the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Assessing long-term tephra fallout hazard in southern Italy from Neapolitan volcanoes
Manuel Stocchi
Beatriz Martínez Montesinos
Laura Sandri
Jacopo Selva
Roberto Sulpizio
Biagio Giaccio
Massimiliano Moscatelli
Edoardo Peronace
Marco Nocentini
Roberto Isaia
Manuel Titos Luzón
Pierfrancesco Dellino
Giuseppe Naso
Antonio Costa
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- Final revised paper (published on 23 Jun 2023)
- Supplement to the final revised paper
- Preprint (discussion started on 22 Feb 2023)
- Supplement to the preprint
Interactive discussion
Status: closed
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RC1: 'Comment on nhess-2023-3', Ricardo Ramalho, 03 Apr 2023
Review of manuscript "Assessing long-term tephra fallout hazard in Southern Italy from Neapolitan volcanoes" by Silvia Massaro and co-authors.
The manuscript concerns a comprehensive long-term volcanic fallout hazard assessment for southern Italy, by considering all possible volcanic sources in the Neapolitan area. Critically, the study employed a multi-volcano probabilistic volcanic hazard assessment, using a methodology akin to seismic and tsunami probabilistic hazard assessments and rarely employed in volcanic settings. In my view the manuscript is very robust, clear and written in an impeccable English. The methodology is explained in detail and is sound, with the particularities of each volcano being taken into account (e.g. introduced eruptive parameters, exceedance probabilities, probability of new volcanic vent opening), resulting in robust mean hazard maps, even considering different levels of aggregation, from the different sources. Overall I found the approach comprehensive, grounded in reasonable approaches and assumptions that incorporate the state of the art in terms of knowledge of the different volcanoes, and also relying on a solid Bayesian analysis. I particularly appreciated the level of detail and objectiveness that the manuscript includes, as to how the different parameters and steps were computed. My only very minor comment concerns the claim that this is the first multi-volcano PVHA, given that similar approaches have been done in monogenetic fields and ocean island volcanoes subjected to monogenetic eruptions of different style (e.g. Becerril et al, 2014, https://doi.org/10.5194/nhess-14-1853-2014) constitute, effectively, a multi-volcano approach. I commend the authors for their work – it is the first time I recommend a paper for publication as it is.
Citation: https://doi.org/10.5194/nhess-2023-3-RC1 -
AC1: 'Reply on RC1', Silvia Massaro, 24 Apr 2023
We warmly thank the reviewer for his comments.
Regarding the multi-volcano PVHA, we would like to note that with “the first multi-volcano PVHA” we referred to the novel methodology in volcanic hazard assessment which provides the aggregation of a set of volcanoes in calculating the mean annual frequency with which a certain hazardous phenomenon (in this case tephra fallout) exceeds a given threshold at a given location during a given exposure time window.
Actually, in the case of Becerril et. (2014), the authors provided a long-term multi-hazard assessment considering lava flows, pyroclastic density currents and fallout for a single volcano (even though it has a monogenetic field). In our case we considered tephra hazard only, applied to the three Neapolitan volcanoes. However, we explained better this point in the Introduction.
Citation: https://doi.org/10.5194/nhess-2023-3-AC1
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AC1: 'Reply on RC1', Silvia Massaro, 24 Apr 2023
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RC2: 'Comment on nhess-2023-3', Karoly Nemeth, 09 Apr 2023
Review of manuscript "Assessing long-term tephra fallout hazard in Southern Italy from Neapolitan volcanoes" by Silvia Massaro and co-authors.
This is a very well-written and logically well-prepared manuscript that deals with the pyroclastic fallout hazard of the greater Neapolitan region. The manuscript unique selling point is that it treats fallout hazard as a complex phenomenon in the Neapolitan context where three complex Holocene volcanic regions viewed as potential hazard sources of tephra fall. The research subject is well placed within the broader hazardscape of a region heavily populated by 3 million+ residents and additional visitors in any part of the year accompanied with the complex and significant infrastructure, lifelines and built environment. The manuscript rightfully state that similar research was conducted in the past and their results form the key elements of volcanic hazard mitigation used by the Civil Defence. The new aspect of this manuscript is that it treats fallout hazard as a multi-volcano hazard hence applies a probabilistic volcanic hazard assessment applicable for multi-sourced scenarios. I liked the novel approach of the manuscript to develop specifically tailored method for such volcanic hazards applying workflow models borrowed from seismic and tsunami probabilistic hazard. This is a clear sign to me that the method outlined in this manuscript is new and form a pioneering hazard estimate potentially can be used and be useful in other regions facing with tephra fallout hazards from various, potentially simultaneous sources. While the manuscript outlines the link to the seismic hazards, there is very little explanation to emphasize the similarities to tsunami hazard modelling and other geohazards briefly mentioned in the text. Some clarification or explanation lines would have been useful for the reader to see the link in a simple but even more direct way.
The manuscript builds up on a super robust data set that is naturally given knowing that the study area is probably the best studied region on Earth for volcanic hazards as the risk is very high, hence such works are in need. While the Authors made everything possible to show the data sources clearly, the amount is so overwhelming, that the reader can easily be get lost among the various level and type of data utilized. Maybe a simple overview table could help for further clarification where the reader quickly can see the exact maps, papers, direct measurements of the utilized parameters been delivered.
