| 15 May 2025
Thrust moraines and rock glaciers: Relationships between subsurface structures and morphodynamics in Swiss glacier forefields dominated by glacier-permafrost interactions
Abstract. Glacier-permafrost interactions in Alpine environments significantly influence geomorphological processes, making it essential to understand the relationship between subsurface structures and surface morphodynamics for predicting landscape evolution under climate change. So far, the direct correlation between subsurface ice distribution and surface movement for thrust moraine complexes and rock glaciers remains poorly understood. This study investigates the internal structure and morphodynamics of both landform types in two Swiss glacier forefields, aiming to determine how subsurface ice content and structure influence recent surface displacements. We combined electrical resistivity tomography (ERT) with Differential Interferometric Synthetic Aperture Radar (DInSAR) to assess subsurface resistivity and surface displacement patterns. The study focuses on two sites in the Valais region (Swiss Alps), analyzing spatial movement patterns and their correlation with subsurface properties through regression analysis. ERT revealed distinct differences between the ice-rich thrust moraine complexes and the more heterogeneous internal structure of the investigated rock glaciers. DInSAR-derived displacement patterns showed that moraine complexes exhibit predominantly vertical subsidence with high seasonal variability, while rock glaciers display more consistent horizontal movement. Regression analysis confirmed strong correlations between high-resistivity zones and intense surface dynamics in moraine complexes, with the logarithm of maximum resistivity correlating with absolute horizontal displacement (R² = 0.75) and elevation change (R² = 0.76). Instead, rock glaciers exhibited weaker correlations (R2 ≤ 0.3), likely due to heterogeneous internal structures and more complex creep processes, which differ from the subsidence-dominated movements in the ice-rich moraines. These findings underscore the importance of distinguishing between these landform types in permafrost studies and climate change assessments.
The paper deals with the current structure and kinematic behavior of landforms resulting from the interaction between advancing glaciers and frozen debris (permafrost) during the Little Ice Age in two areas in the Swiss Alps. It is based on the combination of two techniques, namely electrical resistivity tomography (ERT) to assess the internal structure of the investigated landforms, and DInSAR, satellite-borne radar interferometry, to determine the surface motion of those landforms, the observed movement resulting from the varying combination of the downslope movement of the mass and subsidence induced by the melt of embedding glacier ice.
Whereas the data and results are of good quality, partly innovative, properly presented and discussed, making this paper worth of being published, the latter suffers from a number of weaknesses. Major improvements are required before any further consideration for publication.
I don't grasp the actual goal of the paper : it looks that it is more focusing on the combined application of both methodologies than on solving the question(s) they are applied for (as the title announces). I would suggest to reverse the importance, first clearly stating the question(s), then evaluating the contribution of the applied methodologies to solve them.
I would also strongly suggest to the authors to make use of the Swissimage (orthoimages) made available by Swisstopo for about the last 60 years to :
- analyze the development of the investigated landforms over the last decades (e.g. development of thermokarst depressions),
- determine the current (e.g. 2017-2023) flow fields (direction and velocity) of the investigated landforms by feature tracking; it could be done for single boulders or by applying GIS tools as IMCORR or others.
It would also be helpful to propose a clear labelling (e.g. numbering or naming) for the various investigated landforms. Otherwise, it is sometimes difficult to follow what it is spoken about.
The paper should gain in concision and consistency. It could also be shortened. There are issues with the meaning of sentences or terminologies (I only went into details in the very first part of the paper, but this has to be applied all along). Also a part of the discussion could be moved in the methodological section.
My comments - after a first detailed section - are only limited to some important points (and suggestions). It might be that I misunderstood some aspects, meaning that some of my comments could be disregarded. I would be glad to proceed to a full review of the paper after it has been reworked.
