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Geomorphic Processes

NCERT Class 11 · Geography Based on NCERT Class 11 Geography textbook · Free CBSE study kit

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Chapter Notes

Overview
This chapter explains the dynamic nature of the Earth's surface, focusing on the endogenic (internal) and exogenic (external) forces that shape landforms. It covers geomorphic processes such as weathering, mass movements, erosion, deposition, and soil formation. The one big idea is that the Earth's surface is a result of the continuous interaction between opposing forces: endogenic processes build up relief, while exogenic processes wear it down, and their balance determines the landscape we see.
Key Concepts (18)
Geomorphic processes
The endogenic and exogenic forces causing physical stresses and chemical actions on earth materials and bringing about changes in the configuration of the surface of the earth.
e.g. Weathering of rocks by rain and wind is an exogenic geomorphic process, while volcanic eruptions are endogenic.
Endogenic forces
Internal forces originating from within the earth, driven by energy from radioactivity, rotational and tidal friction, and primordial heat, which cause diastrophism and volcanism.
e.g. Mountain building through folding (orogeny) is an endogenic process.
Exogenic forces
External forces originating from within the earth's atmosphere, driven by solar energy and gravity, which cause weathering, mass wasting, erosion, and deposition.
e.g. Running water eroding a riverbank is an exogenic process.
Diastrophism
All processes that move, elevate, or build up portions of the earth's crust, including orogenic (mountain building), epeirogenic (continental building), earthquakes, and plate tectonics.
e.g. The formation of the Himalayas is a result of orogenic diastrophism.
Orogeny
A mountain building process involving severe folding of the crust, affecting long and narrow belts.
e.g. The Alpine-Himalayan belt was formed by orogeny.
Epeirogeny
A continental building process involving uplift or warping of large parts of the earth's crust, with simple deformation.
e.g. The uplift of the Deccan Plateau is an example of epeirogeny.
Volcanism
The movement of molten rock (magma) onto or toward the earth's surface, including the formation of intrusive and extrusive volcanic forms.
e.g. The eruption of Mount Vesuvius is an example of volcanism.
Weathering
Mechanical disintegration and chemical decomposition of rocks through the actions of various elements of weather and climate, occurring in-situ (on-site).
e.g. The cracking of rocks due to freeze-thaw cycles in cold climates is physical weathering.
Denudation
A general term covering all exogenic geomorphic processes, including weathering, mass wasting/movements, erosion, and transportation.
e.g. The wearing down of a mountain range over millions of years is denudation.
Mass movements
The transfer of mass of rock debris down slopes under the direct influence of gravity, without the involvement of geomorphic agents like water, ice, or wind.
e.g. A landslide in the Himalayas is a rapid mass movement.
Erosion
The acquisition and transportation of rock debris by geomorphic agents like running water, groundwater, glaciers, wind, and waves, leading to degradation of relief.
e.g. A river cutting a deep valley is an example of erosion.
Deposition
The settling of transported materials when erosional agents lose velocity and energy, filling up depressions.
e.g. The formation of a delta at the mouth of a river is deposition.
Geomorphic agent
A mobile medium (like running water, moving ice masses, wind, waves, and currents) that removes, transports, and deposits earth materials.
e.g. A glacier is a geomorphic agent that erodes and transports rock debris.
Exfoliation
The flaking off of more or less curved sheets or shells from over rocks or bedrock, resulting in smooth and rounded surfaces; a result of physical weathering processes like unloading and thermal expansion.
e.g. The rounded domes of granite in the Western Ghats show exfoliation.
Pedogenesis
The process of soil formation, depending first on weathering and then on colonization by organisms, humus accumulation, and profile development.
e.g. The formation of black soil in the Deccan Trap region is pedogenesis.
Soil-forming factors
Five basic factors that control soil formation: parent material, topography, climate, biological activity, and time.
e.g. Climate is an active factor; parent material is a passive factor.
Desilication
The removal of silica from the soil, common in wet equatorial rainy areas with high rainfall.
e.g. In the Amazon rainforest, desilication leads to the formation of laterite soils.
Nitrogen fixation
