BharatNotes The landscape around us — mountains, valleys, plains, and coastlines — is continuously being shaped by forces acting from within the Earth and from the surface environment. This chapter explains the processes that create and destroy landforms. Understanding geomorphic processes is essential for UPSC because they explain natural hazards (landslides, floods), soil formation (crucial for agriculture questions), and the evolution of India's diverse physical landscape.
UPSC Prelims tests the classification of weathering types and mass movements. Mains questions on disaster management, soil degradation, and regional geography all require understanding of these processes.
PART 1 — Quick Reference Tables
Table 1: Endogenic vs Exogenic Forces
| Feature | Endogenic Forces | Exogenic Forces |
|---|---|---|
| Source of energy | Earth's internal heat (radioactive decay, primordial heat) | Sun's energy (external) |
| Direction | From within Earth upward | From surface downward/lateral |
| Effect | Build up relief (constructive) | Wear down relief (destructive) |
| Speed | Slow (geological time) | Slow, but accelerated by human activity |
| Examples | Diastrophism, volcanism | Weathering, erosion, deposition |
| Result | Mountain building, sea floor spreading | Peneplains, sedimentary plains |
Table 2: Types of Weathering
| Type | Sub-type | Process | Climate | Products |
|---|---|---|---|---|
| Physical | Block disintegration | Temperature extremes crack rocks along joints | Arid, high-altitude | Angular blocks |
| Physical | Exfoliation | Thermal expansion/contraction causes layers to peel | Arid | Rounded domes, onion-skin layers |
| Physical | Freeze-thaw (frost action) | Water expands 9% when frozen, prying open cracks | Cold, wet | Angular fragments, scree |
| Physical | Salt weathering | Salt crystallisation in cracks | Arid, coastal | Granular disintegration |
| Chemical | Solution (carbonation) | CO₂ + water → carbonic acid dissolves limestone | Humid | Karst topography |
| Chemical | Oxidation | Oâ‚‚ combines with iron minerals | Warm, humid | Rust-coloured soils, laterite |
| Chemical | Hydration | Water molecules combine with minerals, expanding | Humid | Clay minerals, swelling |
| Chemical | Hydrolysis | Water reacts with silicate minerals | Warm, humid | Clay minerals from feldspars |
| Chemical | Chelation/Organic | Acids from decomposing organic matter dissolve minerals | Humid, forested | Nutrient-rich soils |
| Biological | Root wedging | Plant roots expand in cracks | All climates | Physical breakup |
| Biological | Burrowing | Animals loosen and turn over material | All climates | Mixing of soil |
Table 3: Types of Mass Movements
| Type | Water Content | Speed | Characteristics |
|---|---|---|---|
| Slow movements | — | — | — |
| Soil creep | Low | Very slow | Gradual downslope movement; tilted fence posts, curved tree trunks |
| Solifluction | High (in permafrost areas) | Slow | Soil saturated with water flows downslope over frozen subsoil |
| Rock creep | None | Very slow | Movement of rock fragments on steep slopes |
| Rapid movements | — | — | — |
| Earthflow | High | Moderate | Saturated soil flows; lobate shape |
| Mudflow | Very high | Fast | Liquid mud flows rapidly down valleys; lahars (volcanic mudflows) |
| Debris flow | Variable | Fast | Mix of rock, soil, vegetation in water |
| Landslide | Variable | Fast–very fast | Mass of rock/soil slides on a failure plane; most destructive |
| Rock fall | None | Very fast | Individual rocks fall freely from cliff face |
| Avalanche | None (snow) | Very fast | Snow and ice rushing downslope |
| Slump | Variable | Fast | Rotational failure along curved surface |
Table 4: Erosion vs Deposition
| Feature | Erosion | Deposition |
|---|---|---|
| Definition | Wearing away and removal of material | Laying down of transported material |
| Occurs | Where energy is high (steep slopes, swift water) | Where energy drops (flat areas, still water) |
| Agent | Running water, glaciers, wind, waves | Same agents, different conditions |
| Landforms | V-valleys, gorges, sea cliffs | Deltas, alluvial fans, sand dunes, beaches |
| Soil impact | Soil loss — reduces fertility | Soil gain — increases fertility |
Table 5: Gradation — Degradation vs Aggradation
| Process | Definition | Result |
|---|---|---|
| Degradation | Lowering of land surface by erosion | Peneplain (nearly flat surface at base level) |
| Aggradation | Building up of land surface by deposition | Alluvial plains, flood plains |
| Gradation | Combined process tending toward a graded profile | Equilibrium landforms |
| Base level | Lowest level to which erosion can reduce land (usually sea level) | Controls depth of river erosion |
PART 2 — Detailed Notes
Endogenic Forces
Forces originating within the Earth build up relief over geological time.