Detailed comments:
The title sounds a bit weird to me. I would suggest something as : “Current morphodynamics and subsurface structure of thrust moraines and rock glaciers connected to Little Ice Age glacier forefields : case studies from the Swiss Alps”. Another option could be to emphasize on the applied techniques, e.g. : ERT and DInSAR for investigating the current…
l.9-11 – “Glacier-permafrost interactions in Alpine environments significantly influence geomorphological processes, making it essential to understand the relationship between subsurface structures and surface morphodynamics for predicting landscape evolution under climate change ». Such a sentence has no clear meaning to me. Glacier-permafrost interactions are not specific to Alpine environments. In LIA glacier forefields, there are often not occurring anymore since decades (one should use the past). Subsurface structures and morphodynamics of what ? (the sentence is talking about interactions). Why do we need to predict the landscape evolution there ? Why is it "essential to understand" those relationships between subsurface structures and morphodynamics ? Make all that much clearer.
l. 11 – “direct correlation” – what does it mean? Could it be indirect?
l.11-12 – “…correlation between subsurface ice distribution and surface movement for thrust moraine complexes and rock glaciers… poorly understood”. I don't grasp the actual meaning of this sentence. We would like to know the kinematic behavior (morphodynamics, if I understand right) of the thrust moraines + rgs on one hand, and their internal structure (i.e. ground ice characteristics and distribution) on the other hand, in order to be then able to infer on their dynamics (i.e. the process driving their motion, if any) in the context of connection to a LIA glacier forefield. No ?
l.12-14 – “ This study investigates the internal structure and morphodynamics of both landform types … aiming to determine how subsurface ice content and structure influence recent surface displacements ». Agreed, but I would suggest to write such a sentence in a more efficient way, avoiding repetition (the second half of the sentence must be merged with the first one).
l. 13 – “…both landform types in two Swiss glacier forefields…” : apart altering the formulation, I would suggest to split the Pipji area in two glacier forefield (see comment later) -> both landform types in connection to three LIA glacier forefields in the Swiss Alps.
l. 14-15 – “We combined electrical resistivity tomography (ERT) with Differential Interferometric Synthetic Aperture Radar (DInSAR) to assess subsurface resistivity and surface displacement patterns” – I would suggest to clearly associate the method and its objective, namely ERT for assessing subsurface resistivity and DInAR for surface displacement patterns.
l. 16 – “on two sites in the Valais region (Swiss Alps),” – almost already said three lines above
l. 21 – “intense surface dynamics” – what is meant ?
l. 21 – “moraine complexes” – thrust moraines complexes ?
l. 21 – « logarithm of maximum resisitivity » - what is the maximum resistivity ? why is it talked about its logarithm ? I don’t understand the sense of the latter. Maximum resistivity seems to be sufficient.
l. 24-25 – “These findings underscore the importance of distinguishing between these landform types in permafrost studies and climate change assessments” – Again, I don’t understand the meaning. There are very probably some shortcuts in what the authors would like to say.
l. 27 – “Glaciers and permafrost … occur in close vicinity…” – Note that this paper is not talking about glaciers and permafrost in general, but about a specific interaction which occurred between glaciers at their snout (and/or in their ablation area) and frozen debris during the Little Ice Age, and their consequence it has on the present-day morphodynamics in the related glacier forefield.
l. 28 – “changed precipitation patterns” – What is meant ?
l. 30 – Permafrost degradation in the European Alps is not related to any change in the precipitation patterns (depending however how the latter is defined, what we here don’t know).
l. 30-32 – “These changes are accompanied by morphological processes in the corresponding areas, which can have a wide variety of consequences such as changing creep rates of rock glaciers…” : The meaning is unclear to me. If I understand the sentence right, it gives that changing creep rates of rock glaciers (what are these changes ?) are consequences of morphological processes (but which ones ? is rock glacier creep not itself a morphological process ?) accompanying (what does it mean ?) permafrost warming and degradation (what is the difference ?) due to higher atmospheric temperatures (by how much (large or tiny) ?) and changed precipitation patterns (what are they ?) ? So, plenty of questions.
l. 34 – “Especially in areas where permafrost and glaciers have interacted in the past, high amounts of ground ice are incorporated in moraines…”. I guess it is meant incorporation of glacier ice (not ground ice).
l. 35 – “… and other glacial and periglacial landforms ». What are they ?