The process by which bacteria and other soil organisms take gaseous nitrogen from the air and convert it into a chemical form that can be used by plants.
e.g. Rhizobium bacteria in root nodules of legumes fix nitrogen.
How It Works
Chemical Weathering
  1. Water, air (oxygen and carbon dioxide), and heat must be present to speed up reactions.
  2. Processes like solution, carbonation, hydration, oxidation, and reduction act on rocks.
  3. These reactions decompose, dissolve, or reduce rocks to a fine clastic state.
  4. Carbon dioxide from air and decomposition of plants and animals increases underground carbon dioxide.
💡 Chemical weathering requires water and heat; it is faster in warm, humid climates. Carbonation is an exception — it is more effective in cold climates because cold water dissolves more carbon dioxide.
Physical (Mechanical) Weathering
  1. Applied forces include gravitational forces (overburden pressure, load, shearing stress), expansion forces (temperature changes, crystal growth, animal activity), and water pressures (wetting and drying cycles).
  2. These forces cause rock fracturing, mainly through thermal expansion and pressure release.
  3. Repeated contraction and expansion leads to continued fatigue and damage to rocks.
💡 Physical weathering does not change the chemical composition of rocks; it only breaks them into smaller pieces. Unloading (pressure release) causes exfoliation.
Biological Weathering
  1. Organisms like earthworms, termites, and rodents burrow and wedge, exposing new surfaces to chemical attack.
  2. Plant roots exert tremendous pressure, mechanically breaking rocks apart.
  3. Decaying plant and animal matter produce humic, carbonic, and other acids that enhance decay and solubility of elements.
  4. Human activities like ploughing and cultivating mix and create new contacts between air, water, and minerals.
💡 Biological weathering is both physical (root pressure, burrowing) and chemical (acids from decay). It is often overlooked in answers.
Mass Movements (Landslides, Slump, Debris Slide, Rockfall)
  1. Gravity exerts force on all matter; mass movements occur when force exceeds shearing resistance of materials.
  2. Activating causes include removal of support, increase in gradient, overloading, heavy rainfall, earthquakes, and removal of vegetation.
  3. Movements can be slow (creep) or rapid (landslides, rockfalls).
  4. In landslides, materials are relatively dry; slump involves backward rotation; debris slide is rapid rolling without rotation; rockfall is free falling of rock blocks.
💡 Mass movements are NOT erosion because no geomorphic agent (water, wind, ice) carries the debris; gravity alone is the driving force. Weathering aids mass movements but is not a prerequisite.
Erosion and Deposition
  1. Erosion involves acquisition and transportation of rock debris by geomorphic agents (running water, groundwater, glaciers, wind, waves).
  2. Abrasion by rock debris carried by these agents aids erosion.
  3. Erosion degrades relief (wears down landscape).
  4. Deposition occurs when agents lose velocity and energy on gentler slopes; coarser materials settle first, finer later.
  5. Deposition fills up depressions (aggradation).
💡 Erosion is not the same as weathering; weathering is in-situ breakdown, while erosion involves transport. Deposition is a consequence of erosion, not a separate process of an agent.
Soil Formation (Pedogenesis)
  1. Weathering produces a mantle of weathered material (regolith) — the basic input for soil.
  2. Bacteria, mosses, and lichens colonize the weathered material.
  3. Dead remains of organisms and plants accumulate humus.
  4. Minor grasses and ferns grow, followed by bushes and trees.
  5. Plant roots penetrate, burrowing animals bring up particles, making the mass porous and sponge-like.
  6. A mature soil — a complex mixture of mineral and organic products — forms over time.
💡 Soil formation is not just weathering; it requires biological activity and time. The five soil-forming factors (parent material, topography, climate, biological activity, time) act in union.
Exam Traps — Don't Make These Mistakes
⚠ Confusing weathering with erosion
✗ Weathering is the removal of rock material by wind and water.
→ Weathering is an in-situ (on-site) process with little or no motion of materials; erosion involves acquisition and transportation by geomorphic agents.
✓ Weathering is the mechanical disintegration and chemical decomposition of rocks in place, while erosion is the removal and transport of rock debris by agents like wind and water.
⚠ Mixing up endogenic and exogenic forces
✗ Earthquakes are exogenic forces because they cause destruction on the surface.
→ Earthquakes originate from within the earth due to internal energy (diastrophism), so they are endogenic forces.
