Status: this preprint is open for discussion and under review for Natural Hazards and Earth System Sciences (NHESS).
Reconstruction of the 1989 Laguna Del Cerro Largo GLOF: an Interdisciplinary Understanding of GLOF Impacts
Jonathan W. Burton,Frederick B. Chambers,Lisa Kelley,and Benjamin Soto Narbona
Abstract. The March 16, 1989, glacial lake outburst flood (GLOF) from Laguna del Cerro Largo in Valle Soler, Aysén, Chile, is one of the largest recent moraine-dammed GLOFs in the region. This interdisciplinary approach reconstructs the GLOF downstream impacts using HEC-RAS 2D and GeoClaw from witness accounts. Model results are then validated through field analysis of sediment deposition, dendrogeomorphic surveys, radiocarbon dating. Sediment cores reveal distinct clastic layers attributable to the 1989 event and evidence of an earlier outburst flood from the adjacent Laguna Turbio, dated circa 125 ybp. The model results also indicate a substantially higher peak discharge than official reports, impacting subsequent disaster policy decades later. While dendrogeomorphic sampling was hindered by fungal decay in Nothofagus species, the findings highlight both the potential and limitations of interdisciplinary reconstructions of GLOF events in remote, data-scarce environments.
Received: 21 Nov 2025 – Discussion started: 11 Feb 2026
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“Reconstruction of the 1989 Laguna del Cerro Largo GLOF: an Interdisciplinary Understanding of GLOF Impacts”
General comments
This manuscript presents a comprehensive, interdisciplinary reconstruction of the 1989 Glacial Lake Outburst Flood (GLOF) in Valle Soler, Chile. By combining 2D hydrodynamic modelling with local witness accounts and field validation, the authors revisit an event for which instrumental data are scarce and historical estimates remain uncertain.
The study is significant because it challenges historical estimates of this event using modern hydrodynamic modelling and provides new insights into GLOF processes. The discrepancy identified between the ~2,000 m³ s⁻¹ estimate reported in the original study and the authors’ modelled peak discharge highlights a likely underestimation of GLOF hazards, with implications for regional hazard assessment.
The manuscript is generally well structured and clearly written. The compilation of modelling results, sedimentary evidence, and historical information represents a promising dataset. However, the integration between the different lines of evidence remains somewhat descriptive, and several methodological aspects would benefit from clarification regarding the robustness of the reconstruction.
Overall, the study has clear potential but requires minor revisions to strengthen methodological clarity and interdisciplinary synthesis.
Specific major comments
1. Framework and independence of evidence
The manuscript adopts a transdisciplinary approach combining modelling, field evidence, and witness testimonies. While this integration is a clear strength of the study, the analytical framework linking these datasets could be described more explicitly.
It would be helpful to clarify how the different datasets are used within the reconstruction (e.g. model inputs, validation constraints, contextual evidence). For instance, witness testimonies appear to provide both input parameters for the hydraulic simulations (e.g. timing or duration of the flood) and supporting evidence for the plausibility of the modelling results. The manuscript would benefit from clarifying which elements were used to parameterise the models and which were retained as independent validation constraints, in order to avoid potential circular reasoning.
A short conceptual workflow figure summarising how the different datasets contribute to the reconstruction could help clarify this methodological framework.
2. Pre-event topography and modelling
The hydraulic simulations are based on the Copernicus 30 m DEM acquired several decades after the 1989 event. The manuscript acknowledges that post-flood erosion and deposition may have modified channel geometry and flow pathways, but the implications for the hydraulic reconstruction are not discussed in detail.
Given that fluvio-glacial plains are particularly prone to channel migration, sediment redistribution, and morphological reorganisation, the DEM used may differ substantially from the pre-event terrain that controlled flood routing. The authors may wish to consider whether an approximate reconstruction of the pre-event topography could be attempted; for example, by adjusting DEM contours using georeferenced historical aerial imagery where available (e.g. trimetrogon photography is available for some periods in this region).
Alternatively, a short discussion of how DEM uncertainty may influence model results would strengthen the interpretation of the simulations.
3. "Vanishing Evidence" and Proxy Limitations
The manuscript reports that dendrogeomorphic sampling was hindered by fungal decay affecting Nothofagus species, which limited the usefulness of tree-ring evidence for reconstructing the 1989 event. Such preservation issues are well known in humid Patagonian environments. To help the authors enhance their discussion and better integrate these results, I offer the following comments:
Sampling locations: Were samples collected primarily within the active flood track, along floodplain margins, or within depositional zones? The spatial distribution of affected trees is important for distinguishing between GLOF impacts and smaller torrential floods. A map overlaying sampling sites with the modelled flood extent could help clarify whether the “vanishing evidence” reflects biological preservation issues or geomorphic patterns.
Sampling strategy: I would be interested to learn more about the criteria used to select trees for sampling (e.g. targeting visibly disturbed individuals versus systematic sampling across the floodplain) and how the final sample size was determined.
Please clarify whether the sampling strategy was independent of the model results. Confirming whether the botanical evidence served as an independent test of the model’s reach (rather than being guided by it) would strengthen the validation strategy.
Even if dendrochronological dating proved difficult, physical markers such as scarheight and orientation may still provide useful information on flood magnitude and debris transport. If such observations were recorded, it would be interesting to briefly discuss how these compare with the modelled water surface elevation during the 1989 event.