The manuscript is in its early section introducing the “eruption size class” concept. This gradually became some sort of core of the simulations, but I find not evidently clear what those classes actually mean. Early in the manuscript a dedicated clarification paragraph would be useful on this, where the dimensions of such classes also introduced. Similarly, there are some mentions about eruption styles of the key eruptions used as typical cases, but somehow not evidently documented what exactly eruption style refers to in the context of the manuscript.
Following the previous two points, I was wondering if a narrative table would not be a good addition where the reader (basically those approaching to the manuscript or try to understand it from more traditional geology background) could see clearly what those values meant. Such addition may also help other end-users to understand better your very good report (consider that they work will be open access and potentially councils, businesses etc would be able to access and read it, but for them for clarity such tables would be super critical).
The manuscript has also few very specific terms unlikely would make sense for those readers not deeply involved in geomathematics. Terms like “intra-size-class aleatory variability” would be worth to explain for clarity.
One of the main selling points of the manuscript is to combine the three main hazard source fallout hazards and develop a united hazard model. Somehow, I see why this is important, but I think a clear paragraph to show the benefit of doing this would really set the manuscript far better. Such paragraph also could be feed back to the discussion section where the combined maps are discussed and justify that doing this created something that can be more useful mitigating tephra hazard. Currently such frame of the manuscript is missing. In details indeed there are information, but it would be really better if the Authors would provide a frame along the reader guided.
While I understand that Vesuvius and Campi Flegrei clearly have the threefold classes like small, medium and large somehow it is not evident from the manuscript why Ischia been treated only as a tephra source through large eruptions. Somehow, I have some idea by reading the manuscript few times, but it would be better if an explanatory line would be added to make this justification stronger. According to the info on the geological map, Ischia also had small or medium tephra providing eruptions in the same timescale than the other two volcanoes, so just not really clear why then they are not included. Really, just an explanation line would clear this.
The data presenting and hazard simulation sections are fine as far I can evaluate. The hazard maps are very informative. I was wondering a lot about the concept of hazard disaggregation and the claimed similarity with the seismic source differentiation. I think a bit of explanation is needed here. I am also a bit critical if this is not a superficial step. First, we collect the info based on tephra mapped applying all of our knowledge on the features need to be identified to be able confidentially able to measure thickness associated to specific, unique sources. Then we use these data adding it to a global thickness data to simulate the tephra dispersal and probability of coverage within specific time. Then we try to “deconvolute” this information and rank the relative weight of each source role in the overall distribution pattern the simulation gave us. A little bit circular argument to me. I think a paragraph here for clarification would be really useful.
The hazard maps look good, but I would add a line to the caption with a plain language explanation. Even by adding a graphic explanation what the maps actually mean. Such extra line per figure would make the manuscript more relevant to end-users.
Overall, I think this is an excellent manuscript and its results will impact volcanic hazard mitigation in this heavily populated region. The work fits perfectly to the scope of the Journal and after some minor, mostly clarification style revision I highly recommend it to be published. After revision no need second review, as I think the Editor can decide the final outcome of the manuscript.
Best regards,
Prof Károly Németh
Volcanic Risk Solutions, Massey University, New Zealand
Institute of Earth Physics and Space Science, Hungary
Saudi Geological Survey, Jeddah
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AC2: 'Reply on RC2', Silvia Massaro, 24 Apr 2023
We very appreciated the comments of the reviewer, and we thank him for helping us to clarify the following points:
1) We here provide an additional explanation aimed to emphasize the similarities to tsunami hazard modelling and other geohazards. In the revised manuscript we will add the following paragraph: “Other geohazards, such as for Probabilistic Tsunami Hazard Assessment (PTHA) or Probabilistic Seismic Hazard Assessment (PSHA) methodologies, provide a framework for assessing the exceedance provability of a given measure of the intensity of the phenomeno (e.g. tsunami wave height, peak ground acceleration) at a particular location within a given time window. As for volcanic eruptions, historical catalogs are usually incomplete, and thus it is usually adopted a computational hazard scheme, based on the combination of probabilistic source models and empirical or numerical models of propagation of the hazardous phenomena (e.g., Grezio et al., 2017, Gerstenberger et al 2020). Sometimes, the explicit numerical modeling of individual scenarios is required, like in the case of tsunamis or of the volcanic eruptions(e.g., Selva et al., 2016; Grezio et al., 2017). In all cases, a common description based on the quantification of the mean annual rates of exceedance is possible, making possible an explicit comparison among the different hazard and consequent risks (Gruntal et al 2006; Marzocchi et al. 2012). Beside volcanic activity, other geohazards (as landslides, meteorological events) could be treated within the same computational framework”;
