Q. The Brahmaputra, Irrawaddy and Mekong Rivers originate in Tibet’s 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 (2011)

(a) Uplift of folded Himalayan series 

(b) Syntaxial bending of geologically young Himalayas

(c) Geo-tectonic disturbance in the tertiary folded mountain chains 

(d) Both (a) and (b) above

Answer: (b)

Brahmaputra River has its source in southwest Tibet. It flows there with the name Tsangpo River (flowing from the crest/ summit). The river runs across south Tibet to penetrate the Himalayan Mountain Ranges in huge canyons and subsequently into Arunachal Pradesh (India). In Arunachal Pradesh, it is called Dihang. The river runs to the southwest across the Assam Basin as Brahmaputra and towards the south through Bangladesh as the Jamuna (you should not confuse it with Yamuna of India).

Option (b) is correct: Brahmaputra makes ‘U’ turn in its course to flow into India near Namcha Barwa and it is due to Syntaxial bending of geologically young Himalayas. Additional Information: 

O The gently arching ranges of the Himalayan mountains on their Western and Eastern extremities are sharply bent southward in deep Knee-bend flexures that are called syntaxial bends. 

O On both the ends, the great mountains appear to bend around a pivotal point. The western point is situated south of the Pamir where the Karakoram meets the Hindu Kush. 

O A similar sharp, almost hairpin bend occurs on the eastern limit of Arunachal Pradesh where the strike of the mountain changes sharply from the Easterly to Southerly trend. Besides these two major bends, there are a number of minor syntaxial bends in other parts of Himalayas.