Introduction

Diastrophism is a geomorphological process. Although the crust is stable under the influence of internal forces, some place of the crust is always being stirred or changed. Therefore, the slow, sudden, or rapid changes in the earth’s crust as a result of earthquakes or other movements under the influence of internal forces are called earth movement. There are two types of earth movement. These are slow movement or diastrophism and sudden movement. Below is a discussion of the definition and description of diastrophism.

Diastrophism is a process that means disturbance and dislocation of the earth’s crust including its bending, folding, and breaking. Due to the effect of this earth’s movement, there is a huge change in the topography or the crust on the earth’s surface, so it is called diastrophic forces. 

Among the different types of geomorphological processes, diastrophism is one of them. It is also called tectonism. Diastrophism, also called tectonism, is the large-scale deformation of the earth’s crust by natural processes. This results in the formation of continents, rift valleys, plates, mountain systems, and lithospheric plate movement such as volcanic movement, folding, etc. (1) & (5).

Diastrophism definition

Meaning

The diastrophism word comes from the Greek word ‘diastrophe’ which means distortion or dislocation (2).

Definition

The interior part of the earth is molten due to intense heat. Convection currents generated in this molten material generate tremendous energy in the earth’s interior. As a result, the earth’s surface is stirred, which is called diastrophism (2) & (5). 

Interesting facts

1. This type of earth’s movement occurs slowly.

2. Diastrophism acts under the crust for thousands or millions of years.

3. As a result of this earth’s movement, the height and position of a large part of the crust can be changed.

4. Mountains, plateaus, plains, faults, folds, etc. are formed by this process.

5. The intensity of such earth’s movement is low.

6. Slow movement or diastrophism cannot be measured with instruments.

7. It is a type of earth’s movement of deformation of the earth’s crust that involves folding and faulting.

8. Vertical and horizontal movement of the land occurs in this earth movement.

9. Diastrophism cannot be felt all the time.

10. This type of earth‘s movement covers the movement of solid crust material.

11. It is considered a part of Geotectonics.

12. The processes that come under diastrophism move, lift or build up parts of the earth’s crust.

13. Different parts of the crust change, and evolve, and new landforms are formed as a result of diastrophism (5).

Classification

There are two types of diastrophism. These are

• Epeirogenic movement
• Orogenic movement.

1. Epeirogenic movement

Meaning

The English equivalent of the word epeirogenic is epeirogeny. The Greek word ‘Epeiros’ means continent and ‘Genesis’ means origin. That is, the meaning of the word epeirogenic is the origin and formation of continents.

Definition

The movement that acts vertically on the earth’s surface causing uplift or subsidence of the crust is called epeirogenic movement. Usually, this movement is organized widely across the continent hence it is called epeirogenic movement. 

A characteristic of the epeirogenic force is that it acts vertically along the radius from the earth’s center to the surface. As a result, a part of the crust is upward or downward vertically. As a result, the bedrock is upward or downward. When this earth’s movement occurs over vast areas of the continent, parts of the continent upward from the sea or downward to form oceans. This is called epeirogenic movement (1).

Types

Upward movement

A continent or a coastal region gradually rises upwards under the influence of a heavy epeirogenic movement called upward movement.

Downward movement

A continent or a coastal region gradually moves downward under the influence of a heavy epeirogenic movement called downward movement or submergence (5).

Causes of epeirogenic movement

The primary causes of epeirogenic movement are

• Accumulation of low-density material from the mantle in the lower surface region of the crust.
• Reduction in the volume of matter in the upper crust or lower crust due to various reasons.
• Due to the increase in heat, the upper mantle and the crust expand and increase in volume.

• Uplift is caused by the intrusion of one rock layer below another rock layer (1).

Interesting facts

1. Epeirogenic movement occurs along the earth’s radius.

2. Along the radius of this earth movement, the tectonic force acts towards the center of the earth or outwards from the center of the earth.

3. In this case vertical upward or downward of the rock layer occurs.

4. Although epeirogenic movement is widespread, it is regionally or locally limited.

5. In this process, a fault or fold is created in the rocks.

6. Due to this earth’s movement, landforms such as large continents, rift valleys, block mountains, plateaus, etc. are formed (1) & (3).

2. Orogenic movement

Meaning

The English equivalent of the word orogenic is orogeny. Here the Greek word ‘oros’ means mountain and ‘genesis’ means origin. That is, the word orogenic means the formation of mountains. As a result of this process, Fold Mountains are formed, so it is called orogenic movement (1).

