Temporal Variability of Rockfall in the Bavarian Alps, Germany

Abstract

This paper presents data derived from extensive rockfall investigations in the Karwendel Mountains and in the Ammer Mountains near the German-Austrian border. The rock faces in the areas investigated consist of Mesozoic limestone and dolostone. The debris was quantified by means of more than 60 rockfall collectors, which were emptied regularly. Air and rock temperature data were measured by a meteorological station and by several dataloggers equipped with pT100 temperature probes.The temporal distribution of rockfall was highly variable, which is due to the combination of several trigger parameters. A statistical analysis of the dataset revealed that various meteorological conditions enhance the probability of rockfall occurrence. Deep frost in winter, freezing and thawing during wet weather conditions, and wetting/drying contribute to the weathering of the rock faces investigated. The actual removal, leading to rockfall, is triggered by a complex combination of frost shattering, temperature fluctuations, and downwash by precipitation. Despite the irregular patterns, it is evident that the mean removal in the summer months is much higher than in winter, which is probably due to the lack of water in the cold season. Even a large number of temperature oscillations across zero do not seem to affect weathering as long as there is an insufficient moisture supply.