Previous Year Question
When you travel in Himalayas, you will see the following:
Deep gorges
U-turn river courses
Parallel mountain ranges
Steep gradients causing landsliding
Which of the above can be said to be the evidences for Himalayas being young fold mountains?
1 and 2
1, 2 and 4
3 and 4
All of these
Correct Answer: D
Detailed Solution
The Himalayas are geologically recent or young fold mountains. They were formed by the collision of the Indian Plate with the Eurasian Plate. Convergence between the plates is still continuing; therefore, uplift, earthquakes, faulting, erosion and landslides remain active in the Himalayan region.
1. Deep gorges—Correct
The Indus, Sutlej, Brahmaputra and their tributaries have formed extremely deep valleys and gorges through the Himalayas.
Several of these rivers existed before the uplift of the Himalayas.
As the mountains continued to rise, the rivers maintained their courses through rapid downward erosion.
Such rivers are known as antecedent rivers.
The Indus Gorge, Sutlej Gorge and Dihang Gorge are important examples.
The combined effect of rapid uplift and deep river incision indicates the youthful stage of the mountains.
2. U-turn river courses—Correct
Several Himalayan rivers form sharp bends or U-shaped turns because of mountain barriers, structural changes, faults and river capture.
During the formation of the Himalayas, the mountain ranges did not rise uniformly.
At several places, rivers had to cut across rising ranges, while elsewhere their courses were modified by structural controls.
The sharp turn of the Brahmaputra near Namcha Barwa and that of the Indus around Nanga Parbat are important examples.
These features indicate active tectonics and an unstable landscape.
3. Parallel mountain ranges—Correct
The Himalayas do not constitute a single range but a system of several broadly parallel ranges:
Trans-Himalaya
Himadri or Greater Himalaya
Himachal or Lesser Himalaya
Shiwalik
These parallel ranges were produced by successive folding, faulting and thrusting of rocks under pressure from the Indian Plate. Therefore, this feature provides direct evidence of the folded structure of the Himalayas.
4. Steep gradients and landslides—Correct
Steep slopes, weak and highly fractured rocks, active faults, earthquakes and heavy rainfall increase the occurrence of landslides in the Himalayas.
The slopes of geologically young mountains have not yet attained complete stability.
Undercutting by rivers and human activities such as road construction also destabilise the slopes.
Consequently, the Himalayas constitute one of the world’s most landslide-prone mountain regions.
Therefore, all four features provide evidence that the Himalayas are young fold mountains.