Introduction

Exogenic processes are geomorphic processes. Changes in landforms through physical and chemical methods are called geomorphic processes. Different landforms have been created through this process in different geological periods. 

Geomorphic processes can be broadly divided into three categories, these are as follows

1. Terrestrial processes

2. Extra-terrestrial processes

3. Man-made processes.

Terrestrial processes

The tectonic processes that take place on Earth are called terrestrial processes. Terrestrial processes play a major role in the formation of landforms. These terrestrial processes can be divided into two categories, Such as the endogenic process and the exogenic process.

Different types of landforms are formed on Earth due to the combined effects of exogenic and endogenic processes. So the role of these two processes is very important. The following is a definition and description of exogenic processes (1) & (4). 

Exogenic processes

Meaning

The word exogenic comes from two Greek words exo and genic. The word Exo means ‘from outside’ or ‘external’ and the genic word means ‘origin’. 

Definition

All the forces that act outside the earth’s surface and cause changes in the earth’s surface are called exogenic forces. These forces that are constantly acting on the surface of the crust (erosion, transport, and storage) and are causing the evolution of landforms are called exogenic processes.

Geologist Chamberlin called the exogenic process the gradation process. The surface reaches an equilibrium level through the erosion and accumulation of exogenous energy, which is called the gradation process. Hence the external process is called the gradation process (1).

Some interesting facts about the exogenic process

1. It is a very slow process.

2. These processes act on endogenous processes to form smaller landforms. 

3. The energy required for these processes comes mainly from the atmosphere and the sun. 

4. This process also gets energy from the slope of the land created by the geological process (slope of gradient).

5. Sediments and sedimentary rocks are formed in this process. 

6. This process refers to all the processes that are produced at the surface of the earth. 

7. Weathering, erosion, transportation, etc. are the primary exogenic processes.

8. This process is also known as a destructive process.

9. Exogenic processes are a direct result of the sun’s rays (1) & (2).

Phases of exogenic process

1. Weathering

Surface rock is mechanically broken down and chemically weathered by various elements such as humidity, moisture, temperature, precipitation, etc. This process is called weathering.

2. Erosion

Erosion is the process that removes rock, soil, and other dissolved material from one place on the earth’s surface and then transports it to the other place. Running surface water, wind, glaciers, waves, karst, etc. are the agents of erosion.

3. Transportation

Transportation is the acquisition of rock debris by geomorphic agents like winds, waves, etc.

4. Deposition 

The process in which some substances such as sediment, rocks, or soils are added to the earth’s surface is called deposition (3).

Processes of exogenic process

Aggradation process

• The process by which the elevation of the earth’s surface gradually increases is called the aggradation process. 
• The elements involved in the process of aggradation are currents, groundwater, glaciers, wind, ocean waves, etc. 
• Accumulation and storage of all materials eroded and transported by the river is called the aggradation process. 
• This process occurs in gently sloping parts of rivers and floodplains. 
• In this process, the elevation of the lowlands increases and forms floodplains, deltas, drumlins, sand dunes, etc. 
• Plains are formed as a result of the aggradation process.

Degradation process

• The process by which the height of the lithosphere gradually increases is called the Degradation process. 
• Weathering, mass wasting, deposition, etc. are the elements of the degradation process.
• Degradation is the process of lowering the elevation of land surface by exogenic processes. 
• It occurs on the steep slopes of the river. 
• Different types of erosional landforms are formed in this process. 
• Degradation creates convex and concave slopes.

Biological process

In this process, the entire biosphere i.e. plants, animals, and humans change the landforms. Construction of dams, filling of wetlands, etc. has a huge impact on human beings and wildlife (1) & (5). 

Endogenic and exogenic processes differences

Before discussing the difference between endogenic and exogenic processes, some discussion about endogenic processes is given below.

Endogenic process

• Meaning

The term endogenic is derived from the Greek words endo and genic. The word endo comes from ‘endon’, which means ‘internal’, and the genic word comes from ‘genesis’, which means origin.

