A song of rock and ice

A team of researchers has created an inventory of rock glaciers in the western Himalayas, specifically in Jammu & Kashmir and the Trans-Himalayan Ladakh regions. Rock glaciers are important in mountain hydrology and the study has estimated that 13.7 km³ of water is stored within the mapped rock glaciers, making them an important hydrological reservoir in this ecologically sensitive area.

The researchers from the University of Kashmir, Indian Institute of Technology Bombay, Indian Institute of Science Education and Research Pune, and Indian Institute of Technology Roorkee used satellite images from Google Earth and followed global guidelines to identify a total of 5,807 rock glaciers across six mountain ranges.

While surface glaciers are large masses of ice, rock glaciers are covered by thick rock debris which protects the underlying ice from rapid melting – like a layer of insulation, explains Imtiyaz Ahmad Bhat, Ph.D. student, Department of Geoinformatics, University of Kashmir and the lead author of this study. This makes them more resilient to climate change and allows them to store water over much longer timescales than regular glaciers.

Why are rock glaciers important?

Rock glaciers are an important source of stored water in fragile mountainous regions.

“When it comes to our future water supply, rock glaciers could be a big deal. There are tens of thousands of them around the world; they contain significant volumes of ice and are naturally insulated from warming temperatures and solar radiation by their debris cover,” explains Scott Hotaling, Assistant Professor at the Department of Watershed Sciences, Utah State University who was not involved with this study.

Unlike surface glaciers, which are melting rapidly, rock glaciers are more resilient to climate change impacts and they can also store water for a longer period.

Rock glaciers also release the meltwater slowly, providing a steady water supply during dry periods — a crucial buffer for rivers and communities, especially in the arid and semi-arid regions of the Himalaya, says Bhat.

“Additionally, their movement patterns and stability offer scientists valuable insights into the health of mountain permafrost, helping track long-term climate trends. As climate change accelerates glacier loss, rock glaciers will play an increasingly vital role in regional water security and ecosystem resilience,” Bhat explains.

Mountains across the world are home to ice sources that remain relatively resilient to climate change. However, it is still unclear how much rock glaciers currently contribute to mountain stream flows and how this contribution might shift in the future as the climate continues to warm, Hotaling adds.

Inventorying rock glaciers

The Zanskar range has the most rock glaciers (1,763), while the Pir Panjal range has the fewest (317), found the study by Bhat and team.

Multiple factors are responsible for the unequal distribution of rock glaciers in the study area. Apart from the elevation and temperature, low Mean Annual Air Temperature (MAAT) and limited precipitation establish the broad climatic framework favourable for permafrost and rock glacier development. The Zanskar range, for instance, falls in the rain-shadow region. As a result, low precipitation and colder temperatures provides a conducive environment for the development of rock glaciers.

“Notably, over 60% of rock glaciers in this region have a north-facing aspect, benefiting from lower incoming solar radiation, which aids in preserving internal ice. In contrast, the Pir Panjal Range, positioned closer to the monsoon-influenced belt, experiences comparatively warmer and wetter conditions, making it less favourable for rock glacier development,” explains Bhat.

Another important use of the inventory will be to identify areas sensitive to rock falls, rock-ice avalanches, and glacial lake outburst floods. As temperatures rise and intensify permafrost thaw, the frequency of such events could increase in future.

“The comprehensive rock glacier inventory that we developed provides critical baseline data on the distribution of permafrost, enabling early identification of areas vulnerable to thaw-induced slope failures. This information is invaluable for national and local disaster management agencies, infrastructure planners, and tourism authorities, helping them implement safer, more sustainable development strategies in fragile terrain,” adds Bhat.

Integrating inventory data with environmental variables such as temperature, precipitation, slope, and solar radiation allows for the development of predictive models that aid in hazard mapping and long-term monitoring. This proactive approach not only minimises the exposure of roads, settlements, and hydropower projects to climate-related risks but also enhances water resource management in downstream areas, he adds.

Important time capsules

Of the identified rock glaciers, 5,292 are intact — still containing ice and considered active — while 515 are relict, which means no longer active. Both intact and relict rock glaciers can provide valuable information about how temperature and rainfall have changed over thousands of years, say experts.

Intact rock glaciers, which include both active and inactive types, can be easily identified by their distinct shape. They typically have a convex shape, rounded appearance, surface patterns that resemble ridges and grooves from slow ice movement, and steep edges suggesting they still contain frozen, ice-rich ground inside.

