Q. The 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 "C" turn in its course to flow into India. This "U" turn is due to (UPSC Prelims 2011)
Answer:
Syntaxial bending of geologically young Himalayas
Notes: The correct answer is
[B]. The dramatic "U" turn of the Brahmaputra (known as the Tsangpo in Tibet) as it enters India through Arunachal Pradesh is one of the most striking geological features of the Himalayan range.
- Syntaxial Bends: The Himalayas do not run in a perfectly straight line. At both the western and eastern extremities, the mountain ranges take sharp, knee-like bends southward. These are known as Syntaxial Bends.
- The Eastern Syntaxis: The eastern bend occurs near the peak of Namcha Barwa. Here, the geological strata are sharply folded. The Brahmaputra river, which flows eastward in Tibet, hits this structural "wall" and is forced to carve a deep gorge and turn sharply south and then west into the Assam valley.
- Geological Youth: Because the Himalayas are "Young Fold Mountains," they are still tectonically active. The specific structural weakness and the sharp bending of the mountain folds at this junction provide the path of least resistance for the river to cut through.