l. 35 – “…which are now affected by changing climatic conditions”. Not only “now”, but already since glacier retreat started, many decades ago. However, as the glacier retreat was considered as possibly favoring ground cooling and permafrost aggradation for decades, the climate evolution (dramatic temperature rise by about 2°C) for the last three decades has more than counterbalanced this presumed earlier trend.
l. 36 – “The last intense interactions…” - It must be stated that the sentence is geographically limited to the Alpine context, and to many other mountain ranges, but is not ubiquitous as interactions are still occurring in some other regions in the Andes or Asian high mountain ranges for instance.
l. 38 – “… local permafrost base” - What is the local permafrost base ? The permafrost base is the depth to which the ground is frozen. It is obviously used here in another sense (regional lower limit in elevation ?).
l. 38 – “…real interactions” – There are also apparent ones ?
l. 39 – “only” or mostly ?
l. 39-40 – “.. enabled transmission of glacial stress into the proglacial …” – The “proglacial area” means “debris masses overridden by the glacier or in contact at its front ?
l. 40-41 – “… and resulted in large-scale morphological overprinting in the proglacial areas”. What is this specific large-scale morphological overprinting ? Is not any advancing glacier morphologically overprinting the area on which it develops ? Beside the repetition in the sentence, why are proglacial areas now plural, whereas they weren’t before.
l. 44 – “only few studies focus on thrust moraines in alpine environments” - It could be worth of referring to some of them at least (e.g the earlier works by Evin (Fabre and Assier) in the French Alps in the 1980s, then other works in various regions around 2000 and later (e.g. Kneisel, Reynard et al., Lugon et al., Monnier et al.) as examples)
Evin, M. & Assier, A. 1983. Glaciers et glaciers rocheux dans le Haut-vallon du Loup (Haute-Ubaye, Alpes du Sud, France). Zeitschr. für Gletscherkunde und Glazialgeologie 19: 27–41.
Evin, M. 1992. Une moraine de refoulement au Viso (Italie). Zeitschr. für Gletscherkunde und Glazialgeologie 27/28:11–24.
It should not be so complicated to translate these two first papers. Moraine de refoulement = push moraine = thrust moraine
Reynard, E., Delaloye, R., Baron, L., Chapellier, D., Devaud, G., Lambiel, C., Marescot, L. & Monnet, R. (2003). Glacier/permafrost relationships in recently deglaciated forefields of small alpine glaciers, Penninic Alps, Valais, Western Switzerland. Proceedings of the 8th International Conference on Permafrost, Zurich 2003, Vo. 1, 947-952
Lugon, R., Delaloye, R., Serrano, E., Reynard, E. and Lambiel, C. (2004). Permafrost and Little Ice Age Glaciers Relationships: a Case Study in the Posets Massif, Central Pyrenees, Spain. Perm. Perigl. Process. Vol 15/3, 207-220
Ribolini, A. et al. (2010). The internal structure of rock glaciers and recently deglaciated slopes as revealed by geoelectrical tomography: insights on permafrost and recent glacial evolution in the Central and Western Alps (Italy-France). Quat. Sci. Rev., 29, 507–521 (doi: 10.1016/j.quascirev.2009.10.008)
Monnier, S., Camerlynck, C., Rejiba, F., Kinnard, C., Feuillet, T., Dhemaied, A. (2011). Structure and genesis of the Thabor rock glacier (Northern French Alps) determined from morphological and ground-penetrating radar surveys. Geomorphology 134 (3–4), 269-279. https://doi.org/10.1016/j.geomorph.2011.07.004.
Capt, M., Bosson, J.-B., Fischer, M., Micheletti, N., Lambiel, C. (2016). Decadal evolution of a very small heavily debris-covered glacier in an Alpine permafrost environment. Journal of Glaciology, 62 (233) 535–551. doi: 10.1017/jog.2016.56
l. 44-45 – “… although in mountain areas like the European Alps, these structures can be particularly large compared to the size of the advancing glacier” – I would change “although” by “even”, because thrust moraines complexes can be much larger, also compared to the size of the advancing glaciers, in other mountain ranges.
l. 46 – “…incorporation of massive sedimentary ice” – see also Kääb et al. (1997), Gärtner-Roer et al. (2022) and some of – if not all - the references provided in one of my previous comment.
