the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 27 Jun 2025
Dynamic Analysis of Flowlike Landslides at Brienz/Brinzauls, Graubünden, Switzerland
Abstract. Accurate forecasting of the risk posed by catastrophic failure of rock slopes requires estimates of the potential impact area and emplacement velocity. While most previous work in this context has focused on rock avalanche behaviour, recent and well documented case histories are showing that a more diverse range of landslide classes can occur. In the present work, we analyse two rock slope failures that occurred at Brienz/Brinzauls in Switzerland. These events initiated within 500 m of each other on the same slope, but emplaced with velocities that differed by five orders of magnitude. We describe the derivation and implementation of a GPU accelerated numerical model that can simulate emplacement velocities on the order of m/day. We then perform forensic back-analysis of the two case histories. Our results highlight the role of path material in controlling emplacement behaviour, as well as the effect of moderate changes in source material lithology. We argue that these cases can form the foundation of more accurate hazard and risk analyses at similar sites, where a wider range of potential future behaviour than is typical should be considered.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2025-2788', Anonymous Referee #1, 22 Jul 2025
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RC2: 'Comment on egusphere-2025-2788', Anonymous Referee #2, 31 Jul 2025
This paper presents a detailed dynamic analysis of two flow-like landslides (Igl Rutsch and Insel) in Brienz/Brinzauls, Switzerland. It introduces a novel GPU-accelerated numerical model (Orin-3D) capable of simulating landslide velocities ranging from moderate (meters/day) to extremely rapid (>5 m/s). The research is innovative, methodologically sound, and well-supported by field data, historical records, and modern monitoring techniques. The study provides significant theoretical and practical contributions to landslide hazard assessment and risk prediction. The paper is well-structured, logically organized, and supported by appropriate figures and references. Overall, the manuscript is of high academic merit and merits publication. Several suggestions are listed below for reference.
- The paper notes that pore pressure dynamics were not considered in the simulations, which could be significant for clay-rich landslides. A more detailed discussion of this assumption’s implications should be added.
- The model does not fully capture the seasonal velocity variations observed in the Igl Rutsch landslide. The authors should explore incorporating time-dependent parameters (e.g., viscous coefficient δ) to better match field observations.
- A sensitivity analysis of key parameters (e.g., δ and φ) would strengthen the model’s interpretability.
Citation: https://doi.org/10.5194/egusphere-2025-2788-RC2 -
RC3: 'Comment on egusphere-2025-2788', Anonymous Referee #3, 13 Aug 2025
This study addresses an important and specialized type of landslide—large failures in clay-rich rocks that transition into flow-like movements. The authors present a depth-averaged SPH model with a novel rheology capable of simulating slow-moving landslides (velocities on the order of m/day) and conduct detailed back-analyses of two well-documented events at Brienz/Brinzauls, which exhibited emplacement velocities differing by five orders of magnitude. The topic is highly relevant, and the manuscript is well-structured and clearly written. I recommend minor revisions before publication in NHESS.
Specific Comments:
- The Lgl Rutsch event was simulated using 4,000 SPH particles. Could the authors clarify the rationale for this choice and discuss whether the results are sensitive to particle resolution?
- The adopted SPH model is depth-averaged, which simplifies the real 3D dynamics. Please discuss how this assumption might influence the model’s predictive accuracy, particularly for flow transitions and velocity distributions.
- Table 1 reports best-fit friction angles of 23°–28° for different stages. However, field and experimental studies (e.g., rock avalanches, earthflows) typically suggest much higher friction coefficients. Note that the reviewer is mainly working on fast-moving geophysical flows (e.g., Kong et al., JGR, 2023, 10.1029/2022JF006870). Are these smaller values physically justified for clay-rich rocks?
- For the Insel event (Section 4.2), were the same SPH parameters (fitted to Lgl Rutsch) applied? If so, this seems inconsistent given the five-order magnitude velocity difference between the two events. Please clarify whether material or rheological differences explain this discrepancy.
Citation: https://doi.org/10.5194/egusphere-2025-2788-RC3
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The authors present a numerical model to simulate flow-like landslides from unstable rock slopes over a broad range of velocities (five orders of magnitude), and apply their model for the back-calculation of two events in the landslide area of Brienz, Switzerland. This topic is highly relevant from both a scientific and a practical point of view, and perfectly suits to the scope of the journal. The preprint is generally well written, structured, and illustrated, and I would certainly like to see this work published. I suggest some minor revisions based on the comments below, which might help to further improve an already very good paper.