the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 20 Feb 2025
The influence of a rock glacier on the riverbed hydrological system
Abstract. Climate change is accelerating cryosphere degradation in mountainous regions, altering hydrological and geomorphological dynamics in deglaciating catchments. Among cryospheric features, rock glaciers degrade more slowly than glaciers, providing a sustained influence on water resources in alpine watersheds. This study investigates the role of a rock glacier interacting with the Shár Shaw Tagà River (Grizzly Creek) riverbed in the St. Elias Mountains (Yukon, Canada), using a unique multimethod approach that integrates hydro-physicochemical and isotopic characterization, drone-based thermal infrared (TIR) imagery, and visible time-lapse (TL) imagery. Results assess that rock glaciers, due to their geomorphic properties, can constrict riverbeds and alluvial aquifers, and control shallow groundwater flow, leading to notable changes in channel structure and groundwater discharge. These disruptions promote downstream cryo-hydrological processes by facilitating aufeis formation and modifying the physicochemical properties of streamflow. Additional findings highlight the critical role of rock glaciers and proglacial systems in connecting mountain cryosphere and deep groundwater systems, with consequent implications for mountain hydrology and water resources.
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RC1: 'Comment on egusphere-2025-117', Anonymous Referee #1, 07 Apr 2025
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AC1: 'Reply on RC1', Bastien Charonnat, 09 May 2025
We thank Referees 1 and 2 for their valuable comments, which will significantly contribute to improving the quality of our paper. Below, we respond individually to each of the referee’s comments:
COMMENT 1:
“Introduction: At the end of this chapter I suggest to:
- Define more clearly the general objective / research question of this study;
- Describe the three main part of this work, and for each define the sub-objectives/research questions and hypothesis. In Chapter 3, I would leave only the descriptions of the methods used in each of the three parts of the study to answer the respective sub-objectives.”
REPLY 1:
We agree with Referee 1 that the general objective and research question could be more clearly stated in the Introduction.
We also agree that the three-part multi-method approach would benefit from clearer presentation at the end of the Introduction, including the sub-objectives. These elements are currently outlined in Section 3.1 ("Method overview") but could be moved in the introduction and better structured for improved clarity.
We therefore suggest deleting Section 3.1 and propose to revise the final paragraph of the Introduction (LL 77-83) as follows:“This study examines the influence of rock glaciers on surface and shallow groundwater flow within alpine riverbed hydrological systems. Specifically, it focuses on characterizing water fluxes in a section of the Shár Shaw Tagà catchment (St. Elias Mountains, Yukon, Canada) that is constrained by a rock glacier. We hypothesize that the rock glacier modulates interactions between surface water and shallow groundwater, thereby affecting the overall functioning of the riverbed system.
To investigate these interactions, we employed a multimethod approach that was progressively refined as our observations and understanding of the system evolved:
- We hypothesized that the rock glacier influences the formation of aufeis on the downstream outwash plain. To test this, we used time-lapse camera monitoring to track the development of aufeis and to identify the location and timing of winter outflows.
- Given the rock glacier’s position at the outlet of a subcatchment and the lack of significant surface outflow, we hypothesized that it drains the subcatchment and contributes to river discharge via groundwater exfiltration. To assess this, we conducted a spring inventory, followed by a physico-hydrochemical characterization of springs and streams across the subcatchment. This allowed us to trace water sources and evaluate the rock glacier’s influence on stream composition.
- Building on the previous findings, we hypothesized that a specific section of the riverbed serves as a major zone of groundwater exfiltration. To identify and map these zones, we conducted drone-based thermal infrared (TIR) surveys, enabling us to delineate areas of groundwater emergence and assess their spatial extent and relative magnitude.
The novelty of this research lies in its focus on the indirect hydrological impacts of a rock glacier—particularly in the absence of a visible, well-defined outflow. By integrating hydrological, hydrogeological, and geochemical methods, this study advances our understanding of the complex role rock glaciers play in alpine watershed dynamics and provides insights with broader applicability to similar environments worldwide.”
COMMENT 2:
“Please add information concerning the mean annual air temperature in order to better understand the climate conditions of the study area (only annual precipitation is described).”
REPLY 2:
We appreciate this suggestion. We added the mean annual air temperature alongside the annual precipitation information in the description of the study area as:
“The eastern flank of the St. Elias Mountains experiences a dry subarctic climate, characterized by annual precipitation ranging from 300 to 500 mm yr-1 and a mean annual temperature between –8 °C and –12 °C (Wahl et al., 1987).
COMMENT 3:
“Methods: It would be great to add the coordinates and the altitude for each sampling site in Table S1”
REPLY 3:
We agree with Referee 1 that it would be helpful to add the coordinates and altitude for each sampling site in Table S1. We modified the table to include them.
COMMENT 4:
“Methods/Results: I have some questions regarding the TIR survey:
- Did you calibrate the thermal camera of the drone before the surveys? Did you check the temperature accuracy of the drone sensor? We are also testing the same drone at our institute, and we observed that the error in the temperature measured by the thermal camera increases as the air temperature decreases.
- I am a bit skeptical about using the TIR video approach, since the video does not provide a color scale and therefore the water temperature cannot be determined. As described in text (LL. 240-243), water temperature, however, is key criteria for identifying cold groundwater exfiltration. How did you define “a clear contrast between the dominant stream surface temperature and the suspected exfiltration area” based only on the colors given by the thermal imaging camera (but without knowing the actual water temperatures)? How many degrees Celsius should this clear thermal contrast correspond to?
- When processing thermal images, it is also important to set some parameters (such as flight height, air humidity, thermal emissivity of analyzed surface) to accurately define the temperature. Did you consider these factors when you analyzed the TIR video surveys? Have you noticed any differences in the measured temperature by changing the flight height of the drone?”
REPLY 4:
- Referee 1 raises important points. Absolute temperature inaccuracies with this drone model have been reported in other studies. However, in our case, the TIR survey aimed only to detect relative differences in surface water temperature, not to measure absolute values. We therefore followed the method described in several studies (Antonelli et al., 2017; Briggs et al., 2016 and Iwasaki et al., 2023). Interestingly, Kenta Iwasaki published a new article in 2024 underlining the advantages of using temperature contrasts in TIR videos as a fast yet efficient way to detect groundwater contribution to surface water (Iwasaki et al. 2024). In the present case, we can confirm that the detection of major thermal contrasts (from 2 to 6 °C) was successful without the need for calibration or correction.
- We fully agree that the absence of a color scale in the TIR video prevents direct use of absolute temperatures. Consequently, identification of groundwater exfiltration zones was based on visible thermal contrasts. These zones consistently appeared as distinctly colder areas (blue) compared to the warmer stream (green) and sun-heated boulders (red), as shown in Figure 10. The distinctiveness of the observed contrasts, validated by previous field temperature measurements (spring-to-stream temperature differences typically between >2 °C and <6 °C; see Table S2), supports the reliability of this approach. Plumes visible in TIR imagery, due to contrasts in water temperature, have been shown to effectively indicate groundwater exfiltration (Antonelli et al., 2017; Briggs et al., 2016; Iwasaki et al., 2023; Iwasaki et al., 2024). Groundwater exfiltration zones were mapped only when a clear and strong visible contrast was observed; in the absence of a distinct contrast, no feature was mapped.
- We acknowledge the importance of adjusting parameters like flight height, air humidity, and surface emissivity when precise temperature measurements are needed. However, since our objective was solely to detect visible temperature contrasts, such corrections were not applied. In the case of drone-based TIR, images taken from near nadir reduce inaccuracies linked to surface emissivity and reflected temperature (Torgersen et al., 2001; Dugdale et al., 2016), with uncorrected temperatures up to 0.5 °C colder than real temperatures (Zappa and Jessup, 1998). In our case, we aim to detect contrasts superior to 2 °C, the observed contrasts were sufficiently pronounced to achieve the study’s objectives and were cross-validated through field observations.
- We propose to integrate in the manuscript the clarification provided above by rewriting Section 3.4 as:
“Aerial and handheld thermal infrared (TIR) devices have been demonstrated as effective tools for mapping groundwater discharge into streams (Toran, 2019). Specifically, drone-based TIR technology allows for high spatial resolution observations of surface water–groundwater interactions (Vélez-Nicolás et al., 2021). Two common approaches for TIR surveys were considered: 1) generating stream temperature maps using high-definition TIR image orthomosaics from overlapping images (e.g., Abolt et al., 2018; Casas-Mulet et al., 2020; Rautio et al., 2015), and 2) using TIR videos or real-time scans (handheld or drone-based) to visualize mixing plumes and record GPS coordinates of observed points (e.g., Barclay et al., 2022; Briggs et al., 2016; Iwasaki et al., 2023).
While georeferenced thermal maps provide mesoscale coverage, they require stable flying conditions, ground control points, and extensive post-processing (Webb et al., 2008). In contrast, TIR video or live scans allow for real-time visualization of mixing dynamics in smaller-scale areas (Antonelli et al., 2017). Given our goal to identify and characterize groundwater exfiltration zones, we chose the TIR video approach. This method does not require precise absolute temperature but relies instead on relative contrasts between stream water and suspected groundwater inflows. Prior studies (Antonelli et al., 2017; Briggs et al., 2016; Iwasaki et al., 2023; Iwasaki et al., 2024) have shown that TIR video, even without embedded temperature scales, effectively highlights such contrasts.
