Geomorphic Processes

Why this chapter matters for UPSC: "Geomorphic Processes" is Chapter 5 of Fundamentals of Physical Geography in the current rationalised NCERT (Reprint 2026-27). It was Chapter 6 before Minerals and Rocks was dropped; this site keeps the old number. The rationalised text shortened the detailed accounts of individual weathering processes and of slow and rapid flow movements; this page covers both, marking what comes from the older edition (NCERT's former chapter file; see Sources). Its mass-movement section is the base for the recurring Mains questions on landslides in the Himalaya and the Western Ghats, and on landslide risk management.

Contemporary hook: About 0.42 million km², nearly 12.6% of India's land area, is prone to landslides, according to the Geological Survey of India's 2022 figure, quoted by NDMA in its National Landslide Risk Mitigation Programme document (2025). In the early hours of 30 July 2024, landslides struck Mundakkai (about 1:15 am) and Chooralmala (about 4:10 am) in Wayanad, Kerala, in the Western Ghats; the LBSNAA case study counts 298 deaths and 32 missing (counts in other official reports differ).

🧠 First Principles — Read This First

The Earth's surface is uneven because two sets of forces act on it in opposite directions. Endogenic forces come from inside the Earth. Their energy comes from radioactivity, rotational and tidal friction, and heat left over from the Earth's formation. They raise mountains, warp continents and cause earthquakes and volcanoes: they build relief. Exogenic forces work at the surface. Their energy comes ultimately from the Sun, through the atmosphere, and from the slopes created by tectonic uplift. Rain, rivers, ice, wind and waves wear the high places down and fill the low places up. NCERT puts it this way: the earth is "a playfield for two opposing groups of geomorphic processes". As long as both keep working, the surface never becomes flat.

Three terms need separating from the start. Weathering breaks rock down where it lies; almost nothing moves. Mass movement shifts rock and soil downslope under gravity alone; no river, glacier or wind carries the material. Erosion is removal and transport by a moving agent such as running water, a glacier or wind. In short: weathering loosens, gravity drops, agents carry. Deposition happens when an agent slows down and can no longer carry its load.

Weathered rock is also the raw material of soil, so the chapter ends with how soil forms.

The chapter's practical payoff is landslides: why they are more frequent in the Himalaya than in the Western Ghats, and how the risk can be managed.

PART 1 — Quick Reference

Table 1: NCERT key terms

Source: NCERT FoPG (rationalised), Chapter 5, pp. 37–44. NCERT's definition above is the one its exercise tests.

Table 2: Endogenic and exogenic processes

Table 3: Diastrophism (NCERT)

All four can fault and fracture the crust and cause pressure, volume and temperature (PVT) changes that metamorphose rocks.

Table 4: Weathering processes

Table 5: Mass movements

Table 6: Agents of erosion (NCERT)

Table 7: Soil-forming factors (NCERT)

PART 2 — Concepts & Narrative

Processes and agents

NCERT separates a process (a force applied on earth materials) from an agent (a mobile medium that removes, transports and deposits them). For exogenic processes, NCERT says the two can be treated as one and the same unless stated separately.

Gravity matters in two ways. It is the directional force that drives every downslope movement, and it also creates stresses in earth materials. NCERT notes that without gravity and gradients there would be no mobility and so no erosion, transportation or deposition. All movements, inside the Earth or on its surface, happen down gradients: from higher to lower levels and from high to low pressure.

Endogenic processes

The energy behind endogenic processes comes mostly from radioactivity, rotational and tidal friction, and primordial heat from the Earth's origin. This energy, through geothermal gradients and heat flow, causes diastrophism and volcanism (Table 3). Because heat flow, crustal thickness and crustal strength vary from place to place, endogenic forces act unevenly, and the original crustal surface is uneven.

Volcanism covers the movement of magma onto or towards the surface and the intrusive and extrusive forms it creates; NCERT covers these in Chapter 3, "Interior of the Earth".

Exogenic processes

Exogenic processes take their energy from the atmosphere, driven by the Sun, and from slopes created by tectonics. Gravity acts on every sloping surface. Force per unit area is stress; shear stresses along the faces of materials break rocks and cause slippage. Materials also suffer molecular stresses from temperature change, crystallisation and melting, while chemical processes loosen the bonds between grains. NCERT's conclusion: the basic cause of weathering, mass movement and erosion is the development of stresses in earth materials.

