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Chapter 9: Geomorphic Processes
Chapter Test10 topics•Estimated reading: 30 minutes
Geomorphic Processes (Expanded)
Key Point
Geomorphic processes are natural forces that shape Earth's landforms through the combined action of internal (endogenic) and external (exogenic) forces. Endogenic forces uplift, fold, fault, and create relief, while exogenic forces erode, transport, and deposit materials, constantly modifying the surface.
Geomorphic processes are natural forces that shape Earth's landforms through the combined action of internal (endogenic) and external (exogenic) forces. Endogenic forces uplift, fold, fault, and create relief, while exogenic forces erode, transport, and deposit materials, constantly modifying the surface.
Detailed Notes (44 points)
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Definition
Endogenic and exogenic forces apply stress and chemical action on Earth's crust, reshaping relief features over time.
Geomorphic Agents
Running water, glaciers, wind, groundwater, ocean currents, waves, and even human activity.
Endogenic Forces
# Nature
Originate from within Earth due to thermal and radioactive energy, mantle convection, and tectonic plate movements.
Cause large-scale landform creation and restructuring.
# Types of Movements
1. **Sudden Forces (Catastrophic):**
- Rapid, unpredictable.
- Examples: earthquakes, tsunamis, volcanic eruptions.
- Create cones, lava plateaus, fault scarps.
2. **Diastrophic Forces (Slow, Long-term):**
- Responsible for large structural features of continents.
- Two categories:
**Epeirogenic (Vertical Movements):**
- Broad, gentle uplift or subsidence of continental masses.
- Example: Rise of the Deccan Plateau, African Plateau.
**Orogenic (Horizontal Movements):**
- Compression, tension, and lateral movements leading to folding and faulting.
- Example: Himalayas (folding), Great Rift Valley of Africa (faulting).
Exogenic Forces
# Nature
Operate on Earth's surface, driven by external factors such as solar energy, wind, rainfall, ice, and gravity.
Tend to wear down relief created by endogenic forces.
# Types of Processes
1. **Weathering:**
- Mechanical (disintegration, frost action, exfoliation).
- Chemical (oxidation, carbonation, hydration).
- Biological (plants, animals, humans).
2. **Mass Wasting:**
- Downslope movement of weathered material due to gravity.
- Examples: landslides, rockfalls, soil creep, debris flow, avalanches.
3. **Erosion and Transportation:**
- Performed by geomorphic agents like rivers, glaciers, wind, and waves.
- Agents erode materials, transport them, and deposit elsewhere.
4. **Deposition:**
- Process of laying down eroded material.
- Creates features like flood plains, deltas, moraines, loess plains, sand dunes, beaches.
Balance of Forces
Endogenic forces = constructive, uplifting and building landforms.
Exogenic forces = destructive, leveling, and denuding landforms.
Together, they maintain Earth's dynamic equilibrium and geomorphic cycle.
Comparison of Endogenic and Exogenic Processes
| Aspect | Endogenic Processes | Exogenic Processes |
|---|---|---|
| Origin | Internal (within Earth) | External (climate, atmosphere) |
| Forces | Thermal, tectonic, radioactive | Solar energy, weather, gravity |
| Nature | Constructive (build landforms) | Destructive (erode/denude landforms) |
| Examples | Volcanoes, earthquakes, mountains, faults | Rivers, glaciers, wind, waves |
| Rate | Sudden (quakes) or long-term (folds) | Slow, continuous (weathering, erosion) |
Mains Key Points
Endogenic processes are constructive; exogenic are destructive, but both work together.
Sudden forces create short-term dramatic changes; diastrophic forces reshape continents over millions of years.
Exogenic processes gradually modify relief into peneplains if unchecked by uplift.
Dynamic balance between uplift and denudation explains geomorphic cycle (Davisian model).
Study of geomorphic processes is crucial for hazard management (earthquakes, landslides, floods) and resource planning.
Prelims Strategy Tips
Epeirogenic = vertical uplift/subsidence; Orogenic = folding/faulting.
