Definition and Explanation of Geomorphic Cycle

Many of us love visiting hill stations for vacations. It is a balm for the tired soul and does wonders for the mind. Some of us might love trekking up mountains and settling down on the top to either view sunrise or sunset or just stare in awe at the magnificent landscape all around. 

 

Have we ever looked at those fascinating mountains or the green plains and wondered how they might have been formed? Certainly, the process would not be simple! 

 

Set by William M. Davis, the theory of the geomorphic cycle tries to tell us how terrains are developed across landscapes. The model involves explanations for many different structures such as hilltops, valleys, mountains, and rivers. Because it describes the processes of erosion and deposition which eventually lead to relief or terrain formation, it is also known as the cycle of erosion or the theory of land evolution. 

 

Meaning of Geomorphic Cycle

The geomorphic cycle is any cycle of events that leads to the formation of any relief (terrain) development in landscapes. It is a model explaining the formation of many different terrain structures such as hilltops, valleys, mountains, and river drainage systems. It is also known as the geographic cycle or the cycle of erosion for the development of various landscapes. Hence, a geomorphic cycle is the theory of evolution of landforms that includes many distinct events of erosion and deposition due to a variety of reasons that will be discussed below in this article. 

 

The Geomorphic Cycle

William M. Davis first set the theory of the geomorphic cycle and laid down some concepts of geomorphic cycles and landscape development. According to the theory, there are commonly three stages of the cycle of erosion and the development of any landforms. The three periods are classified from youth to maturity and old age. 

 

These stages were considered to be gradually transitioning from one period to another. This model that explains the concepts of geomorphic cycles and landscape development is known as the Davis geomorphic cycle. Although certain aspects of the Davis geomorphic cycle are not currently accepted, it is still the primary and widely proclaimed theory of the geomorphic cycle that describes the various events leading to the formation of landscapes. 

 

Stages of the Geomorphic Cycle 

The Youthful Stage

The initial stage as put forward by the Davis geomorphic cycle is the youthful stage of landscape development. This stage of terrain development begins with the upliftment of the landform. It includes either the uplifted or to-be-uplifted periods of the development process. During this stage due to the processes that favour the uplifting of the landform, significant folds are produced in the crust of the Earth. These folds are generally the mountains or the block mountains. 

 

This uplifting process of mountain formation is widely known and an accepted phenomenon. The folding or uplifting can occur due to a variety of phenomena such as the movement and clashing of the tectonic plates of which the Himalayan mountain range is an example. During the youthful stage, the rivers flowing through the uplifted landform would create another distinction between the uplands and valley bottoms. The differences between the uplands and the valley bottoms increase rapidly throughout this stage and even during the height of the youthful stage. 

 

The Mature Stage

Following the youthful or the youth stage, comes the mature stage of the geographical landscape development. During this stage, due to the dissection of the streams or rivers, the ever-increasing difference in-between the valley bottoms and the uplands or the mountains reaches its height. These height differences are the greatest in the mature stage of relief development. 

 

Another factor that plays a significant role in the mature stage is the slope decline. When the height difference between the uplands and the valley bottoms reaches the maximum, slope decline becomes an important phenomenon. The slope of the upland begins to decline faster than the incision or dissection by any river stream. This effectively leads to the decrease in the relief features of height and the difference between the uplands and the bottom of valleys starts to lessen and diminish gradually.

 

The Old Age Stage

The stage following the mature stage is the ‘old age’ stage of relief development. In old age, the initially uplifted terrain feature gradually diminishes or reduces to a surface known as the peneplain. During the old age, which is the latest stage in the process, the erosion has been acting upon the terrain so long that although the terrain was at a significant height when uplifted, it is now reduced to a lowland which is known as the peneplain. 

 

The peneplain is usually at sea level and sometimes is reduced so much that it drowns around the nearest water bodies. Although some of the peneplains may be submerged, some may maintain the residual height from the initial upliftment.

 

The Second Geomorphic Cycle

Following old age, the second geomorphic cycle starts again with the upliftment of the terrain. One of the important factors according to this theory of Davis geomorphic cycle which explains the concepts of geomorphic cycles and landscape development, is the contribution of time in the process of erosion. Time plays an important role according to the theory in the entire cycle of erosion. 

 

But, there are certain cases when during any of the stages of the geomorphic cycle the upliftment can start before completion of old age. This event when it occurs is known as rejuvenation. It may or may not be a common phenomenon for a particular relief structure. This is because according to Davis, the full geomorphic cycle was a rare or special case as there are continuous geological changes taking place throughout the world which can cause changes in the stages of the geomorphic cycle. 

