the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 26 Jul 2024
Experimental study on the shear strength and failure mechanism of mountain glacier ice
Abstract. As global warming increases the frequency of ice avalanches, understanding the mechanical behavior of mountain glacier ice becomes critical. Through more than 250 field and laboratory tests, the variations of four kinds of glacier media with temperature and debris content were analyzed. The four types of glacial media are polycrystalline ice, ice-rock composite, fine debris ice, and coarse debris ice. Our comprehensive analysis reveals a positive correlation between ice density and debris content, but with a notable nonlinear decrease in porosity as debris content escalates. All types of ice have strain-softening characteristics in the shearing process. Shear strength is significantly modulated by debris content and temperature gradients. Fine debris ice exhibits the highest strength, followed by coarse debris ice, polycrystalline ice, and ice–rock composite. Polycrystalline ice displays the strength of nonlinear degradation with increasing temperature and ice– rock composite shows the strength of linear degradation with increasing temperature. Fine and coarse debris ice display the strength of the nonlinear enhancements with increasing debris content. The mechanism by which the strength of polycrystalline ice and ice-rock composites decreases with temperature increases is discussed. The strength enhancement of debris ice caused by increased debris content is expounded. It is believed that the emergence of liquid water is one of the reasons for the strength degradation. The solid particle effects (biting, friction, and crushing) are essential reasons for strength enhancement. This study addresses the research gap in mountain glacier ice mechanics driven by global warming, a previously underexplored subject. This investigation expounds on the nuanced interdependencies between temperature and debris content in determining glacier ice' shear strength, paving the way for force avalanche prediction models and disaster prevention strategies. It provides pivotal insights into mountain glacier ice behavior under different environmental conditions.
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RC1: 'Comment on egusphere-2024-1522', Anonymous Referee #1, 13 Aug 2024
With global warming, the ice avalanche and instability of glacier is becoming more frequent. Taking the mountain glacier ice as object, this manuscript studies the shear strength and failure mechanism of pure ice, ice-rock composite and debris ice, which is not only of great scientific value, but also has practical significance for the prevention and control of glacier disasters. The results reveal the shear strength of glacier ice with temperature and debris content, as well as the shear failure mechanism of four kinds of glacier media. And it is commendable that the field test experience at Gongga Mountain Glacier and valuable test data are carried out. The experiment and result is novel and insightful. Generally, the structure and logic of this manuscript is complete and well-prepared for this type of publication. The figures are exquisite and clear to deliver the ideas. Except some minor problem to be improved in the next version, this manuscript has met the standard for publication. Therefore, I would suggest a MINOR REVISION before accepting for publication.
Specific comments and suggestions are outlined below.
- The abstract is not concise, particularly when presenting the highlights and kind findings.
- Provide detailed explanations of key terms and concepts to aid reader understanding. For example, Line 31: How does the author define ice avalanche? Add a definition in the introduction.
- Line 67: "... has not been thoroughly investigated. "Does that mean glacial ice type or detrital ice? Some clarification is needed.
- Line 80-82 and line 42 had logical problems and needed to be adjusted. It is proposed that line 80-82 "Moore, (2014) ... between the ice and the rock "in the" Systematic consideration..." The front.
- Line 91: The text in Figure 1 is not very clear. "debris-ice" in the figure is inconsistent with "debris ice" in the text. Check and modify similar situations in the manuscript.
- Line 119: The details of "preconsolidation pressure freezing" should be explained.
- The citation format should be consistent. Such as line 200 "(Fan 2021)" and line 67 "(Moore, 2014)".
- Line 239: "be-tween "should be changed to "between". Similar situations in the paper should be modified.
- Line 305 and 378: The subheadings do not match the content below.
- Line 406: Replace "A high debris-content ice crystal can break into fragments" with "A high debris-content ice can break into fragments".
- Line 417: The field glacier ice experiment in this paper is a new attempt on the Tibetan Plateau, but there are still room for improvement. Therefore, it is recommended to discuss the uncertainty of the test method.
- It's recommended to polish the manuscript or check by a native person.
- Reduce Chinese references in articles. At the same time, ensure the standardization and consistency of references, especially conference papers and reports.
- The conclusion should be further refined.
Citation: https://doi.org/10.5194/egusphere-2024-1522-RC1 -
AC1: 'Reply on RC1', Huanle Zhao, 28 Aug 2024
With global warming, the ice avalanche and instability of glacier is becoming more frequent. Taking the mountain glacier ice as object, this manuscript studies the shear strength and failure mechanism of pure ice, ice-rock composite and debris ice, which is not only of great scientific value, but also has practical significance for the prevention and control of glacier disasters. The results reveal the shear strength of glacier ice with temperature and debris content, as well as the shear failure mechanism of four kinds of glacier media. And it is commendable that the field test experience at Gongga Mountain Glacier and valuable test data are carried out. The experiment and result is novel and insightful. Generally, the structure and logic of this manuscript is complete and well-prepared for this type of publication. The figures are exquisite and clear to deliver the ideas. Except some minor problem to be improved in the next version, this manuscript has met the standard for publication. Therefore, I would suggest a MINOR REVISION before accepting for publication.
A: Thank you for the reviewer's comments and support. Ice avalanches on the Tibetan Plateau are beginning to be widely noticed as a new type of natural disaster. We believe that as global climate change intensifies (UN Secretary-General Guterres declared on July 27, 2023: The era of global boiling has arrived), ice avalanches will continue to occur in the future. This is exactly what we are worried about, as these natural disasters can have devastating effects on communities living near glaciers. Therefore, to cope with the increasing threat of glacier melt on the Tibetan Plateau, we propose a dynamic evaluation of the glacier stability as a means of predicting and mitigating potential disasters. The shear strength characteristics and failure mechanism of mountain glaciers that we are currently studying are the basis of this work. It provides researchers with an understanding of glacier ice strength, sliding-shear failure mechanisms, and mechanical parameters for evaluating glacier stability.
Specific comments and suggestions are outlined below.
The abstract is not concise, particularly when presenting the highlights and kind findings.
A: Thank you for the reviewer's suggestion. We have streamlined the abstract and reorganized the sentences involving highlights and findings. The revised abstract is as follows:
Global warming increases the frequency of ice avalanches in mountain areas. Ice avalanches are the macroscopic manifestation of the deformation and failure of glacier ice materials. Understanding the mechanical behavior of mountain glacier ice becomes critical. Through more than 250 field and laboratory tests, the variations of four types (polycrystalline ice, ice-rock composite, fine debris ice, and coarse debris ice) of glacier materials with temperature and debris content were analyzed. Our analysis reveals: In terms of physical characteristics, a positive correlation between ice density and debris content, with a notable nonlinear decrease in porosity as debris content escalates. In terms of deformation characteristics, all types of ice have strain-softening characteristics in the shearing process. In terms of strength characteristics, the shear strength is significantly modulated by debris content and temperature gradients. Fine debris ice exhibits the highest strength, followed by coarse debris ice, polycrystalline ice, and ice–rock composite. This means that the ice-rock interface is quite fragile. Polycrystalline ice displays the strength of nonlinear degradation with increasing temperature and ice–rock composite shows the strength of linear degradation with increasing temperature. Fine and coarse debris ice display the strength of the nonlinear enhancements with increasing debris content. In terms of failure mechanism, it is believed that the liquid water produced by temperature rise or pressure melting is one of the reasons for the decrease in strength. The strength enhancement of debris ice is caused by increased debris content. The solid particle effects (biting, friction, and crushing) are essential reasons for strength enhancement. This study addresses the research gap in mountain glacier ice mechanics driven by global warming, a previously underexplored subject. This study complements the study of mountain glacier ice mechanics driven by global warming, which is a subject that has not been fully explored before. This investigation expounds on the nuanced interdependencies between temperature and debris content in determining glacier ice' shear strength, paving the way for force avalanche prediction models and disaster prevention strategies. It provides pivotal insights into mountain glacier ice behavior under different environmental conditions.
