Rock glaciers in the Hindu Kush Himalaya: A regional synthesis

Rock glaciers are cryospheric landforms in high-mountain regions and indicators of permafrost occurrence and change under accelerating climate warming. This review synthesizes 67 peer-reviewed studies on rock glaciers across the Hindu Kush Himalaya (HKH) published between 1970 and 2024 to assess the research landscape. Publications increased after 2016, with growth after 2020 and a peak in 2024. Large-scale inventories published through 2024 contain more than 61,000 mapped rock glacier records within the HKH boundary but differ in mapping framework and remain spatially incomplete. In the Himalayan subregion, an upscaled first-order assessment estimated approximately 3,747 km2 of rock glacier area and a water volume equivalent of 51.80 ± 10.36 km3. Although substantially less than glacier storage at the Himalayan scale, local model-based studies indicate that rock glacier storage may be comparable to, or exceed, glacier storage in some semi-arid subregions. Earlier studies focused on geomorphological mapping and permafrost assessment, whereas recent research increasingly integrates remote sensing, geophysics, machine learning, and hydrological modeling. Rock glaciers can contribute to sustaining streamflow and supporting livelihoods, while changes in their condition can influence permafrost-related hazards. Nevertheless, HKH rock glaciers remain incompletely inventoried, with uncertainties and limited hydrological understanding, requiring interdisciplinary research into climate–rock glacier interactions.