Why this topic matters for UPSC
Prelims: NCERT-anchored MCQs on volcano types (shield/composite/caldera), intrusive forms (batholith vs laccolith vs sill vs dike), fault types (normal/reverse/strike-slip/thrust), weathering types (frost wedging, exfoliation, carbonation, hydrolysis), mass-movement classification (creep/landslide/mudflow), Richter vs Mercalli scales, India's seismic zones (II–V) and Barren/Narcondam volcanoes.
Mains GS-1: "Explain how endogenic and exogenic forces together shape Earth's surface", "Distinguish weathering from erosion with examples", "Discuss the geomorphic significance of mass movements in the Himalayas", "Why is the Himalayan belt seismically more active than the Peninsula?", "Account for the absence of active volcanism on the Indian mainland".
Contents
- Geomorphic processes — concept & classification
- Endogenic forces — energy & agents
- Diastrophism — folds, faults, warping
- Volcanism — eruptions & landforms
- Earthquakes — causes, scales, zones
- Exogenic forces & denudation
- Weathering — physical · chemical · biological
- Mass movement — slow & rapid
- Erosion, transportation, deposition
- Indian context — seismic zones & volcanism
- Previous Year Questions (Prelims + Mains)
- 15 must-know facts
1 · Geomorphic processes — concept & classification NCERT XI Ch 6GS-1
NCERT XI · Fundamentals of Physical Geography · Ch 6 "Geomorphic Processes"
A geomorphic process is any natural mechanism — physical, chemical, biological — that creates, modifies or destroys the configuration of Earth's surface. Earth's relief at any instant is the net balance between two opposing force-systems:
| Axis | Endogenic (internal) | Exogenic (external) |
|---|---|---|
| Energy source | Primordial + radiogenic heat of Earth's interior | Solar insolation (95%) + gravity |
| Direction | Constructive — builds up relief | Destructive — wears down relief |
| Operating depth | Crust + mantle | Atmosphere · hydrosphere · surface |
| Speed | Sudden (quake, eruption) or imperceptible (orogeny over Ma) | Slow but unrelenting (mm–cm / yr) |
| Examples | Folding, faulting, volcanism, earthquakes | Weathering, mass movement, erosion, deposition |
| Net effect | Relief amplifier — creates mountains, plateaus, rifts | Relief leveller — denudation → gradation |
Mnemonic"Inside Builds, Outside Bleeds" — endogenic constructs vertical relief; exogenic strips it back to base-level.
1.1 · The diastrophism vs gradation duel
Pioneer geomorphologist W.M. Davis (1899) formalised this as the geographical cycle — every landscape oscillates between uplift (endogenic) and erosion (exogenic) until reduced to a peneplain (near-flat surface at base-level). Walther Penck (1924) challenged this — landscapes evolve under simultaneous uplift + erosion, not sequential. Modern view = continuous interaction.
Why endogenic wins at Himalaya, exogenic wins at Peninsula: Indian plate convergence rate (5 cm/yr) at Himalaya exceeds erosion rate → net uplift continues. Peninsular India is tectonically dormant since Deccan eruption (66 Mya) → exogenic agents have had 66 Ma of uninterrupted leveling → Aravalli reduced from once-Himalayan stature to stubs of 300–900 m.
2 · Endogenic forces — energy & agents GS-1
2.1 · Energy budget
- Primordial heat — residual heat from Earth's accretion + core differentiation 4.5 Bya (still leaking outward).
- Radiogenic heat — ongoing decay of long-lived isotopes ²³⁸U, ²³⁵U, ²³²Th, ⁴⁰K in mantle + crust. Provides ~50% of present heat flow.
- Tidal friction — minor contribution.
- Total surface heat flow ≈ 47 TW (vs solar input ≈ 174,000 TW — yet endogenic does all the relief-building because solar is dissipated as climate/weather).
2.2 · Two speeds of endogenic action
| Type | Examples | Time-scale | Trigger |
|---|---|---|---|
| Sudden (paroxysmal) | Earthquakes, volcanic eruptions | Seconds–days | Stress release / magma rise |
| Slow (diastrophic) | Folding, faulting, epeirogeny, orogeny | 10⁴–10⁸ yr | Plate convergence / mantle flow |
2.3 · Diastrophism — two flavours
Epeirogenic (continent-building)
- Vertical movements over broad regions
- Crust rises or sinks without major folding
- Upwarp: raises continents / plateaus
- Downwarp: creates basins, submerged shelves
- Examples — Scandinavian post-glacial rebound (~10 mm/yr), African plateau uplift
Orogenic (mountain-building)
- Horizontal compression along narrow belts
- Severe folding + faulting → fold mountains
- Associated with convergent plate margins
- Examples — Himalayan, Andean, Alpine, Rockies orogenies
- Time-scale: 10–100 Ma per cycle
Mnemonic"OH-EV" — Orogenic = Horizontal compression (mountains); Epeirogenic = Vertical movement (continents).
