in 1991 and again in 2017, and Narcondam is a dormant one. The islands are covered with dense evergreen forest, fringed by coral reefs and mangroves, and inhabited by ancient tribes, the Great Andamanese, Onge, Jarawa and Sentinelese, and by settlers from the mainland. Port Blair, with its Cellular Jail where freedom fighters were imprisoned, is the capital. The islands suffered greatly in the tsunami of 2004, which drowned parts of the Nicobars.

The Lakshadweep Islands lie in the Arabian Sea between 8 and 12 degrees north, about 200 to 450 kilometres off the coast of Kerala. They are 36 tiny islands with a total area of only 32 square kilometres, the smallest union territory, of which ten are inhabited, with a population of about 64,000, almost all Muslim and Malayalam-speaking. Unlike the Andamans they are coral islands: rings of coral reef called atolls that grew on the rims of submerged volcanic peaks, enclosing shallow lagoons, and never rising more than a few metres above the sea. The northern islands were once called the Amindivi, the middle the Laccadive and the southern island Minicoy, which is separated from the rest by the Nine Degree Channel and from the Maldives by the Eight Degree Channel. The islands have no rivers or hills; coconut, fishing and tourism are the livelihood, and Kavaratti is the capital. Their low height makes them the most vulnerable part of India to a rising sea.

Near the coasts lie many smaller islands: Sagar Island and the islands of the Sundarbans at the mouth of the Ganga in West Bengal; Wheeler Island off Odisha, used for missile tests; Sriharikota off Andhra Pradesh, the launch site of Indian rockets; Pamban and Rameswaram in the Palk Strait; Salsette on which Mumbai stands; Diu and the islands of the Gulf of Kutch; and Majuli in the Brahmaputra, the largest river island in the world.

West Bengal is a small state, but it contains samples of three of India's great divisions, and its own relief is described in five regions from north to south.

The Darjeeling Himalaya in the north, covering Darjeeling and Kalimpong districts, is a section of the Nepal Himalaya between the Mechi and the Jaldhaka rivers, rising from the plain at 100 metres to over 3,000 metres within 50 kilometres. Its highest point is Sandakphu, 3,636 metres, on the Singalila ridge along the Nepal border, from which Everest and Kangchenjunga are both seen; other peaks are Phalut, Tonglu and Tiger Hill. The Tista cuts through it in a deep gorge, and the Rangit, Jaldhaka, Mahananda and Balason drain its slopes. The hills carry tea gardens on the middle slopes, oak and rhododendron forests above, and the hill towns of Darjeeling, Kurseong, Kalimpong and Mirik. Landslides in the monsoon are the great hazard.

The Terai and the Duars at the foot of the hills, in Darjeeling, Jalpaiguri, Alipurduar and Cooch Behar, form a belt 20 to 30 kilometres wide of gravel fans and wet, forested plain crossed by the Tista, Torsa, Jaldhaka, Raidak and Sankosh rivers, which spread boulders and shift their channels. The part west of the Tista is the Terai and the part east, the doors to Bhutan, is the Duars. It has the tea gardens of the plains and the forests of Jaldapara, Gorumara and Buxa. Its rivers are the source of the floods of north Bengal.

The western plateau and highlands, or Rarh region in its eastern part, cover Purulia, western Bankura, Jhargram, western Paschim Medinipur, Birbhum and western Bardhaman: the eastern fringe of the Chota Nagpur plateau, a rolling, lateritic upland at 100 to 300 metres, with isolated hills such as the Ajodhya hills of Purulia, 677 metres, Susunia in Bankura, 448 metres, and Biharinath. Its rivers, the Damodar, Dwarakeswar, Kangsabati and Ajay, are seasonal torrents. The soil is red and stony, the forest is sal, and this is the state's dry belt and its coal and mineral region around Raniganj and Asansol.

The Ganga plain and the delta occupy the whole middle and south of the state from Malda to the 24 Parganas and form the greater part of it: a flat alluvial plain sloping imperceptibly to the sea. In the north the Barind tract of Malda and the Dinajpurs is an old, slightly raised terrace of Bangar alluvium; south of the Ganga's bend at Farakka the river throws off the Bhagirathi-Hooghly and the delta begins, spreading across Murshidabad, Nadia, Hooghly, Howrah and Kolkata. The delta is divided into the moribund delta of Nadia and Murshidabad, whose old channels, the Jalangi, Mathabhanga and Churni, are decaying and silted; the mature delta of Kolkata, Howrah and Hooghly, well settled; and the active delta of the 24 Parganas, where the rivers still build new land.

The coastal plain and the Sundarbans in the south: the low sandy coast of Purba Medinipur, with the beaches and dunes of Digha, Mandarmani and the Kanthi coast, and the Sundarbans, the tidal forest of the active delta in South and North 24 Parganas, a maze of 100-odd islands, creeks and mangrove swamps at sea level, named for the sundari tree, the largest mangrove forest in the world and the home of the Royal Bengal tiger. Sagar Island lies at its western end.

The Himalaya is more than a mountain range on the border; it is one of the conditions of India's existence as a country, and the examination frequently asks the student to explain its importance.

