Geomorphic Processes and Earth Movements Notes for UPSC

Dear students, if you look at the Himalayas, the Ganga plain and the Thar desert, you will see that the Earth's surface is not the same everywhere. Mountains rise, rivers cut valleys, deserts spread and coasts change shape. Why does this happen? The answer is in the chapter on geomorphic processes. This is the base of the entire physical geography. In the Prelims, the questions come on the types of the movements, the folding and faulting, the landforms and the difference between the endogenic and exogenic forces. Let me explain in simple language.

What Are Geomorphic Processes?

"Geo" means Earth, "morph" means form. Geomorphic processes are the physical and chemical actions that change the form of the Earth's surface. The landform that we see today is the result of the two opposite sets of forces working for millions of years: forces that build and forces that destroy.

Students, remember: endogenic = uplift (land-building) and exogenic = gradation (land-levelling). The process of levelling by the exogenic forces is called gradation, which has two parts: degradation (lowering of high areas by erosion) and aggradation (filling of low areas by deposition).

Earth Movements: The Endogenic Forces

The movements of the Earth's crust are classified as follows.

1. Epeirogenic Movements (Continent Building)

The slow vertical movements of the crust over a wide area. When a large land mass is raised, it is called upheaval; when it sinks, it is called subsidence. They produce plateaus, raised beaches and drowned coasts. Example: the raised portion of the coast of Saurashtra, the sinking of the Rann of Kachchh, the Deccan plateau's uplift.

2. Orogenic Movements (Mountain Building)

The horizontal forces working in the crust are of two kinds:

• Compressional forces (tangential, converging): The crustal rocks are pushed towards each other. They cause folding (bending of the rock layers into wave-like shapes) and reverse or thrust faults. Example: the Himalayas, the Alps, the Rockies and the Andes, which are fold mountains.
• Tensional forces (pulling apart, diverging): The rocks are pulled away. They cause normal faults, cracks, rift valleys and block mountains. Example: the East African Rift Valley, the Narmada and Tapi rift valleys in India, the Rhine valley.

Folds and Faults: The Two Key Structures

Folds

When compressional force acts on the rock layers, they bend. The upfold is called an anticline and the downfold a syncline. Depending on the force, the fold can be symmetrical, asymmetrical, overturned, recumbent or isoclinal. The study of folds helps petroleum geologists, as oil and gas are often trapped in the anticlines (as in the Digboi and Ankleshwar fields).

Faults

A fault is a fracture in the rocks along which the blocks have moved relative to each other. The movement can be vertical, horizontal or both.

• Rift valley (graben): A depressed block between two parallel faults. Example: the Narmada and Tapi valleys, the Dead Sea and the Jordan valley.
• Block mountain (horst): A raised block between two faults. Example: the Vosges in France and the Black Forest in Germany; the Salt Range in Pakistan.

Sudden Movements

• Earthquakes: The shaking of the ground due to the sudden release of energy in the crust. The point of origin is the focus (hypocentre), and the point on the surface just above it is the epicentre. Seismic waves: P-waves (primary, compressional, fastest, pass through solids and liquids), S-waves (secondary, transverse, only through solids) and surface waves (L-waves, most destructive). Intensity is measured on the Mercalli scale, magnitude on the Richter scale (moment magnitude scale now), by the seismograph.
• Volcanoes: The vents through which molten magma, gases and ash come out. They build the landforms such as cones, lava plateaus (the Deccan Traps) and calderas.

(See our separate chapters on Earthquakes and Volcanoes for more details.)

Exogenic Processes: The Levelling Forces

The exogenic processes act on the surface and include four steps:

1. Weathering: The breaking and decay of rocks in their place (in situ) by atmospheric agents, without movement. Types: physical or mechanical (temperature changes, frost action, exfoliation, pressure release), chemical (oxidation, carbonation, hydration, solution) and biological (roots of the plants, burrowing animals, humans).
2. Mass wasting (mass movement): The downslope movement of rock and soil under gravity, such as landslides, mudflows, creep, slumps and rockfalls.
3. Erosion: The removal of the weathered material by the moving agents (water, wind, glaciers, waves, groundwater).
4. Transportation and deposition: The carrying of the material and its laying down at another place when the energy of the agent falls.

(Details of these are in the separate chapters on erosion and deposition.)

