Dynamic Analysis of Flowlike Landslides at Brienz/Brinzauls, Graub&uuml;nden, Switzerland

Aaron, Jordan; de Palézieux, Larissa; Langham, Jake; Gischig, Valentin; Thoeny, Reto; Figi, Daniel

doi:10.5194/egusphere-2025-2788

Preprints

https://doi.org/10.5194/egusphere-2025-2788

Preprints

27 Jun 2025

| 27 Jun 2025

Dynamic Analysis of Flowlike Landslides at Brienz/Brinzauls, Graubünden, Switzerland

Jordan Aaron, Larissa de Palézieux, Jake Langham, Valentin Gischig, Reto Thoeny, and Daniel Figi

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.

Received: 12 Jun 2025 – Discussion started: 27 Jun 2025

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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.

Journal article(s) based on this preprint

23 Jan 2026

Dynamic analysis of flowlike landslides at Brienz/Brinzauls, Graubünden, Switzerland

Jordan Aaron, Larissa de Palézieux, Jake Langham, Valentin Gischig, Reto Thoeny, and Daniel Figi

Nat. Hazards Earth Syst. Sci., 26, 449–464, https://doi.org/10.5194/nhess-26-449-2026,https://doi.org/10.5194/nhess-26-449-2026, 2026

Short summary

Jordan Aaron, Larissa de Palézieux, Jake Langham, Valentin Gischig, Reto Thoeny, and Daniel Figi

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2025-2788', Anonymous Referee #1, 22 Jul 2025
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.
There are some minor issues of language and formatting (e.g., in L176 and L197, the closing brackets after the equation numbers are missing).

Section 3.1: past tense and present tense are mixed, there should be consistent use of one of them.

Caption of Fig. 9: Allgaü Schist -> Allgäu Schist

7 and Fig. 10: in Fig. 7, the observed outline is included in all panes, in Fig. 10 only for the last time step – maybe better to make this consistent.

L290: You should also include work by others than Hungr and colleagues.

L290f: There have been attempts of slow-flow simulation models also in GIS environments: the r.avaflow software now has a function for slower movements: https://link.springer.com/article/10.1007/s10346-023-02146-z and https://egusphere.copernicus.org/preprints/2025/egusphere-2025-213/ Recently, a dynamic earth flow model was published: https://www.sciencedirect.com/science/article/pii/S0013795225000559

L396: I am not sure about the statement “The failures documented at this site represent two landslide classes rarely considered …”. I think landslides of such type are often considered by practitioners. Maybe better reformulate the statement to make clearer what you mean.

L402: research contact --> research contract
Citation: https://doi.org/10.5194/egusphere-2025-2788-RC1
- AC1:
  'Reply on RC1', Jordan Aaron, 06 Oct 2025
  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.
  Thanks for your constructive and thorough review.
  There are some minor issues of language and formatting (e.g., in L176 and L197, the closing brackets after the equation numbers are missing).
  
  Thanks for catching this, we fixed these examples and checked the rest of the text for similar typos.
  Section 3.1: past tense and present tense are mixed, there should be consistent use of one of them.
  
  Great catch, we have fixed this.
  Caption of Fig. 9: Allgaü Schist -> Allgäu Schist
  
  Fixed
  7 and Fig. 10: in Fig. 7, the observed outline is included in all panes, in Fig. 10 only for the last time step – maybe better to make this consistent.
  
  We agree, and will fix this in the revision
  L290: You should also include work by others than Hungr and colleagues.
  
