| 22 Dec 2025
Analysis of factors influencing rockfall activity with a new method to estimate the release frequency in case of scarce data
Abstract. Understanding the relationship between rockfall release frequency and volume is essential for quantitative hazard and risk analyses. The volume–frequency relationship is usually modelled with a power law distribution determined by an exponent and an activity parameter that can be estimated based on volume distributions from rockfall event inventories. Here, a new method is presented, which allows for the estimation of a confidence interval for the activity parameter, even if the inventory contains a small number of events. It was applied to estimate the spatio-temporal frequency of failures larger than 1 m3 for 22 natural mountain rock walls located in temperate climate zones and below the permafrost area. The obtained frequencies were similar to those given by power law fitting of the inventories. The meta-analysis showed that these frequencies vary by at least three orders of magnitude from 0.01 to 20 yr−1.hm−2, depending mainly on the geomorphological context of the cliff, the homogeneity of the cliff and the joint spacing. The exponent of the power law varies between 0.3 and 1.0 and tends to be lower for massive rock than for bedded rock. A primary classification is proposed that enables an estimation of the volume–frequency relationship parameters when no inventory is available. More inventories are needed to enhance this classification.