Exogenic processes vary between climatic regions, mainly with temperature and precipitation. Within a region they also vary with altitude, aspect (north- and south-facing slopes receive different insolation), wind, rainfall intensity, daily temperature range and frost frequency. Where climate is the same, rock type and structure decide the rate: folds, faults, joints, bedding planes, hardness, chemical susceptibility and permeability. A rock may resist one process and give way to another, and the same rock may behave differently in different climates. The result is differential rates of denudation and therefore differences in topography.

Weathering

NCERT defines weathering as "mechanical disintegration and chemical decomposition of rocks through the actions of various elements of weather and climate". Since very little or no motion takes place, it is in situ. Climate controls both the type of weathering and the depth of the weathering mantle. The three groups rarely act alone, but one usually dominates.

Chemical weathering (older-edition detail):

• Solution: solids dissolve in water or weak acids. Nitrates, sulphates, potassium and common salt are affected; such minerals are leached away in rainy climates and accumulate in dry ones. Calcium carbonate in limestone dissolves in water containing carbonic acid.
• Carbonation: carbon dioxide from the air and soil air dissolves in water to form weak carbonic acid, which breaks down feldspars and carbonate minerals. Calcium and magnesium carbonates are removed in solution without residue, which forms caves.
• Hydration: chemical addition of water. Minerals take up water and expand; calcium sulphate turns to gypsum. The process is reversible, and repeated swelling and shrinking (as in clays) causes fatigue and cracking.
• Oxidation: combination with oxygen to form oxides or hydroxides, where there is ready access to air and oxygenated water. Iron, manganese and sulphur minerals are most affected.
• Reduction: where oxygen is absent (below the water table, in stagnant water and waterlogged ground), oxidised minerals are reduced; the red colour of iron turns greenish or bluish grey.

Hydration, carbonation and oxidation usually act together and speed each other up.

Physical weathering (older-edition detail):

• Unloading and expansion: erosion removes overlying rock, the pressure drops, and the upper layers expand and fracture roughly parallel to the surface. On curved surfaces this produces massive exfoliation sheets and large, smooth exfoliation domes.
• Temperature change and expansion: minerals expand and contract with daily heating and cooling and push against each other. This is most effective in dry climates and at high elevations, where daily temperature changes are large. NCERT links it to tors, the rounded granite boulders and stacks of hill tops (see the note on tors below).
• Freezing, thawing and frost wedging: ice grows in pores and cracks during repeated freezing and melting, widening them until the rock breaks. Most effective at high elevations in middle latitudes; rapid freezing is most damaging. Ice is about 9 per cent less dense than liquid water (USGS), so water expands by roughly a tenth when it freezes.
• Salt weathering: salts expand through heat, hydration and crystallisation. Desert surface temperatures of 30–50 °C favour it. Salt crystallisation is the most effective form; grains fall off one by one (granular disintegration). Chalk breaks down most readily, followed by limestone, sandstone, shale, gneiss and granite.

Biological weathering is covered in Table 4. NCERT's point about human beings is that disturbing vegetation, ploughing and cultivating expose new surfaces to air and water.

Significance of weathering

NCERT gives four reasons why weathering matters:

1. It breaks rocks into fragments and so prepares the way for regolith and soil, and for erosion and mass movement. Erosion cannot be significant if rocks are not weathered.
2. Biomes and biodiversity depend on forests, and forests depend on the depth of the weathering mantle. This is NCERT's answer to "It is weathering that is responsible for bio-diversity on the earth. How?"
3. It concentrates valuable ores of iron, manganese, aluminium and copper by enrichment: leaching removes other material and raises the concentration of what remains, to a level that may be economic to mine.
4. It is an important process in soil formation.

Mass movements

Mass movements transfer rock debris downslope under the direct influence of gravity. Air, water or ice do not carry the debris, though the debris may carry them. Movements range from slow to rapid and shallow to deep, and include creep, flow, slide and fall.

NCERT draws two conclusions that are often tested:

• Weathering is not a prerequisite for mass movement, because gravity acts on bedrock too. Weathering helps, and mass movements are much more active on weathered slopes.
• Mass movements are not erosion. No geomorphic agent takes part, even though material shifts from one place to another.

