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Geography – Complete Study Notes

UPSC CSE Prelims Mains GS I

Complete Study Notes for UPSC CSE Prelims GS Paper I

Ch 1 · Physical Geography Ch 2 · Indian Landforms Ch 3 · Climate & Monsoon Ch 4 · Rivers & Water Bodies Ch 5 · World Geography Ch 6 · Natural Resources Quick Revision
1Physical Geography Fundamentals►

Physical geography covers the Earth's structure, landforms, and the processes that shape them. UPSC Prelims tests plate tectonics, types of rocks, earthquake and volcano distribution, and landform terminology.

Internal Structure of the Earth

LayerDepthCompositionState
Crust0–35 km (continental) / 0–10 km (oceanic)Sial (Si + Al) — continental; Sima (Si + Mg) — oceanicSolid
Mantle35–2900 kmSilicates of Fe and Mg; Asthenosphere (partially molten) at ~100–300 kmSolid (plastic asthenosphere)
Outer Core2900–5100 kmFe and Ni (liquid)Liquid — generates Earth's magnetic field
Inner Core5100–6371 kmFe and Ni (solid — under immense pressure)Solid

Plate Tectonics

  • Major plates: Pacific, North American, South American, African, Antarctic, Eurasian, Indo-Australian (7 major)
  • Divergent boundaries: Plates move apart; seafloor spreading; Mid-oceanic ridges (Mid-Atlantic Ridge); rift valleys on land (East African Rift)
  • Convergent boundaries: Plates collide; subduction (oceanic under continental → volcanoes, trenches); collision (two continental → fold mountains — Himalayas)
  • Transform boundaries: Plates slide past; earthquakes; San Andreas Fault (California)
  • Himalayan formation: Indian Plate collided with Eurasian Plate ~50 million years ago (ongoing)

Types of Rocks

Rock TypeFormationExamplesKey Properties
IgneousCooling of magma/lava; no fossilsGranite (intrusive/plutonic), Basalt (extrusive/volcanic), Obsidian, PumiceCrystalline; forms parent rocks; no fossils
SedimentaryDeposition and lithification of sediments; fossils found hereSandstone, Limestone, Shale, Coal, ConglomerateLayered (stratified); fossils; most common at surface
MetamorphicHeat + pressure transforms existing rocksMarble (from limestone), Slate (from shale), Quartzite (from sandstone), Schist, GneissBanded/foliated; harder than parent rock

Earthquakes and Volcanoes

  • Earthquake focus (hypocenter): Point inside Earth where earthquake originates
  • Epicenter: Point on surface directly above focus
  • Richter scale: Logarithmic; measures amplitude of seismic waves; 1 unit = 10× more ground motion
  • Ring of Fire: Pacific Ocean rim — most earthquakes and volcanoes; ~75% of world's volcanoes
  • Seismic waves: P-waves (primary; fastest; travel through all media); S-waves (secondary; don't travel through liquid → proof of liquid outer core); Surface waves (slowest; most destructive)
  • India's seismic zones: Zone II (low) to Zone V (very high); Zone V includes NE India, J&K, Uttarakhand, Gujarat (Kutch)

Geomorphic Processes

ProcessTypeExample Landforms
River/Fluvial erosionExogenicV-valley, gorge, waterfall, meander, oxbow lake, delta, floodplain
Glacial erosionExogenicU-valley, cirque (corrie), arête, horn, fjord, hanging valley, drumlin (deposition)
Wind/AeolianExogenicSand dunes (Barchan — crescent shaped), deflation hollows, mushroom rocks, yardangs
CoastalExogenicSea cave, stack, arch, wave-cut platform, beach, spit, lagoon
Karst (limestone)ExogenicStalactite (ceiling), stalagmite (floor), limestone pavement, sink holes, caves
UPSC Tip: Stalactite hangs from ceiling (think "tight to ceiling"); stalagmite grows from floor (think "mighty from ground"). Barchan dunes are crescent-shaped wind dunes. S-waves cannot travel through liquid — this proved the outer core is liquid.
2Indian Landforms►

India's physical geography includes the Himalayan mountains, Indo-Gangetic Plains, Peninsular Plateau, Coastal Plains, and Islands. UPSC tests the classification of Himalayas, river systems, and geographical terminology specific to India.