Kääb, A., Haeberli, W., and Gudmundsson, G.H.: Analysing the creep of mountain permafrost using high precision aerial photogrammetry: 25 years of monitoring Gruben rock glacier, Swiss Alps, Permafrost and Periglacial Processes, 8, 4, 409–426, 1997
l. 48 – “…and often very high ice content in the interior of these landforms have favoured a transition to periglacial conditions”. I don’t see the point (why a very high ice content favors the transition), and the actual meaning of periglacial conditions.
l. 50-51 – “…some of these landforms also show recent surface changes”. This is just because they have only been investigated recently. They are presumed (or known) as having been subject to large(r) surface changes (what is actually the meaning of this ?) in earlier time after glacier interaction ceased.
l. 51 – “…could react sensitively in the context of global warming due to their high ice content.”. What kind of reaction is it talked about ? Except for the subsidence or the development of thermokarst features, I don't see the point related to the high ice content.
l. 54 – “… and confirmed some direct relationships between morphodynamics and the distribution and type of ground ice.” What are these relationships ?
l. 55 - “correlations” – Note that correlation is a statistical term, which doesn’t imply any causal effect. It is just expressing the similarity in the development of two variables.
l. 56. – “..information on correlations between the recent displacement rates and the existing subsurface structures as well as ice contents and ice types are still scarce”. Unclear meaning. If I am right, it is talked about the possible influence (driving) of either the “existing subsurface structures” (what does it mean ?), or the “ice contents” (why plural ?), or the “ice types” (what is meant ?” on the “recent displacement rates” (meaning permafrost creep rate ?). But it has never been talked about displacement (and the related motion mechanism) until then and we don’t know if we are talking about rock glaciers in general, rock glaciers connected to a glacier forefield, back-creeping push-moraines or whatever else.
l. 57-58 – “this study builds on a combined approach of geophysical surveying and remote-sensing-based surface displacement analysis using Differential Interferometric Synthetic Aperture Radar (DInSAR)…”. It must be explained why having chosen this approach and these techniques. It means that the research questions and their motivation should come before the selection/presentation of the approach and not after (l. 71-74).
l. 63 – “…DInSAR – an increasingly common method to study alpine periglacial geomorphology and morphodynamics” – DInSAR is not just one method. It is therefore used since more than 25 years to detect and monitor slope movements in mountain areas, and rock glaciers in particular.
Rott, H., Scheuchl, B., Siegel, A. & Grasemann, B. 1999. Monitoring very slow slope movements by means of SAR interferometry: A case study from a mass waste above a reservoir in the Ötztal Alps, Austria. Geophysical Research Letters, 26(11): 1629-1632.
Kenyi, L. & Kaufmann, V. 2003. Measuring rock glacier surface deformation using SAR Interferometry. Proceedings of the Eighth International Conference on Permafrost, Zürich, Switzerland, June 2003. Balkema, 1: 537-541. rticular (e.g. Rott et al. 1999, Kenyi and Kaufmann 2003 for some of the earliest publications)
l. 68-68 – “the use of satellite-based SAR data now enables a higher temporal resolution and a large spatial coverage so that also seasonal changes can be explored more systematically”. But there are also plenty of limitations, which would be worth of mentioning already here.
l. 72-73 – “What is the current internal structure of alpine thrust moraine complexes and are there differences to neighbouring rock glaciers?” The study is limited to two or three sites only. The objective cannot be generalized to alpine thrust moraine complexes from there only. Therefore, it must be stated that the neighbouring rock glaciers are specific ones only, namely glacier forefield-connected landforms that you morphologically identify as rock glaciers. Basically the latter move outward of the area presumably covered by the glacier during its LIA advance(s).
“What kind of surface morphodynamics takes place within the respective glacier forefields?”. So, the study is not restricted to the thrust moraine complexes and adjacent rock glaciers, right ?
