the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 29 Aug 2025
Multi-annual and seasonal patterns of Murtèl rock glacier borehole deformation, environmental controls and implications for kinematic monitoring
Abstract. Information about rock glacier deformation with depth is crucial for understanding the kinematic processes responsible for variations in rock glacier velocity. The majority of studies on rock glacier kinematics have been limited to surface measurements. Here we present the unique, almost eight-year long record from Murtèl rock glacier of borehole deformation at high temporal resolution. The extracted velocity time series with depth shows that seasonal variations are only observed in the active layer (AL), while in the main ice-rich core and the shear zone deformation rates remain relatively stable. At interannual timescales the variability in movement reaches beyond the AL and into the ice-rich core. The AL, ice-rich core and shear zone make up 20 %, 24 % and 56 % of surface displacement respectively. Compared to previous borehole inclinometer data, we find an unusually high fraction of deformation in the AL at Murtèl for the observation period. There are multiple rock glacier studies which report that water input dominates over temperature as a control for the seasonal variations in velocity. In contrast, at Murtèl we find that the years with the highest seasonal peaks in velocity are the years with the warmest summers; while the years with the highest meltwater input have a lower seasonal acceleration in deformation. The borehole deformation and temperature data suggest that the seasonal cycle in AL deformation is strongly related to thermal processes, rather than controlled by water input. Beyond this, three independent approaches for measuring surface displacement were applied and show that the borehole inclinometer and geodetic measurements agree well over a period of almost eight years. The continuous GNSS surface observations slightly overestimate the seasonal acceleration, but match the general background displacement well. Rock glacier velocity has recently been included in the essential climate variable (ECV) of "permafrost". Our borehole deformation data provide novel insight on how representative surface velocities are for rock glacier deformation at depth and on various timescales.
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Status: final response (author comments only)
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RC1: 'Comment on egusphere-2025-3029', Robert Kenner, 23 Sep 2025
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AC1: 'Reply on RC1', Giulio Saibene, 10 Nov 2025
First, we would like to thank the reviewer for their time invested in this discussion. The relevant comments of the reviewer for the following response will be grouped based on the topic and written in italics while the response below will be in normal text.
"One of the most important issues is the need for a more careful treatment of the SAA dataset. A general assessment of the challenges and limitations of this measurement system, along with an accuracy analysis, is sorely lacking. Inconsistencies in some of the given values are evident.”
“135: It is essential to add a paragraph about the accuracy of the Inclinometer somewhere to proof the significance of the results.”
“178/179: This is weird. A deformation can’t become negative. A directional displacement can but it won’t happen in this case. What you describe here is a measurement artefact which calls for an accuracy analysis even before presenting any results”
“4.3: It is important that you finally say at least something about challenges of the measurement system. The section is however rather confusing with a lot of speculation. Since this dataset is the core of your paper, this section must be transformed into an extensive analysis of the measurement system, including its accuracy and limitations. Therefore, a literature review is necessary and this section must be placed before the result section and not in the discussion. All results must be reconsidered under the light of this evaluation of the measurement system.”
We agree that a more detailed evaluation of the SAA borehole data should be carried out. However, the assessment of the accuracy of the SAA borehole data analysis is challenging as there is no direct validation data, but all information we have available will be given. We will make sure to include the instrument uncertainty as reported by the manufacturer in the methods chapter and consider it in our interpretation. Given the small magnitudes of the daily velocities, we will resample them for both the SAA and GNSS data to monthly velocities, such that the time span and hence the instrument uncertainty is well below the signal magnitudes and thereby improving the significance of the results. Preliminary analysis shows that the same seasonal patterns can still be observed at a monthly resolution. We will emphasize that the mandatory use of the proprietary software Measurand SAASuite limits our evaluation of the SAA data precision given that we do not have access to its processing steps. We will elaborate on the limitations of the SAA deformation data regarding the processing, the precision and the potential movement of the chain within the filling material causing artefacts such as the negative peak in the borehole velocity in 2021. The 2021 and 2022 unique borehole SAA data events we believe belong to the discussion where we explore them in light of the limitations of the measuring system. Interestingly, the old inclinometer data from the 1987 borehole (based on a different method) shows generally similar deformation patterns with depth (including enhanced deformation in the active layer, also for other sites - see Arenson et al. 2002). This helps to back up the credibility of the SAA dataset. We will integrate this more explicitly in the discussion by suggesting future opportunities to better evaluate the accuracy of the borehole SAA data.