• Definition

The process by which all the natural forces that are constantly working in the interior of the earth’s surface are called endogenic processes. That is, the change in the topography that occurs through construction, expansion, uplift, and degradation etc. of the earth under the influence of convection currents generated in the atmosphere is an endogenic process. 

There are different types of semi-liquids in the earth’s interior. The physical and chemical properties of these substances change mainly due to pressure and heat. As a result, an endogenic force is created from the ground. It affects the crust suddenly or slowly in different ways. These methods together are called endogenic processes (1) & (5).

Interesting facts

1. Endogenic processes are the mechanisms by which internal geologic forces act to form primary landforms.

2. Endogenic force involved in this process is caused by changes in the physical and chemical properties of the elastic material within the inner sphere. 

3. These processes act on the crust both suddenly and slowly over long periods.

4. In this process, the relative movement of the crust occurs, and the main landforms that form are continents and oceans or mountains, plateaus, and plains.

5. Endogenic processes are responsible for the formation of the earth’s relief and the formation of important mineral resources. 

6. This process plays an important role in maintaining other structural features of the earth’s crust. 

7. Earth’s internal heat is the ultimate source of energy that drives the endogenic process (4).

Differences between endogenic and exogenic process

The endogenic process and exogenic process both are geomorphic processes. But some differences can be noticed between them.

Similarities between endogenic and exogenic process

1. Endogenic and exogenic processes are geomorphological processes.

2. They both participate in the formation of the earth’s landforms.

3. Both are natural processes that do not require human intervention.

The exogenic processes of the rock cycle

There are three types of rocks in the Earth’s crust

1. Igneous rocks

2. Sedimentary rocks

3. Metamorphic rocks

The origin or creation of these three types of rock is rotating cyclically. Underground magma flows to the surface as lava. In different parts of the crust, it forms igneous rocks.

These igneous rocks are again crushed by various exogenic forces, especially weathering. Later transported by rivers, wind, glaciers, ocean, groundwater, etc. Then it deposits in layers on the seafloor and creates sedimentary rocks. 

The sedimentary rocks are again altered by heat and pressure to form metamorphic rocks. But not only sedimentary rocks, igneous rocks also become metamorphic rocks under heat and pressure. Again, sometimes intrusions of hot magma come into contact with many metamorphic and sedimentary rocks that melt and form igneous rocks. 

Thus it can be seen that three types of rocks are successively changing from one rock to another and this is called the rock cycle. In this way, exogenic forces help in the rock cycle (1).

Q&A

1. What is exogenic process?

The process by which natural forces such as rivers, wind, glaciers, etc. act on the surface of the earth to change the landform is called the exogenic process. This process is also called an external process.

2. What are the sources of energy for exogenic processes?

Natural forces on the earth’s surface such as rivers, wind, glaciers, weathering, groundwater, etc. are the forces involved in this process. The sources of energy for exogenic processes is sunlight. Sunlight causes air to move, and water to be lifted in the mountain. 

3. How do endogenic processes differ from exogenic processes?

• Endogenic processes act on the crust both suddenly and slowly over long periods. However exogenic processes work only slowly over long periods on the crust.
• The primary processes of the endogenic process are eperogenic movement, orogenic movement, isostasy, earthquake, volcanism, etc. On the other hand wind, glaciers, aggradation, degradation, etc. are the main processes of the exogenic process.
• In the endogenic process, the relative movement of the crust occurs, and the main landforms that form are continents and oceans or mountains, plateaus, and plains. But exogenic processes erode the main landforms create a variety of small and fine landforms and form natural landscapes.

4. How the rate of endogenic processes is influenced by the rate of exogenic processes?

The endogenic process creates after-effects that become visible only after sudden damage. Exogenic processes produce visible changes over thousands or millions of years.

5. What is the definition of exogenic processes?

The external natural forces or exogenic forces in which the surface and subsurface are exposed or modified to form landforms through erosion, transport, and accumulation are called exogenic processes.

Reference

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

Written By: Manisha Bharati