“Are there any linkages between subsurface structure and recent morphodynamics, and are there any differences in this relationship considering the different landform types?” Be more precise. There are mainly three types of movement to be expected, sometimes combined, which could make their detection/disentangling challenging : permafrost (rock glacier) creep (which could also affect thrust moraines) / subsidence (caused by the melting of embedded glacier ice, mostly occurring at shallow depth during the warm/snow free season) / landslide (generic term for mass movement, which could be restricted to debris/ice masses or impacts bedrock as well.
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I stop with the detailed reading/commenting here.
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l. 76. “ … an inner-alpine dry region “. To be clear, what is the meaning of dry ? continental ? We are here talking of 1000 mm/year at Pipji and 1500 mm/year at Oberferden...
l. 82. Pipji glacier forefield. As explained in the description, there are two distinct glacier forefields at play in the Pipji valley. The Pipji glacier forefield on the orographic right side and an unnamed (Barrwang ?) glacier to the left. Both were only touching at a very tiny and insignificant uppermost section and not influencing each other. It would make much easier for the paper to distinguish them from the beginning and talk about two distinct sites, because the morphologies in both glacier forefields are fully differing one from the other.
l. 87. “previous activities”. Is it meant former Holocene glacier advances ?
l. 87. “…which provided the basis for rock glacier formation in the area of the former main glacier.” What is it meant ? This is unclear to me.
l. 88. “Due to several glacial advances and successive phases of rock glacier formation, the rock glacier consists of three different units (Units I - III, see Fig. 2a), which are characterized by different ages”. What are these ages ? It is important to know (if possible).
l. 104. Why are you not talking about the part having overridden the rock ridge to the north-east and has developed down to 2580-2600 m a.s.l. ?
l. 108-109. What is meant by a former glacier advance ? Before the last one of the LIA, but still during the LIA ? Something older ? Or you don’t know ?
A look at the orographic right side obviously gives the impression that the so-called rock glacier overrode the bottom part of the talus, without clearly deforming them. I presume this is mostly just a glacier deposit. The coarse material at its surface is resulting from the glacial deposit and the erosion of rock walls upstream of the “rock glacier” tongue, but is not derived from the talus slopes adjacent to it. The present-day movement (comparison of Swissimage 2017-2023, not provided in the paper) gives the impression to be in the continuation of the talus slopes only. If so, the glacial deposit is just a deposit currently embedded in the terminal part of a talus-connected rock glacier development.
l. 115 – Fig. 1 – a-b) Please, legend the images (draw oultlines); d) the LIA glacier extent in its terminal margins is only presumed; it could have been significantly larger. e) the thermokarst depressions which have developed over the last decades must be mapped; legend) the layout between glacial-gravitational and glacial-periglacial is not possible to be distinguished on the maps.
l. 155 – “The final output was a 6-day Line-of-Sight (LOS)” – Could it not be an issue when also using 12-18 days interferograms ?
l.160 – Multiplying by three the values of the stacked DInSAR times series to expand the “summer” observation to the entire year is to me an issue, because the downslope movement is susceptible to change over the year and the subsidence due to ice melt is probably restricted to the summer time.
l. 164 – The correction “for slope-induced effects by local inclination” presumes that the downslope component of any mass movement is following the local inclination of the surface topography, right ? This must be clearly stated.
l. 165 – “seasonal variations” - So, that's what is called later the seasonality? But I cannot figure out what it is. I tried to read several times the sentence, but it didn't help me. Please make this explanation clearer, and use here the term “seasonality”.
l. 184-186 - The limits are arbitrary. Permafrost could occur at much lower resistivities than 10 kohm.m. The "ice-poor" and "ice-rich" terminologies have to be left aside as many other factors affect the resistivity (e.g. lithology, temperature, water content) and there are so many different uses and meaning of these two terms that it is better to avoid them. Just talk about very low, low, high, very high resistivity. It would be also very good later to clearly mark these limits on the ERT plots, because just using a degraded color scale is making this delimitation impossible for the reader.
l. 191 - Please provide larger and clearer geomorphological maps of the investigated areas. Investigate the past development (e.g. thermokarst lakes at Pipji). Map/determine the flow fields.