Material on a slope yields only when the disturbing force exceeds its shearing resistance. Weak unconsolidated materials, thinly bedded rocks, faults, steeply dipping beds, vertical cliffs or steep slopes, heavy or torrential rain and scarce vegetation favour mass movement. NCERT lists nine activating causes:

1. Removal of support from below, naturally or artificially.
2. Increase in the gradient and height of slopes.
3. Overloading by adding material, naturally or by artificial filling.
4. Overloading by heavy rainfall, saturation and lubrication.
5. Removal of material or load from the original slope surface.
6. Earthquakes, explosions or machinery.
7. Excessive natural seepage.
8. Heavy drawdown of water from lakes, reservoirs and rivers, causing slow outflow of water from under slopes or banks.
9. Indiscriminate removal of natural vegetation.

Slow movements (older-edition detail). Creep occurs on moderately steep, soil-covered slopes and is imperceptible except over long observation; fence posts and telephone poles leaning downslope are the sign. Solifluction is the slow downslope flow of soil or fine debris saturated with water, common where the surface of deeply frozen ground melts or rain continues for long periods, and the lower layers are impervious.

Rapid flow movements (older-edition detail). These are mostly in humid regions. Earthflow is the movement of water-saturated clayey or silty material down low-angle terraces or hillsides. Mudflow occurs where thick weathered material without vegetation is saturated by heavy rain and flows down definite channels like a stream of mud; it is frequent on the slopes of erupting or recently erupted volcanoes, where ash turns to mud. Debris avalanche occurs in narrow tracks on steep slopes in humid regions and can be much faster than a mudflow. NCERT's exercise classes it as a rapid flow mass movement, not a landslide.

Landslides (current edition). These are relatively rapid, perceptible movements of relatively dry material. The size and shape of the mass depend on the discontinuities in the rock, the degree of weathering and the steepness of slope. NCERT's types:

• Slump: one or more units of debris slip with a backward rotation relative to the slope.
• Debris slide: rapid rolling or sliding of earth debris without backward rotation.
• Debris fall: nearly free fall of earth debris from a vertical or overhanging face.
• Rockslide: individual rock masses slide down bedding, joint or fault surfaces; very fast and destructive on steep slopes; planar failure along steeply dipping discontinuities.
• Rock fall: free fall of rock blocks from any steep slope, keeping away from the slope. It affects only the superficial layers of the rock face, unlike a rockslide, which affects material to a substantial depth.

Erosion and deposition

Erosion is the acquisition and transportation of rock debris by running water, groundwater, glaciers, wind and waves. Abrasion by the debris these agents carry adds to it. Through erosion, relief degrades. Weathering aids erosion but is not a pre-condition for it. Weathering, mass wasting and erosion are all degradational processes, and erosion is largely responsible for the continuous change of the surface.

Erosion and transport are controlled by kinetic energy. The older edition defined erosion as the "application of the kinetic energy associated with the agent to the surface of the land along which it moves", with KE = ½mv². Energy depends on mass as well as speed, so glaciers, though slow, are more effective agents of erosion than wind because of their enormous mass. Of the five agents, wind, running water and glaciers are controlled by climate; waves and groundwater are not (Table 6).

Deposition is a consequence of erosion. Agents lose velocity, and so energy, on gentler slopes, and their load settles. NCERT stresses that "deposition is not actually the work of any agent". Coarser materials are deposited first and finer ones later, and depressions fill up. The same five agents act as depositional (aggradational) agents.

Human influence

NCERT's opening section notes that the surface has been shaped over very long periods, and that "humans have caused extensive damage to the environment through over use of resources", diminishing its potential at a fast rate. Several of NCERT's nine activating causes of mass movement are human: removal of support from below, artificial filling, explosions and machinery, drawdown of reservoirs and removal of vegetation.

Human activity also speeds erosion. A global compilation of studies found that erosion from conventionally ploughed agricultural fields averages one to two orders of magnitude (roughly 10 to 100 times) higher than rates of soil production, erosion under native vegetation and long-term geological erosion (Montgomery, PNAS, 2007).

Soil formation

Soil is a dynamic medium in which chemical, physical and biological activity goes on constantly. NCERT calls it "a result of decay" and "also the medium for growth". Pedology is soil science.

Process (pedogenesis). Soil formation depends first on weathering: the weathering mantle is the basic input. The weathered material or transported deposit is first colonised by bacteria and simple plants such as mosses and lichens. Dead remains build up humus. Grasses and ferns follow, then bushes and trees from seeds brought by birds and wind. Roots penetrate, burrowing animals bring up particles, and the material becomes porous and sponge-like, able to hold water and let air pass. The result is a mature soil, a complex mixture of mineral and organic products.