Definition

As a result of the earth’s movement, the rock layers are folded and Fold Mountains are formed, and when the compressive force is strong, faults are created, it is called orogenic movement. This type of movement works horizontally on the surface, so it is also called horizontal movement. In fact, it is tangential to the elliptical surface of the earth.

Orogenic movement acts horizontally or tangentially on the surface. As a result of this movement, two land areas move towards each other (convergence) and somewhere they move in opposite directions (divergence) (1) & (4). 

Causes of orogenic movement

Causes of orogenic movement are

• The substances inside the earth are in a molten state. As such material cools by radiating heat, the surface of the crust contracts. 
• Earth’s interior is molten and unstable at high altitudes. As a result, the convection currents that are created in the interior of the earth, when they create horizontal pressure on the surface, the rock layers are folded and mountains are formed.
• Folds are formed by tectonic pressure in the thick sedimentary layers accumulated in the geosyncline. For example, the Himalayas and the Alps were formed by the strong pressure of Gondwanaland and Angara land on the sediments deposited in the Tethys Sea. 
• At present, scientists attribute the horizontal movement of continent-continent or continent-ocean plates as the cause of the orogenic movement (1) & (6).

Interesting facts

1. Orogenic movement helps in forming Fold Mountains.

2. This earth’s movement acts horizontally on the surface.

3. Formation of folds in the crust due to the effects of this earth’s movement.

4. This type of earth’s movement occurs along the tangent of the earth.

5. Here the forces act horizontally towards each other. 

6. Horizontal displacement of the crustal part occurs in this earth’s movement.

7. This earth’s movement takes place over a wide and vast area.

8. In this type of earth movement, the force acts horizontally along the tangent.

9. Such earth’s movement results in the compression of rocks and folds.

10. Its impact only resulted in the emergence of the Fold Mountains. However, due to extreme pressure, many thrusts were created throughout the hilly areas (6).

What are the three processes in which diastrophism is involved

Diastrophism is involved in folding, faulting, and board warping.

Theory of isostasy of diastrophism

Definition

The earth’s movement which occurs to establish the height balance between different landforms of the earth is called isostasy of diastrophism.

Theory of isostasy of diastrophism

Theory of Airy

This model describes the elevation of different areas as being sustained by changes in crustal thickness, with a constant density of crust. Sir George Airy presented his isostasy theory in 1855 AD. Airy’s isostasy theory is based on the theory of the buoyancy of matter. He said in his theory that just as icebergs float in water, so the continental land, ie, the oceanic crust, floats on the boundary. 

Boundary density is 2.87 g/cubic cm and sial density is 2.65 g/cubic cm. So within the boundary layer of higher density, different parts of the continental crust like mountains, plateaus, and plains height and depth are floating at a proportional rate.

Incidentally, the height of the continental part is higher, and its root or depth is also higher. 

Theory of Pratt

In 1859 the scientist J. H. Pratt proposed a different theory about isostasy. His theory is based on the difference in density of crustal particles. He said, the masses of crustal particles are proportional to their diameters and their densities are different. Therefore, even though they have unequal densities, they exert the same pressure for equal weight. There is an inverse relationship between the height of a landform and its density. Higher landforms have less density and lower landforms have higher density.

Vening Meinesz or flexural isostasy 

This model describes the lithosphere acting as an elastic plate and bending its internal rigidity to distribute local locational loads over a wide area (7).

Q&A

1. What are the three processes in which diastrophism is involved?

The three processes in which diastrophism involves are faulting, folding, and board warping.

2. What are the effects of diastrophism?

• Diastrophism has many effects on the earth’s surface and including the formation of mountains, plateaus, and can cause tremors and earthquakes. 
• It is related to any movement of the solid part of the earth.
• This process causes the deformation of the earth’s crust.
• Slow bending, folding, faulting, etc. occurs in this process. 

3. What is diastrophism?

Diastrophism is the very slow vertical and horizontal movement of a part of the crust usually under the influence of internal forces.

4. Which of the following is not a feature of diastrophism?

Metamorphism is not a feature of diastrophism.

5. What is faster when a mountain range is still rising?

Diastrophism 

Written By: Manisha Bharati

Reference

1. Savindra Singh. Geomorphology. Pravalika Publications, Allahabad. Chapter 9: Earth’s movement. Page No: 158 to 169.