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Forces of Tension - Orogenic Processes - Geography Notes

Tension is the force that is transmitted through a body when pushed by forces acting from opposite sides. Forces of tension work horizontally but in opposite directions thereby stretching the rock. The rock strata are split or fractured when intense tensional pressure is applied, resulting in the creation of cracks and fractures in the crust. Faulting is the upward or downward movement of rock along a crack from its initial position. In this article, we will learn about the orogenic processes due to faulting, which occurs due to forces of tension and is an integral part of the geography syllabus of the UPSC/IAS Exam.

Table of Contents

Forces of Tension
Features
Faulting
Types of Faulting
Conclusion
FAQs
MCQs

Forces of Tension

Tension forces operate horizontally but in opposite directions.
The rock strata are split or fractured when intense tensional pressures are applied, resulting in the creation of cracks and fractures in the crust.
Faulting is the upward or downward movement of rock along a crack from its initial position.
The fault line is defined as the line along which the broken rock strata are displaced.
Rift Valleys and Block Mountains are examples of well-known relief features formed by faulting. The Vindhya and Satpura Mountains are examples of faulting.
The lowering of rock strata between two roughly parallel faults creates a rift valley. The Nile Valley, the Narmada Valley, and the Tapti Valley are the examples of the rift valley
Graben are rift valleys with steep parallel walls along the fault, while Horst is an uplifted landmass with steep slopes on both sides.
The escarpment is a very steep slope that runs in a straight line along a fault.

Diagram showing the force of tension

Other Relevant Links
Exogenic Processes	Endogenic Processes
Slow Movements (Diastrophism)	Forces of Compression
Orogenic processes	Epeirogenic processes
Sudden Movements	Earthquakes and Volcanoes
Folding - Fold Mountains	Faulting - Fault Mountains

Faulting

Faulting is a geological process by which rocks fracture and undergo displacement due to tectonic forces.
It results from the Earth's lithospheric plates' movement, leading to stress buildup in the Earth's crust.
When the stress surpasses the rock's strength, it results in a sudden fracture or break, known as a fault.
The movement along these faults can lead to earthquakes.
Faults are formed due to the combined effect of both the compressional and tensional forces, but a tensional force plays a significant role in it.
Exclusive stress and strains produce fracturing and are usually accompanied by dislocation.
Such relatively rapid movement produced crustal blocks (Horsts) and rift valleys or depressions (Graben).
Horsts and Graben are found in association with one another.
The plane along which the rocks are displaced is called the fault plane.

Rift Valleys or Depression

Types

Types of Faulting

Normal Fault: It is caused by extensional forces where the Earth's crust is being pulled apart. The hanging wall (the block above the fault plane) moves downward relative to the footwall.
Reserve Fault (Thrust Fault): Resulting from compressional forces where the Earth's crust is being pushed together. In this case, the hanging wall moves upward relative to the footwall.
Strike Slip Fault: It is caused by horizontal shearing forces. The blocks on either side of the fault move horizontally past each other with little vertical movement.
Oblique Fault: It is a combination of vertical and horizontal displacements due to both shearing and compressional or extensional forces.
Listric Fault: These are curved faults where the fault plane is concave upwards. The fault starts nearly vertically at the surface and becomes more horizontal with depth.
Blind Fault: These faults do not reach the surface, so their existence is not directly observable at the ground level. They are known primarily through indirect methods, like seismic investigations.
Transform Fault: A specific type of strike-slip fault that offsets segments of the mid-oceanic ridge. The movement on these faults is horizontal, and they link two segments of a diverging boundary or ridge. An example is the transform fault between the North American and Pacific Plates.

Diagram of Reverse Fault

Conclusion

Forces of tension refer to the forces that act to pull the Earth's lithosphere apart. These tensional forces are opposite to the compressional forces that result in features like nappes and fold mountains. Tensional forces can lead to rifting, thinning, and eventual breakup of the continental lithosphere.

Other Relevant Links
Geography Notes	Physical Geography
Geomorphic Processes	Geomorphology
Distribution of Oceans and Continents Basins	Minerals and Rocks

FAQs

Question 1: What is meant by the forces of tension in geology?

Answer: In geology, forces of tension refer to the forces that act in opposite directions horizontally, pulling rock bodies apart. This type of stress is responsible for stretching the Earth's crust and often leads to the formation of cracks and fractures in the lithosphere. These forces are primarily involved in the formation of rift valleys and faulting and play a key role in the creation of landforms such as block mountains.

Question 2: How do forces of tension lead to the formation of rift valleys and block mountains?

Answer: When the forces of tension act on the Earth's crust, they cause the rock strata to split or fracture. The lower portion of the crust between two parallel fault lines sinks, forming a rift valley. Examples include the Narmada Valley and the Tapti Valley. Conversely, areas of land that are uplifted between faults form block mountains. The Vindhya and Satpura mountain ranges in India are examples of block mountains formed due to such faulting processes.

Question 3: What is faulting, and how is it related to the forces of tension?

Answer: Faulting is the process by which rocks fracture and displace along a fault line due to tectonic stresses. In the case of tensional forces, the Earth’s crust is pulled apart, creating fractures that lead to either the sinking (graben) or uplifting (horst) of landforms along the fault line. Faulting is a common result of both tensional and compressional forces acting on the Earth's crust, though tension plays a significant role in creating features like rift valleys.

Question 4: What are Horst and Graben?

