the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
30 Mar 2021
30 Mar 2021
Debris Flow event on Osorno volcano, Chile, during summer 2017: New interpretations for chain processes in the Southern Andes
- 1Department of Civil Engineering, University of La Frontera, Francisco Salazar 1145, Temuco, Chile
- 2Departamento de Obras Civiles y Geología, Facultad de Ingeniería, Universidad Católica de Temuco, Rudecindo Ortega 02950, Temuco, Chile
- 3Department of Forest Sciences, Faculty of Agriculture and Forest Sciences, Universidad de La Frontera, Av. Francisco Salazar 01145, Temuco, Chile, 4780000
- 4Butamallín Research Center for Global Change, University of La Frontera, Av. Francisco Salazar 01145, Temuco, Chile, 4780000
- 5Department of Geoscience, University of Wisconsin–Madison, 1215 West Dayton St., Madison, WI 53706, USA
- 6Key Laboratory of Mountain Hazards and Surface Processes, Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, Chengdu 610041, China
- 1Department of Civil Engineering, University of La Frontera, Francisco Salazar 1145, Temuco, Chile
- 2Departamento de Obras Civiles y Geología, Facultad de Ingeniería, Universidad Católica de Temuco, Rudecindo Ortega 02950, Temuco, Chile
- 3Department of Forest Sciences, Faculty of Agriculture and Forest Sciences, Universidad de La Frontera, Av. Francisco Salazar 01145, Temuco, Chile, 4780000
- 4Butamallín Research Center for Global Change, University of La Frontera, Av. Francisco Salazar 01145, Temuco, Chile, 4780000
- 5Department of Geoscience, University of Wisconsin–Madison, 1215 West Dayton St., Madison, WI 53706, USA
- 6Key Laboratory of Mountain Hazards and Surface Processes, Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, Chengdu 610041, China
Abstract. Debris flow generation on volcanic zones at the Southern Andes has not widely studied, despite the enormous economic and infrastructure damage that these events can generate. The present work contributes to the understanding of these dynamics based on a study of the 2017 Petrohué debris flow event from two complementary points of view. First, a comprehensive field survey allowed to delimitate that a rockfall initiated the debris-flow due to intense rainfall event. The rockfall lithology corresponds to lava blocks and autobrecciated lavas, predominantly over 1500 m.a.s.l. Second, the process was numerically modelled and constrained by in situ data collection and geomorphological mapping. The event was studied by back analysis using the height of flow measured in road CH-255 with errors of 5%. Debris flow volume has a high sensitivity with the initial water content in the block fall zone, ranging between 4.7x105 up to 5.5x105 m3, depending on the digital elevation model (DEM) used. Therefore, debris flow showed that the zone is controlled by the initial water content available previous to the block fall. Moreover, our field data suggest that future debris flows events can take place removing material from the volcanic edifice. We conclude that similar events could occur in the future and that it is necessary to increase the mapping of zones with autobrecciated lava close to the volcano summit. Finally, the study contributes to understanding debris flows in the Southern Andes since the Osorno volcano shares similar features with other stratovolcanoes in the region.
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Ivo Janos Fustos-Toribio et al.
Status: final response (author comments only)
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RC1: 'Comment on nhess-2021-74', Roberto J. Marin, 18 Apr 2021
The authors studied a "relevant" volcanic debris-flow event that occurred in Chile and combined field work analysis with numerical modeling to present relevant information about these phenomena. The research study is valuable for the scientific community. Minor errors should be corrected and some modifications to the conclusions and introduction are suggested as follows (I'm sorry to combine small corrections with suggestions and questions indistinctibly):
The English is good but some specific parts have errors that need to be corrected (I addressed some of them but I am not a native English speaker).
Abstract
The abstract is comprehensive and appropriate for the paper.
*I suggest to remove the word "Finally" at the end of the abstract.Introduction
I think the description of the volcanic flow-type landslides in the Andes is very interesting. Probably mentions of the numerical modeling of debris flows in the scientific literature should be included.
Line 38. "Nevertheless, debris flows in volcanic zones have not been evaluated in detail"
I think this phrase is too risky. You can only say that it requires more investigation or not many research studies have been carried out...Lines 39-40. "The present work evaluates the generation of debris flows, taking the 2017 Petrohué event as a case study. This event caused severe economic losses to one of the most popular tourist attractions in southern Chile (INE, 2018)."
Not too common but I think it is ok to read this starting the introduction.The objetive is relevant and it was clearly stated. Probably it's a bit general.
Figure 1. It is difficult to read the text of the figure. Maybe the font size is too small or probably it is solved easily increasing the size of the figure.
Line 114. I suggest to mention Figure 2 better (in the text).
"Different soil deposits allowed understood the mobilization features, checking if it corresponds to a non-Newtonian flow."