✓ Earthquakes are endogenic forces as they are caused by internal earth movements (diastrophism), not by external atmospheric or solar energy.
⚠ Thinking mass movements are a type of erosion
✗ Landslides are a form of erosion caused by running water.
→ Mass movements are driven solely by gravity; no geomorphic agent (water, wind, ice) participates. Erosion requires an agent to transport material.
✓ Landslides are mass movements where rock debris moves downslope under direct influence of gravity, without the involvement of geomorphic agents like running water.
⚠ Confusing orogeny and epeirogeny
✗ Orogeny is the building of continents, and epeirogeny is mountain building.
→ The definitions are reversed. Orogeny is mountain building (severe folding, narrow belts), epeirogeny is continental building (uplift of large areas, simple deformation).
✓ Orogeny is a mountain building process involving severe folding of long and narrow belts, while epeirogeny is a continental building process involving uplift or warping of large parts of the crust.
⚠ Assuming weathering is a prerequisite for erosion
✗ Erosion cannot occur without weathering.
→ The chapter states 'weathering is not a pre-condition for erosion to take place' — erosion can occur on unweathered rocks through abrasion by rock debris.
✓ Weathering aids erosion by breaking rocks into fragments, but erosion can also occur directly through abrasion by rock debris carried by geomorphic agents.
Compare & Contrast
Source of energy
Endogenic forces
Exogenic forces
Endogenic forces derive energy from within the earth (radioactivity, rotational and tidal friction, primordial heat), while exogenic forces derive energy from the sun and gravity.
Type of crustal movement
Orogeny
Epeirogeny
Orogeny is mountain building with severe folding affecting long and narrow belts; epeirogeny is continental building with simple uplift or warping of large areas.
Movement of material
Weathering
Erosion
Weathering is an in-situ (on-site) process with little or no motion of materials; erosion involves acquisition and transportation of rock debris by geomorphic agents.
Driving force and agent involvement
Mass movements
Erosion
Mass movements are driven solely by gravity with no geomorphic agent (water, wind, ice) carrying debris; erosion involves geomorphic agents that acquire and transport debris.
Exam Focus
Marks pattern: 2 MCQs (1 mark each), 1 SA (3 marks) on weathering or mass movements, 1 LA (5 marks) on soil formation or geomorphic processes overview.
Most asked: Difference between endogenic and exogenic forces · Weathering processes (chemical, physical, biological) and their examples · Mass movements — types and causes · Soil-forming factors and their roles · Orogeny vs epeirogeny
Don't skip: Explain the role of climate and biological activity in soil formation (5 marks).; Distinguish between endogenic and exogenic forces with examples (3 marks).; Describe the processes of chemical and physical weathering (3 marks).
One-Line Revision (read aloud before the exam)
  1. Geomorphic processes are endogenic (internal) and exogenic (external) forces that change the earth's surface.
  2. Endogenic forces derive energy from within the earth and include diastrophism and volcanism.
  3. Exogenic forces derive energy from the sun and gravity and include weathering, mass wasting, erosion, and deposition.
  4. Diastrophism includes orogeny (mountain building) and epeirogeny (continental building).
  5. Weathering is the in-situ mechanical disintegration and chemical decomposition of rocks.
  6. Chemical weathering processes include solution, carbonation, hydration, oxidation, and reduction.
  7. Physical weathering is caused by thermal expansion, pressure release, and other forces leading to rock fracturing.
  8. Biological weathering involves root pressure, burrowing, and organic acids from decay.
  9. Mass movements are downslope transfers of rock debris under gravity, without geomorphic agents.
  10. Landslides, slumps, debris slides, and rockfalls are rapid mass movements.
  11. Erosion is the acquisition and transport of rock debris by agents like running water, wind, and glaciers.
  12. Deposition occurs when erosional agents lose energy, filling depressions with sediment.
  13. Soil formation (pedogenesis) depends on weathering, biological activity, and five factors: parent material, topography, climate, biological activity, and time.
  14. Climate is an active soil-forming factor; parent material and topography are passive factors.
  15. Desilication is the removal of silica from soil in wet equatorial climates.
  16. Nitrogen fixation by bacteria converts atmospheric nitrogen into a form usable by plants.

