Geomorphic Processes and Landforms

Forces that shape the surface

The Earth's surface is constantly being built up and worn down. Endogenic forces, which come from inside the Earth, raise mountains, create plateaus and cause earthquakes and volcanoes. Exogenic forces, driven by the Sun's energy and gravity, wear the land down through weathering, mass movement, erosion and deposition by rivers, glaciers, wind, groundwater and waves. Landforms are the result of the balance between these two sets of forces. UPSC asks about types of weathering and the landforms made by each agent, often with matching questions such as "drumlin – glacier" or "barchan – wind".

Endogenic processes

• Diastrophism – slow, large-scale movements of the crust.
• Orogenic (mountain-building) – folding and faulting along plate boundaries.
• Epeirogenic (continent-building) – broad uplift or subsidence of large areas.
• Folding produces anticlines (up-folds) and synclines (down-folds); intense folding forms recumbent folds and nappes, as in the Alps and Himalayas.
• Faulting – rocks break and move along a fault. A block that sinks between two faults forms a rift valley or graben (the Narmada and Tapi valleys, East African Rift); a block raised between faults forms a block mountain or horst (the Vosges and Black Forest of Europe; the Satpura is often cited as a horst).
• Volcanism – intrusive landforms (batholiths, laccoliths, sills, dykes) and extrusive landforms (cones, lava plateaus such as the Deccan).

Weathering and mass movement

Weathering is the breaking down of rocks in place.

• Physical (mechanical) – exfoliation (onion-like peeling) in hot deserts due to daily heating and cooling; frost wedging in cold regions; salt crystal growth.
• Chemical – solution (limestone dissolving in rainwater with carbon dioxide), oxidation (rusting of iron-rich rocks, giving red colour), hydration and carbonation; most active in hot, humid climates.
• Biological – roots, burrowing animals and lichens.

Weathering produces the regolith, which becomes soil. It also concentrates minerals: bauxite and laterite are residues of intense chemical weathering in the tropics.

Mass movement is the downslope movement of material under gravity – landslides, rockfalls, slumps, mudflows and slow soil creep. It is common in the Himalayas and Western Ghats during the monsoon, especially where slopes are cut for roads.

Fluvial (river) landforms

Rivers are the most widespread agent of erosion.

Youth stage (upper course): steep gradient, vertical erosion.

• V-shaped valleys, gorges and canyons (Grand Canyon of the Colorado; the Indus, Sutlej and Brahmaputra gorges in the Himalayas).
• Waterfalls and rapids where hard rock overlies soft rock; potholes drilled by swirling pebbles; interlocking spurs.

Mature stage (middle course): lateral erosion widens the valley.

• Meanders – wide loops; erosion on the outer bank (river cliff) and deposition on the inner bank (point bar).
• Oxbow lakes formed when a meander is cut off.
• Alluvial fans where streams leave hills (the bhabar belt at the Himalayan foothills).

Old stage (lower course): gentle gradient, deposition dominates.

• Floodplains and natural levees.
• Braided channels, as in the Brahmaputra.
• Deltas at the mouth where rivers drop sediment into calm seas – arcuate (the Nile), bird's-foot (the Mississippi), and the Ganga–Brahmaputra delta, the world's largest. Where tides are strong, rivers form estuaries instead (the Narmada and Tapi on India's west coast).
• Peneplain – a nearly flat surface at the end of the cycle (W.M. Davis's "cycle of erosion").

Glacial landforms

Glaciers erode by plucking and abrasion.

• Erosional: cirques (corries) – armchair-shaped hollows; arêtes – sharp ridges between cirques; horns – pyramidal peaks (the Matterhorn); U-shaped valleys; hanging valleys with waterfalls; fjords – drowned glacial valleys (Norway).
• Depositional: moraines (terminal, lateral, medial, ground) of unsorted till; drumlins – egg-shaped hills of till; eskers – long winding ridges of sand and gravel from melt-water streams; outwash plains; kettle holes.

