MinVoellmy v1: a lightweight model for simulating rapid mass movements based on a modified Voellmy rheology

Abstract

The Voellmy rheology has been widely used for simulating snow avalanches and also for rock avalanches. Recently, a modified version of this rheology was proposed. While the conventional version of Voellmy's rheology uses the sum of Coulomb friction and a velocity-dependent friction term, the modified version assigns the two terms to different regimes of velocity. The software MinVoellmy presented here provides the first numerical implementation of the modified rheology in a two-dimensional, depth-averaged model. It consists of MATLAB and Python classes, where simplicity and parsimony were the design goals. In contrast to the majority of the models in this field, MinVoellmy uses a Cartesian coordinate system with the thickness of the fluid measured vertically and the velocity averaged vertically instead of perpendicularly to the bed. Furthermore, MinVoellmy implements a simple upstream scheme, which turns out to be sufficient for rheologies of the Voellmy type. Numerical tests reveal that the modified Voellmy rheology reproduces the empirical relation between runout length, height drop, and volume of large rock avalanches fairly well. Furthermore, there seems to be a large potential for further research on hummocky deposit morphologies and longitudinal striations.