the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 11 Feb 2026
Reconstruction of the 1989 Laguna Del Cerro Largo GLOF: an Interdisciplinary Understanding of GLOF Impacts
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.
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RC1: 'Comment on egusphere-2025-5791', Anonymous Referee #1, 04 Mar 2026
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AC1: 'Reply on RC1', Jonathan Burton, 13 Mar 2026
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Thank you for your insight for this article. I appreciate your encouraging comments and in-depth review. I look forward to taking this feedback into account for future drafts.
For specific comments:
1) This is a great suggestion to further detail which data were used as input and which were independent constraints. I think a figure flowchart would be an excellent and efficient addition to the manuscript.
2) This is a consideration that I was looking into in previous work. I have not tried to generate a DEM from trimetrogon imagery and ultimately decided that the magnitude of the event supersedes the level of uncertainty from a DEM difference, as the flood had likely evolved to a more newtonian fluid at the analyzed stretches. I think that, as you suggested, a short discussion of DEM uncertainty would certainly be merited, and will be included in the manuscript.
3) Thank you for your feedback here. To be honest, the original draft had a much more detailed description of the information you indicated in your comment, but ultimately was scraped for the necessity of brevity. However, it does seem like I can and should address your concerns with a careful edit to respond to your questions. I will add a short description to incorporate your comments, but will describe our process briefly: We were limited by the duration of our field campaign and opted for a sample of 50. We sought out trees that had clear indications of disturbances, ie scares, scratches, etc. Additionally, we were looking for trees that were old enough to have likely been impacted by the flood. We found several trees that had scars and other disturbances, (I'd have to look at the numbers specifically) but the samples of those did not penetrate enough to capture pre-1989 growth. Generally, we followed sampling methods established in Gorsic et al 2025 and Ballesteros-Canovas 2015, trying to get one control sample and one sample on the disturbance for disturbance impacted trees. For the general sampling of visibly unaffected trees, (looking here for variations of growth rings), we selected trees which were higher than interannual flood plains to limit impacts from recent non-glof flooding, yet within the nominally affected zone of 4-8 meters above the river. In the manuscript I have several pictures of physical markers which maybe I didn't describe as thoroughly as I could have, with residual woody debris, scars, and remnant deposition in tree canopy. I will better link these observations to the model results, as you've suggested.
4) I think this is a huge consideration, thanks for bringing this up. I think certainly this has an impact on the modeling results, and merits discussion. Such sediment-rich flood waves are often described as hyperconcentrated flows occupying the continuum between clear-water floods and debris flows, and my guess is that much of the initial flood energy was dissipated at the 90° turn upstream, seen by the immense sand and gravel deposition upstream of that corner, such that the downstream flood was closer to a clear-water flood than the upper reaches with large boulders mobilized. I will add an additional paragraph with considerations.
5) We thank the reviewer for this crucial input. I have another publication in-review that is an in-depth analysis of regional GLOF risk policy that I can pilfer some insights for this topic. In short, prior to our work, the largest GLOF Qpeak were those that came from Colonia, and the new cycle emanating from HPN4 near Steffan. These GLOF discharges seem to attenuate due to the impounding glacier that extends drainage to over the course of several days, with peak discharges near 5k m3. I collaborated with the DGA to model HPN4 and this is also in-review. The balance between low-probability / high-impact of moraine dammed glacial lakes aren't actively mitigated for because of the prior underestimate of potential magnitudes, and thus have important consequences for the scope of DRR work in the area.
We thank the author again for the valuable insights and comments, and look forward to incorporating these edits and further discussion.
Citation: https://doi.org/10.5194/egusphere-2025-5791-AC1
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AC1: 'Reply on RC1', Jonathan Burton, 13 Mar 2026
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- 1
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