• The continuous formation and deformation of Earth's landforms result from the ongoing influence of both external and internal forces. These processes, collectively known as geomorphic processes, bring about changes on the Earth's surface.

Earth Movements

• The Earth's crust and surface undergo constant evolution due to a variety of forces, resulting in physical and chemical changes to the geomorphic structure. These large-scale alterations on the Earth's surface are caused by both endogenic and exogenic forces.
• Earth movements are categorized based on the forces that drive them. There are two main classifications: Endogenic forces, which act within the Earth's interior, and Exogenic forces, which operate on the Earth's surface.

Classification of Earth Movements:

Endogenic Movements:

• Result from the works of endogenetic forces.
• Endogenetic forces lead to land upliftment, subsidence, folding, fracturing, and volcanic eruptions.
• Endogenic movements are further classified into two major categories.

(i) Catastrophic Movements:

• These sudden movements are caused by abrupt endogenetic forces originating deep within the Earth.
• Result in sudden and rapid events at and below Earth's surface.
• Termed as destructive movements, examples include volcanic eruptions, earthquakes, and tsunamis.

(ii) Diastrophic Movements:

• Diastrophic movements involve vertical and horizontal movements leading to the formation of primary landforms like mountains, plateaus, plains, lakes, and major faults.
• Vertical movements can be categorized as upward and downward movements.
• Upward movements result in the emergence of continents, either as a whole or coastal land. For instance, the Allah Bund, an elongated ridge of emergent land bordering the Gulf of Kutch.
• Operate slowly, and their effects become observable over thousands and millions of years, termed as constructive movements.
• Diastrophic Movements are further divided into three processes: isostatic, eustatic, and tectonic.

(a) Isostatic Movement:

• According to this concept, the less dense materials of Earth's surface (Sial) float over the denser magma (Sima) in the Earth's interior.
• The core comprises denser materials, while the Earth's surface is composed of lighter material.
• Isostasy maintains a balance between the upstanding and low-lying parts of the Earth's crust, as explained by Airy and Pratt.
• The term "isostasy," derived from the German word "isostasios," was first proposed by American geologist Dutton in 1889 to express the state of balance.

(b) Eustatic Movement:

• Eustatic changes occur when the volume of seawater changes, influenced by factors such as global warming and the melting of ice sheets.
• This results in either a rise in sea level or a fall during ice ages.

(c) Tectonic Movement:

• Tectonic changes are associated with alterations in the level of the land.
• Sub-divided into Epeirogenic and Orogenic forces.
• Epeirogenic Movement: Refers to regional uplift without marked deformation.
• Caused by radial forces operating at right angles to the Earth's surface, resulting in vertical movement like uplift or subsidence.
• Upwarping and downwarping are outcomes of this vertical movement.
• Uplifted areas form continents, while subsided areas form ocean basins.
• Evidence includes raised beaches, elevated wave-cut terraces, and fossiliferous beds above sea level for uplift, and submerged forests and valleys for subsidence.
• Orogenic Movement: Involves mountain-building, causing deformation in the crust and Earth's surface.
• Far more localized, occurring episodically and widely spaced in geological time.
• Orogeny is a horizontal Earth movement, with tangential forces parallel to the Earth's surface.
• Compression and tension forces result in horizontal movements, leading to folding, faulting, and continental drift.
• Compression forces push rock strata against a hard plane, leading to the bending of rock layers and the formation of fold mountains.

Folding:

• Folding is the result of rock strata bending due to compressional forces acting tangentially or horizontally towards a common point or plane from opposite directions.
• This process leads to the crumbling of strata into folds, forming a series of alternating troughs and crests.
• Upfolds are known as anticlines, and downfolds are termed synclines.
• Along the crest of the anticline, a zone of tension and weakness is present.
• Rivers flowing in this area breach the anticline, erode the material, and deepen the valley. Once fully eroded, the ridge is replaced by a valley, known as an anticlinal valley.
• This phenomenon exemplifies what is commonly referred to as inversion or relief topography.
• Between two anticlinal valleys, the synclinal portion stands higher than the valleys, forming a synclinal ridge.
• Approximately 400 million years ago, the great fold mountains of the world formed as a result of folding.
• Fold mountains are created when two or more of Earth's tectonic plates are pushed together.
• Different types of folding include:
  • Monocline: Formed when horizontally laid beds are tilted and then flatten out, resulting in simple flexure.
• Symmetrical Fold A fold is said to be symmetrical, if both the limbs are equal and inclined at the same angle.
• Asymmetrical Fold These types of folds are generated when one limb in a fold structure is steeper than the other.
• Overturned Fold When one limb occupies the normal position, while the other bends more than 90°, it is said to be an overturned fold.
• Isoclinal Fold Isoclinal folds are formed as a result of continued lateral compression upon an overturned fold. Here, both the limbs dip at equal angles in the same direction.
• Recumbent Fold These are fold lying down. These are formed as a result of continuation of pressure. The axial plane and both limbs of a fold lie roughly and horizontally.