3 · Diastrophism — folds, faults, warping NCERT XI Ch 6GS-1
3.1 · Folding — response of ductile rocks to compression
When sedimentary strata are subjected to slow horizontal compression at elevated temperatures & pressures, they deform plastically into wave-like undulations called folds. The up-arch is the anticline, the down-trough is the syncline. The imaginary surface bisecting the fold = axial plane; the line where this plane meets the bedding = fold axis; each side = limb.
Fig 5.1 · Five fold types arranged by increasing compression intensity. Compression arrows (maroon) show horizontal stress direction. Axial planes shown as red dashes. NCERT XI Fig 6.2 adapted.
3.2 · Faulting — response of brittle rocks to stress
When rocks at shallow crustal depths (cool, brittle regime) cannot deform plastically, they fracture and the two sides displace along the break-surface. The break = fault plane; the block above the inclined plane = hanging wall; below = foot wall. The vertical offset = throw; horizontal offset = heave.
Fig 5.2 · Fault classification — block diagrams of normal, reverse, thrust, strike-slip + horst/graben pair. Hanging wall = block above the inclined plane; foot wall = below. Adapted from NCERT XI Fig 6.4–6.5 + Strahler.
| Fault | Stress | Hanging wall | Dip angle | Real example |
|---|---|---|---|---|
| Normal | Tensional | Drops down | ~60° | Rhine Graben · East African Rift · Narmada–Son |
| Reverse | Compressional | Rises up | ~60° | Andean foothills · Bhuj 2001 (Mw 7.7) |
| Thrust | Compressional | Over-rides at low angle | <30° | MCT, MBT, HFT (Himalayan thrust system) |
| Strike-slip | Shear | Horizontal slide (no vertical offset) | ~90° (vertical) | San Andreas · North Anatolian · Chaman (Pak-Afgh) |
Mnemonic"Normal drops, Reverse pops" — Normal = hanging wall drops (tension pulls apart); Reverse = hanging wall pops up (compression pushes together).
3.3 · Warping — gentle bending without breaking
Upwarping = broad upward bulge (eg African super-swell). Downwarping = broad sag (eg Hudson Bay, Ganga depression). Differs from folding in scale (continent-wide) and gentleness (no acute angles). Belongs to epeirogenic family.
4 · Volcanism — eruptions & landforms NCERT XI Ch 3, 6GS-1
Volcanism = movement of molten rock (magma) and gases from Earth's interior to or near the surface. Underground magma chamber → conduit → vent → surface eruption (extrusive) or magma solidifies before reaching surface (intrusive). Drives ~80% of fresh juvenile water + atmosphere to the surface over geologic time.
4.1 · Lava chemistry decides volcano shape
| Magma type | SiO₂ | Viscosity | Gas content | Eruption style | Volcano shape |
|---|---|---|---|---|---|
| Basaltic (mafic) | 45–52% | Low (runny) | Low | Effusive (quiet) | Shield · fissure flows |
| Andesitic (intermediate) | 52–63% | Medium | Medium | Explosive intermittent | Composite (stratovolcano) |
| Rhyolitic (felsic) | >63% | Very high (sticky) | High | Cataclysmic Plinian / caldera | Lava domes · calderas |
RuleMore silica → more viscous → more gas trapped → more violent. Hawai‘ian basalts ooze; Indonesian andesites explode; Yellowstone rhyolites cataclysm.
4.2 · Extrusive landforms — volcano types
Fig 5.3 · Five extrusive volcanic landforms — shield (gentle, basaltic), composite/stratovolcano (steep, layered ash+lava), cinder cone (small, pyroclastic), caldera (collapsed summit) and fissure (flood-basalt plateau). Adapted from NCERT XI Fig 6.6 + USGS.
4.3 · Intrusive landforms — magma that solidified underground
Fig 5.4 · Cross-section of intrusive landforms — concordant forms (sill, laccolith, lopolith, phacolith) lie parallel to bedding; discordant forms (dike, batholith) cut across it. Sizes shown schematically — real batholiths are 100× larger than dikes. Adapted from NCERT XI Fig 6.7.
Mnemonic"BLLP-SD" — Batholith (deep dome) · Laccolith (mushroom up) · Lopolith (saucer down) · Phacolith (in fold crest) · Sill (horizontal) · Dike (vertical).
