Structure and Physiography of India: Himalayas, Plains, Peninsula, Coasts and Islands

1. Geological structure: the Peninsular Block, the Himalayas and the Indo-Ganga-Brahmaputra plain

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• The earth is about 4,600 million years old. Two kinds of force shaped it: endogenic forces from inside the earth and exogenic forces at its surface. The Indian plate once lay south of the equator and included the Australian plate. The two split, Australia moved southeast and India moved north. That northward drift still continues (Class 11, Structure and Physiography).
• Class 7: India broke away from Gondwana and hit Eurasia about 50 million years ago. It still pushes north about 5 cm a year, and the Himalayas rise about 5 mm a year. The plate history belongs to plate-tectonics.
• These events give India three geological divisions of India: the Peninsular Block, the Himalayas and other Peninsular mountains, and the Indo-Ganga-Brahmaputra plain.
• Peninsular Block: the oldest and most rigid part of India.
• Northern edge: Kachchh → the western flank of the Aravallis near Delhi → roughly parallel to the Yamuna and Ganga → the Rajmahal hills and the Ganga delta.
• Detached parts: Karbi Anglong and the Meghalaya plateau in the north-east, and Rajasthan in the west.
• Rocks and history: mostly ancient gneisses and granites. It has stayed rigid since the Cambrian, apart from the sunken west coast. It has seen up-and-down movements and block faulting. Examples are the Narmada, Tapi and Mahanadi rift valleys and the Satpura block mountains.

• Landforms: relict hills (worn-down stumps of old mountains) such as the Aravalli, Nallamala, Javadi, Veliconda, Palkonda and Mahendragiri. Valleys are shallow and gentle, and east-flowing rivers build deltas.

• Himalayas and other Peninsular mountains: young, weak and flexible, so faults, folds and thrusts still form. Fast young rivers cut gorges, V-shaped valleys, rapids and waterfalls (Figure 2.1).

• Himalayan orogeny (mountain-building; beyond NCERT): India hit Eurasia about 40-50 million years ago, and Tethys sea sediments were folded upward in several phases. Three great thrust faults run from north to south:
• the Main Central Thrust, between the Greater and Lesser Himalaya;
• the Main Boundary Thrust, between the Lesser Himalaya and the Shiwalik;

• the Main Frontal Thrust, between the Shiwalik and the plain. These are why the Himalayan belt lies in seismic zones V and IV (natural-hazards-disasters).

• Indo-Ganga-Brahmaputra plain: once a geosynclinal depression (a long sinking trough). Himalayan and Peninsular rivers filled it with 1,000-2,000 m of alluvium. NCERT dates its peak to the "third phase" of Himalayan uplift, "about 64 million years ago". Flag this: the third phase is usually placed far later, in the Pliocene-Pleistocene.

• Why structure matters: minerals lie in the Peninsula, fertile soil and dense population in the plain, and earthquakes and landslides in the mountains.

2. Physiographic divisions and the Himalayas as a whole

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• Physiography (the shape of the land) is the result of three things: structure, process and stage of development. The north is rugged mountains. The south is a stable, cut-up tableland with scarps (steep cliff edges). The vast plain lies between them.

• The six physiographic divisions of India (Figure 2.2): 1. the Northern and North-eastern Mountains 2. the Northern Plain 3. the Peninsular Plateau 4. the Indian Desert 5. the Coastal Plains 6. the Islands Class 7 uses five regions instead: mountains, plains, desert, southern peninsula and islands.

• The Himalayas are a set of parallel ranges. The Great Himalayan range (the central axial range) is about 2,500 km long east to west and 160-400 km wide. It stands like a wall between India and Central and East Asia (Figure 2.3).

• The orientation of the Himalayas (the direction they run) changes along the arc:

Region	Direction of the ranges
North-west India	northwest–southeast
Darjiling and Sikkim	east–west
Arunachal Pradesh	southwest–northeast (NCERT misprints this as "southwest to the northwest")
Nagaland, Manipur, Mizoram	north–south

• Beyond NCERT:
• Ends of the arc: the Nanga Parbat bend (Indus gorge) in the west and the Namcha Barwa bend (Tsangpo gorge) in the east.

