the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
MinVoellmy v1: a lightweight model for simulating rapid mass movements based on a modified Voellmy rheology
Stefan Hergarten
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. 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 and 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 quite well. Furthermore, there seems to be a large potential for further research on hummocky deposit morphologies and longitudinal striations. However, the MinVoellmy software is only designed for research and teaching, but not for operational use in real-world hazard assessment.
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Stefan Hergarten
Status: open (until 09 Oct 2023)
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RC1: 'Comment on egusphere-2023-802', Anonymous Referee #1, 09 Jul 2023
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The paper introduces a numerical model based on a modified Voellmy friction model that is currently under review in a different manuscript. The mechanical concept follows Hergarten and Robl (2015).
From a scientific point of view, this work does not provide many novelties and innovations. The modified friction model is mentioned as the motivation for this work and seems to be its focal point. Therefore I would merge this manuscript with the other manuscript under review.
The model seems to follow the same concept as SHALTOP (Brunet et al. 2017) but comes to different conclusions and governing equations. SHALTOP also provides an exact solution of the Savage-Hutter model projected to a flat surface, while this work provides an approximation only. This should be discussed. What is the upside form the approximations done in this work? How do they compare?
Considering this is a new piece of code, I miss basic tests, e.g. comparisons with experiments, analytical solutions or existing software.
Citation: https://doi.org/10.5194/egusphere-2023-802-RC1 -
AC1: 'Reply on RC1', Stefan Hergarten, 12 Jul 2023
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Dear Reviewer,
thanks for your comments! I guess that merging two manuscripts in journals with different foci is not thought to be a serious suggestion. Model description papers in GMD should not present scientific results (the runout scaling as a function of volume in the ESurf manuscript), while ESurf is not a good place for technical descriptions of software.
A 100 line code (for the timestep) probably cannot compete with the model SHALTOP, and I do not mind mentioning this. On the other hand, readers have to pick information from multiple papers and to rely on the authors providing them with the source code before being able to work with SHALTOP. For me, this is an argument in favor of having all relevant information in one paper and to be able to download the code.
Concerning the approach, the main difference towards the Savage-Hutter model (and presumably also SHALTOP and the rather crude Cartesian approach by Hergarten & Robl 2015) is that averaging is not performed normal to the bed, but vertically. As long as the layer
is sufficiently thin in relation to the radius of curvature of the bed, this seems to be an unnecessary approximation to the Savage-Hutter model.
In many applications, however, this condition is not satisfied, e.g., if the bed is rough. Then measuring and averaging vertically instead
of normal to the rough bed is presumably better, although I cannot quantify it mathematically and do not want to put too much weight on this aspect. So your statement that SHALTOP provides and exact solution of the Savage-Hutter model is formally correct, but is not the whole truth.
As a second aspect, it is shown that shock-preserving numerical schemes are not as important as usually assumed for a certain type of rheologies (if friction decreases with thickness). This is illustrated quite in detail, although probably unimportant for you because SHALTOP uses a shock-preserving scheme. Anyway, the manuscript is not about arguing against any established model, but rather for illustrating how simple the numerical treatment can be.
Finally, your comment about the missing basic tests confuses me. I thought that the comparison with the analytical solution for a front (with and without the approximation) was such a test.
Best regards,
Stefan HergartenCitation: https://doi.org/10.5194/egusphere-2023-802-AC1
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AC1: 'Reply on RC1', Stefan Hergarten, 12 Jul 2023
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Stefan Hergarten
Stefan Hergarten
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