the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 09 Dec 2025
How ice apron loss and permafrost degradation promote the Platteikogel rock slide: A thermo-mechanical reconstruction
Abstract. The Alpine cryosphere changes at unprecedented speed, affecting the thermal, hydrological, and mechanical state and behaviour of rock slopes. While numerous studies investigated singular drivers for progressive rock slope failures, the knowledge of hydro-thermo-mechanically coupled processes remains scarce. In this manuscript, we investigate the 2024 permafrost rock slide at Platteikogel with a volume of 50,000 m³ (3,395 m a.s.l., above Vernagtferner, Austria). We aim to assess how observed ice apron loss and related permafrost warming promote the release mechanism. We reconstructed multidecadal thermal evolution accounting for the thermal impact of ice apron loss. Based on field observations, we derived a conceptual model on how ice apron loss potentially affects rock slope destabilization. Integrating the outcome of the preceding steps, we performed a mechanical stability analysis assuming that the rock slide failed along ice-filled discontinuities. The mechanical model indicates that the rock slide can not be solely explained by a warming-driven decrease in shear strength of ice-filled discontinuities, suggesting that other failure processes superimpose or even dominate. The implemented system feedback related to ice apron loss suggests that hydrostatic pressure buildup due to water infiltration and rockfall-induced unloading thereby promoted the Platteikogel rock slide release. In summary, we demonstrate that ice apron loss not only leads to increased rockfall activity but also accelerates progressive rock slope failure, promoting the release of rock slides. In upcoming decades, ice aprons on steep rock slopes above 3000 m in the European Alps are expected to experience drastic area loss, exposing potential source zones for future rock slides.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Earth Surface Dynamics.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
(25959 KB) - Metadata XML
-
Supplement
(4057 KB) - BibTeX
- EndNote
Status: open (until 02 Mar 2026)
- RC1: 'Comment on egusphere-2025-5985', Reginald Hermanns, 30 Jan 2026 reply
-
RC2: 'Comment on egusphere-2025-5985', Florence Magnin, 24 Feb 2026
reply
The paper entitled « How ice apron loss and permafrost degradation promote the Platteikogel rock slide: A thermo-mechanical reconstruction » investigate the thermal, hydrological and mechanical evolution o a steep alpine ice-covered rock face to decipher potential failure mechanisms of a « rock slide » that as occurred in 2024 in Austria.
In my view, this article presents a truly innovative methodological approach by proposing the explicit coupling of thermal, mechanical and even hydrological processes through numerical modeling to explain a real case of rock slope destabilization. Indeed, the coupling of these processes has so far remained a significant methodological bottleneck, which this paper seeks to overcome. It also presents the first thermo-hydro-mechanical couplings of ice aprons, glaciers, and permafrost in rock slopes. Furthermore, the manuscript is very well written, and the figures are of excellent quality.
Therefore, based on the novelty of the modeling approaches and the inherently innovative nature of the results, I strongly recommend this paper for publication. Nevertheless, despite the overall high quality of the work, I have several substantive and formal comments that should be addressed before the article is published.
General comments
1) Characterization of the gravitational event: similarly to the first reviewer, I would suggest reconsidering the designation of the event, as it does not strictly correspond to a rock slide, and ensuring consistent terminology throughout the manuscript. « Rock slope failure » is neutral but « rock fall » is also frequently used for such volumes. And a minor remark : would the title be more precise with « promoted » instead of « promote ». At first sight, the combination of present tense + « rock slide » let me thought that it was an active rockwall deformation, not a past and sudden vent.
2) The consideration of hydrological processes is frequently mentioned in the manuscript; however, it is not investigated at the same level as the thermal and mechanical processes. Its treatment remains more arbitrary and is not calibrated as the thermal and mechanical processes. It is also unclear how the approach for testing the water-related pressure was defined (determination of a hydraulic head of 30 m). I would therefore recommend clarifying this difference in approach in order to better structure the conclusions and to more clearly distinguish the respective contributions of the different methods and approaches.
