Class 11 Geography Notes Chapter 6 (Geomorphic processes) – Fundamental of Physical Geography Book

Detailed Notes with MCQs of a crucial chapter for understanding how the Earth's surface gets its shape – Chapter 6: Geomorphic Processes. This is fundamental for physical geography and frequently tested in government exams. Pay close attention to the definitions and classifications.

Chapter 6: Geomorphic Processes - Detailed Notes

1. Introduction

• Geomorphology: The study of landforms, their evolution, and the processes that shape them.
• Geomorphic Processes: The physical and chemical interactions between Earth's materials and the natural forces acting upon them, resulting in changes to the configuration of the Earth's surface.
• The Earth's crust is dynamic, constantly undergoing changes due to forces originating both from within (endogenic) and outside (exogenic) the Earth.

2. Geomorphic Agents

• These are the mobile mediums (like running water, moving ice, wind, waves, currents, groundwater) which remove, transport, and deposit earth materials.
• Gravity is a directional force activating downslope movement and stressing earth materials. Indirect gravitational stresses activate waves and tides.
• Without agents and gravity, there would be little change on the Earth's surface.

3. Classification of Geomorphic Processes

• A. Endogenic Processes (Internal Forces):

  • Originate from within the Earth.
  • Main energy source: Earth's internal heat (primordial heat, radioactive decay), rotation, tidal friction.
  • Generally land-building forces.
  • Lead to vertical irregularities on the Earth's surface.
  • Major Types:
    • Diastrophism: All processes that move, elevate, or build up portions of the Earth's crust. Includes:
      • Orogenesis (Mountain Building): Involves intense folding and faulting, affecting long, narrow belts of the Earth's crust.
      • Epeirogenesis (Continent Building): Involves uplift or subsidence of large parts of continents or ocean basins, often with little folding.
      • Earthquakes: Involve local, relatively minor movements.
      • Plate Tectonics: Involves horizontal movements of crustal plates.
    • Volcanism: Movement of molten rock (magma) onto or toward the Earth's surface, including the formation of intrusive (below surface) and extrusive (on surface) volcanic forms.

• B. Exogenic Processes (External Forces):

  • Originate from the Earth's atmosphere (driven primarily by solar energy).
  • Main energy source: Sun (heating, temperature differences, precipitation cycles), gradients created by tectonic factors (slope).
  • Generally land-wearing forces (denudation).
  • Act to level down the irregularities created by endogenic forces.
  • Major Types (collectively called Denudation):
    • Weathering: The in-situ (in place) breakdown and alteration of rocks at or near the Earth's surface due to physical disintegration and chemical decomposition. No significant movement of material is involved except fall under gravity.
    • Mass Movement (Mass Wasting): The transfer of rock debris down slopes under the direct influence of gravity. Water often acts as a lubricant or adds weight but is not the primary transporting medium like in a river.
    • Erosion: The acquisition and transportation of rock debris by geomorphic agents like running water, wind, glaciers, waves, and groundwater. Involves detachment and movement.
    • Transportation: The movement of eroded material by geomorphic agents.
    • Deposition: The laying down of transported material when the energy of the transporting agent decreases.

4. Weathering

• A fundamental process preparing rocks for erosion and contributing to soil formation.

• Types of Weathering:

  • i. Chemical Weathering: Decomposition of rocks through chemical reactions. More effective in warm, humid climates.
    • Solution: Minerals dissolve in water (e.g., rock salt, gypsum, some aspects of limestone).
    • Carbonation: Reaction of carbonic acid (H₂CO₃ - formed when CO₂ dissolves in water) with minerals, especially carbonates like limestone (CaCO₃), forming soluble bicarbonates (Ca(HCO₃)₂). Key in karst topography.
    • Hydration: Chemical addition of water to minerals, causing expansion and stress within the rock (e.g., anhydrite becoming gypsum).
    • Oxidation & Reduction: Reaction of minerals with oxygen (oxidation) or in an environment lacking oxygen (reduction). Common with iron-bearing minerals (e.g., rusting). Oxidation adds oxygen, often changing colour (red/brown/yellow); Reduction removes oxygen, often in waterlogged conditions.
  • ii. Physical (Mechanical) Weathering: Disintegration of rocks without changing their chemical composition. More dominant in cold or arid climates.
    • Unloading & Expansion (Exfoliation): Removal of overlying pressure causes underlying rocks to expand and fracture parallel to the surface, leading to sheeting or exfoliation domes.
    • Temperature Changes & Expansion/Contraction: Diurnal (day/night) or seasonal temperature fluctuations cause minerals within rocks to expand and contract at different rates, creating stress and eventual breakdown. Granular disintegration or shattering.
    • Freezing, Thawing & Frost Wedging: Water seeps into cracks, freezes (expands by ~9%), widens the crack, and thaws. Repeated cycles (freeze-thaw) break rocks apart. Very effective in mid/high latitudes or high altitudes.
    • Salt Weathering (Haloclasty): Salt crystals grow in rock pores/cracks (from evaporating saline solutions), exerting pressure and causing disintegration. Common in coastal and arid regions.
  • iii. Biological Weathering: Contribution of living organisms.
    • Physical: Plant roots growing into cracks, burrowing animals.
    • Chemical: Decomposition of plant/animal matter produces acids (humic, fulvic) that cause chemical weathering; chelation by organisms.

• Significance of Weathering:

  • Breaks down rocks into smaller fragments (regolith).
  • Prepares material for erosion and mass movement.
  • Essential for soil formation (provides mineral matter).
  • Can lead to enrichment of certain ores by removing unwanted minerals.