Provide detailed explanations of key terms and concepts to aid reader understanding. For example, Line 31: How does the author define ice avalanche? Add a definition in the introduction.
A: Thank you very much. We fully accept the reviewer's suggestion. We define ice avalanche as follows:
Ice avalanches (IAs) are sudden releases of large amounts of ice from a glacier. The ice quickly collapses or slides down the slope while breaking into smaller pieces (Cuffey and Paterson, 2010). The terms "glacier avalanche", "glacier collapse", "glacier detachment" and "ice collapse" are all included in this definition. In addition, we believe that ice-rock avalanches, glacier landslides (different from periglacial landslides), and ice-rich landslides also belong to the broad sense of ice avalanches.
At the same time, we have explained other abbreviations in the manuscript:
The second generation of the multi-functional Yeya Direct Shear machine (YDS-2)
The second generation of the XieJian direct shear machine (XJ-2)
Line 67: "... has not been thoroughly investigated. "Does that mean glacial ice type or detrital ice? Some clarification is needed.
A: Thank you for the reviewer's reminder. There is indeed ambiguity here, and we have clarified it here to make the innovation of our research clearer:
Mountain glacier ice, with its unique formation process, structure, and composition, particularly due to the incorporation of bedrock powder (Moore, 2014). Its shear strength difference and failure mechanism under the influence of structure and environmental factors have not been fully explored.
Line 80-82 and line 42 had logical problems and needed to be adjusted. It is proposed that line 80-82 "Moore, (2014) ... between the ice and the rock "in the" Systematic consideration..." The front.
A: Thank you, this is a very good suggestion and we fully accept it. We have revised the manuscript to make it more logical.
Line 91: The text in Figure 1 is not very clear. "debris-ice" in the figure is inconsistent with "debris ice" in the text. Check and modify similar situations in the manuscript.
A: Thank you for the reviewer's comments. We have carefully checked the figures in the manuscript in light of this comment and made the following changes:
In addition to changing "debris-ice" to "debris ice" in the supplement file Figure 1, we have bolded the text in the legend.
We have simplified Figure 15 to make it clearer. As shown in the supplement file Figure 15.
Line 119: The details of "preconsolidation pressure freezing" should be explained.
A: Thanks to the reviewer. The "preconsolidation pressure freezing" in the manuscript is consistent with the "consolidated by a weight pan" in Huang et al. (2023), Huang et al. (2024), and Meng et al. (2024). That is, in a fixed container, a specific pressure is applied to compact the sample so that the density of the sample is consistent with the density of glacial ice. The whole process needs to be carried out in a low-temperature environment.
The citation format should be consistent. Such as line 200 "(Fan 2021)" and line 67 "(Moore, 2014)".
A: Thank you for the careful review. We check the full text against this comment, for example:
"(Fitzsimons et al. (2024))" -- "(Fitzsimons et al. 2024)"
"(Bondesan et al. 2023)" -- "(Bondesan et al., 2023)"
"Fish and Zaretsky, (1997)" -- "Fish and Zaretsky (1997)"
Line 239: "be-tween "should be changed to "between". Similar situations in the paper should be modified.
A: Thank you for the kind reminder from the reviewer. We apologize for such editing errors. We have carefully checked the full text:
"be-tween" -- "between"
"Consequent-ly" -- "Consequently"
"adhe-sion" -- "adhesion"
"pre-ferred" -- "preferred"
"Geosci-ence" -- "Geoscience"
"Ti-bet" -- "Tibet"
"progres-sive" -- "progressive"
"polycrys-talline" -- "polycrystalline"
"de-structiveness" -- "destructiveness"
"Bul-letin" -- "Bulletin"
"Ti-betan" -- "Tibetan"
" ℃" -- "℃"
Line 305 and 378: The subheadings do not match the content below.
A: Thank you for the reviewer's comments. We adopted this comment and modified the subheading according to the context. Specifically:
"4.1 Inference of the strength degradation mechanism with increasing temperature" -- "4.1 Shear strength and failure mechanism of glacier ice under temperature influence"
"4.2 Inference of strength reinforcement mechanism with increased debris content" -- "4.2 Shear strength and failure mechanism of glacier ice under debris"
Line 406: Replace "A high debris-content ice crystal can break into fragments" with "A high debris-content ice can break into fragments".
A: Thank you for the reviewer's careful review. We have revised the language issues here.
Line 417: The field glacier ice experiment in this paper is a new attempt on the Tibetan Plateau, but there are still room for improvement. Therefore, it is recommended to discuss the uncertainty of the test method.
A: Thank you for the good suggestions from the reviewer. At the beginning of the experiment, we carefully searched for international standards and specifications for glacier ice mechanics tests and found "ITTC Quality System Manual Recommended Procedures and Guidelines- Test Methods for Model Ice Properties", but there was nothing available. Therefore, we can only refer to the geotechnical mechanics standards, which will indeed have some inadaptability. In this regard, we actively discuss the uncertainty of the method to make the method more valuable as a reference. The discussion is as follows:
4.3.1 Standardized testing methods
There is no consistent standard and specification for the glacier ice mechanic test. As can be seen from Table 5, there is no uniformity in the test methods for glacier ice mechanics, and there is potential to construct a set of method standards for glacier ice mechanics tests in the future. As a geological material, glacier ice exhibits a strength value that falls between that of soil and rock but is more akin to soil in terms of properties and behavior. For this reason, our method of preparing reshaped ice samples for indoor testing adheres to the established standards used in soil mechanics tests. Numbers 4, 5, 7, and 8 in Table 5 also refer to similar standards, although numbers 4 and 8 are not explicitly mentioned. Our difference lies in the test instrument, sample shape, size, and thermal equilibration time. Due to the difference in test instruments, the shape and size of the sample are different, and the required thermal equilibrium time is also different. It is well known that the size effect of laboratory tests cannot be avoided, which may affect the specific value of the test, but this does not affect the trend analysis we focus on. In addition, it is more appropriate for us to choose a multifunctional testing instrument for rock and soil mechanics properties when researching glacier ice. Using soil mechanics instruments alone would be insufficient (Full-Scale Range) due to the different properties of glacier ice, and using rock mechanics instruments would provide a range that is too large. At present, the use of instruments on the market to carry out glacial ice mechanics tests requires improved instruments (except for No.1 and 8 in Table 5), such as adding environmental control parts. Although our use of liquid nitrogen to control temperature is not the best method, it is sufficient to control the temperature within the error range under a fast shear test.
Table 5. Comparison of glacier ice mechanics test methods, As shown in the supplement file Table 5_01 and Table 5_02.
References：
Akroyd, T. N. W.: Laboratory testing in soil engineering. Soil Mechanics Ltd., London, 1957.
Fitzsimons, S. J., McManus, K. J., and Lorrain, R. D.: Structure and strength of basal ice and substrate of a dry-based glacier: evidence for substrate deformation at sub-freezing temperatures, Annals of Glaciology, 28, 236-240, https://doi.org/10.3189/172756499781821878, 1999.
Fitzsimons, S. J., Lorrain, R. D., and Vandergoes, M. J.: Behaviour of subglacial sediment and basal ice in a cold glacier, Geological Society, London, Special Publications, 176, 181-190, https://doi.org/10.1144/GSL.SP.2000.176.01.14, 2000.
Fitzsimons, S. J., McManus, K. J., Sirota, P., and Lorrain, R. D.: Direct shear tests of materials from a cold glacier: implications for landform development, Quaternary international, 86, 129-137, https://doi.org/10.1016/S1040-6182(01)00055-6, 2001.
Kang, J., Liu, E. L., Song, B. T., Su, Y., Wang, P., Wang, D., and Ma, F. L.: Study on mechanical properties and constitutive model for polycrystalline ice samples, Environmental Earth Sciences, 82, 585, https://doi.org/10.1007/s12665-023-11218-1, 2023.