4.4 · Eruption styles & classification
| Style | Character | Volcano type | Type example |
|---|---|---|---|
| Hawai'ian | Gentle effusive basalt lava fountains | Shield | Kīlauea |
| Strombolian | Mild rhythmic bursts of incandescent tephra | Cinder cone | Stromboli (Italy) |
| Vulcanian | Short violent ash-laden explosions | Composite | Vulcano (Italy) |
| Plinian | Sustained column 20–45 km high, pumice + ash | Composite / caldera | Vesuvius 79 AD, Pinatubo 1991 |
| Peléan | Pyroclastic flows (nuée ardente) | Composite / dome | Mt Pelée 1902 |
| Icelandic | Fissure basalt flows | Flood basalt | Laki 1783 |
News 2024Iceland Reykjanes Peninsula: 7 fissure eruptions Dec 2023 – June 2024, evacuating Grindavík permanently. Demonstrates classic Icelandic-type rift volcanism at the divergent Mid-Atlantic Ridge surfacing on land. Source: IMO Iceland Meteorological Office bulletins.
4.5 · Global distribution — three concentrations
- Pacific Ring of Fire — 75% of world's active volcanoes (~452). Andes, Cascades, Aleutians, Kamchatka, Japan, Philippines, Indonesia, NZ. Convergent + subduction belt.
- Mid-ocean ridges — >90% of Earth's annual lava output but submarine. Divergent boundaries.
- Mediterranean-Himalayan belt — Vesuvius, Etna, Stromboli. Alpine convergence.
- Intra-plate hotspots — Hawai'i, Yellowstone, Réunion, Iceland (covered in T4).
5 · Earthquakes — causes, scales, zones NCERT XI Ch 3, 6GS-1
An earthquake is the violent shaking of Earth's surface caused by sudden release of accumulated elastic strain energy in the lithosphere — the rebound theory of H.F. Reid (1906). Rocks deform elastically until shear stress exceeds frictional strength, then slip on a fault plane and snap back (elastic rebound), radiating seismic waves.
5.1 · Anatomy of a quake
| Term | Meaning |
|---|---|
| Focus / Hypocentre | Subsurface point where rupture initiates |
| Epicentre | Point on the surface vertically above the focus |
| Fault plane | Plane along which rupture spreads |
| Focal depth | Shallow < 70 km · Intermediate 70–300 km · Deep 300–700 km |
| Foreshock / Aftershock | Smaller quakes before / after the main shock |
| Isoseismal line | Contour joining places of equal intensity |
5.2 · Seismic waves
Fig 5.5 · Earthquake anatomy + seismic-wave types. LEFT: Focus underground, epicentre vertically above, body waves into interior, surface waves along surface, fault plane shown. RIGHT: Four wave types with motion diagrams + arrival order + media restrictions. Adapted from NCERT XI Fig 3.1 + Lowrie's Fundamentals of Geophysics.
5.3 · Magnitude vs intensity scales
| Aspect | Magnitude scale | Intensity scale |
|---|---|---|
| Measures | Energy released at focus | Felt damage at surface |
| Scale | Richter (1935) · Moment magnitude Mw (modern) | Mercalli (1902) · Modified Mercalli MMI (I–XII) |
| Nature | Logarithmic (1 unit = 10× amplitude = ~32× energy) | Roman numerals · qualitative descriptions |
| Value per quake | One number regardless of location | Many values (varies with distance from epicentre, soil, construction) |
| Instrument | Seismograph reading | Human observation + damage survey |
| UPSC pitfall | Richter has no upper bound in theory; ~9.5 is the practical max (Chile 1960) | MMI XII = "total destruction" — used after quake, not predictive |
Mnemonic"Richter = Released energy · Mercalli = Mansion damage"
UPSC trap: Modern global agencies have largely replaced Richter with Moment-magnitude (Mw) for M > 7 because Richter saturates at high magnitudes. USGS, IMD-NCS report Mw. Don't confuse Richter (ML) with Mw — Mw is the standard reported in news today.
5.4 · Causes of earthquakes
- Tectonic (95%) — fault slip at plate boundaries (Himalaya, Pacific Rim).
- Volcanic — magma rise / chamber inflation (Hawai'i, Iceland).
- Collapse — cave-in over mining cavity or sinkhole.
- Explosion — anthropogenic (nuclear tests, large blasts).
- Reservoir-induced — water-loading on faults (Koyna 1967 Mw 6.5; allegedly Zipingpu before Sichuan 2008).
