CHAPTER 6
GEOGRAPHIC PROCESSES

 

Landform-Changing Processes

The Earth’s surface is dynamic and continuously changes due to the action of natural forces. These forces are responsible for the formation and modification of landforms. They are broadly classified into Endogenic Processes and Exogenic Processes.

1. Endogenic Processes (Internal Forces)

Endogenic processes originate inside the Earth and are driven by internal heat and pressure. These forces create new landforms by uplifting, folding, faulting, volcanic eruptions, and earthquakes.

Examples:

  • Volcanism
  • Diastrophism (folding and faulting)
  • Earthquakes

2. Exogenic Processes (External Forces)

Exogenic processes operate on the Earth’s surface. They obtain energy from the Sun, gravity, and atmospheric conditions. These processes wear down existing landforms and reshape the landscape.

Examples:

  • Weathering
  • Erosion
  • Deposition

 

Soil

Soil is the thin upper layer of the Earth’s crust formed from weathered rock particles mixed with organic matter, water, air, and living organisms. It provides nutrients and support for plant growth and is essential for agriculture.

Components of Soil

  • Mineral particles
  • Organic matter (Humus)
  • Soil water
  • Soil air
  • Living organisms

Factors of Soil Formation

The formation of soil is controlled by five major factors.

1. Parent Material

The type of rock from which soil is formed determines its texture, colour, and mineral content.

2. Climate

Temperature and rainfall influence the rate of weathering and soil formation.

3. Biological Activity

Plants, animals, microorganisms, and humans contribute organic matter and help in soil development.

4. Topography

Slope and relief affect drainage, erosion, and soil thickness.

5. Time

Soil formation is a slow process. Mature soils require thousands of years to develop.

 

Weathering

Weathering is the breaking down, disintegration, and decomposition of rocks at or near the Earth’s surface without transporting the broken materials. It is the first step in soil formation.

Unlike erosion, weathering occurs at the same place (in situ).

Agents of Weathering

Weathering is caused by several natural agents:

  • Sunlight (Insolation)
  • Frost (Ice)
  • Pressure Release
  • Water
  • Atmospheric gases
  • Plants, animals, and human activities

Types of Weathering

Weathering is divided into three main types.

1. Physical (Mechanical) Weathering

Physical weathering breaks rocks into smaller pieces without changing their chemical composition.

Main Processes

a) Insolation Weathering (Thermal Expansion)

In hot desert regions, rocks expand during the day due to heat and contract at night due to cooling. Repeated expansion and contraction create cracks that eventually break the rocks.

b) Frost Wedging

Water enters cracks in rocks and freezes during cold weather. As water expands on freezing, it exerts pressure on the rocks, causing them to crack and split.

c) Exfoliation (Onion Peeling)

The outer layers of rocks expand more rapidly than the inner layers. Over time, these outer layers peel off like the layers of an onion.

d) Pressure Release (Unloading)

Deep underground rocks form under high pressure. When the overlying rocks are removed by erosion, the pressure decreases, causing the rocks to expand and crack.

Chemical Weathering

Chemical weathering is the decomposition and alteration of rocks through chemical reactions with water and atmospheric gases. It is most active in hot and humid climates.

Main Processes

1. Oxidation

Oxygen reacts with minerals, especially iron, forming rust-like compounds that weaken rocks.

2. Carbonation

Carbon dioxide mixes with rainwater to form carbonic acid, which dissolves limestone, marble, and other carbonate rocks.

3. Hydration

Water combines chemically with minerals, causing them to expand and change into new minerals. For example, feldspar changes into clay (kaolin).

4. Solution

Some minerals such as rock salt and gypsum dissolve directly in water and are carried away.

 

Biological Weathering

Biological weathering is caused by the activities of plants, animals, microorganisms, and humans. These living organisms help break rocks into smaller pieces and contribute to soil formation.

Major Contributors

Animals and Insects

Burrowing animals such as rabbits, rats, termites, and earthworms loosen and break the soil and rocks while digging.

Plants

Plant roots grow into cracks in rocks. As the roots expand, they exert pressure that splits the rocks apart.

Human Activities

Mining, quarrying, construction, road building, and deforestation accelerate the breaking of rocks and increase weathering.

 

Erosion

Erosion is the wearing away and transportation of weathered rock materials from one place to another by natural agents.

Unlike weathering, erosion always involves movement of materials.

Main Agents of Erosion

  • Running water
  • Wind
  • Glaciers (moving ice)
  • Sea waves

 

Soil Erosion

Soil erosion is the removal of the fertile top layer of soil by natural agents such as water and wind. Human activities often accelerate this process, reducing soil fertility and agricultural productivity.

Causes of Soil Erosion

1. Wind Erosion

Strong winds remove loose soil from dry and barren regions.

2. Water Erosion

Heavy rainfall washes away fertile topsoil, especially on steep slopes.

