the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 09 Apr 2025
Controls over debris flow initiation in glacio-volcanic environments in the Southern Andes
Abstract. The southern Andes is an active zone of mass wasting processes. Several conditioning factors could have an impact on the generation of debris-flows, influencing by water storage and slope stability. We assessed the generation of the Ñisoleufu debris-flow, an active area of debris-flow generation, reviewing the interplay between geomorphological, geotechnical and hydrometeorological controls in debris flow dynamics. Our results highlight significant changes in soil moisture content on critical days associated with debris flow events. We revealed that the combination of areas with high water accumulation capacity from local runoff and slopes that capture precipitation effectively were crucial in the generation of debris-flows. Areas with granular volcanic soils acted as storage mediums for water, which, coupled with decreased shear strength, facilitated debris flow initiation. The thin and fine-grained layers of glacial deposits located beneath the volcanic soil, characterized by low hydraulic conductivity, created localized accumulation zones that reinforced the storage capacity of adjacent areas, particularly in pyroclastic volcanic deposits in the release zone. By understanding the combined effects of water accumulation, soil properties, and slope dynamics, this study contributes valuable insights into managing and mitigating debris-flow hazards in vulnerable regions.
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Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
(2069 KB)
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(2069 KB) - Metadata XML
- BibTeX
- EndNote
- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2025-1394', Anonymous Referee #1, 05 May 2025
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AC1: 'Reply on RC1', Daniel Basualto, 01 Jul 2025
We would like to thank Reviewer #1 for their thoughtful and constructive feedback. Their suggestions significantly contributed to improving the clarity, depth, and scientific robustness of our manuscript, particularly in clarifying regional representativeness, restructuring the introduction, refining figures and tables, and expanding the discussion of soil properties and triggering mechanisms.
In the attached document, we provide a detailed point-by-point response to each general, specific, and technical comment raised by Reviewer #1. Revisions include the addition of new figures, improved methodological clarity, correction of textual inconsistencies, and the expansion of geotechnical and climatic interpretations relevant to debris flow initiation in glacio-volcanic terrains of the Southern Andes.
We sincerely appreciate the reviewer’s efforts and time, which were essential in enhancing the scientific quality of our work.
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AC1: 'Reply on RC1', Daniel Basualto, 01 Jul 2025
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RC2: 'Comment on egusphere-2025-1394', Anonymous Referee #2, 12 May 2025
General Comment
The manuscript titled "Controls over debris flow initiation in glacio-volcanic environments in the Southern Andes" presents a comprehensive analysis of the mechanisms responsible for debris flow initiation in the Ñisoleufu sector, Southern Chile. It effectively integrates geomorphological, geotechnical, hydrometeorological, and remote sensing analyses to assess the factors controlling debris flow occurrence in a complex glacio-volcanic setting. The study’s use of multi-source data strengthens the reliability of the findings. However, the manuscript would benefit from a clearer presentation of the connections between controlling factors and observed events, as well as a more explicit discussion of implications for hazard assessment.
Specific Comments
Introduction
The introduction provides a comprehensive background but could be more focused, particularly in the discussion of previous studies. Some references to regional climate impacts could be condensed to streamline the narrative.
The citations provided lack robustness for a proper framing of debris flows, as most references are from the last 3-4 years. Correct this by adding relevant and foundational studies. Additionally, the transition between topics is somewhat abrupt, lacking fluidity.
Methodology
It would be important to include the location of the meteorological stations in one of the displayed figures to provide spatial context for the data collection.
Results
The results are comprehensive, but the presentation is occasionally repetitive. For example, the discussion of soil stratigraphy (Lines 200-240) could be condensed to highlight the most critical observations.
Figure 6A does not appear to indicate an anomalous trend in soil moisture compared to previous years. It should be emphasized that the combination of saturated soil and intense rainfall plays a key role in triggering debris flows.
Discussion
The discussion appropriately addresses the key findings but could benefit from a more critical evaluation of the limitations of the study.
The role of climate change in debris flow initiation is briefly mentioned but not fully explored. Given the relevance of this factor, a more detailed discussion would enhance the manuscript’s impact.
