Duns
Explanation
The Himalayas consist of three parallel ranges: the Great Himalayas (Himadri), the Lesser Himalayas (Himachal), and the Outer Himalayas (Shiwaliks). The structural formation of these ranges creates distinct longitudinal valleys between them.
Analysis of Options:
- Passes Passes: These are navigable routes or gaps through a mountain range, often used for transportation (e.g., Zoji La, Nathu La). They are not longitudinal valleys.
- Gorges Gorges: A gorge is a deep, narrow valley with very steep sides, typically formed by river erosion cutting through a mountain range (e.g., the Indus Gorge).
- Duns Duns: These are the longitudinal valleys lying between the Lesser Himalaya and the Shiwaliks. These valleys are typically filled with gravel and alluvial deposits brought down by rivers. Prominent examples include Dehra Dun, Kotli Dun, and Patli Dun.
- Doabs Doabs: This term refers to the tract of land lying between two converging or confluent rivers. It is a feature associated with plains (e.g., the Punjab plains) rather than the longitudinal valleys of the mountains.
Key Takeaway: "Duns" are specific longitudinal valleys situated between the Lesser Himalayas and the Shiwaliks, distinguished by their alluvial deposits and location, unlike "Doabs" which are inter-river plains.