“Later you are talking about “daily deformation rate”, what I assume is the deformation velocity of a certain layer on a daily basis? Again, an accuracy analysis is absolutely essential here. If you later calculate the daily deformation velocity changes in the AL, which deforms 26 millimeter per year, this makes on average 70 micrometer displacement per day and of these 70 micrometers per day you calculate seasonal deviations!? I do not believe that your system is that accurate. In contrast, referring to the findings of Buchli et al. we are far of an accuracy that would allow such interpretations: https://doi.org/10.2136/vzj2015.09.0132”
“Line 180: With 0.25 mm/day deformation velocity you end up with 9.1 cm deformation per year, which deviates strongly from the 5.9 cm given as annual deformation rate. This shows again that an accuracy analysis is very important to distinguish a measurement signal from noise and systematic errors.”
The 2.6 cm in the AL or the 5.9 cm in the shear zone, mentioned in the comment here, are not an average annual velocity of how much the layer moves but a velocity differential across the layer. These values represent the difference in velocity from the top to the bottom of the layer and are not normalized by its thickness. The definition will be made more clear in the methods and a different term than deformation rate or velocity will be used, such as “layer-specific velocity differential”. So, you can’t convert this velocity differential from yearly to daily resolution to compare it with the daily or monthly velocity values as they are different variables. The seasonal deviations we observe have amplitudes in the range of a few centimeters per month after the daily velocity is resampled to monthly, and our system is accurate enough to measure such signals.
The accuracy discussed in the Buchli et al. (2016) paper is regarding the large differences between the results using different SAASuite software versions to process the raw SAA data. In the case of our measuring system, it will be emphasized that over the long term we can confirm that at the surface the SAA measurements align well with the data from the geodetic survey point. This suggests that at least there are no large systematic errors in the SAA data produced using the given version of the SAASuite software used.
“Comparing an inclinometer with a GNSS sensor/Total station sounds a bit odd. Perhaps comparing the surface displacements measured by system xyz.”
“4.4: This is all very descriptive and speculative. Why do you suggest correcting the rotational component in future studies but don’t do it yourself? You could then easily say if tilting is the main reason for the observed differences between GNSS and SAA displacements!”
“Good that you have summed up the daily GNSS displacements. I have not checked in Cicoira how GNSS was processed but I am sure velocities are somehow calculated over a longer basis than daily. Otherwise the difference between the sum of daily displacements and total displacement would have been more than 11cm. It is impossible to calculate significant daily velocities using GNSS. GNSS can’t measure submillimeters, your device not even subcentimeters. However, the same applies to SAA!”
“At least we know that GNSS can measure the total displacement over the entire monitoring period accurate to a (few) centimeter. So 101 cm (102 cm in figure 8, what is correct??) total displacement is the benchmark!”
“89 cm for the total station (~13cm error) reflect the sum of annual errors. You have to recalculate the total displacement from the raw coordinates instead of summing up the annual observations. This gives a horrible error propagation. The fact that GNSS and the surveyed total station prism were mounted on the same boulder, strongly indicates that the 13 cm are indeed a measurement error.”
It will be made more clear that it’s only the surface displacement measured by the three systems that will be compared. Moreover, the comparison between the three different methods to derive surface movements will be adjusted to distinguish better between total displacement and the integrated displacement from the monthly velocity data. The daily data will not be integrated anymore to report a displacement value. The total displacement values for the GNSS and geodetic data will be calculated directly from the difference between the raw initial and final coordinates and these are taken to be the “true” values for the given measuring system. So, in Figure 8 it would be the 101 cm total displacement to be the correct value for the GNSS system. As suggested, we will calculate the additional displacement from the tilting of the GNSS mast and deduct it from the total displacement measured. The calculation will be limited to simple trigonometry accounting for the tilt and azimuth angles measured by the GNSS inclinometer.
