Maarg Manthan · Topic 3.12

Endogenic Processes: Diastrophism, Orogenic and Epeirogenic Processes

Geography › Geomorphic Processes and Landform Evolution · Topic 3.12

Endogenic processes are those that originate inside the Earth. The slow movements are called diastrophism, the deformation of the crust by forces within, and include orogenic processes, which build mountains by folding and faulting along narrow belts, and epeirogenic processes, which raise or lower large parts of continents without much folding. The sudden endogenic processes are earthquakes and volcanic eruptions. Compression gives folds and reverse faults, tension gives normal faults and rifts.

6 min read · UPSC Prelims · Geography · Geomorphic Processes and Landform Evolution

At a Glance

Diastrophism Slow deformation of the crust
Orogenic Mountain building along narrow belts
Epeirogenic Uplift or sinking of large areas
Compression Folds, reverse faults
Tension Normal faults, rift valleys
Exam link UPSC Prelims, Geography: Geomorphic Processes and Landform Evolution

Where Does It Fit?

This topic expands the endogenic side of the previous topic on forces. It describes how the crust is bent and broken, and links the processes to mountains, plateaus and rifts studied in later topics. Previous topic: Exogenic and Endogenic Forces: Gradation, Degradation and Aggradation. Next topic: Exogenic Processes: Denudation, Weathering, Mass Movements, Erosion, Transportation, Deposition.

What Are Endogenic Movements?

In short: endogenic movements are internal forces that raise, fold, break and shift the crust.

The surface of the Earth is shaped by two sets of forces. Endogenic forces originate inside the Earth and mostly build relief, creating mountains, plateaus and basins, while exogenic forces act at the surface and wear relief down. The endogenic forces are driven by heat in the interior, which comes mainly from the decay of radioactive elements and from the residual heat of the formation of the planet. Geomorphic movements are of two kinds. Sudden movements, such as earthquakes and volcanic eruptions, produce rapid changes. Slow movements, called diastrophism, work over thousands to millions of years. The structure of the interior that powers them is described in Internal Structure of the Earth: Crust, Mantle, Outer Core, Inner Core.

What Is Diastrophism?

Diastrophism is the general term for all processes that deform the crust, producing continents, mountains, plateaus, folds and faults. It includes two broad types of movement.

Feature	Orogenic movements	Epeirogenic movements
Meaning	Mountain building	Continent building
Direction	Mainly horizontal	Mainly vertical
Extent	Narrow belts	Broad regions or whole continents
Results	Folding and faulting; fold mountains	Upliftment and subsidence; plateaus, basins, shoreline changes
Force	Compression or tension	Upward or downward warping

An example of epeirogenic upliftment is the rise of Scandinavia after the melting of the ice sheet, and an example of orogenic movement is the formation of the Himalayas.

How Do Folds Form?

Horizontal compressive forces squeeze the crust and bend layers of rock into folds. The upward arch is an anticline, and the downward trough is a syncline. Folding is the main process in the making of fold mountains such as the Himalayas, the Alps and the Rockies. Folds are classified by the shape of their limbs.

Symmetrical fold: both limbs dip at about the same angle.
Asymmetrical fold: the limbs have unequal slopes.
Monocline: one limb is steep and the other is almost horizontal.
Isoclinal fold: the limbs are parallel to each other.
Overturned and recumbent folds: the fold is pushed so far that one limb lies over the other, and in a recumbent fold the axial plane is nearly horizontal.

How Do Faults Form?

When the crust is stretched, compressed or sheared beyond its strength, rocks break along a plane, and the movement along it is called faulting. The plane is the fault plane. The main types of faults depend on the direction of movement.

Fault	Movement	Caused by
Normal fault	Hanging wall moves down relative to the footwall	Tension
Reverse fault	Hanging wall moves up relative to the footwall	Compression
Thrust fault	Reverse fault with a gentle dip, often moving large masses over great distances	Strong compression
Strike-slip fault	Blocks slide horizontally past each other	Shear

Two features of faulting are important. A block that is raised between two parallel faults is a horst, and a block that has sunk between two faults is a graben, which forms a rift valley, as in the Narmada and Tapi valleys of India and the Great Rift Valley of East Africa. The origin of rift valleys is covered in Plate Boundaries: Divergent, Convergent, Transform.

How Do Orogenic and Epeirogenic Movements Differ?