 

This theory of the evolution of landscapes applies to hilltops, valleys, mountains, and river drainage systems. Based on this theory, it is assumed that once the stage of any landform is known, the history of the landform development can be known according to the established principles.

 

Drawbacks of the Common Theories of the Geomorphic Cycle

Although Davis had been able to acknowledge the factors affecting the geomorphic cycle as rock type, structure, and processes of erosion, he emphasised the importance of time. But it is currently believed that time does play a significant role as Davis suggested and the contribution by it is the same as other factors in relief development. 

 

This theory of the cycle of erosion has been widely accepted although there is accumulating evidence that refutes the theory of the Geomorphic cycle. It is now usually considered that the initial conditions or the conditions surrounding the upliftment of the landform may not significantly guide the stages towards the end products. Instead of a gradual transition of the landforms through various stages, there is a dynamic equilibrium reached in-between the landforms and the processes that act upon them, which in turn leads to erasing of the physiographic history of the region. 

 

Another drawback of the theory is that originally the theory intended to provide explanations for the development of temperate landscapes as the major focus was put on the erosive activities by the river streams on the uplands or uplifted regions. Also, the nature of surface processes was poorly represented by the model. It was mostly theoretical and deductive and did not take into account the complexity of tectonic movements and climate change. Nevertheless, the cycle of erosion has been accepted by extending and including certain modifications that involve the arid, glacial, karst, coastal and periglacial areas. 


Conclusion

This is all about the different types, stages, and drawbacks of the geomorphic cycle. Learn the important features of this theory with the aspects defined and explained in this article. 

FAQs on Geomorphic Cycle

1. What Do You Mean by the Cycle of Erosion?

The sequence of events that guide the changes in the landscape development, starting from the erosion by running water, waves, water, and air currents, or glaciers, until an initially risen relief structure, is reduced to a low-level land which is at sea level, is known as the cycle of erosion. The cycle of erosion is also known as the geomorphic cycle. 

2. What are the Steps in Erosion?

There are four common steps that are involved in erosion. They are weathering, detachment, transport, and deposition. This sequence of events follows exactly in the same order as mentioned. 

3. Describe the youthful stage in the geomorphic cycle.

In the Davis geomorphic cycle, the first stage of landform formation is the youthful stage where the upliftment of land takes place. Certain processes cause the upliftment of the landform at this stage which in turn leads to the formation of folds in the crust of the earth. Usually, these folds produce mountains or block mountains. We are familiar with how mountains are formed due to folds. It is quite a well-studied and well-accepted phenomenon all over. 


This uplifting or folding process has a wide variety of causes. It could happen because of the moving or clashing of tectonic plates for instance. The mighty Himalayan mountain ranges are the perfect example of this. As forms form and flow through the heartlands of these mountains, they create a clearer distinction between the hill slopes or uplands and the valleys which can be inhabited by people. These distinctions appear to increase during the youthful stage.

4. How will you explain the mature stage in the geomorphic cycle?

Various changes happen during the mature stage which follows the youthful stage. At its peak, the flowing rivers create further dissections between the uplands and the valley ranges. However, a sloping decline happens when this differentiation reaches its maximum level. During this period, the slope of the upland goes on a decline despite the separations caused by river streams. This eventually leads to a decrease in the features that distinguish valleys and uplands from one another. 

5. What are the characteristics of the old age stage in a geomorphic cycle?

The final stage in Davis geomorphic cycle which follows the mature stage, is the old age stage. Here, the uplifted terrain reduces to a small surface called the peneplain. Because the terrain has been eroded due to multiple factors for a long time, its uplifted features vanish and it becomes a low-lying plain that can get submerged in nearby water bodies of sea levels so much as even rise. Not all peneplains get submerged though. Some are still able to maintain residual forms of the height they had once in time.

6. Explain the drawbacks of the theory of the geomorphic cycle in a concise manner.

Following are some of the key criticisms of this theory - 

  • Evidence has been growing which refutes Davis theory of the geomorphic cycle

  • Unlike Davis’s suggestion that the initial stages of landform formation also dictate the final products, current research is leaning towards a dynamic equilibrium being formed between processes acting upon the land and the land itself as it moves through various stages of growth. 

  • The theory was only limited to providing explanations for temperate landscapes

  • Surface processes are insufficiently represented in the theory

  • It mostly sticks to theory and does not take into account how intricate and complex, tectonic movements can be. 

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