Factors (Table 7) act together and affect one another.

• Parent material (passive) can be weathered rock in place (residual soils) or transported deposits (transported soils). Similar bedrocks may carry different soils and different bedrocks similar soils, but young soils and soils on some limestones show a strong link to the parent rock.
• Topography (passive) works through sunlight exposure and drainage. Soils are thin on steep slopes and thick on flat uplands; gentle slopes with slow erosion and good percolation are most favourable. Flat areas may develop a thick clay layer rich in organic matter and dark in colour.
• Climate (active) works through moisture and temperature. Excess water moves soil components downward (eluviation) and deposits them lower down (illuviation). In wet equatorial climates calcium, sodium, magnesium, potassium and much of the silica are removed; removal of silica is desilication. In dry climates evaporation exceeds precipitation, groundwater rises by capillary action and leaves salts that form a crust called a hardpan. In tropical climates with intermediate rainfall, calcium carbonate nodules (kankar) form. Chemical activity rises with temperature, falls in cool conditions (except carbonation) and stops at freezing; tropical soils therefore have deeper profiles, while tundra soils are mostly mechanically broken material.
• Biological activity (active) adds organic matter, moisture retention and nitrogen. Humus accumulates in cold climates, where bacteria work slowly, and peat forms in sub-arctic and tundra climates. In humid tropical and equatorial climates bacterial action is intense, dead vegetation oxidises quickly and humus is low. Bacteria fix atmospheric nitrogen; Rhizobium lives in the root nodules of leguminous plants and fixes nitrogen for the host. Ants, termites, earthworms and rodents rework the soil mechanically, and earthworms change its texture and chemistry as it passes through them.
• Time (passive) decides maturity. Soils on recent alluvium or glacial till are young and show no or poorly developed horizons. No fixed absolute time can be given for a soil to mature.

PART 3 — UPSC Integration

Mains frameworks

1. Landslide causes = slope conditions + activating causes. Use NCERT's favouring conditions (weak materials, steep slopes, heavy rain, scarce vegetation) and its nine activating causes, then separate natural from human causes.
2. Himalaya vs Western Ghats. Tectonic activity and weak sedimentary or unconsolidated rocks in the Himalaya; steep cliffs, strong temperature-driven mechanical weathering and intense short-duration rain on hard rock in the Ghats and Nilgiris (NCERT's box).
3. Process-to-landform chain. Weathering prepares, mass movement and erosion remove, deposition builds, with climate selecting the dominant process.

Exam Strategy

Prelims fact-traps (NCERT text and exercises):

• In NCERT, gradation is wearing down of relief through erosion. Its exercise asks which of deposition, diastrophism, volcanism and erosion is a gradational process; on NCERT's definition the answer is erosion. Texts that treat gradation as degradation plus aggradation would also count deposition, and diastrophism and volcanism are endogenic, so they are wrong either way.
• Hydration is the chemical addition of water: calcium sulphate turns to gypsum, clay minerals swell and shrink, and salts in pore spaces undergo rapid, repeated hydration (older-edition text). NCERT's exercise on hydration offers granite, clay, quartz and salts: on NCERT's own text both clay and salts are affected, so read the options with care.
• NCERT's exercise keys debris avalanche as a rapid flow mass movement. The USGS classes it as a very rapid debris flow under "flows", one of its five basic landslide types, so outside an NCERT question it counts as a kind of landslide.
• Exfoliation is a result, not a process. Exfoliation domes come from unloading; tors, in NCERT, from thermal expansion.
• Mass movement is not erosion: no agent carries the debris.
• Weathering is not a prerequisite for mass movement or for erosion, though it helps both.
• Deposition is not the work of any agent; coarse material settles first.
• Endogenic energy sources are radioactivity, rotational and tidal friction, and primordial heat.
• Diastrophism includes earthquakes and plate tectonics, not only orogeny and epeirogeny.
• Landslide material is relatively dry; slump has backward rotation; debris slide does not.
• Of the five erosional agents, waves and groundwater are not climate-controlled.
• Active soil factors: climate and biological activity. Passive: parent material, topography, time.
• Chemical activity falls in cool conditions except carbonation.

