Q. When you travel in Himalayas, you will see the following: - Deep gorges
- U-turn river courses
- Parallel mountain ranges
- Steep gradients causing land sliding
Which of the above can be said to be the evidences for Himalayas being young fold mountains? (UPSC Prelims 2012)
Answer:
1, 2, 3 and 4
Notes: The correct answer is
[D] 1, 2, 3 and 4. The Himalayas are classified as "Young Fold Mountains" because they were formed relatively recently in geological history (about 40 to 50 million years ago) by the collision of the Indian and Eurasian plates. The features mentioned are direct consequences of this ongoing tectonic activity and the resulting high elevation.
- Deep Gorges (Statement 1 is Correct): As the Himalayas rose, the pre-existing (antecedent) rivers like the Indus, Brahmaputra, and Satluj continued to flow in their paths. To maintain their course against the rising land, these rivers cut vertically into the rocks at a very high rate, creating deep, narrow V-shaped valleys or gorges. This indicates that the mountains are still rising and the rivers are actively eroding them.
- U-turn River Courses (Statement 2 is Correct): Many Himalayan rivers exhibit sharp, hairpin bends or "syntaxial bends." The most famous is the Brahmaputra (Tsangpo) taking a sharp U-turn near Namcha Barwa to enter India. This is evidence of the intense folding and the specific southward-bending structural trend of the mountain range at its eastern and western extremities.
- Parallel Mountain Ranges (Statement 3 is Correct): The Himalayas consist of three distinct, parallel longitudinal ranges: the Great Himalayas (Himadri), the Lesser Himalayas (Himachal), and the Outer Himalayas (Shiwaliks). This parallel arrangement is a classic characteristic of fold mountains formed by the compressional forces of tectonic plates.
- Steep Gradients causing Landslides (Statement 4 is Correct): The Himalayas are still geologically active and rising. The steep slopes combined with unstable, folded rock structures and high seismic activity make the region highly prone to landslides. Younger mountains typically have steeper, more rugged profiles compared to old, eroded mountains like the Aravalis.