5.5 · BIS seismic zones of India
| Zone | MMI | PGA range (g) | Region |
|---|---|---|---|
| V (Very high) | IX+ | >0.36 | Kashmir, Himachal, Uttarakhand (parts), NE India (entirety), Kachchh, Andaman & Nicobar |
| IV (High) | VIII | 0.24 | Delhi NCR, Sikkim, parts of UP/Bihar, J&K, north Punjab, north Gujarat, west Maharashtra coast |
| III (Moderate) | VII | 0.16 | Most of Peninsular India · Kerala · MP · Odisha · WB |
| II (Low) | VI | 0.10 | Stable core: parts of Karnataka, AP, Rajasthan, TN interior |
(BIS removed Zone I in 2002 revision — IS 1893:2002 — merging it with Zone II.)
News 2026National Seismological Network expansion: Ministry of Earth Sciences NCS expanded to 165 observatories nationwide by 2026 with real-time data telemetry to BSNL VSAT; aimed at sub-minute alerts via the National Earthquake Early Warning System being tested for Uttarakhand. Source: MoES annual report.
6 · Exogenic forces & denudation NCERT XI Ch 6GS-1
Powered by solar insolation + gravity, exogenic agents continuously strip relief built by endogenic forces. Their integrated work is called denudation — literally "un-clothing" the land. Three sequential stages:
- Weathering — in-situ breakdown of rock (no transport).
- Mass movement — gravity-driven down-slope shift of weathered material (no medium needed).
- Erosion → Transportation → Deposition — work done by mobile agents (river, glacier, wind, wave, groundwater).
Why this sequence matters: Without weathering first, rivers/glaciers/wind would have no loose material to erode. Weathering is the silent preparatory phase of all denudation — examiners love this distinction.
| Process | Energy | Medium | Net effect |
|---|---|---|---|
| Weathering | Solar (temp), chemical, biological | None (in-situ) | Loosens rock → produces regolith |
| Mass movement | Gravity | None | Down-slope transfer |
| Erosion | Solar (drives water cycle, wind) | Water · ice · wind · waves | Sculpts new landforms |
| Deposition | Loss of energy by agent | Same agents | Builds depositional landforms |
DistinctionWeathering ≠ Erosion. Weathering = in-situ breakdown (no movement). Erosion = breakdown plus removal by a mobile agent. A boulder cracked by frost on a mountain is weathering; the same boulder tumbling in a river is erosion.
7 · Weathering — physical · chemical · biological NCERT XI Ch 6GS-1
7.1 · Physical (mechanical) weathering — disintegration without composition change
| Process | Mechanism | Climate | Landform produced |
|---|---|---|---|
| Frost wedging (freeze-thaw) | Water in joints freezes → expands 9% → prises rock apart | Cold high-altitude / latitude (Himalaya, Alps) | Talus / scree slopes |
| Thermal expansion (insolation) | Differential heating + cooling → grains expand at different rates → fractures | Hot deserts (Thar, Sahara) — large diurnal range | Block disintegration · granular disintegration |
| Exfoliation (unloading) | Removal of overlying load reduces pressure → buried rock expands upward → curved sheets peel off | Any (esp. granite domes) | Exfoliation domes (Half Dome USA; Stone Mountain; Mahabalipuram boulders) |
| Salt weathering | Salt crystals grow in pores, exert wedging pressure | Arid + coastal | Tafoni cavities · honeycomb weathering |
| Wetting-drying | Clay-rich rocks swell on wetting, shrink on drying → micro-cracks | Monsoon climates | Surface flaking |
7.2 · Chemical weathering — decomposition with composition change
| Process | Reaction example | Target rocks | Product / landform |
|---|---|---|---|
| Solution | NaCl + H₂O → dissolved ions | Halite, gypsum | Disappeared rock |
| Carbonation | CaCO₃ + H₂CO₃ → Ca(HCO₃)₂ (soluble) | Limestone, marble | Karst landscape · caves · sinkholes · stalactites |
| Hydration | CaSO₄ + 2H₂O → CaSO₄·2H₂O (gypsum) — volume up 60% | Anhydrite, feldspar | Spalling, surface bulging |
| Hydrolysis | Feldspar (KAlSi₃O₈) + H₂O + CO₂ → kaolinite clay + dissolved silica + K⁺ | Granite, gneiss | Clay-rich regolith · spheroidal weathering |
| Oxidation | 4Fe + 3O₂ → 2Fe₂O₃ (hematite — red/brown) | Iron-bearing minerals | Rust crusts · laterite (humid tropics) |
| Reduction | Loss of O₂ in waterlogged conditions → grey/blue colour | Iron-bearing minerals | Gleyed soils (paddies) |
Why laterite is India's signature product: Western Ghats / NE / Chhota Nagpur humid tropical climate → intense hydrolysis + oxidation → silica leached out, Fe + Al sesquioxides residually enriched → red porous laterite. Building stone in Goa, Kerala; basis of bauxite (Al) ore in Eastern Ghats.
