Fold - Endogenous Force on Upper Surface of the Earth

Fold - Endogenous Force

The relief of our earth is full of variations and contrasts. Due to the fold-endogenous force on the upper surface of the earth, there are high mountains at some places, and flat plains at some places. Somewhere there are deep trenches, and somewhere there is sea. In some places there are snow-filled glaciers and mountain ranges, where there is no trace of vegetation, then there are also marshy places, which are full of oddities and mysteries. Have we ever thought, what is the reason for all these differences? The answer is – 

Mainly two types of forces work on the earth, which are as follows –

1. Endogenous forces – By these, disparities are created on the earth. Like – Earthquake, Tsunami, Long term force etc.
2. Exogenous Forces – These are the plane stabilizing forces of the earth. Like – flowing water, sea water, glacier, wind etc.

1. Endogenous Force

As we said above, inequalities are created on the earth by endogenic forces. Endogenous i.e. the creation of disparities on the earth by the force generated from inside the earth. Earthquakes, tsunamis, volcanoes etc. come under this. 

Endogenous force can be divided into two parts, which are as follows –

1. Sudden Force : Like – earthquakes, tsunamis, volcanoes etc.
2. Long-Term Force or Plate Deformation Force
1. Vertical Movement – Continent Builder
1. Upward – In this the land rises upwards. Like – 24 km 0 land near the Gulf of Kutch has risen several km 0, which is also called Allah's dam.
2. Downward – In this the land is sunk towards the bottom. For example – Submerged forests of Prince Dak area of Mumbai.
2. Horizontal Movement – Mountain Builder
1. Compression Force – In this, the layers of rocks are folded, that is, folds occur in the layers of rocks.
1. Anticline – The raised part in the action of folding is called anticline.
2. Syncline or Abhinati  – The part of the trough sunk down in the process of folding is called Abhinati or Syncline.
2. Tension Force – In this, there is a change in the land between two cracks, that is, due to the tension force, fault action takes place.

Fold

According to the above description, the action of folding is a compressional force under the horizontal movement force. In this, due to the effect of horizontal and tangential forces, there is pressure in the rocks, as a result of which the action of folding takes place and the layers of rocks are folded. Peaks and basins are formed due to the process of folding. Two types of structures are formed as a result of folding action – Anticline and Syncline. In this, the raised part of the rocks is called anticline and the sunken part or trough is called syncline.

Rock & It's Types

Types of Fold 

Due to the difference in compression force, differences are seen in the types of folds, the details of which are as follows –

1. Symmetrical Fold Or Simple Fold  
2. Asymmetric Fold 
3. Monoclinal fold
4. Open Fold
5. Closed Fold 
6. Overlfold
7. Isoclinal Fold
8. Recumbent Fold 
9. Overthrust Fold
   • Nappe 
10. Fan Fold 
    • Anticlinorium
    • Synclinorium

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1. Symmetrical Fold or Simple Fold

It is formed when the intensity of the compressive strength is less and equally in both the directions. Both its sides are equally inclined and the axis line is perpendicular. These are straight open. It is also called Simple Fold. Like – Jura mountain of Switzerland.

2. Asymmetric Fold

Asymmetric means in this both the sides of the fold are unequal. In this, the side with less inclination is longer and the side with more inclination is shorter. Like – Southern Pennine Mountains of England.

3. Monoclinal Fold

In this, one arm of the fold is exactly vertical, which makes a right angle with the ground. And the other arm is normally inclined. Like – Australia's Great Dividing Range.

4. Open Fold

When the angle between the two sides of the fold is greater than 90 and less than 180, then this type of fold is called an open fold.

5. Closed Fold

When an acute angle (angle less than 90) is formed between the arms of a fold, it is called a closed fold.

     Rock & It's Types

6. Overfold

It is formed due to intense compressive force in one direction. In this, one arm of the fold protrudes forward to form a steep slope. While the other arm, which is relatively longer, bends less to form a slow slope. Like – Pirpanjal range of Kashmir (Himalaya).

7. Isoclinal Fold

When there is equal pressure in both the directions due to compression, both the arms of the fold bend in the same direction. And almost become parallel to each other. The front part appears to be hanging in it. Like – Kalachinta mountain of Pakistan.

8. Recumbent Fold or Double Fold

When the intensity of horizontal movement is high, due to the folding both the arms are folded so much and come on top of each other in horizontal position. Along with this, they also become almost parallel to the ground. It is also called double fold. Like – Carrick Castle mountain of United Kingdom.

9. Overthrust Fold or Overturned Fold

When the compressive force is very strong, the perihelion folds break away from their axis and climb on each other or they move forward and get superimposed on another block. In this, the raised part of the fold is called superimposed fold. In this, the order of folding is reversed, that is, the lower layer comes up and the upper layer goes down. Like – Pir Panjal range of Kashmir

a. Nappe

Due to the extreme intensity of the compressional force, when the superimposed fold is several kilometers away and climbs on other types of rocks, it is called Nappe or Prachhed. Nappe means 'tablecloth' in French. Meaning Just as the structure of the tablecloth is different from its table, in the same way the neck section is also different from its bottom layer. Like – Garhwal, Himalayas.

Mountains and It's types

10. Fan Fold

When due to variation of compressive force or uneven compression, many small dips and declinations are seen under a large tilt or a large tilt. Their structure is similar to a fan (hand fan or bena), due to which they are called fan folds. 

We can divide them into two parts.

• Anticlinorium
• Synclinorium

a. Anticlinorium

When a fan fold is formed in the direction of the dip, it is called anticlinorium. Many small anticlines and synclines are seen in this great inclination. Like – the mountainous region of Southern Scotland and the Singhbhum Sampanati of Chhotanagpur.

b. Synclinorium

When a fan fold is formed in the direction of the thrust, it is called synclinorium. Many small synclines and anticlines are also formed in this broad orientation. Like – Potawar mountain region of Pakistan.

Volcanoes and Its Types