MCQs — 10 Questions with Answers

Q1. Which of the following is NOT an endogenic geomorphic process?

  • A. Diastrophism
  • B. Orogeny
  • C. Weathering ✓
  • D. Volcanism

Answer: C — Weathering is an exogenic process driven by atmospheric energy; diastrophism, orogeny, and volcanism are all endogenic processes driven by internal earth energy.

Q2. The difference between orogeny and epeirogeny is that:

  • A. Orogeny affects large areas while epeirogeny affects narrow belts
  • B. Orogeny involves severe folding in narrow belts while epeirogeny involves uplift of large crustal areas ✓
  • C. Orogeny causes earthquakes while epeirogeny causes volcanism
  • D. Orogeny is an exogenic process while epeirogeny is endogenic

Answer: B — Orogeny is a mountain-building process with severe deformation in narrow belts; epeirogeny is a continental-building process with simpler deformation affecting large areas.

Q3. A geomorphic agent is best defined as:

  • A. A force that applies stress to earth materials
  • B. A mobile medium capable of removing, transporting, and depositing earth materials ✓
  • C. A process that wears down the earth's surface
  • D. An internal energy source that builds up the earth's crust

Answer: B — A geomorphic agent is a mobile medium like running water, ice, or wind that actively removes and transports materials; a process is the force applied.

Q4. Why is gravity considered a crucial geomorphic factor?

  • A. It only operates within the earth's interior
  • B. It activates all downslope movements and provides directional stresses on earth materials ✓
  • C. It is responsible for volcanic eruptions
  • D. It prevents erosion and deposition from occurring

Answer: B — Gravity is the directional force activating downslope material movement and causing stresses; without it, there would be no erosion, transport, or deposition on the surface.

Q5. The phenomenon of wearing down of relief variations through erosion is called:

  • A. Aggradation
  • B. Diastrophism
  • C. Gradation ✓
  • D. Epeirogeny

Answer: C — Gradation is the specific process of wearing down relief variations; aggradation refers to filling up depressions.

Q6. Which statement about exogenic processes is correct? (A) Exogenic processes are driven by solar energy through the atmosphere. (B) Exogenic processes include weathering, mass wasting, and erosion-deposition.

  • A. Both (A) and (B) are correct ✓
  • B. (A) is correct but (B) is incorrect
  • C. (B) is correct but (A) is incorrect
  • D. Both (A) and (B) are incorrect

Answer: A — Both statements are correct: exogenic processes are powered by solar energy through atmospheric circulation and include weathering, mass wasting, and erosion-deposition cycles.

Q7. If the earth had no gradient (all land at same elevation), which would be impossible?

  • A. Weathering of rocks
  • B. Movement of water and material downslope ✓
  • C. Metamorphism of rocks
  • D. Orogeny and mountain building

Answer: B — Gradients are essential for activating mobility; without elevation differences, water and materials cannot flow downslope, making erosion and transport impossible.

Q8. Consider two regions: Region X has active plate tectonics with narrow folded belts; Region Y has broad stable continental uplift. Which processes are responsible respectively? (A) Epeirogeny in X and orogeny in Y. (B) Orogeny in X and epeirogeny in Y.