Physiographic Divisions of India

DivisionSub-divisions / Key Facts
The Himalayan MountainsTrans-Himalayas (Karakoram, Ladakh range, Zaskar); Greater Himalayas (Himadri — highest, permanent snow); Lesser Himalayas (Himachal — Mussoorie, Shimla, Nainital); Outer Himalayas (Shivaliks — terai zone at foot)
The Northern PlainsBhabar (pebble belt below Shivaliks); Terai (marshy forest); Bhangar (old alluvium, higher); Khadar (new alluvium, lower, fertile, flood-prone)
The Peninsular PlateauDeccan Plateau (basalt, black cotton soil); Central Highlands (Malwa, Chota Nagpur); Eastern Ghats (discontinuous, lower — avg 600m); Western Ghats (continuous, higher — avg 1000m; highest: Anamudi 2695m)
The Coastal PlainsWestern: narrow, straight, steep (Konkan, Malabar); Eastern: wider, deltaic, flat (Coromandel/Carnatic, Northern Circars)
The IslandsAndaman & Nicobar (Bay of Bengal — 572 islands; volcanic origin; largest = Great Andaman); Lakshadweep (Arabian Sea — coral; 36 islands; smallest UT)

Important Mountain Passes in India

PassLocationConnects
Khyber PassAfghanistan–Pakistan borderAfghanistan to Pakistan (historical invasion route)
Bolan PassPakistan (Balochistan)Pakistan to Afghanistan
Rohtang PassHimachal PradeshKullu–Lahaul-Spiti; NH-3; Atal Tunnel bypass now
Nathu LaSikkim–Tibet borderIndia–China trade; 4310m; reopened 2006
Shipki LaHimachal Pradesh–TibetSutlej river enters India; India–China border
LipulekhUttarakhand–TibetKailash Mansarovar yatra route
Zoji LaJ&K (Kashmir–Ladakh)NH-1D; Srinagar to Leh

Soils of India

Soil TypeRegionFormed FromCrop Suitability
AlluvialNorthern plains, river deltasRiver depositsMost fertile; wheat, rice, sugarcane, pulses
Black (Regur)Deccan Plateau — Maharashtra, MP, GujaratBasalt lava weatheringCotton, sorghum, oilseeds; self-ploughing (swells/shrinks)
RedTamil Nadu, Andhra, Odisha, ChhattisgarhCrystalline/metamorphic rockCoarse grains, groundnut; red due to iron oxide
LateriteHigh rainfall areas — Kerala, Karnataka, NE India, OdishaLeaching of silica; iron/aluminium oxides remainTea, coffee, cashew; low fertility; hardened when dry
Desert/AridRajasthan, GujaratWind depositsDrought-resistant crops; low organic matter
Mountain/ForestHimalayas, NE India, Western GhatsDecomposed organic matterTea, spices, fruit; acidic
UPSC Tip: Anamudi (2695m) in Western Ghats = highest peak in Peninsular India. Highest peak in India overall = K2 (8611m) in J&K. Western Ghats are a Biodiversity Hotspot. Bhangar = older alluvium; Khadar = newer alluvium (more fertile).
3Climate and Indian Monsoon►

India has a monsoon-dominated climate with significant regional variation. UPSC tests the mechanism of Indian Monsoon, factors affecting climate, Koppen classification, and causes of El Niño/La Niña.

Indian Monsoon — Mechanism

  • Summer (Southwest) Monsoon: June–September; onshore winds from Arabian Sea and Bay of Bengal; brings ~75% of India's annual rainfall
  • Arabian Sea Branch: Hits Western Ghats first; Kerala receives first rain (~1 June); Maharashtra Konkan coast, Gujarat
  • Bay of Bengal Branch: Hits Andaman Islands first (~20 May); then NE India, Bangladesh; turns west along Himalayan foothills; eventually meets Arabian Sea branch
  • Onset of Monsoon: Kerala ~1 June; NW India (Delhi) ~late June/July; entire India by mid-July
  • Withdrawal: September–December; NW India first; Kerala last
  • ITCZ: Inter-Tropical Convergence Zone shifts northward in summer — brings monsoon winds

