Multistage 54,000 m3 rockfall (Stampa, Western Norway): Insights from comprehensive monitoring and failure analysis

Abstract In 2023, a 54,000 m 3 large rock section failed catastrophically from the unstable rock slope Stampa (Western Norway). The failure occurred in a multistage process with two major failure events on July 1 st and 3 rd . In this study, we present a detailed analysis of the pre-failure displacement patterns, the failure mechanisms, and failure events. After exponential acceleration, the base (12,200 m 3 ) of the rock section failed, leading to a further destabilization of the remaining rock column (41,800 m 3 ), which failed 2 days later. The monitoring data includes in situ displacement sensors, a robotic total station, and close range and remote sensing data spanning over 14 years. The rock section showed seasonal displacement patterns clearly influenced by meteorological factors: (1) late spring (May–July) accelerations, controlled by positive temperatures, thawing ground, and meltwater infiltration, followed by (2) summer stabilizations characterized by low displacement, and (3) autumn (October–November) accelerations driven by precipitation events over a longer period, followed by (4) winter stabilizations approaching zero displacement. The deformation rates increased from 0.06 m a −1 in 1991–2019 more than a tenfold to 0.78 m a −1 in 2022 and indicate progressive damage and weakening of the rock section, which increased its sensitivity to rainfall and infiltration. Our findings highlight the importance of long-term, high-resolution monitoring using different, independent sensors, alongside detailed failure analyses, in understanding the evolution of unstable rock slopes. This study contributes to the understanding of progressive medium-scale rock slope failures, aiding in the prediction and mitigation of potential failures.