Drone-based TIR video surveys were conducted on 28 June 2024, between 08:00 and 10:00, to maximize the coverage of shaded sections of the stream. The surveys were conducted using a DJI Mavic 3T Enterprise, equipped with a DJI RTK module and a DJI D-RTK 2 mobile station for GNSS base-station support. The Mavic 3T features a 48-megapixel RGB camera with a 24 mm focal length and a 640 × 512-pixel thermal camera with a 40 mm focal length. The drone was manually controlled to optimize the capture of surface temperatures across wide sections of the Shár Shaw Tagà River, recording both TIR and RGB videos simultaneously. Flight altitudes ranged from 5 to 20 m above ground level, depending on the section. All flights were manually piloted at low altitudes and near-nadir angles to reduce geometric distortion and minimize emissivity-related error (Torgersen et al., 2001; Dugdale et al., 2016). The survey began approximately 180 m upstream of the N1 subsection and ended around 800 m downstream of the N2 subsection (Fig. 2). Due to difficulties in flying over the narrow section, it was surveyed twice at different elevations.
The TIR video was visually analyzed to identify cold groundwater exfiltration areas using two criteria: 1) a clear contrast between the dominant stream surface temperature and the suspected exfiltration area, with an area larger than 10 cm², and 2) the presence of a turbulent mixing zone at least 1 m in length immediately downstream of the suspected area (flight data and information are available as Supplemental Material in Charonnat and Baraer, 2025). Absolute temperatures were not derived due to the absence of a calibrated color scale in the TIR video; instead, detection relied on qualitative identification of relative temperature differences appearing as visual color contrasts in the TIR video—typically, colder areas appeared as blue-toned patches compared to the green-toned stream and red-toned sunlit boulders.
When both criteria were met, the RGB video was used for confirmation. The Shár Shaw Tagà River, originating from glacial melt, has a substantial suspended sediment load, whereas groundwater is nearly free of suspended sediments. This contrast is visible in the RGB video frames.
The observed thermal contrasts were consistent with previously measured field temperature differences between springs and stream water, typically >2°C and <6°C (Table S2), and exceeded the uncertainty range of uncorrected thermal imagery under field conditions (Zappa and Jessup, 1998).
Finally, images of confirmed groundwater exfiltration areas were extracted from the videos for size evaluation. Exfiltration areas from the left bank were labeled TIR-L#, and those from the right bank were labeled TIR-R#.”
COMMENT 5:
“Results: In this chapter, the results should only be described: their interpretation and discussion are to be included in the next chapter (5. Discussion). Please move the interpretation of the results to the dedicated chapter (e.g. LL. 388-392 and LL.447-449)”
REPLY 5:
We agree with Referee 1. We revised the manuscript to ensure that only the description of results appears in the Results section. The interpretations have been moved to the Discussion section.
COMMENT 6:
“Discussion: Physical-chemical analysis showed that the springs located along the N1 subsection increase solute concentrations and radon activities of the Shár Shaw Tagà River, especially during dry periods. These springs have a depleted isotopic composition (similar to those of glacial outlet samples) but a high solute content. How do you explain the solute enrichment observed in these springs? How does the rock glacier influence the physical-chemical characteristics of downstream surface waters?”
REPLY 6:
We appreciate this important point and will clarify it more explicitly in the revised manuscript. Overall, the rock glacier exerts a strong influence by promoting localized groundwater resurgence in the N1 subsection, which leads to a sharp increase in solute concentrations over a short river reach (~300 meters).
We propose to add this clarification about the origins of solute enrichment at L.542 in Section 5.2:
“The solute enrichment observed in these springs is attributed to water-rock interactions along groundwater flow paths. Prolonged residence time in aquifers and facilitates the accumulation of dissolved solutes (Hem, 1985). In addition, the springs may be partially connected to internal drainage systems within the rock glacier, which are known to generate solute-rich outflows (Colombo et al., 2018). Lastly, the proximity to buried ground ice and permafrost – both within the rock glacier and in adjacent talus slopes – may enhance the release of mineral elements through thermal erosion of the ice-sediment matrix (Jones et al., 2019).”COMMENT 7:
“Figure captions: Overall, the caption texts are very long and dense. Please consider moving some parts not strictly necessary for understanding the figure directly into the manuscript text. For example, the information described in LL. 361-362 regarding the LMWL can be moved in the main text.”
REPLY 7:
We agree and appreciate this suggestion. We revised the figure captions to make them shorter and more focused, moving supplementary details into the main text as appropriate.
Here are our proposed modifications for some of the figure captions:
“Fig. 1: (a) Overview map showing the location of the Shár Shaw Tagà valley in southwestern Yukon, Canada. (b) Enlarged view of the study area from panel (a), highlighting key geomorphological features. The black frame outlines the extent of the map shown in Fig. 2b. ArcticDEM data: Polar Geospatial Center (Porter et al., 2023). Basemap credits: Esri.”
“Fig. 2: Map illustrating the methods used in this study. Panel (a) corresponds to the area shown in Fig. 1b, while panel (b) provides a zoom-in of panel (a). A bedrock outcrop on the talus slope opposite to RG-A1 marks the division of the Shár Shaw Tagà River’s “narrow section” into two subsections, N1 and N2, as shown on the map. The spring locations represent the outflow points observed during the August 2022 campaign, though their positions may vary depending on hydro-meteorological conditions. Basemap credits: Esri.”
“Fig. 6: (a) PCA scores for June 2022 samples. The explained variance for each PC is indicated in the legend of the horizontal axis. (b) Distribution of clusters formed from June 2022 samples following PCA and k-means clustering. Symbols represent different sample types, and ellipses illustrate the distribution of each cluster. (c) Distribution of total dissolved solids (TDS) concentrations and water temperature for the June 2022 samples. (d) Isotopic composition of the June 2022 samples.”
“Fig. 7: (a) PCA scores for August 2022 samples. The explained variance for each PC is indicated in the legend of the horizontal axis. (b) Distribution of clusters formed from August 2022 samples following PCA and k-means clustering. Symbols represent different sample types, and ellipses illustrate the distribution of each cluster. (c) Distribution of total dissolved solids (TDS) concentrations and water temperature for the August 2022 samples. (d) Isotopic composition of the August 2022 samples.”
“Fig. 8: (a) PCA scores for June 2023 samples. The explained variance for each PC is indicated in the legend of the horizontal axis. (b) Distribution of clusters formed from June 2023 following PCA and k-means clustering. Symbols represent different sample types, and ellipses illustrate the distribution of each cluster. (c) Distribution of total dissolved solids (TDS) concentrations and water temperature for the June 2023 samples. (d) Isotopic composition of the June 2023 samples.”
“Fig. 9: Location of cold water outflows detected by the TIR survey along the Shár Shaw Tagà riverbed. The zoomed-in view of the “narrow section” highlights an area with a high density of cold groundwater outflows detected on both sides of the river, upstream of a bedrock outcrop constraining the riverbed. Additional cold water outflows are observed in the downstream outwash plain, originated from either snow patch melt on the left side or from the right bank of the outwash plain. Springs that outflow from RG-A1 or the opposite talus slope and were sampled during the 2022 and 2023 campaigns are marked in the zoomed-in panel. Basemap credits: Esri.”
COMMENT 8:
“Specific comments
- 48: Please note that the permafrost creep is the result of the deformation of ice-debris matrix and the deformation concentrated in the shear horizon (most of the displacement occurs in the shear horizon). See for example Arenson et al. (2002)
- 85-89: The reference to Figure 1a is missing.
- 104-105: “The black frame outlines the extent of the map shown in Fig. 2a” (and not 2b)
- 122-125: The reference to Figure 2 is missing (location of subsections N1 and N2)
- 164-170: Could you please indicate the coordinates of the TL camera positions?
- 346-347: The reference to Figure 6d is missing.”
REPLY 8:
We thank Referee 1 for these detailed suggestions. We have made the necessary corrections to the manuscript as indicated.
REFERENCES:
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Antonelli, M., Klaus, J., Smettem, K., Teuling, A. J., and Pfister, L.: Exploring Streamwater Mixing Dynamics via Handheld Thermal Infrared Imagery, Water, 9(5), Article 5, https://doi.org/10.3390/w9050358, 2017.
Barclay, J. R., Briggs, M. A., Moore, E. M., Starn, J. J., Hanson, A. E. H., and Helton, A. M.: Where groundwater seeps: Evaluating modeled groundwater discharge patterns with thermal infrared surveys at the river-network scale, Advances in Water Resources, 160, 104108, https://doi.org/10.1016/j.advwatres.2021.104108, 2022.
Briggs, M. A., Hare, D. K., Boutt, D. F., Davenport, G., and Lane, J. W.: Thermal infrared video details multiscale groundwater discharge to surface water through macropores and peat pipes, Hydrological Processes, 30(14), 2510–2511, https://doi.org/10.1002/hyp.10722, 2016.
Casas-Mulet, R., Pander, J., Ryu, D., Stewardson, M. J., and Geist, J.: Unmanned Aerial Vehicle (UAV)-Based Thermal Infra-Red (TIR) and Optical Imagery Reveals Multi-Spatial Scale Controls of Cold-Water Areas Over a Groundwater-Dominated Riverscape, Frontiers in Environmental Science, 8, https://doi.org/10.3389/fenvs.2020.00064, 2020.
Colombo, N., Gruber, S., Martin, M., Malandrino, M., Magnani, A., Godone, D., Freppaz, M., Fratianni, S., and Salerno, F.: Rainfall as primary driver of discharge and solute export from rock glaciers: The Col d’Olen Rock Glacier in the NW Italian Alps, Science of the Total Environment, 639, 316–330, https://doi.org/10.1016/j.scitotenv.2018.05.098, 2018.
Dugdale S. J.: A practitioner’s guide to thermal infrared remote sensing of rivers and streams: recent advances, precautions and considerations, WIREs Water, vol. 3, no. 2, pp. 251–268, , https://doi.org/10.1002/wat2.1135, 2016.
Hem, J.D.:Study and Interpretation of the Chemical Characteristics of Natural Water. 3rd Edition, US Geological Survey Water-Supply Paper 2254, University of Virginia, Charlottesville, 263 p., https://doi.org/10.3133/wsp2254, 1985.