Answer: Horst and Graben are types of landforms formed by faulting due to tensional forces. A Graben is a block of land that sinks between two parallel faults, forming a depressed area such as a rift valley. In contrast, a Horst is an uplifted block of land, typically found between two parallel faults. These features are often found in tectonically active regions, contributing to the creation of valleys and mountain ranges.

Question 5: What are the different types of faults caused by tensional forces?

Answer: The primary types of faults caused by tensional forces include:

Normal Faults: Occur when the Earth's crust is stretched, causing the hanging wall to move downward relative to the footwall.
Strike-Slip Faults: Caused by horizontal shearing, where two blocks of rock slide past each other laterally, with minimal vertical movement.
Oblique Faults: A combination of vertical and horizontal movements, created by both extensional and shearing forces.

MCQs

Which of the following features are formed by tensional forces?

A) Fold Mountains

B) Rift Valleys

C) Plateau

D) Hills

Answer: B) See the Explanation

Rift valleys are formed when tensional forces stretch the Earth's crust, causing it to crack and the central block to sink. Examples include the Narmada and Tapti valleys.

Which type of fault is caused by tensional forces where the hanging wall moves downward?

A) Reverse Fault

B) Normal Fault

C) Strike-Slip Fault

D) Oblique Fault

Answer: B) See the Explanation

Normal faults occur when tensional forces cause the Earth's crust to pull apart, resulting in the hanging wall moving downward relative to the footwall.

What is the primary cause of the formation of Graben and Horst?

A) Compressive Forces

B) Tensional Forces

C) Volcanic Activity

D) Wind Erosion

Answer: B) See the Explanation

Graben and Horst are formed due to tensional forces. A Graben is a depressed block of land between two parallel faults, while a Horst is an uplifted block of land formed between two faults.

Which of the following is an example of a block mountain formed by faulting?

A) Himalayas

B) Vindhya Range

C) Aravalli Range

D) Western Ghats

Answer: B) See the Explanation

The Vindhya Range is an example of a block mountain formed by faulting due to tensional forces, where blocks of land were uplifted between parallel faults.

Which of the following is associated with the movement of the Earth's lithosphere due to tensional stress?

A) Fold Mountains

B) Earthquakes

C) Rifts and Faults

D) Volcanoes

Answer: C) See the Explanation

Tensional stress causes the Earth's lithosphere to crack, forming rifts and faults. These can lead to features like rift valleys and block mountains, depending on the nature of the movement.

GS Mains Questions and Model Answers

Q1: Examine the role of tensional forces in the formation of geological features such as rift valleys and block mountains.

Answer: Tensional forces play a critical role in the formation of geological features by stretching and pulling apart the Earth's crust. When these forces are applied to a region, the crust fractures along fault lines, leading to the creation of rift valleys and block mountains. Rift valleys are formed when the crust is stretched between two parallel faults, resulting in the sinking of the crust in between (known as Graben). Examples include the Narmada and Tapti valleys. On the other hand, block mountains (or Horsts) are formed when the land between two faults is uplifted. These features are commonly found in tectonically active regions and are crucial for understanding the dynamic processes that shape the Earth's surface.

Q2: Discuss the significance of faulting in understanding the geological history and evolution of Earth’s crust.

Answer: Faulting is a fundamental geological process that provides key insights into the history and evolution of the Earth’s crust. Faulting occurs when the Earth's crust is subjected to stress, leading to fractures and displacements along fault lines. By studying the types of faults, such as normal faults, reverse faults, and strike-slip faults, geologists can reconstruct past tectonic activities and understand the forces that have shaped the Earth's surface. For instance, faulting helps in identifying regions that have undergone rifting, leading to the formation of rift valleys and mountain ranges. Additionally, the study of faulting provides insights into seismic activity, as movement along faults often results in earthquakes. Fault zones also play a role in the formation of mineral deposits and are key areas for the exploration of natural resources.

Q3: Evaluate the impact of faulting on landscape evolution and its significance in orogenic processes.

Answer: Faulting plays a significant role in landscape evolution and is an integral part of orogenic processes, which are responsible for the formation of mountains and other geological features. In orogeny, faulting occurs due to tectonic forces, leading to the displacement of rock strata along fault lines. The type of faulting—whether normal, reverse, or strike-slip—affects the landscape by uplifting, sinking, or laterally displacing rock layers. For instance, rift valleys formed by tensional faulting create low-lying areas between faults, while block mountains result from the uplift of land between faults. These processes contribute to the formation of major mountain ranges, plateaus, and valleys. Faulting also plays a role in the redistribution of land and rock materials, which influences erosion, sedimentation, and the distribution of natural resources. Understanding faulting is thus crucial for studying the Earth’s geological history and the evolution of its surface features.

Previous Year Questions on Forces of Tension and Orogenic Processes

1. UPSC 2020

Question: Discuss the role of faulting in the formation of rift valleys and mountain ranges.

Answer: This question required an understanding of how faulting due to tensional and compressional forces leads to the formation of rift valleys and mountain ranges. The answer should have covered the process of faulting, the formation of Horsts and Graben, and examples like the Narmada Valley and Vindhya Range.

2. UPSC 2019

Question: Explain the concept of faulting and its implications for the study of Earth’s geological evolution.

Answer: This question aimed at evaluating the role of faulting in shaping the Earth's surface. It required candidates to explain how faulting occurs due to tectonic stress and the different types of faults. Additionally, the implications of faulting for understanding the history of Earth's crust, including the formation of mountains, valleys, and earthquakes, were key aspects of the answer.

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