Glaciers, a dense body composed of persistent and constantly moving ice, are the largest reservoirs of freshwater, storing drinkable water for millennia. Today, climate change and the resulting shifts in weather patterns are causing glaciers across the world, including those in the Himalayas, to shrink gradually. A recent study has found that glaciers in the Himalayas are losing mass at an accelerated rate, especially since the last decade.
Amid these concerns, a new study by the University of Kashmir, Indian Institute of Technology (IIT) Bombay, Indian Institute of Science Education and Research (IISER) Pune, and Indian Institute of Technology (IIT) Roorkee brings attention to a different type of glaciers - Rock glaciers which are landforms composed of rocks and ice—that may serve as important, though often overlooked, water reservoirs. The research maps the rock glaciers in the Western Himalayas, specifically in the Jammu-Kashmir and Ladakh regions.
Because they depend on cold, dry conditions to form, the presence of rock glaciers can tell us a lot about the climate, both what it is like now and how it used to be. Tracking where rock glaciers occur helps determine the lowest elevations at which permafrost, a type of permanently frozen soil, can exist in the mountains. Rock glaciers also store significant amounts of ice that could become increasingly crucial for both local communities and downstream populations.
Although automatic methods and specialised algorithms are commonly employed to map glaciers, especially “clean” glaciers that are not covered by debris, rock glaciers are trickier to identify. Because the overall movement is slow—just a few centimetres or meters per year—it often goes undetected. While intact rock glaciers still move downhill slowly, relict (or inactive) rock glaciers are basically frozen relics that no longer contain much ice or movement and often look like large piles of rock fragments on a slope. Inside these debris piles, ice can be present and slowly creeping downhill.
Because of this complexity, the team employed high-resolution satellite imagery available through Google Earth. They then used a manual, grid-based approach: They overlaid a one-kilometre grid across the entire study area, which included western Himalayan regions of Jammu-Kashmir and Trans-Himalayan Ladakh, spanning six mountain ranges. Within each grid cell, they zoomed in on satellite imagery to look for typical rock glacier shapes and surface features.
When ice deforms and creeps under the surface in a rock glacier, it drags the rocks above it forward, creating a series of ridges and furrows. These distinctive furrows and ridges, steep fronts, and what are sometimes called a “swollen” or lumpy surface are signs that ice is present and deforming the ground. Once they noticed these signs, they carefully marked the boundaries of the rock glaciers.
In addition, they classified the rock glaciers based on whether they are connected to a glacier, are entirely fed by loose debris from rocky slopes, or formed in an empty glacial valley once the main glacier had retreated. Using a 30-meter-resolution elevation model, they calculated each rock glacier’s average height, slope angle, and direction aspect. Climate data, such as temperature and precipitation, came from a global climate database known as WorldClim.
The research team identified a total of 5,807 rock glaciers in their study region. Of these, 5,292 are classified as intact, which still contains a considerable amount of ice and shows signs of movement, and 515 are relict, which contains little or no ice and shows no new movement. Altogether, these rock glaciers cover around 712 square kilometres in the Western Himalayas. By applying estimates of ice content (ranging from about 40% to 70% of their volume), the researchers calculated that the intact rock glaciers could collectively hold anywhere between about nine cubic kilometres and 17 cubic kilometres of water if their ice were to melt. For context, that is roughly the amount of water one would find in several large lakes combined.
The researchers also found that many of these rock glaciers lie in areas where regular glaciers are either smaller or absent altogether. Glaciers dominate the water supply in many cold regions, but in parts of the Western Himalayas that receive less precipitation (like Ladakh’s largely desert-like environment), rock glaciers can become extremely important for storing ice and gradually releasing meltwater over long periods. In some high-altitude desert mountain ranges, the rock glaciers may store almost as much, or even more, water than smaller glaciers.
In a time when climate change, glacier shrinkage, and water scarcity dominate global discussions, rock glaciers emerge as hidden gems of the mountains. Unlike regular glaciers, which often appear bright white or bluish due to exposed ice, rock glaciers have a heavy load of debris—in other words, a thick layer of rock fragments on top. This rocky cover helps insulate the ice below from heat, making rock glaciers more resistant to melting than debris-free glaciers. These features are essential to the mountain water cycle. During summers or whenever temperatures rise enough, some of the ice within these rock glaciers can melt, releasing water that flows downstream. Over lengthy intervals, especially if glaciers retreat due to rising temperatures, rock glaciers can continue to supply meltwater, albeit at a slow pace.
Through detailed satellite mapping and analysis, the study presents the most extensive inventory of rock glaciers in the region. The Western Himalayan regions of Jammu-Kashmir and Ladakh have thousands of these debris-covered ice bodies—some small, some sprawling across entire valleys. This wide distribution suggests that although the region hosts world-famous glaciers, rock glaciers may play an equally important if subtler, role in storing water. In semi-arid zones like Ladakh, rock glaciers may well outlast many shrinking glaciers and continue supplying vital meltwater to communities below.
This research article was written with the help of generative AI and edited by an editor at Research Matters.