Mamot, P., Weber, S., Schröder, T., and Krautblatter, M.: A temperature- and stress-controlled failure criterion for ice-filled permafrost rock joints, The Cryosphere, 12, 3333–3353, https://doi.org/10.5194/tc-12-3333-2018, 2018.
Sirota, P. J.: The structure and strength of basal ice in the Suess Glacier, Antarctica, PhD thesis, University of Otago, Dunedin, New Zealand, 1999.
It's recommended to polish the manuscript or check by a native person.
A: Thank you for the reviewer's suggestions. After we have revised the manuscript, we are looking for a professional native person to check the language of the manuscript. At the same time, we are also considering the polishing plan.
Reduce Chinese references in articles. At the same time, ensure the standardization and consistency of references, especially conference papers and reports.
A: Thank you for the reviewers' comments. We fully adopted these comments. We deleted some Chinese literature in the article, supplemented it with similar international journal literature, and also added several reference-worthy literature. Corresponding changes have also been made in the text. The specific changes are as follows:
(1) Delete:
Dai, Z. H., and Lu, C. J.: Mechanical explanations on mechanism of slope stability, Chinese Journal of Geotechnical Engineering, 28, 1191-1197, 2006, (in Chinese).
Guo, Y. K., and Meng, W. Y.: Experimental investigations on mechanical properties of ice, Journal of North China University of Water Resources and Electric Power (Natural Science Edition), 36, 40-43, https://doi.org/10.3969/j.issn.1002-5634. 2015.03.010, 2015 (in Chinese).
Li, Y., Tang, M. G., Shuai, Y. Y., Zhao, H. L., Li, C. R., Ni, W. T., and Li, G.: Inversion and prediction simulation study of Aru Ice Avalanche-Debris flow motion process. Journal of Disaster Prevention and Mitigation Engineering [preprint], http://kns.cnki.net/kcms/detail/32.1695.P.20231214.1834.002.html, 15 December 2023 (in Chinese).
(2) Replacement:
"Xu, L. M., Wang, T. Z., Qi, D. Q., Yu, C. H., and Gu, L.: Study on geotechnical shear band localization retrospect and prospect, Chinese Quarterly of Mechanics, 25, 484-489, https://doi.org/10.15959/j.cnki.0254-0053.2004.04.008, 2004 (in Chinese)." -- "Hobbs, B. E., Mühlhaus, H. B., and Ord, A.: Instability, softening and localization of deformation, Geological Society, London, Special Publications, 54, 143-165, https://doi.org/10.1144/GSL.SP.1990.054.01.15, 1990."
(3) Supplement：
Akroyd, T. N. W.: Laboratory testing in soil engineering. Soil Mechanics Ltd., London, 1957.
Fitzsimons, S. J., McManus, K. J., and Lorrain, R. D.: Structure and strength of basal ice and substrate of a dry-based glacier: evidence for substrate deformation at sub-freezing temperatures, Annals of Glaciology, 28, 236-240, https://doi.org/10.3189/172756499781821878, 1999.
Fitzsimons, S. J., Lorrain, R. D., and Vandergoes, M. J.: Behaviour of subglacial sediment and basal ice in a cold glacier, Geological Society, London, Special Publications, 176, 181-190, https://doi.org/10.1144/GSL.SP.2000.176.01.14, 2000.
Fitzsimons, S. J., McManus, K. J., Sirota, P., and Lorrain, R. D.: Direct shear tests of materials from a cold glacier: implications for landform development, Quaternary international, 86, 129-137, https://doi.org/10.1016/S1040-6182(01)00055-6, 2001.
Kang, J., Liu, E. L., Song, B. T., Su, Y., Wang, P., Wang, D., and Ma, F. L.: Study on mechanical properties and constitutive model for polycrystalline ice samples, Environmental Earth Sciences, 82, 585, https://doi.org/10.1007/s12665-023-11218-1, 2023.
Li, K. Q. and Yin, Z. Y.: State of the art of coupled thermo–hydro-mechanical–chemical modelling for frozen soils, Archives of Computational Methods in Engineering, 2024, 1-58, https://doi.org/10.1007/s11831-024-10164-w, 2024.
Mamot, P., Weber, S., Schröder, T., and Krautblatter, M.: A temperature- and stress-controlled failure criterion for ice-filled permafrost rock joints, The Cryosphere, 12, 3333–3353, https://doi.org/10.5194/tc-12-3333-2018, 2018.
Pfluger, F., Weber, S., Steinhauser, J., Zangerl, C., Fey, C., Fürst, J., and Krautblatter, M.: Massive permafrost rock slide under warming polythermal glacier (Bliggspitze, Austria), EGUsphere, 2024, 1-44, https://doi.org/10.5194/egusphere-2024-2509, 2024.
Sirota, P. J.: The structure and strength of basal ice in the Suess Glacier, Antarctica, PhD thesis, University of Otago, Dunedin, New Zealand, 1999.
We checked the correctness and consistency of the references and revised them as follows:
"Cuffey, K. M., and Paterson, W. S. B.: The physics of glaciers. Academic Press, America, ISBN 978-0-12-369461-4, 2010." -- "Cuffey, K. M. and Paterson, W. S. B.: The physics of glaciers, 4th edn. Butterworth-Heinemann, Oxford, ISBN 9780123694614, 2010."
"IPCC.: Sections. In Climate Change 2023: Synthesis Report. Contribution of Working Groups I, II and III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, H. Lee and J. Romero (eds.)]. IPCC, Geneva, Switzerland, pp 35-115. https://doi.org/10.59327/IPCC/AR6-9789291691647, 2023." -- "IPCC: Climate Change 2023: Synthesis Report. Contribution of Working Groups I, II and III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change, edited by: Core Writing Team, Lee, H., and Romero, J., IPCC, Geneva, Switzerland., Intergovernmental Panel on Climate Change (IPCC), https://doi.org/10.59327/IPCC/AR6-9789291691647, 2023."
"Mizukami, N., and Maeno, N.:" -- "Mizukami, N. and Maeno, N.:"
"Nater, P., Arenson, L. U., Springman, S. M.:" -- " Nater, P., Arenson, L. U., and Springman, S. M.:"
"Journal of glaciology and geocryology" -- "Journal of Glaciology and Geocryology"
"50 Mm3" -- "50 Mm3"
The conclusion should be further refined.
A: Thank you for the reviewer's comments. We have improved the conclusions:
To deepen the understanding of the physical and mechanical characteristics of mountain glacier ice. we selected the Gongga Mountain glacier as our main study site, aiming to comprehensively investigate the shear strength characteristics of glacier ice under varying temperatures and debris contents. In situ studies at the Gongga Glacier examined glacial ice properties, with direct shear tests conducted at -0.5°C under normal stresses ranging from 100 to 500 kPa. These tests established a baseline for indoor reshaped polycrystalline ice's physical and mechanical properties. Further tests on polycrystalline ice and ice–rock composites were performed at temperatures of -0.5, -10, -20, -30, and -40°C, using remodeled polycrystalline ice, gneiss under the same range of normal stresses. Direct shear tests were carried out on fine and coarse debris ice with fine debris contents of 10, 15, 20, 25, and 30% and coarse debris contents of 20, 30, 40, 50, and 60% under identical normal stresses. The variations in deformation failure and shear strength for glacier ice under different conditions were obtained, and the deformation evolution process and shear strength mechanism were analyzed. The four main conclusions were as follows:
(1) The debris content is positively correlated with density, negatively correlated with porosity, and shows a nonlinear decreasing trend.
(2) Different types of glacier ice have strain-softening phenomena in the shear process. The peak strength is displayed: fine debris ice (466 kPa) > coarse debris ice (367 kPa) > polycrystalline ice (259 kPa) > ice–rock composite (192 kPa).
