Occurrence and characteristics of rock glaciers in the Poiqu River basin – Central Himalaya

Abstract

Rock glaciers are important to study as they can be of hydrological importance and could have serious hazard potentials. Existing investigations about rock glaciers in High Mountain Asia indicate that the landforms are abundant, but information is still rare for large parts of the region. We compiled a rock glacier inventory for the Poiqu River basin, Central Himalaya. The mapping was conducted using very high-resolution Pléiades imagery and digital elevation model and imagery available from Google Earth. Rock glaciers were classified either active or inactive based on interferograms generated using ALOS-1 PALSAR data. Moreover, we developed a new method to automatically map the frontal slopes of the rock glaciers to investigate their activity. The results reveal 370 rock glaciers including 148 active and 222 inactive ones. We found nine rock glaciers damming lakes, three of which could be potentially dangerous. The overall rock glacier area is about 20.9 km which is more than 10% of the glacier area. The two largest rock glaciers cover 0.50 and 0.45 km². The rock glaciers are located at elevations between ~4000 and ~6000 m above sea level (mean elevations ~5100 m). Most of the rock glaciers face towards East and Southwest. The mean overall slope is 19.3° with the active ones being on average only slightly steeper (active: 19.7°, inactive: 19.0°). Their frontal slopes, however, are clearly steeper. The availability of very high-resolution data was key to generate a rock glacier inventory and allowed assessment of the rock glacier characteristics with high accuracy.