• Width and height: wider in Kashmir (about 400 km) than in Arunachal (about 160 km), but the peaks are higher in the east.

• The Himalayas as a divide:

• Physical and climatic: they block cold Central Asian winds and make the monsoon drop its rain inside India (indian-climate-monsoon).
• Drainage: they are the "Water Tower of Asia" and feed rivers that flow all year (india-drainage-rivers).

• Cultural: they are sacred. Hima + alaya means "abode of snow".

• Extent and peaks: the range crosses six countries: India, Nepal, Bhutan, China, Pakistan and Afghanistan. Its peaks above 8,000 m are the "Eight Thousanders". All 14 in the world are in the Himalaya and Karakoram.

3. The parallel ranges: Trans-Himalaya, Greater Himalaya, Lesser Himalaya and Shiwalik

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Range (north → south)	Height	Key facts
Trans-Himalaya	—	Karakoram, Ladakh, Zaskar, Kailash ranges
Greater Himalaya (Himadri)	about 6,000 m average	granite core, permanent snow, few people
Lesser Himalaya (Himachal)	about 3,700-4,500 m	Pir Panjal, Dhauladhar; hill stations
Shiwalik (Outer Himalaya)	about 900-1,100 m	loose gravel; duns

• Trans-Himalaya:
• The Karakoram holds K2 (Godwin Austen, 8,611 m) in Indian-claimed Gilgit-Baltistan, and the Siachen and Baltoro glaciers.
• In the Ladakh and Zaskar ranges, the Indus flows northwest between the two ranges and then cuts through the Ladakh range near Gilgit.

• The Kailash range in Tibet is near the sources of the Indus, Satluj and Brahmaputra.

• Greater Himalaya (Himadri):

• Mount Everest: 8,848.86 m (2020 survey). It is called Sagarmatha in Nepal and Chomolungma in Tibet. Tenzing Norgay and Edmund Hillary first climbed it in 1953.
• Kanchenjunga: 8,586 m, on the Sikkim-Nepal border and the world's third highest. It is the highest peak in Indian-administered land, though India officially counts K2 as its highest.
• Nanda Devi: 7,816 m, the highest peak wholly inside India. Kamet and Trisul are other big peaks.

• Namcha Barwa: about 7,755 m, the eastern anchor in Tibet. The Tsangpo cuts one of the world's deepest gorges around it. Nanga Parbat (8,126 m) is the western anchor.

• Lesser Himalaya (Himachal):

• Pir Panjal range: the longest range of the Lesser Himalaya, south of the Kashmir valley. The Jhelum rises at Verinag at its foot. The Banihal pass crosses it, and the Jawahar and Banihal-Qazigund tunnels pass under it.
• Other ranges are the Dhauladhar and Mussoorie ranges and Nepal's Mahabharat range.
• Its valleys are Kashmir, Kangra and Kullu. Its hill stations are Shimla, Mussoorie, Nainital and Darjeeling.

• Class 7: kath-kuni houses, built of stone and timber, stay warm and resist earthquakes.

• Shiwalik:

• It is 10-50 km wide and made of loose river gravel and boulders, so it erodes easily and has many landslides.
• Duns are flat valleys between the Shiwalik and the Lesser Himalaya: Dehra Dun, Kotli Dun and Patli Dun.
• In Punjab and Himachal, its bare slopes are cut by seasonal torrents called chos.