  • A. Only (A) is correct
  • B. Only (B) is correct ✓
  • C. Both (A) and (B) are correct
  • D. Both (A) and (B) are incorrect

Answer: B — Orogeny creates narrow mountain belts through intense folding (Region X); epeirogeny causes broad continental uplift with simpler deformation (Region Y).

Q9. The earth's surface remains uneven despite continuous exogenic processes because: (A) Endogenic forces continuously build up the crust. (B) Exogenic forces are not strong enough. (C) Gravity prevents material from moving downslope.

  • A. (A) only ✓
  • B. (B) only
  • C. (A) and (C) only
  • D. None of the above

Answer: A — The dynamic equilibrium maintaining surface unevenness results from endogenic forces continuously building up portions while exogenic forces wear them down; (B) and (C) are incorrect.

Q10. Analyze: In the Himalayan region, continuous orogeny is occurring yet valleys still deepen. This is best explained by:

  • A. Orogeny causes deepening of valleys
  • B. Exogenic weathering and erosion are opposing and working against the endogenic mountain-building process ✓
  • C. Gravity prevents further mountain uplift
  • D. Epeirogeny is stronger than orogeny in this region

Answer: B — The Himalayas demonstrate the dynamic balance: endogenic orogeny elevates mountains while simultaneous exogenic weathering, erosion, and mass wasting deepen valleys—both processes occur together.

Flashcards

Define geomorphic processes.

Endogenic and exogenic forces causing physical stresses and chemical actions on earth materials, changing the configuration of the earth's surface.

What is the difference between diastrophism and volcanism?

Diastrophism involves movement, elevation, and deformation of crustal rock (folding, faulting, plate tectonics); volcanism involves the movement of molten magma to or toward the earth's surface.

Distinguish between a geomorphic agent and a geomorphic process.

A geomorphic agent is a mobile medium (running water, ice, wind) that removes, transports, and deposits materials; a geomorphic process is the force applied to earth materials affecting them.

What is orogeny?

A mountain-building process involving severe deformation and folding of the earth's crust affecting long, narrow belts.

What is epeirogeny?

A continental-building process involving uplift or warping of large portions of the earth's crust with relatively simple deformation.

Define gradation in geomorphology.

The phenomenon of wearing down of relief variations on the earth's surface through erosion.

What are exogenic forces?

External forces originating from the earth's atmosphere and induced by solar energy that wear down and degrade landforms.

What are endogenic forces?

Internal forces originating from within the earth that build up and elevate portions of the earth's crust.

Why is gravity essential to geomorphic processes?

Gravity is the directional force activating all downslope movements of matter and induces stresses on earth materials, enabling erosion, transport, and deposition.

What role do gradients play in surface processes?

Gradients (from higher to lower elevation, pressure, or temperature) activate the mobility of earth materials and enable all surface movement and erosion.

Important Board Questions

Define weathering and explain how it differs from erosion. (2 marks) [2 marks]

Weathering = in-situ breaking of rock (chemical/physical), no transport. Erosion = wearing away AND removal of material by agents like water/wind.

Explain why the earth's surface remains uneven despite continuous exogenic processes. Support your answer with the roles of both endogenic and exogenic forces. (5 marks) [5 marks]

Build answer around dynamic equilibrium: endogenic forces (diastrophism, volcanism) continuously elevate and build crust; exogenic forces (weathering, erosion, deposition) continuously wear it down. Neither dominates permanently, so variations persist. Include example like Himalayas (ongoing orogeny + erosion).

Distinguish between geomorphic agents and geomorphic processes. Explain with examples how they work together to shape the earth's surface, and discuss the critical role of gravity and gradients in these processes. (6 marks) [6 marks]

Define agent (mobile medium: water, ice, wind) vs process (force applied to materials). Example: running water is agent; erosion is process. Explain gravity activates all downslope movement and gradients enable mobility—without both, no transport possible. Use specific example: river valley formation where water (agent) erodes (process) slope to lower level via gravity and gradient.

Assertion-Reason Questions for Geomorphic Processes

Q1. Assertion (A):

The earth's surface remains uneven and will continue to have relief variations.