Sudden forces: volcanoes & earthquakes → constructive in nature.
Exogenic agents: rivers, glaciers, wind, ocean currents, groundwater.
Weathering vs Mass wasting: Weathering = in-situ disintegration, Mass wasting = downslope movement.
Tectonic Landforms: Folds and Faults
Key Point
Folds and faults are tectonic landforms created by endogenic forces due to plate movements. Folds result from compressional forces causing rocks to bend, while faults occur due to tension or compression leading to cracks and displacement of rock strata.
Folds and faults are tectonic landforms created by endogenic forces due to plate movements. Folds result from compressional forces causing rocks to bend, while faults occur due to tension or compression leading to cracks and displacement of rock strata.
Detailed Notes (39 points)
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Folds
# Definition:
Wavy undulations formed when crustal rocks are subjected to compressional forces from horizontal tectonic plate movements.
# Parts of a Fold:
**Anticline:** Up-folded rock strata forming an arch-like structure.
**Syncline:** Down-folded rock strata resembling a trough.
**Limbs:** Two sides of the fold, dipping away or towards the axis.
**Axial Plane:** Plane bisecting the angle between limbs.
**Axis:** Line formed by intersection of axial plane with rock bed surface.
**Dip:** Angle of inclination of strata with the horizontal plane.
**Strike:** Line of intersection between a horizontal plane and an inclined rock bed.
# Types of Folds:
1. **Symmetrical Fold:** Limbs dip equally away from the axis.
2. **Asymmetrical Fold:** One limb steeper than the other.
3. **Overturned Fold:** One limb tilted beyond the vertical plane.
4. **Recumbent Fold:** Axial plane almost horizontal, both limbs parallel.
5. **Isoclinal Fold:** Both limbs parallel and dipping in the same direction.
6. **Monocline:** One limb nearly horizontal, the other steeply inclined.
# Importance of Folds:
Associated with mountain building (e.g., Himalayas, Alps).
Trap oil, natural gas, and groundwater in anticlines and synclines.
Indicate compressional tectonic settings.
Faults
# Definition:
Faults are fractures in the Earth’s crust along which displacement of rock strata has occurred due to tectonic forces.
# Components of a Fault:
**Fault Plane:** Surface along which displacement occurs.
**Fault Line:** Intersection of fault plane with Earth's surface.
**Hanging Wall:** Block above the fault plane.
**Footwall:** Block below the fault plane.
# Types of Faults:
1. **Normal Fault:** Formed due to tensional forces; hanging wall moves downward relative to footwall. (Example: Rift Valley of East Africa).
2. **Reverse Fault (Thrust Fault):** Formed due to compressional forces; hanging wall moves upward relative to footwall.
3. **Strike-Slip Fault:** Horizontal displacement along fault plane caused by shearing forces (Example: San Andreas Fault, California).
4. **Horst and Graben Structures:** Raised block (Horst) and depressed block (Graben) formed due to parallel normal faults.
# Significance of Faults:
Responsible for earthquakes.
Create features like rift valleys, block mountains, escarpments.
Control drainage patterns and mineral localization.
Comparison of Folds and Faults
| Aspect | Folds | Faults |
|---|---|---|
| Definition | Bending of rock strata under compression | Fracture with displacement due to stress |
| Forces | Mainly compressional | Tensional, compressional, or shear forces |
| Resulting Landforms | Fold mountains, anticlines, synclines | Rift valleys, block mountains, fault scarps |
| Example | Himalayas (fold mountains) | San Andreas Fault (California), East African Rift Valley |
Mains Key Points
Folds and faults are fundamental tectonic landforms reflecting compressional and tensional regimes.
Folding results in orogeny and hydrocarbon traps; faulting leads to rift valleys, horsts, grabens, and seismicity.
Both processes showcase crustal deformation and plate tectonics in action.
Analysis of folds and faults provides insight into structural geology, natural resources, and hazards.
Prelims Strategy Tips
Anticline = arch, Syncline = trough.