2) Regarding the rewiever's comment "While the Authors made everything possible to show the data sources clearly, the amount is so overwhelming, that the reader can easily be get lost among the various level and type of data utilized. Maybe a simple overview table could help for further clarification where the reader quickly can see the exact maps, papers, direct measurements of the utilized parameters been delivered", we would like to stress that the mean Annual Probabilities for each volcano are based on the study of Selva et al. (2022), who report a detailed catalog of eruptions over a long reference period for each volcano. Other parameters were taken from Sandri et al. (2016) for Somma-Vesuvius and Campi Flegrei, and from Primerano et al. (2021) and Selva et al. (2019) for Ischia. The above studies already presented reviews and several tables that summarize the sources needed for such pieces of information. We think adding a further composite table would not be easy and useful because it would become difficult to be presented and read;
3) Regarding the rewiever's comment "The manuscript is in its early section introducing the “eruption size class” concept. This gradually became some sort of core of the simulations, but I find not evidently clear what those classes actually mean.", we would like to stress that with the term “eruption size class” we referred to the broad range of possible eruptive sizes identified by the total erupted mass which is used to define the eruption magnitude. Following Sandri et al. (2016), we consider splitting the eruptive size range into a few classes that can be linked to representative members like the classical approach used in past studies. These classes ideally span the general range continuously, whereas representative members, by definition, discretize it. We added a short explanation in the revised manuscript;
4) Regarding the rewiever's comment "I was wondering if a narrative table would not be a good addition where the reader (basically those approaching to the manuscript or try to understand it from more traditional geology background) could see clearly what those values meant.", as explained above, we think that such a kind of very heterogeneous table would not be feasible and useful, and in any case, all the relevant references are clearly indicated;
5) Regarding the rewiever's comment "the manuscript has also few very specific terms unlikely would make sense for those readers not deeply involved in geomathematics. Terms like “intra-size-class aleatory variability” would be worth to explain for clarity.", as explained in the previous points, we split the eruptive size range into a few representative classes. Within each class there is a variability in size that is indicated as “intra-size-class aleatory variability”, as described in Sandri et al. (2016). In this regard, the “intra-size-class” variability represents the aleatory variability due to combinations of parameters characterizing eruptions which belong to the same eruptive class. As for the previous point, in the revised version, we will add an explanation about this point;
6) Regarding the rewiever's comment "One of the main selling points of the manuscript is to combine the three main hazard source fallout hazards and develop a united hazard model. Somehow, I see why this is important, but I think a clear paragraph to show the benefit of doing this would really set the manuscript far better. ", we agree with the reviewer, therefore we will provide the following paragraph in the revised manuscript: “The total mean hazard maps shown in Fig. 3d provide a unified representation of the potential tephra ground load coming from one of the three volcanoes. This means that, for different ARPs, we can evaluate the main tephra ground load exceeding the defined thresholds, in each point of the whole domain. As expected, the shorter ARP (100 years) represents the most frequent hazardous scenario related with the most frequent eruptions having lower magnitudes, while for the longer ARP (1000 years) prevails heavier tephra load distribution related with less frequent eruptions having the highest magnitude. In this way, such overall tephra hazard picture is more useful for mitigation actions (e.g., road viability, roofs damaging) with respect to the previous tephra hazard maps which accounted for a single volcano.”;
7) Regarding the rewiever's comment "According to the info on the geological map, Ischia also had small or medium tephra providing eruptions in the same timescale than the other two volcanoes, so just not really clear why then they are not included. Really, just an explanation line would clear this.", we thank the reviewer for this comments that lets us to clarify the choice made for Ischia. We only considered the Large eruptive size class (i.e., Cretaio eruption) because it is the best characterized eruption in terms of ESP (Primerano et al., 2021) and is the only eruptive scenario which can have a significative impact beyond the island (Selva et al., 2019). On the contrary, the other eruptions having lower magnitude do not have a significant impact beyond the island (Selva et al., 2019). We will add this explanation in the revised manuscript;
8) Regarding the rewiever's comment "The hazard maps are very informative. I was wondering a lot about the concept of hazard disaggregation and the claimed similarity with the seismic source differentiation. I think a bit of explanation is needed here.", we would like to stress that, as reported in Bazzurro and Cornell (1999), the hazard disaggregation scheme permits to postprocess hazard results to display the relative contributions to the hazard of the different source. This is not trivial, as the contribution of each individual source depend on many factors, like the size and the position of the event, the annal rates of each specific size and position, and the propagation. These are all ingredients of the hazard, but their combination and their balance is not trivial at all. For example, is more impacting in one unlikely big event or a more likely smaller event with favorable wind? Is more impacting one unlikely event in a location usually upwind, or a more likely event in a location usually downwind, but with a rare variable wind direction? To answer these questions, the only solution is to post-process the hazard combination and balance the different contribution. We will try to add a few sentences in the text to better explain this very important point;
9) Regarding the rewiever's comment "The hazard maps look good, but I would add a line to the caption with a plain language explanation. ", we would like to note that hazard maps showed in the Figures are already a graphical representation of the tephra hazard. We think that the captions are already written in a clear way and trying to make the explanation plainer may introduce misunderstandings;
Finally, we thank the reviewer for his appreciation of our work.
Citation: https://doi.org/10.5194/nhess-2023-3-AC2
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AC2: 'Reply on RC2', Silvia Massaro, 24 Apr 2023