Iwasaki, K., Fukushima, K., Nagasaka, Y., Ishiyama, N., Sakai, M., and Nagasaka, A.: Real-Time Monitoring and Postprocessing of Thermal Infrared Video Images for Sampling and Mapping Groundwater Discharge, Water Resources Research, 59(4), e2022WR033630, https://doi.org/10.1029/2022WR033630, 2023.
Iwasaki, K., Nagasaka Y., Ishiyama N., and Nagasaka A.: Thermal imaging survey for characterizing bedrock groundwater discharge: comparison between sedimentary and volcanic catchments, Hydrological Research Letters 18(3): 79-86, http://dx.doi.org/10.3178/hrl.18.79, 2024.
Jones, D. B., Harrison, S., Anderson, K., and Whalley, W. B.: Rock glaciers and mountain hydrology: A review, Earth-Science Reviews, 193, 66–90, https://doi.org/10.1016/j.earscirev.2019.04.001, 2019.
Porter, C., Howat, I., Noh, M.-J., Husby, E., Khuvis, S., Danish, E., Tomko, K., Gardiner, J., Negrete, A., Yadav, B., Klassen, J., Kelleher, C., Cloutier, M., Bakker, J., Enos, J., Arnold, G., Bauer, G., and Morin, P.: ArcticDEM - Mosaics, Version 4.1 [Dataset], Harvard Dataverse, https://doi.org/10.7910/DVN/3VDC4W, 2023.
Rautio, A., Kivimäki, A.-L., Korkka-Niemi, K., Nygård, M., Salonen, V.-P., Lahti, K., and Vahtera, H.: Vulnerability of groundwater resources to interaction with river water in a boreal catchment, Hydrology and Earth System Sciences, 19(7), 3015–3032, https://doi.org/10.5194/hess-19-3015-2015, 2015.
Torgersen C. E., Faux R. N., McIntosh B. A., Poage N. J., and Norton D. J.: Airborne thermal remote sensing for water temperature assessment in rivers and streams, Remote Sensing of Environment, vol. 76, no. 3, pp. 386–398, https://doi.org/10.1016/S0034-4257(01)00186-9 , 2001.
Wahl, H. E., Fraser, D. B., Harvey, R. C., and Maxwell, J. B.: Climate of Yukon, Atmospheric Environment Service, Environment Canada, 1987.
Webb, B. W., Hannah, D. M., Moore, R. D., Brown, L. E., and Nobilis, F.: Recent advances in stream and river temperature research, Hydrological Processes, 22(7), 902–918, https://doi.org/10.1002/hyp.6994, 2008.
Zappa C. J., Jessup A. T., and Yeh H.: Skin layer recovery of free-surface wakes: Relationship to surface renewal and dependence on heat flux and background turbulence, Journal of Geophysical Research: Oceans, vol. 103, no. C10, pp. 21711–21722, 1998, https://doi.org/10.1029/98JC01942, 1998.
Citation: https://doi.org/10.5194/egusphere-2025-117-AC1
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AC1: 'Reply on RC1', Bastien Charonnat, 09 May 2025
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RC2: 'Comment on egusphere-2025-117', Anonymous Referee #2, 15 Apr 2025
In this article the authors investigate hydrological features in a riverbed below several rock glaciers in a mountainous valley in southwestern Yukon, Canada. The paper is well written and addresses understudied phenomena in a difficult and remote research environment. The dataset is a nice contribution to the literature and the paper worthy of publication after some improvements are made. Some suggestions are:
Figures 1 and 2: I found myself flipping between these two figures a lot. I know it may become quite large, but could I suggest merging these two into one big figure with four panels?
L 76 – 83: I agree with the first reviewer that the major goals of the research need to be better articulated. The experimental design sometimes comes across as a diversity of disparate field observations that are not tied together to address a couple key research hypotheses. A good example of this disconnect is on Line 79, where the authors talk about “hydrological dynamics”, but what does that mean? Is that the water budget or specific fluxes? Further to this point, on L 144, the authors state the primary hypothesis is that the rock glacier A1 influences aufeis formation in the outwash plain, but this is not mentioned in the Introduction.
L 297: I apologize, I am not a fan of supplementary information, and I suggest you bring important data into the main body of the text rather than have a reader dig for it in a different document.
Figures 6 – 8: It would be helpful for context if the axes of panels c and d in these figures were standardized. I found it hard to compare among them. Also, I am not sure you need the site labels. You could include select sites that are mentioned in the text to highlight your message, if that works.
L 452: I would like to make sure I understand correctly, the evidence that springs are snowmelt and rain fed is because their water plots directly on the local meteoric water line? I probably missed this, but stating explicitly so would help. Even better would be data from snow and rain itself. I believe the authors include some glacier water already.
L 477 – 480: I find it curious that the cold water outflow locations do not necessarily align with the aufeis location. Some thoughts on this disparity would be good to include in the paper.
L 501: Perhaps reference Figures 6 – 8 here.
L 528: I am not sure what “frozen content” means. Is this ice in the rock glacier, or any material that is below 0°C?
L 539: Perhaps rephrase this sentence as “ ….. aquifer provide the water but the decrease in river velocity and channel depth …. creates conditions favourable for the formation of aufeis.” This makes it explicit the role of each contributing factor.
Conclusion: This could all be merged into one paragraph.
Citation: https://doi.org/10.5194/egusphere-2025-117-RC2 -
AC2: 'Reply on RC2', Bastien Charonnat, 09 May 2025
We thank Referees 1 and 2 for their valuable comments, which will significantly contribute to improving the quality of our paper. Below, we respond individually to each of the referee’s comments:
COMMENT 1:
“Figures 1 and 2: I found myself flipping between these two figures a lot. I know it may become quite large, but could I suggest merging these two into one big figure with four panels?”
REPLY 1:
We appreciate Referee 2’s suggestion and recognize that visualizing the different scales may be challenging when the figures are separated. We have tentatively merged the two figures but without success. Not only the resulting map was very difficult to read but we realized that this merged figure would be placed within the Study Site section, presenting measurement and survey locations before their first mention in the Methods. This caused additional back-and-forth for readers as well. Therefore, we suggest to keep Figures 1 and 2 separate.
COMMENT 2:
“L 76 – 83: I agree with the first reviewer that the major goals of the research need to be better articulated. The experimental design sometimes comes across as a diversity of disparate field observations that are not tied together to address a couple key research hypotheses. A good example of this disconnect is on Line 79, where the authors talk about “hydrological dynamics”, but what does that mean? Is that the water budget or specific fluxes? Further to this point, on L 144, the authors state the primary hypothesis is that the rock glacier A1 influences aufeis formation in the outwash plain, but this is not mentioned in the Introduction.”
REPLY 2:
We thank Referee 2 for this relevant comment. We agree that the objectives and research questions should be expressed more clearly at the end of the Introduction. We also acknowledge that the term "hydrological dynamics" should be specified, as it refers to specific fluxes and processes influencing the water and hydrochemical budget at the catchment scale.
We also agree that the three-part multi-method approach would benefit from clearer presentation at the end of the Introduction, including the sub-objectives. These elements are currently outlined in Section 3.1 ("Method overview") but could be moved in the introduction and better structured for improved clarity.
We therefore suggest deleting Section 3.1 and propose to revise the final paragraph of the Introduction (LL 77-83) as follows:“This study examines the influence of rock glaciers on surface and shallow groundwater flow within alpine riverbed hydrological systems. Specifically, it focuses on characterizing water fluxes in a section of the Shár Shaw Tagà catchment (St. Elias Mountains, Yukon, Canada) that is constrained by a rock glacier. We hypothesize that the rock glacier modulates interactions between surface water and shallow groundwater, thereby affecting the overall functioning of the riverbed system.
To investigate these interactions, we employed a multimethod approach that was progressively refined as our observations and understanding of the system evolved:
- We hypothesized that the rock glacier influences the formation of aufeis on the downstream outwash plain. To test this, we used time-lapse camera monitoring to track the development of aufeis and to identify the location and timing of winter outflows.
- Given the rock glacier’s position at the outlet of a subcatchment and the lack of significant surface outflow, we hypothesized that it drains the subcatchment and contributes to river discharge via groundwater exfiltration. To assess this, we conducted a spring inventory, followed by a physico-hydrochemical characterization of springs and streams across the subcatchment. This allowed us to trace water sources and evaluate the rock glacier’s influence on stream composition.
- Building on the previous findings, we hypothesized that a specific section of the riverbed serves as a major zone of groundwater exfiltration. To identify and map these zones, we conducted drone-based thermal infrared (TIR) surveys, enabling us to delineate areas of groundwater emergence and assess their spatial extent and relative magnitude.
The novelty of this research lies in its focus on the indirect hydrological impacts of a rock glacier—particularly in the absence of a visible, well-defined outflow. By integrating hydrological, hydrogeological, and geochemical methods, this study advances our understanding of the complex role rock glaciers play in alpine watershed dynamics and provides insights with broader applicability to similar environments worldwide.”
COMMENT 3:
“L 297: I apologize, I am not a fan of supplementary information, and I suggest you bring important data into the main body of the text rather than have a reader dig for it in a different document.”
REPLY 3:
This is a pertinent comment. Since the sampling sites are already shown in Figure 2, we initially considered Table S1 as providing supplementary detail, following HESS guidelines. However, we are willing to incorporate Table S1 at the end of Section 3.3.1 and reference it in the text as Table 1.
COMMENT 4:
“Figures 6 – 8: It would be helpful for context if the axes of panels c and d in these figures were standardized. I found it hard to compare among them. Also, I am not sure you need the site labels. You could include select sites that are mentioned in the text to highlight your message, if that works.”