Normal fault = tension; Reverse fault = compression; Strike-slip = shear.
Hanging wall vs Footwall is key for fault identification.
Folds trap hydrocarbons, faults often host earthquakes.
Types of Folds
Key Point
Folds are bends in rock strata caused by compressional tectonic forces. Their type depends on rock nature, pressure intensity, and direction of stress. They are classified based on axial plane orientation, limb inclination, and degree of compressional force.
Folds are bends in rock strata caused by compressional tectonic forces. Their type depends on rock nature, pressure intensity, and direction of stress. They are classified based on axial plane orientation, limb inclination, and degree of compressional force.
Detailed Notes (41 points)
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Factors affecting Fold Formation:
The nature of the rock (ductile rocks fold more easily than brittle ones).
The intensity and duration of compressional force.
Temperature and depth (higher temperature and depth make rocks more pliable).
Presence of fluids within rock pores.
Types of Folds:
# Symmetrical Fold:
Axial plane is vertical, both limbs dip equally in opposite directions.
Formed when compressional forces act regularly with moderate intensity.
# Asymmetrical Fold:
Axial plane is inclined, limbs dip in opposite directions with unequal angles.
One limb steeper and shorter, the other gentler and longer.
# Overturned Fold:
Axial plane inclined, both limbs dip in the same direction at different angles.
# Isoclinal Fold:
Both limbs dip at equal angles in the same direction, nearly parallel.
Indicates very strong compressional force.
# Recumbent Fold:
Axial plane nearly horizontal, limbs parallel and horizontal.
Found commonly in the Alps, indicating intense compression.
# Chevron Fold:
Folds with sharp, angular crests and troughs.
Common in resistant rock strata.
# Fan Fold:
Limbs overturned so much that the fold looks like a fan.
# Open Fold:
Angle between limbs 90°–180°.
Rock beds retain equal thickness throughout.
Formed by moderate compression.
# Closed Fold:
Angle between limbs less than 90°.
Limbs thinner, crests and troughs thicker.
Formed by high compression.
# Nappe:
Formed from recumbent folds subjected to further compression.
One limb slides over the other due to intense horizontal force.
Common in the Alps.
# Anticlinorium:
Large anticline containing several minor anticlines and synclines within it.
# Synclinorium:
Large syncline containing several minor anticlines and synclines within it.
Types of Folds – Summary
| Type | Characteristics | Formation |
|---|---|---|
| Symmetrical Fold | Vertical axial plane; equal limb dip | Moderate uniform compression |
| Asymmetrical Fold | Inclined axial plane; unequal limb dip | Unequal compressional force |
| Overturned Fold | Both limbs dip same direction at different angles | Strong inclined compression |
| Isoclinal Fold | Parallel limbs dip same direction | Very strong compression |
| Recumbent Fold | Horizontal axial plane; limbs parallel | Extreme compression (Alps) |
| Chevron | Sharp angular crests and troughs | Strong stress on resistant rocks |
| Fan Fold | Limbs overturned like fan | Excessive compression |
| Open Fold | Limb angle 90°–180° | Moderate compression |
| Closed Fold | Limb angle < 90°; thick crests | Intensive compression |
| Nappe | One limb overrides the other | Intense horizontal pressure |
| Anticlinorium | Series of small folds in a large anticline | Continued compression |
| Synclinorium | Series of small folds in a large syncline | Continued compression |
Mains Key Points
Fold types reflect tectonic stress intensity and rock ductility.
Simple folds like symmetrical, asymmetrical indicate moderate stress; complex folds like nappes, recumbent reflect extreme tectonic forces.
Nappes and recumbent folds play key role in alpine orogeny.
Folds influence groundwater, petroleum traps, and mountain structure.
Prelims Strategy Tips
Symmetrical = equal dip; Asymmetrical = unequal dip.
Overturned = both limbs dip same direction.
Recumbent and Nappe folds common in Alps.
Chevron = angular; Fan = looks like a fan.
Open fold (>90°) vs Closed fold (<90°).