Reason (R):

Endogenic forces continuously build up portions of the earth's crust while exogenic forces simultaneously wear them down, and as long as both continue, variations persist.

Answer: A — Both A and R are true, and R is the correct explanation of A — Both the assertion and reason are true. The reason correctly explains WHY the surface remains uneven—the continuous opposition between building (endogenic) and wearing (exogenic) forces maintains topographic variation indefinitely.

Q2. Assertion (A):

Diastrophism is a more important endogenic process than volcanism for shaping the earth's crust.

Reason (R):

Diastrophism involves mountain building through orogeny, while volcanism only creates isolated volcanic cones.

Answer: C — A is true but R is false — The assertion cannot be proven as 'more important'—both processes are significant. More critically, the reason is false: volcanism includes extensive lava plains, calderas, and intrusions that affect large areas. The reason oversimplifies volcanism's role.

Q3. Assertion (A):

Chemical weathering occurs more rapidly in tropical regions compared to polar regions.

Reason (R):

Tropical regions receive less solar energy than polar regions, creating optimal conditions for accelerated chemical reactions.

Answer: C — A is true but R is false — The assertion is true—chemical weathering is faster in tropical climates. However, the reason is false: tropical regions receive MORE (not less) solar energy, and higher temperature and moisture (not less energy) accelerate chemical weathering. The cause-effect link is inverted.

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Case-Based Questions (CBQ) for Geomorphic Processes

Case Study:

The Western Ghats in India are a tectonically active mountain range experiencing continuous orogeny-induced uplift while simultaneously facing intense exogenic erosion from the Southwest Monsoon. Annual rainfall exceeds 250 cm in some areas. Scientists observe that despite 5 mm/year of tectonic uplift, the peak elevations haven't increased significantly over the past century. Meanwhile, in the Deccan Plateau to the east with similar rock types but only 50 cm annual rainfall, elevation changes are negligible, and weathering rates are much lower. River valleys in the Western Ghats show steep, V-shaped profiles, while Deccan rivers display broader, mature valleys.

Q1. The relatively stable peak elevations in the Western Ghats despite active uplift primarily indicate that:

  • A. Endogenic forces are stronger than exogenic forces in this region
  • B. Exogenic erosion is nearly balancing endogenic uplift, demonstrating the dynamic equilibrium between opposing forces ✓
  • C. The monsoon rainfall has decreased significantly, reducing erosion rates
  • D. The rock types in the Western Ghats are resistant to all forms of weathering

Answer: B

Q2. The difference between V-shaped valleys (Western Ghats) and broader valleys (Deccan Plateau) best reflects:

  • A. Different rock types in each region causing different erosion rates
  • B. The interaction between steep gradients maintained by active tectonics and high erosive capacity of abundant water, versus gentle gradients and lower precipitation ✓
  • C. Greater river discharge in the Deccan due to higher temperatures
  • D. Older age of the Deccan valleys compared to Western Ghat valleys

Answer: B

Q3. Why is the weathering rate significantly lower in the Deccan Plateau than the Western Ghats, despite similar geology?

  • A. Climatic differences—lower precipitation and temperature in the Deccan reduce the intensity of chemical weathering and water-driven erosion processes ✓
  • B. The Deccan Plateau experiences stronger endogenic forces that stabilize rocks
  • C. The Deccan Plateau has younger soils that weather more slowly
  • D. Geomorphic agents are absent in the Deccan Plateau region

Answer: A

Q4. If the Southwest Monsoon patterns shifted to deliver more rainfall to the Deccan Plateau while reducing Western Ghat rainfall, the most likely consequence over geological time would be:

  • A. The Deccan Plateau valleys would gradually shift from mature to V-shaped profiles as erosive capacity increases ✓
  • B. Peak elevations of the Western Ghats would increase as erosion decreases
  • C. All elevation differences between regions would disappear within 100 years
  • D. Endogenic processes would cease operating in response to climatic change

Answer: A

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