“Line 206: The discussion about the displacements in the active layer is rather poor. The fact that so much displacement occurs in such flat terrain in such a shallow depth (most likely no high pore pressures) is very remarkable and calls for an explanation. A possible explanation was given in the study of your colleague Marcel Frehner et al., which convincingly explains the formation of ridges and furrows in the active layer on top of the ice core, due to a compressional flow regime. The formation of such a structure is of course a major reason for deformation in the active layer.”
“322: Melting and not only warming the ice at the bottom of the AL. At one point, the refrozen water (independent if it originates from the snowmelt or from the previous summer) must melt again, if the AL depth stays constant. And as you wrote before, frozen debris with low ice contents deforms slower than ground with high ice contents. Here however, you measure higher strain rates in the ice poor AL than in the ice rich core. The acceleration is thus likely to be triggered by melting of ice in the AL. This melting strongly weakens the shear resistance of the water saturated fine materials at the base of the AL and this is the explanation for the increasing strain rates. The argumentation in this paragraph is very lengthy but does not get to the point. You can shorten this clearly. Be more precise and only show correlations which are relevant.”
The processes inferred from the data presented will be analysed more precisely and concisely. The explanation behind the enhanced active layer deformation will refrain from mentioning links to temperature-sensitive ice creep, but rather structural adjustments (consolidation) after the seasonal thaw and the role of melting refrozen ice at the bottom of the active layer. We agree that the higher strain rates measured in the active layer during the summer are in large part caused by the meltwater lowering the shear resistance. We are convinced that the buckling of the active layer as described by Frehner et al. (2015) is not responsible for the seasonal fluctuations in AL deformation observed given the timescale considered and the fact that the model output illustrated in Fig. 7 in his paper does not show this extra movement in the active layer as observed in the measured borehole deformation profile. We will ensure that only relevant statistical correlations are described to make this paragraph more concise.
“Line 107: There is also data from Ritigraben, where we did a similar analysis here: doi: 10.1002/ppp.1953”
The borehole inclinometer data from the Ritigraben rock glacier will be included in Table 2.
“On top of it all, this broader discussion of the driving processes could lead to a final, overarching interpretation of your results from the Murtèl site, which I would personally find very interesting. Murtèl is a very famous permafrost study site. How representative is it for rock glaciers in general? [...] Should we compare it to other rock glaciers, or is it even justified to compare its dynamics to those of cold glaciers? Have you looked at this?”
“Line 118/119: If you have such a good dataset, why don’t you calculate a (winter) surface energy balance instead of working with such statistical approximations?”
It will be made more clear that the apparent lack of hydrological controls on deformation can be expected for a cold rock glacier like Murtèl where water is less likely to make it to large depths around the shear zone. We will reiterate that the hydrological processes inferred are limited to the snow height and precipitation data available. A surface energy balance calculation is out of scope for this study because it would be a study in itself and we argue that the statistical descriptions of surface snow and temperature are sufficient to extract meaningful relationships for our purpose. The representativeness of driving processes described here for Murtèl rock glacier to other sites will be further discussed in light of its especially ice-rich and cold permafrost core.
“171: What are daily deformation data? Be precise with “rate”, “deformation”, “velocity”, “strain”… throughout the text. I think you are talking about total deformation per layer here, right? So, it would be best if you define a term such as deformation velocity at the beginning and use it consequently afterwards.”
“Line 177: it will increase the readability and clarity a lot if you stick to a predefined term such as deformation velocity instead of daily deformation rate or other paraphrases”
“Line 214: Vertical strain rate? If I understood right, you measure horizontal strain in a vertical borehole.”
We will limit to using the term “velocity” when referring to the change of horizontal displacement with time either at the surface or at a specific depth. The layer-specific values are differences in velocity from the top to the bottom of the given layer, so these will be referred to as layer-specific velocity differential. The term “vertical strain rate” will be replaced by “shear strain rate” to better convey that it is a measure of how horizontal velocity changes with depth.
