Climate change impact on rock avalanches in metamorphic rock masses in Tyrol, Austria

Rockfalls and rockslides are a common hazard in alpine terrain and are major factor of alpine landscape evolution. They are characterized by a complex combination of geological, hydrological, geomechanical and meteorolocical processes and occur in a wide variety of geological and structural settings and in response to various loading and triggering processes. In the Alps in particular, extremely rapid rock avalanches reaching a volume of several 10000 m³ or more have the potential to cause serious damage to both humans and infrastructure. As global warming progresses, the meteorological and climatological factors that influence rock avalanche formation will change. Especially, in the high mountain environment rock avalanches are strongly influenced by climate change due to thawing of permafrost and the retreat of glaciers. Less obvious is the influence of climate change on the formation of rock avalanches at lower altitudes, and thus there is a need for additional research.

In this study, we investigate the impact of global warming on selected rock avalanche case studies with volumes above several tens of thousands of cubic meters. The study area covers approx. 3400 km² in the metamorphic rock mass of the Ötztal Stubai Crystalline, the Silvretta and the Glockner Nappes as well as the units of the Engadin Window of the Tyrolian Alps, Austria.

The aim of this work is to identify the processes that led to our case studies and if these processes are influenced by climate change factors, such as changes in temperature, precipitation, freeze-thaw cycles, snow coverage, etc. The climatic factors will be investigated in terms of both their short-term and long-term influence on the trigger mechanisms.

Advanced remote sensing techniques were used on site to carry out small to large-scale investigations. Terrestrial laser scanning (TLS) and Airborne laser scanning (ALS) enables us to create high-resolution recordings of inaccessible rock faces, supported by 3D point cloud analyzing tools. In addition, where TLS campaigns are not possible, we use an unmanned aerial vehicle (UAV) photogrammetry system that provides 3D point clouds and delivers a 3D model of the site. Geological field investigations were performed to record lithological, hydrogeological and structural features. This results in a comprehensive geological model of the failure area. A 3D discontinuity network was developed based on the combined analyses of remote sensing and discontinuity mapping data, providing the basis for structural geological analyses and distinct element modelling studies.

With regard to the above criteria, we have selected several case studies. Most of the case studies are located well above 2500 m above sea level in glaciated or recently glaciated areas. For all case studies, we were able to document at least one rock avalanche event with a volume exceeding several 10000 m³. A high-resolution climate model was created for the documented events. We then began to collect and evaluate the existing literature on the individual case studies.