Preprints
https://doi.org/10.5194/egusphere-2023-144
https://doi.org/10.5194/egusphere-2023-144
21 Mar 2023
 | 21 Mar 2023
Status: this preprint is open for discussion.

Scaling between volume and runout of rock avalanches explained by a modified Voellmy rheology

Stefan Hergarten

Abstract. Rock avalanches reach considerably greater runout lengths than predicted by Coulomb friction. While it has been known for a long time that runout length increases with volume, explaining the increase qualitatively is still a challenge. In this study, the widely used Voellmy rheology is reinterpreted and modified. Instead of adding a Coulomb friction term and a velocity-dependent term, the modified rheology assigns the two terms to different regimes of velocity. While assuming a transition between Coulomb friction and flow at a given velocity is the simplest approach, a reinterpretation of an existing model for the kinetic energy of random particle motion predicts a dependence of the crossover velocity on the thickness of the rock avalanche. Analytical solutions for a lumped mass on a simple 1-D topography reveal the existence of a slope-dominated and a height-dominated regime within the regime of flow. In the slope-dominated regime, the kinetic energy at the foot of the slope depends mainly on the slope angle, while the absolute height relative to the valley floor has little effect, and vice versa. Both regimes can be distinguished by the ratio of a length scale derived from the rheology and the length scale of the topography. Long runout occurs in the height-dominated regime. In combination with empirical relations between volume, thickness, and height, the approach based on the random kinetic energy model reproduces the scaling of runout length with volume observed in nature very well.

Stefan Hergarten

Status: open (until 06 Jul 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-144', Anonymous Referee #1, 28 Mar 2023 reply
  • CC1: 'Comment on egusphere-2023-144', Matthias Rauter, 20 May 2023 reply

Stefan Hergarten

Stefan Hergarten

Viewed

Total article views: 228 (including HTML, PDF, and XML)
HTML PDF XML Total BibTeX EndNote
163 57 8 228 2 1
  • HTML: 163
  • PDF: 57
  • XML: 8
  • Total: 228
  • BibTeX: 2
  • EndNote: 1
Views and downloads (calculated since 21 Mar 2023)
Cumulative views and downloads (calculated since 21 Mar 2023)

Viewed (geographical distribution)

Total article views: 227 (including HTML, PDF, and XML) Thereof 227 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
1
 
 
 
 
Latest update: 04 Jun 2023
Download
Short summary
Large landslides turn into an avalanche-like mode of flow at high velocities, which allows for a much longer runout than predicted for a sliding solid body. In this study, the Voellmy rheology widely used in models for hazard assessment is reinterpreted and extended. The new approach predicts the increase in runout length with volume observed in nature quite well and may thus be a major step towards a more consistent modeling of rock avalanches and improve hazard assessment.