“Line 233/234: If you bring that into connection here, you should not only cite Glens law but apply it to show, if the implied connection is indeed reasonable. 3.2 mm Y^(-2) is a deformation increase by 10% per year in the ice core. Can this be caused by 0.03°C/y warming?”
As suggested, we applied the Glen’s ice flow law to the case presented in the discussion where an average ice core warming rate of 0.03˚C/year is linked to the 3.2 mm^2/year acceleration (or 10% annual increase in displacement) in ice core deformation. Using a 10% higher displacement (assuming it’s proportional to stress) we calculate an hypothetical required temperature increase of 0.4˚C, assuming other variables remain constant. This then leads to a discussion as to how temperature effects can not alone explain temporal variation in velocity in the ice core of Murtèl rock glacier, and this will be included in the paper.
“271/272: This is more results and misses interpretation. This might be because the ice core is a heat sink and damps the temperature signal in both directions due to its high heat capacity, while the AL is much closer coupled to atmosphere”
We will shorten the description of the correlation analysis results and focus more on explaining the connections between snow and permafrost temperatures throughout a year for the cold phase controls. We will clarify that the long wavelength of the temperature cycle in the ice core is due to its high heat capacity and this plays an important role in linking the snow conditions to the summer ice core temperature.
All the other comments not directly addressed here will be taken into account and appropriate changes made in the revised version.
Citation: https://doi.org/10.5194/egusphere-2025-3029-AC1
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AC1: 'Reply on RC1', Giulio Saibene, 10 Nov 2025
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RC2: 'Comment on egusphere-2025-3029', Lukas U. Arenson, 06 Oct 2025
The review of the manuscript took longer than anticipated. First, I'd like to congratulate the authors for very interesting data that they managed to collect and that offer insight into rock glacier dynamics. Overall, I enjoyed reading the paper, and while the paper presents useful information, some fundamental revisions and additions could further improve the manuscript. Comments regarding these suggestions are included in the annotated version.
I would have like to see a critical discussion on the ECV Rock Glacier Velocity in the light of your findings. I do believe that this ECV is very important, but your data highlight that things are often very complex, and rock glaciers can be different. What we measure at the surface originates from different processes. And in some instances, it is simply the response of the active layer dynamics and the deformations within the rock glacier remain constant, unaffected from interannual variability. Others react immediately to runoff, because water can likely infiltrate to the shear horizon, something that doesn’t happen at Murtel rock glacier. Hence, this example shows us that we have to be very careful when relying on surface deformations only as they may not provide the full picture and they must be evaluated in combination with the rock glacier characteristics and morphology. Your work offers a unique opportunity to add these points, and I think that this would add value to your manuscript beyond simply presenting data.
In terms of editing, the paper is generally well written. However, I do encourage you to complete a detailed review, correcting some of the minor spelling mistakes as well as adjusting some of the wording, such as using “however” too often, staring sentences with “for …” or using long sentences with repetitions.
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AC2: 'Reply on RC2', Giulio Saibene, 10 Nov 2025
First, we would like to thank the reviewers for their time invested in this discussion. The relevant comment/s of the reviewer for the following response will be grouped based on the topic and written in italics while the response below will be in normal text.
“I would have like to see a critical discussion on the ECV Rock Glacier Velocity in the light of your findings. I do believe that this ECV is very important, but your data highlight that things are often very complex, and rock glaciers can be different. What we measure at the surface originates from different processes. And in some instances, it is simply the response of the active layer dynamics and the deformations within the rock glacier remain constant, unaffected from interannual variability. Others react immediately to runoff, because water can likely infiltrate to the shear horizon, something that doesn’t happen at Murtel rock glacier. Hence, this example shows us that we have to be very careful when relying on surface deformations only as they may not provide the full picture and they must be evaluated in combination with the rock glacier characteristics and morphology. Your work offers a unique opportunity to add these points, and I think that this would add value to your manuscript beyond simply presenting data.”