REPLY 4:
We appreciate this suggestion. Standardizing the axes would indeed facilitate comparison between figures. However, we note that it could reduce the readability of each individual figure by increasing the density of point clouds. Since our interpretations are made within each specific figure rather than through direct comparison, we propose to keep the current axes for clarity.
COMMENT 5:
“L 452: I would like to make sure I understand correctly, the evidence that springs are snowmelt and rain fed is because their water plots directly on the local meteoric water line? I probably missed this, but stating explicitly so would help. Even better would be data from snow and rain itself. I believe the authors include some glacier water already.”
REPLY 5:
This important question highlights a need for clarification.
The local meteoric water line (LMWL) is shown for reference but is not used as the primary basis for interpretation, given that it was derived from studies in the Whitehorse area, 220 km east (Birks et al., 2004). Although similar to Lhù’ààn Mân’ data 25 km east (Brahney et al., 2010), we prefer not to assume direct applicability.We propose to add this clarification LL. 201-202:
“The LMWL is displayed alongside the analyses results as reference (Fig. 6d, Fig. 7d and Fig. 8d) but we prefere not to assume direct applicability to our data.”
Across Canada, precipitation is expected to be enriched in heavy isotopes during the snow-free period and depleted in heavy isotopes during winter and spring (Gibson et al., 2020). Evidence for snowmelt- and rain-fed springs comes primarily from the observed depleted isotopic compositions, low mineral concentrations, and cold temperatures in early June (LL 301, 306–307, 312–313, 348–350), indicating snowmelt, and the enriched isotopic compositions in August reflecting rainfall influence (LL 388–389). This distinction is reinforced by contrasting results from N1 subsection springs, which display groundwater and glacier-fed signatures (LL 349–350, 386–388).
We propose to explicitly clarify this interpretation in Section 5.1 (Discussion), by changing the paragraph LL. 508-515 as:
“Contrary to initial hypotheses, no evidence was found of outflow originating from the head of the rock glacier’s subcatchment (comprising glaciers G-B1 and G-B2). Instead, the physico-hydrochemical characterization suggests that glacial meltwater entering the water to the river derives from upstream outwash plains of the main Shár Shaw Tagà catchment. In contrast, the other springs emerging at the front of the rock glacier appear to be linked to internal drainage systems within the rock glacier itself. These springs are primarily fed by snowmelt in the early season and by summer precipitation later in the season, with minimal or negligible glacier melt contribution, as shown by the physico-hydrochemical characterization of the samples collected in June 2022 and August 2022, respectively. Across Canada, precipitation is typically enriched in heavy isotopes during the snow-free period and depleted during winter and spring (Gibson et al., 2020). Accordingly, the depleted isotopic compositions, low solute concentrations, and cold temperatures measured in early June point to a snowmelt origin, while the enriched isotopic compositions in August reflect a stronger influence from rainfall. This seasonal distinction is further supported by contrasting results from springs in the N1 subsection, which exhibit characteristics of both groundwater and glacier-fed sources. Some springs likely reflect a mix of these sources, with their physicochemical parameters and clustering reflecting these dual influences depending on hydro-meteorological conditions and time periods.”
COMMENT 6:
“L 477 – 480: I find it curious that the cold water outflow locations do not necessarily align with the aufeis location. Some thoughts on this disparity would be good to include in the paper.”
REPLY 6:
Referee 2 raises an excellent point.
Specifically, the steeper slope in the N1 subsection may prevent aufeis formation at the cold outflow locations, as aufeis typically develop where river flow velocity decreases, such as braided channels and outwash plains (Hu and Pollard, 1997). Following this comment and Comment 9, we propose to modify LL. 538-540 as:
“Aufeis typically develop in areas where river flow velocity decreases, such as braided channels and outwash plains (Hu and Pollard, 1997). The TL monitoring suggests that the resurgences from the alluvial aquifer provide the water from the N1 subsection but the decrease in river flow velocity and channel depth creates conditions favourable for the formation of aufeis in the outwash plain immediately downstream of the rock glacier. In contrast, the steeper slope in the N1 subsection likely inhibits aufeis formation directly at the springs locations.”
COMMENT 7:
“L 501: Perhaps reference Figures 6 – 8 here.”
REPLY 7:
We agree. We will add references to Figures 6–8 at this point in the text.
COMMENT 8:
“L 528: I am not sure what “frozen content” means. Is this ice in the rock glacier, or any material that is below 0°C?”
REPLY 8:
This is a valid question. By "frozen content," we refer to any material below 0°C, including both massive ice and frozen ground within the rock glacier or talus slope. We clarified this in the manuscript LL. 526-527 as:
“The cold temperatures measured in the springs of the N1 subsection indicate that outflows from the alluvial aquifer are cooled by adjacent frozen content, such as massive ice or permafrost.”
COMMENT 9:
“L 539: Perhaps rephrase this sentence as “ ….. aquifer provide the water but the decrease in river velocity and channel depth …. creates conditions favourable for the formation of aufeis.” This makes it explicit the role of each contributing factor.”
REPLY 9:
We agree with this suggestion and we propose to rephrase the sentence accordingly to explicitly distinguish the role of each contributing factor, and in accordance with Comment 6:
“Aufeis typically develop in areas where river flow velocity decreases, such as braided channels and outwash plains (Hu and Pollard, 1997). The TL monitoring suggests that the resurgences from the alluvial aquifer provide the water from the N1 subsection but the decrease in river flow velocity and channel depth creates conditions favourable for the formation of aufeis in the outwash plain immediately downstream of the rock glacier. In contrast, the steeper slope in the N1 subsection likely inhibits aufeis formation directly at the springs locations.”
COMMENT 10:
“Conclusion: This could all be merged into one paragraph.”
REPLY 10:
We fully agree. We merged the Conclusion into a single paragraph, as suggested.
REFERENCES
Birks, S. J., Edwards, T. W. D., Gibson, J. J., Drimmie, R. J. and Michel, F. A.: Canadian network for isotopes in Precipitation, http://www.science.uwaterloo.ca/~twdedwar/cnip/cniphome.html, 2004.
Brahney, J., Clague, J. J., Edwards, T. W. D., and Menounos, B.: Late Holocene paleohydrology of Kluane Lake, Yukon Territory, Canada, Journal of Paleolimnology, 44(3), 873–885, https://doi.org/10.1007/s10933-010-9459-8,673, 2010.
Gibson J.J., Holmes T., Stadnyk T.A., Birks S.J., Eby P., and Pietroniro A.: 18O and 2H in streamflow across Canada, Journal of Hydrology: Regional Studies, Volume 32, 100754, ISSN 2214-5818, https://doi.org/10.1016/j.ejrh.2020.100754, 2020.
Hu, X., and Pollard, W.H.: The hydrologic analysis and modelling of river icing growth, North Fork Pass, Yukon Territory, Canada, Permafrost and Periglacial Processes, 8: 279–294, https://doi.org/10.1002/(SICI)1099-1530(199709)8:3<279::AID-PPP260>3.0.CO;2-7, 1997.
Citation: https://doi.org/10.5194/egusphere-2025-117-AC2
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AC2: 'Reply on RC2', Bastien Charonnat, 09 May 2025
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2025-117', Anonymous Referee #1, 07 Apr 2025
In this manuscript, Charonnat B. et al. investigated the influence of a rock glacier on a riverbed hydrological system located in St. Elias Mountains (Yukon, Canada), using a multimethod approach. The first part of the study focused on the monitoring of the aufeis formation in an outwash plain through the installation of timelapse cameras. The second part investigated the water origin of the springs located in the upper Shár Shaw Tagà catchment and their impact on the river hydrochemistry through sampling and analysis of numerous water samples. The last part of the study examined groundwater exfiltration zones along the Shár Shaw Tagà River using a drone equipped with a thermal infrared camera. Results revealed that the rock glacier influences the riverbed hydrological system through mainly its geomorphic properties, by obstructing proglacial outwash plains and changing the channel structure and groundwater discharge. This geomorphic constraint allows groundwater resurgences from the alluvial aquifer, which promote aufeis formation and hydro-chemical disruption of streamflow.
This work is well written and contributes to increase knowledge on the hydrological role of rock glaciers in deglaciating catchments, highlighting the impact they have on the hydrogeomorphology of riverbeds due to their geomorphic properties. However, before the publication of this manuscript, the authors should address some general and specific comments, which are listed in the following sections.
General comments
- Introduction: At the end of this chapter I suggest to:
- Define more clearly the general objective / research question of this study;
- Describe the three main part of this work, and for each define the sub-objectives/research questions and hypothesis. In Chapter 3, I would leave only the descriptions of the methods used in each of the three parts of the study to answer the respective sub-objectives.
- Study site: Please add information concerning the mean annual air temperature in order to better understand the climate conditions of the study area (only annual precipitation is described).
- Methods: It would be great to add the coordinates and the altitude for each sampling site in Table S1.
- Methods/Results: I have some questions regarding the TIR survey:
- Did you calibrate the thermal camera of the drone before the surveys? Did you check the temperature accuracy of the drone sensor? We are also testing the same drone at our institute, and we observed that the error in the temperature measured by the thermal camera increases as the air temperature decreases.
- I am a bit skeptical about using the TIR video approach, since the video does not provide a color scale and therefore the water temperature cannot be determined. As described in text (LL. 240-243), water temperature, however, is key criteria for identifying cold groundwater exfiltration. How did you define “a clear contrast between the dominant stream surface temperature and the suspected exfiltration area” based only on the colors given by the thermal imaging camera (but without knowing the actual water temperatures)? How many degrees Celsius should this clear thermal contrast correspond to?
- When processing thermal images, it is also important to set some parameters (such as flight height, air humidity, thermal emissivity of analyzed surface) to accurately define the temperature. Did you consider these factors when you analyzed the TIR video surveys? Have you noticed any differences in the measured temperature by changing the flight height of the drone?