Aeolian (wind) landforms

Wind is most effective in arid regions with little vegetation.

• Erosional: deflation hollows (the Qattara Depression in Egypt); mushroom rocks (pedestal rocks) shaped by abrasion near the ground; yardangs and zeugens – ridges of rock; inselbergs – isolated residual hills.
• Depositional: sand dunes – crescent-shaped barchans with horns pointing downwind; seif (longitudinal) dunes parallel to wind; star dunes; and loess – fine wind-blown silt deposits, as in north China's Loess Plateau.
• The Thar desert in Rajasthan has barchans and shifting dunes called dhrians.

Karst (groundwater) landforms

In limestone regions, rainwater with carbon dioxide dissolves the rock.

• Sinkholes (dolines), swallow holes, uvalas (merged sinkholes), poljes (large flat-floored depressions), and underground caves.
• In caves: stalactites hang from the roof, stalagmites rise from the floor, and they join as pillars.
• Named after the Karst region of Slovenia. Indian examples: Borra caves (Andhra Pradesh), Mawsmai and Krem Liat Prah caves (Meghalaya), Kotumsar caves (Chhattisgarh), and the Guptadham caves (Bihar).

Coastal landforms

Waves, currents and tides shape coasts.

• Erosional: sea cliffs, wave-cut platforms, sea caves, arches and stacks (as at the coast of Varkala in Kerala, and the Twelve Apostles in Australia).
• Depositional: beaches, spits, bars, tombolos (a bar linking an island to the mainland), and lagoons behind bars – Chilika (Odisha), Pulicat (Andhra–Tamil Nadu border) and the Vembanad backwaters (Kerala).
• India's east coast is mostly an emergent coast with wide deltas and beaches; the west coast is largely submergent, with cliffs, estuaries and narrow plains (with some emergent features in Kerala).

Landforms, hazards and human use

Landforms are not just exam terms; they decide where people live and what risks they face. River floodplains and deltas are the most fertile and densely populated parts of India, but they are also the most flood-prone; embankments that confine rivers such as the Kosi can raise the river bed and lead to catastrophic breaches, as in 2008. Alluvial fans and the bhabar–terai belt at the Himalayan foot are porous and swampy, which shaped the location of settlements and forests. Glacial valleys hold lakes dammed by moraines, which can burst in glacial lake outburst floods (GLOFs), as in Kedarnath (2013) and South Lhonak, Sikkim (2023). Mass movement on steep slopes threatens hill towns such as Joshimath, where land subsidence was reported in 2023, and the Western Ghats, where landslides struck Wayanad in 2024. In deserts, shifting dunes bury roads and fields, and planting shelter belts helps fix them. On the coasts, natural spits, bars and mangroves protect the mainland from storm surges, while sand mining and ports can increase erosion. Planners use these geomorphic insights in disaster risk reduction, land-use zoning, road design and river management, which is why GS3 disaster management questions often expect a geomorphological explanation.

Theories of landform development

Two classic models explain how landscapes evolve. W.M. Davis (1899) proposed the cycle of erosion – youth, maturity and old age – driven by uplift followed by long periods of stability. Walther Penck argued instead that uplift and erosion happen at the same time, so slope shapes depend on the rate of uplift. Modern geomorphology adds climatic and tectonic controls, and the idea of dynamic equilibrium.

Mains practice question

Explain how rivers and glaciers produce contrasting valley forms. Give examples from India. (150 words)

Answer framework

• Rivers: vertical erosion in youth → V-shaped valleys, gorges (Indus, Sutlej); meanders and floodplains downstream (Ganga).
• Glaciers: plucking and abrasion → U-shaped valleys, cirques, hanging valleys (Zanskar, Gangotri region), moraines.
• Contrast: shape, sorting of deposits, process.
• Conclusion: landscape as record of past climate.