Conclusions
The conclusions effectively summarize the main findings but lack specific recommendations for hazard mitigation. Consider adding a few practical insights based on the study’s results.
Citation: https://doi.org/10.5194/egusphere-2025-1394-RC2 -
RC3: 'Additional comments', Anonymous Referee #2, 14 May 2025
Additional specific Comments
Upon further consideration I have identified additional points that may require other clarifications:
- Laboratory Measurements (Table 2)
The values reported for liquid limit (WL) and plastic limit (WP) for S-3, as well as WL, WP, and Ku for S-7, appear inconsistent with their geological descriptions. S-3. S-7 represents an active, developing soil, likely rich in organic material, where higher hydraulic conductivity (Ku) would be expected. However, the reported Ku is surprisingly low, potentially indicating compaction, fine-grained content, or measurement errors. Please verify these values and, if accurately, provide additional context to justify these unexpected results. - Limited Number of PS (Figure 7)
The analysis includes only five PS, of which three are located near the boundary and only two within the landslide niche. This sparse dataset may not provide a sufficiently robust basis for reliable precursor identification, especially given that these PS do not appear to exhibit significantly different displacement patterns compared to surrounding points. This raises questions about the reliability of these PS as early warning indicators. I recommend adjusting the color scale in Figure 7 to better distinguish between PS displacement and elevation, which may improve the interpretability of the figure. - To improve clarity, consider presenting the data in Table 3 as a graph, which may provide a more intuitive visualization of the variation in saturated hydraulic conductivity across different soil types.
Citation: https://doi.org/10.5194/egusphere-2025-1394-RC3 -
AC2: 'Reply on RC2', Daniel Basualto, 01 Jul 2025
We sincerely thank Reviewer #2 for their thoughtful and comprehensive evaluation of our manuscript. The review offered valuable recommendations for enhancing the clarity, coherence, and scientific robustness of our work, particularly regarding the connection between controlling factors and debris flow initiation, the presentation of soil stratigraphy, and the discussion of climatic influences and methodological limitations.
We have carefully addressed all general and specific comments provided. In particular, we revised the Introduction to improve focus and narrative fluidity, incorporating both foundational and recent literature to contextualize the study. We also restructured the Discussion and Conclusion sections to better highlight the study’s contributions to hazard assessment, including explicit recognition of data limitations, soil stratigraphy, and climate-driven processes. Moreover, we clarified figures, improved stratigraphic descriptions, and reinforced key methodological aspects such as the spatial distribution of meteorological stations.
All these revisions are detailed in the attached document, where we provide a point-by-point response to each comment. Once again, we appreciate the reviewer’s insights, which were highly constructive and instrumental in improving the manuscript’s scientific impact.
-
AC3: 'Reply on RC3', Daniel Basualto, 01 Jul 2025
We thank Reviewer #3 for their attentive and constructive observations. The additional points raised provided a valuable opportunity to further improve the quality and clarity of our manuscript.
In particular, we verified and contextualized the geotechnical results for soil types S-3 and S-7, justifying their liquid limits and hydraulic conductivity values with reference to regional analogs and laboratory standards. We also acknowledged and critically discussed the limitations of the Persistent Scatterer (PS) dataset, both in terms of its sparse distribution and its utility for early warning, adding clarifications in Sections 5.2 and 5.3. Furthermore, in response to the reviewer’s suggestions, we revised Figure 7 to improve interpretability, converted Table 3 into a graphical format for better visualization of saturated hydraulic conductivity, and enhanced Figure 6 to better represent granulometric data.
We appreciate these recommendations, which helped strengthen the scientific value and communicative effectiveness of the study. A detailed point-by-point response is provided in the attached document.
- Laboratory Measurements (Table 2)
-
AC2: 'Reply on RC2', Daniel Basualto, 01 Jul 2025
We sincerely thank Reviewer #2 for their thoughtful and comprehensive evaluation of our manuscript. The review offered valuable recommendations for enhancing the clarity, coherence, and scientific robustness of our work, particularly regarding the connection between controlling factors and debris flow initiation, the presentation of soil stratigraphy, and the discussion of climatic influences and methodological limitations.