- Results: In this chapter, the results should only be described: their interpretation and discussion are to be included in the next chapter (5. Discussion). Please move the interpretation of the results to the dedicated chapter (e.g. LL. 388-392 and LL.447-449)
- Discussion: Physical-chemical analysis showed that the springs located along the N1 subsection increase solute concentrations and radon activities of the Shár Shaw Tagà River, especially during dry periods. These springs have a depleted isotopic composition (similar to those of glacial outlet samples) but a high solute content. How do you explain the solute enrichment observed in these springs? How does the rock glacier influence the physical-chemical characteristics of downstream surface waters?
- Figure captions: Overall, the caption texts are very long and dense. Please consider moving some parts not strictly necessary for understanding the figure directly into the manuscript text. For example, the information described in LL. 361-362 regarding the LMWL can be moved in the main text.
Specific comments
L. 48: Please note that the permafrost creep is the result of the deformation of ice-debris matrix and the deformation concentrated in the shear horizon (most of the displacement occurs in the shear horizon). See for example Arenson et al. (2002)
LL. 85-89: The reference to Figure 1a is missing.
LL. 104-105: “The black frame outlines the extent of the map shown in Fig. 2a” (and not 2b)
LL. 122-125: The reference to Figure 2 is missing (location of subsections N1 and N2)
LL. 164-170: Could you please indicate the coordinates of the TL camera positions?
LL. 346-347: The reference to Figure 6d is missing.
References
Arenson, L., Hoelzle, M., & Springman, S. (2002). Borehole deformation measurements and internal structure of some rock glaciers in Switzerland. Permafrost and periglacial processes, 13(2), 117-135. https://doi.org/10.1002/ppp.414
Citation: https://doi.org/10.5194/egusphere-2025-117-RC1 -
AC1: 'Reply on RC1', Bastien Charonnat, 09 May 2025
We thank Referees 1 and 2 for their valuable comments, which will significantly contribute to improving the quality of our paper. Below, we respond individually to each of the referee’s comments:
COMMENT 1:
“Introduction: At the end of this chapter I suggest to:
- Define more clearly the general objective / research question of this study;
- Describe the three main part of this work, and for each define the sub-objectives/research questions and hypothesis. In Chapter 3, I would leave only the descriptions of the methods used in each of the three parts of the study to answer the respective sub-objectives.”
REPLY 1:
We agree with Referee 1 that the general objective and research question could be more clearly stated in the Introduction.
We also agree that the three-part multi-method approach would benefit from clearer presentation at the end of the Introduction, including the sub-objectives. These elements are currently outlined in Section 3.1 ("Method overview") but could be moved in the introduction and better structured for improved clarity.
We therefore suggest deleting Section 3.1 and propose to revise the final paragraph of the Introduction (LL 77-83) as follows:“This study examines the influence of rock glaciers on surface and shallow groundwater flow within alpine riverbed hydrological systems. Specifically, it focuses on characterizing water fluxes in a section of the Shár Shaw Tagà catchment (St. Elias Mountains, Yukon, Canada) that is constrained by a rock glacier. We hypothesize that the rock glacier modulates interactions between surface water and shallow groundwater, thereby affecting the overall functioning of the riverbed system.
To investigate these interactions, we employed a multimethod approach that was progressively refined as our observations and understanding of the system evolved:
- We hypothesized that the rock glacier influences the formation of aufeis on the downstream outwash plain. To test this, we used time-lapse camera monitoring to track the development of aufeis and to identify the location and timing of winter outflows.
- Given the rock glacier’s position at the outlet of a subcatchment and the lack of significant surface outflow, we hypothesized that it drains the subcatchment and contributes to river discharge via groundwater exfiltration. To assess this, we conducted a spring inventory, followed by a physico-hydrochemical characterization of springs and streams across the subcatchment. This allowed us to trace water sources and evaluate the rock glacier’s influence on stream composition.
- Building on the previous findings, we hypothesized that a specific section of the riverbed serves as a major zone of groundwater exfiltration. To identify and map these zones, we conducted drone-based thermal infrared (TIR) surveys, enabling us to delineate areas of groundwater emergence and assess their spatial extent and relative magnitude.
The novelty of this research lies in its focus on the indirect hydrological impacts of a rock glacier—particularly in the absence of a visible, well-defined outflow. By integrating hydrological, hydrogeological, and geochemical methods, this study advances our understanding of the complex role rock glaciers play in alpine watershed dynamics and provides insights with broader applicability to similar environments worldwide.”
COMMENT 2:
“Please add information concerning the mean annual air temperature in order to better understand the climate conditions of the study area (only annual precipitation is described).”
REPLY 2:
We appreciate this suggestion. We added the mean annual air temperature alongside the annual precipitation information in the description of the study area as:
“The eastern flank of the St. Elias Mountains experiences a dry subarctic climate, characterized by annual precipitation ranging from 300 to 500 mm yr-1 and a mean annual temperature between –8 °C and –12 °C (Wahl et al., 1987).
COMMENT 3:
“Methods: It would be great to add the coordinates and the altitude for each sampling site in Table S1”
REPLY 3:
We agree with Referee 1 that it would be helpful to add the coordinates and altitude for each sampling site in Table S1. We modified the table to include them.
COMMENT 4:
“Methods/Results: I have some questions regarding the TIR survey:
- Did you calibrate the thermal camera of the drone before the surveys? Did you check the temperature accuracy of the drone sensor? We are also testing the same drone at our institute, and we observed that the error in the temperature measured by the thermal camera increases as the air temperature decreases.
- I am a bit skeptical about using the TIR video approach, since the video does not provide a color scale and therefore the water temperature cannot be determined. As described in text (LL. 240-243), water temperature, however, is key criteria for identifying cold groundwater exfiltration. How did you define “a clear contrast between the dominant stream surface temperature and the suspected exfiltration area” based only on the colors given by the thermal imaging camera (but without knowing the actual water temperatures)? How many degrees Celsius should this clear thermal contrast correspond to?
- When processing thermal images, it is also important to set some parameters (such as flight height, air humidity, thermal emissivity of analyzed surface) to accurately define the temperature. Did you consider these factors when you analyzed the TIR video surveys? Have you noticed any differences in the measured temperature by changing the flight height of the drone?”
REPLY 4:
- Referee 1 raises important points. Absolute temperature inaccuracies with this drone model have been reported in other studies. However, in our case, the TIR survey aimed only to detect relative differences in surface water temperature, not to measure absolute values. We therefore followed the method described in several studies (Antonelli et al., 2017; Briggs et al., 2016 and Iwasaki et al., 2023). Interestingly, Kenta Iwasaki published a new article in 2024 underlining the advantages of using temperature contrasts in TIR videos as a fast yet efficient way to detect groundwater contribution to surface water (Iwasaki et al. 2024). In the present case, we can confirm that the detection of major thermal contrasts (from 2 to 6 °C) was successful without the need for calibration or correction.
- We fully agree that the absence of a color scale in the TIR video prevents direct use of absolute temperatures. Consequently, identification of groundwater exfiltration zones was based on visible thermal contrasts. These zones consistently appeared as distinctly colder areas (blue) compared to the warmer stream (green) and sun-heated boulders (red), as shown in Figure 10. The distinctiveness of the observed contrasts, validated by previous field temperature measurements (spring-to-stream temperature differences typically between >2 °C and <6 °C; see Table S2), supports the reliability of this approach. Plumes visible in TIR imagery, due to contrasts in water temperature, have been shown to effectively indicate groundwater exfiltration (Antonelli et al., 2017; Briggs et al., 2016; Iwasaki et al., 2023; Iwasaki et al., 2024). Groundwater exfiltration zones were mapped only when a clear and strong visible contrast was observed; in the absence of a distinct contrast, no feature was mapped.
- We acknowledge the importance of adjusting parameters like flight height, air humidity, and surface emissivity when precise temperature measurements are needed. However, since our objective was solely to detect visible temperature contrasts, such corrections were not applied. In the case of drone-based TIR, images taken from near nadir reduce inaccuracies linked to surface emissivity and reflected temperature (Torgersen et al., 2001; Dugdale et al., 2016), with uncorrected temperatures up to 0.5 °C colder than real temperatures (Zappa and Jessup, 1998). In our case, we aim to detect contrasts superior to 2 °C, the observed contrasts were sufficiently pronounced to achieve the study’s objectives and were cross-validated through field observations.
- We propose to integrate in the manuscript the clarification provided above by rewriting Section 3.4 as:
“Aerial and handheld thermal infrared (TIR) devices have been demonstrated as effective tools for mapping groundwater discharge into streams (Toran, 2019). Specifically, drone-based TIR technology allows for high spatial resolution observations of surface water–groundwater interactions (Vélez-Nicolás et al., 2021). Two common approaches for TIR surveys were considered: 1) generating stream temperature maps using high-definition TIR image orthomosaics from overlapping images (e.g., Abolt et al., 2018; Casas-Mulet et al., 2020; Rautio et al., 2015), and 2) using TIR videos or real-time scans (handheld or drone-based) to visualize mixing plumes and record GPS coordinates of observed points (e.g., Barclay et al., 2022; Briggs et al., 2016; Iwasaki et al., 2023).
While georeferenced thermal maps provide mesoscale coverage, they require stable flying conditions, ground control points, and extensive post-processing (Webb et al., 2008). In contrast, TIR video or live scans allow for real-time visualization of mixing dynamics in smaller-scale areas (Antonelli et al., 2017). Given our goal to identify and characterize groundwater exfiltration zones, we chose the TIR video approach. This method does not require precise absolute temperature but relies instead on relative contrasts between stream water and suspected groundwater inflows. Prior studies (Antonelli et al., 2017; Briggs et al., 2016; Iwasaki et al., 2023; Iwasaki et al., 2024) have shown that TIR video, even without embedded temperature scales, effectively highlights such contrasts.