(3) Polycrystalline ice displays the strength of nonlinear degradation with increasing temperature and ice–rock composites show the strength of linear degradation with increasing temperature display strength degradation with increasing temperature. Fine and coarse debris ice display exhibits the strength of the nonlinear enhancements with increasing debris content.
(4) The emergence of liquid water is one of the reasons for the degradation of strength, which can be observed in the destructive samples; also, the mechanism by which the increase in debris content leads to the strength enhancement of debris ice is discussed. It is believed that solid particle effects (biting, friction, and crushing) are essential reasons for strength enhancement, which can also be observed in destructive samples.
(5) We discussed future work and believed that standardization of glacier ice mechanics test methods is necessary, which will facilitate the integration of experimental data. Furthermore, it would be more valuable to establish a statistically significant glacier ice physics and mechanics model for application in glacier stability assessment, as this would provide more representative data for predicting potential hazards and mitigating risks in high-altitude regions.
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RC2: 'Comment on egusphere-2024-1522', Adrien Gilbert, 25 Oct 2024
This study presents the results of direct shear test experiments on ice as a function of temperature and rock debris content, carried out according to the standard geotechnical approach to determine the shear strength of materials. The ice samples, collected in the field and replicated in the laboratory, are intended to be representative of natural mountain glacier ice. This provides valuable data for determining the maximum shear stress that can be accommodated by glacier ice and has direct application to better anticipate and model gravity-driven glacier instabilities that generate ice avalanches.
I think this manuscript gives a useful quantification of the shear strength of natural glacier ice that can be used as a stress threshold to determine the occurrence of potential glacier collapse. The topic and results are thus valuable for the glaciology community and could be published in The Cryosphere.
However, at this stage, the writing is generally very difficult to follow and the logical links between sentences and ideas are missing throughout the manuscript. Many sentences are vague and seem unrelated to the topic of the paragraph. The reader is often left wondering why a statement is made without any explanation of how it supports the idea being developed. There is also a lack of rigour in how the work of others is described and compared with this study.
Although the language is correct, the quality of the writing definitely does not meet the journal's requirements for publication. I suggest major revisions that need to be made for the manuscript to be considered for publication. I hope that my comments will help the authors to make the necessary improvements.
Best regards,
Adrien Gilbert
General comments
- The abstract needs to be rewritten. The current one does not fulfil what is expected from an abstract where the topic, method, results and main implications of the study should be clearly stated. Instead, it gives a random, exhaustive list of results with sentences juxtaposed. The method is not clear and we do not know how your results are interpreted and what the implications are. For example, instead of saying "The strength enhancement of debris ice caused by increased debris content is expounded", the authors should explicitly tell the reader what their findings are regarding the mechanism of strength enhancement caused by debris. Further comments on the abstract can be found in the attached pdf.
- Introduction: The same comments that can be made about the abstract apply to the introduction section, which is difficult to read because of the juxtaposition of sentences that lack logical connections between them. The reference to other studies is also poorly done, as the authors often limit their statement to "XX et al. studied this and that ..." instead of actually saying what the results of the cited references are. See my comments in the attached pdf.
- As the manuscript is trying to reach the glaciological community, which is not necessarily familiar with geoengineering, a better description of the method should be done. For example, it should be explicitly stated that you are doing direct shear strength tests, what they are and what they are usually done for (soil mechanics...). Also a general explanation of what the stress vs displacement curve is and what it shows would be good. For example, it was not obvious to me that the residual stress after peak is actually friction along the failure interface (if I am correct?). You should also say why this approach is relevant to your goal of estimating glacier stability.
- In the glaciology community, ice is known more as a viscous material and it should be clear in your study that you are working in the brittle regime and a reference to the work of E.M. Schulson (2001) is missing. Also, you don't even specify the strain rate regime imposed in your experiment, which is important to know in order to make it clear that you are looking at the elastic response and the brittle regime, not viscous deformations.
- My final general comment concerns the lack of synthesis of your results in relation to the application of your findings to modelling glacier collapse. I think this is attempted in section 4.3, but this section is really vague with many unclear statements. The glaciologist reader would like to know what is the most likely shear strength of the ice at the glacier base, where the maximum stress is usually reached. Your study could provide some useful values. For example, Kääb et al. (2021) used the glacier-scale force balance done in Gilbert et al. (2018) for the Aru glacier collapse to give a rough estimate of the shear stress at which the frozen margin (~-4°C according to Gilbert et al. (2018)) of the detachment broke. They found 280 kPa, how does this compare with your results?
Specific comments
You will find a list of 70 corrections and specific comments embedded in the annotated PDF in attachment. Some are redundant with my general comments but may help to clarify them.
References
Kääb, A., Jacquemart, M., Gilbert, A., Leinss, S., Girod, L., Huggel, C., Falaschi, D., Ugalde, F., Petrakov, D., Chernomorets, S., Dokukin, M., Paul, F., Gascoin, S., Berthier, E., and Kargel, J. S.: Sudden large-volume detachments of low-angle mountain glaciers – more frequent than thought?, The Cryosphere, 15, 1751–1785, https://doi.org/10.5194/tc-15-1751-2021, 2021.
Schulson, E. M.: Brittle failure of ice, Engineering Fracture Mechanics, 68, 1839–1887, https://doi.org/10.1016/S0013-7944(01)00037-6, 2001.
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RC3: 'Comment on egusphere-2024-1522', Anonymous Referee #3, 16 Dec 2024
Minggao Tang and co-author present a manuscript related to an experimental study on the shear strength and failure mechanism of mountain glacier ice. The manuscript aims to investigate the mechanical behavior of glacier ice in the context of global warming. The study involves over 250 field and laboratory tests to analyze the variations in shear strength and failure mechanisms of four types of glacier materials: polycrystalline ice, ice-rock composite, fine debris ice, and coarse debris ice. The study focuses on the Gongga Glacier in Sichuan Province, China. It involves field investigations for in-situ glacier ice and laboratory tests on various samples. Based on the results, the authors conclude that debris content and temperature significantly influence the shear strength of glacier ice. They emphasizes the importance of these factors in developing models for predicting ice avalanches and implementing disaster prevention strategies.
I’ve been struggling with this paper as I understand that the authors put a lot of effort into their material testing and laboratory work. I read it more than once, but finally came to the conclusion that I cannot recommend the study to be published as I see a lack of fundamental understanding of the problem the authors like to address with their study. There are other, more minor issues with the manuscript, but the main problem with this manuscript, i.e. the research conducted, is the relevance and applicability of the testing on the problem the authors are trying to solve. Most notably, the authors want to address the challenges of glacier instability in a warming climate. As such, we are talking about changes in ice and bedrock temperatures of a few degrees centigrade and most critically, changes just below 0°C. However, the authors only tested at -0.5°C and then at -10°C to -40°C, i.e. temperature ranges that are absolutely irrelevant for the problem. Most importantly, and also shown by many of the references cited by the authors, we cannot simply extrapolate the trends observed at these temperatures to the behaviour between 0°C and -2°C, the range of highest interest. Similarly, the effect of debris must be studied at these warm temperatures and not simply at -20°C as the unfrozen water content is very different at these warmer conditions and therefore the strength behaviour would be vary substantially. The authors presented laboratory study that does show some interesting data, but those are completely irrelevant and must not be used for the problem discussed. In fact, I do find it irresponsible if those data would be used to try to solve the problems of glacier instabilities as they would misrepresent the actual conditions. For those reasons, I’m recommending rejecting the manuscript.
I do have some other concerns regarding the laboratory testing. For example, freezing the samples with liquid nitrogen generates completely different ice crystals than how ice forms in nature. While the authors claim that the density and the porosity of the samples are similar in the field as in the laboratory, the mechanical behaviour also depends on the ice crystals. I suggest that the authors spend some time reading literature by E.M. Schulson and the familiarize themselves with some ice fracture mechanics.
