the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 11 Jun 2026
Thermal regime and geometry of a hanging glacier and its interaction with permafrost: the Pointes du Mourti, Swiss Alps
Abstract. Hanging glaciers are diagnostic features of high-mountain permafrost, but their response to climate forcing and links with surrounding permafrost remain poorly understood. We investigated the hanging glacier at Pointes du Mourti (3653 m a.s.l., Swiss Alps; mean annual air temperature = -4.6 °C) between 2020 and 2025, a period that covers Switzerland’s four warmest years on record. Geometric changes were quantified using uncrewed aerial vehicle photogrammetry and ice-based ground-penetrating radar, while permafrost conditions were assessed using rock surface temperatures, thermal modelling (CryoGrid2), and electrical resistivity tomography. Between 2021 and 2024, the ice thinned by up to 7 ± 0.12 m (20–45 %), with peak losses in 2022 (6.8 ± 0.5 % volume loss). Accelerated melt exposed pre-existing crevasses, enabling more efficient meltwater infiltration, which advanced basal temperature maxima and minima by ~2 months. Despite this, basal temperatures in the upper glacier remain low and continue decreasing due to enhanced winter cooling associated with ice thinning. The lower glacier exhibits temperate conditions with prolonged zero-curtain periods (146–193 days), indicating significant volumes of stored meltwater. The surrounding rock wall permafrost is discontinuous and strongly controlled by topography: only the shaded north-facing slope where the glacier lies maintains negative mean annual rock surface temperature (-3.67 °C), while sun-exposed aspects reach +3.05 °C. Model results indicate active-layer thickening that has doubled since 2015. Our observations suggest a transition toward polythermal conditions driven by rapid ice thinning, meltwater infiltration, and subsequent water storage, increasing the potential for destabilisation of small Alpine hanging glaciers under current climate conditions.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2026-2455', Suvrat Kaushik, 16 Jul 2026
- RC2: 'Comment on egusphere-2026-2455', Anonymous Referee #2, 20 Jul 2026
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- 1
The manuscript presents a multidisciplinary investigation of the Pointes du Mourti hanging glacier, combining UAV photogrammetry, ground-penetrating radar (GPR), borehole thermometry, rock-surface temperature monitoring, CryoGrid2 thermal modelling and electrical resistivity tomography (ERT) over a five-year observation period. Overall, the study is timely given the recent, unprecedented glacier losses in the European Alps and addresses an important knowledge gap concerning the coupled evolution of hanging glaciers and surrounding permafrost. The major strength of the study is the extensive field campaign conducted on such a steep hanging glacier. Considering the physical and technical challenges of working in such harsh environments, the author's effort and willingness to conceptualise this study have to be commended.
Overall, I found the paper to be a very interesting read. It is generally well written and logically structured. The methods are described in sufficient detail (maybe a bit too much sometimes, check additional comments), the figures are generally of high quality, and the observational dataset could provide a valuable benchmark for comparison with regional and global studies. I believe the manuscript would be a valuable contribution to the cryosphere community and falls well within the scope of The Cryosphere.
I have listed a few suggestions that I believe would further improve the manuscript. My comments mainly concern the presentation and interpretation of the results, as well as a few methodological aspects that could benefit from additional clarification.
General comments:
1. Scope and interpretation of the results: One limitation of the study, which the authors also acknowledge in Section 5.4, is that the field data are spatially limited due to the physically demanding and time-consuming nature of data acquisition. This naturally limits how far the results can be generalized, both to other hanging glaciers and, to some extent, to the entire Pointes du Mourti glacier. I acknowledge that acquiring additional field data is not feasible and is beyond the scope of the current study; the results should be interpreted within the extent of the surveyed areas. However, I think the implications of these limitations are not always fully reflected in the interpretation of the results. For example:
The GPR survey covers only about 20% of the total glacier area, yet some of the subsequent interpretations are extended to describe the geometry of the entire hanging glacier more generally. I think the manuscript would benefit from a clearer discussion of how representative the surveyed area is of the entire glacier and how this limitation affects the interpretation of glacier-wide geometry and volume changes.