Drone-based TIR video surveys were conducted on 28 June 2024, between 08:00 and 10:00, to maximize the coverage of shaded sections of the stream. The surveys were conducted using a DJI Mavic 3T Enterprise, equipped with a DJI RTK module and a DJI D-RTK 2 mobile station for GNSS base-station support. The Mavic 3T features a 48-megapixel RGB camera with a 24 mm focal length and a 640 × 512-pixel thermal camera with a 40 mm focal length. The drone was manually controlled to optimize the capture of surface temperatures across wide sections of the Shár Shaw Tagà River, recording both TIR and RGB videos simultaneously. Flight altitudes ranged from 5 to 20 m above ground level, depending on the section. All flights were manually piloted at low altitudes and near-nadir angles to reduce geometric distortion and minimize emissivity-related error (Torgersen et al., 2001; Dugdale et al., 2016). The survey began approximately 180 m upstream of the N1 subsection and ended around 800 m downstream of the N2 subsection (Fig. 2). Due to difficulties in flying over the narrow section, it was surveyed twice at different elevations.
The TIR video was visually analyzed to identify cold groundwater exfiltration areas using two criteria: 1) a clear contrast between the dominant stream surface temperature and the suspected exfiltration area, with an area larger than 10 cm², and 2) the presence of a turbulent mixing zone at least 1 m in length immediately downstream of the suspected area (flight data and information are available as Supplemental Material in Charonnat and Baraer, 2025). Absolute temperatures were not derived due to the absence of a calibrated color scale in the TIR video; instead, detection relied on qualitative identification of relative temperature differences appearing as visual color contrasts in the TIR video—typically, colder areas appeared as blue-toned patches compared to the green-toned stream and red-toned sunlit boulders.
When both criteria were met, the RGB video was used for confirmation. The Shár Shaw Tagà River, originating from glacial melt, has a substantial suspended sediment load, whereas groundwater is nearly free of suspended sediments. This contrast is visible in the RGB video frames.
The observed thermal contrasts were consistent with previously measured field temperature differences between springs and stream water, typically >2°C and <6°C (Table S2), and exceeded the uncertainty range of uncorrected thermal imagery under field conditions (Zappa and Jessup, 1998).
Finally, images of confirmed groundwater exfiltration areas were extracted from the videos for size evaluation. Exfiltration areas from the left bank were labeled TIR-L#, and those from the right bank were labeled TIR-R#.”
COMMENT 5:
“Results: In this chapter, the results should only be described: their interpretation and discussion are to be included in the next chapter (5. Discussion). Please move the interpretation of the results to the dedicated chapter (e.g. LL. 388-392 and LL.447-449)”
REPLY 5:
We agree with Referee 1. We revised the manuscript to ensure that only the description of results appears in the Results section. The interpretations have been moved to the Discussion section.
COMMENT 6:
“Discussion: Physical-chemical analysis showed that the springs located along the N1 subsection increase solute concentrations and radon activities of the Shár Shaw Tagà River, especially during dry periods. These springs have a depleted isotopic composition (similar to those of glacial outlet samples) but a high solute content. How do you explain the solute enrichment observed in these springs? How does the rock glacier influence the physical-chemical characteristics of downstream surface waters?”
REPLY 6:
We appreciate this important point and will clarify it more explicitly in the revised manuscript. Overall, the rock glacier exerts a strong influence by promoting localized groundwater resurgence in the N1 subsection, which leads to a sharp increase in solute concentrations over a short river reach (~300 meters).
We propose to add this clarification about the origins of solute enrichment at L.542 in Section 5.2:
“The solute enrichment observed in these springs is attributed to water-rock interactions along groundwater flow paths. Prolonged residence time in aquifers and facilitates the accumulation of dissolved solutes (Hem, 1985). In addition, the springs may be partially connected to internal drainage systems within the rock glacier, which are known to generate solute-rich outflows (Colombo et al., 2018). Lastly, the proximity to buried ground ice and permafrost – both within the rock glacier and in adjacent talus slopes – may enhance the release of mineral elements through thermal erosion of the ice-sediment matrix (Jones et al., 2019).”COMMENT 7:
“Figure captions: Overall, the caption texts are very long and dense. Please consider moving some parts not strictly necessary for understanding the figure directly into the manuscript text. For example, the information described in LL. 361-362 regarding the LMWL can be moved in the main text.”
REPLY 7:
We agree and appreciate this suggestion. We revised the figure captions to make them shorter and more focused, moving supplementary details into the main text as appropriate.
Here are our proposed modifications for some of the figure captions:
“Fig. 1: (a) Overview map showing the location of the Shár Shaw Tagà valley in southwestern Yukon, Canada. (b) Enlarged view of the study area from panel (a), highlighting key geomorphological features. The black frame outlines the extent of the map shown in Fig. 2b. ArcticDEM data: Polar Geospatial Center (Porter et al., 2023). Basemap credits: Esri.”
“Fig. 2: Map illustrating the methods used in this study. Panel (a) corresponds to the area shown in Fig. 1b, while panel (b) provides a zoom-in of panel (a). A bedrock outcrop on the talus slope opposite to RG-A1 marks the division of the Shár Shaw Tagà River’s “narrow section” into two subsections, N1 and N2, as shown on the map. The spring locations represent the outflow points observed during the August 2022 campaign, though their positions may vary depending on hydro-meteorological conditions. Basemap credits: Esri.”
“Fig. 6: (a) PCA scores for June 2022 samples. The explained variance for each PC is indicated in the legend of the horizontal axis. (b) Distribution of clusters formed from June 2022 samples following PCA and k-means clustering. Symbols represent different sample types, and ellipses illustrate the distribution of each cluster. (c) Distribution of total dissolved solids (TDS) concentrations and water temperature for the June 2022 samples. (d) Isotopic composition of the June 2022 samples.”
“Fig. 7: (a) PCA scores for August 2022 samples. The explained variance for each PC is indicated in the legend of the horizontal axis. (b) Distribution of clusters formed from August 2022 samples following PCA and k-means clustering. Symbols represent different sample types, and ellipses illustrate the distribution of each cluster. (c) Distribution of total dissolved solids (TDS) concentrations and water temperature for the August 2022 samples. (d) Isotopic composition of the August 2022 samples.”
“Fig. 8: (a) PCA scores for June 2023 samples. The explained variance for each PC is indicated in the legend of the horizontal axis. (b) Distribution of clusters formed from June 2023 following PCA and k-means clustering. Symbols represent different sample types, and ellipses illustrate the distribution of each cluster. (c) Distribution of total dissolved solids (TDS) concentrations and water temperature for the June 2023 samples. (d) Isotopic composition of the June 2023 samples.”
“Fig. 9: Location of cold water outflows detected by the TIR survey along the Shár Shaw Tagà riverbed. The zoomed-in view of the “narrow section” highlights an area with a high density of cold groundwater outflows detected on both sides of the river, upstream of a bedrock outcrop constraining the riverbed. Additional cold water outflows are observed in the downstream outwash plain, originated from either snow patch melt on the left side or from the right bank of the outwash plain. Springs that outflow from RG-A1 or the opposite talus slope and were sampled during the 2022 and 2023 campaigns are marked in the zoomed-in panel. Basemap credits: Esri.”
COMMENT 8:
“Specific comments
- 48: Please note that the permafrost creep is the result of the deformation of ice-debris matrix and the deformation concentrated in the shear horizon (most of the displacement occurs in the shear horizon). See for example Arenson et al. (2002)
- 85-89: The reference to Figure 1a is missing.
- 104-105: “The black frame outlines the extent of the map shown in Fig. 2a” (and not 2b)
- 122-125: The reference to Figure 2 is missing (location of subsections N1 and N2)
- 164-170: Could you please indicate the coordinates of the TL camera positions?
- 346-347: The reference to Figure 6d is missing.”
REPLY 8:
We thank Referee 1 for these detailed suggestions. We have made the necessary corrections to the manuscript as indicated.
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Antonelli, M., Klaus, J., Smettem, K., Teuling, A. J., and Pfister, L.: Exploring Streamwater Mixing Dynamics via Handheld Thermal Infrared Imagery, Water, 9(5), Article 5, https://doi.org/10.3390/w9050358, 2017.
Barclay, J. R., Briggs, M. A., Moore, E. M., Starn, J. J., Hanson, A. E. H., and Helton, A. M.: Where groundwater seeps: Evaluating modeled groundwater discharge patterns with thermal infrared surveys at the river-network scale, Advances in Water Resources, 160, 104108, https://doi.org/10.1016/j.advwatres.2021.104108, 2022.
Briggs, M. A., Hare, D. K., Boutt, D. F., Davenport, G., and Lane, J. W.: Thermal infrared video details multiscale groundwater discharge to surface water through macropores and peat pipes, Hydrological Processes, 30(14), 2510–2511, https://doi.org/10.1002/hyp.10722, 2016.
Casas-Mulet, R., Pander, J., Ryu, D., Stewardson, M. J., and Geist, J.: Unmanned Aerial Vehicle (UAV)-Based Thermal Infra-Red (TIR) and Optical Imagery Reveals Multi-Spatial Scale Controls of Cold-Water Areas Over a Groundwater-Dominated Riverscape, Frontiers in Environmental Science, 8, https://doi.org/10.3389/fenvs.2020.00064, 2020.
Colombo, N., Gruber, S., Martin, M., Malandrino, M., Magnani, A., Godone, D., Freppaz, M., Fratianni, S., and Salerno, F.: Rainfall as primary driver of discharge and solute export from rock glaciers: The Col d’Olen Rock Glacier in the NW Italian Alps, Science of the Total Environment, 639, 316–330, https://doi.org/10.1016/j.scitotenv.2018.05.098, 2018.