It is also important to study the strain rates at which the samples are sheared. The faster the shearing the stronger the sample, making it more brittle. But since the strength depends on the applied strain rate, this influence must also be studied, which it wasn’t. Again, several of the references cited to discuss this point and I strongly recommend that the authors go back and do a detailed literature review. And while they do a detailed review, they may also find some additional references that they have missed, including papers by Guentzel, Krautblatter, Davies, Yasufuku, Arenson and Schulson.
Finally, if the authors decide to submit a paper again, they must improve the language. Overall, it is reasonably well written, and I understand that this is not easy. However, they must pay attention that words are properly used, that details are adequately described and that they stay humble. Words such as “glacial media”, “escalating debris content”, “nonlinear enhancements”, “biting”, “expounds”, “force avalanche”, “natives”, “scrutinize” etc. were often used wrongly.
Citation: https://doi.org/10.5194/egusphere-2024-1522-RC3
Status: closed
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RC1: 'Comment on egusphere-2024-1522', Anonymous Referee #1, 13 Aug 2024
With global warming, the ice avalanche and instability of glacier is becoming more frequent. Taking the mountain glacier ice as object, this manuscript studies the shear strength and failure mechanism of pure ice, ice-rock composite and debris ice, which is not only of great scientific value, but also has practical significance for the prevention and control of glacier disasters. The results reveal the shear strength of glacier ice with temperature and debris content, as well as the shear failure mechanism of four kinds of glacier media. And it is commendable that the field test experience at Gongga Mountain Glacier and valuable test data are carried out. The experiment and result is novel and insightful. Generally, the structure and logic of this manuscript is complete and well-prepared for this type of publication. The figures are exquisite and clear to deliver the ideas. Except some minor problem to be improved in the next version, this manuscript has met the standard for publication. Therefore, I would suggest a MINOR REVISION before accepting for publication.
Specific comments and suggestions are outlined below.
- The abstract is not concise, particularly when presenting the highlights and kind findings.
- Provide detailed explanations of key terms and concepts to aid reader understanding. For example, Line 31: How does the author define ice avalanche? Add a definition in the introduction.
- Line 67: "... has not been thoroughly investigated. "Does that mean glacial ice type or detrital ice? Some clarification is needed.
- Line 80-82 and line 42 had logical problems and needed to be adjusted. It is proposed that line 80-82 "Moore, (2014) ... between the ice and the rock "in the" Systematic consideration..." The front.
- Line 91: The text in Figure 1 is not very clear. "debris-ice" in the figure is inconsistent with "debris ice" in the text. Check and modify similar situations in the manuscript.
- Line 119: The details of "preconsolidation pressure freezing" should be explained.
- The citation format should be consistent. Such as line 200 "(Fan 2021)" and line 67 "(Moore, 2014)".
- Line 239: "be-tween "should be changed to "between". Similar situations in the paper should be modified.
- Line 305 and 378: The subheadings do not match the content below.
- Line 406: Replace "A high debris-content ice crystal can break into fragments" with "A high debris-content ice can break into fragments".
- Line 417: The field glacier ice experiment in this paper is a new attempt on the Tibetan Plateau, but there are still room for improvement. Therefore, it is recommended to discuss the uncertainty of the test method.
- It's recommended to polish the manuscript or check by a native person.
- Reduce Chinese references in articles. At the same time, ensure the standardization and consistency of references, especially conference papers and reports.
- The conclusion should be further refined.
Citation: https://doi.org/10.5194/egusphere-2024-1522-RC1 -
AC1: 'Reply on RC1', Huanle Zhao, 28 Aug 2024
With global warming, the ice avalanche and instability of glacier is becoming more frequent. Taking the mountain glacier ice as object, this manuscript studies the shear strength and failure mechanism of pure ice, ice-rock composite and debris ice, which is not only of great scientific value, but also has practical significance for the prevention and control of glacier disasters. The results reveal the shear strength of glacier ice with temperature and debris content, as well as the shear failure mechanism of four kinds of glacier media. And it is commendable that the field test experience at Gongga Mountain Glacier and valuable test data are carried out. The experiment and result is novel and insightful. Generally, the structure and logic of this manuscript is complete and well-prepared for this type of publication. The figures are exquisite and clear to deliver the ideas. Except some minor problem to be improved in the next version, this manuscript has met the standard for publication. Therefore, I would suggest a MINOR REVISION before accepting for publication.
A: Thank you for the reviewer's comments and support. Ice avalanches on the Tibetan Plateau are beginning to be widely noticed as a new type of natural disaster. We believe that as global climate change intensifies (UN Secretary-General Guterres declared on July 27, 2023: The era of global boiling has arrived), ice avalanches will continue to occur in the future. This is exactly what we are worried about, as these natural disasters can have devastating effects on communities living near glaciers. Therefore, to cope with the increasing threat of glacier melt on the Tibetan Plateau, we propose a dynamic evaluation of the glacier stability as a means of predicting and mitigating potential disasters. The shear strength characteristics and failure mechanism of mountain glaciers that we are currently studying are the basis of this work. It provides researchers with an understanding of glacier ice strength, sliding-shear failure mechanisms, and mechanical parameters for evaluating glacier stability.
Specific comments and suggestions are outlined below.
The abstract is not concise, particularly when presenting the highlights and kind findings.
A: Thank you for the reviewer's suggestion. We have streamlined the abstract and reorganized the sentences involving highlights and findings. The revised abstract is as follows:
Global warming increases the frequency of ice avalanches in mountain areas. Ice avalanches are the macroscopic manifestation of the deformation and failure of glacier ice materials. Understanding the mechanical behavior of mountain glacier ice becomes critical. Through more than 250 field and laboratory tests, the variations of four types (polycrystalline ice, ice-rock composite, fine debris ice, and coarse debris ice) of glacier materials with temperature and debris content were analyzed. Our analysis reveals: In terms of physical characteristics, a positive correlation between ice density and debris content, with a notable nonlinear decrease in porosity as debris content escalates. In terms of deformation characteristics, all types of ice have strain-softening characteristics in the shearing process. In terms of strength characteristics, the shear strength is significantly modulated by debris content and temperature gradients. Fine debris ice exhibits the highest strength, followed by coarse debris ice, polycrystalline ice, and ice–rock composite. This means that the ice-rock interface is quite fragile. Polycrystalline ice displays the strength of nonlinear degradation with increasing temperature and ice–rock composite shows the strength of linear degradation with increasing temperature. Fine and coarse debris ice display the strength of the nonlinear enhancements with increasing debris content. In terms of failure mechanism, it is believed that the liquid water produced by temperature rise or pressure melting is one of the reasons for the decrease in strength. The strength enhancement of debris ice is caused by increased debris content. The solid particle effects (biting, friction, and crushing) are essential reasons for strength enhancement. This study addresses the research gap in mountain glacier ice mechanics driven by global warming, a previously underexplored subject. This study complements the study of mountain glacier ice mechanics driven by global warming, which is a subject that has not been fully explored before. This investigation expounds on the nuanced interdependencies between temperature and debris content in determining glacier ice' shear strength, paving the way for force avalanche prediction models and disaster prevention strategies. It provides pivotal insights into mountain glacier ice behavior under different environmental conditions.
Provide detailed explanations of key terms and concepts to aid reader understanding. For example, Line 31: How does the author define ice avalanche? Add a definition in the introduction.
A: Thank you very much. We fully accept the reviewer's suggestion. We define ice avalanche as follows:
Ice avalanches (IAs) are sudden releases of large amounts of ice from a glacier. The ice quickly collapses or slides down the slope while breaking into smaller pieces (Cuffey and Paterson, 2010). The terms "glacier avalanche", "glacier collapse", "glacier detachment" and "ice collapse" are all included in this definition. In addition, we believe that ice-rock avalanches, glacier landslides (different from periglacial landslides), and ice-rich landslides also belong to the broad sense of ice avalanches.
