the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 14 Oct 2024
Optical images reveal the role of high temperatures in triggering the 2021 Chamoli landslide
Abstract. The 2021 Chamoli ice-rock landslide formed a landslide-flood hazard chain by claiming 200 lives and destroying two hydroelectric power plants. The reason for this landslide has been elusive due to difficulty in retrieving reliable deformation time series before the landslide. Here we proposed a histogram-based method to reconcile deformation inconsistencies measured in different optical sensors. We find the Chamoli ice-rock deformed >80 m from 2013 to 2021 with exceptionally high deformations in summers of 2017/18, which were related to high summer temperatures. Final collapse in February 2021 is also related to high temperature. Rising temperatures weakened shear strength of the ice on the sliding plane triggering the Chamoli landslide to move. With climate warming, more similar, hard to predict ice-rock landslides in deglaciating high mountains are inevitable, posing new challenges to local communities and beyond. Optical remote sensing images provide an indispensable data in deciphering early precursors of similar hazards.
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RC1: 'Comment on egusphere-2024-2786', Anonymous Referee #1, 04 Mar 2025
I am reviewing the paper by Tian et al. on the 2021 Chamoli landslide, which seeks to reconcile deformation measurements from different optical sensors and suggests that high summer temperatures weakened ice-filled discontinuities, ultimately triggering the event. While I am unable to evaluate the applicability and advancement of the (new?) optical imaging methodology and analysis, the manuscript in its current form has significant weaknesses. My main concerns are as follows:
- Inappropriate Title
The authors propose that warm summer temperatures decreased the strength of ice-filled discontinuities at depth, ultimately triggering the failure – a hypothesis that, in my view, is neither sufficiently validated nor applicable. However, this interpretation is presented as a fact in the title, which is misleading. - Introduction Only Partly Fulfilling Its Role
While the introduction begins with a broad motivation, it lacks a clear focus and a well-defined research gap. The attempt to link the Chamoli landslide to rock glacier dynamics is, in my view, entirely inappropriate, as these involve different landforms, processes, regions, and climatic conditions. Additionally, the second half of the introduction is more of a site and event description rather than a logical build-up to the study's objective. The study’s aims formulated in the last sentence are only loosely connected to the introduction and are addressed only partially later in the manuscript. - Methodological Issues in Deriving Displacements
The final displacement time series exhibits a reversible/backward pattern when multiple data points are available within consecutive months, raising concerns about the reliability of the derived displacements. More broadly, given the inconsistent time series and long data gaps, can intra-annual patterns truly be inferred with confidence? While my knowledge of remote sensing data processing is limited, these issues appear significant and warrant further clarification. - Representativeness of Temperature and Precipitation Data
There is too little information and no critical discussion on the representativeness of the temperature data (measured 170 km away, at a completely different elevation and topography) and the monthly precipitation data used for the site-specific analysis. Potential uncertainties in transferring these data to the Chamoli site could have significant impacts on the study’s interpretation and conclusions. - Inappropriate Comparisons and Invalid Implementations
- Misleading Comparison to the Schafberg Rock Glacier: The authors use the Schafberg rock glacier study by Bast et al. (2024) to support the observed dynamic response at Chamoli during summer 2017/2018 due to pre-summer winter snowfall. This comparison is inappropriate, as the two sites represent different landforms with distinct internal structures, are located in different regions and elevations, and experience entirely different in-situ hydrological and thermal regimes. There is no clear justification for drawing a direct relation between them.
- Misapplication of the Failure Criterion by Mamot et al. (2020): Mamot et al. empirically derived a temperature- and stress-dependent failure criterion for ice-filled fractures, which is valid for normal stresses of 100–400 kPa, corresponding to an overburden of 4–20 m. However, the authors attempt to apply this criterion to a rock overburden of up to 180 m, which equates to approximately 3600 kPa – far beyond the valid range of the criterion and without any critical discussion.
- Oversimplified Interpretation of Summer Warming as the Main Trigger: The authors conclude that warm summer temperatures were the primary driver of increased displacement and the final failure. However, they do not account for the phase shift of warming at depth due to slow conductive heat transport. They briefly mention the potential role of water infiltration but provide no evidence for its presence and do not consider that a significant water flux would be required to reach the deep detachment zone.
- Missing Critical Discussion
The current discussion does not fully address the aims formulated in the introduction; for example, it fails to adequately focus on the strengths and limitations of the methods and analyses employed by the authors themselves. Instead, it predominantly addresses potential influences of environmental forcing and related changes in ground conditions. However, there is a lack of critical discussion, and some conceptual approaches are either repetitive (e.g., factor of safety, Van Wyk de Vries et al., 2022) or not directly applicable (as noted above). Moreover, the conclusions are primarily based on the assumed decrease in the strength of ice-filled discontinuities, as outlined by Mamot et al. (2018), without sufficiently considering or integrating the authors' own analysis of optical images. - Suitability of the Manuscript for the Journal
Finally, as the authors propose a (new?) method to reconcile deformation inconsistencies measured by different optical sensors, I am left wondering if this paper might be better suited for a different journal. Given the methodological focus, it may align more with journals that specialize in remote sensing techniques, rather than The Cryosphere.
Citation: https://doi.org/10.5194/egusphere-2024-2786-RC1 - Inappropriate Title
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RC2: 'Comment on egusphere-2024-2786', Anonymous Referee #2, 24 Mar 2025
The manuscript adopted a new method to reconcile the deformation inconsistency by different optical sensors, which is regarded as the key point. Besides this, there is no new insights about the initiation of Chamoli rock-ice avalanche. My feeling is that a remote sensing journal would be a better choice for publication.