Diastrophism refers to all movements of the solid crust:
- Folding: Compressional forces buckle rocks into folds — anticlines (upward arch) and synclines (downward trough). The Himalayas, Alps, and Andes are fold mountain ranges.
- Faulting: Tensional or shear forces cause rocks to fracture and slip. Creates fault scarps, rift valleys (normal faults), and strike-slip faults. The East African Rift is an active rift; the Western Ghats escarpment is partly fault-controlled.
- Epeirogeny: Broad, slow vertical movements — uplift or submergence of large landmasses. Isostatic adjustments are a form of epeirogeny.
- Orogeny: Mountain-building episodes driven by plate collision — the most dramatic form of diastrophism.
Volcanism: The movement of magma toward and onto Earth's surface. Creates shield volcanoes (gentle basaltic lava), composite/strato-volcanoes (explosive, ash-rich), and lava plateaus (like the Deccan Traps).
Exogenic Forces: The Surface Shapers
Exogenic forces are driven by solar energy, operating through water, ice, wind, and gravity. They work by:
- Weathering — breaking down rocks in place (no movement)
- Mass movements — movement of material under gravity
- Erosion — removal of weathered material by an agent (water, ice, wind, waves)
- Transportation — carrying eroded material
- Deposition — laying down transported material
💡 Explainer: Types of Weathering in Detail
Physical (mechanical) weathering disintegrates rocks without changing their chemical composition. The key processes:
Thermal expansion and contraction: Daily heating and cooling causes differential expansion in rock minerals, eventually cracking the rock. Important in deserts where temperature swings are extreme.
Freeze-thaw (frost action): Water seeps into cracks. When it freezes, it expands by ~9%, exerting enormous pressure (~2,000 kg/cm²) and widening the crack. Repeated cycles shatter rocks into angular fragments — the dominant weathering process in high mountain zones. The scree slopes of the Himalayas are products of freeze-thaw weathering.
Salt crystal growth: In arid and coastal zones, dissolved salts enter rock pores. As water evaporates, salt crystals grow, exerting pressure that disaggregates the rock surface.
Chemical weathering alters the mineral composition of rocks, often forming clay minerals. Key processes:
Carbonation: Carbon dioxide dissolves in rainwater to form weak carbonic acid (H₂CO₃). This acid dissolves calcium carbonate (limestone and dolomite) very effectively. This is the process that creates karst topography — caves, sinkholes, stalactites. The Meghalaya caves (Krem Liat Prah) and limestone landscapes of Madhya Pradesh are examples.
Oxidation: Oxygen combines with iron-bearing minerals to form iron oxides (rust). The characteristic red-orange colour of tropical soils reflects oxidation of iron minerals. Intense oxidation in humid tropical conditions produces laterite — a rock-hard surface layer rich in iron and aluminium oxides.
Hydrolysis: The most important chemical weathering process for feldspar (the most common mineral). Feldspars react with water to form clay minerals (kaolinite, smectite, illite). Clay minerals are the basis of fertile soils. This is why feldspar-rich granite weathers into soil, while quartz-rich sandstone produces coarser, less fertile sandy soils.
Biological weathering involves living organisms:
- Plant roots penetrate cracks, exerting mechanical pressure (root wedging)
- Decomposing organic matter produces humic acids, which chemically attack minerals
- Burrowing animals (earthworms, termites) physically displace and mix soil
Mass Movements: Gravity in Action
Mass movements occur when the driving force (gravity acting on slope material) exceeds the resisting force (friction, cohesion). Triggers include:
- Rainfall saturating soil (reduces friction, increases weight)
- Earthquake vibrations
- Undercutting by rivers or waves
- Freeze-thaw cycles
- Human excavation
Landslides are sudden, rapid movements of rock, soil, or debris down a slope. India's Himalayan region (high rainfall, steep slopes, young, friable rocks, heavy road construction) and the Western Ghats (heavy monsoon rainfall, steep terrain) are highly susceptible.