We will expand on the possible implications of our findings to the concept of RGV as an ECV parameter in the discussion. The focus will be that we should be careful in the interpretation of rock glacier velocities, when only surface displacement data is available. Our findings suggest that depending on the internal structure and thermal regime of a rock glacier a year with high surface displacement may only represent high movement within the active layer and not necessarily at the shear zone. We will emphasize that Murtèl is a relatively cold rock glacier and it can be expected that its movement is less reactive to changes in meltwater and precipitation inputs as its ice core permeability is lower. Comparable studies from other rock glaciers would be useful to further assess these observations.“Yes, but as the transition layer is thawing, additional deformation can occur at depth, which then result in rocks within the active layer also being able to move and slowly consolidate under their own weight. It isn't a simple static system.”
We agree that it should be mentioned that the active layer, even though being mostly ice-free, can still deform due to readjustments of the debris under its own weight after the seasonal thaw. We will claim that this, in combination with the role of the melting refrozen ice, drives the AL seasonal cycle in deformation.
“Sometimes you just use "Murtel" without rock glacier. For consistency it would be better to always use it as you have it here.”
“Please reduce the number of "howevers" used in this paragraph.”
“Slope inclinometers and SAAs are different and it is suggested to differentiate between the different deformation measurement types.”
The grammatical and syntax comments will be addressed in order to make the writing clearer, for example by making sure ‘Murtèl rock glacier’ is always written in full instead of only referring to ‘Murtèl’. The distinction between the terms “inclinometer” and “SAA” will be made more consistent by carefully selecting which term is used depending on the data that is referred to.
Citation: https://doi.org/10.5194/egusphere-2025-3029-AC2
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AC2: 'Reply on RC2', Giulio Saibene, 10 Nov 2025
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Thank you for sharing these interesting insights into the kinematics of the Murtèl rock glacier. The variety of processes involved in permafrost creep is impressively demonstrated, and I am sure that this dataset will be a valuable contribution to our understanding of periglacial displacement processes. However, significant improvements are necessary before the work can be published.
You will find many detailed remarks below, many of which can be resolved through more precise and concise writing. However, there are also several issues that require substantial additional work. One of the most important issues is the need for a more careful treatment of the SAA dataset. A general assessment of the challenges and limitations of this measurement system, along with an accuracy analysis, is sorely lacking. Inconsistencies in some of the given values are evident. Several statements in the manuscript appear to be insignificant. Also, the total station data should be reprocessed when analysing the total displacement.
Numerous hypotheses were formulated that could easily be tested, but the study did not do so. This is a pity, as additional work would clearly strengthen your results. (See detailed comments for examples, such as Glens Law, GNSS toppling energy balance...)
Room for improvement is also evident in the discussion of possible processes that cause the observed displacement pattern. As the authors state, many observations are unusual and call for a better physical explanation. Why is there so much deformation in the AL? What is the physical reason? Why is the basal creep component so small? Why does hydrology play a minor role here? You will find some inputs to these questions in the detailed remarks.
On top of it all, this broader discussion of the driving processes could lead to a final, overarching interpretation of your results from the Murtèl site, which I would personally find very interesting. Murtèl is a very famous permafrost study site. How representative is it for rock glaciers in general? Given its massive pure ice core, it is possible that Murtèl is glacier-derived. Perhaps it formed as a result of a single rockfall event onto glacier ice? Does it represent a distinct type of rock glacier? Or is it simply one extreme of a continuum? Should we compare it to other rock glaciers, or is it even justified to compare its dynamics to those of cold glaciers? Have you looked at this?
All the best
Robert Kenner
Detailed comments.
Line 8-13: I see that surface water input does not play a major role for Murtèl, but here in the Abstract I would phrase it differently and would rather refrain from presenting these factors as generally competing. Both are in general highly interdependent. The mentioned studies about water input mainly refer to pore water pressures in the basal shear/creep layer. Here, high pore water pressures are not necessarily related to high surface water input but are also a function of permeability which might be related to temperature in turn. Moreover, high surface water input is often related to a thick winter snow cover and a thick snow cover also reduces winter cooling. It is thus difficult to distinguish these factors on a statistical basis. As an alternative, you would have to talk about the processes, i.e. temperature driven plastic deformation of ice and pore water pressure in a basal creep layer.