3) Simulations consider various scenarios such as thermal evolution, hydrological forcings and changes in mechanical properties that are treated independently following initial mechanical conditions with 2 possible setups. I found it somewhat challenging to clearly understand the different scenario combinations and the specific novelty each one brings to the understanding of rock slope failure predisposition and triggering mechanisms. While the overall approach is comprehensive, it is also relatively complex. I would therefore suggest clarifying more explicitly the respective contribution of each scenario in comparison with the initial conceptual model. I acknowledge that efforts have been made to make the results as clear and traceable as possible; however, in its current form, it remains difficult to clearly identify the actual contributions. I believe greater clarity is needed regarding the a priori conceptual model and how the different simulations and process combinations either refine this model or allow the quantification of the underlying processes.
4) Following this previous comment, Figures 1 and 12 are somewhat similar and, in my interpretation, Figure 1 presents the a priori hypotheses, whereas Figure 12 corresponds to an enriched version of Figure 1 incorporating the modeling results. However, it remains difficult to clearly distinguish from Figure 12 which elements are firmly supported by the results and which remain more or less speculative after consideration of the modeling outcomes. I believe it would be useful to more clearly differentiate the results that are robustly established from those that merely maintain or confirm the initial a priori hypotheses within this conceptual model.
5) I have been somewhat confused through the manuscript, as the failure depths (mean/max) are not clearly specified and the basal shear strength does not correspond to the V/A ratio. I believe this point should be clarified to ensure that the initial assumptions, as well as the contributions and limitations of the results, are more easily understandable and identifiable.
6) Despite the very high quality and richness of the figures, they are sometimes difficult to read due to the large amount of detail, with text that is occasionally too small.L41 : I would use « multi-method approach » rather than « cross-disciplinary »
Minor comments
L67-75: how was this measured?
L90-99: how are all these changes calculated?
L105 and following: a few words decribing the Cryogrid (coding, physics…) would be useful
L110: Any performance metrics beyond the visual in Figure A2 for the calibration?
L145: the Equation neglects the effect of permafrost on the snow-covered surface as the RST generally falls well < 0°C below snow under permafrost conditions, especially on the NW aspect where permafrost is cold. This limitation deserves to be taken into consideration in some ways.
L167: the meaning of TIAS is not detailed.
L 193: I didn’t get what these 100 simulations correspond to. This deserves clarification.
L 259: I get confused by « varying model geometry ». If I look at figure 6, A & B are two different rock structure/jointing systems setups, right? Could the sentence be more precise? In my opinion « geometry » could also refers to the topography, rock/ice distribution, and varying sounds like a dynamical parameters, while it seems 2 different setups.
L285: how the value of 30 m for the hydraulic head was decided?
L308: low rather than « cold » temperature.
L 314: why 20 m depth? Is it the failure depth? Basal shear plane?
L320: « extrusion-like form » is not clear to me
L322: « (« is missing before « Fig.8) »
L344: permafrost temperature is lowest rather than « coldest »
L405: for this study, the concept of peri-paraglacial would be more appropriate
L440: fatigue
L 520: unclear sentence, any word missin?
L525: what would be « sufficient information »?
Table 1: any idea of the max mean/depth? Looking at the volume/surface area it seems that the event is really shallow and this has strong implications for the thermal models that may not be realistic at all at shallow depths. And in Figure A2 a there is a « depth of basal shear plane ». Is it between 15 and 25 m? I a ma bit confused as this information is not clearly reported.
Fig. 7: I didn’t get why is the reference line -3°C?
Fig. 8: what is the dark-brown color?
