Deciphering meteorological influencing factors for Alpine rockfalls: a case study in Aosta Valley

Greta Bajni,Corrado A S Camera,Tiziana Apuani

doi:10.1007/s10346-021-01697-3

Abstract

This study exploited the historical rockfall inventory and the meteorological stations database of Mont Cervin and Mont Emilius Mountain Communities (Aosta Valley, northern Italy) to decipher relationships between climate processes, typical of mountain environments and rockfall phenomena. The period from 1990 to 2018 was selected as reference to perform the analysis. Climate processes were translated into four climate indices, namely short-term rainfall (STR), effective water inputs (EWI, including both rainfall and snow melting), wet and dry episodes (WD) and freeze-thaw cycles (FT). The comparison between climate indices values at each rockfall occurrence and the statistical distributions describing the whole indices dataset allowed to define not ordinary climatic conditions for each index and their influence on rockfall occurrence. Most of the events analysed (>95% out of 136) occurred in correspondence of the defined not ordinary climatic conditions for one or for a combination of the indices. The relationships between rockfalls and climate showed a seasonality. In spring, most of the events resulted to be connected to FT (70%) while in autumn to EWI (49%). The relative seasonal importance of WD reached its maximum in summer with 23% of the events related to this index alone. Based on these results, different strategies to define empirical critical thresholds for each climate index were explored, in order to make them valid for the whole study area. A preliminary exploratory analysis of the influence of high temperatures and temperature gradients was carried out for some summertime rockfalls, not correlated to the other investigated indices. The presented approach is exportable in neighbouring regions, given the availability of a dated rockfall dataset, and could be adapted to include different processes.

Highlights

Rockfalls are a common type of fast-moving landslide (Hungr et al 2014)
Rockfall database For the reference period (1990–2018), 243 rockfall records were extracted from the Landslide Regional Database and validated
The temporal distribution of the events in the study area (Fig. 2a) seems to suggest a slight increase in rockfall frequency in recent years, such evidence could be linked to a reporting bias, following the establishment of more sophisticated monitoring networks and technologies

Summary

Introduction

Rockfalls are a common type of fast-moving landslide (Hungr et al 2014). As such, they can deeply affect human society and infrastructures in mountainous environments (Ravanel and Deline 2010, Duvillard et al 2015, Scavia et al 2020). For the quantification of timing-frequency-volume of rockfall events, Matsuoka (2013) employed time-lapse cameras, Krautblatter and Moser (2009) used traps, while Ravanel et al (2013) and Hartmeyer et al (2020) used terrestrial laser scanners These acquisition methods, and the exploitation of accurate historical and multitemporal (i.e. inventories prepared for the same area but for different time periods, as defined by Reichenbach et al (2018)) rockfall inventories, are often combined with the monitoring and analysis of meteorological data to evaluate preparatory and triggering factors for rockfall occurrence (Delonca et al 2014; D’Amato et al 2016; Paranunzio et al 2015, 2016, 2019; Draebing et al 2017a; Nigrelli et al 2018; Matsuoka 2019)

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Results

Discussion

Conclusion