At the same time, we have explained other abbreviations in the manuscript:
The second generation of the multi-functional Yeya Direct Shear machine (YDS-2)
The second generation of the XieJian direct shear machine (XJ-2)
Line 67: "... has not been thoroughly investigated. "Does that mean glacial ice type or detrital ice? Some clarification is needed.
A: Thank you for the reviewer's reminder. There is indeed ambiguity here, and we have clarified it here to make the innovation of our research clearer:
Mountain glacier ice, with its unique formation process, structure, and composition, particularly due to the incorporation of bedrock powder (Moore, 2014). Its shear strength difference and failure mechanism under the influence of structure and environmental factors have not been fully explored.
Line 80-82 and line 42 had logical problems and needed to be adjusted. It is proposed that line 80-82 "Moore, (2014) ... between the ice and the rock "in the" Systematic consideration..." The front.
A: Thank you, this is a very good suggestion and we fully accept it. We have revised the manuscript to make it more logical.
Line 91: The text in Figure 1 is not very clear. "debris-ice" in the figure is inconsistent with "debris ice" in the text. Check and modify similar situations in the manuscript.
A: Thank you for the reviewer's comments. We have carefully checked the figures in the manuscript in light of this comment and made the following changes:
In addition to changing "debris-ice" to "debris ice" in the supplement file Figure 1, we have bolded the text in the legend.
We have simplified Figure 15 to make it clearer. As shown in the supplement file Figure 15.
Line 119: The details of "preconsolidation pressure freezing" should be explained.
A: Thanks to the reviewer. The "preconsolidation pressure freezing" in the manuscript is consistent with the "consolidated by a weight pan" in Huang et al. (2023), Huang et al. (2024), and Meng et al. (2024). That is, in a fixed container, a specific pressure is applied to compact the sample so that the density of the sample is consistent with the density of glacial ice. The whole process needs to be carried out in a low-temperature environment.
The citation format should be consistent. Such as line 200 "(Fan 2021)" and line 67 "(Moore, 2014)".
A: Thank you for the careful review. We check the full text against this comment, for example:
"(Fitzsimons et al. (2024))" -- "(Fitzsimons et al. 2024)"
"(Bondesan et al. 2023)" -- "(Bondesan et al., 2023)"
"Fish and Zaretsky, (1997)" -- "Fish and Zaretsky (1997)"
Line 239: "be-tween "should be changed to "between". Similar situations in the paper should be modified.
A: Thank you for the kind reminder from the reviewer. We apologize for such editing errors. We have carefully checked the full text:
"be-tween" -- "between"
"Consequent-ly" -- "Consequently"
"adhe-sion" -- "adhesion"
"pre-ferred" -- "preferred"
"Geosci-ence" -- "Geoscience"
"Ti-bet" -- "Tibet"
"progres-sive" -- "progressive"
"polycrys-talline" -- "polycrystalline"
"de-structiveness" -- "destructiveness"
"Bul-letin" -- "Bulletin"
"Ti-betan" -- "Tibetan"
" ℃" -- "℃"
Line 305 and 378: The subheadings do not match the content below.
A: Thank you for the reviewer's comments. We adopted this comment and modified the subheading according to the context. Specifically:
"4.1 Inference of the strength degradation mechanism with increasing temperature" -- "4.1 Shear strength and failure mechanism of glacier ice under temperature influence"
"4.2 Inference of strength reinforcement mechanism with increased debris content" -- "4.2 Shear strength and failure mechanism of glacier ice under debris"
Line 406: Replace "A high debris-content ice crystal can break into fragments" with "A high debris-content ice can break into fragments".
A: Thank you for the reviewer's careful review. We have revised the language issues here.
Line 417: The field glacier ice experiment in this paper is a new attempt on the Tibetan Plateau, but there are still room for improvement. Therefore, it is recommended to discuss the uncertainty of the test method.
A: Thank you for the good suggestions from the reviewer. At the beginning of the experiment, we carefully searched for international standards and specifications for glacier ice mechanics tests and found "ITTC Quality System Manual Recommended Procedures and Guidelines- Test Methods for Model Ice Properties", but there was nothing available. Therefore, we can only refer to the geotechnical mechanics standards, which will indeed have some inadaptability. In this regard, we actively discuss the uncertainty of the method to make the method more valuable as a reference. The discussion is as follows:
4.3.1 Standardized testing methods
There is no consistent standard and specification for the glacier ice mechanic test. As can be seen from Table 5, there is no uniformity in the test methods for glacier ice mechanics, and there is potential to construct a set of method standards for glacier ice mechanics tests in the future. As a geological material, glacier ice exhibits a strength value that falls between that of soil and rock but is more akin to soil in terms of properties and behavior. For this reason, our method of preparing reshaped ice samples for indoor testing adheres to the established standards used in soil mechanics tests. Numbers 4, 5, 7, and 8 in Table 5 also refer to similar standards, although numbers 4 and 8 are not explicitly mentioned. Our difference lies in the test instrument, sample shape, size, and thermal equilibration time. Due to the difference in test instruments, the shape and size of the sample are different, and the required thermal equilibrium time is also different. It is well known that the size effect of laboratory tests cannot be avoided, which may affect the specific value of the test, but this does not affect the trend analysis we focus on. In addition, it is more appropriate for us to choose a multifunctional testing instrument for rock and soil mechanics properties when researching glacier ice. Using soil mechanics instruments alone would be insufficient (Full-Scale Range) due to the different properties of glacier ice, and using rock mechanics instruments would provide a range that is too large. At present, the use of instruments on the market to carry out glacial ice mechanics tests requires improved instruments (except for No.1 and 8 in Table 5), such as adding environmental control parts. Although our use of liquid nitrogen to control temperature is not the best method, it is sufficient to control the temperature within the error range under a fast shear test.
Table 5. Comparison of glacier ice mechanics test methods, As shown in the supplement file Table 5_01 and Table 5_02.
References：
Akroyd, T. N. W.: Laboratory testing in soil engineering. Soil Mechanics Ltd., London, 1957.
Fitzsimons, S. J., McManus, K. J., and Lorrain, R. D.: Structure and strength of basal ice and substrate of a dry-based glacier: evidence for substrate deformation at sub-freezing temperatures, Annals of Glaciology, 28, 236-240, https://doi.org/10.3189/172756499781821878, 1999.
Fitzsimons, S. J., Lorrain, R. D., and Vandergoes, M. J.: Behaviour of subglacial sediment and basal ice in a cold glacier, Geological Society, London, Special Publications, 176, 181-190, https://doi.org/10.1144/GSL.SP.2000.176.01.14, 2000.
Fitzsimons, S. J., McManus, K. J., Sirota, P., and Lorrain, R. D.: Direct shear tests of materials from a cold glacier: implications for landform development, Quaternary international, 86, 129-137, https://doi.org/10.1016/S1040-6182(01)00055-6, 2001.
Kang, J., Liu, E. L., Song, B. T., Su, Y., Wang, P., Wang, D., and Ma, F. L.: Study on mechanical properties and constitutive model for polycrystalline ice samples, Environmental Earth Sciences, 82, 585, https://doi.org/10.1007/s12665-023-11218-1, 2023.
Mamot, P., Weber, S., Schröder, T., and Krautblatter, M.: A temperature- and stress-controlled failure criterion for ice-filled permafrost rock joints, The Cryosphere, 12, 3333–3353, https://doi.org/10.5194/tc-12-3333-2018, 2018.
Sirota, P. J.: The structure and strength of basal ice in the Suess Glacier, Antarctica, PhD thesis, University of Otago, Dunedin, New Zealand, 1999.
It's recommended to polish the manuscript or check by a native person.
A: Thank you for the reviewer's suggestions. After we have revised the manuscript, we are looking for a professional native person to check the language of the manuscript. At the same time, we are also considering the polishing plan.
Reduce Chinese references in articles. At the same time, ensure the standardization and consistency of references, especially conference papers and reports.