Faults
Key Point
Faults are fractures in the Earth's crust where displacement of rock blocks has occurred due to tectonic forces. They can be vertical, horizontal, or inclined, and are classified into types such as normal, reverse, and strike-slip faults, each shaping major geomorphic landforms like rift valleys, horsts, and escarpments.
Faults are fractures in the Earth's crust where displacement of rock blocks has occurred due to tectonic forces. They can be vertical, horizontal, or inclined, and are classified into types such as normal, reverse, and strike-slip faults, each shaping major geomorphic landforms like rift valleys, horsts, and escarpments.
Detailed Notes (34 points)
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Definition:
A fracture or crack in the Earth's crust along which displacement of rock blocks occurs.
Caused by tensional, compressional, vertical, or horizontal tectonic forces.
Anatomy of a Fault:
**Fault Plane:** Surface along which displacement occurs; can be vertical, inclined, or horizontal.
**Fault Dip:** Angle between fault plane and horizontal plane.
**Hade:** Angle between fault plane and vertical plane.
**Upthrow Side:** Block displaced upward relative to the other.
**Downthrow Side:** Block displaced downward relative to the other.
**Hanging Wall:** Rock block above the fault plane.
**Footwall:** Rock block below the fault plane.
**Fault Line:** Line where fault intersects Earth's surface.
**Fault Zone:** Area with multiple small fractures when displacement is distributed.
Types of Faults:
# 1. Normal Faults:
Formed due to tensional forces pulling the crust apart.
One block slips down relative to the other, forming steep fault scarps.
Landforms:
- **Graben (Rift Valley):** Sunken block between two normal faults. Example: East African Rift Valley.
- **Horst:** Raised block between two normal faults, flat-topped with steep sides.
# 2. Reverse Faults:
Caused by compressional forces pushing blocks toward each other.
Hanging wall moves upward relative to footwall.
Results in overthrusting, forming thrust faults at shallow angles.
# 3. Strike-Slip Faults:
Rocks slide past one another horizontally, parallel to the strike.
Can be right-lateral (dextral) or left-lateral (sinistral).
**Transform Faults:** Special strike-slip faults forming plate boundaries.
- Example: San Andreas Fault (between Pacific & North American plates).
Significance of Faults:
Control earthquake activity (major seismic zones align with fault systems).
Influence drainage and river courses (fault-guided valleys).
Associated with mineralization zones (ores often concentrated in fault planes).
Create spectacular landforms like rift valleys, block mountains, and escarpments.
Comparison of Fault Types
| Type | Forces | Movement | Example |
|---|---|---|---|
| Normal Fault | Tension (pull-apart) | Hanging wall moves down | East African Rift Valley |
| Reverse Fault | Compression (push-together) | Hanging wall moves up | Himalayan thrust faults |
| Strike-Slip Fault | Shearing (horizontal sliding) | Blocks move sideways | San Andreas Fault, USA |
Mains Key Points
Faults represent brittle deformation in the crust under tectonic stress.
Normal faults produce rift valleys and block mountains, reverse faults create overthrust structures, and strike-slip faults form transform boundaries.
Faulting is directly linked to seismic activity and structural landform development.
Understanding faults is crucial for earthquake hazard assessment and resource exploration.
Prelims Strategy Tips
Normal = tension → hanging wall down.
Reverse = compression → hanging wall up.
Strike-slip = shearing → sideways movement.
Horst = uplifted block; Graben = sunken block.
San Andreas = transform fault (strike-slip).
Exogenic Processes
Key Point
Exogenic processes are destructive processes that wear down Earth's surface, collectively called denudation. Powered by solar energy, they include weathering, mass wasting, erosion, and transportation, driven by agents like rivers, wind, glaciers, and waves.
Exogenic processes are destructive processes that wear down Earth's surface, collectively called denudation. Powered by solar energy, they include weathering, mass wasting, erosion, and transportation, driven by agents like rivers, wind, glaciers, and waves.
