Preprints
https://doi.org/10.5194/esurf-2022-70
https://doi.org/10.5194/esurf-2022-70
 
12 Dec 2022
12 Dec 2022
Status: this preprint is currently under review for the journal ESurf.

Shape still matters – rockfall experiments with deadwood reveal a new facet of rock shape relevance

Adrian Ringenbach1,2,4, Peter Bebi1,2, Perry Bartelt1,2, Andreas Rigling3,4, Marc Christen1,2, Yves Bühler1,2, Andreas Stoffel1,2, and Andrin Caviezel1,2 Adrian Ringenbach et al.
  • 1Climate Change, Extremes and Natural Hazards in Alpine Regions Research Center CERC, 7260 Davos Dorf, Switzerland
  • 2WSL Institute for Snow and Avalanche Research SLF, 7260 Davos Dorf, Switzerland
  • 3Swiss Federal Institute for Forest, Snow and Landscape Research WSL, 8903 Birmensdorf, Switzerland
  • 4Department of Environmental Systems Science, Institute of Terrestrial Ecosystems, ETH Zurich, 8092 Zurich, Switzerland

Abstract. Mountain forests have a substantial protective function in preventing natural hazards. Rates of deadwood production have already increased and are predicted to rise further, due to natural disturbances. In particular, higher windthrow event frequencies are expected, primarily due to the emerging even-aged forest stands in alpine regions combined with climate change. Here, we quantified the rockfall protection effect of mountain forests with and without deadwood in unprecedented detail. Repetitive experiments were conducted in which the two most important rock shapes from a hazard potential point of view and masses of 200 kg up to 3200 kg were considered. Based on a multi-camera setup, pre-and post-experimentally retrieved high- resolution lidar data, and rock data measured in situ, we completely reconstructed 63 trajectories. Every parameter of interest describing the rockfall kinematics was retrieved for each trajectory. A total of 164 tree impacts and 55 deadwood impacts were observed, and the currently applied energy absorption curves – partially only derived theoretically – could consequently be corroborated or even expanded to a greater absorption performance of certain species than hitherto assumed. Standing trees in general and deadwood, in particular, were found to strongly impede the notorious lateral spreading of platy rocks. Platy rocks featured a shorter mean run-out distance than their compact counterparts of similar weight, even in the absence of deadwood. These results indicate that the higher hazard potential of platy rocks compared with more compact rocks, previously postulated for open field terrain, applies less to forested areas. Lastly, reproducing the experimental setting showcases how complex forest states can be treated within rockfall simulations. Overall, the results of this study highlight the importance of incorporating horizontal forest structures that are as accurate as possible into simulations in order to obtain realistic deposition patterns.

Adrian Ringenbach et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on esurf-2022-70', Louise M. Vick, 13 Jan 2023
  • RC2: 'Comment on esurf-2022-70', Christine Moos, 18 Jan 2023

Adrian Ringenbach et al.

Adrian Ringenbach et al.

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Short summary
Swiss researchers carried out repeated rockfall experiments with rocks up to human-sized in a steep mountain forest. This study focuses mainly on the effects of the rock shape and of lying deadwood. The results show that cubic shape rocks have a longer mean runout distance in forested areas than platy-shaped rocks with the same mass. The findings enrich common practices in modern rockfall hazard zoning assessments and urge strongly to incorporate rock shape effects.