Dugdale S. J.: A practitioner’s guide to thermal infrared remote sensing of rivers and streams: recent advances, precautions and considerations, WIREs Water, vol. 3, no. 2, pp. 251–268, , https://doi.org/10.1002/wat2.1135, 2016.
Hem, J.D.:Study and Interpretation of the Chemical Characteristics of Natural Water. 3rd Edition, US Geological Survey Water-Supply Paper 2254, University of Virginia, Charlottesville, 263 p., https://doi.org/10.3133/wsp2254, 1985.
Iwasaki, K., Fukushima, K., Nagasaka, Y., Ishiyama, N., Sakai, M., and Nagasaka, A.: Real-Time Monitoring and Postprocessing of Thermal Infrared Video Images for Sampling and Mapping Groundwater Discharge, Water Resources Research, 59(4), e2022WR033630, https://doi.org/10.1029/2022WR033630, 2023.
Iwasaki, K., Nagasaka Y., Ishiyama N., and Nagasaka A.: Thermal imaging survey for characterizing bedrock groundwater discharge: comparison between sedimentary and volcanic catchments, Hydrological Research Letters 18(3): 79-86, http://dx.doi.org/10.3178/hrl.18.79, 2024.
Jones, D. B., Harrison, S., Anderson, K., and Whalley, W. B.: Rock glaciers and mountain hydrology: A review, Earth-Science Reviews, 193, 66–90, https://doi.org/10.1016/j.earscirev.2019.04.001, 2019.
Porter, C., Howat, I., Noh, M.-J., Husby, E., Khuvis, S., Danish, E., Tomko, K., Gardiner, J., Negrete, A., Yadav, B., Klassen, J., Kelleher, C., Cloutier, M., Bakker, J., Enos, J., Arnold, G., Bauer, G., and Morin, P.: ArcticDEM - Mosaics, Version 4.1 [Dataset], Harvard Dataverse, https://doi.org/10.7910/DVN/3VDC4W, 2023.
Rautio, A., Kivimäki, A.-L., Korkka-Niemi, K., Nygård, M., Salonen, V.-P., Lahti, K., and Vahtera, H.: Vulnerability of groundwater resources to interaction with river water in a boreal catchment, Hydrology and Earth System Sciences, 19(7), 3015–3032, https://doi.org/10.5194/hess-19-3015-2015, 2015.
Torgersen C. E., Faux R. N., McIntosh B. A., Poage N. J., and Norton D. J.: Airborne thermal remote sensing for water temperature assessment in rivers and streams, Remote Sensing of Environment, vol. 76, no. 3, pp. 386–398, https://doi.org/10.1016/S0034-4257(01)00186-9 , 2001.
Wahl, H. E., Fraser, D. B., Harvey, R. C., and Maxwell, J. B.: Climate of Yukon, Atmospheric Environment Service, Environment Canada, 1987.
Webb, B. W., Hannah, D. M., Moore, R. D., Brown, L. E., and Nobilis, F.: Recent advances in stream and river temperature research, Hydrological Processes, 22(7), 902–918, https://doi.org/10.1002/hyp.6994, 2008.
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Citation: https://doi.org/10.5194/egusphere-2025-117-AC1
- Introduction: At the end of this chapter I suggest to:
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RC2: 'Comment on egusphere-2025-117', Anonymous Referee #2, 15 Apr 2025
In this article the authors investigate hydrological features in a riverbed below several rock glaciers in a mountainous valley in southwestern Yukon, Canada. The paper is well written and addresses understudied phenomena in a difficult and remote research environment. The dataset is a nice contribution to the literature and the paper worthy of publication after some improvements are made. Some suggestions are:
Figures 1 and 2: I found myself flipping between these two figures a lot. I know it may become quite large, but could I suggest merging these two into one big figure with four panels?
L 76 – 83: I agree with the first reviewer that the major goals of the research need to be better articulated. The experimental design sometimes comes across as a diversity of disparate field observations that are not tied together to address a couple key research hypotheses. A good example of this disconnect is on Line 79, where the authors talk about “hydrological dynamics”, but what does that mean? Is that the water budget or specific fluxes? Further to this point, on L 144, the authors state the primary hypothesis is that the rock glacier A1 influences aufeis formation in the outwash plain, but this is not mentioned in the Introduction.
L 297: I apologize, I am not a fan of supplementary information, and I suggest you bring important data into the main body of the text rather than have a reader dig for it in a different document.
Figures 6 – 8: It would be helpful for context if the axes of panels c and d in these figures were standardized. I found it hard to compare among them. Also, I am not sure you need the site labels. You could include select sites that are mentioned in the text to highlight your message, if that works.
L 452: I would like to make sure I understand correctly, the evidence that springs are snowmelt and rain fed is because their water plots directly on the local meteoric water line? I probably missed this, but stating explicitly so would help. Even better would be data from snow and rain itself. I believe the authors include some glacier water already.
L 477 – 480: I find it curious that the cold water outflow locations do not necessarily align with the aufeis location. Some thoughts on this disparity would be good to include in the paper.
L 501: Perhaps reference Figures 6 – 8 here.
L 528: I am not sure what “frozen content” means. Is this ice in the rock glacier, or any material that is below 0°C?
L 539: Perhaps rephrase this sentence as “ ….. aquifer provide the water but the decrease in river velocity and channel depth …. creates conditions favourable for the formation of aufeis.” This makes it explicit the role of each contributing factor.
Conclusion: This could all be merged into one paragraph.
Citation: https://doi.org/10.5194/egusphere-2025-117-RC2 -
AC2: 'Reply on RC2', Bastien Charonnat, 09 May 2025
We thank Referees 1 and 2 for their valuable comments, which will significantly contribute to improving the quality of our paper. Below, we respond individually to each of the referee’s comments:
COMMENT 1:
“Figures 1 and 2: I found myself flipping between these two figures a lot. I know it may become quite large, but could I suggest merging these two into one big figure with four panels?”
REPLY 1:
We appreciate Referee 2’s suggestion and recognize that visualizing the different scales may be challenging when the figures are separated. We have tentatively merged the two figures but without success. Not only the resulting map was very difficult to read but we realized that this merged figure would be placed within the Study Site section, presenting measurement and survey locations before their first mention in the Methods. This caused additional back-and-forth for readers as well. Therefore, we suggest to keep Figures 1 and 2 separate.
COMMENT 2:
“L 76 – 83: I agree with the first reviewer that the major goals of the research need to be better articulated. The experimental design sometimes comes across as a diversity of disparate field observations that are not tied together to address a couple key research hypotheses. A good example of this disconnect is on Line 79, where the authors talk about “hydrological dynamics”, but what does that mean? Is that the water budget or specific fluxes? Further to this point, on L 144, the authors state the primary hypothesis is that the rock glacier A1 influences aufeis formation in the outwash plain, but this is not mentioned in the Introduction.”
REPLY 2:
We thank Referee 2 for this relevant comment. We agree that the objectives and research questions should be expressed more clearly at the end of the Introduction. We also acknowledge that the term "hydrological dynamics" should be specified, as it refers to specific fluxes and processes influencing the water and hydrochemical budget at the catchment scale.
We also agree that the three-part multi-method approach would benefit from clearer presentation at the end of the Introduction, including the sub-objectives. These elements are currently outlined in Section 3.1 ("Method overview") but could be moved in the introduction and better structured for improved clarity.
We therefore suggest deleting Section 3.1 and propose to revise the final paragraph of the Introduction (LL 77-83) as follows:“This study examines the influence of rock glaciers on surface and shallow groundwater flow within alpine riverbed hydrological systems. Specifically, it focuses on characterizing water fluxes in a section of the Shár Shaw Tagà catchment (St. Elias Mountains, Yukon, Canada) that is constrained by a rock glacier. We hypothesize that the rock glacier modulates interactions between surface water and shallow groundwater, thereby affecting the overall functioning of the riverbed system.
To investigate these interactions, we employed a multimethod approach that was progressively refined as our observations and understanding of the system evolved:
- We hypothesized that the rock glacier influences the formation of aufeis on the downstream outwash plain. To test this, we used time-lapse camera monitoring to track the development of aufeis and to identify the location and timing of winter outflows.
- Given the rock glacier’s position at the outlet of a subcatchment and the lack of significant surface outflow, we hypothesized that it drains the subcatchment and contributes to river discharge via groundwater exfiltration. To assess this, we conducted a spring inventory, followed by a physico-hydrochemical characterization of springs and streams across the subcatchment. This allowed us to trace water sources and evaluate the rock glacier’s influence on stream composition.
- Building on the previous findings, we hypothesized that a specific section of the riverbed serves as a major zone of groundwater exfiltration. To identify and map these zones, we conducted drone-based thermal infrared (TIR) surveys, enabling us to delineate areas of groundwater emergence and assess their spatial extent and relative magnitude.
The novelty of this research lies in its focus on the indirect hydrological impacts of a rock glacier—particularly in the absence of a visible, well-defined outflow. By integrating hydrological, hydrogeological, and geochemical methods, this study advances our understanding of the complex role rock glaciers play in alpine watershed dynamics and provides insights with broader applicability to similar environments worldwide.”
COMMENT 3:
“L 297: I apologize, I am not a fan of supplementary information, and I suggest you bring important data into the main body of the text rather than have a reader dig for it in a different document.”
REPLY 3:
This is a pertinent comment. Since the sampling sites are already shown in Figure 2, we initially considered Table S1 as providing supplementary detail, following HESS guidelines. However, we are willing to incorporate Table S1 at the end of Section 3.3.1 and reference it in the text as Table 1.