7.3 · Biological weathering — both physical and chemical aided by organisms
- Root wedging — tree roots widen joints (banyan on temples).
- Lichens + mosses — secrete organic acids (oxalic, citric) → chemical attack.
- Burrowing animals — earthworms, termites, rodents loosen + mix soil.
- Human activity — quarrying, ploughing, urbanisation; now a dominant weathering force (Anthropocene).
7.4 · Weathering profile
Fig 5.6 · Vertical weathering profile (O–A–B–C–R horizons) with depth scale + controlling factors and Goldich mineral-stability series. Most weathered material is residual; transported soils (alluvial, aeolian) have different profiles. Adapted from NCERT XI Fig 6.8 + Brady & Weil.
Exfoliation explained physically: Granite forms 10–20 km deep under huge confining pressure. When overburden erodes off, the rock is pressure-released → expands upward → cracks form parallel to surface (sheet joints) → outer layers peel off like onion skin. Result: smooth domes (Yosemite Half Dome, Mahabalipuram).
8 · Mass movement — slow & rapid NCERT XI Ch 6GS-1
Mass movement (mass wasting) = down-slope movement of weathered material under direct action of gravity, without needing a mobile carrier (no river, glacier, wind). Triggered when shear stress exceeds shear strength — driven up by water saturation, vegetation loss, seismic shock, slope undercutting.
8.1 · Classification by speed + water content
Fig 5.7 · Six mass-movement types ordered by speed and water content — creep (slowest), solifluction, earthflow/mudflow, landslide, slump, rockfall (fastest). All driven purely by gravity; water acts as lubricant + load. Adapted from NCERT XI Fig 6.10 + Cruden & Varnes classification.
8.2 · Triggers
- Water saturation — monsoon, cloudburst, snowmelt (reduces inter-grain friction; adds weight).
- Seismic shock — Kashmir 2005, Sikkim 2011, Sichuan 2008 caused tens of thousands of landslides.
- Slope steepening — undercutting by river, sea, road-cutting, mining.
- Deforestation — root cohesion lost; Western Ghats, Uttarakhand vulnerability.
- Anthropogenic loading — buildings, reservoirs on slope crests.
News 2024Wayanad landslides (30 July 2024): Cloudburst-triggered debris flows in Mundakkai-Chooralmala wiped out villages, killing 200+. NCESS post-event survey identified weathered laterite + saturated overburden + 30°+ slopes as triggers — textbook earthflow / debris-flow event. GSI placed Wayanad in landslide-prone Zone H1. Source: NCESS-MoES report 2024.
9 · Erosion, transportation, deposition GS-1
Once material is weathered + gravity-moved to a mobile agent, the three-step cycle erosion → transportation → deposition sculpts most of Earth's surface landforms (covered in T6).
| Agent | Erosional mechanism | Erosional landforms | Depositional landforms |
|---|---|---|---|
| Running water (fluvial) | Hydraulic action · abrasion · attrition · solution | V-valley · gorge · canyon · waterfall · pothole · meander cliff | Floodplain · delta · alluvial fan · natural levee · ox-bow lake |
| Glacier (glacial) | Plucking · abrasion (rock flour, striations) | U-valley · cirque · arête · horn · hanging valley · roche moutonnée | Moraine (lateral, medial, terminal) · drumlin · esker · outwash plain |
| Wind (aeolian) | Deflation · abrasion (sand-blasting) | Yardang · zeugen · mushroom rock · ventifact · blowout | Sand dunes (barchan, seif, longitudinal) · loess plains |
| Waves & currents (marine) | Hydraulic shock · abrasion · solution | Sea cliff · sea cave · stack · stump · arch · wave-cut platform | Beach · spit · bar · tombolo · lagoon |
| Groundwater (karst) | Solution of CaCO₃ | Sinkhole · doline · uvala · polje · cave | Stalactite · stalagmite · pillar · travertine |
Detailed landforms by each agent are covered in Topic 6 — Major Landforms. Here we note only the principle: each mobile agent erodes upstream and deposits downstream when energy falls below carrying capacity.