4. Regional divisions of the Himalayas and the cold desert of Ladakh

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• The current NCERT edition dropped the regional divisions. They come from the earlier edition. West to east: 1. Kashmir or North-western Himalaya: the Karakoram, Ladakh, Zaskar and Pir Panjal ranges. The Kashmir valley has Dal and Wular lakes and karewas (clay beds left by old glacial lakes, used for saffron or zafran). 2. Himachal and Uttarakhand Himalaya (between the Ravi and Kali rivers): the Valley of Flowers, and Bhotia herders who move to summer pastures called bugyals. The Great Himalayan National Park is a UNESCO site (2014) and home to the Himalayan monal and snow leopard. 3. Darjeeling and Sikkim Himalaya (between Nepal and Bhutan): tea gardens, the Duars, Lepcha people and Kanchenjunga. 4. Arunachal Himalaya (from Bhutan to the Diphu pass): Kangto peak and Namcha Barwa. Peoples include the Monpa, Abor, Mishmi, Nishi and Naga, who practise jhum (shifting cultivation). Its valleys are the Kameng, Subansiri, Dihang, Dibang and Lohit. 5. Eastern Hills or Purvachal (see the next bullet).

• Purvachal: north-south hills of sedimentary rock along the Myanmar border, where the Himalayan system bends south. They are the Patkai Bum, Naga hills, Manipur hills and Mizo (Lushai) hills, with the Barail range between them. Manipur's Loktak lake lies here. Mizoram's "Molassis basin" is made of soft, loose deposits.

• Hindukush and Sulaiman ranges: these form the north-western wall of the subcontinent in Afghanistan and Pakistan (Class 11, India: Location). The Khurram, Tochi and Gomal rise in the Sulaiman and join the Indus.
• Cold desert: a dry, high, freezing region.
• Where: Ladakh and Lahaul-Spiti, in the rain shadow (the dry side, sheltered from rain-bearing winds) of the Greater Himalaya.
• Climate: under about 10 cm of rain a year (Class 11, Climate). Winters fall below −30°C (Class 7), and Drass reaches about −45°C.

• Ranges to name: Karakoram, Ladakh and Zaskar.

• Life in Ladakh (Class 7):

• Land: a "moonland" of eroded sand and clay that was once ocean-floor sediment. Pangong Tso is a salty lake.
• Animals: snow leopards, ibex and Tibetan antelopes. Yaks give milk, wool and dung, and carry loads.
• Culture: monasteries, and the Losar and Hemis festivals.

5. Himalayan passes: routes across the wall

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• Class 11, India: Location names the Khyber, Bolan, Shipki La, Nathu La and Bomdi La as gaps in the mountain wall. The Khyber and Bolan belong in india-neighbours.
• Heights below are approximate, and tunnel status needs checking (verify current).

Pass	State/UT	Key facts
Zoji La (~3,500 m)	Ladakh–J&K	Srinagar-Leh highway; often snowbound; Zojila tunnel (~13-14 km) under construction (verify current)
Khardung La	Ladakh (Ladakh range, north of Leh)	to the Nubra and Shyok valleys and Siachen; among the highest motorable passes
Banihal	J&K (Pir Panjal)	Jammu-Srinagar route
Rohtang Pass (~3,980 m)	Himachal (Pir Panjal)	links Kullu with Lahaul-Spiti; the Beas rises nearby; bypassed by the Atal Tunnel (9.02 km, opened 3 October 2020)
Shipki La (~3,930 m)	Himachal (Kinnaur)	the Satluj enters India here; India-China border trade point
Lipulekh, Mana, Niti	Uttarakhand	Lipulekh is on the Kailash Mansarovar route and is disputed by Nepal
Nathu La (~4,310 m)	Sikkim (Dongkya range)	Silk Route offshoot from Gangtok to Tibet's Chumbi valley; trade reopened 2006; Kailash yatra route since 2015
Jelep La	Sikkim	near Nathu La
Bomdi La (~2,600 m)	Arunachal (west)	Assam plains to Tawang road; key route in the 1962 war
Sela Pass (~4,170 m)	Arunachal	road to Tawang; Sela Tunnel (opened March 2024) gives all-weather access
Diphu, Pangsau	Arunachal	routes to Myanmar; Pangsau is on the Stilwell (Ledo) road

• Why passes matter:
• Trade: Nathu La, Shipki La and Lipulekh.
• Pilgrimage: the Kailash Mansarovar Yatra.
• Defence: they carry army supplies. Roads and tunnels give the army all-weather access (india-transport-communication).

