Abstract
Permafrost degradation in mountainous regions increasingly influences slope stability and hydrological hazards. Lakes forming on active rock glaciers are visible manifestations of subsurface ice melt and can act as precursors to outburst floods and debris flows. This study presents a remote-sensing workflow utilizing multispectral Sentinel-2 and PlanetScope satellite imagery to detect and monitor rock glacier lakes across five active rock glaciers in the European Alps. At Hüttekar (Ötztal Alps, Austria), a lake of approximately 33,000 m 2 developed rapidly during early summer 2019, draining gradually over several weeks before triggering a debris flow that dammed the downstream river. At Cadin del Ghiacciaio (Dolomites, Italy), a newly formed lake located immediately upstream of the steep rock glacier front progressively expanded from 400 m 2 in 2019 to 1300 m 2 in 2023, indicating a potentially hazardous lake–front configuration. At Bürkelspitz (Samnaun Group, Austria), slow long-term expansion superimposed by strong seasonal fluctuations exemplifies the contrasting process timescales that influence lake development. Conversely, at Murfreit (Dolomites, Italy) and Kühgrube (Ötztal Alps, Austria), the method approached its limits due to topographic shading and shallow lake geometries. Together, these case studies demonstrate the operational potential of satellite-based monitoring for early hazard detection, while simultaneously highlighting the limitations imposed by sensor inconsistencies, terrain shadows, and spatial resolution. By combining expert-guided lake detection with rock glacier monitoring, this study takes a step toward an early warning system for cryospheric and hydrological hazards.