3. Overgrazing

Excessive grazing removes grasses and exposes the soil to erosion.

4. Deforestation

Cutting down forests removes tree roots that bind the soil, making it more vulnerable to erosion.

Soil Conservation

Soil conservation refers to the protection and proper management of soil to prevent erosion and maintain its fertility.

Methods of Soil Conservation

1. Afforestation

Planting trees helps bind the soil with roots and reduces erosion caused by wind and water.

2. Contour Ploughing

Ploughing along contour lines on hill slopes slows down water flow and reduces soil loss.

3. Terrace Farming

Step-like terraces are made on hillsides to reduce runoff and prevent erosion.

4. Strip Cropping

Different crops are grown in alternate strips to reduce wind speed and protect soil.

5. Shelter Belts

Rows of trees are planted around fields to reduce the speed of strong winds.

6. Controlled Grazing

Regulating livestock grazing prevents excessive removal of vegetation and protects the soil.

 

Difference Between Weathering and Erosion

 

WeatheringErosion
Breakdown of rocks at the same place (in situ).Wearing away and transportation of rock materials.
No movement of materials.Involves movement of materials.
Leads to soil formation.Leads to removal of soil and sediments.
Caused by heat, water, frost, gases, and organisms.Caused by water, wind, glaciers, and waves.

 

Short Answer Questions 

 
Q1) What are landform-changing processes?
 
Ans: The Earth’s crust is not static; it is dynamic and ever-changing. Change is nature’s law. The forces responsible for changing the Earth’s surface are classified as follows:
  1. Endogenic Processes (Internal Forces): Processes occurring due to the action of forces deep within the Earth. Example: Volcanism, diastrophism.
  2. Exogenic Processes (External Forces): Processes that derive their energy from the atmosphere (determined by ultimate solar energy) as well as gravity and gradients created by tectonic factors. Example: Weathering, erosion.

 

Q2) Write the definition of soil. What are the major factors of soil formation?
 
Ans: Definition of Soil: Soil is the thin surface layer on the Earth’s crust comprising mineral particles formed by the breaking down of rocks, decayed organic materials, living organisms, soil water, and the soil atmosphere.
  • Factors of Soil Formation: The five major factors regulating soil development are:
    1. Parent Material (Bedrock)
    2. Climate
    3. Biological Activity
    4. Topography
    5. Time

 

Q3) What do you mean by weathering, and what are the main agents of weathering?
 
Ans: Weathering: Weathering is the in-situ breaking, disintegration, and chemical decomposition of rocks by static elements of weather and geomorphic agents at the surface of the Earth. Unlike erosion, it does not involve the large-scale transport of materials.
  • Main Agents of Weathering:
    • Insolation (Sunlight/Heat)
    • Frost
    • Pressure Release
    • Gases (Oxidation, Carbonation)
    • Water (Hydration, Solution)
    • Biological Organisms (Animals, insects, vegetation, and man)

 

Q4) What do you mean by erosion?
 
Ans: Erosion is the active geomorphic process in which earthen materials are worn away and mechanically transported by mobile natural forces such as running water, wind, moving ice (glaciers), and waves. While weathering breaks down or dissolves rocks in a fixed place, erosion always involves lateral movement and transport.
 
 

Long Answer Questions 

Q5) What do you mean by weathering? Write the types of weathering and explain physical weathering in detail.
 
Ans: Weathering describes the static mechanical mechanical fragmentation or chemical dissolution of rocks and minerals on the Earth’s surface due to water, ice, acids, salts, flora, fauna, and rapid temperature fluctuations.
Types of Weathering
There are three principal categories of weathering:
  1. Physical or Mechanical Weathering
  2. Chemical Weathering
  3. Biological Weathering

Detailed Processes of Physical / Mechanical Weathering
Physical weathering involves the pure mechanical disintegration of rocks without altering their underlying chemical or mineral composition. The primary sub-processes include:
  1. Insolation Weathering (Thermal Expansion): Highly prevalent in hot desert areas experiencing severe diurnal (daily) temperature variations. During the scorching day, rocks absorb heat and expand. At night, temperatures plummet, causing rapid contraction. This alternate expansion and contraction builds up immense internal tension, creating cracks and splitting joints.
  2. Frost Wedging: An active mechanical force in cold climates, high altitudes, and high latitudes. Water accumulates inside rock fractures during the day. At night, temperatures drop below freezing, turning water into ice. Because water expands by 9% when it freezes, it exerts massive outward pressure against the fracture walls, splitting the rock apart.
  3. Exfoliation (Onion Peeling): Because rocks are poor conductors of heat, thermal expansion and contraction are heavily concentrated in the outermost layers compared to the interior core. Consequently, the outer layers flake or peel away from the main rock mass in concentric shells, resembling the peeling of an onion layer.
  4. Pressure Release (Unloading): Deep intrusive igneous and metamorphic rocks form under intense pressure. When overlying rock layers are removed over millions of years by erosion, the underlying rocks expand outward due to the sudden release of confinement pressure. This expansion produces structural cracks that trigger mechanical disintegration.