• Closed Fold occurs when the angle between the two sides of the fold is acute (less than 90 degrees), and it is formed due to excessive compression.
• Open Fold, on the other hand, is characterized by an obtuse angle between the two sides of the fold (greater than 90 degrees and less than 180 degrees). These folds are typically created through undulating folds caused by compression.
• Fan Fold has a fan-like appearance, consisting of numerous minor anticlines and synclines known as anticlinorium and synclinorium, respectively.
• Anticlinorium is a large anticline with superimposed minor folds, while Synclinorium is a large syncline with superimposed minor folds.
• Plunge Fold forms when the axis of the fold becomes tilted instead of being parallel to the horizontal plane.
• Warp Fold, a short form of Warping, is created by convergent forces, resulting in crustal bending. Warping involves the upward or downward warping (raising) of the crust over a large area.
• Nappe occurs when the pressure exerted on a recumbent fold is strong enough to tear it from its roots and thrust it forward.

Tension

• Tension forces lead to the breaking or fracturing of rock strata, forming rocks and fractures in the crust.
• The upward or downward displacement of rocks from their original position along such fractures is termed faulting.

Faulting

• Faults are formed when tensional forces play a significant role in it. Excessive stresses and strains produce fracturing and are usually accompanied by dislocation. This rapid movement results in the creation of horsts and rift valley or graben.
• Horsts and grabens are found in association with one another. The plane along which the rocks are displaced is called the fault plane
• When the rocks are compressed from two opposite directions, the rock blocks move forwar or backward instead of upward or downward.
• The part above the fault plane is known as the hanging block and the one below it is termed the foot block.
• The surface of the hanging block on the fault plane is the hanging wall and that of the foot block on the fault plane is the footwall.
• Normal Faults occur when rock blocks are displaced in opposite directions, causing one block to move downwards. This results in the stretching of the surface, and the fault plane is typically situated between and in the vertical direction.
• Reverse Faults involve rock blocks moving towards each other, with one block overriding the other. This compression during a reverse fault is also referred to as Thrust faults. The fault plane in this case is usually inclined at an angle between 40 and 90 degrees.
• Lateral Faults form when rock blocks are horizontally displaced along the fault plane due to horizontal movement. These faults are a consequence of shear stresses in the crust.
• Strike-slip Faults are vertical (or nearly vertical) fractures where the blocks predominantly move horizontally.
•  The slip style is termed right-lateral if the block opposite an observer moves to the right, and left-lateral if it moves to the left. An example of a right-lateral fault is the San Andreas Fault.

• Thrust Faults are dip-slip faults where the upper block, above the fault plane, moves up and over the lower block. This type of reverse fault has a dip of 45 degrees or less and can be observed in geological formations such as the Rocky Mountains and the Himalayas.
• Step Faults occur when a series of faults in an area have fault planes with slopes in the same direction. These resultant faults are termed Step faults, and an example is found in the Rhine valley in Europe.

Landforms Resulting from Faulting Process include:

• Rift Valley: Formed in lowland regions where Earth's tectonic plates move apart or rift, creating a fault system. An example is the Great Rift Valley.
• Ramp Valley: Develops when crustal blocks are thrust towards each other and onto an intervening crustal block.
• Block and Horst Mountains: Block mountains represent elevated areas between two faults or on either side of a rift valley or a graben. These mountains are formed due to faulting caused by tensile and compressive forces driven by endogenetic forces. The uplifted blocks are called horsts, and the lowered blocks are termed graben.

Exogenic Movements

• Exogenic Movements derive their energy from atmospheric and tectonic factors. 
• Gravitational forces act on Earth materials, causing downslope movement. Stress from pushing or pulling induces deformation.
• Shear stresses, acting along the faces of Earth materials, break rocks, resulting in angular displacement or slippage.
• Diagrammatic Representation of Faulting illustrates how Earth materials experience molecular stresses caused by temperature changes, crystallization, and melting.
• Chemical processes result in the weakening of bonds between grains, dissolution of soluble minerals, or cementing materials.
• This is the fundamental cause of weathering, mass movements, and erosion, all of which stem from the development of stresses within Earth's materials.
• Examples of exogenetic movements such as weathering, erosion, and mass movement are described below.

(i) Weathering

• Weathering involves the mechanical disintegration and chemical decomposition of rocks due to the influences of various weather and climate elements.
• As weathering is predominantly an in-situ or on-site process with minimal material motion, factors affecting it include rock composition, climate, topography, and vegetation. The depth and nature of weathering also vary across different climates.
• Three types of weathering include:
  • Physical Weathering: Caused by factors like insolation and frost.
  • Chemical Weathering: Involves dissolution of rocks through processes such as hydration, oxidation, degradation, and carbonization.
  • Biological Weathering: Results from living organisms such as plants, trees, and humans contributing to the dissolution of rocks.

Erosion

• When massive rocks undergo weathering and break into smaller fragments, erosional geomorphic agents transport these fragments to other locations based on the dynamics of each agent.