6. The Northern Plain: bhabar, tarai, bhangar, khadar and the deltas

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• The Indo-Ganga-Brahmaputra plain is built of alluvium from the Indus, Ganga and Brahmaputra (Figure 2.4).
• Size: about 3,200 km east to west and 150-300 km wide.
• Alluvium: up to 1,000-2,000 m deep.

• Height: a nearly flat plain only 50-150 m above sea level.

• Water divide and the Dhubri turn: Haryana and Delhi separate the Indus and Ganga systems. The Brahmaputra flows northeast to southwest, then turns almost 90° south at Dhubri into Bangladesh.

• Zones from north to south: 1. Bhabar (8-10 km wide): lies at the foot of the Shiwalik, where the slope breaks. Rivers drop boulders and gravel, and small streams sink into the porous ground and vanish. 2. Tarai (10-20 km wide): the streams come back up without proper channels, so the land is marshy with thick forest and wildlife. Much of it was cleared for farms after 1950. Corbett, Dudhwa and Valmiki tiger reserves remain. 3. Bhangar: older alluvium on raised terraces above flood level. It holds kankar (lime nodules) and is less fertile. 4. Khadar: newer alluvium on floodplains, renewed by floods almost every year. It is fine and very fertile.

• Piedmont alluvial plains are plains at the foot of mountains where rivers drop coarse sediment. Examples are the Duars (north Bengal and Assam foothills, with tea), the chos of the Punjab Shiwaliks, and the tarai.

• River features: the plains show mature-stage landforms: sand bars, meanders, oxbow lakes and braided channels (landforms-evolution).
• A riverine island is land ringed by river channels in a wide, braided river.

• Majuli in the Brahmaputra (Assam) is often called the world's largest river island. It is a centre of Vaishnavite satras (monasteries) and became a district in 2016. Erosion has shrunk it from about 1,250 sq km to roughly 350-500 sq km (verify current).

• Ganga-Brahmaputra delta (the Sundarbans) is the world's largest delta and largest mangrove forest. It is home to the Royal Bengal tiger and is a UNESCO site.

• India's share: NCERT books disagree. Class 7 says "about half"; another NCERT book says "about one-third". Flag this.

• Threats: sea-level rise and cyclones.

• Why it matters: fertile soil grows wheat, rice, sugarcane and jute, so the plain supports a dense population. Flat land made dense road and rail networks easy to build (Class 7).

7. The Peninsular Plateau and the Central Highlands

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• Peninsular Plateau: an irregular triangle that rises from 150 m to 600-900 m. It is one of India's oldest and most stable landmasses.
• Edges: the Delhi ridge (the Aravallis' northern tip) in the northwest, the Rajmahal hills in the east, the Gir range in the west and the Cardamom hills in the south. The Shillong and Karbi Anglong plateaus extend it to the north-east.

• Slope: it slopes from west to east, which the rivers show.

• Patland plateau: flat-topped, step-like surfaces such as Hazaribagh, Palamu, Ranchi, Malwa, Coimbatore and Karnataka. In Chotanagpur the flat tops are called pats.

• Landforms: tors, block mountains, rift valleys, spurs, hummocky hills and quartzite dykes (wall-like rock bands that make natural dam sites). The west and northwest have black soil.
• History: the plateau has been uplifted, sunk and faulted again and again. The Bhima fault is still seismically active.
• Chambal ravines: deep gullies in the soft alluvium of Bhind, Morena and Dholpur. These badlands are hard to farm and long sheltered dacoits.
• Central Highlands: they lie between the Aravallis (west) and the Rajmahal hills (east), stand 700-1,000 m high and slope north and northeast. They contain metamorphic rocks (marble, slate, gneiss) and reach Jaisalmer under dunes. Most Yamuna tributaries rise in the Vindhyan and Kaimur ranges. The Banas is the Chambal's only big tributary and rises in the Aravallis.
• Aravalli range:
• Age and extent: one of the world's oldest fold mountains, about 2.5 billion years old and now a relict range. It runs from Gujarat through Rajasthan and Haryana to the Delhi ridge.
• Height: most hills are 300-900 m. Guru Shikhar (Mount Abu, 1,722 m) is the highest point.
• Role: it blocks the Thar from spreading east.
• Minerals and history: it holds zinc (Zawar's ancient zinc smelting, over eight centuries old), copper and marble. The Chittorgarh and Kumbhalgarh forts stand on it.