Rainfall Distribution

RegionAnnual RainfallReason
Cherrapunji/Mawsynram (Meghalaya)> 1100 cm (highest)Funnel-shaped terrain; Bay of Bengal branch concentrated
Western Ghats (windward)200–400 cmOrographic rainfall
Deccan Plateau (leeward)50–100 cmRain shadow — drier
Rajasthan / Thar Desert< 25 cm (lowest)Far from moisture source; Aravalli range parallel to winds
Western Himalayas (J&K)Winter rainfall from Western Disturbances (not monsoon)Mediterranean depressions
Tamil Nadu (SE coast)Receives rainfall in October–DecemberNortheast (retreating) Monsoon

El Niño and La Niña

  • El Niño: Warming of central-eastern Pacific Ocean; weakens trade winds; reduces Indian monsoon rainfall (drought tendency in India)
  • La Niña: Cooling of central-eastern Pacific; strengthens trade winds; enhances Indian monsoon (above-normal rainfall)
  • ENSO: El Niño–Southern Oscillation; irregular cycle; every 2–7 years
  • Indian Ocean Dipole (IOD): Temperature difference between western and eastern Indian Ocean; positive IOD enhances Indian monsoon

Koppen Climate Classification — India

TypeRegion in IndiaCharacteristics
Tropical Rainforest (Af)Kerala, Andaman IslandsNo dry season; >60 mm rain every month
Tropical Monsoon (Am)Western coastal IndiaHeavy seasonal rain; short dry season
Tropical Savanna (Aw)Interior Peninsular IndiaDry winter; wet summer
Semi-Arid (BSh)Rajasthan fringe, DeccanSteppe; insufficient rain
Arid (BWh)Thar Desert (Rajasthan)Desert; very low rainfall
Humid Subtropical (Cwa)North/NE IndiaDry winter; hot wet summer
Mountain/Alpine (H)HimalayasAltitude controls temperature
UPSC Tip: Mawsynram (Meghalaya) holds the world record for highest average annual rainfall. Tamil Nadu gets winter rainfall from Northeast Monsoon (Oct–Dec) when rest of India has dry winter. El Niño typically weakens Indian monsoon; La Niña typically strengthens it.
4Indian Rivers and Water Bodies►

India has two distinct river systems — Himalayan (perennial, snowfed) and Peninsular (seasonal, rain-fed). UPSC tests tributaries, drainage basins, important lakes, and Ramsar Wetlands.

Himalayan Rivers

River SystemOriginKey TributariesDrains Into
IndusMansarovar (Tibet); enters India at LadakhJhelum, Chenab, Ravi, Beas, Sutlej (5 rivers of Punjab)Arabian Sea
GangaGangotri glacier (Bhagirathi); meets Alaknanda at DevprayagYamuna, Ramganga, Kosi, Gandak, Ghaghra, SonBay of Bengal (Sundarban delta)
BrahmaputraChemayungdung glacier (Tibet) as Tsangpo; enters India at Arunachal as DihangDibang, Lohit, Tista, SubansiriBay of Bengal (world's largest delta with Ganga)

Peninsular Rivers

RiverOriginDirectionDrains Into
MahanadiChhattisgarh (Raipur dist.)EastBay of Bengal; Hirakud Dam
GodavariNasik (Maharashtra)EastBay of Bengal; longest Peninsular river
KrishnaMahabaleshwar (Western Ghats)EastBay of Bengal; Nagarjuna Sagar Dam
KaveriCoorg/Kodagu (Karnataka)EastBay of Bengal; Mettur Dam; dispute between Karnataka–TN
NarmadaAmarkantak Plateau (MP)WestArabian Sea; flows through rift valley; Sardar Sarovar Dam
Tapti/TapiSatpura Range (Betul, MP)WestArabian Sea; flows through rift valley
LuniAravalli (near Pushkar)SouthwestRann of Kutch; saline in lower course

Important Lakes in India

LakeStateTypeKey Fact
Wular LakeJ&KFreshwater (tectonic)Largest freshwater lake in India
Dal LakeJ&KFreshwaterFamous for houseboats; Srinagar
Chilika LakeOdishaSaltwater lagoonLargest brackish water lagoon in Asia; Ramsar site; Irrawaddy dolphins
Kolleru LakeAndhra PradeshFreshwaterLargest freshwater lake in South India; Ramsar site
Sambhar LakeRajasthanSaline (inland)Largest saline lake in India; salt production; migratory flamingos
Loktak LakeManipurFreshwaterLargest freshwater lake in NE India; floating islands (phumdis); Keibul Lamjao NP
Vembanad LakeKeralaLagoonLongest lake in India; Ramsar site; Kuttanad below sea level farming
Pangong TsoLadakh (India–China)Saline (high altitude)Spans LAC; 3 Film (3 Idiots); ~60% in China