In contrast, relict rock glaciers are no longer active and don’t contain ice. Their surfaces appear much smoother, showing no signs of movement or growth, and their front slopes are often covered with stable vegetation. These characteristics indicate that relict rock glaciers have been inactive for a long time and serve as historical markers of past climate conditions.

“Relict rock glaciers in the Himalaya serve as valuable archives for reconstructing past climate conditions,” says Bhatt. These inactive landforms store clues about the historical cryospheric changes, particularly during colder and drier periods when they were actively forming.

“By examining their distribution, structure, and sediment composition, along with dating techniques such as cosmogenic nuclide and optically stimulated luminescence dating, researchers have gathered evidence indicating that the Himalayan region experienced significantly colder temperatures in the past,” he explains.

As important hydrological resources, rock glaciers store significant amounts of water and have the potential to serve as water reservoirs, especially in semi-arid and arid mountain regions, finds the study. With climate change and rising temperatures reshaping the environment, rock glaciers could contribute to maintaining consistent streamflow in these areas.

The rock glacier’s sediment makeup and internal water system are important for storing and moving groundwater, particularly during dry periods.

Sharing an example of rock glaciers as water stores, Hotaling says, “In Utah (U.S.) I know of at least one reservoir used for agriculture that receives almost 100% of its water from a rock glacier in late summer. Nearby, a small ski community’s municipal water supply also comes from another rock glacier. It’s much more common than people realise.” He emphasises the importance of rock glaciers for mountain communities.

Another example of how rock glaciers contribute water is from a 2023 study that investigated the impact of discharge from an intact rock glacier on the water, temperature, and chemicals in a stream in the North Western Italian Alps. The study found that the rock glaciers drained only 39% of the watershed area but contributed a significant amount of water to the stream, especially from late summer to early autumn, when it can provide up to 63% of the flow.

Rock glaciers need more studies

Even though they appear as piles of rocks, rock glaciers are actually slow-moving masses of ice and debris that flow downhill over time. Despite their ecological significance, rock glaciers remain largely understudied.

“Pretty much everything about rock glaciers makes them hard to investigate,” Hotaling explains. “Because they are remote and often located in protected areas, they are difficult to access. Additionally, their debris cover adds a layer of complexity that makes them challenging to study with standard tools, such as ground-penetrating radar.”

A major breakthrough in mapping rock glaciers has been the use of satellite imagery combined with computer programs that help identify these landforms. While this method is not perfect, it provides scientists with a useful starting point for estimating the number of rock glaciers in a given area or even worldwide. These estimates can then be validated by visiting the sites in person, a process known as “ground-truthing,” according to Hotaling.

There is currently not enough data about the activity of rock glaciers in the Himalayan region, says Bhat.

“We aim to utilize Synthetic Aperture Radar (SAR) data, Unmanned Aerial Vehicles (UAVs), and time-lapse photography to monitor the dynamics and surface deformation of rock glaciers,” explains Bhat. Meanwhile, to estimate the water stored in these glaciers, Bhat intends to use geophysical methods such as Ground Penetrating Radar (GPR), Electrical Resistivity Tomography (ERT), and stable isotope analysis. These methods will help us better understand the hydrological importance and climate response of Himalayan rock glaciers.

Hope in rock glaciers

On May 12, 2025, more than 50 people, including glaciologists from four countries along the Hindu Kush Himalayas (HKH), gathered in Langtang, Nepal, to pay tribute to the Yala Glacier, which is rapidly disappearing. Yala Glacier holds special significance for glaciologists, as approximately 100 researchers have been trained on its site since the International Centre for Integrated Mountain Development (ICIMOD) began conducting training field visits there in 2011. The glacier has served as a research site for the past 50 years.

The event featured Buddhist speeches and ceremonies, along with the installation of two granite memorial plaques at the base of the glacier. One of the plaques bears an inscription from author Andri Snaer Magnason, highlighting that Yala is one of 54,000 glaciers in the Hindu Kush Himalayas, most of which are expected to disappear this century due to global warming.

This tribute, akin to a funeral for a glacier, serves as a stark reminder of the peril our fragile glaciers face. However, amidst this reality, there is hope nearby as rock glaciers could be the key to saving mountain ecosystems, local communities, and the rivers that originate from surface glaciers.

Read more: Digging into icy depths to understand glacial melt

Banner image: Studying rock glaciers can contribute to the long term understanding of permafrost melt and hazard mapping. Image by Irfan Rashid.