l. 208 – Note that the massive ice core was visible when e.g. both thermokarst lakes/depressions have developed over the last decades.
l. 215 - Is Unit I actually a rock glacier ?
a) b) It could be worth of providing a detailed view on the investigated area
c) What is the orientation of the profile ?
l. 245-248 and related figures – “Resistivities of more than 1 MΩm indicate the presence of sedimentary ice within the moraine complex. This detected structure fits well with observations made in the field in late, where massive sedimentary ice could be observed in a thermo-erosional cave in the distal flank of the moraine ». No, it is not correct. The observed massive sedimentary ice outcrop is the obviously the remnant of a snow/ice field which developed outside of the moraine and was partly covered by the crumbling and northward advancing movement of its front in recent years. The permanent snow field is well observable on the Swissimages time series.
l. 266 - Please make use of Swissimage to determine the flow fields.
l. 273 – The “uplifting” area is pretty large. Could it be possible to explain it ? It looks it might be partly due to a convergent flow, with both N-S and S-N components, not depicted by the DInSAR approach.
l. 279 (and other) – I would suggest to be very careful when using the term ”movement”. In fact, it is talked about the surface movement, which is the combination of the movement of the entire mass (here a back-creeping one) and subsidence due to melting of embedded glacier ice.
l. 290 – Figure 5 – I have some issues with the E-W component, because the N-S, which is significant in some areas, is missed. So, again, it would be worth of providing the flow field as well (derived from orthoimages).
l. 302-303 – “In the upper part, close to the source area of the rock glacier, only elevation changes occurred during the investigated period” – It is difficult to see (this is small), but an eastward movement seems to occur having a look to Fig. 5. A look at Swissimage confirms that a horizontal movement in the range of 0.1 m/y is occurring there.
l. 309 – It would be better to undertake an analysis comparing the resistivity (namely the ice type) with the 2D horizontal movement, not only its E-W component, except if it has been demonstrated that the latter is well correlated to the former.
l. 316 (and other) – To avoid any misunderstanding I would avoid talking about moraine complexes only, but strongly suggest to systematically name them “thrust moraine complexes” or “push moraine complexes”.
l. 317-318 – “… suggests that the morphodynamics of moraines are more consistently influenced by internal structures and, consequently, by ice content, whereas rock glaciers exhibit greater variability”. Thrust moraines (push moraines) are often containing embedded glacier ice in their internal (facing former glacier) section. This ice is located close to surface, covered by an insufficient layer of debris to protect it from melting during the warm season. This is not a question of ice content (for sure there is a lot of ice there), but a question of internal structure of the thrust moraine, ice type and its location at depth.
l. 320-321 – “…linkages with permafrost properties for both kinds of landforms”. Probably not with permafrost properties, but with the internal distribution of ice types. Moreover, it cannot be generalized to “both kinds of landforms”, but only to those having been investigated in this study.
l. 325-326 – “Striking is the bimodal distribution of horizontal displacement in the second class for the rock glacier data points”. What is the second class ?
l. 328-329 – “…which higher resistivities (probably also higher ice contents) mean higher morphodynamics and seasonal variation. This is valid, especially for the vertical movement and the seasonality”. Agree. This is due to the occurrence of glacier ice at shallow depth. Note that on an inclined surface, the melt-out of the ice and the subsidence is also conducting to some downslope movement, which is not related to a deeper-seated creep process (permafrost creep).
l. 335 – Figure 6 – I don’t understand the unit of the seasonality (mm/6 days). I might have missed the necessary explanation.
The elevation change values are the seasonal ones multiplied by three, or the actual ones during the summer time only (which would be preferable).
l. 340 – Figure 7 – Would it not make more sense to provide a seasonality value for both the vertical change and the E-W component separately ? Because one can assume that the former is mostly related to glacier ice melt (very high resistivity) and the latter to the permafrost (rock glacier) creep. To my understanding, the seasonality is mixing both component, no ?