Important Ramsar Wetlands in India

  • India has 75+ Ramsar sites (as of 2023) — most in Asia
  • First two: Chilika Lake (Odisha) and Keoladeo Ghana NP (Rajasthan) — both 1981
  • Key sites: Sundarbans (WB), Loktak (Manipur), Sambhar (Rajasthan), Deepor Beel (Assam), Point Calimere (Tamil Nadu)
UPSC Tip: Narmada and Tapti flow west through rift valleys (not east like most Peninsular rivers). Wular = largest freshwater lake in India. Chilika = largest brackish water lagoon in Asia. Loktak has floating islands called phumdis; Keibul Lamjao National Park is world's only floating national park.
5World Geography►

World Geography covers continents, oceans, latitudes, longitudes, ocean currents, and major geographical features. UPSC tests locations, superlatives, and economic/political geography of world regions.

World's Largest Features

FeatureNameLocation
Largest continentAsia~44.6 million km²
Largest oceanPacific Ocean~165 million km²
Largest country (area)Russia17.1 million km²
Longest riverNile (disputed with Amazon)Africa; ~6650 km
Highest mountainMt Everest (8848.86m)Nepal–China border (Sagarmatha)
Deepest ocean trenchMariana Trench (11,034m)Western Pacific
Largest desertAntarctic DesertAntarctica (Sahara = largest hot desert)
Largest lakeCaspian SeaLandlocked — Eurasia
Deepest lakeLake BaikalRussia; ~1642m deep; 20% world freshwater
Largest islandGreenlandNorth Atlantic (Australia is a continent)

Ocean Currents

CurrentOceanTypeEffect
Gulf StreamAtlanticWarmWarms NW Europe; enables mild climate
Labrador CurrentAtlanticColdCools NE Canada; Grand Banks fog + fishing
Humboldt/Peru CurrentPacific (South America)ColdDriest desert (Atacama) on coast; rich fishing until El Niño
Kuroshio CurrentPacificWarmWarms Japan's eastern coast; Japan's "Black Current"
Canary CurrentAtlantic (Africa)ColdContributes to Sahara and Namib desert formation
North Atlantic DriftAtlanticWarmExtension of Gulf Stream; keeps North Sea ports ice-free
Benguela CurrentSouth Atlantic (Africa)ColdContributes to Namib Desert

Important Straits and Channels

Strait / ChannelConnectsLocation
Strait of HormuzPersian Gulf – Arabian SeaIran–Oman; critical oil transit chokepoint
Strait of MalaccaIndian Ocean – South China SeaBetween Malaysia and Indonesia; busiest maritime chokepoint
Bab-el-MandebRed Sea – Gulf of AdenYemen–Djibouti; near Suez Canal route
Strait of GibraltarAtlantic – MediterraneanSpain–Morocco
Palk StraitBay of Bengal – Palk BayIndia–Sri Lanka; Adam's Bridge
10° ChannelAndaman Sea – Bay of BengalBetween Little Andaman and Nicobar Islands
8° Channel / MinicoyArabian SeaBetween Lakshadweep and Minicoy; India exclusive
UPSC Tip: Strait of Hormuz controls ~20% of world oil trade. Strait of Malacca is the world's busiest maritime chokepoint. Palk Strait separates India from Sri Lanka. 10° Channel separates Andaman Islands from Nicobar Islands (India).
6Natural Resources, Vegetation, and Biodiversity►

India is among the world's 17 megadiverse countries. UPSC tests forest types, biodiversity hotspots, national parks, and natural resources distribution — especially minerals and energy.