Detailed Notes (39 points)
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Definition:
Exogenic processes are external forces acting on Earth's surface, leading to its degradation.
They result in lowering and leveling of landmasses through denudation.
Sources of Energy:
Solar energy – causes temperature variations, weather patterns, winds, rainfall.
Gravity – helps in downslope movement of material and water.
Major Processes:
**Weathering:** Mechanical, chemical, and biological breakdown of rocks in situ.
**Mass Movement:** Downslope movement of rock/soil under gravity (landslides, soil creep).
**Erosion:** Wearing away of Earth's surface by agents (water, wind, glaciers, waves).
**Transportation:** Movement of weathered material by geomorphic agents.
Driving Agents:
Running water (rivers, streams).
Groundwater.
Glaciers.
Ocean waves and currents.
Wind (in arid regions).
Factors Affecting Exogenic Processes:
# 1. Climate:
Temperature and precipitation are key controls.
Intensity, amount, and type of precipitation influence erosion and mass wasting.
Evaporation–precipitation balance impacts soil moisture and weathering.
Wind velocity and direction affect erosion (e.g., dunes, deflation).
Freezing and thawing frequency impacts frost weathering.
Depth of frost penetration alters geomorphic activity in cold regions.
# 2. Vegetation:
Dense vegetation reduces erosion by stabilizing soil.
Sparse vegetation in deserts and semi-arid regions enhances wind/water erosion.
# 3. Aspect and Insolation:
North-facing vs south-facing slopes receive different insolation, influencing snowmelt, vegetation, and weathering rates.
East–west slopes show seasonal variation in solar heating.
# 4. Lithology (Rock Type and Structure):
Hard rocks (granite, basalt) resist weathering.
Soft rocks (limestone, shale) weather and erode more quickly.
Rock joints, faults, and bedding planes provide pathways for weathering and erosion.
Overall Impact:
Continuous wearing down of landforms.
Creation of plains, valleys, pediments, and basins.
Balances endogenic processes (mountain building) by leveling land surfaces.
Exogenic Processes and Their Characteristics
| Process | Description | Agent |
|---|---|---|
| Weathering | Breakdown of rocks in situ | Temperature, water, biological factors |
| Mass Movement | Downslope movement under gravity | Gravity, water saturation |
| Erosion | Wearing away of rock surface | Rivers, wind, glaciers, waves |
| Transportation | Movement of eroded material | Rivers, glaciers, wind, waves |
Mains Key Points
Exogenic processes balance endogenic mountain-building by lowering relief.
Climate and lithology together dictate landscape evolution.
Exogenic agents shape valleys, plains, coasts, deserts, and karst landscapes.
They are key in soil formation, sediment cycles, and earth system balance.
Prelims Strategy Tips
Exogenic = Sun-driven processes (denudation).
Main components: Weathering, mass wasting, erosion, transportation.
Climate (temp + rainfall) = key controller.
Vegetation and lithology influence intensity of processes.
Weathering – Physical / Mechanical Weathering
Key Point
Physical weathering is the breakdown of rocks into smaller fragments without any change in chemical composition. Dominant in arid, cold, and high-altitude regions due to temperature variation, frost action, and pressure release.
Physical weathering is the breakdown of rocks into smaller fragments without any change in chemical composition. Dominant in arid, cold, and high-altitude regions due to temperature variation, frost action, and pressure release.
Detailed Notes (23 points)
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Definition
Primary stage of denudation: rocks break, disintegrate or decompose in situ.
Physical disintegration without chemical alteration.
Provides raw material for erosion and soil formation.
Processes of Mechanical Weathering
# Frost Shattering (Freeze–Thaw)
Water seeps into cracks → freezes → expands by 9% → pressure breaks rock.
Dominant in temperate and glacial regions (Himalayas, Alps).
# Unloading / Exfoliation
Pressure release due to erosion of overlying rocks.
Rock expands, peels in onion-skin layers → exfoliation domes.
Examples: Sierra Nevada (USA), Mahabaleshwar (India).
