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:

1. 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.
2. 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.
3. L104: The authors mention that three complementary methodologies were used, yet only two are listed in the introductory paragraph of the methodology section.
4. 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.
5. 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?
6. 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.
7. 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:

1. L19: The phrase "influencing by" is unclear. Consider rephrasing as "influenced by" or revising the sentence for clarity.
2. L20: Does ‘an active area’ refer to ‘The southern Andes’?
3. L83: The sentence "Recent events become a significant geological hazard" is unclear.
4. L115: The subheading appears incomplete.
5. L134-136: The sentence "Finally, the changes …" is incomplete and ambiguous.
6. Table 2: Please ensure consistency in the formatting of units. For example, "moisture [w](%)" and "density[ρ](g/cm³)".
7. L439: ‘to’ should be removed from ‘can to deliver’.

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.