High mountain rockfall dynamics: rockfall activity and runout assessment under the aspect of a changing cryosphere

Abstract

ABSTRACT Rockfalls are a major aspect concerning morphodynamics in high mountain areas and represent a serious hazard for people and infrastructure. Recently, an increase of rockfall activity has been observed which is probably related to the destabilization of rock slopes through climate-related changes of the mountain cryosphere. This study investigates the rockfall distribution during a 4-year monitoring period by systematic observation with bi-temporal Airborne Laser Scanning DTMs in an area of 610.7 km² in the Ötztal Alps/Tyrol, Austria. The analyses of the 93 detected rockfall events indicate that rockfall activity is highest in proglacial areas. Further 83.9% of all rockfall source areas were mapped in bedrock where the modelled mean annual ground temperature (MAGT) indicates perennial frozen conditions. The results demonstrate the importance of thermal effects on the destabilization of rock faces and show that the triggering of rockfalls is closely related to changes in the glacier and permafrost regime. 18 low-magnitude rockfalls with volumes between 69 ± 3 m³ and 8420 ± 89 m³ are examined in detail. On the base of the analysis of these events energy line angles of 28.7° for the Fahrböschung and 19.9° for the minimum shadow angle can be derived and significantly longer runout distances on glaciated rockfall paths are observed.