# Insolation Weathering
Rocks expand by day, contract by night → cracks form.
Strong in deserts with high diurnal range (Sahara, Thar).
# Salt Weathering (Haloclasty)
Saline water enters rock pores → evaporates → salt crystals grow.
Crystal growth exerts stress → honeycomb structures.
Examples: Red Sea coasts, Rann of Kutch.
# Other Types
Granular disintegration: unequal heating of minerals.
Block disintegration: alternate heating & cooling.
Pressure release joints: granite expansion.
Processes of Physical Weathering
| Process | Description | Examples |
|---|---|---|
| Frost Shattering | Water freezes in cracks, expands and breaks rock | Himalayas, Alps |
| Unloading / Exfoliation | Pressure release forms sheet joints and domes | Sierra Nevada, Mahabaleshwar |
| Insolation Weathering | Expansion & contraction due to temperature change | Sahara, Thar |
| Salt Weathering | Salt crystals grow in pores, exert pressure | Red Sea coast, Rann of Kutch |
Mains Key Points
Mechanical weathering provides raw materials for erosion and soil formation.
Important in shaping arid & mountain landscapes.
Often works together with chemical weathering.
Exfoliation domes, tors, block disintegration are classic case studies.
Helps explain structural weaknesses in monuments and engineering projects.
Prelims Strategy Tips
Weathering occurs in situ, erosion involves movement.
Frost shattering dominates in cold/temperate regions.
Exfoliation domes linked with granite pressure release.
Salt weathering is common in deserts & coasts.
Chemical and Biological Weathering
Key Point
Chemical weathering alters the internal structure of minerals through reactions with water, oxygen, carbon dioxide, and acids. Biological weathering involves plants, animals, and human activities that physically or chemically break down rocks.
Chemical weathering alters the internal structure of minerals through reactions with water, oxygen, carbon dioxide, and acids. Biological weathering involves plants, animals, and human activities that physically or chemically break down rocks.
Detailed Notes (35 points)
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Definition – Chemical Weathering
Decomposition of rocks forming new chemically different materials.
Alters internal molecular structure of minerals through reactions.
Agents: Oxygen, CO2, other gases, rain and snow water.
Processes of Chemical Weathering
# Oxidation
Reaction of oxygen with minerals forming oxides and hydroxides.
Weakens rocks by fragmentation.
Common in iron, manganese, sulfur minerals.
# Reduction
Opposite of oxidation, occurs without oxygen (below water table).
Alters stability of minerals, often in swampy conditions.
# Solution
Rock materials dissolve in acids or water, forming solutions.
Affects soluble minerals like nitrates, potassium, and sulfates.
Common in limestone and gypsum areas.
# Carbonation
Carbon dioxide + water → carbonic acid.
Reacts with carbonates forming bicarbonates (soluble).
Creates features like karst topography, caves, sinkholes.
# Hydration
Chemical addition of water molecules into minerals.
Causes expansion, stress, and disintegration.
Common in minerals like anhydrite turning into gypsum.
Biological Weathering
Weathering caused by plants, animals, and human activities.
# Role of Plants
Roots penetrate cracks → wedge effect, breaking rocks mechanically.
Roots excrete organic acids → dissolve minerals chemically.
# Role of Animals
Burrowing animals (rabbits, rodents, termites) break rocks mechanically.
Microbes and lichens secrete acids that enhance chemical weathering.
# Role of Humans (Anthropogenic Weathering)
Mining, quarrying, deforestation, construction accelerate weathering.
Combines both physical disintegration and chemical alteration.
Processes of Chemical Weathering
| Process | Description | Example |
|---|---|---|
| Oxidation | Minerals react with oxygen → oxides & hydroxides | Rusting of iron-bearing rocks |
| Reduction | Occurs without oxygen, reverses oxidation | Swampy alluvial plains |
| Solution | Minerals dissolve in acids/water | Limestone caves |
| Carbonation | Carbonic acid reacts with carbonates | Karst topography |
| Hydration | Water added to minerals, expansion & cracking | Gypsum formation |
Mains Key Points
Chemical weathering plays a key role in soil fertility and mineral cycling.