Discussion
l. 345 – Most of this section 5.1 is related to the methodological section (3) and should be moved there, because most of the challenges or limitations here discussed are known before the application of the methods or are linked to the conducted measurements themselves.
l. 389 – I would suggest to relate this section 5.2 more closely to the existing literature (see previous comments in the introduction section) and not only to refer to a few recent studies. In addition, it shows again the importance of disposing of the flow field data (already pointed out earlier).
l. 403 - I would avoid the use of “displacement”, which could easily be understood as downslope movement due to deep-seated permafrost creep, but surface movement (or subsidence).
l. 423-424 – “The area of uplift on the Pipji rock glacier (cf. Fig 5c) indicates compressive flow (cf. Haeberli et al., 2006) due to higher rock glacier velocities in the upper part and lower velocities in the lower units (Unit I & II)”. I don’t agree with this statement as this area of uplift is located at distance 300-400 m along the profile, what is 200 m upstream of the front of Unit III. There is just a tiny section of apparent lower E-W velocity, which, as written by the authors later, might be due to some unwrapping issues. The uplift might rather be due to the convergence of the flow field in this narrowing section of the rock glacier (again, which might be checked if this flow field is established).
l. 456-458 – “…, as so far no distinction has been made between thrust moraines and rock glaciers in many rock glacier inventories (Bertone et al., 2022; Nyenhuis, 2005; Rock glacier inventories and kinematics (RGIK), 2023).” This is a wrong statement. RGIK (2023, p. 9) specifies for the “glacier forefield-connected” category : the rock glacier develops within or from a (formerly) glaciated area. Interaction between the glacier or ice patch and the rock glacier feature is prevalent, but essentially restricted to phases of glacier advance (e.g., Little Ice Age). Embedded glacier ice within the rock glacier is possible. When receding, which is a common pattern today, the glacier has disconnected from the rock glacier or may have disappeared entirely. This category includes till-derived rock glaciers, which correspond to the classical debris rock glacier definition and to some push-moraines (glacitectonized frozen sediments)”. It means that push-moraines (thrust moraines) are included in rock glacier inventories if they express the morphological criteria of a rock glacier, or in other words, if they are back-creeping or creeping outward of the glacier forefield and develop a distinct front. If they are only subsiding, they are disregarded. It shows the importance of treating the morphodynamics caused by creep and subsidence separately.
l. 459-464 – “As morphodynamical parameters such as rock glacier velocity are derived as essential climate variable (ECV) based on such inventories (Hu et al.,2025; Streletskiy et al., 2021; World Meteorological Organization (WMO), 2022), a lack of distinction between the different landforms may lead to a distortion of the parameters and thus of the assessment of morphodynamic changes in the context of climate change.”
The community having written the “Baseline concepts for Rock Glacier Velocity as an associated parameter of ECV Permafrost”, available from the RGIK website (www.rgik.org), is fully aware about this issue. On p. 9, one can read that: “Rock glacier velocity time series must refer to a consistent flow field representing the downslope movement of a rock glacier unit or a part of it. Considered surface displacements should represent the downslope movement of the rock glacier related to permafrost creep and should not be significantly altered by local disturbing processes (e.g. movement of isolated boulders, ice melt induced subsidence). Areas affected by such local processes should be avoided for the measurement/computation of the time series”. On p. 11 (see also Hu et al. 2025), RGV is defined as “time series of annualized surface velocity (…) of single or a part of rock glacier unit (…) and refers to observed surface velocities related to permafrost creep.” It also means that surface movement related to subsidence must be excluded.
I could suggest the authors to alter their statement in support of the RGIK guidelines.
l. 484-485 : “…distinguishing between thrust moraines and rock glaciers is essential due to their distinct internal structures and morphodynamic processes”. Just note that the present study has only been undertaken on two thrust moraines and two rock glaciers and that the findings cannot be extended to all thrust moraines and rock glaciers.
l. 487-489 : “Since many rock glacier inventories do not yet differentiate between these landforms, this omission may lead to inaccuracies in assessing morphodynamic changes, particularly when rock glacier velocity is used as an essential climate variable”. See my comments above.