9.1 · Three classical models of landscape evolution
W.M. Davis (1899) — "Geographical cycle"
- Sequential: uplift, then erosion
- Stages: youth → maturity → old age → peneplain
- "Structure, process, stage"
Walther Penck (1924)
- Simultaneous uplift + erosion
- Slope retreat parallel to itself
- Three slope segments: waxing → free face → debris
L.C. King (1953)
- Tropical / arid: pediplanation by scarp retreat
- Inselbergs as remnants (Eastern Ghats, southern Africa)
10 · Indian context — seismic zones & volcanism GS-1
10.1 · Why India has many quakes but few volcanoes
India sits in an intra-plate continental collision setting — the Indian plate pushes north into Eurasia at ~5 cm/yr, generating continuous compression across the Himalaya–Tibet–Hindu Kush belt. This produces frequent thrust-fault earthquakes (Himalayan zone) but no active subduction beneath mainland India — hence no andesitic arc volcanism. The only active volcanism is on the Andaman fore-arc, where the Indian plate subducts beneath the Burma micro-plate, melting mantle wedge → Barren + Narcondam.
10.2 · Indian active volcanism
| Volcano | Type | Location | Status |
|---|---|---|---|
| Barren Island | Composite stratovolcano | Andaman Sea (~135 km NE of Port Blair) | India's only active volcano · last erupted May 2017; intermittent steaming continues |
| Narcondam | Andesitic composite | Andaman Sea (NE of Barren) | Dormant (last eruption pre-historic) |
| Deccan Traps | Flood-basalt (extinct) | Maharashtra–Gujarat–MP | Erupted 66 Mya (Réunion hotspot, K-Pg boundary) · now extinct |
| Rajmahal Traps | Flood-basalt (extinct) | Jharkhand–WB | Erupted 117 Mya (Kerguelen hotspot) · extinct |
| Dhinodhar / Dhosi | Ancient volcanic neck | Gujarat / Haryana | Extinct Mesozoic remnants |
10.3 · Indian earthquake history (Mw > 6 highlights)
| Year | Event | Mw | Tectonic setting | Toll |
|---|---|---|---|---|
| 1819 | Allah Bund (Kachchh) | ~7.7 | Intra-plate reverse fault | ~1,500 |
| 1897 | Shillong / Assam | 8.1 | Pop-up structure | ~1,500 |
| 1934 | Bihar–Nepal | 8.0 | MFT thrust | ~10,700 |
| 1950 | Assam–Tibet | 8.6 | Eastern Himalayan syntaxis | ~4,800 |
| 1967 | Koyna | 6.5 | Reservoir-induced | ~180 |
| 1991 | Uttarkashi | 6.8 | Himalayan thrust | ~770 |
| 1993 | Latur (Killari) | 6.3 | Stable continent (intraplate) | ~9,750 |
| 2001 | Bhuj | 7.7 | Intra-plate reverse | ~20,000 |
| 2004 | Sumatra-Andaman | 9.1 | Megathrust → Indian Ocean tsunami | ~2,30,000 |
| 2005 | Kashmir (PoK) | 7.6 | MBT thrust | ~86,000 |
| 2011 | Sikkim | 6.9 | Strike-slip in Indian plate | ~110 |
| 2015 | Nepal (Gorkha) | 7.8 | MHT thrust | ~9,000 |
| 2023 | Doda (J&K) | 5.4 | Himalayan thrust | 0 |
The unsolved Central Himalayan seismic gap: No M ≥ 8 quake has ruptured the segment between Kangra (1905) and Bihar–Nepal (1934) for ~500 years despite continued strain accumulation. GPS data shows ~2 cm/yr convergence locked along this segment → potential for a Mw 8+ "Great Himalayan Earthquake" affecting Uttarakhand–HP–western Nepal. Bilham & Wallace estimate accumulated slip deficit could release Mw 8.0–8.7. Source: Bilham (Nature, 2019); Wadia Institute reports.
10.4 · Disaster-management framework
- NDMA (National Disaster Management Authority, 2005) — apex body, framing guidelines.
- NCS (National Centre for Seismology, MoES) — 165 observatories (2026); issues alerts.
- BIS IS-1893 — seismic-design zoning code for buildings.
- NDRF — federal response force (16 battalions).
- Hyogo (2005) & Sendai (2015) Frameworks — global DRR commitments India is signatory to.
Previous Year Questions — Prelims & Mains
Prelims and Mains are kept in separate blocks below to avoid confusion. PYQs are followed by model questions framed in the UPSC pattern. Paraphrased where required for fair-use; year-tagged for traceability.
