What is a Residual Mountain?
A residual mountain or mountains of denudation is a type of landform that gets made over the years following the erosion of already elevated lands. The shape of the earth's surface can be altered by forces both within and outside the earth. Geomorphic powers have also been discussed in previous Geography notes. Many different landforms can be created by endogenic and exogenic forces. A landform is a normal characteristic of the Earth's solid surface.
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The Formation of Residual Mountains
In the subjects of geography and geology, we get to learn about different types of landforms that we find on the land surface of the earth. These landforms are formed by different external factors or geological forces acting over a long period of time. Mountains are such a special feature on the face of the earth. These are the structures present as an elevation with respect to their surrounding area. The most common identification is by the presence of steep on all its sides. The summits are usually conical. but the top can also be in the shape of a ridgeline if the mountain is a part of the mountain range. The forces or processes responsible for the formation of mountains or their rising can be many. The movement of tectonic plates and volcanoes are identified as the primary forces for the uplift of the land at certain points and are termed as fold mountains, volcanic mountains.
After the formation of mountains, it again undergoes various external forces of nature and changes continuously. As erosion is the natural phenomenon of degradation and transfer of soil particles it also affects the soils on the surface of mountains. Blowing winds and flowing water during rains wash away the top fine layer of the soil present on it. Then the bedrock present beneath this layer gets exposed and the mountain looks rocky devoid of any vegetation. Though this rocky surface is resistant to the forces of erosion, over time it can also degrade and erode gradually. After a long period of time, the height decreases and the size gets smaller and smaller. These degraded mountains left after the denudation are known as residual mountains in general terms.
FAQs on Residual Mountains
1. What are residual mountains, and how do they form?
Residual mountains are the remnants of older, pre-existing mountains (such as fold, block, or volcanic mountains) that have been worn down over millions of years. They are formed through a process called denudation, which involves weathering and erosion. Agents like wind, rain, ice, and running water gradually erode the softer, less resistant rocks, leaving behind the harder, more resistant rock masses. These surviving, weathered-down structures are what we identify as residual mountains.
2. What are the main characteristics of residual mountains?
Residual mountains have several distinct characteristics that differentiate them from younger mountain types. These include:
- Low Altitude: Due to prolonged erosion, they are generally much lower in height compared to young fold mountains like the Himalayas.
- Rounded Peaks: Their summits are typically rounded or flattened, not sharp and conical, because the sharp edges have been weathered away.
- Gentle Slopes: The constant process of erosion results in gentle, less steep slopes.
- Ancient Origin: They are the remains of very old mountain systems, representing ancient geological landscapes.
3. What are some important examples of residual mountains in India?
India has several prominent examples of residual mountains, which are remnants of ancient mountain ranges. Key examples include:
- The Aravalli Range in North-Western India, one of the oldest fold mountain systems in the world, now heavily eroded.
- The Vindhya and Satpura Ranges in Central India.
- The Parasnath hills in Jharkhand.
- The Nallamala hills, Javadi hills, and Palkonda ranges in the Eastern Ghats region of Southern India.
- Mahendragiri in Odisha.
4. How are residual mountains fundamentally different from fold mountains?
The primary difference between residual and fold mountains lies in their formation process and age. Fold mountains (like the Himalayas or the Alps) are formed by the compressional forces of two tectonic plates colliding, which causes the Earth's crust to buckle and fold upwards. They are relatively young and have high, pointed peaks. In contrast, residual mountains are not formed by uplift but by the erosion of existing mountains. They are the old, hard 'skeletons' left behind after the softer rock has been stripped away over geological time, resulting in lower heights and rounded tops.
5. Why are the Aravalli Ranges in India a classic example of residual mountains?
The Aravalli Ranges are a classic example because they were once a mighty range of young fold mountains, formed millions of years ago, possibly taller than the Himalayas are today. Over hundreds of millions of years, they have been continuously subjected to weathering and erosion by natural forces. This has worn them down so significantly that what we see today is merely the eroded stump, or the hard, resistant core, of that ancient mountain system. Their current low altitude, rounded peaks, and vast age perfectly illustrate the life cycle of a mountain range transforming into a residual form.
6. What are the other names used for residual mountains in geography?
In geography, residual mountains are also known by other names that describe their origin. The most common alternative terms are relict mountains or mountains of circum-erosion. The term 'relict' signifies that they are a relic or remnant of a past landscape, while 'circum-erosion' points to the process of being shaped by erosion from all sides.
7. Why do residual mountains often appear as isolated hills rather than a continuous chain?
Residual mountains often appear as isolated hills or scattered ranges because the process of erosion does not happen uniformly. Over millions of years, erosion targets the softest and weakest parts of an ancient mountain chain or plateau first. The harder, more resistant rock bodies withstand this erosion for much longer. As the surrounding softer land is worn down and lowered, these durable rock masses are left standing in isolation, disconnected from each other, thus appearing as individual hills or small ranges like the Mesas and Buttes in the USA.
