An Analysis of the Mechanisms Involved in Glacial Lake Outburst Flooding in Nyalam, Southern Tibet, in 2018 Based on Multi-Source Data

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Based on optical and radar remote sensing images, meteorological data, and seismicity catalog, this study focuses on the spatiotemporal evolution, triggering factors, and outburst mechanism of a glacial lake outburst flood (GLOF) that occurred in Nyalam County. The results show that it is applicable to monitor the spatiotemporal evolution and evaluate the risk of an upcoming GLOF through this method, which is helpful in comprehensively understanding the mechanism of GLOF events and is of great significance for glacial lake risk assessment. However, the reviewer has the following concerns which the authors should consider during revision:

 [Comment] 1) Does Figure 6 show the G-c terminus change in 1991-2019 corresponding to Figure 5? Please make a clear statement for a better understanding.

 

[Comment] 2) It is suggested that the author adjust the contents of Section 4 (Results) and Section 5 (Discussion), showing the whole results of optical and radar remote sensing images, meteorological data, and seismicity catalog respectively in Section 4, and focusing on the triggering factors of GLOF in Section 5.

 [Comment] 3) The conclusion of this article is slightly simplistic, and the detailed results are case-specific of a glacial lake outburst flood (GLOF) that occurred in Nyalam County. As a scientific paper, in addition to summarizing the advantages of this combined method, it is suggested that the author should also give the precautions and limitations of this method for a better promotion(such as the scope of application).

 [Comment] 4) There are minor grammatical issues in the article, which deserve careful examination during revision. It is recommended that the author check the long sentences of the full text, and use the correct tense. Some examples are given below: Line 44 '2.28×106m3' should be '2.28×10⁶ m³'. Line 385 'Figure 12 showed' should be ' Figure 12 shows'. Line 523 and Line 531 'the' should be 'The'. Delete the extra full stop at the end of line 531.

Comments on the Quality of English Language

Please further improve the quality of English language.

Author Response

 [Comment] 1) Does Figure 6 show the G-c terminus change in 1991-2019 corresponding to Figure 5? Please make a clear statement for a better understanding.

Response1: Thank you for pointing this out. I have changed the title of Figure 6 to “G-c terminus change in 1991-2019. The yellow line is the extent of the glacier in 1991; the pink line is the extent of the glacier in each year. Images (1)-(20) are Landsat 30 m TM/ETM+ images; images (21)-(22) and (24)-(25) are 16 m Gaofen-1 WFV images; and images (23), (26), and (27) are 2 m Gaofen-1 PMS, Gaofen-2 PMS, and Gaofen-6 PMS images, respectively.”

[Comment] 2) It is suggested that the author adjust the contents of Section 4 (Results) and Section 5 (Discussion), showing the whole results of optical and radar remote sensing images, meteorological data, and seismicity catalog respectively in Section 4, and focusing on the triggering factors of GLOF in Section 5.

Response2: Thank you very much for your valuable suggestions on my dissertation, however, for the structure of the article I was conceived in this way: each result in Section 4 (Results) corresponds to Section 3 (Methods), and it would be illogical to put the contents of the discussion in Chapter 3, which is a comprehensive analysis of the triggering factors of glacial lake outbursts to support the discussion section. So I have not revised this part for the time being, but thank you very much.

[Comment] 3) The conclusion of this article is slightly simplistic, and the detailed results are case-specific of a glacial lake outburst flood (GLOF) that occurred in Nyalam County. As a scientific paper, in addition to summarizing the advantages of this combined method, it is suggested that the author should also give the precautions and limitations of this method for a better promotion(such as the scope of application).

Response3：I feel great thanks for your professional review work on our article. I've added the limitations of the method to lines 516-528 of the article.

 [Comment] 4) There are minor grammatical issues in the article, which deserve careful examination during revision. It is recommended that the author check the long sentences of the full text, and use the correct tense. Some examples are given below: Line 44 '2.28×106m3' should be '2.28×10⁶ m³'. Line 385 'Figure 12 showed' should be ' Figure 12 shows'. Line 523 and Line 531 'the' should be 'The'. Delete the extra full stop at the end of line 531.

Response4：I apologize for my carelessness and have corrected all the issues you mentioned, and I sincerely thank the reviewer for reading it carefully. In addition, I also used the recommended author service to overhaul the language of the paper.

Reviewer 2 Report

Comments and Suggestions for Authors

 

The study utilizes a combination of optical and radar remote sensing images, meteorological data, and seismicity catalogs. This multi-source approach provides a framework for analyzing the spatiotemporal evolution and triggering factors of the GLOF event. Some points that need to be considered in this paper include:

What is the novelty and contribution of the research? What is the research gap? There is a need to further review the previous methods used for such case studies. What were their findings, etc.?