A · Prelims — Actual PYQs (UPSC CSE)
- 2024 Consider statements about Barren Island: (1) It is the only confirmed active volcano in South Asia. (2) It lies in the Andaman Sea on a subducting plate boundary. (3) It last erupted in 2017. — Which are correct? paraphrased
- 2023 Which of the following is/are chemical weathering process(es)? (1) Hydrolysis (2) Oxidation (3) Frost wedging (4) Carbonation — Select correct. paraphrased
- 2022 With reference to seismic waves, which statement is correct? (a) P-waves cannot pass through liquids (b) S-waves can pass through liquid outer core (c) P-waves are longitudinal and arrive first (d) Love waves travel into the Earth's interior. paraphrased
- 2022 Consider statements about the Deccan Traps: (1) Formed by fissure eruptions at the K-Pg boundary. (2) Associated with the Réunion hotspot. (3) Cover > 5,00,000 km² in India. paraphrased
- 2021 Match List I (Volcano) with List II (Type) — Krakatoa : Caldera · Mauna Loa : Shield · Stromboli : Cinder cone · Vesuvius : Composite. paraphrased
- 2020 Which one of the following best describes a laccolith? (a) Vertical sheet-like intrusion cutting across strata (b) Mushroom-shaped intrusion arching overlying strata upward (c) Saucer-shaped intrusion sagging strata downward (d) Huge dome-shaped pluton at great depth. paraphrased
- 2019 Consider landslides and statements: (1) Western Ghats are more vulnerable than Himalayas. (2) Monsoon rainfall is the dominant trigger. (3) Landslides do not occur in stable continental shields. paraphrased
- 2018 Which mass-movement type is associated with the indicators "tilted gravestones, bent trees, leaning fence posts"? (a) Landslide (b) Mudflow (c) Soil creep (d) Solifluction. paraphrased
- 2017 Which of the following is a feature of karst topography? (1) Sinkholes (2) Stalactites (3) Yardangs (4) Polje. paraphrased
- 2016 The Richter scale for earthquakes is: (a) linear (b) logarithmic (c) exponential (d) arithmetic. paraphrased
- 2015 San Andreas Fault is an example of: (a) Normal fault (b) Reverse fault (c) Transform / strike-slip fault (d) Thrust fault. paraphrased
- 2014 Which fold has its axial plane horizontal and one limb inverted? (a) Symmetrical (b) Asymmetrical (c) Overturned (d) Recumbent. paraphrased
B · Mains — Actual PYQs (UPSC CSE · GS Paper 1)
- 2024 "Discuss the geomorphological processes responsible for the formation of the Deccan Traps and analyse their role in shaping the present-day landscape of the Indian peninsula." (15 marks · 250 words) paraphrased
- 2023 "Examine the causes of recurrent landslides in the Himalayan region. Suggest measures for mitigation." (10 marks · 150 words) paraphrased
- 2022 "Distinguish between weathering and erosion. How do these processes interact in the formation of soil?" (10 marks · 150 words) paraphrased
- 2021 "Explain the mechanism of plate tectonics and its relationship with earthquakes and volcanism. Substantiate with Indian examples." (15 marks · 250 words) paraphrased
- 2021 "How does chemical weathering contribute to the development of laterite soils in India? Why are these soils significant economically?" (10 marks · 150 words) paraphrased
- 2020 "Differentiate between the types of seismic waves and explain how they help in determining the structure of Earth's interior." (10 marks · 150 words) paraphrased
- 2019 "What are the characteristics of volcanism in India? Examine why Indian mainland has no active volcanoes while the Andaman fore-arc does." (15 marks · 250 words) paraphrased
- 2018 "Discuss the causes and consequences of the 2001 Bhuj earthquake. What measures has India taken since then for earthquake preparedness?" (15 marks · 250 words) paraphrased
- 2017 "Explain the role of endogenic forces in shaping Earth's surface. Use Indian examples." (10 marks · 150 words) paraphrased
- 2016 "How do mass-movement processes differ from erosion? Discuss their significance in mountain environments." (10 marks · 150 words) paraphrased
- 2014 "Explain the formation of folds and faults. How do they account for the geomorphology of the Himalayas and the Indian peninsula?" (15 marks · 250 words) paraphrased
C · Model Prelims (UPSC-style)
- Which intrusive landform forms a concordant lens-shaped body in the crest of a fold? (a) Sill (b) Phacolith (c) Laccolith (d) Lopolith.
- Consider statements about BIS seismic zoning: (1) Zone V has the highest seismic risk. (2) The entire NE region falls in Zone V. (3) Zone I was abolished in 2002. — Correct?
- Which is NOT a chemical-weathering process? (a) Hydrolysis (b) Carbonation (c) Hydration (d) Exfoliation.
