Geomorphic Processes: Weathering, Mass Movements and the Forces that Shape the Earth
It explains how opposing internal (endogenic) and external (exogenic) forces continuously build up and wear down the earth's surface, producing its uneven relief and varied landforms.
This is core physical geography that Prelims tests through definitions and classifications — endogenic vs exogenic forces, the sub-types of diastrophism, chemical vs physical weathering, and what does or doesn't count as 'erosion'. In GS-I Mains it underpins geomorphology, soil formation and landform evolution, and it feeds disaster-vulnerability answers on landslides and mass movements.
Understand the chapter
Why the Earth's Surface is Uneven: Endogenic vs Exogenic Forces
The earth's crust is dynamic, shaped by two opposing sets of forces. Endogenic (internal) forces originate within the earth and mainly build up or elevate the crust, while exogenic (external) forces, powered ultimately by the sun, wear it down. Wearing down relief is degradation and filling up basins is aggradation; the overall leveling tendency through erosion is called gradation. Because endogenic forces keep raising new relief, exogenic forces never fully even out the surface, so variations persist.
- Endogenic = land-building forces; Exogenic = land-wearing forces
- Degradation = wearing down elevations; Aggradation = filling up depressions
- Gradation = wearing down of relief through erosion
- Relief stays uneven as long as the two forces oppose each other
Geomorphic Processes and Geomorphic Agents
Geomorphic processes are the endogenic and exogenic forces that cause physical stresses and chemical actions on earth materials, changing the configuration of the surface. A geomorphic process is a force applied on earth materials; a geomorphic agent is a mobile medium — running water, glaciers, wind, waves, currents — that removes, transports and deposits material. Gravity is the master force: it drives all downslope movement and, indirectly, generates winds, waves and tidal currents. Without gravity and gradients there would be no mobility, hence no erosion, transport or deposition.
- Process = force applied; Agent = mobile transporting medium
- For exogenic action, process and agent are usually treated as the same
- Gravity plus gradients = precondition for all movement
- Movement is always high-to-low: elevation, pressure, etc.
Endogenic Processes: Diastrophism and Volcanism
Endogenic processes are powered by the earth's internal energy — radioactivity, rotational and tidal friction, and primordial heat — which drives diastrophism and volcanism. Diastrophism covers all processes that move, elevate or build up the crust, while volcanism is the movement of magma onto or toward the surface, forming intrusive and extrusive features. Orogeny, epeirogeny, earthquakes and plate tectonics all cause pressure-volume-temperature (PVT) changes that trigger metamorphism of rocks.
- Diastrophism's four: orogenic (mountain-building, folding, narrow belts), epeirogenic (uplift/warping of large areas), earthquakes (local minor), plate tectonics (horizontal)
- Orogeny = mountain building; Epeirogeny = continental building
- PVT (Pressure-Volume-Temperature) changes induce metamorphism
- Diastrophism and volcanism are endogenic geomorphic processes
Exogenic Processes and Denudation
Exogenic processes draw energy from the atmosphere — ultimately the sun — acting on gradients created by tectonic forces. Gravitational and molecular stresses (from temperature change, crystallisation, melting) develop within earth materials, and shear stresses break rocks apart. All exogenic processes are grouped under the umbrella term denudation, which means to strip off or uncover. Their intensity depends on climate (temperature and precipitation) and on the type and structure of the rocks involved.
- Denudation = weathering + mass wasting + erosion + transportation
- Ultimate driving force of all exogenic processes = the sun
- Stress = force per unit area; shear stress breaks rocks
- A rock may resist one process but yield to another, giving differential topography
Weathering and its Three Types
Weathering is the mechanical disintegration and chemical decomposition of rocks by the elements of weather and climate. It is an in-situ (on-site) process — there is little or no movement of material, which is precisely why weathering is not transportation. Climate is the most important control, governing both the type of weathering and the depth of the weathering mantle. The three groups — chemical, physical/mechanical and biological — rarely act alone, though one usually dominates.
- Chemical: solution, carbonation, hydration, oxidation, reduction
- Physical: driven mainly by thermal expansion and pressure release (overburden, crystal growth, wetting-drying)
- Biological: burrowing organisms, plant roots, decaying matter producing acids
- Exfoliation is a result, not a process — domes from unloading, tors from thermal expansion
Significance of Weathering: Soils, Ores and Enrichment
Weathering breaks rock into fragments, preparing the regolith and soil and making erosion and mass movements possible — erosion cannot be significant unless rocks are first weathered. Biomes and biodiversity ultimately depend on vegetation, which in turn depends on the depth of the weathering mantle. Weathering also concentrates valuable ores: as soluble material is leached away by groundwater, the remaining valuable minerals are enriched. This enrichment is what makes deposits of iron, manganese, aluminium and copper economically viable.
- Weathering leads to regolith and soil formation
- Enrichment: leaching removes solubles, concentrating ores of Fe, Mn, Al, Cu
- Weathering-mantle depth controls forests, hence biomes and biodiversity
- Weathering aids (precedes) erosion and mass wasting
Mass Movements: Gravity Alone, Not Erosion
Mass movements transfer rock debris down slopes under the direct influence of gravity alone. No geomorphic agent — running water, glaciers, wind, waves or currents — carries the debris; instead the debris may carry air, water or ice with it. For this reason mass movements are NOT classified as erosion. They are most active over weathered slopes, but weathering is not a prerequisite, since gravity acts on bedrock too.