Citation: https://doi.org/10.5194/egusphere-2025-5985-RC2
Viewed
| HTML | XML | Total | Supplement | BibTeX | EndNote | |
|---|---|---|---|---|---|---|
| 339 | 398 | 19 | 756 | 49 | 20 | 18 |
- HTML: 339
- PDF: 398
- XML: 19
- Total: 756
- Supplement: 49
- BibTeX: 20
- EndNote: 18
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1
This manuscript is a back analysis of the Plattikogel rock slope failure, a mountain that is characterized by permafrost and a retreating ice apron. The manuscript is based on a detailed description of the event including the lowering of the surrounding glaciers and decay of ice aprons. It includes a rock fall analysis in the years prior to the event. The model includes both a thermal model using the model CryoGrid and a rock mechanical model using the model UDEC. Assumptions in the model are based on field observations and are sound. The manuscript is well written and figures in general are very good and appropriate. I recommend publication after minor revisions:
The event is called a rock slide in the title and abstract and indeed is the stability strongly controlled by the stability of the toe following the UDEC model. However, structural geology is complex. This allows taht the rock slope failure might have occurred in small subsequent events (also suggested in Figure A5). The event was not observed by eyewitnesses during the event nor days later. It was not recorded in any other records (It is indicated that nearby seismic stations were checked and had no apparent signal). Rock slope failures that form rock avalanches (suggested in the manuscript on lines 54, 61 and table title 1 have sudden strong energy releases, that can be detected in seismic data. (e.g. Karasözen, E., & West, M. E. (2024). Toward the Rapid Seismic Assessment of Landslides in Coastal Alaska. The Seismic Record, 4(1), 43-51. doi:10.1785/0320230044.). This event is with 50.000 m3 extremely small for a rock avalanche. See the used terminology in this paper is by: Hungr, O., Leroueil, S., & Picarelli, L. (2014). The Varnes classification of landslide types, an update. Landslides, 11(2), 167-194.) which suggests a volume of about 1.000.000 m3 for rock avalanches. Hermanns et al., 2022 (Hermanns, R. L., Penna, I. M., Oppikofer, T., Noël, F., & Velardi, G. (2022). 5.06 - Rock Avalanche. In J. F. Shroder (Ed.), Treatise on Geomorphology (Second Edition) (pp. 85-105). Oxford: Academic Press. doi:https://doi.org/10.1016/B978-0-12-818234-5.00183-8.) suggest that rock avalanche can be of smaller size than earlier suggested but 50.000 m3 is at the absolute end of rock avalanches ever recorded. This opens the question if the material indeed failed in a single short (seconds) event but may be in several failures over hours or even days and thus would more classify as a rock collapse (following the extended definition of Hermanns et al. 2022 after Hungr et al., 2014). The H/L ratio and Fahrböschung as given in table 1 indeed suggest a rock avalanche but this high mobility might just be related to the steepness of the terrain so that the failed material tumbled further downslope and never moved as a fluidized stream of rock material as in a rock avalanche. Anyhow the authors should be more carful and accept different failure scenarios than a single event failure. Thus, I would also recommend neither using rock slide nor rock avalanche as specific terms but the broader term “rock slope failure”.
I actually still have some problems putting the event in front of an inner eye. This is likely due to the lack of a detailed map. I would call Figure 1A unreadable as the only map and would strongly recommend a detailed map that also allows to assess the steepness of the terrain. Similar to Figure 1 are also Figure 2, 5, 6b, 11, A3, A5 below a size that is acceptable to read.
Beside these comments, I have only a few other minor observations:
Line 66 and 67: why is schistose and muscovite written in capital letters?
Line 68: numbering of supplementary material different to numbering of supplementary material in line 101.
Line 70: I actually see gullies on the image with two orientations.
Line 86,87: I cannot see this on the figures.
Figure 2: Include orientation of figure.
Line 102: I think the profile line should be included in the main body of the paper as many figures reference to that.
Line 213: This was nicely documented by: Kuhn, D., Hermanns, R. L., Fuchs, M., Schüßler, N., Torizin, J., Aga, J., et al. (2025). Warming-induced destabilization of polar coastal rock cliffs and the role of thermokarst: A case study of Forkastningsfjellet on Svalbard. Science of The Total Environment, 968, 178807.
Figure 5: This figure strongly suggests that several subsequent failures are feasible.
Line 399, 400: This concept was discussed much earlier using different terminology: static boundary conditions (conditions that do not change in time), dynamic boundary conditions (conditions that change in time), triggering factors. (Hermanns, R., Niedermann, S., Villanueva Garcia, A., & Schellenberger, A. (2006). Rock avalanching in the NW Argentine Andes as a result of complex interactions of lithologic, structural and topographic boundary conditions, climate change and active tectonics. Landslides from massive rock slope failure, NATO Science Series IV, 49, 539-569.). However, ice aprons and permafrost were not included in the list by Hermanns et al., 2006.
Discussion: I think a short paragraph could be included discussing if the event was indeed a one event failure in seconds or if it could have occurred in more length in time or in several events. Does the geomechanically model suggest something?
I was happy reviewing this manuscript as it changed my view looking on such high alpine landscapes. Very nice contribution to science.