A: Thank you for the reviewers' comments. We fully adopted these comments. We deleted some Chinese literature in the article, supplemented it with similar international journal literature, and also added several reference-worthy literature. Corresponding changes have also been made in the text. The specific changes are as follows:
(1) Delete:
Dai, Z. H., and Lu, C. J.: Mechanical explanations on mechanism of slope stability, Chinese Journal of Geotechnical Engineering, 28, 1191-1197, 2006, (in Chinese).
Guo, Y. K., and Meng, W. Y.: Experimental investigations on mechanical properties of ice, Journal of North China University of Water Resources and Electric Power (Natural Science Edition), 36, 40-43, https://doi.org/10.3969/j.issn.1002-5634. 2015.03.010, 2015 (in Chinese).
Li, Y., Tang, M. G., Shuai, Y. Y., Zhao, H. L., Li, C. R., Ni, W. T., and Li, G.: Inversion and prediction simulation study of Aru Ice Avalanche-Debris flow motion process. Journal of Disaster Prevention and Mitigation Engineering [preprint], http://kns.cnki.net/kcms/detail/32.1695.P.20231214.1834.002.html, 15 December 2023 (in Chinese).
(2) Replacement:
"Xu, L. M., Wang, T. Z., Qi, D. Q., Yu, C. H., and Gu, L.: Study on geotechnical shear band localization retrospect and prospect, Chinese Quarterly of Mechanics, 25, 484-489, https://doi.org/10.15959/j.cnki.0254-0053.2004.04.008, 2004 (in Chinese)." -- "Hobbs, B. E., Mühlhaus, H. B., and Ord, A.: Instability, softening and localization of deformation, Geological Society, London, Special Publications, 54, 143-165, https://doi.org/10.1144/GSL.SP.1990.054.01.15, 1990."
(3) Supplement：
Akroyd, T. N. W.: Laboratory testing in soil engineering. Soil Mechanics Ltd., London, 1957.
Fitzsimons, S. J., McManus, K. J., and Lorrain, R. D.: Structure and strength of basal ice and substrate of a dry-based glacier: evidence for substrate deformation at sub-freezing temperatures, Annals of Glaciology, 28, 236-240, https://doi.org/10.3189/172756499781821878, 1999.
Fitzsimons, S. J., Lorrain, R. D., and Vandergoes, M. J.: Behaviour of subglacial sediment and basal ice in a cold glacier, Geological Society, London, Special Publications, 176, 181-190, https://doi.org/10.1144/GSL.SP.2000.176.01.14, 2000.
Fitzsimons, S. J., McManus, K. J., Sirota, P., and Lorrain, R. D.: Direct shear tests of materials from a cold glacier: implications for landform development, Quaternary international, 86, 129-137, https://doi.org/10.1016/S1040-6182(01)00055-6, 2001.
Kang, J., Liu, E. L., Song, B. T., Su, Y., Wang, P., Wang, D., and Ma, F. L.: Study on mechanical properties and constitutive model for polycrystalline ice samples, Environmental Earth Sciences, 82, 585, https://doi.org/10.1007/s12665-023-11218-1, 2023.
Li, K. Q. and Yin, Z. Y.: State of the art of coupled thermo–hydro-mechanical–chemical modelling for frozen soils, Archives of Computational Methods in Engineering, 2024, 1-58, https://doi.org/10.1007/s11831-024-10164-w, 2024.
Mamot, P., Weber, S., Schröder, T., and Krautblatter, M.: A temperature- and stress-controlled failure criterion for ice-filled permafrost rock joints, The Cryosphere, 12, 3333–3353, https://doi.org/10.5194/tc-12-3333-2018, 2018.
Pfluger, F., Weber, S., Steinhauser, J., Zangerl, C., Fey, C., Fürst, J., and Krautblatter, M.: Massive permafrost rock slide under warming polythermal glacier (Bliggspitze, Austria), EGUsphere, 2024, 1-44, https://doi.org/10.5194/egusphere-2024-2509, 2024.
Sirota, P. J.: The structure and strength of basal ice in the Suess Glacier, Antarctica, PhD thesis, University of Otago, Dunedin, New Zealand, 1999.
We checked the correctness and consistency of the references and revised them as follows:
"Cuffey, K. M., and Paterson, W. S. B.: The physics of glaciers. Academic Press, America, ISBN 978-0-12-369461-4, 2010." -- "Cuffey, K. M. and Paterson, W. S. B.: The physics of glaciers, 4th edn. Butterworth-Heinemann, Oxford, ISBN 9780123694614, 2010."
"IPCC.: Sections. In Climate Change 2023: Synthesis Report. Contribution of Working Groups I, II and III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, H. Lee and J. Romero (eds.)]. IPCC, Geneva, Switzerland, pp 35-115. https://doi.org/10.59327/IPCC/AR6-9789291691647, 2023." -- "IPCC: Climate Change 2023: Synthesis Report. Contribution of Working Groups I, II and III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change, edited by: Core Writing Team, Lee, H., and Romero, J., IPCC, Geneva, Switzerland., Intergovernmental Panel on Climate Change (IPCC), https://doi.org/10.59327/IPCC/AR6-9789291691647, 2023."
"Mizukami, N., and Maeno, N.:" -- "Mizukami, N. and Maeno, N.:"
"Nater, P., Arenson, L. U., Springman, S. M.:" -- " Nater, P., Arenson, L. U., and Springman, S. M.:"
"Journal of glaciology and geocryology" -- "Journal of Glaciology and Geocryology"
"50 Mm3" -- "50 Mm3"
The conclusion should be further refined.
A: Thank you for the reviewer's comments. We have improved the conclusions:
To deepen the understanding of the physical and mechanical characteristics of mountain glacier ice. we selected the Gongga Mountain glacier as our main study site, aiming to comprehensively investigate the shear strength characteristics of glacier ice under varying temperatures and debris contents. In situ studies at the Gongga Glacier examined glacial ice properties, with direct shear tests conducted at -0.5°C under normal stresses ranging from 100 to 500 kPa. These tests established a baseline for indoor reshaped polycrystalline ice's physical and mechanical properties. Further tests on polycrystalline ice and ice–rock composites were performed at temperatures of -0.5, -10, -20, -30, and -40°C, using remodeled polycrystalline ice, gneiss under the same range of normal stresses. Direct shear tests were carried out on fine and coarse debris ice with fine debris contents of 10, 15, 20, 25, and 30% and coarse debris contents of 20, 30, 40, 50, and 60% under identical normal stresses. The variations in deformation failure and shear strength for glacier ice under different conditions were obtained, and the deformation evolution process and shear strength mechanism were analyzed. The four main conclusions were as follows:
(1) The debris content is positively correlated with density, negatively correlated with porosity, and shows a nonlinear decreasing trend.
(2) Different types of glacier ice have strain-softening phenomena in the shear process. The peak strength is displayed: fine debris ice (466 kPa) > coarse debris ice (367 kPa) > polycrystalline ice (259 kPa) > ice–rock composite (192 kPa).
(3) Polycrystalline ice displays the strength of nonlinear degradation with increasing temperature and ice–rock composites show the strength of linear degradation with increasing temperature display strength degradation with increasing temperature. Fine and coarse debris ice display exhibits the strength of the nonlinear enhancements with increasing debris content.
(4) The emergence of liquid water is one of the reasons for the degradation of strength, which can be observed in the destructive samples; also, the mechanism by which the increase in debris content leads to the strength enhancement of debris ice is discussed. It is believed that solid particle effects (biting, friction, and crushing) are essential reasons for strength enhancement, which can also be observed in destructive samples.
(5) We discussed future work and believed that standardization of glacier ice mechanics test methods is necessary, which will facilitate the integration of experimental data. Furthermore, it would be more valuable to establish a statistically significant glacier ice physics and mechanics model for application in glacier stability assessment, as this would provide more representative data for predicting potential hazards and mitigating risks in high-altitude regions.