I suggest to rewrite this sentence."Liberation zones close to the Volcano summit, were physical weathering of the lava flow deposits exposed by pluvial erosion was assessed in the field."
And to check (and correct) this one."in the follow numerical model."
..."The estimated values of the cohesion and internal friction angle was integrated into a database to be used during the back analysis phase"
...were integratedLine 153. The first time you mention "SERNAGEOMIN" you should specify what it is.
Line 160. "If we take the ?f correspond to the fluid viscosity with isotropic stress distribution."
Please rewrite it clearer."Table 2Model parameters usd in r.avaflow."
A space is missing. Correct the word "used." Why is there an asterisk (*) in the internal friction angle?Line 168. "parameters presenting serious discrepancies were..."
What do you mean serious discrepancies? Is it discrepancies between the simulations and the real event? Or measurements?Line 170. Do you consider a 30-m spatial resolution is appropriate for the modeling? Now, I think that if the reason for the selection of the spatial resolution is the availability or considerable computing efforts it should be stated in the paper.
Line 184. "Surface representation"
Good, partially answering my previous questions.Line 205. "These which favours a faster movement, increasing lateral erosion according to field results"
Please rewrite if it can be clearer.Figure 4 is referenced before Figure 3.
Line 233. "allowed understood"
Probably mispelled.Line 234. "(¡Error! No se encuentra el origen de la referencia)"
Figure 5. "Volumen"
Volume.Figure 6. "Escarp". "Error backanalysis".
Scarp.Results
I think the results presented are relevant to the scientific community. I wonder if the authors consider that figures including more modeling results were not so relevant. In my opinion, since different scenarios, projections and zones were modeled, more maps of the debris flows would be interesting. Probably to include it (I suppose the journal have this option) as supplementary material if the authors justify that they were not so relevant for the paper.I'm not sure if it was specified how the error calculation was done.
"DEM SRTM (...) DEM ASTER concentrated a larger part of the material towards the north"
Not clear for me.I consider many figures (e.g. 5-7) should be referenced better if divided to Figure 7a, b, c...
Lines 315-320. It is good for my previous comment about the DEM resolutions.
"Finally, water-rich mass flows are distinguished by material type, water content, the presence of excess pore pressure, or liquefaction at the source (Calhoun & Clague, 2018)."
This phrase is repeated in lines 337 and 349. Then, both paragraphs have the same contents. Probably you were supposed to remove one of them.Not clear about "best modelled scenario" and "worse scenario for...".
Conclusions
I suggest to shorten the first three paragraphs of the conclusions. A summary may be acceptably but I consider it is not necessary to present results to conclude about them (at least taking so many long phrases).
The last conclusion is very accurate.- AC1: 'Reply on RC1', Ivo Fustos, 03 Aug 2021
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RC2: 'Comment on nhess-2021-74', Anonymous Referee #2, 11 Jul 2021
This paper is mainly focused on the back-analysis of a debris flow event
occurred in 2017 at Osorno volcano (Chile). The analysis was carried on by
collecting field data and by numerical simulations with the r.avaflow
model. The authors found a possible range of initial water content of the
debris flow with an uncertainty related to the adopted DEM (ASTER vs SRTM).
Moreover, the trigger mechanisms and a "Liberation Zone" of the debris flow
were identified, which represent an important input for evaluating the hazard
from future events, both on Osorno and to other similar volcanoes.Minor corrections:
Equation 1:
Please, define the symbol "A" and the underscore symbol.Figure 6: It would be useful to report the boundaries of the real debris
flow for comparison with the simulations.Table 1 reports parameters with different units respect to those used elsewere
in the text. I suggest the following corrections:
Natural unit weight -> Natural density
Dry unit weight -> Density density
Unit weight after consolidation -> Density after consolidation
Concerning the last to lines of Table 1, "shear force" and "normal force" are
actually "shear stress" and "normal stress". Moreover, I suggest to adopt SI
units and convert the stress unit from kg/cm2 to N/m2 or N/cm2.
Table 2 reports the density in kg/m3, differently from Table 1, which reports
densities in g/cm3. This is not an error, but it would be better to adopt
the same units across the paper (See previous comment on Table 1).
I propose to mantain the units adopted in Table 2 and modify those of Table 1.
Moreover, in Table 2, the decimal separator (dot) is intermixed with the
decimal separator (comma). I suggest to uniform the separators by using the dot
for separating the decimals.Typos
Header of Table 2: usd -> used
Line 78: "routethe" -> "route the"
Line 125: cannel -> channel
Lines 234-235: It seems that a reference cannot be found
Line 342: 105 -> 10^5- AC2: 'Reply on RC2', Ivo Fustos, 03 Aug 2021
Ivo Janos Fustos-Toribio et al.
Ivo Janos Fustos-Toribio et al.
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