We have carefully addressed all general and specific comments provided. In particular, we revised the Introduction to improve focus and narrative fluidity, incorporating both foundational and recent literature to contextualize the study. We also restructured the Discussion and Conclusion sections to better highlight the study’s contributions to hazard assessment, including explicit recognition of data limitations, soil stratigraphy, and climate-driven processes. Moreover, we clarified figures, improved stratigraphic descriptions, and reinforced key methodological aspects such as the spatial distribution of meteorological stations.
All these revisions are detailed in the attached document, where we provide a point-by-point response to each comment. Once again, we appreciate the reviewer’s insights, which were highly constructive and instrumental in improving the manuscript’s scientific impact.
-
RC3: 'Additional comments', Anonymous Referee #2, 14 May 2025
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2025-1394', Anonymous Referee #1, 05 May 2025
General comments:
This manuscript presents a comprehensive investigation into the initiation mechanisms of debris flows in the Southern Andes, with a focus on the Ñisoleufu event. The authors attribute this event to increasing soil saturation during an extreme rainfall episode under typical glacio-volcanic geological conditions, where a low-permeability basal layer promotes water retention in the overlying soil. However, the extent to which this case represents common conditions across the Southern Andes, as implied by the title, has not been adequately discussed. Additionally, the overall structure and clarity of the manuscript require improvement, which currently undermines the value of the research. Further comments are detailed below.
Specific comments:
- L32: The opening sentence suggests that debris flows may result in extreme rainfall, which is likely a typographical error. Please carefully review the manuscript for similar errors.
- Introduction: The introduction requires restructuring. A clearer overview of the Southern Andes in terms of debris flow features and glacio-volcanic environments is needed. The current structure lacks coherence; for instance, the paragraph starting at Line 41 introduces the importance of understanding debris flows in inhabited regions but abruptly shifts to discussing the impact of climate change. At the same time, please reduce repetitive content about the research’s significance.
- L104: The authors mention that three complementary methodologies were used, yet only two are listed in the introductory paragraph of the methodology section.
- Figure 4D: It is recommended to display the position of the profile line in a plan view (e.g., in Figure 4A). Additionally, please consider replacing the north arrow with one indicating the slope direction angle, which would aid reader comprehension.
- L146: Data from four weather stations were used, but only the Pucon station is plotted in the figure. Where is this station located and why do you select it as representative? Furthermore, based on this data, the debris flow appears linked to intense rainfall approximately 15 days prior to the event. Why is the pre-event described as occurring two months earlier?
- Table 2: Both plastic and liquid limits of samples S-3 and S-7 are exceptionally high, approaching or exceeding 100%, which is unusual in geotechnical testing. Have these results been validated? If so, the unique nature of these soil layers should be highlighted and discussed in detail.
- Figure 6: The ERA5-based analysis reveals a clear annual cycle in soil moisture content. However, similar levels of high soil moisture appear to have occurred in previous years, such as around 5 February 2015. What additional factors, beyond soil moisture, may explain the occurrence of the 2023 event compared to those previous intervals?
Technical corrections:
- L19: The phrase "influencing by" is unclear. Consider rephrasing as "influenced by" or revising the sentence for clarity.
- L20: Does ‘an active area’ refer to ‘The southern Andes’?
- L83: The sentence "Recent events become a significant geological hazard" is unclear.
- L115: The subheading appears incomplete.
- L134-136: The sentence "Finally, the changes …" is incomplete and ambiguous.
- Table 2: Please ensure consistency in the formatting of units. For example, "moisture [w](%)" and "density[ρ](g/cm3)".
- L439: ‘to’ should be removed from ‘can to deliver’.
Citation: https://doi.org/10.5194/egusphere-2025-1394-RC1 -
AC1: 'Reply on RC1', Daniel Basualto, 01 Jul 2025
We would like to thank Reviewer #1 for their thoughtful and constructive feedback. Their suggestions significantly contributed to improving the clarity, depth, and scientific robustness of our manuscript, particularly in clarifying regional representativeness, restructuring the introduction, refining figures and tables, and expanding the discussion of soil properties and triggering mechanisms.