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RC2: 'Comment on egusphere-2024-1522', Adrien Gilbert, 25 Oct 2024
This study presents the results of direct shear test experiments on ice as a function of temperature and rock debris content, carried out according to the standard geotechnical approach to determine the shear strength of materials. The ice samples, collected in the field and replicated in the laboratory, are intended to be representative of natural mountain glacier ice. This provides valuable data for determining the maximum shear stress that can be accommodated by glacier ice and has direct application to better anticipate and model gravity-driven glacier instabilities that generate ice avalanches.
I think this manuscript gives a useful quantification of the shear strength of natural glacier ice that can be used as a stress threshold to determine the occurrence of potential glacier collapse. The topic and results are thus valuable for the glaciology community and could be published in The Cryosphere.
However, at this stage, the writing is generally very difficult to follow and the logical links between sentences and ideas are missing throughout the manuscript. Many sentences are vague and seem unrelated to the topic of the paragraph. The reader is often left wondering why a statement is made without any explanation of how it supports the idea being developed. There is also a lack of rigour in how the work of others is described and compared with this study.
Although the language is correct, the quality of the writing definitely does not meet the journal's requirements for publication. I suggest major revisions that need to be made for the manuscript to be considered for publication. I hope that my comments will help the authors to make the necessary improvements.
Best regards,
Adrien Gilbert
General comments
- The abstract needs to be rewritten. The current one does not fulfil what is expected from an abstract where the topic, method, results and main implications of the study should be clearly stated. Instead, it gives a random, exhaustive list of results with sentences juxtaposed. The method is not clear and we do not know how your results are interpreted and what the implications are. For example, instead of saying "The strength enhancement of debris ice caused by increased debris content is expounded", the authors should explicitly tell the reader what their findings are regarding the mechanism of strength enhancement caused by debris. Further comments on the abstract can be found in the attached pdf.
- Introduction: The same comments that can be made about the abstract apply to the introduction section, which is difficult to read because of the juxtaposition of sentences that lack logical connections between them. The reference to other studies is also poorly done, as the authors often limit their statement to "XX et al. studied this and that ..." instead of actually saying what the results of the cited references are. See my comments in the attached pdf.
- As the manuscript is trying to reach the glaciological community, which is not necessarily familiar with geoengineering, a better description of the method should be done. For example, it should be explicitly stated that you are doing direct shear strength tests, what they are and what they are usually done for (soil mechanics...). Also a general explanation of what the stress vs displacement curve is and what it shows would be good. For example, it was not obvious to me that the residual stress after peak is actually friction along the failure interface (if I am correct?). You should also say why this approach is relevant to your goal of estimating glacier stability.
- In the glaciology community, ice is known more as a viscous material and it should be clear in your study that you are working in the brittle regime and a reference to the work of E.M. Schulson (2001) is missing. Also, you don't even specify the strain rate regime imposed in your experiment, which is important to know in order to make it clear that you are looking at the elastic response and the brittle regime, not viscous deformations.
- My final general comment concerns the lack of synthesis of your results in relation to the application of your findings to modelling glacier collapse. I think this is attempted in section 4.3, but this section is really vague with many unclear statements. The glaciologist reader would like to know what is the most likely shear strength of the ice at the glacier base, where the maximum stress is usually reached. Your study could provide some useful values. For example, Kääb et al. (2021) used the glacier-scale force balance done in Gilbert et al. (2018) for the Aru glacier collapse to give a rough estimate of the shear stress at which the frozen margin (~-4°C according to Gilbert et al. (2018)) of the detachment broke. They found 280 kPa, how does this compare with your results?
Specific comments
You will find a list of 70 corrections and specific comments embedded in the annotated PDF in attachment. Some are redundant with my general comments but may help to clarify them.
References
Kääb, A., Jacquemart, M., Gilbert, A., Leinss, S., Girod, L., Huggel, C., Falaschi, D., Ugalde, F., Petrakov, D., Chernomorets, S., Dokukin, M., Paul, F., Gascoin, S., Berthier, E., and Kargel, J. S.: Sudden large-volume detachments of low-angle mountain glaciers – more frequent than thought?, The Cryosphere, 15, 1751–1785, https://doi.org/10.5194/tc-15-1751-2021, 2021.
Schulson, E. M.: Brittle failure of ice, Engineering Fracture Mechanics, 68, 1839–1887, https://doi.org/10.1016/S0013-7944(01)00037-6, 2001.
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RC3: 'Comment on egusphere-2024-1522', Anonymous Referee #3, 16 Dec 2024
Minggao Tang and co-author present a manuscript related to an experimental study on the shear strength and failure mechanism of mountain glacier ice. The manuscript aims to investigate the mechanical behavior of glacier ice in the context of global warming. The study involves over 250 field and laboratory tests to analyze the variations in shear strength and failure mechanisms of four types of glacier materials: polycrystalline ice, ice-rock composite, fine debris ice, and coarse debris ice. The study focuses on the Gongga Glacier in Sichuan Province, China. It involves field investigations for in-situ glacier ice and laboratory tests on various samples. Based on the results, the authors conclude that debris content and temperature significantly influence the shear strength of glacier ice. They emphasizes the importance of these factors in developing models for predicting ice avalanches and implementing disaster prevention strategies.
I’ve been struggling with this paper as I understand that the authors put a lot of effort into their material testing and laboratory work. I read it more than once, but finally came to the conclusion that I cannot recommend the study to be published as I see a lack of fundamental understanding of the problem the authors like to address with their study. There are other, more minor issues with the manuscript, but the main problem with this manuscript, i.e. the research conducted, is the relevance and applicability of the testing on the problem the authors are trying to solve. Most notably, the authors want to address the challenges of glacier instability in a warming climate. As such, we are talking about changes in ice and bedrock temperatures of a few degrees centigrade and most critically, changes just below 0°C. However, the authors only tested at -0.5°C and then at -10°C to -40°C, i.e. temperature ranges that are absolutely irrelevant for the problem. Most importantly, and also shown by many of the references cited by the authors, we cannot simply extrapolate the trends observed at these temperatures to the behaviour between 0°C and -2°C, the range of highest interest. Similarly, the effect of debris must be studied at these warm temperatures and not simply at -20°C as the unfrozen water content is very different at these warmer conditions and therefore the strength behaviour would be vary substantially. The authors presented laboratory study that does show some interesting data, but those are completely irrelevant and must not be used for the problem discussed. In fact, I do find it irresponsible if those data would be used to try to solve the problems of glacier instabilities as they would misrepresent the actual conditions. For those reasons, I’m recommending rejecting the manuscript.
I do have some other concerns regarding the laboratory testing. For example, freezing the samples with liquid nitrogen generates completely different ice crystals than how ice forms in nature. While the authors claim that the density and the porosity of the samples are similar in the field as in the laboratory, the mechanical behaviour also depends on the ice crystals. I suggest that the authors spend some time reading literature by E.M. Schulson and the familiarize themselves with some ice fracture mechanics.
It is also important to study the strain rates at which the samples are sheared. The faster the shearing the stronger the sample, making it more brittle. But since the strength depends on the applied strain rate, this influence must also be studied, which it wasn’t. Again, several of the references cited to discuss this point and I strongly recommend that the authors go back and do a detailed literature review. And while they do a detailed review, they may also find some additional references that they have missed, including papers by Guentzel, Krautblatter, Davies, Yasufuku, Arenson and Schulson.
Finally, if the authors decide to submit a paper again, they must improve the language. Overall, it is reasonably well written, and I understand that this is not easy. However, they must pay attention that words are properly used, that details are adequately described and that they stay humble. Words such as “glacial media”, “escalating debris content”, “nonlinear enhancements”, “biting”, “expounds”, “force avalanche”, “natives”, “scrutinize” etc. were often used wrongly.
Citation: https://doi.org/10.5194/egusphere-2024-1522-RC3
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