The Brahmaputra, Irrawaddy and Mekong rivers originate in Tibet narrow and parallel mountain ranges in their upper reaches. Of these rivers, Brahmaputra makes a “U” turn in its course to flow into India. This “U” turn is due to?
[UPSC Civil Services Exam – 2011 Prelims]
(a) Uplift of folded Himalayan series.
(b) Syntaxial bending of geologically young Himalayas.
(c) Geotectonic disturbance in the tertiary folded mountain chains.
(d) Both (a) and (b) above
Answer: (b)
Explanation:
- The Brahmaputra River originates as Siang or Dihang from the Chemayungdung glacier in the Kailash range near Mansarovar lake, and enters India west of Sadiya town in Arunachal Pradesh.
- It has several tributaries, including Dibang, Lohit, Siang, Burhi Dihing, Tista, and Dhansari.
- The average width of the Brahmaputra Valley is approximately 80 Km, and the river itself is one of the largest in the world, ranking fifth with respect to its average discharge.
- Namcha Barwa, a mountain peak in the Tibetan Himalayas that rises to a height of 7757 meters, is located in the area where the Tsangpo-Brahmaputra River takes a U-turn before entering India through a gorge in Arunachal Pradesh.
- The Himalayas extend from the Indus gorge in the west to the Brahmaputra gorge in the east, with the gently arching ranges of the mountain range’s Western and Eastern extremities sharply bending southward in deep Knee-bend flexures called syntaxial bends.
- These bends occur near Nanga Parbat in the west and Namche Barwa in the east, which is one reason for the Brahmaputra’s U-turn.
Therefore, option (b) is the correct answer.