• Current issues: illegal mining, the Aravalli Green Wall (2023), and the Supreme Court's 2025 definition of the hills (verify current).

• Other Central Highland units:

• Malwa plateau: a lava plateau in western Madhya Pradesh. The Chambal rises near Mhow, and black soil grows cotton and soybean.
• Vindhyan range: an escarpment (a long steep slope) north of the Narmada rift and the old north-south divide. The Betwa and Ken rise here.
• Satpura range: scarped block plateaus between the Narmada and Tapi, 600-900 m high. It is the northern edge of the Deccan, and Dhupgarh near Pachmarhi is its highest point.
• Maikal range: links the Satpura and Chotanagpur. Its Amarkantak plateau is the source of the Narmada and Son.
• Gir range: in Saurashtra, the last wild home of the Asiatic lion.
• Rajmahal hills: basalt hills in Jharkhand that the Ganga bends around.
• Chotanagpur plateau: in Jharkhand, made of the Hazaribagh, Ranchi and Palamu plateaus. It is India's richest mineral store (coal, iron ore, mica).

8. The Deccan Plateau and the Western and Eastern Ghats

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• Deccan Plateau: bordered by the Western Ghats, the Eastern Ghats, and the Satpura-Maikal-Mahadeo hills in the north.
• Rock: much of its northwest is Deccan Trap basalt, poured out about 66 million years ago, which weathers into black soil.

• Slope: it tilts east, so most rivers flow to the Bay of Bengal.

• Western Ghats: a continuous wall that averages about 1,500 m and rises from north to south. Local names are:

• the Sahyadri in Maharashtra;
• the Nilgiri hills in Karnataka and Tamil Nadu;

• the Anaimalai and Cardamom hills in Kerala.

• Anamudi (2,695 m): the Peninsula's highest peak. It is in the Anaimalai hills of Idukki, Kerala, inside Eravikulam National Park, home of the Nilgiri tahr.

• Dodabetta (2,637 m): the second highest peak, in the Nilgiris near Ooty.
• Nilgiri hills: the two Ghats meet here. They have shola forests and India's first biosphere reserve (1986).
• Western Ghats ecology: a UNESCO site (2012) and a biodiversity hotspot, home to the lion-tailed macaque and king cobra. The Gadgil (2011) and Kasturirangan (2013) reports disagree on how much area to protect.
• Gaps and passes:
• Palghat Gap (30-40 km wide, between the Nilgiris and the Anaimalai) links Kerala and Tamil Nadu by road and rail and lets monsoon winds reach Coimbatore.

• Thal Ghat and Bhor Ghat carry the Mumbai-Nashik and Mumbai-Pune road and rail lines up the Sahyadri.

• Eastern Ghats: low, broken hills. The Mahanadi, Godavari, Krishna and Kaveri cut through them. Ranges are the Javadi, Palkonda, Mahendragiri and Nallamala hills (Andhra Pradesh and Telangana). The Nallamala hold the Nagarjunasagar-Srisailam Tiger Reserve.

Feature	Western Ghats	Eastern Ghats
Continuity	continuous	broken
Height	~1,500 m, higher	lower
Rivers	most Peninsular rivers rise here	cut through by rivers
Rain	windward 250-400 cm	less; the Deccan lies in rain shadow
Breaks	Palghat, Thal, Bhor	river gaps

9. The North-eastern Plateau: Meghalaya and Karbi Anglong

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• The northeastern plateau is part of the Peninsular plateau. It became separated in three steps: 1. During Himalayan uplift, India's northeastward push opened a huge fault between the Rajmahal hills and Meghalaya. 2. Rivers later filled this gap with sediment. 3. Today the Meghalaya and Karbi Anglong plateaus stand apart from the main block.