Climate. The Himalaya is a wall 6,000 metres high across the whole northern frontier. In winter it shuts out the bitterly cold winds from central Asia and Siberia, so that north India at 25 to 30 degrees north has mild winters where China at the same latitude has snow and frost; without the wall Delhi would have the climate of Lanzhou. In summer it stops the moist south-west monsoon winds from passing on into Tibet and forces them to rise and drop their rain on the plains and foothills; the Bay of Bengal branch, turned west by the mountains, waters the whole Ganga plain. The Himalaya is the reason India has a monsoon climate and not a desert one.

Rivers and water. The snows and glaciers of the Himalaya, more than 15,000 glaciers holding about 12,000 cubic kilometres of ice, are the source of the Indus, Ganga and Brahmaputra and their tributaries, the perennial rivers that flow through the dry months when the rain-fed rivers of the peninsula shrink. They supply the irrigation canals of Punjab and Uttar Pradesh, the drinking water of the northern cities and the hydro-electric power of the Bhakra, Tehri and Teesta dams; a fifth of humanity depends on water from the Himalaya.

The plain. The silt that the rivers strip from the young, soft rocks of the Himalaya and spread across the foredeep built the Northern Plain, the granary of India, and continues to renew its fertility every monsoon.

Defence. For thousands of years the mountains have been a barrier against invasion from the north; the few passes are high and closed by snow for half the year. The Chinese incursion of 1962 showed that the barrier is not absolute, but it remains the strongest natural frontier in the world.

Forests, minerals and pasture. The Himalayan slopes carry the forests of sal, pine, deodar, oak and rhododendron that supply timber, resin, medicinal plants and fuel, and their meadows feed the flocks of the Gaddis, Gujjars and Bhotias. The mountains hold copper, lead, zinc, limestone, slate and gypsum, and the tea gardens of Darjeeling and the apple orchards of Himachal and Kashmir grow on their slopes.

Tourism, pilgrimage and culture. The hill stations of Shimla, Darjeeling, Nainital and Gulmarg, the pilgrim shrines of Amarnath, Kedarnath, Badrinath, Vaishno Devi and Kailash, the mountaineering of Everest and Kangchenjunga and the trekking of Sikkim and Ladakh draw millions of visitors and give a livelihood to the hill peoples. In Indian thought the Himalaya is the abode of the gods, the source of the sacred Ganga and the symbol of the country's northern boundary in the national anthem itself.

Against these gifts the Himalaya also sends earthquakes, landslides and floods, and its fragile slopes are threatened by deforestation, road-building and the retreat of its glaciers under a warming climate, a reason why its protection is now a national concern.

The other two great divisions serve India in ways as important as the Himalaya, and their contrast, the young fertile plain and the old mineral-rich plateau, is the basis of the country's economy.

The Northern Plain is the most productive region of India because of four advantages. Its soil is deep, fine alluvium, renewed each year on the khadar lands, that grows wheat, rice, sugar-cane, jute, cotton and pulses; the Punjab and the Ganga plain produce most of the country's food grain. Its rivers are perennial, fed by the Himalayan snows, and its flat surface makes canal irrigation easy, so that the Ganga canal, the Bhakra canals and the Sarda canal water millions of hectares; its water table is high and wells and tube-wells are everywhere. Its flatness made it easy to build roads and railways, so that the plain has the densest transport network in the country and the great cities of Delhi, Kanpur, Lucknow, Patna and Kolkata. And its history follows from all this: the plain has been the seat of every great Indian empire from the Mauryas to the Mughals and the British, the cradle of the Hindi and Bengali languages and the home of about 40 per cent of India's people on about 20 per cent of its land. Its weaknesses are the floods of the Kosi and Brahmaputra, the waterlogging and salinity of over-irrigated tracts, and the pressure of its huge population on its land.

The Peninsular Plateau is the mineral store and the power house of India. Its ancient crystalline rocks contain almost all the country's minerals: the coal of the Damodar, Mahanadi and Godavari valleys, the iron ore of Jharkhand, Odisha, Chhattisgarh and Karnataka, the manganese, bauxite, mica, copper, gold of Kolar and Hutti, limestone and the diamonds of Panna, and on these rest the steel plants of Jamshedpur, Durgapur, Rourkela, Bhilai and Bokaro and the industrial belt of the Chota Nagpur plateau. The black soil of the Deccan Trap grows the cotton of Maharashtra and Gujarat, and the red soils of the south grow millets, groundnut and, with irrigation, rice and sugar-cane. The plateau's rivers, the Mahanadi, Godavari, Krishna and Kaveri, falling from the plateau edge, give the hydro-electric power of the Hirakud, Nagarjunasagar, Sivasamudram and Mettur dams and the irrigation of the eastern deltas. Its forests of teak, sal and sandalwood, its hill stations at Ooty, Kodaikanal, Mahabaleshwar and Pachmarhi, its plantations of coffee and tea in the Western Ghats, and its stable, earthquake-free ground for the cities of Bengaluru, Hyderabad and Pune complete the picture. Its weakness is water: the plateau is dependent on the monsoon, its rivers shrink in the dry season and its rain-shadow districts are the drought belt of India.

The three divisions thus complement one another: the mountains give water and shelter, the plain gives food and people, the plateau gives minerals and power, and the coasts and islands give the trade and the fish of the sea. India's unity is written in its physiography.