🎯 UPSC Connect: Mass Movements and Disaster Management
India's National Disaster Management Authority (NDMA) has identified several key landslide-prone states: Uttarakhand, Himachal Pradesh, Jammu & Kashmir, Sikkim, Arunachal Pradesh, Meghalaya, and the Western Ghats states (Kerala, Karnataka, Maharashtra).
The 2013 Kedarnath disaster was a combination of cloud burst, flash flood, and landslide — a compound disaster. Understanding geomorphic processes helps in:
- Identifying vulnerability zones for land use planning
- Designing early warning systems
- Understanding the role of vegetation removal (deforestation) in destabilising slopes
Erosion and the Role of Climate
The rate of erosion depends heavily on climate:
- Humid tropical: Intense chemical weathering; thick lateritic soils; rivers carry heavy suspended load
- Arid: Mechanical weathering dominant; wind erosion important; sparse vegetation provides little protection
- Cold/alpine: Freeze-thaw; glacial erosion; mass movements (rockfalls, avalanches)
Human activities (deforestation, agriculture, construction) dramatically accelerate erosion rates — sometimes by 100–1,000 times the natural rate.
PART 3 — Frameworks & Analysis
Weathering Controls: Climate vs Rock Type
| Factor | Effect on Weathering |
|---|---|
| Temperature | Higher temperature → faster chemical reactions → more chemical weathering |
| Rainfall | More rainfall → more carbonation, hydrolysis → faster chemical weathering |
| Rock type | Limestone dissolves readily; quartzite resists; granite weathers slowly |
| Joints and fractures | More fractures → more surface area → faster physical weathering |
| Vegetation | Root wedging increases physical; organic acids increase chemical |
| Slope angle | Steep slopes remove weathered material quickly → fresh rock exposed |
Mass Movement Classification
| Speed | Water content | Type | Indian Hazard Example |
|---|---|---|---|
| Very slow | Low | Soil creep | Subtle hillslope instability |
| Slow | High (cold) | Solifluction | Alpine and sub-alpine zones |
| Fast | Low | Rock fall | Himalayan and Western Ghats roads |
| Fast | High | Mudflow | Post-monsoon debris flows, Uttarakhand |
| Very fast | Low–medium | Landslide | Kedarnath, Aarey (Mumbai), Idukki (Kerala) |
Exam Strategy
Prelims Traps:
- Weathering = breakdown of rock in place (no transport). Erosion = removal of material.
- Carbonation dissolves limestone specifically (carbonic acid). Do not confuse with general corrosion.
- Laterite forms from intense chemical weathering (oxidation) in humid tropical conditions — iron and aluminium accumulate as silica is leached away.
- Mass movements include both slow (soil creep) and rapid (landslide) processes — do not assume "mass movement" = only landslides.
- Freeze-thaw is the dominant mechanical weathering process in cold regions, not thermal expansion (which dominates in hot deserts).
Mains Frameworks:
- Disaster management answers on landslides: physical trigger (geomorphic processes) + human aggravation (deforestation, road cutting) + NDMA response framework.
- Soil degradation answers: link to weathering (parent material), erosion (loss of topsoil), and mass movements.
- India's diverse landscapes: Himalayan (freeze-thaw, mass movements) vs Deccan (oxidation, chemical weathering) vs Thar (wind, salt weathering).
Practice Questions
- UPSC Prelims 2016: Which of the following types of weathering is responsible for the formation of karst topography? (Carbonation / chemical weathering of limestone)
- UPSC Prelims 2019: What are the factors responsible for the occurrence of landslides in India? (Physical and human factors)
- UPSC Mains GS1 2016: Discuss the geomorphic processes responsible for the diverse relief features of the Indian subcontinent.
- UPSC Mains GS3 2020: What are the factors that cause mass movements? Discuss their impact on settlements in the Himalayan region.
