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 "U" turn in its course to flow into India. This "U" turn is due to

1. The Brahmaputra River, originating in Tibet, flows eastwards roughly parallel to the main Himalayan range. 2. As it reaches the eastern end of the Himalayas, near the peak Namcha Barwa, it takes a dramatic, sharp "U" turn to the south and southwest, cutting through the mountains to enter India (Arunachal Pradesh). 3. This sharp bend in the river's course closely follows a similar sharp bend in the geological structure of the Himalayas themselves. This structural feature is known as a syntaxial bend. 4. The Himalayas are geologically young, folded mountains formed during the Tertiary period. The eastern syntaxial bend represents a major change in the trend of the mountain ranges. 5. Therefore, the "U" turn of the Brahmaputra is primarily due to the syntaxial bending of the geologically young Himalayas. 6. While uplift and general geo-tectonic disturbance are involved in the formation of the Himalayas, the specific term syntaxial bending most accurately describes the structural feature responsible for the river's sharp turn.