Which major river valley in Sikkim is carved out primarily as a steep, U-shaped glacial trough before transitioning into a V-shaped fluvial valley in its lower reaches?

💡 Solution & Explanation

The Teesta River valley in Sikkim showcases classic glaciated U-shaped upper sections formed during past glacial periods, which gradually transform into deep V-shaped valleys due to rapid vertical river incision as the stream descends through steep Himalayan terrain. Other river choices are completely unrelated to the Himalayan topography of Sikkim and lie in peninsular or northern plains regions. The Teesta originates from the Pahunri glacier and serves as the lifeline of Sikkim, supporting diverse endemic flora and fauna along its steep gradient.