Factors Affecting Geomorphic Processes

• Climate: Rainfall, temperature and humidity decide the type of weathering and erosion (chemical weathering is strong in humid areas, physical in deserts and cold regions).
• Rock type and structure: The hardness, the joints and the permeability of the rocks (limestone dissolves, granite resists).
• Slope and relief: A steep slope speeds up mass movement and erosion.
• Vegetation: Plants protect the soil, bind it with the roots and reduce erosion.
• Human activity: Deforestation, mining, construction and agriculture speed up the natural processes.

Significance of the Study

• It explains the origin of the major landforms: the Himalayas (fold mountains from the collision of the Indian and the Eurasian plates), the Deccan plateau (volcanic), the Indo-Gangetic plain (alluvial deposition).
• It helps to understand and manage the natural hazards: earthquakes, landslides, floods and volcanic eruptions.
• It supports the planning of agriculture, dams, roads and cities, and the study of soil formation.

Common Mistakes Students Make

• Writing "earthquake is an exogenic process". No: earthquakes and volcanoes are endogenic (internal) processes. Landslides are exogenic (mass wasting), even though an earthquake may trigger them.
• Mixing weathering and erosion. If the broken rock stays where it is, it is weathering. If water, wind or ice carries it away, it is erosion.
• Thinking that all mountains are fold mountains. There are also block mountains (horst), volcanic mountains (Mount Fuji, Kilimanjaro) and residual mountains (Aravallis, Nilgiris, Vindhyas), which are old and worn down.
• Forgetting the time scale. Diastrophic movements take millions of years, but the sudden movements (earthquakes) take seconds. The Himalayas are still rising by a few millimetres every year, which is why the region is earthquake-prone.

How This Helps in Understanding India

The Himalayas (young fold mountains), the Peninsular plateau (an old stable block with the lava cover of the Deccan Traps), the Aravallis (very old, much eroded fold mountains), and the Narmada-Tapi rift valleys are all examples of the endogenic processes at work, while the Ganga plain, the deltas of the Ganga-Brahmaputra and the Thar dunes are examples of the exogenic processes of deposition. If you link each Indian landform with the process that made it, geography becomes a story rather than a list.

Teacher's Tip for the Exam

Students, make a small table in your notebook: Endogenic vs Exogenic and Epeirogenic vs Orogenic. Remember that "epeiro" means continent (vertical), "oro" means mountain (horizontal). Also remember the force-landform pairs: compression = fold mountains and thrust faults; tension = rift valleys and block mountains. Most Prelims questions test these pairs.

Important Points for the Exam

• Endogenic forces create relief; exogenic forces level it (gradation).
• Diastrophic movements: epeirogenic (vertical) and orogenic (horizontal).
• Folding by compression: anticline and syncline; faulting by tension or compression.
• Weathering is in situ; erosion involves the removal of material by an agent.

Related Reading

Students, read this chapter together with our notes on World Geography, Indian Geography and our UPSC blog for the current-affairs links.

Frequently Asked Questions (FAQ)

What are geomorphic processes?

The natural physical and chemical processes that shape the Earth's surface.

What are endogenic forces?

Internal forces originating inside the Earth that create relief, such as folding, faulting, earthquakes and volcanoes.

What are exogenic forces?

External forces such as weathering, rivers, glaciers, wind and waves that wear down the surface.

What is gradation?

The levelling of the Earth's surface by the exogenic forces through degradation and aggradation.

What are diastrophic movements?

Slow, large-scale crustal movements such as folding, faulting and warping that form mountains and plateaus.

What are epeirogenic movements?

Slow vertical movements that raise or lower large areas of the crust.

What are orogenic movements?

Horizontal movements that cause folding and faulting and build mountains.

What is an anticline?

The upward fold of rock layers.

What is a syncline?

The downward fold of rock layers.

What is a normal fault?

A fault formed by tension in which the hanging wall moves down.

What is a rift valley?

A depressed block between two parallel faults, such as the Narmada valley.

What is a horst?

A raised block between two faults, forming a block mountain.

What is weathering?

The breakdown of rocks in place by atmospheric agents.

What is the difference between weathering and erosion?

Weathering breaks rocks in place; erosion removes and transports the broken material.

Which forces form fold mountains?

Compressional forces.

Which are examples of fold mountains?

The Himalayas, Alps, Rockies and Andes.