Glaciers are large, slow-moving masses of ice formed where snowfall exceeds melting over many years; India's glaciers lie in the high Himalayas and Karakoram and feed its major perennial rivers.
- The Siachen Glacier in the Karakoram (eastern Karakoram, Ladakh) is one of the longest non-polar glaciers and the world's highest battlefield, held by the Indian Army since Operation Meghdoot (1984).
- The Gangotri Glacier in Uttarakhand is the source of the Bhagirathi, a headstream of the Ganga, with its snout at Gaumukh; the Yamunotri Glacier feeds the Yamuna.
- Other major glaciers include Zemu (Sikkim, in the Kanchenjunga massif, the largest in the eastern Himalayas), Pindari and Milam (Kumaon Himalaya), Bara Shigri (Himachal, in Lahaul-Spiti), and Hispar and Biafo (Karakoram).
- Himalayan glaciers are the "water towers of Asia," sustaining the perennial flow of the Indus, Ganga, and Brahmaputra; many are retreating because of warming, raising concern over glacial lake outburst floods (GLOFs).
- The snowline (the lower limit of permanent snow) is higher in the western and trans-Himalaya and lower in the wetter eastern Himalaya.
Siachen as the highest battlefield and Operation Meghdoot, Gangotri-Gaumukh as the Ganga source, glaciers as the source of perennial rivers, and GLOF risk are recurring physiography and security facts.
Gangotri feeds the Ganga (via Bhagirathi) while Yamunotri feeds the Yamuna; Siachen is in the Karakoram, not the main Himalaya; the snout of the Gangotri glacier is Gaumukh, the source point, not the glacier's whole length.
Himalayan and Karakoram glaciers (Siachen, Gangotri, Zemu, Pindari) are Asia's water towers feeding the Indus, Ganga, and Brahmaputra.