The analysis of the high-altitude landslide is hindered by the limited in-situ monitoring data. This manuscript still suffers from this limitation. Specially, the EAR5 and a remote monitoring station cannot reliably reflect the inner temperature of Chamoli landslide.
The title is misleading. The deformation is revealed by the optical images, rather than the high temperature.
Citation: https://doi.org/10.5194/egusphere-2024-2786-RC2
Status: closed
-
RC1: 'Comment on egusphere-2024-2786', Anonymous Referee #1, 04 Mar 2025
I am reviewing the paper by Tian et al. on the 2021 Chamoli landslide, which seeks to reconcile deformation measurements from different optical sensors and suggests that high summer temperatures weakened ice-filled discontinuities, ultimately triggering the event. While I am unable to evaluate the applicability and advancement of the (new?) optical imaging methodology and analysis, the manuscript in its current form has significant weaknesses. My main concerns are as follows:
- Inappropriate Title
The authors propose that warm summer temperatures decreased the strength of ice-filled discontinuities at depth, ultimately triggering the failure – a hypothesis that, in my view, is neither sufficiently validated nor applicable. However, this interpretation is presented as a fact in the title, which is misleading. - Introduction Only Partly Fulfilling Its Role
While the introduction begins with a broad motivation, it lacks a clear focus and a well-defined research gap. The attempt to link the Chamoli landslide to rock glacier dynamics is, in my view, entirely inappropriate, as these involve different landforms, processes, regions, and climatic conditions. Additionally, the second half of the introduction is more of a site and event description rather than a logical build-up to the study's objective. The study’s aims formulated in the last sentence are only loosely connected to the introduction and are addressed only partially later in the manuscript. - Methodological Issues in Deriving Displacements
The final displacement time series exhibits a reversible/backward pattern when multiple data points are available within consecutive months, raising concerns about the reliability of the derived displacements. More broadly, given the inconsistent time series and long data gaps, can intra-annual patterns truly be inferred with confidence? While my knowledge of remote sensing data processing is limited, these issues appear significant and warrant further clarification. - Representativeness of Temperature and Precipitation Data
There is too little information and no critical discussion on the representativeness of the temperature data (measured 170 km away, at a completely different elevation and topography) and the monthly precipitation data used for the site-specific analysis. Potential uncertainties in transferring these data to the Chamoli site could have significant impacts on the study’s interpretation and conclusions. - Inappropriate Comparisons and Invalid Implementations
- Misleading Comparison to the Schafberg Rock Glacier: The authors use the Schafberg rock glacier study by Bast et al. (2024) to support the observed dynamic response at Chamoli during summer 2017/2018 due to pre-summer winter snowfall. This comparison is inappropriate, as the two sites represent different landforms with distinct internal structures, are located in different regions and elevations, and experience entirely different in-situ hydrological and thermal regimes. There is no clear justification for drawing a direct relation between them.
- Misapplication of the Failure Criterion by Mamot et al. (2020): Mamot et al. empirically derived a temperature- and stress-dependent failure criterion for ice-filled fractures, which is valid for normal stresses of 100–400 kPa, corresponding to an overburden of 4–20 m. However, the authors attempt to apply this criterion to a rock overburden of up to 180 m, which equates to approximately 3600 kPa – far beyond the valid range of the criterion and without any critical discussion.
- Oversimplified Interpretation of Summer Warming as the Main Trigger: The authors conclude that warm summer temperatures were the primary driver of increased displacement and the final failure. However, they do not account for the phase shift of warming at depth due to slow conductive heat transport. They briefly mention the potential role of water infiltration but provide no evidence for its presence and do not consider that a significant water flux would be required to reach the deep detachment zone.
- Missing Critical Discussion
The current discussion does not fully address the aims formulated in the introduction; for example, it fails to adequately focus on the strengths and limitations of the methods and analyses employed by the authors themselves. Instead, it predominantly addresses potential influences of environmental forcing and related changes in ground conditions. However, there is a lack of critical discussion, and some conceptual approaches are either repetitive (e.g., factor of safety, Van Wyk de Vries et al., 2022) or not directly applicable (as noted above). Moreover, the conclusions are primarily based on the assumed decrease in the strength of ice-filled discontinuities, as outlined by Mamot et al. (2018), without sufficiently considering or integrating the authors' own analysis of optical images. - Suitability of the Manuscript for the Journal
Finally, as the authors propose a (new?) method to reconcile deformation inconsistencies measured by different optical sensors, I am left wondering if this paper might be better suited for a different journal. Given the methodological focus, it may align more with journals that specialize in remote sensing techniques, rather than The Cryosphere.
Citation: https://doi.org/10.5194/egusphere-2024-2786-RC1 - Inappropriate Title
-
RC2: 'Comment on egusphere-2024-2786', Anonymous Referee #2, 24 Mar 2025
The manuscript adopted a new method to reconcile the deformation inconsistency by different optical sensors, which is regarded as the key point. Besides this, there is no new insights about the initiation of Chamoli rock-ice avalanche. My feeling is that a remote sensing journal would be a better choice for publication.
The analysis of the high-altitude landslide is hindered by the limited in-situ monitoring data. This manuscript still suffers from this limitation. Specially, the EAR5 and a remote monitoring station cannot reliably reflect the inner temperature of Chamoli landslide.
The title is misleading. The deformation is revealed by the optical images, rather than the high temperature.
Citation: https://doi.org/10.5194/egusphere-2024-2786-RC2
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