The methodology section is limited. You need to further elaborate on the methods used, metrics, and preprocessing steps. Why have the authors chosen this method? Can the authors compare their results with those obtained using another method?

Discuss the applicability of the study's findings to other regions and under different climatic and geological conditions to ensure the broader relevance of the research. The abstract mentions an increase in the runoff area at the end of glaciers by 167% during 2015-2018 but also states that the area of study glacial lakes decreased. This contradictory information could confuse readers and needs further clarification in the paper.

 

Comments on the Quality of English Language

Moderate proofreading is recommended 

Author Response

[Comment] 1) What is the novelty and contribution of the research? What is the research gap? There is a need to further review the previous methods used for such case studies. What were their findings, etc.?

Response1: Thank you very much for your valuable suggestions on my dissertation. 

(1) The innovativeness of this paper is mainly reflected in the following aspects:

First, this paper adopts the joint active-passive remote sensing technique, an innovative approach that not only improves the comprehensiveness and accuracy of data acquisition, but also realizes the multi-dimensional and high-precision monitoring of GLOF. By combining the penetrating and high-resolution characteristics of active remote sensing (e.g., radar detection) and the advantages of wide coverage and continuity of passive remote sensing (e.g., satellite imagery), this paper is able to reveal the complexity and dynamic process of the GLOF events in a deeper way.

Second, this paper innovatively incorporates the comprehensive consideration of meteorological and seismic factors when analyzing the triggering factors and mechanisms of GLOF. While traditional studies tend to focus on the analysis of a single factor, this paper provides a richer and more scientific perspective for a comprehensive understanding of the causes of GLOFs by integrating multiple external triggering conditions, including extreme climatic events (e.g., heavy rainfall, accelerated snowmelt) and potential seismic activities.

Finally, the glacial lake studied in this paper is an object that has not been explored in depth by previous researchers, and this innovative choice not only broadens the field of glacier and glacial hazards research, but also provides valuable case studies and data support for risk assessment and disaster prevention in similar areas in the future. Through detailed analysis of this unknown glacial lake, this paper reveals its unique geographic, climatic, and geological features, and how these features interact with GLOF events, thus further enriching our understanding of glacial hazard formation mechanisms.

In summary, the novelty of this paper lies in its unique research methodology, comprehensive analytical framework, and in-depth exploration of the unknown glacial lake, all of which will make important contributions to the development of the field of glacier and glacial disaster research. 

(2) There are also some research gaps in this paper, firstly, the lack of field observation data, and secondly, the simulation of GLOF process is still insufficient to fully capture its complex dynamics and potential impacts. Furthermore, when exploring the spatial and temporal evolution of the long time series of GLOFs, a single assessment index has been chosen, which fails to comprehensively reflect the multidimensional characteristics of the changes. Finally, there is a significant gap in the systematic risk assessment and prediction of other glacial lakes in the region that have not yet experienced outbursts. In summary, these research gaps need to be filled by strengthening field observation, improving simulation techniques, enriching analytical indicators, and expanding the scope of risk assessment. I will strengthen my study and research on these aspects in my future work.

(3) For previous findings in such cases, GLOF is usually associated with the change of glacial lake water volume, ice avalanches, heavy rainfall, seismic activity, and dam composition, etc., as shown in lines 58-61 of the article. And for the study of glacial lake area changes, I added this section to lines 278-281 of the article.

[Comment] 2) The methodology section is limited. You need to further elaborate on the methods used, metrics, and preprocessing steps. Why have the authors chosen this method? Can the authors compare their results with those obtained using another method?

Response2: Thank you very much for your advice. We fully understand your doubt. Therefore I added a description of the methodology in lines 244-246, 257-263 of the article.

And I chose SBAS-InSAR because the technique provides millimeter to centimeter surface deformation measurement accuracy, which can cover a large surface area and monitor a wide range of surface deformation phenomena, such as crustal movement and ground subsidence. Meanwhile, by combining SAR images from multiple time phases, the effects of atmospheric and orbital errors can be reduced and data quality can be improved. And the noise and out-of-phase problems in InSAR measurements are reduced by minimizing baseline and time differences. In summary, I chose this method to conduct a study on GLOF inducing factors and mechanisms. At the same time I chose the manual outlining method because of its accuracy in calculating the exact metrics needed.

[Comment] 3) Discuss the applicability of the study's findings to other regions and under different climatic and geological conditions to ensure the broader relevance of the research. The abstract mentions an increase in the runoff area at the end of glaciers by 167% during 2015-2018 but also states that the area of study glacial lakes decreased. This contradictory information could confuse readers and needs further clarification in the paper.

Response3: Thank you for your guidance on the article. The results of the study are applicable to the study of glacial lake outburst predisposing factors and mechanisms in other regions, especially in the Himalayan region. And in response to your reference to contradictory information, we think this is a very good suggestion. I've added this section of changes to line 24 of the article.