  This is a great point which we completely agree with. We have updated this line to read:
  Numerical models of landslide motion have typically been implemented to simulate the motion of extremely-rapid, flowlike landslides (e.g. Aaron & Hungr, 2016; Bouchut et al., 2003; Christen et al., 2010; Hungr, 1995; Hungr & McDougall, 2009; Pirulli, 2005; Pudasaini & Mergili, 2019)
  L290f: There have been attempts of slow-flow simulation models also in GIS environments: the r.avaflow software now has a function for slower movements: https://link.springer.com/article/10.1007/s10346-023-02146-z and https://egusphere.copernicus.org/preprints/2025/egusphere-2025-213/ Recently, a dynamic earth flow model was published: https://www.sciencedirect.com/science/article/pii/S0013795225000559
  
  Thanks for pointing us to this important reference, we will add it to the introduction and discussion.
  L396: I am not sure about the statement “The failures documented at this site represent two landslide classes rarely considered …”. I think landslides of such type are often considered by practitioners. Maybe better reformulate the statement to make clearer what you mean.
  
  We agree, and upon reading your comment have realised that this statement was poorly formulated. We have rephrased as below (new text in bold):
  These results thus show that consideration of source zone lithology and mobility enhancement factors, such as the presence of saturated substrate, must be incorporated in the analysis of landslide hazard at similar sites. As the two analysed cases show, ignoring these factors could lead to substantial overestimates of both impact area and velocity.
  L402: research contact --> research contract
  
  Fixed, thanks!
  
  Citation: https://doi.org/10.5194/egusphere-2025-2788-AC1
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
- AC2: 'Reply on RC2', Jordan Aaron, 06 Oct 2025
  
  Thank you so much for your kind words and great comments. As our reply includes a Figure we have uploaded a PDF (attached to this comment) which contains all our answers.
  
  Citation: https://doi.org/10.5194/egusphere-2025-2788-AC2
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
- AC3: 'Reply on RC3', Jordan Aaron, 06 Oct 2025
  
  Thanks for taking the time to provide this feedback, we really appreciate it. As we have edited text in the manuscript it is easier to see the changes as a formatted PDF file, which is uploaded below.
  
  Citation: https://doi.org/10.5194/egusphere-2025-2788-AC3

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2025-2788', Anonymous Referee #1, 22 Jul 2025
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.
There are some minor issues of language and formatting (e.g., in L176 and L197, the closing brackets after the equation numbers are missing).

Section 3.1: past tense and present tense are mixed, there should be consistent use of one of them.

Caption of Fig. 9: Allgaü Schist -> Allgäu Schist

7 and Fig. 10: in Fig. 7, the observed outline is included in all panes, in Fig. 10 only for the last time step – maybe better to make this consistent.

L290: You should also include work by others than Hungr and colleagues.

L290f: There have been attempts of slow-flow simulation models also in GIS environments: the r.avaflow software now has a function for slower movements: https://link.springer.com/article/10.1007/s10346-023-02146-z and https://egusphere.copernicus.org/preprints/2025/egusphere-2025-213/ Recently, a dynamic earth flow model was published: https://www.sciencedirect.com/science/article/pii/S0013795225000559

L396: I am not sure about the statement “The failures documented at this site represent two landslide classes rarely considered …”. I think landslides of such type are often considered by practitioners. Maybe better reformulate the statement to make clearer what you mean.

L402: research contact --> research contract
Citation: https://doi.org/10.5194/egusphere-2025-2788-RC1
- AC1:
  'Reply on RC1', Jordan Aaron, 06 Oct 2025
  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.
  Thanks for your constructive and thorough review.
  There are some minor issues of language and formatting (e.g., in L176 and L197, the closing brackets after the equation numbers are missing).
  
  Thanks for catching this, we fixed these examples and checked the rest of the text for similar typos.
  Section 3.1: past tense and present tense are mixed, there should be consistent use of one of them.
  
  Great catch, we have fixed this.
  Caption of Fig. 9: Allgaü Schist -> Allgäu Schist
  
  Fixed
  7 and Fig. 10: in Fig. 7, the observed outline is included in all panes, in Fig. 10 only for the last time step – maybe better to make this consistent.
  
  We agree, and will fix this in the revision
  L290: You should also include work by others than Hungr and colleagues.
  