2. Uncertainty analysis: The authors carefully quantify the observational uncertainties associated with the GPR ice thickness, UAV DEM differences and LoD calculations. However, the manuscript gives much less attention to modelling and parameter uncertainties, particularly for the CryoGrid simulations. I suggest including a short subsection in the Discussion that summarizes the different sources of uncertainty (observational, modelling and interpretation). This would help readers distinguish between directly observed changes and the inferred physical mechanisms. Below are a couple of examples where the discussion of uncertainties could be expanded:
A. First point is regarding the borehole observations (which I felt is one of the strongest aspects of the paper). The authors state that since more than 5 m of surface ablation occurred during the monitoring period, the thermistors progressively changed their position relative to the glacier surface. This likely introduces additional uncertainty when comparing temperature trends between different years. Although the authors acknowledge this, I think it deserves a more explicit discussion, particularly regarding how it influences the interpretation of the observed temporal temperature trends.
B. Similarly, the quantified glacier volume changes are an important result from the study. However, since the authors acknowledge that the 2021 UAV survey had lower quality due to fresh snow, it would be useful to discuss how this may influence the reported volume loss during the 2021–2022 period, which is identified as the year with the largest changes.
3. Section 3.5: Although I am not an expert in this, I felt the CryoGrid thermal modelling section would benefit from a little more justification of the chosen model parameters, particularly porosity values. The manuscript states that sensitivity tests were performed and that porosity had little influence on the results, but these tests are not shown. Even a brief summary or supplementary figure would help readers assess the robustness of the model outputs.
4. Similarly, the laboratory resistivity measurements are useful for supporting the interpretation of the ERT results. However, they are based on a very limited number of rock samples. I suggest mentioning this limitation more explicitly when interpreting the field resistivity data, as rock properties, fractures and water content at the field site may produce a wider range of resistivity values than those measured in the laboratory experiments.
Additional comments:
- The paper would benefit from a short table summarising the timing of all field campaigns and measurements. This would make it easier for readers to follow the chronology of the different datasets.
- The Methods section is very detailed. Maybe some equipment specifications (e.g. tablet, software, or hardware details) could potentially be moved to the Supplementary Material without affecting reproducibility.
- Results versus interpretation
In a few places, the Results section moves directly into interpretation (for example, when discussing the causes of spatial variability in melt or thermal evolution). These are not major issues, but some of the following sentences may be moved to the Discussion section. For example:
Page 13, Section 4.1.1 : "...we therefore concluded that the borehole intersected a crevasse wall during drilling…"
Page 13, Section 4.1.2 : ...which explains its location..." and later "...which can also be explained by this bedrock configuration."
Page 14, Section 4.1.3 : "This pattern is likely related to enhanced shading and reduced solar irradiation in this zone."
Page 16, Section 4.1.4 : "Basal temperature at B1 indicates cold-based ice conditions…"
Minor editorial comments:
Line 107 : replace with ‘which has been monitored by MeteoSwiss since 1864’
Line 186 : "...potentially generates some errors…" sounds a bit strange; maybe rewrite as "...may introduce errors…"
There are a few minor inconsistencies in tense throughout the Methods section. It would be better to use the same tense consistently throughout the Methods section.
Lines 235–253: I found the paragraph describing porosity values rather long. It could be split into two shorter paragraphs:
a. Porosity values estimation
b. selected values
This would improve the readability.
Figure 5 : Figure caption says "saturated conditons", probably a typo here, should be ‘conditions’
Lines 315 : "leaving little doubt" slightly strong wording, replace with "...strongly suggesting…"
Table 2 : Ice melt values ... are estimated… instead of ‘is’
Line 514: typo : "This is also the case…"
Line 515 : "...which manifest in vertical orientations." sounds a bit strange, maybe a better rephrasing would be "...which consistently exhibit near-vertical orientations."
Lines 516–526 : This is indeed a great section which compares melt rates with other Alpine glaciers. I think the comparison would be stronger if the authors briefly acknowledged that differences in glacier geometry, elevation and climatic setting may influence the comparability of these values
Lines 527–533 : "This spatial contrast likely reflects the intermittent development of a protective snow cover…" this is highly plausible, but seem more like an interpretation. Maybe the sentence can be balanced a bit by adding "...although other local factors may also contribute."
Lines 535–540 : Again, this paragraph is super interesting, however I felt the conclusions are slightly stronger than the available evidence from the study. For example, the absence of observed ice avalanches during a five-year monitoring period does not necessarily challenge the concept of unbalanced avalanching glaciers, particularly if avalanche recurrence intervals are longer than the observation period. I would rewrite this paragraph using slightly more cautious wording.
Lines 665- 687 : Future of the PdM hanging glacier and others : Really enjoyed reading this section as well.
I also noticed some issues with hyphenation throughout the manuscript, for example surface based / surface-based, multi frequency / multi-frequency, slope normal / slope-normal etc. It would be more consistent if the same hyphenation were used throughout the manuscript.