5. Mass Movement

• Downslope movement of weathered material (regolith) and bedrock under the influence of gravity.
• Can be slow or rapid. Water plays a critical role (adds weight, reduces friction). Steep slopes favour movement. Lack of vegetation increases susceptibility. Earthquakes can trigger movements.
• Classification (based on speed and material):
  • Slow Movements:
    • Creep: Slow, gradual downslope movement of soil and regolith. Often indicated by tilted trees, fences, poles. Universal on slopes. Includes soil creep, talus creep, rock creep.
    • Solifluction: Slow flow of water-saturated soil/regolith over impermeable material (like permafrost or bedrock). Common in tundra/alpine regions during thaw season.
  • Rapid Movements:
    • Flows (material behaves like a viscous fluid):
      • Earthflow: Movement of water-saturated clay-rich soil/regolith on moderate slopes. Often leaves a scarp at the head.
      • Mudflow: Rapid flow of water-saturated fine-grained material (mud) down channels, often in arid/semi-arid regions after heavy rain. Can travel long distances. If contains volcanic ash, called a Lahar.
      • Debris Avalanche: Very rapid, turbulent flow of water-saturated debris (soil, rock, vegetation) down steep slopes. Extremely destructive.
    • Slides (material moves as a coherent mass along a defined plane):
      • Slump: Downward slipping of a mass of rock/unconsolidated material moving as a unit along a curved (concave) slip surface. Creates step-like terraces.
      • Debris Slide: Rapid movement of relatively dry unconsolidated material.
      • Rockslide: Rapid sliding of bedrock blocks along a planar surface (like a bedding plane or fault).
    • Falls:
      • Rockfall: Free fall of detached rock pieces from a cliff or steep slope. Accumulates as talus/scree at the base.

6. Erosion and Deposition

• Erosion: The process of detachment (acquisition) and transportation of weathered material by geomorphic agents.
• Agents of Erosion: Running water (fluvial), groundwater, glaciers, wind (aeolian), waves & currents. Each agent produces characteristic erosional and depositional landforms (studied in later chapters).
• Deposition: Occurs when the velocity/energy of the transporting agent decreases, causing it to drop its load. Leads to the formation of depositional landforms (e.g., alluvial fans, deltas, moraines, dunes, beaches).

7. Soil Formation (Pedogenesis)

• Soil is a dynamic natural body composed of mineral and organic matter, air, and water, capable of supporting plant life.
• It forms through the interaction of weathering and biological processes acting on parent material over time.
• Factors Controlling Soil Formation (CLORPT):
  • Climate: Temperature and precipitation (influences weathering type/rate, vegetation).
  • Organisms (Biota): Vegetation, microbes, animals (supply organic matter, nutrient cycling, soil structure).
  • Relief (Topography): Slope and aspect (influences drainage, erosion rates, microclimate).
  • Parent Material: Underlying geological material (influences soil texture, chemistry). Can be bedrock (residual soil) or transported material (transported soil).
  • Time: Duration of soil development processes (influences soil thickness, horizon development).

Conclusion:

The Earth's surface is a product of a continuous struggle between internal (endogenic) forces that create relief and external (exogenic) forces that wear down the surface. Weathering prepares the material, gravity drives mass movement, and dynamic agents (water, ice, wind) erode, transport, and deposit this material, constantly sculpting the landscapes we see. Understanding these processes is key to interpreting landforms and appreciating the dynamic nature of our planet.

Multiple Choice Questions (MCQs)

1. Which of the following is primarily considered an Endogenic geomorphic process?
   a) Weathering
   b) Erosion
   c) Volcanism
   d) Mass Movement

2. The in-situ breakdown of rocks at the Earth's surface without significant movement of the resulting material is called:
   a) Erosion
   b) Mass Wasting
   c) Deposition
   d) Weathering

3. Carbonation is a type of chemical weathering most effective on which rock type?
   a) Granite
   b) Basalt
   c) Sandstone
   d) Limestone

4. Frost wedging, where water freezes and expands in rock cracks, is an example of:
   a) Chemical Weathering
   b) Physical Weathering
   c) Biological Weathering
   d) Mass Movement

5. The slow, gradual downslope movement of soil and regolith, often indicated by tilted trees and fences, is known as:
   a) Rockfall
   b) Mudflow
   c) Creep
   d) Slump

6. Which of the following is NOT a primary agent of erosion?
   a) Running Water
   b) Gravity
   c) Wind
   d) Glaciers
   (Note: Gravity is the driving force for mass movement, but agents like water, wind, ice actively acquire and transport material)

7. Exfoliation, the peeling off of outer rock layers due to pressure release, is associated with which physical weathering process?
   a) Frost Wedging
   b) Salt Weathering
   c) Unloading
   d) Thermal Expansion

8. Denudation encompasses which set of processes?
   a) Volcanism and Diastrophism
   b) Weathering, Mass Movement, Erosion, Transportation
   c) Only Erosion and Deposition
   d) Only Weathering and Mass Movement

9. A rapid flow of water-saturated soil and regolith down a channel, common in arid regions after heavy rain, is termed:
   a) Earthflow
   b) Solifluction
   c) Mudflow
   d) Debris Slide

10. Which factor in the CLORPT model of soil formation refers to the underlying geological material from which soil develops?
    a) Climate
    b) Organisms
    c) Relief
    d) Parent Material

Answer Key:

1. c) Volcanism
2. d) Weathering
3. d) Limestone
4. b) Physical Weathering
5. c) Creep
6. b) Gravity
7. c) Unloading
8. b) Weathering, Mass Movement, Erosion, Transportation
9. c) Mudflow
10. d) Parent Material

Study these notes thoroughly. Focus on understanding the definitions, classifications, examples, and the interplay between different processes. Good luck with your preparation!