EGU25-19826, updated on 15 Mar 2025
https://doi.org/10.5194/egusphere-egu25-19826
EGU General Assembly 2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
Adaptation of a 3D rockfall code to assess the hazard of sliding deadwood logs in mountain forests
Joël Borner1,2,4, Peter Bebi1,2, Adrian Ringenbach1,2,3, Perry Bartelt5, Marc Christen5, and Remco Leine4
Joël Borner et al.
  • 1WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland (joel.borner@slf.ch)
  • 2Climate Change, Extremes and Natural Hazards in Alpine Regions Research Centre CERC, Davos, Switzerland
  • 3Institute of Terrestrial Ecosystems, ETH Zurich, Zurich, Switzerland
  • 4Institute for Nonlinear Mechanics, University of Stuttgart, Stuttgart, Germany
  • 5RAMMS AG, Davos Wiesen, Switzerland

Mountain forests play a crucial role in mitigating natural hazards such as rockfalls and avalanches. Recent studies show that the presence of deadwood within these forests enhances the protective effect by increasing surface roughness, leading to a reduction of jump heights, kinetic energies and run-out lengths of rockfalls as well as an additional stabilisation of the snow cover to prevent avalanche releases. Conversely, deadwood provides a habitat for bark beetles, which can lead to significant tree mortality on a large scale, compromising the protective effect of the forest in the long term. These two contrasts form a key part in the discussion of mountain forest management with the main question whether deadwood should be cleared or not.

This paper explores a less common aspect of this discussion, focusing on the damage potential of sliding deadwood as a new, unknown form of natural hazard itself. Recent events in Switzerland reveal deadwood logs with lengths of up to 35 metres, which were mobilised and travelled several hundred metres of elevation in a single rapid descent, causing damage to civil infrastructure.

By adapting the non-smooth mechanics framework of RAMMS::Rockfall in combination with hard contact laws and Coulomb friction, we develop a physical model to simulate potential trajectories of such sliding deadwood logs from mobilisation to deposition. The model parameters are preliminarily calibrated with five well-documented case studies from Switzerland.

Preliminary results show that a specific predisposition of the deadwood in temporal and spatial dimensions is essential for the occurrence of such events. Firstly, for a sliding motion, a low friction to slope angle ratio is required. The low friction can either occur due to terrain conditions (e.g. wet soil, snow, foliage cover), the condition of the deadwood (wet log without bark and branches) or, in most cases, a combination of both. Secondly, the deadwood must be of a specific age, with sufficient decay to lose bark and branches but also sufficient residual strength so that it does not break on impact with the ground or standing trees (decay stages II – III after Maser & Trappe).

This new simulation tool contributes to the discussion of mountain forest management, indicating potentially dangerous areas for deadwood clusters as well as the critical decay stages of individual logs or snags to further optimise existing forest management strategies for an efficient and sustainable protection against natural hazards.

How to cite: Borner, J., Bebi, P., Ringenbach, A., Bartelt, P., Christen, M., and Leine, R.: Adaptation of a 3D rockfall code to assess the hazard of sliding deadwood logs in mountain forests, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19826, https://doi.org/10.5194/egusphere-egu25-19826, 2025.