Rock slope failure evolution towards a sensitive close-to-failure system

Rock slope instabilities cause significant risk in populated alpine areas. To anticipate the final failure, a detailed understanding of the preparatory process dynamics including all potential promoting and triggering factors is needed. While standard external and internal drivers are known, measured evidence and a quantification of their relevance at a specific site is often lacking.

Here, we present the evolution of the imminent Hochvogel summit failure (200,000–600,000 m³) over multiple decades towards the current highly sensitive system. We identified the three most relevant potential drivers at the Hochvogel instability: (i) earthquakes, (ii) seasonal and short-term meteorological effects and (iii) increasing internal stress. To quantify these, we use diverse sources of information. Earthquake catalogues and the records of the regional seismic broadband stations help to constrain known historical rock fall events at the Hochvogel. The effect of precipitation events, snowmelt and temperature is quantified by the analysis of high-resolution crack opening and rain data of the last four years. Finally, we exploit the record of our local seismic network to reveal internal rock bridge failures, rock fall activity in the flanks and the seismic stressing of the instable mass due to local earthquakes.

The current process dynamics prove a close-to-failure status of the instability. The combination of historic records and high-resolution real-time data not only makes the Hochvogel a benchmark site for alpine hazard early warning but also enables the comprehensive definition and quantification of its relevant drivers. This will improve the global understanding of rock failure dynamics and so the anticipation ability for instable rock slopes.