  This is a great point which we completely agree with. We have updated this line to read:
  Numerical models of landslide motion have typically been implemented to simulate the motion of extremely-rapid, flowlike landslides (e.g. Aaron & Hungr, 2016; Bouchut et al., 2003; Christen et al., 2010; Hungr, 1995; Hungr & McDougall, 2009; Pirulli, 2005; Pudasaini & Mergili, 2019)
  L290f: There have been attempts of slow-flow simulation models also in GIS environments: the r.avaflow software now has a function for slower movements: https://link.springer.com/article/10.1007/s10346-023-02146-z and https://egusphere.copernicus.org/preprints/2025/egusphere-2025-213/ Recently, a dynamic earth flow model was published: https://www.sciencedirect.com/science/article/pii/S0013795225000559
  
  Thanks for pointing us to this important reference, we will add it to the introduction and discussion.
  L396: I am not sure about the statement “The failures documented at this site represent two landslide classes rarely considered …”. I think landslides of such type are often considered by practitioners. Maybe better reformulate the statement to make clearer what you mean.
  
  We agree, and upon reading your comment have realised that this statement was poorly formulated. We have rephrased as below (new text in bold):
  These results thus show that consideration of source zone lithology and mobility enhancement factors, such as the presence of saturated substrate, must be incorporated in the analysis of landslide hazard at similar sites. As the two analysed cases show, ignoring these factors could lead to substantial overestimates of both impact area and velocity.
  L402: research contact --> research contract
  
  Fixed, thanks!
  
  Citation: https://doi.org/10.5194/egusphere-2025-2788-AC1
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
- AC2: 'Reply on RC2', Jordan Aaron, 06 Oct 2025
  
  Thank you so much for your kind words and great comments. As our reply includes a Figure we have uploaded a PDF (attached to this comment) which contains all our answers.
  
  Citation: https://doi.org/10.5194/egusphere-2025-2788-AC2
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
- AC3: 'Reply on RC3', Jordan Aaron, 06 Oct 2025
  
  Thanks for taking the time to provide this feedback, we really appreciate it. As we have edited text in the manuscript it is easier to see the changes as a formatted PDF file, which is uploaded below.
  
  Citation: https://doi.org/10.5194/egusphere-2025-2788-AC3

Peer review completion

AR – Author's response | RR – Referee report | ED – Editor decision | EF – Editorial file upload

ED: Publish subject to minor revisions (review by editor) (15 Oct 2025) by Mihai Niculita

AR by Jordan Aaron on behalf of the Authors (31 Oct 2025) Author's response Author's tracked changes Manuscript

ED: Publish subject to minor revisions (review by editor) (06 Nov 2025) by Mihai Niculita

ED: Publish subject to technical corrections (22 Nov 2025) by Mihai Niculita

AR by Jordan Aaron on behalf of the Authors (05 Dec 2025) Author's response Manuscript

Journal article(s) based on this preprint

23 Jan 2026

Dynamic analysis of flowlike landslides at Brienz/Brinzauls, Graubünden, Switzerland

Jordan Aaron, Larissa de Palézieux, Jake Langham, Valentin Gischig, Reto Thoeny, and Daniel Figi

Nat. Hazards Earth Syst. Sci., 26, 449–464, https://doi.org/10.5194/nhess-26-449-2026,https://doi.org/10.5194/nhess-26-449-2026, 2026

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Jordan Aaron, Larissa de Palézieux, Jake Langham, Valentin Gischig, Reto Thoeny, and Daniel Figi

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Short summary

In mid-May, 2023, the village of Brienz/Brinzauls in the Swiss canton of Graubunden was evacuated, and one month later a flowlike landslide emplaced with velocities of ~25 m/s and narrowly missed impacting the village. Landslides at this site have emplaced with velocities that can vary by 5 order-of-magnitude, a puzzling observation which we analyse in the present work. Our results show that the range of scenarios usually considered in landslide risk analyses must be expanded.


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