Most effective in tropical, humid climates with abundant rainfall.
Carbonation and solution processes are critical in Karst landform development.
Biological weathering links ecology with geomorphology.
Human-induced weathering accelerates landscape changes and environmental degradation.
Prelims Strategy Tips
Chemical weathering dominates in hot & humid climates.
Karst landforms (caves, sinkholes) are linked to carbonation.
Hydration expands minerals → physical disintegration.
Biological weathering can be both mechanical & chemical.
Mass Movements
Key Point
Mass movements involve the downslope transfer of rock, soil, and debris solely under the influence of gravity. Unlike erosion, they are not driven by external geomorphic agents such as rivers, glaciers, or wind. They are common in unstable slopes with weak materials, heavy rainfall, or sparse vegetation.
Mass movements involve the downslope transfer of rock, soil, and debris solely under the influence of gravity. Unlike erosion, they are not driven by external geomorphic agents such as rivers, glaciers, or wind. They are common in unstable slopes with weak materials, heavy rainfall, or sparse vegetation.
Detailed Notes (20 points)
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Definition
Downhill movement of soil, rock, and debris under direct gravitational pull.
Independent of geomorphic agents like water, ice, or wind.
Common in regions with unconsolidated sediments, thinly bedded rocks, faults, heavy rainfall, and sparse vegetation.
Weathering aids mass movement but is not a prerequisite.
Modes of Mass Movement
# Slide
Downslope movement occurs along a well-defined shear plane.
The maximum motion is at the base of the moving mass.
A visible plane separates the mobile upper mass and the stable lower mass.
Slides can occur in dry conditions, but water increases speed and instability.
# Flow
The moving material behaves like a fluid.
Maximum movement at the top, gradually reducing towards the shear plane.
Water saturation enhances flow movement.
Includes earthflows, mudflows, and debris flows.
# Heave
Very slow, almost imperceptible movement.
Involves particles ranging from clay to large boulders.
Often caused by repeated cycles of wetting-drying, freezing-thawing, or soil creep.
Modes of Mass Movements
| Mode | Description | Examples |
|---|---|---|
| Slide | Movement along a shear plane with maximum motion at the base | Landslides in Himalayas |
| Flow | Material behaves like fluid; water saturation enhances flow | Debris flows in Western Ghats |
| Heave | Very slow movement caused by freeze-thaw or wetting-drying cycles | Soil creep in temperate regions |
Mains Key Points
Mass movements reshape slopes and contribute to rapid landscape changes.
They pose hazards to human settlements, roads, and infrastructure in hilly regions.
Water saturation is a key trigger for landslides and debris flows.
Deforestation, construction, and mining accelerate mass movement risks.
Important geomorphic process in mountains like Himalayas, Andes, Rockies.
Prelims Strategy Tips
Mass movement is driven only by gravity, not external agents.
Water plays a critical role in both slides and flows.
Soil creep (heave) is the slowest type of mass movement.
Common in regions with steep slopes and weak geology.
Types of Mass Movements
Key Point
Mass movements are downslope movements of soil, debris, or rock under gravity. They range from very slow (soil creep) to rapid and destructive events (landslides, avalanches).
Mass movements are downslope movements of soil, debris, or rock under gravity. They range from very slow (soil creep) to rapid and destructive events (landslides, avalanches).
Detailed Notes (29 points)
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Solifluction
Downslope flow of water-saturated soil mass.
Occurs in cold climates with permafrost or frozen ground.
Produces gentle, terrace-like surface features.
Very slow compared to other movements.
Soil Creep
Slowest type of mass movement, almost imperceptible.
Affects slopes covered with loose, weathered material.
Evidenced by tilted trees, leaning fences, and cracked walls.
Mudflow
Extremely rapid flow of water-saturated fine materials.
Occurs on a large scale, typically in valleys.
Triggered by heavy rainfall or volcanic eruptions (lahars).