Please also clarify what you mean with “temperature” and “warmest summers”. MSAT? MSGT? I guess ground temperature in a depth corresponding to the analyzed deformation process would be appropriate as a reference. If you refer to air temperatures instead, you must explain the physical connection.
Line 63: Temperatures could be important
Line 63: The lack of high temporal resolution.
Line 63: Agreed with reservations. Of course it is important to have more continuous deformation timeseries. However, the existing sporadic measurements already give some indications. They show variability in the basal shear/creep layer in between the measurements and – except the Murtèl case – a constant parabolic deformation above, pointing towards plastic deformation. If you argue with the temperature dependent deformation of ice, the seasonal accelerations at the surface are often much too strong and have the wrong timing to be explained by a power law. See also my comment on line 107.
Line 66/67: “The third aim is to compare the three measurement systems available at Murtèl to monitor surface kinematics: borehole inclinometer, GNSS and geodetic survey using a total station.”
Comparing an inclinometer with a GNSS sensor/Total station sounds a bit odd. Perhaps comparing the surface displacements measured by system xyz.
Line 107: There is also data from Ritigraben, where we did a similar analysis here: doi: 10.1002/ppp.1953
Line 116: ()
Line 118/119: If you have such a good dataset, why don’t you calculate a (winter) surface energy balance instead of working with such statistical approximations?
128/129: Also here exist perhaps better and more reliable methods to calculate precipitation deficits/surplus on different time scales than such a threshold.
135: It is essential to add a paragraph about the accuracy of the Inclinometer somewhere to proof the significance of the results.
144: “This AL-specific deformation increases with time” What does this mean? The displacements increase (what is trivial) or the displacement velocity increases (If yes how strong?)
Line 146/147: That is why it is so important to add a section about the accuracy and diverse challenges and uncertainties when measuring with an inclinometer.
Line 159: “of” instead of “at “
Line 164ff: I daut that this is significant. Do an accuracy analysis.
171: What are daily deformation data? Be precise with “rate”, “deformation”, “velocity”, “strain”… throughout the text. I think you are talking about total deformation per layer here, right? So, it would be best if you define a term such as deformation velocity at the beginning and use it consequently afterwards.
Later you are talking about “daily deformation rate”, what I assume is the deformation velocity of a certain layer on a daily basis? Again, an accuracy analysis is absolutely essential here. If you later calculate the daily deformation velocity changes in the AL, which deforms 26 millimeter per year, this makes on average 70 micrometer displacement per day and of these 70 micrometers per day you calculate seasonal deviations!? I do not believe that your system is that accurate. In contrast, referring to the findings of Buchli et al. we are far of an accuracy that would allow such interpretations: https://doi.org/10.2136/vzj2015.09.0132
Line 175: rewrite to: During the seasonal peaks, the deformation velocity at the surface is about four times higher than in the shear zone.
Line 176: peaks in deformation velocity
Line 177: it will increase the readability and clarity a lot if you stick to a predefined term such as deformation velocity instead of daily deformation rate or other paraphrases
178/179: This is weird. A deformation can’t become negative. A directional displacement can but it won’t happen in this case. What you describe here is a measurement artefact which calls for an accuracy analysis even before presenting any results
Line 180: With 0.25 mm/day deformation velocity you end up with 9.1 cm deformation per year, which deviates strongly from the 5.9 cm given as annual deformation rate. This shows again that an accuracy analysis is very important to distinguish a measurement signal from noise and systematic errors.
Line 180:/181 missplaced and out of context. This is a figure caption.
Line 182: overestimated by which system? What is your reference? And how can you say that one system is more precise than the other?
Line 190 ff: Have you defined warm and cold phases somewhere?
