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Formation of Mountain – Faults and Folds

Grade 6
Jun 5, 2023

Formation of Mountain


You’ve studied that the Earth is the place where we live. Earth is a unique planet. It supports life for many years. Earth is round in shape, and it is not a solid piece of rock. It is made up of various layers.

There are many features on the Earth’s surface, such as mountains, hills, plains, waterfalls, etc. These features are called landforms.


The Earth’s surface is divided into several massive rock plates. The crust is used to make plates. The crust is firm. The upper mantle can flow whenever the Earth’s plates move as the mantle flows.

Earth’s plates move at roughly the same rate as your fingernails develop. The plates’ edges are where the crust changes. You can’t see or hear anything. The majority of the changes are felt. Others are not to be missed!

Earth's surface


ductile rocks

Deformation of Ductile Rocks

Over its four-and-a-half-thousand-year history, the Earth has undergone incredible deformation. Although this term is used in geology, the forces that act on rock formations are the same forces that are used when creating a clay model.

Deformation is the outcome of physical stress acting on an object, causing it to alter its shape. Depending on the physical composition of the object, physical forces such as weight and gravity can bend, compress, stretch, pull apart, and crack it.

3 phases of deformation

When a rock is exposed to increasing stress, it undergoes 3 phases of deformation.


Elastic deformation is characterized by reversible strain.

Ductile deformation is characterized by irreversible strain.

Fracture – an irreversible strain that causes the material to break.

Folds and faults are the two most common types of deformation in geology.


Some plates slide from one side to the other. A fault is an area where they rub together. A fault is a long, narrow crack in the crust of the Earth.

A plate on one side of a fault can slide up while the plate on the other side slides down. Rising plates can cause fault blocks to form mountains.

A plateau may form if the lifting is spread out over a large area. A plateau is a flat-topped high landform.

On rocks, three types of forces act:

Tension, compression, and shear. Tension is the force that separates rocks, while compression is the force that brings rocks together. The force that causes rocks on either side of a fault to slide past each other is known as shear.


Faults form when rocks break as a result of forces acting on them. Stress may accumulate over many years until the fault unexpectedly moves – maybe a few centimeters or even a few meters. When this occurs, a massive amount of energy is released in the form of an earthquake.

The direction of motion on a fault is determined by the type of force at work, as explained below. There are three types of faults.


Normal Fault (Divergent fault):

When rocks are pulled apart and the crust is stretched, normal faults form.

Tensional forces within the Earth pull rocks apart. When these forces stretch the rocks, a normal fault can form. Along a normal fault, the movement of rocks takes place where rock above the fault surface moves downward in relation to the rock below the fault surface.

Normal fault

Reverse Fault:

When the crust is squashed and shortened, reverse faults occur. Thrusts are shallow-sloping reverse faults.

Compression forces squeeze rock, resulting in reverse faults. When the rock breaks due to opposing forces, the rock above a reverse fault surface is forced up and over the rock below the fault surface.

Reverse fault

Strike-Slip Fault (Transform plate boundary):

Rocks on either side of a strike-slip fault slide past one another with little upward or downward movement. The San Andreas fault, which stretches more than 1,100 kilometers through California, is depicted in the photo below. The San Andreas fault is the boundary between two plates moving sideways past each other on Earth.

Strike-slip fault


Some plates collide near the edges of continents. A fold forms when the land scrunches up between them. A fold in the rock layers is a bend.

A fold becomes a mountain if the land continues to scrunch. A mountain is a tall landform with a peak. Wind and rain can break off bits and pieces over time.

When rocks change shape in a ductile manner, rather than fracturing to form faults or joints, the subsequent structures are known as folds.

Folds are caused by compressional or shear stresses [stress is a force used over an area] acting over a long period. Because the strain rate is low and/or the temperature is high, normally brittle rocks can behave ductile, which results in such folds.


Formation of Fold

Folds Form in Two Ways:

Flexural folds form when stratified rocks bend and layers slip. As a result, the layers retain their thickness even as they bend and slide over one another. These are commonly formed as a result of compressional stresses acting from either side.

  • When rocks are very ductile and flow like a fluid, flow folds form. This flow draws out different parts of the fold to varying degrees, resulting in layers that are thinner in some places and thicker in others. The flow causes shear stresses, which smear out the layers.
  • Folds can also form as a result of faulting in other areas of the rock body. In this case, the more ductile rocks bend to comply with the fault movement.

Flexural folds

  • Furthermore, because even ductile rocks can fracture under high stress, rocks may fold up to a point and then fracture to form a fault.

Types of Folds:

Monoclines are the most basic type of fold. Monoclines form when horizontal strata are bent upward so that the fold’s two limbs remain horizontal.

Anticlines are folds formed when originally horizontal strata are folded upward and the fold’s two limbs dip away from the hinge.

Synclines, on the other hand, are downwardly convex folds. The younger strata form the core of a syncline fold, and the older strata extend outwards.