- Which sequence is correct in the Goldich Stability Series, from least to most weathering-resistant? (a) Quartz → Olivine → Biotite (b) Olivine → Pyroxene → Quartz (c) Quartz → Biotite → Olivine (d) Pyroxene → Quartz → Olivine.
- A "lahar" is best described as: (a) Mudflow on a volcano slope (b) Mass of snow + ice rapidly descending (c) Slow soil creep in tropical climates (d) Wedging by salt crystals.
D · Model Mains (UPSC-style)
- "Endogenic forces build relief; exogenic forces level it. Examine this duel with reference to the Indian sub-continent." (15 marks · 250 words)
- "Discuss the distinguishing features of physical, chemical, and biological weathering with appropriate landform examples." (10 marks · 150 words)
- "Account for the absence of active volcanism on the Indian mainland despite its location on a converging plate." (10 marks · 150 words)
- "Critically evaluate India's earthquake-preparedness framework in light of the unsolved Central Himalayan seismic gap." (15 marks · 250 words)
- "Explain the genesis of various fold and fault types. Diagrammatically distinguish nappe, klippe, horst, graben." (15 marks · 250 words) Diagram cue: 2 panel — fold types · fault types
Honest disclaimer: PYQs above are paraphrased for fair use and brevity. Year tags reflect the UPSC CSE year of original appearance to the best of editorial knowledge. For exact wording and authoritative reproduction, consult UPSC question-paper archives at upsc.gov.in or trusted secondary compilations (Disha, Drishti, Vision IAS). Always cross-check before relying on a particular phrasing in an essay or revision note.
Mains Template · 15-mark sample answer skeleton
Q: "Distinguish weathering from erosion. How do they interact in shaping landforms?"
- Intro (40 w) — define both; weathering is in-situ breakdown, erosion is removal by mobile agent; both belong to exogenic regime.
- Body 1 — Weathering (60 w) — three types (physical, chemical, biological) with one example each (frost wedging in Himalayas; hydrolysis in Deccan; root-wedging on monuments).
- Body 2 — Erosion (60 w) — five agents (water, ice, wind, waves, groundwater) with landforms.
- Body 3 — Interaction (60 w) — weathering loosens rock → mass movement transfers it → rivers/glaciers/wind erode-transport-deposit. Without weathering, erosion would have no raw material.
- Conclusion (30 w) — together = denudation; net result = gradation toward base-level (peneplain).
- Diagram cue: weathering profile (O-A-B-C-R) + agent table
15 must-know facts for revision
- Endogenic = inside-driven (radiogenic heat); exogenic = outside-driven (solar + gravity).
- Diastrophism = slow deformation of crust; splits into orogenic (horizontal → mountains) and epeirogenic (vertical → continents).
- Anticline = up-arch, oldest at core; syncline = down-trough, youngest at core.
- Recumbent fold + thrust over neighbour = nappe; Himalayan MCT and MBT are major nappe thrusts.
- Normal fault drops, Reverse fault pops; thrust = low-angle reverse; strike-slip = horizontal shear (San Andreas, Chaman).
- Horst = uplifted block (Vosges); graben = down-dropped (Rhine, Narmada-Tapi, East African Rift).
- Lava chemistry decides shape — basalt → shield · andesite → composite · rhyolite → caldera/dome.
- Intrusive mnemonic BLLP-SD — batholith, laccolith, lopolith, phacolith, sill (horizontal), dike (vertical).
- Deccan Traps = flood basalts, 66 Mya, Réunion hotspot, 1 million km², 2 km thick. Indian mainland = no active volcanism. Barren Island = only active Indian volcano (Andaman fore-arc).
- P-waves = longitudinal, fastest, all media; S-waves = transverse, no liquid (proves liquid outer core); arrival order P → S → L → R.
- Richter = magnitude (log, energy); Mercalli = intensity (felt damage, I–XII). Modern global standard = Mw (Moment magnitude).
- BIS seismic zones II–V (Zone V = NE India + Kashmir + Kachchh + Andaman; Zone IV = Delhi NCR; Zone I abolished 2002).
- Weathering ≠ erosion. Weathering is in-situ; erosion needs a mobile agent (water/ice/wind/wave/groundwater).
- Mass-movement order by speed — creep < solifluction < earthflow/mudflow < landslide < rockfall. Lahar = volcanic mudflow.
- Central Himalayan seismic gap (Kangra 1905 ↔ Bihar-Nepal 1934) = unsolved zone potentially storing Mw 8+ strain; Bilham & Wadia warn of a "Great Himalayan Earthquake".