Feature	Orogenic	Epeirogenic
Meaning	Mountain-building	Continent-building: broad uplift or sinking
Area	Narrow linear belts	Wide areas, whole plateaus or continents
Direction	Horizontal compression, with folds and thrusts	Mainly vertical, with little folding
Speed	Over millions of years	Very slow
Results	Fold mountains such as the Himalaya	Plateaus, emergent and submergent coasts, warped basins
Examples	Himalaya, Alps, Andes	Uplift of the Scandinavian shield after the ice melted; sinking of coastal areas

In India the Himalaya are the product of orogenic movement as the Indian plate collides with Eurasia, as explained in Plate Boundaries: Divergent, Convergent, Transform. The upwarping of the Peninsula and the subsidence of the Gulf of Khambhat and the Kachchh region are epeirogenic in nature. The sinking of land along the Narmada and Tapi valleys, which lie in rift valleys, is the result of faulting.

What Are Earthquakes and Volcanism Doing Here?

The sudden endogenic movements are earthquakes, which release stress built up along faults, and volcanism, in which molten rock from the mantle reaches the surface. They are treated in epicentre above it Main cause Sudden slip along faults at plate boundaries Scales Magnitude…">Earthquakes: Types, Causes, Effects and Frequency and in Types of Lava: Andesitic (Acidic) and Basaltic (Basic) Lava. As an analytical point, the older idea of separate causes for each movement has been replaced by plate tectonics, which explains folding, faulting, earthquakes and volcanoes as results of the same plate motions, as developed in Plate Tectonics: Major and Minor Lithospheric Plates.

Why Is This Topic Important?

Foundation Basis of relief formation
Terms Orogenic and epeirogenic often asked
Link Leads to plate tectonics

What Came Next?

The next topic turns to the exogenic processes that wear the land down. Next topic: Exogenic Processes: Denudation, Weathering, Mass Movements, Erosion, Transportation, Deposition.

Key People and Terms

Diastrophism Deformation of the crust
Anticline Upward fold
Syncline Downward fold
Fault Break with movement of rocks
Horst Raised block between faults
Graben Sunken block between faults

Exam Corner

Points to Remember

Orogenic means mountain building; epeirogenic means continent building.
Compression makes folds; tension makes faults.
A graben forms a rift valley.
A horst is a raised block.
Earthquakes and volcanoes are sudden endogenic movements.

Do Not Confuse With

Orogenic and epeirogenic Horizontal and narrow versus vertical and broad
Horst and graben Raised versus sunken block
Anticline and syncline Upfold versus downfold

Memory Hook

Orogenic builds mountains, epeirogenic lifts lands; squeeze folds, stretch faults.

Mains Angle

Questions ask for processes that build relief. These points add depth.

Forces Compression and tension
Scale Narrow orogens, broad epeirogeny
Link Explained by plate tectonics

A Question You May Face

An original practice question, not a past paper question.

“Distinguish between orogenic and epeirogenic movements and explain how folds and faults are formed.”

How to Answer

Define Diastrophism.
Compare Orogenic and epeirogenic.
Folds and faults Compression and tension.
Link Plate tectonics.

GS Relevance

Prelims: orogenic versus epeirogenic movements, folds and faults. GS Paper 1: geomorphic processes.

Frequently Asked Questions

What is diastrophism?

Diastrophism is the term for all slow deformation of the Earth's crust by internal forces. It includes orogenic movements, which build mountains through folding and faulting, and epeirogenic movements, which raise or lower large parts of continents.

What is the difference between orogenic and epeirogenic movements?

Orogenic movements are mainly horizontal and act in narrow belts, producing fold mountains by compression. Epeirogenic movements are mainly vertical and affect broad regions, causing the upliftment or subsidence of continents, plateaus and shorelines, often without folding or breaking of rock layers.

What are anticlines and synclines?

An anticline is an upward arch of folded rock layers, and a syncline is a downward trough. Both are formed when horizontal compressive forces bend the rock layers, and they are the basic units of fold mountains such as the Himalayas and the Alps.

What are horst and graben?

A horst is a block of the crust raised between two parallel faults, while a graben is a block that has sunk between two faults. A graben forms a rift valley, such as the valleys of the Narmada and the Tapi rivers.

What causes normal and reverse faults?

A normal fault forms under tension, when the hanging wall moves down relative to the footwall as the crust stretches. A reverse fault forms under compression, when the hanging wall moves up relative to the footwall as the crust shortens.

PYQ Practice — Statement Analysis

1 Orogenic movements are responsible for the formation of mountains.

True

They involve folding and faulting.

2 A graben is a raised block between two faults.

False

A raised block is a horst; a graben has sunk.

3 Epeirogenic movements mainly act vertically over large areas.