COMMENT 4:
“Figures 6 – 8: It would be helpful for context if the axes of panels c and d in these figures were standardized. I found it hard to compare among them. Also, I am not sure you need the site labels. You could include select sites that are mentioned in the text to highlight your message, if that works.”
REPLY 4:
We appreciate this suggestion. Standardizing the axes would indeed facilitate comparison between figures. However, we note that it could reduce the readability of each individual figure by increasing the density of point clouds. Since our interpretations are made within each specific figure rather than through direct comparison, we propose to keep the current axes for clarity.
COMMENT 5:
“L 452: I would like to make sure I understand correctly, the evidence that springs are snowmelt and rain fed is because their water plots directly on the local meteoric water line? I probably missed this, but stating explicitly so would help. Even better would be data from snow and rain itself. I believe the authors include some glacier water already.”
REPLY 5:
This important question highlights a need for clarification.
The local meteoric water line (LMWL) is shown for reference but is not used as the primary basis for interpretation, given that it was derived from studies in the Whitehorse area, 220 km east (Birks et al., 2004). Although similar to Lhù’ààn Mân’ data 25 km east (Brahney et al., 2010), we prefer not to assume direct applicability.We propose to add this clarification LL. 201-202:
“The LMWL is displayed alongside the analyses results as reference (Fig. 6d, Fig. 7d and Fig. 8d) but we prefere not to assume direct applicability to our data.”
Across Canada, precipitation is expected to be enriched in heavy isotopes during the snow-free period and depleted in heavy isotopes during winter and spring (Gibson et al., 2020). Evidence for snowmelt- and rain-fed springs comes primarily from the observed depleted isotopic compositions, low mineral concentrations, and cold temperatures in early June (LL 301, 306–307, 312–313, 348–350), indicating snowmelt, and the enriched isotopic compositions in August reflecting rainfall influence (LL 388–389). This distinction is reinforced by contrasting results from N1 subsection springs, which display groundwater and glacier-fed signatures (LL 349–350, 386–388).
We propose to explicitly clarify this interpretation in Section 5.1 (Discussion), by changing the paragraph LL. 508-515 as:
“Contrary to initial hypotheses, no evidence was found of outflow originating from the head of the rock glacier’s subcatchment (comprising glaciers G-B1 and G-B2). Instead, the physico-hydrochemical characterization suggests that glacial meltwater entering the water to the river derives from upstream outwash plains of the main Shár Shaw Tagà catchment. In contrast, the other springs emerging at the front of the rock glacier appear to be linked to internal drainage systems within the rock glacier itself. These springs are primarily fed by snowmelt in the early season and by summer precipitation later in the season, with minimal or negligible glacier melt contribution, as shown by the physico-hydrochemical characterization of the samples collected in June 2022 and August 2022, respectively. Across Canada, precipitation is typically enriched in heavy isotopes during the snow-free period and depleted during winter and spring (Gibson et al., 2020). Accordingly, the depleted isotopic compositions, low solute concentrations, and cold temperatures measured in early June point to a snowmelt origin, while the enriched isotopic compositions in August reflect a stronger influence from rainfall. This seasonal distinction is further supported by contrasting results from springs in the N1 subsection, which exhibit characteristics of both groundwater and glacier-fed sources. Some springs likely reflect a mix of these sources, with their physicochemical parameters and clustering reflecting these dual influences depending on hydro-meteorological conditions and time periods.”
COMMENT 6:
“L 477 – 480: I find it curious that the cold water outflow locations do not necessarily align with the aufeis location. Some thoughts on this disparity would be good to include in the paper.”
REPLY 6:
Referee 2 raises an excellent point.
Specifically, the steeper slope in the N1 subsection may prevent aufeis formation at the cold outflow locations, as aufeis typically develop where river flow velocity decreases, such as braided channels and outwash plains (Hu and Pollard, 1997). Following this comment and Comment 9, we propose to modify LL. 538-540 as:
“Aufeis typically develop in areas where river flow velocity decreases, such as braided channels and outwash plains (Hu and Pollard, 1997). The TL monitoring suggests that the resurgences from the alluvial aquifer provide the water from the N1 subsection but the decrease in river flow velocity and channel depth creates conditions favourable for the formation of aufeis in the outwash plain immediately downstream of the rock glacier. In contrast, the steeper slope in the N1 subsection likely inhibits aufeis formation directly at the springs locations.”
COMMENT 7:
“L 501: Perhaps reference Figures 6 – 8 here.”
REPLY 7:
We agree. We will add references to Figures 6–8 at this point in the text.
COMMENT 8:
“L 528: I am not sure what “frozen content” means. Is this ice in the rock glacier, or any material that is below 0°C?”
REPLY 8:
This is a valid question. By "frozen content," we refer to any material below 0°C, including both massive ice and frozen ground within the rock glacier or talus slope. We clarified this in the manuscript LL. 526-527 as:
“The cold temperatures measured in the springs of the N1 subsection indicate that outflows from the alluvial aquifer are cooled by adjacent frozen content, such as massive ice or permafrost.”
COMMENT 9:
“L 539: Perhaps rephrase this sentence as “ ….. aquifer provide the water but the decrease in river velocity and channel depth …. creates conditions favourable for the formation of aufeis.” This makes it explicit the role of each contributing factor.”
REPLY 9:
We agree with this suggestion and we propose to rephrase the sentence accordingly to explicitly distinguish the role of each contributing factor, and in accordance with Comment 6:
“Aufeis typically develop in areas where river flow velocity decreases, such as braided channels and outwash plains (Hu and Pollard, 1997). The TL monitoring suggests that the resurgences from the alluvial aquifer provide the water from the N1 subsection but the decrease in river flow velocity and channel depth creates conditions favourable for the formation of aufeis in the outwash plain immediately downstream of the rock glacier. In contrast, the steeper slope in the N1 subsection likely inhibits aufeis formation directly at the springs locations.”
COMMENT 10:
“Conclusion: This could all be merged into one paragraph.”
REPLY 10:
We fully agree. We merged the Conclusion into a single paragraph, as suggested.
REFERENCES
Birks, S. J., Edwards, T. W. D., Gibson, J. J., Drimmie, R. J. and Michel, F. A.: Canadian network for isotopes in Precipitation, http://www.science.uwaterloo.ca/~twdedwar/cnip/cniphome.html, 2004.
Brahney, J., Clague, J. J., Edwards, T. W. D., and Menounos, B.: Late Holocene paleohydrology of Kluane Lake, Yukon Territory, Canada, Journal of Paleolimnology, 44(3), 873–885, https://doi.org/10.1007/s10933-010-9459-8,673, 2010.
Gibson J.J., Holmes T., Stadnyk T.A., Birks S.J., Eby P., and Pietroniro A.: 18O and 2H in streamflow across Canada, Journal of Hydrology: Regional Studies, Volume 32, 100754, ISSN 2214-5818, https://doi.org/10.1016/j.ejrh.2020.100754, 2020.
Hu, X., and Pollard, W.H.: The hydrologic analysis and modelling of river icing growth, North Fork Pass, Yukon Territory, Canada, Permafrost and Periglacial Processes, 8: 279–294, https://doi.org/10.1002/(SICI)1099-1530(199709)8:3<279::AID-PPP260>3.0.CO;2-7, 1997.
Citation: https://doi.org/10.5194/egusphere-2025-117-AC2
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AC2: 'Reply on RC2', Bastien Charonnat, 09 May 2025
Peer review completion
Journal article(s) based on this preprint
Data sets
Supplemental Material: Drone-Based Thermal Infrared Imagery for Detection of Cold Groundwater Exfiltration in Shár Shaw Tagà, Yukon, Canada Bastien Charonnat and Michel Baraer https://doi.org/10.5683/SP3/O57OMY
Video supplement
Supplemental Material: Drone-Based Thermal Infrared Imagery for Detection of Cold Groundwater Exfiltration in Shár Shaw Tagà, Yukon, Canada Bastien Charonnat and Michel Baraer https://doi.org/10.5683/SP3/O57OMY
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Bastien Charonnat
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Jeffrey M. McKenzie
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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In this manuscript, Charonnat B. et al. investigated the influence of a rock glacier on a riverbed hydrological system located in St. Elias Mountains (Yukon, Canada), using a multimethod approach. The first part of the study focused on the monitoring of the aufeis formation in an outwash plain through the installation of timelapse cameras. The second part investigated the water origin of the springs located in the upper Shár Shaw Tagà catchment and their impact on the river hydrochemistry through sampling and analysis of numerous water samples. The last part of the study examined groundwater exfiltration zones along the Shár Shaw Tagà River using a drone equipped with a thermal infrared camera. Results revealed that the rock glacier influences the riverbed hydrological system through mainly its geomorphic properties, by obstructing proglacial outwash plains and changing the channel structure and groundwater discharge. This geomorphic constraint allows groundwater resurgences from the alluvial aquifer, which promote aufeis formation and hydro-chemical disruption of streamflow.
This work is well written and contributes to increase knowledge on the hydrological role of rock glaciers in deglaciating catchments, highlighting the impact they have on the hydrogeomorphology of riverbeds due to their geomorphic properties. However, before the publication of this manuscript, the authors should address some general and specific comments, which are listed in the following sections.
General comments
Specific comments
L. 48: Please note that the permafrost creep is the result of the deformation of ice-debris matrix and the deformation concentrated in the shear horizon (most of the displacement occurs in the shear horizon). See for example Arenson et al. (2002)
LL. 85-89: The reference to Figure 1a is missing.
LL. 104-105: “The black frame outlines the extent of the map shown in Fig. 2a” (and not 2b)
LL. 122-125: The reference to Figure 2 is missing (location of subsections N1 and N2)
LL. 164-170: Could you please indicate the coordinates of the TL camera positions?
LL. 346-347: The reference to Figure 6d is missing.
References