Absence of vegetation increases risk.
Earth Flow
Localized downslope movement of saturated soil and debris.
Slower than mudflows, confined to smaller areas.
Landslides
Sudden, rapid downslope movement of rock, debris, or soil.
Common in steep, unconsolidated slopes.
Triggered by earthquakes, heavy rainfall, or human activities (quarrying, railway construction).
Form distinct scars and may block rivers forming temporary lakes.
Liquefaction
Occurs when water-saturated sediments temporarily lose strength during earthquakes.
Ground behaves like a liquid, causing buildings and structures to sink or tilt.
Avalanches
Swift movement of snow, rock, ice, and debris down a mountain slope.
Triggered by slope instability, heavy snowfall, or seismic activity.
Extremely destructive and hazardous in mountainous regions.
Comparison of Major Mass Movements
| Type | Speed | Material Involved | Trigger |
|---|---|---|---|
| Solifluction | Very Slow | Water-saturated soil | Permafrost thawing |
| Soil Creep | Extremely Slow | Loose weathered soil | Gravity + freeze-thaw |
| Mudflow | Very Rapid | Mud, silt, water | Heavy rainfall, volcano |
| Earth Flow | Moderate | Soil and debris | Rainfall, localized saturation |
| Landslide | Sudden & Fast | Rock, soil, debris | Rainfall, earthquake, human activity |
| Liquefaction | Instantaneous | Saturated sediments | Earthquake shaking |
| Avalanche | Extremely Fast | Snow, ice, rock | Snowfall, slope instability, tremors |
Mains Key Points
Mass movements reshape landscapes and pose risks to infrastructure.
Human activities like deforestation, quarrying, and road-building amplify risks.
Different mass movements vary in speed, triggers, and destructive potential.
Climate change increases frequency of avalanches and landslides in mountain regions.
Mitigation measures: slope stabilization, afforestation, early warning systems.
Prelims Strategy Tips
Soil creep is the slowest form of mass movement.
Mudflows are associated with valleys and volcanic regions (lahars).
Liquefaction is common in earthquake-prone, water-saturated sediments.
Avalanches are mass movements of snow, ice, and rock down slopes.
Comparison – Weathering, Erosion and Mass Movement
Key Point
Weathering is the breakdown of rocks in place, erosion is the wearing away and transportation of materials by agents, and mass movement is the downslope motion of debris solely under gravity.
Weathering is the breakdown of rocks in place, erosion is the wearing away and transportation of materials by agents, and mass movement is the downslope motion of debris solely under gravity.
Comparison of Weathering, Erosion and Mass Movement
| Aspect | Weathering | Erosion | Mass Movement |
|---|---|---|---|
| Definition | Breaking up or decomposing of rocks by water, air, chemicals, plants, or animals. | Earth materials worn away and transported by wind, water, ice, etc. | Transfer of rock and debris downslope solely under gravity. |
| Material Displacement | Rocks break but remain in place. | Broken materials are displaced by natural agents. | Rocks and debris move downslope without agents like wind/water. |
| Types | Physical, chemical, and biological weathering. | Soil erosion, coastal erosion, glacial erosion, etc. | Slow and rapid movements (soil creep, landslides, avalanches). |
| Causes | Atmospheric factors like rainfall, frost, air pressure, temperature changes. | Agents include water, wind, ice, human activities. | Caused entirely by gravity, though aided by rainfall or earthquakes. |
Mains Key Points
Weathering provides raw materials (soil, sediments) for erosion and mass movements.
Erosion shapes landforms by removing and transporting materials to new places.
Mass movements are the most hazardous, often sudden and destructive.
These processes are interlinked in landscape evolution: weathering → erosion → mass movement → deposition.
Understanding differences helps in hazard mitigation, soil conservation, and geomorphology studies.
Prelims Strategy Tips
Weathering = breakdown in place, no displacement.
Erosion = removal and transport by external agents.
Mass movement = downslope motion due to gravity.
Mass movement differs as it does not need agents like wind or water.
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