Mains question patterns:

• Comparative landslide questions (Himalaya vs Western Ghats) want NCERT's box points, set out side by side.
• "Causes and mitigation" questions want NCERT's nine activating causes followed by measures such as hazard zonation mapping, slope stabilisation, drainage and vegetation cover.
• "Earth is a playfield" style questions want endogenic and exogenic processes with their energy sources and effects.

Practice Questions

Practice (UPSC-pattern, not past papers). Questions 1 to 3 are NCERT's own exercise MCQs.

Prelims:

1. Which one of the following processes is a gradational process?
   (a) Deposition
   (b) Diastrophism
   (c) Volcanism
   (d) Erosion
   On NCERT's definition, gradation is the wearing down of relief through erosion.

2. Which one of the following materials is affected by the hydration process?
   (a) Granite
   (b) Clay
   (c) Quartz
   (d) Salts
   NCERT's older-edition text says both clay minerals and salts in pore spaces undergo hydration; clay is the conventional key, but salts are also defensible. Granite and quartz are the wrong options either way.

3. Debris avalanche can be included in the category of:
   (a) Landslides
   (b) Slow flow mass movements
   (c) Rapid flow mass movements
   (d) Subsidence
   NCERT's key; general geoscience usage treats debris avalanches within the wider family of landslides.

4. With reference to geomorphic processes in NCERT, consider the following statements: 1. Exfoliation domes result from thermal expansion. 2. Mass movements do not come under erosion. 3. Landslide material is relatively dry. Which of the statements given above are correct?
   (a) 1 and 2 only
   (b) 2 and 3 only
   (c) 1 and 3 only
   (d) 1, 2 and 3
   Exfoliation domes result from unloading.

5. Which of the following are the sources of energy for endogenic processes, according to NCERT? 1. Radioactivity 2. Rotational and tidal friction 3. Primordial heat from the origin of the earth 4. Insolation
   (a) 1, 2 and 3 only
   (b) 1 and 3 only
   (c) 2, 3 and 4 only
   (d) 1, 2, 3 and 4
   Insolation drives exogenic processes.

Mains (practice, NCERT Ex. 3, 150 words each):

1. "Our earth is a playfield for two opposing groups of geomorphic processes." Discuss.
2. Exogenic geomorphic processes derive their ultimate energy from the sun's heat. Explain.
3. Are physical and chemical weathering processes independent of each other? If not, why? Explain with examples.
4. How do you distinguish between the process of soil formation and soil-forming factors? What is the role of climate and biological activity in soil formation?
5. Why are landslides more frequent in the Himalaya than in the Western Ghats? (practice) Approach: NCERT's box, set out side by side.

📦 Revision Capsule

Sources

• NCERT, Fundamentals of Physical Geography, Class XI, ch 5 "Geomorphic Processes", Reprint 2026-27: kegy205.pdf; contents: kegy2ps.pdf.
• NCERT, Fundamentals of Physical Geography, Class XI, Chapter 6 "Geomorphic Processes", pre-rationalisation edition, archived copy of the former chapter file (ncert.nic.in/ncerts/l/kegy206.pdf, no longer served) captured 23 December 2018: https://web.archive.org/web/20181223050004/http://www.ncert.nic.in/ncerts/l/kegy206.pdf. This is the "older edition" on this page. It is not the 2019-20 print, which had already dropped the slow and rapid flow passages (creep, solifluction, earthflow, mudflow) and shortened the weathering section; the same file, unchanged, stayed at that address until 2023 (Wayback captures from 2016 to 2023 carry one checksum).
• NCERT, Fundamentals of Physical Geography, Chapter 3 "Interior of the Earth", Reprint 2026-27: https://ncert.nic.in/textbook/pdf/kegy203.pdf
• Montgomery, D.R. (2007), "Soil erosion and agricultural sustainability", PNAS 104(33): https://pmc.ncbi.nlm.nih.gov/articles/PMC1948917
• NDMA, National Landslide Risk Mitigation Programme document (2025), citing GSI (2022): https://ndma.gov.in/sites/default/files/PDF/NLRMP_NDMA2025.pdf
• LBSNAA, "Chooralmala - Mundakai Landslide" case study: lbsnaa.gov.in.
• USGS, "Water Density" (Water Science School): usgs.gov; USGS Fact Sheet 2004-3072, "Landslide Types and Processes": pubs.usgs.gov.
• A. Michniewicz, "Tors in Central European Mountains", Bulletin of Geography. Physical Geography Series 16 (2019): 67–87 (on Linton's two-stage model): doi:10.2478/bgeo-2019-0005.