 

Q6) Explain Chemical Weathering and its primary processes.
 
Ans: Chemical Weathering is the decomposition and chemical transformation of rock-forming minerals due to reactions with air and water. These processes alter the mineral structure and are highly accelerated in hot, humid tropical climates.
The four primary chemical weathering mechanisms are:
  1. Oxidation: Occurs when atmospheric oxygen dissolved in water reacts with minerals inside rocks, particularly iron compounds. This triggers decomposition, causing the rock to crumble while shifting its surface color to distinct rusty red, yellow, or brown hues.
  2. Carbonation: Occurs when atmospheric carbon dioxide mixes with rainwater to create weak carbonic acid. This acidic solution reacts with and dissolves calcareous elements inside rocks like limestone, marble, and gypsum, carving out large-scale underground karst systems.
  3. Hydration: The chemical addition of water molecules to the mineral structure. Certain minerals expand in volume, place mechanical stress on surrounding crystals, and alter their composition. For example, Feldspar mechanically degrades into Kaolin (clay) via hydration.
  4. Solution: Rainwater directly dissolves highly soluble rock minerals (such as rock salt/halite and gypsum) and leaches them down into lower soil horizons.

 

Q7) Explain Biological Weathering and its major contributors.
Ans: Biological weathering involves rock breakdown driven directly by the actions of animals, insects, plants, and human beings.
  1. Animals and Insects: Burrowing fauna like rabbits, rats, earthworms, and termites move massive volumes of rock and soil matrix to build habitats or scavenge food. This shifts and structurally undermines the rock framework.
  2. Vegetation: Plant root systems work down into small bedrock joints. As shrubs and trees grow, their expanding roots act as mechanical wedges, applying immense force that cracks open and dislodges massive blocks from cliffs.
  3. Anthropogenic Factors (Man): Human activities like open-pit quarrying, underground mining, rapid deforestation, and reckless land cultivation structurally break up massive bedrock formations on an unprecedented scale.

 
Q8) What is soil erosion? Discuss its main causes and measures for conservation.
Ans: Soil Erosion: The mechanical detachment and removal of nutrient-rich topsoil from the upper profile by natural agents like wind and running water, heavily accelerated by unsustainable human agricultural management.
 
Main Causes of Soil Erosion
  1. Wind Erosion: Strong winds lift up and carry away loose topsoil and organic particles. This occurs primarily in arid and semi-arid desert landscapes where the ground lacks protective vegetative cover.
  2. Water Erosion: Intense rainfall on hilly slopes washes loose surface soil downward. This sediment blocks riverbeds downstream, altering river courses over time, triggering flash floods, and stripping agricultural lands of their productivity.
  3. Overgrazing: Repeatedly grazing cattle on the same pasture fields causes them to strip away all available grasses, including the root networks. This leaves the topsoil vulnerable to sudden wind and surface water runoff.
  4. Deforestation: Large-scale clearing of forests for farming, urbanization, and industrial corridors removes the protective tree cover. Tree root structures act as natural anchors that hold soil matrices together; removing them leaves the land exposed to rapid degradation.

Soil Conservation Measures
  • Soil Conservation: The comprehensive prevention of accelerated topsoil loss through structured environmental and land management.
  • Afforestation: The most effective conservation methodology involving planting new tree belts and ground vegetation. Forests form the foundation of global ecosystems; because tree root matrices hold soil in place and reduce wind velocity, proactive replanting programs are vital to safeguarding global topsoil resources.

 

Multiple Choice Questions 

 

Q1) Which one of the following is an example of endogenic forces?
  • a) Erosion
  • b) Volcanism (Correct Answer)
  • c) Deposition
  • d) Gradation

Q2) Which one of the following is not associated with diastrophism?
  • a) Orogenic processes
  • b) Plate tectonics
  • c) Epeirogenic processes
  • d) Gradation (Correct Answer)

Q3) Which one of the following processes is a gradational process?
  • a) Deposition
  • b) Volcanism
  • c) Diastrophism
  • d) Erosion (Correct Answer)

Q4) Which one of the following is not a geomorphic agent?
  • a) Running Water
  • b) Wind
  • c) Glacier
  • d) Earthquake (Correct Answer)

Q5) Which one of the following processes is not associated with mechanical weathering?
  • a) Block disintegration
  • b) Granular disintegration
  • c) Carbonation (Correct Answer – It is a chemical weathering process)
  • d) Exfoliation

Q6) Which one of the following materials is affected by the hydration process?
  • a) Granite
  • b) Quartz
  • c) Clay (Correct Answer)
  • d) Salts

Q7) Debris avalanche comes under the category of:
  • a) Landslide
  • b) Rapid flow mass movement (Correct Answer)
  • c) Slow flow mass movement
  • d) Subsidence
 
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