Line 198/199: unclear
Line 206: The discussion about the displacements in the active layer is rather poor. The fact that so much displacement occurs in such flat terrain in such a shallow depth (most likely no high pore pressures) is very remarkable and calls for an explanation. A possible explanation was given in the study of your colleague Marcel Frehner et al., which convincingly explains the formation of ridges and furrows in the active layer on top of the ice core, due to a compressional flow regime. The formation of such a structure is of course a major reason for deformation in the active layer.
Line 214: Vertical strain rate? If I understood right, you measure horizontal strain in a vertical borehole.
Line 233/234: If you bring that into connection here, you should not only cite Glens law but apply it to show, if the implied connection is indeed reasonable. 3.2 mm Y^(-2) is a deformation increase by 10% per year in the ice core. Can this be caused by 0.03°C/y warming?
Table 2: If you like you can also include Ritigraben. See previous comment.
Line 254: Anisotropy is not the right term for what you describe here.
255/266: Unclear, language, reasoning?
258/259: “The shallower shear zones are more likely to be above the depth of zero annual amplitude, and hence experience […] more deformation.” Logic?
271/272: This is more results and misses interpretation. This might be because the ice core is a heat sink and damps the temperature signal in both directions due to its high heat capacity, while the AL is much closer coupled to atmosphere
273ff: As mentioned before, an energy balance would show the effect of snow cover much better than the 70 cm threshold.
277: mild is not a precise adjective here.
293: mild?
322: Melting and not only warming the ice at the bottom of the AL. At one point, the refrozen water (independent if it originates from the snowmelt or from the previous summer) must melt again, if the AL depth stays constant. And as you wrote before, frozen debris with low ice contents deforms slower than ground with high ice contents. Here however, you measure higher strain rates in the ice poor AL than in the ice rich core. The acceleration is thus likely to be triggered by melting of ice in the AL. This melting strongly weakens the shear resistance of the water saturated fine materials at the base of the AL and this is the explanation for the increasing strain rates. The argumentation in this paragraph is very lengthy but does not get to the point. You can shorten this clearly. Be more precise and only show correlations which are relevant.
325: delete these cross-references throughout the paper
336: Another cliff hanger cross-ref. This is obsolete with an accuracy analysis at the beginning.
4.3: It is important that you finally say at least something about challenges of the measurement system. The section is however rather confusing with a lot of speculation. Since this dataset is the core of your paper, this section must be transformed into an extensive analysis of the measurement system, including its accuracy and limitations. Therefore, a literature review is necessary and this section must be placed before the result section and not in the discussion. All results must be reconsidered under the light of this evaluation of the measurement system.
4.4: This is all very descriptive and speculative. Why do you suggest correcting the rotational component in future studies but don’t do it yourself? You could then easily say if tilting is the main reason for the observed differences between GNSS and SAA displacements!
Good that you have summed up the daily GNSS displacements. I have not checked in Cicoira how GNSS was processed but I am sure velocities are somehow calculated over a longer basis than daily. Otherwise the difference between the sum of daily displacements and total displacement would have been more than 11cm. It is impossible to calculate significant daily velocities using GNSS. GNSS can’t measure submillimeters, your device not even subcentimeters. However, the same applies to SAA!
At least we know that GNSS can measure the total displacement over the entire monitoring period accurate to a (few) centimeter. So 101 cm (102 cm in figure 8, what is correct??) total displacement is the benchmark!
89 cm for the total station (~13cm error) reflect the sum of annual errors. You have to recalculate the total displacement from the raw coordinates instead of summing up the annual observations. This gives a horrible error propagation. The fact that GNSS and the surveyed total station prism were mounted on the same boulder, strongly indicates that the 13 cm are indeed a measurement error.
The 87 cm for the SSA (~15cm error) total displacement perhaps reflect the accuracy of the SAA if rotation of the GNSS wasn’t particularly strong and gives an alternative explanation for the difference.
Line 381: Noise filtering should decrease velocity peaks (smoothing) but you are claiming the opposite here!?
Conclusions
Must be rewritten after revision. Total station & SAA match well but are probably similar inaccurate.