Types of folds


The formation of mountain ranges is one of the most amazing results of deformation acting within the Earth’s crust. Mountains are frequently found in long, linear belts. They are formed due to tectonic plate interactions, a process known as orogenesis.

The Process of Mountain Building (Orogenesis) Includes:

  1. Structural deformation
  2. Faulting
  3. Folding
  4. Igneous processes
  5. Metamorphism
  6. Glaciation
  7. Erosion
  8. Sedimentation

Deformation, folding, faulting, igneous processes, and sedimentation are examples of constructive processes; erosion and glaciation are examples of destructive processes.

Mountains are created and have a limited lifespan. Young mountains are tall, steep, and rising. Erosion has carved a path through the middle-aged mountains. Old mountains have been deeply eroded and are frequently buried. Ancient orogenic belts are observed in continental interiors, far from plate boundaries, but they contain information on ancient tectonic processes. Because orogenic continental crust has a low density and is thus too buoyant to subduct, it is usually preserved if it escapes erosion.


Causes of Mountain Formation

There are three main causes of mountain building:

  • Convergence at convergent plate boundaries
  • Continental collisions
  • Rifting

Formation of Mountains:

  • Mountains form as a result of movement within the Earth’s crust.
  • The crust is made up of several large free-floating plates known as tectonic plates. These massive chunks of Earth’s crust move within molten rock known as magma, allowing them to shift and collide over time.
  • Even though humans live on the crust, they are rarely aware of these movements due to their slowness and the sheer size of each plate. Nonetheless, these shifts have a significant impact on human life because plate movement is what causes changes in the geographical structure of the earth’s surface. Mountains are formed in this manner over time.
  • When the continental crust is undergoing extensional deformation, continental rifting occurs. This causes the lithosphere to thin and the asthenosphere to rise, resulting in an uplift.
  • Depending on the movement and collision of these plates, various types of mountains are formed.
  • Volcanic, dome, fold, and block mountains are the types of mountains.

Types of Mountains

Fold Mountains:

  • When two tectonic plates of the Earth’s crust collide, they fold over each other and form fold mountains.

Fold mountains

  • Fold mountains are among the youngest mountains on the planet.
  • The presence of fossils suggests that the sedimentary rocks of these folded mountains formed as a result of silt and sediment accumulation and consolidation in a marine environment.
  • Fold mountains stretch for long distances but have a narrow width.
  • Fold mountains typically have a concave slope on one side and a convex slope on the other.
  • Fold mountains are typically found along continental margins that face oceans (C-O Convergence).
  • Fold mountains are distinguished by massive granite intrusions (formed when magma crystallizes and solidifies beneath the earth to form intrusions).
  • In folded mountain belts, recurrent seismicity is common.
  • Volcanic activity is frequently characterized by high heat flow (the Himalayas is an exception due to C-C convergence).
  • These mountains are by far the most numerous and significant.
  • They also have abundant mineral resources like tin, copper, gold, and so on.
  • Fold mountains are a very common type of mountain on the planet, and they contain some of the most well-known mountain ranges. For example, the Himalayas, Appalachian Mountains, and the Rocky Mountains.

Fault Block Mountains:

  • Block mountains are formed as a result of large-scale faulting (when large areas or blocks of earth are broken and displaced vertically or horizontally).
  • The elevated blocks are known as horsts, while those that are lowered are known as graben.
  • Block mountains are also known as fault-block mountains because they are formed by faulting caused by tensile and compressive forces.
  • Block mountains are classified into two types:
  • Tilted block mountains have a steep on one side and a gentle slope on the other.
  • The top of lifted block mountains is flat, with extremely steep slopes.
  • Some examples of mountains in Europe are – the Great African Rift Valley (valley floor is Graben), the Rhine Valley (graben), Sierra Nevada in the USA, and the Vosges Mountain (Horst).

Fault Block mountains

Dome Mountain:

  • When a large amount of melted rock (magma) pushes up through the earth’s crust, dome mountains
  • Dome mountains are shorter than folded mountains because the magma beneath them does not press as hard. Over time, the lava cools to form cold, hard rock. The result is a mountain with a dome shape.

Dome mountain

Volcanic Mountains:

  • Volcanoes are formed along the edges of tectonic plates by plate movement, and when volcanoes erupt, they form volcanic mountains.
  • Volcanic mountains include Mt. Kilimanjaro and Mt. Fujiyama.
  • The western United States’ Cascade Mountains, the mountain present in the Hawaiian Islands and Icelands are examples of volcanic mountains.

Volcanic mountains

Importance of Mountains:

  • Mountains hold a lot of water, and glaciers in the mountains are the source of many rivers.
  • Water reservoirs are constructed in the mountains, and the water is used to irrigate fields and generate electricity.
  • River valleys and terraces are ideal for crop cultivation, and mountains are home to a diverse range of flora and fauna.
  • Mountain forests provide food, shelter, fuel, and so on, and mountains are also excellent locations for tourism.
Formation of mountain


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