(iii) Mass Movement

• Mass movement refers to the transfer of rock debris down slopes under the direct influence of gravity. 
• Movements can range from slow to rapid, affecting shallow to deep columns of materials, including creep, flow, slide, and fall.
• Gravity exerts force on all matter, be it bedrock or products of weathering, and mass movements are more active over weathered slopes than unweathered materials. 
• Unlike erosion processes, mass movements are solely influenced by gravity, with no participation from geomorphic agents like running water, glaciers, wind, waves, or currents.

Prelims Facts

•  What is the diameter of the Earth?
  • -12800 km [UKPSC (Mains) 2006]
• An effective Coriolis force results from
  • -Earth rotation [BPSC (Pre) 2022
• Approximately, how much distance per minute the Earth is rotating?
  • -28 km [BPSC (Pre) 2002)
• In the Northern Hemisphere, the longest day of the year normally occurs in the Second half of the month of June [IAS (Pre) 2021)
• Who was the first person to state that the Earth was spherical?
  • - Aristotle [IAS (Pre) 2001)
• Unlike the fluid core of the Earth, the core of the Moon is
  • - Viscous liquid (UPPSC (Mains) 2004)
• The equatorial circumference of the Earth is 40,000 km [UKPSC (Pre) 2016
• Earth's axis is tilted at an. angle of 231 [MPPSC (Pre) 1990
• Who was the first person to explain that the rotation of the Earth on its own axis causes day and night?
  • - Aryabhatta [BPSC (Pre) 2018
• What causes the change of season?
  • - Earth's revolution and inclination of its axis [JPSC (Pre) 2013
• The possibility of a desert on Earth is more
  • - Nearby 23° latitude [BPSC (Pre) 1999
• A ball thrown outside from an artificial satellite revolving around the Earth will
  • - Revolve around the Earth in the same orbit [UPPSC (Pre) 1995

Self Check

1. Glaciated regions are associated with

(a) 'V' shaped valley

(b) U' shaped valley

(c) sand dunes

(d) stalactites

2. Which of the following landforms is formed by MPPSC (Pre) 2011 glacier?

(a) Tarn

(b) Lagoon

(c) Lappies

(d) Doline

3. Which one of the following is not an old folded mountain?

UKPSC (Pre) 2016

(a) Ural mountain

(b) Andes mountain

(c) Aravalli mountain

(d) Appalachian mountain

4. Among the following, which one is not a young folded mountain?

MPPSC (Pre) 2022

(a) Sierra Nevada

(b) Rocky

(c) Himalaya

(d) Alps

5. Why do fold mountains have enormous thickness of sedimentary rocks?

(a) Due to deposition of sediments in a valley for millions of years.

1. b) Due to accumulation of sediments in a geosyncline.

(c) The plains were folded into mountains.

1. d) The sediments were folded into recumbent and nappe folds.
2. Approximately how many million years ago were the great fold mountains of the world formed?

(a) 400

(b) 320

(c) 220 

(d) 30

7. Which of the following processes helps in the formation of rift valley?

APSC (Pre) 2015

(a) Seismic activity

(b) Volcanic eruption

(c) Folding

(d) Faulting

8. Folding is the result of BPSC (Pre) 2011

(a) epeirogenetic force

(b) coriolis force

(c) orogenetic force

(d) exogenetic force

9. Exfoliation is which of the following types of weathering?

MPSC (Pre) 2014

(a) Chemical

(c) Biological

(b) Physical

(d) Oxidation

10. Which one of the following processes of weathering belongs to both mechanical and chemical weathering?

(a) Crystallisation

(b) Exfoliation

(c) Hydration

(d) Carbonation

11. Till, moraine and boulder clay are depositional landforms due to APPSC (Pre) 2017

(a) surface water activity

(b) underground water activity

(c) aerial activity

(d) glacial activity

12. Which of the following statements are concerned with eskers and drumlins?

BPSC (Pre) 2022

1. Eskers are ridges of crudely bedded gravels and sands.
2. Drumlins are constituted mostly of boulders and clay.
3. Basket of eggs topography is the characteristic of terrains with eskers.
4. While eskers are built by glacier streams, drumlins result from glacier action.

Choose the correct answer from the option given below.

(a) 1, 2 and 3

(b) 1, 2 and 4

(c) 3 and 4

(d) 1 and 2

13. Consider the following statements.
14. Epeirogenic movements are mainly vertical movements on Earth.
15. Orogenic movements are horizontal movements of the Earth.

Which of the statements) given above is/are correct?

(a) Only 1

(b) Only 2

(c) Both 1 and 2

(d) Neither 1 nor 2

14. Which of the following forces are acting as destructing agents over Earth surface?
15. Wind
16. Glacier
17. Earthquake
18. Sea waves

Select the correct answer using the codes given below.

(a) 1, 2 and 3

(b) Only 3

(c) 1, 2 and 4

(d) All of the above

Know Right Answer

1 (b)

2 (a)

3 (c)

4 (b)

5 b)

6 (a)

7 (d)

8 (c)

9 (b)

10 (a)

11 (d)

12 (b)

13 (b)

14 (a)