How water, temperature and seismicity control the preparation of massive rock slope failure (Hochvogel, DE/AT)

Abstract. The increasing hazard of major rock slope failures, exacerbated by climate change, underscores the importance of anticipating pre-failure process dynamics. While standard triggers are recognized for small rockfalls, few comprehensive driver quantifications exist for massive pre-failure rock slopes. Here we exploit >4 years multi-method high-resolution monitoring data from a well-prepared high-magnitude rock slope instability. To quantify and understand the effect of possible drivers – water from rain and snowmelt, internal rock fracturing and earthquakes – we correlate slope displacements with environmental data, local seismic recordings and earthquake catalogues. During the snowmelt phase, displacements are controlled by meltwater infiltration with high correlation and a time lag of 4–9 days. During the snow-free summer, rainfall drives the system with a time lag of 1–16 h for up to several days without a minimum activation rain sum threshold. Detected rock fracturing, linked to temperature and freeze-thaw cycles, is predominantly surface-near and unrelated to displacement rates. A classic Newmark analysis of recent and historic earthquakes indicates a low potential for immediate triggering of a major failure at the case site, unless it is already very close to failure. Seismic topographic amplification of the peak ground velocity at the summit ranges from a factor of 2–11 and is spatially heterogeneous, indicating a high criticality of the slope. The presented methodological approach enables a comprehensive rockfall driver evaluation and indicates where future climatic changes, e.g. in precipitation intensity and frequency, may alter the preparation of major rock slope failures.