In the attached document, we provide a detailed point-by-point response to each general, specific, and technical comment raised by Reviewer #1. Revisions include the addition of new figures, improved methodological clarity, correction of textual inconsistencies, and the expansion of geotechnical and climatic interpretations relevant to debris flow initiation in glacio-volcanic terrains of the Southern Andes.
We sincerely appreciate the reviewer’s efforts and time, which were essential in enhancing the scientific quality of our work.
-
RC2: 'Comment on egusphere-2025-1394', Anonymous Referee #2, 12 May 2025
General Comment
The manuscript titled "Controls over debris flow initiation in glacio-volcanic environments in the Southern Andes" presents a comprehensive analysis of the mechanisms responsible for debris flow initiation in the Ñisoleufu sector, Southern Chile. It effectively integrates geomorphological, geotechnical, hydrometeorological, and remote sensing analyses to assess the factors controlling debris flow occurrence in a complex glacio-volcanic setting. The study’s use of multi-source data strengthens the reliability of the findings. However, the manuscript would benefit from a clearer presentation of the connections between controlling factors and observed events, as well as a more explicit discussion of implications for hazard assessment.
Specific Comments
Introduction
The introduction provides a comprehensive background but could be more focused, particularly in the discussion of previous studies. Some references to regional climate impacts could be condensed to streamline the narrative.
The citations provided lack robustness for a proper framing of debris flows, as most references are from the last 3-4 years. Correct this by adding relevant and foundational studies. Additionally, the transition between topics is somewhat abrupt, lacking fluidity.
Methodology
It would be important to include the location of the meteorological stations in one of the displayed figures to provide spatial context for the data collection.
Results
The results are comprehensive, but the presentation is occasionally repetitive. For example, the discussion of soil stratigraphy (Lines 200-240) could be condensed to highlight the most critical observations.
Figure 6A does not appear to indicate an anomalous trend in soil moisture compared to previous years. It should be emphasized that the combination of saturated soil and intense rainfall plays a key role in triggering debris flows.
Discussion
The discussion appropriately addresses the key findings but could benefit from a more critical evaluation of the limitations of the study.
The role of climate change in debris flow initiation is briefly mentioned but not fully explored. Given the relevance of this factor, a more detailed discussion would enhance the manuscript’s impact.
Conclusions
The conclusions effectively summarize the main findings but lack specific recommendations for hazard mitigation. Consider adding a few practical insights based on the study’s results.
Citation: https://doi.org/10.5194/egusphere-2025-1394-RC2 -
RC3: 'Additional comments', Anonymous Referee #2, 14 May 2025
Additional specific Comments
Upon further consideration I have identified additional points that may require other clarifications:
- Laboratory Measurements (Table 2)
The values reported for liquid limit (WL) and plastic limit (WP) for S-3, as well as WL, WP, and Ku for S-7, appear inconsistent with their geological descriptions. S-3. S-7 represents an active, developing soil, likely rich in organic material, where higher hydraulic conductivity (Ku) would be expected. However, the reported Ku is surprisingly low, potentially indicating compaction, fine-grained content, or measurement errors. Please verify these values and, if accurately, provide additional context to justify these unexpected results. - Limited Number of PS (Figure 7)
The analysis includes only five PS, of which three are located near the boundary and only two within the landslide niche. This sparse dataset may not provide a sufficiently robust basis for reliable precursor identification, especially given that these PS do not appear to exhibit significantly different displacement patterns compared to surrounding points. This raises questions about the reliability of these PS as early warning indicators. I recommend adjusting the color scale in Figure 7 to better distinguish between PS displacement and elevation, which may improve the interpretability of the figure. - To improve clarity, consider presenting the data in Table 3 as a graph, which may provide a more intuitive visualization of the variation in saturated hydraulic conductivity across different soil types.
