Prelims 2011 · archive
MediumThe Brahmaputra, Irrawady and Mekong rivers originate in Tibet and flow through 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
Answer & explanation
Answer: (b) Syntaxial bending of geologically young Himalayas
The Brahmaputra flows eastward through southern Tibet as the Tsangpo. Near Namcha Barwa, at the eastern end of the Himalayas, the young fold mountains bend sharply; this bend is called a syntaxis. The river turns around this bend and enters India. The U-turn is tied to this syntaxial bend, not to Himalayan uplift in general.
- ✗ (a) Uplift of the folded Himalaya is the general mountain-building process. It does not explain why the river turns at one particular place, the eastern end of the range. So (a) is not the specific cause the question asks for.
- ✓ (b) The Tsangpo runs eastward for about 1,200 km through southern Tibet. It then cuts through the Himalaya near Namcha Barwa (7,755 m) and emerges as the Siang/Dihang, entering India west of Sadiya in Arunachal Pradesh. Namcha Barwa is the eastern Himalayan syntaxis, the sharp bend at the eastern end of these young fold mountains, and the river makes its U-turn around it.
- ✗ (c) This option is a vague, general statement about tectonic disturbance. It names no specific structure at the place where the river turns, and it does not point to the syntaxial bend.
- ✗ (d) This option needs (a) to be a correct cause as well. (a) is the general uplift process, not the cause of the turn, so 'both' fails.
Remember · Brahmaputra: Tsangpo in Tibet, then a U-turn around Namcha Barwa, the eastern syntaxis (sharp bend) of the Himalayas, then Siang/Dihang in Arunachal Pradesh.
📘 Read it in NCERT: Class 11 India: Physical Environment, Ch 3 (practise this chapter) · Class 11 India: Physical Environment, Ch 3 (practise this chapter)
Sources
- NCERT Class 11 · India: Physical Environment, Chapter 3 “Himalayas near Namcha Barwa (7,755 m). The river emerges from the foothills under the name of Siang or Dihang. It enters India west of Sadiya town in Arunachal Pradesh.”
- NCERT Class 11 · India: Physical Environment, Chapter 3 “From here, it traverses eastward longitudinally for a distance of nearly 1,200 km in a dry and flat region of southern Tibet, where it is known as the Tsangpo”
- Mio-Pliocene piracy, relict landscape and drainage reorganization in the Namcha Barwa syntaxis zone of eastern Himalaya (Scientific Reports, 2019, via PubMed Central, NIH) ↗ “The Namcha Barwa (NB) syntaxis at the orographic edge of Tibetan plateau and Himalaya has witnessed large-scale drainage reorganizations since Miocene”
Question: UPSC Civil Services (Preliminary) 2011, General Studies paper. Explanation: Minimalist IAS, checked 25 Oct 2026 (how we verify). ·