• Malda fault: the sunken zone in West Bengal that splits the north-east from the Chotanagpur plateau. Its mid-Pleistocene sinking turned the Ganga and Brahmaputra toward the Bay of Bengal.

• Meghalaya plateau: very heavy southwest monsoon rain has left a highly eroded surface. Cherrapunji is bare rock with no permanent vegetation.
• Garo, Khasi and Jaintia hills (west to east): named after their tribes.
• Garo hills: Tura and Nokrek peak.
• Khasi hills: Shillong, Cherrapunji (Sohra) and Mawsynram.

• Jaintia hills: the eastern end.

• Karbi Anglong plateau: in central Assam, another detached piece of the Peninsula. It is one of the few landslide-prone parts of Assam.

• Minerals: like Chotanagpur, the region is rich in coal, iron ore, sillimanite, limestone and uranium.
• Life in the hills (Class 7):
• Nature: lush forests, heavy rain and the Seven Sisters falls.
• Culture: the Khasi festival Shad Suk Mynsiem.

• Villages: Mawlynnong is called the "cleanest village in Asia". Living root bridges grow near Nongriat.

• Current issue: unsafe "rat-hole" coal mining in the Jaintia hills. The NGT banned it in 2014, and the Ksan mine disaster followed in 2018 (verify current).

10. The Indian (Thar) Desert and the Rann of Kachchh

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• Thar Desert (Marusthali): lies northwest of the Aravallis.
• Landscape: rolling land with longitudinal dunes (long sand ridges) and barchans (crescent-shaped dunes) (Figure 2.6).

• Climate: under 150 mm of rain a year.

• Once under the sea: in the Mesozoic the region lay under the sea. Two sites prove it:

• Akal Wood Fossil Park near Jaisalmer, with fossil tree trunks about 180 million years old;

• marine deposits at Brahmsar.

• How wind shapes it: the rock below belongs to the Peninsula. On top, heat, cold and wind have carved:

• mushroom rocks (rocks worn thin at the base);
• shifting dunes;

• oases, mostly in the south.

• Drainage:

• Slope: the north slopes toward Sindh and the south toward the Rann.
• Rivers: they flow only after rain, and the Luni is the main one.

• Inland drainage: streams end in salt lakes and playas (shallow desert lake beds) whose brackish water gives salt.

• Extent and life (Class 7):

• Spread: the Thar covers parts of Rajasthan, Gujarat, Punjab and Haryana.
• Climate and dunes: dunes reach 150 m, days are hot and nights cold.
• Places: Jaisalmer, the "Golden City", whose fort is a UNESCO site, and the Pushkar fair.

• Saving water: people store rainwater in taanka or kunds and scour pots with sand.

• Rann of Kachchh: a vast seasonal salt marsh with two parts.

• Great and Little Rann: the Little Rann is home to the Indian wild ass.
• Seasons: it floods in the monsoon and becomes a white salt flat in the dry season.
• Other facts: the Luni ends here, flamingos breed here, and the area has a very high earthquake risk.

• Dholavira (UNESCO 2021) lies on Khadir island, and the Sir Creek dispute is in india-neighbours.

• Banni grassland: one of Asia's largest tropical grasslands, on the edge of the Great Rann. It is home to Maldhari herders and Banni buffalo, and is threatened by the invasive Prosopis juliflora.

11. The Coastal Plains: a submerged west and an emergent east

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• The coastal plains of India are two lowland strips between the plateau and the sea.
• Western coastal plain: a submerged coast (land that sank under the sea). Dwaraka is believed to lie under water.
• Shape: narrow, wider in the north and south.
• Ports: the drowned coast gives natural harbours: Kandla (now Deendayal), Mazagaon (Mumbai), JLN Port (Nhava Sheva), Marmagao, Mangaluru and Kochi.

• Parts, north to south: the Kachchh-Kathiawar coast (Gujarat), the Konkan coast, the Goan coast and the Malabar coast.

• Why the west coast has no deltas:

• Its rivers are short and swift on a steep slope.

• The sinking coast drowns river mouths into estuaries (wide tidal mouths), such as those of the Narmada and Tapi.

• Konkan coast (Maharashtra, Daman to Goa): narrow, rocky, full of creeks and very rainy. The Konkan Railway (1998) runs along it.

• Malabar coast (Kerala and coastal Karnataka): known for kayals, coconuts, spices and heavy rain.
• Kerala backwaters: these kayals are lagoons cut off from the sea by sand bars. They are used for fishing, boats and tourism, and Vembanad is the largest.

• The Nehru Trophy Vallamkali boat race is held each year on Punnamada Kayal.

• Eastern coastal plain: broad and an emergent coast (land that rose out of the sea).

• Deltas: it has big deltas of the Mahanadi, Godavari, Krishna and Kaveri.
• Ports: NCERT says the continental shelf runs up to 500 km out, so there are fewer good harbours. East-coast ports include Kolkata-Haldia, Paradip, Visakhapatnam, Chennai, Ennore (Kamarajar) and Tuticorin (V.O. Chidambaranar).
• Regional names: Utkal plain (Odisha), Northern Circars (Andhra) and Coromandel (Tamil Nadu).

• Lagoons: Chilika and Pulicat. A lagoon is water cut off from the sea by a natural barrier.

• Coromandel Coast: low and sandy, with the Kaveri delta.

• Rain: it stays dry in the southwest monsoon and gets most of its rain from the northeast monsoon and cyclones in October-December.
• Tsunami: the 2004 tsunami struck here and in the Andamans.

12. The Islands: Andaman and Nicobar, and Lakshadweep

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• Andaman and Nicobar Islands: about 572 islands in the Bay of Bengal, at 6°-14°N, 92°-94°E.
• Origin: they are the raised tops of an undersea mountain chain that continues the Arakan Yoma. Some small islands are volcanic.
• Islet groups: Ritchie's archipelago and the Labyrinth islands.
• Volcanoes: Barren Island is India's only active volcano. Narcondam is dormant.
• Climate: convectional rain (daily rain from rising hot air) and equatorial forest.

• History and strategy (Class 7): India's "outposts" with a naval presence. Freedom fighters were jailed in the Cellular Jail.

• Channels:

• The Ten Degree Channel (about 150 km wide, along 10°N) separates Little Andaman from Car Nicobar.
• The Duncan Passage separates South Andaman from Little Andaman.

• The Six Degree Channel lies between Great Nicobar and Sumatra.

• Peaks: Saddle Peak (North Andaman, 738 m, the highest), Mount Diavolo (Middle Andaman, 515 m), Mount Koyob (South Andaman, 460 m) and Mount Thuiller (Great Nicobar, 642 m).

• Lakshadweep Islands: about 36 coral islands in the Arabian Sea, at 8°-12°N, 71°-74°E, 220-440 km off Kerala.
• People: 10-11 islands are inhabited, and Kavaratti is the capital.

• Storm beaches: banks of loose pebbles, shingle and boulders line the eastern side.

• Lakshadweep channels:

• The Nine Degree Channel separates Minicoy from the main group, with the Amindivi islands north and the Cannanore islands south.

• The Eight Degree Channel separates Minicoy from the Maldives.

• Minicoy Island: the southernmost island. NCERT calls it the largest island at 453 sq km, but this is wrong. All of Lakshadweep's land is only about 32 sq km. Minicoy is about 4.4 sq km, and Andrott (about 4.9 sq km) is the largest.

	Bay of Bengal	Arabian Sea
Number	~572	~36
Origin	tectonic, some volcanic	coral
Relief	hilly, large	flat, tiny
Cover	dense forest	coconut, beaches

• Great Nicobar project (from 2021):
• What it includes: a transshipment port at Galathea Bay, an airport, a township and a power plant, costing about ₹72,000 crore.
• Concerns: loss of forests, leatherback turtle nesting beaches, the Shompen and Nicobarese peoples, and earthquake risk.
• Status: verify current.

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Exam angles

Prelims — high-yield facts and traps

• Divisions: 3 geological divisions vs 6 physiographic divisions.
• Peninsular Block:
• Northern edge: Kachchh → Aravalli flank near Delhi → parallel to the Yamuna-Ganga → Rajmahal.

• Detached parts: Meghalaya and Karbi Anglong, cut off by the Malda fault.

• Himalayan ranges, north → south:

• Trans-Himalaya: Karakoram, Ladakh, Zaskar.
• Greater Himalaya: about 6,000 m.
• Lesser Himalaya: Pir Panjal, Dhauladhar.
• Shiwalik: 900-1,100 m.

• Duns lie between the Shiwalik and the Lesser Himalaya.

• Peaks: Everest 8,848.86 m (2020) · K2 8,611 m · Kanchenjunga 8,586 m · Nanda Devi 7,816 m (highest wholly in India) · Namcha Barwa 7,755 m · Anamudi 2,695 m · Dodabetta 2,637 m · Guru Shikhar 1,722 m · Saddle Peak 738 m.

• Passes by state:
• Ladakh: Zoji La, Khardung La.
• J&K: Banihal.
• Himachal: Rohtang, Shipki La.
• Uttarakhand: Lipulekh, Mana, Niti.
• Sikkim: Nathu La, Jelep La.

• Arunachal: Bomdi La, Sela.

• Tunnels: Atal (2020, under Rohtang), Sela (2024), Zojila (under construction).

• Northern plain order: bhabar (8-10 km) → tarai (10-20 km) → bhangar (old, kankar) → khadar (new, fertile). The Brahmaputra turns south at Dhubri.
• Ghats:
• Western: Sahyadri, Nilgiri, Anaimalai, Cardamom; continuous.
• Eastern: Javadi, Palkonda, Nallamala, Mahendragiri; broken.

• They meet at the Nilgiris. The Palghat gap is between the Nilgiri and the Anaimalai.

• Coasts:

• West: submerged, narrow, no deltas: Kachchh-Kathiawar, Konkan, Goan, Malabar.

• East: emergent, broad, deltas: Utkal, Northern Circars, Coromandel.

• Channels:

• Andaman side: Ten Degree (Andaman-Nicobar), Duncan Passage (South-Little Andaman), Six Degree (Great Nicobar-Sumatra).

• Lakshadweep side: Nine Degree (Minicoy-main group), Eight Degree (Minicoy-Maldives).

• Desert: barchans are crescent dunes. The Akal fossils show a Mesozoic sea. The Luni ends in the Rann, and playas give salt.

• Traps (all FALSE):
• "Minicoy is the largest Lakshadweep island at 453 sq km." Andrott is the largest.
• "The Himalayas in Arunachal run southwest to northwest." They run southwest to northeast.
• "West-coast rivers build deltas."
• "Lakshadweep islands are volcanic." They are coral.
• "The Banas rises in the Vindhyas." It rises in the Aravallis.

Mains — GS-I themes

1. How geological structure (rigid block, young fold mountains, alluvial trough) shapes India's relief, minerals and earthquake risk.
2. The Himalayas as a physical, climatic, drainage and cultural divide, and how fragile they are (roads, tunnels, hydropower, Joshimath 2023).
3. Western vs eastern coastal plains: submergence vs emergence, and what that means for ports, deltas, fishing and livelihoods.
4. The Northern Plain as India's farm and population heartland, and what limits it (floods, waterlogging, falling groundwater).
5. The Aravallis and Western Ghats as ecological barriers: conservation vs mining and development.
6. Strategic and ecological value of India's islands, and the Great Nicobar project debate.

Current-affairs hooks

• Border infrastructure: Zojila, Sela and Shinku La tunnels and the Arunachal Frontier Highway (verify current).
• Disasters: Joshimath subsidence (2023), the Sikkim GLOF (a sudden glacial-lake flood, October 2023), the Wayanad landslides (July 2024) and cloudbursts.
• Conservation rulings: the Aravalli definition and mining orders, and Western Ghats eco-sensitive area notifications (verify current).
• Islands: Great Nicobar clearances and court cases, and Barren Island eruptions (verify current).
• Erosion and climate: Majuli erosion, Sundarbans sea-level rise and Himalayan glacier retreat (verify current).