Vegetation Zones of India

Forest TypeRainfallRegionKey Species
Tropical Evergreen>200 cmWestern Ghats, Andamans, NE IndiaRosewood, Mahogany, Ebony; trees never shed all leaves together
Tropical Deciduous (Monsoon)100–200 cmMost of India; MP, UP, BiharTeak, Sal, Sandalwood; shed leaves in dry season
Tropical Dry Deciduous75–100 cmEastern UP, Rajasthan fringeTeak, Acacias, Tendu
Tropical Thorn/Scrub<75 cmRajasthan, Gujarat, Punjab plainsBabul, Cactus, Khejri; thorny; xerophytic
MangroveCoastal, tidal zonesSundarbans (largest), Bhitarkanika, PichavaramSundari tree (Sundarbans named after it); Rhizophora; salt-tolerant
Alpine / MontaneHigh altitudeHimalayas >3600mConiferous below snowline; grassland (bugyals) above; rhododendron

Biodiversity Hotspots in India

  • India has 4 of the 36 global biodiversity hotspots
  • Western Ghats + Sri Lanka
  • Indo-Burma (NE India, Myanmar, parts of SE Asia)
  • Eastern Himalayas (Himalayan hotspot)
  • Sundaland (includes Andaman & Nicobar Islands)

Project Tiger and Important Tiger Reserves

  • Project Tiger launched 1973; currently 54 tiger reserves
  • India has ~70% of world's wild tigers
  • Largest tiger reserve: Nagarjunasagar-Srisailam (AP/Telangana)
  • Oldest: Jim Corbett (Uttarakhand) — first tiger reserve 1936; first national park in India
  • Tiger population: ~3167 (2022 census)

Important National Parks and Wildlife Sanctuaries

Protected AreaStateKnown For
Kaziranga NPAssamIndian one-horned rhinoceros (~70% of world pop); UNESCO WHS; tigers
Sundarbans NPWest BengalBengal Tiger; world's largest mangrove; UNESCO WHS; Irrawaddy dolphins
Gir NPGujaratAsiatic Lions (only wild population outside Africa)
Periyar NPKeralaElephants; tiger reserve; Western Ghats
Bharatpur (Keoladeo)RajasthanMigratory birds; UNESCO WHS; Siberian Cranes (rare)
Valley of FlowersUttarakhandAlpine meadows; UNESCO WHS; endemic flora
Manas NPAssamRoyal Bengal Tiger; Golden Langur; UNESCO WHS; Project Elephant
Namdapha NPArunachal PradeshAll 4 big cats of India (tiger, leopard, snow leopard, clouded leopard)
UPSC Tip: India has 4 biodiversity hotspots (out of global 36). Gir Forest = only place in world with Asiatic Lions. Kaziranga = largest one-horned rhino population. Jim Corbett = India's first national park (1936). Sundari tree = Sundarbans name origin.
★Key Facts & Exam Essentials►
TopicKey Fact
AnamudiHighest peak in Peninsular India (2695m) — Kerala (Western Ghats)
K2Second highest peak in world (8611m); highest in India; Karakoram
Wular LakeLargest freshwater lake in India (J&K); tectonic origin
Chilika LakeLargest brackish water lagoon in Asia (Odisha); Ramsar site
Sambhar LakeLargest saline lake in India (Rajasthan)
Loktak LakeLargest freshwater lake in NE India (Manipur); floating islands = phumdis
MawsynramHighest average annual rainfall (Meghalaya)
Thar Desert rainfallLowest rainfall in India (<25 cm)
Monsoon onset Kerala~1 June (Arabian Sea branch)
NE MonsoonTamil Nadu gets Oct–Dec rainfall from retreating monsoon
Narmada directionFlows west through rift valley → Arabian Sea (not typical east for Peninsular rivers)
GodavariLongest Peninsular river; "Dakshin Ganga"; originates Nasik
Brahmaputra in TibetCalled Tsangpo; enters India as Dihang (Arunachal)
India Ramsar sites75+ (2023); most in Asia; first two (1981) = Chilika and Keoladeo
Strait of Hormuz~20% world oil passes; Iran–Oman
Strait of MalaccaBusiest maritime chokepoint; Malaysia–Indonesia
Barchan duneCrescent-shaped wind dune
Biodiversity hotspots India4: Western Ghats+SL, Indo-Burma, E. Himalayas, Sundaland
Gir NPOnly wild Asiatic Lions — Gujarat
Jim Corbett NPIndia's first national park (1936) — Uttarakhand
Project Tiger launched1973; 54 tiger reserves; ~3167 tigers (2022)
El Niño effect on IndiaWeakens monsoon; drought tendency
Largest mangrove IndiaSundarbans (West Bengal)