- Types: creep, flow, slide, fall (slow to rapid)
- Driven by gravity only — no transporting agent involved
- Not erosion, because no geomorphic agent participates
- Weathering aids but is not required for mass movement
Key terms
- Geomorphic process
- An endogenic or exogenic force causing physical stress and chemical action that changes the earth's surface configuration.
- Geomorphic agent
- A mobile medium (running water, ice, wind, waves, currents) that removes, transports and deposits earth materials.
- Endogenic forces
- Internal earth forces that mainly build up or elevate the crust.
- Exogenic forces
- External, sun-powered forces that mainly wear down the crust.
- Gradation
- Wearing down of surface relief through erosion; comprises degradation and aggradation.
- Diastrophism
- All endogenic processes that move, elevate or build up parts of the crust (orogeny, epeirogeny, earthquakes, plate tectonics).
- Denudation
- Umbrella term for all exogenic processes — weathering, mass wasting, erosion, transportation; literally to strip off.
- Weathering
- In-situ mechanical disintegration and chemical decomposition of rocks by weather and climate.
- Exfoliation
- Flaking off of curved rock sheets giving smooth, rounded surfaces; a result, not a process.
- Enrichment
- Concentration of valuable ore as weathering and leaching remove surrounding soluble material.
Must-know facts exam-ready
- Endogenic forces are land-building; exogenic forces are land-wearing.
- Endogenic energy comes from radioactivity, rotational and tidal friction, and primordial heat.
- Diastrophism and volcanism are the two endogenic geomorphic processes.
- Weathering, mass wasting, erosion and deposition are the exogenic geomorphic processes.
- Diastrophism's four components: orogenic, epeirogenic, earthquakes, plate tectonics.
- Orogeny = mountain building (folding, narrow belts); Epeirogeny = continental building (uplift/warping of large areas).
- PVT (Pressure-Volume-Temperature) changes induce metamorphism of rocks.
- Denudation = weathering + mass wasting + erosion + transportation; 'denude' means to strip off.
- The sun is the ultimate driving force of all exogenic processes.
- Weathering is an in-situ process — mechanical disintegration plus chemical decomposition.
- Chemical weathering processes: solution, carbonation, hydration, oxidation, reduction.
- Mass movements act under gravity alone and are NOT erosion; types are creep, flow, slide, fall.
Memory tricks remember it for good
Traps to avoid
- Weathering is in-situ — the slight movement it causes is NOT transportation; erosion (which transports material) is a separate process.
- Mass movements are NOT erosion: only gravity acts, with no geomorphic agent (water/ice/wind) carrying the debris.
- Weathering is not a prerequisite for mass movement (gravity acts on bedrock too) — it only aids and accelerates it.
- Orogeny (mountain building, folding, narrow belts) vs Epeirogeny (continental building, uplift/warping of large areas) — don't swap the two.
- Exfoliation is a RESULT, not a process; exfoliation domes come from unloading, while tors come from thermal expansion.
- Exogenic energy is ultimately solar (plus gravity and tectonic gradients), not internal heat — only endogenic processes use the earth's internal energy.
Exam focus
🧠 Prelims angles
- Classifying processes as endogenic (diastrophism, volcanism) vs exogenic (weathering, mass wasting, erosion, deposition).
- Match-the-column on chemical weathering: solution, carbonation, hydration, oxidation, reduction.
- Sub-types of diastrophism and the orogeny-vs-epeirogeny distinction.
- Definitions: denudation, gradation, degradation, aggradation, weathering, enrichment.
- Statement-based questions: mass movements involve gravity alone and are not erosion.
- PVT changes leading to metamorphism, and the sources of endogenic energy.
✍️ Mains angles GS-I
- Examine how the interplay of endogenic and exogenic forces shapes the earth's surface.Contrast endogenic building (diastrophism, volcanism) with exogenic wearing (denudation); relief persists because both act continuously and oppose each other.
- Weathering is the foundation of soils and economic mineral wealth — discuss.Link weathering to regolith/soil formation, ore enrichment (Fe, Mn, Al, Cu) via leaching, and biodiversity through weathering-mantle depth.
- Distinguish mass movements from erosion and relate them to landslide vulnerability.Gravity-only with no transporting agent means it is not erosion; weathered slopes are most prone — bridge to GS-III disaster management.
Last-minute revision tick as you recall
- Endogenic = build, Exogenic = wear; relief persists as both keep fighting.
- Gradation = degradation (wear relief) + aggradation (fill basins).
- Endogenic geomorphic processes = diastrophism + volcanism; energy = radioactivity + tidal/rotational friction + primordial heat.
- Diastrophism four: orogeny, epeirogeny, earthquakes, plate tectonics; PVT changes cause metamorphism.
- Orogeny = mountains/folds; Epeirogeny = continents/uplift.
- Exogenic energy = sun; umbrella term = denudation = weathering + mass wasting + erosion + transportation.
- Weathering = in-situ; chemical (SCHOR) + physical (thermal/pressure) + biological.
- Exfoliation = result not process; domes from unloading, tors from thermal expansion.
- Mass movement = gravity only, NOT erosion; creep, flow, slide, fall.
Distilled from NCERT Class 11 · Fundamentals of Physical Geography for UPSC. Always cross-check facts with the original NCERT.