Citation: https://doi.org/10.5194/egusphere-2025-1394-RC3 -
AC2: 'Reply on RC2', Daniel Basualto, 01 Jul 2025
We sincerely thank Reviewer #2 for their thoughtful and comprehensive evaluation of our manuscript. The review offered valuable recommendations for enhancing the clarity, coherence, and scientific robustness of our work, particularly regarding the connection between controlling factors and debris flow initiation, the presentation of soil stratigraphy, and the discussion of climatic influences and methodological limitations.
We have carefully addressed all general and specific comments provided. In particular, we revised the Introduction to improve focus and narrative fluidity, incorporating both foundational and recent literature to contextualize the study. We also restructured the Discussion and Conclusion sections to better highlight the study’s contributions to hazard assessment, including explicit recognition of data limitations, soil stratigraphy, and climate-driven processes. Moreover, we clarified figures, improved stratigraphic descriptions, and reinforced key methodological aspects such as the spatial distribution of meteorological stations.
All these revisions are detailed in the attached document, where we provide a point-by-point response to each comment. Once again, we appreciate the reviewer’s insights, which were highly constructive and instrumental in improving the manuscript’s scientific impact.
-
AC3: 'Reply on RC3', Daniel Basualto, 01 Jul 2025
We thank Reviewer #3 for their attentive and constructive observations. The additional points raised provided a valuable opportunity to further improve the quality and clarity of our manuscript.
In particular, we verified and contextualized the geotechnical results for soil types S-3 and S-7, justifying their liquid limits and hydraulic conductivity values with reference to regional analogs and laboratory standards. We also acknowledged and critically discussed the limitations of the Persistent Scatterer (PS) dataset, both in terms of its sparse distribution and its utility for early warning, adding clarifications in Sections 5.2 and 5.3. Furthermore, in response to the reviewer’s suggestions, we revised Figure 7 to improve interpretability, converted Table 3 into a graphical format for better visualization of saturated hydraulic conductivity, and enhanced Figure 6 to better represent granulometric data.
We appreciate these recommendations, which helped strengthen the scientific value and communicative effectiveness of the study. A detailed point-by-point response is provided in the attached document.
- Laboratory Measurements (Table 2)
-
AC2: 'Reply on RC2', Daniel Basualto, 01 Jul 2025
We sincerely thank Reviewer #2 for their thoughtful and comprehensive evaluation of our manuscript. The review offered valuable recommendations for enhancing the clarity, coherence, and scientific robustness of our work, particularly regarding the connection between controlling factors and debris flow initiation, the presentation of soil stratigraphy, and the discussion of climatic influences and methodological limitations.
We have carefully addressed all general and specific comments provided. In particular, we revised the Introduction to improve focus and narrative fluidity, incorporating both foundational and recent literature to contextualize the study. We also restructured the Discussion and Conclusion sections to better highlight the study’s contributions to hazard assessment, including explicit recognition of data limitations, soil stratigraphy, and climate-driven processes. Moreover, we clarified figures, improved stratigraphic descriptions, and reinforced key methodological aspects such as the spatial distribution of meteorological stations.
All these revisions are detailed in the attached document, where we provide a point-by-point response to each comment. Once again, we appreciate the reviewer’s insights, which were highly constructive and instrumental in improving the manuscript’s scientific impact.
-
RC3: 'Additional comments', Anonymous Referee #2, 14 May 2025
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Journal article(s) based on this preprint
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Ivo Fustos-Toribio
Daniel Basualto
Ardy Gatica
Alvaro Bravo-Alarcón
José-Luis Palma
Gabriel Fuentealba
Sergio A. Sepúlveda
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(2069 KB) - Metadata XML
General comments:
This manuscript presents a comprehensive investigation into the initiation mechanisms of debris flows in the Southern Andes, with a focus on the Ñisoleufu event. The authors attribute this event to increasing soil saturation during an extreme rainfall episode under typical glacio-volcanic geological conditions, where a low-permeability basal layer promotes water retention in the overlying soil. However, the extent to which this case represents common conditions across the Southern Andes, as implied by the title, has not been adequately discussed. Additionally, the overall structure and clarity of the manuscript require improvement, which currently undermines the value of the research. Further comments are detailed below.
Specific comments:
Technical corrections: