Influence of permafrost degradation and glacier retreat on recent high mountain rockfall distribution in the eastern European Alps

Abstract

High mountain environments are among the regions most affected by global warming, with glacier retreat and permafrost degradation leading to significant changes in slope stability. This study investigates the spatial distribution of rockfalls above the timberline in the Stubaier and Ötztaler Alps (Eastern Alps, Austria). Rockfalls were identified using an automated pre-classification approach and manual verification of detected rockfalls based on digital surface models (DSMs) derived from 2006 and 2017 airborne laser scanning (ALS) datasets and orthoimages. To assess the influence of permafrost, the mean annual ground surface temperature (MAGST) was modelled using a simplified surface energy balance that accounts for altitude and solar radiation. The impact of glacier retreat in recent decades was assessed on the basis of historical glacier inventories. A total of 1989 rockfalls were identified, with volumes ranging from 200 m3 to 200,000 m3. Notably, 76% of the rockfalls occurred in areas with a MAGST below 0°C, which represents only 22% of the potential rockfall area. In addition, 40% of the events occurred in areas that have been deglaciated since 1969, representing only 4.7% of the potential rockfall area. The results are consistent with published local rockfall inventories focusing on individual rock faces or glacial cirques and extend to a wider region spanning altitudes from 1800 to 3,770 m a.s.l. and an area of 1,350 km2. This study provides the first comprehensive regional inventory of recent rockfalls for a large area in the Eastern Alps and shows a strong spatial relationship of rockfall to permafrost degradation and glacier retreat areas.