4. Process interpretation versus modelling assumptions
The discussion suggests that the initial flood may have behaved as a dense, debris-flow-like slurry given the mobilisation of very large boulders. However, both modelling approaches are based on shallow-water, Newtonian flow assumptions. It could be interesting to briefly discuss how this interpretation of potentially debris-rich flow conditions relates to the modelling framework, and whether such processes could influence the reconstructed peak discharge or flow depths.
5. Contextualizing the revised peak discharge estimate
A key conclusion of the study is that peak discharge during the 1989 event may have been substantially higher than estimates initially reported in Hauser (1993). This is an important result, and the discussion could be strengthened by placing these revised estimates in a broader regional context.
For example, it may be useful to briefly compare the reconstructed discharge with other documented GLOF events in Patagonia or to clarify how such revised estimates might influence current interpretations of regional hazard.
Minor/Technical suggestions
Consider adding a detailed map showing the locations of dendrogeomorphic samples and sediment cores relative to the modelled flood extent.
Data Summary: A summary table correlating each dataset (witness, sediment, tree-rings) with the specific flood characteristic it constrains (magnitude, timing, extent) would greatly improve readability.
This research presents an interdisciplinary case study of a glacial lake outburst flood that occurred in 1989. Combining witness interviews, hydrologic modeling, and field methods, we discuss the long term impacts of the flood, as much on the physical terrain, as on contemporary policy creation regarding development and disaster mitigation. These findings provide interdisciplinary insights into a relatively rare and remote processes in data-sparse regions.
This research presents an interdisciplinary case study of a glacial lake outburst flood that...
Referee report on
“Reconstruction of the 1989 Laguna del Cerro Largo GLOF: an Interdisciplinary Understanding of GLOF Impacts”
General comments
This manuscript presents a comprehensive, interdisciplinary reconstruction of the 1989 Glacial Lake Outburst Flood (GLOF) in Valle Soler, Chile. By combining 2D hydrodynamic modelling with local witness accounts and field validation, the authors revisit an event for which instrumental data are scarce and historical estimates remain uncertain.
The study is significant because it challenges historical estimates of this event using modern hydrodynamic modelling and provides new insights into GLOF processes. The discrepancy identified between the ~2,000 m³ s⁻¹ estimate reported in the original study and the authors’ modelled peak discharge highlights a likely underestimation of GLOF hazards, with implications for regional hazard assessment.
The manuscript is generally well structured and clearly written. The compilation of modelling results, sedimentary evidence, and historical information represents a promising dataset. However, the integration between the different lines of evidence remains somewhat descriptive, and several methodological aspects would benefit from clarification regarding the robustness of the reconstruction.
Overall, the study has clear potential but requires minor revisions to strengthen methodological clarity and interdisciplinary synthesis.
Specific major comments
1. Framework and independence of evidence
The manuscript adopts a transdisciplinary approach combining modelling, field evidence, and witness testimonies. While this integration is a clear strength of the study, the analytical framework linking these datasets could be described more explicitly.
It would be helpful to clarify how the different datasets are used within the reconstruction (e.g. model inputs, validation constraints, contextual evidence). For instance, witness testimonies appear to provide both input parameters for the hydraulic simulations (e.g. timing or duration of the flood) and supporting evidence for the plausibility of the modelling results. The manuscript would benefit from clarifying which elements were used to parameterise the models and which were retained as independent validation constraints, in order to avoid potential circular reasoning.
A short conceptual workflow figure summarising how the different datasets contribute to the reconstruction could help clarify this methodological framework.
2. Pre-event topography and modelling
The hydraulic simulations are based on the Copernicus 30 m DEM acquired several decades after the 1989 event. The manuscript acknowledges that post-flood erosion and deposition may have modified channel geometry and flow pathways, but the implications for the hydraulic reconstruction are not discussed in detail.
Given that fluvio-glacial plains are particularly prone to channel migration, sediment redistribution, and morphological reorganisation, the DEM used may differ substantially from the pre-event terrain that controlled flood routing. The authors may wish to consider whether an approximate reconstruction of the pre-event topography could be attempted; for example, by adjusting DEM contours using georeferenced historical aerial imagery where available (e.g. trimetrogon photography is available for some periods in this region).
Alternatively, a short discussion of how DEM uncertainty may influence model results would strengthen the interpretation of the simulations.
3. "Vanishing Evidence" and Proxy Limitations
The manuscript reports that dendrogeomorphic sampling was hindered by fungal decay affecting Nothofagus species, which limited the usefulness of tree-ring evidence for reconstructing the 1989 event. Such preservation issues are well known in humid Patagonian environments. To help the authors enhance their discussion and better integrate these results, I offer the following comments:
4. Process interpretation versus modelling assumptions
The discussion suggests that the initial flood may have behaved as a dense, debris-flow-like slurry given the mobilisation of very large boulders. However, both modelling approaches are based on shallow-water, Newtonian flow assumptions. It could be interesting to briefly discuss how this interpretation of potentially debris-rich flow conditions relates to the modelling framework, and whether such processes could influence the reconstructed peak discharge or flow depths.
5. Contextualizing the revised peak discharge estimate
A key conclusion of the study is that peak discharge during the 1989 event may have been substantially higher than estimates initially reported in Hauser (1993). This is an important result, and the discussion could be strengthened by placing these revised estimates in a broader regional context.
For example, it may be useful to briefly compare the reconstructed discharge with other documented GLOF events in Patagonia or to clarify how such revised estimates might influence current interpretations of regional hazard.
Minor/Technical suggestions