the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 25 Sep 2026
Towards the European Tephra Hazard Map: Methodology and Catalogue of Footprints
Abstract. Many parts of Europe are exposed to tephra hazards that jeopardise regions around volcanoes and the continental airspace. Quantifying and mapping the impacts from future eruptions is relevant to aviation stakeholders and to national and regional civil protection administrations and agencies. This paper presents a novel methodology for long- and short-term Probabilistic Volcano Hazard Assessment (PVHA) from tephra based on a large catalogue of footprints and associated metadata, each footprint representing a single-scenario model realisation. The methodology is used to generate a first version of the European Tephra Hazard Map (ETHM), a collaborative initiative aiming at providing single- and multi-volcano mappings consistent and homogeneous across spatiotemporal scales and volcanoes. More than 53,000 footprints from 12 European volcanoes were computed by running the FALL3D atmospheric dispersal model on the accelerated partition of the MareNostrum-5 supercomputer. In regional model nests (2 km model grid resolution), footprints identify areas prone to hazardous tephra fallout. At European scale (10 km model grid resolution), footprints delineate hazardous airspace regions in terms of ash concentration at critical flight-level layers. The catalogue of footprints is stored in a Simulation Data Lake (SDL@CINECA) to ensure accessibility and re-usability, as well as to ease the addition of footprints from other volcanoes in the future. In parallel, a lightweight service facilitates downstream hazard mapping and dynamic update of hazard based on user-given Probability Density Functions (PDFs), decoupling the computational workload of simulating the physical process from the actual hazard quantification.
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Status: open (until 21 Nov 2026)
- RC1: 'Comment on egusphere-2026-4485', Rodrigo Calderon, 20 Oct 2026 reply
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Referee comment on “Towards the European Tephra Hazard Map: Methodology and Catalogue of Footprints”
The manuscript presents a framework for probabilistic tephra hazard mapping across Europe, based on the European Tephra Hazard Map (ETHM) methodology. The main idea is to separate the computationally expensive physical simulations from the probabilistic assumptions used to produce hazard maps. This is achieved through a large catalogue of precomputed FALL3D footprints, each representing a plausible eruption and meteorological scenario, together with its associated metadata. This allows users to apply different probability density functions to the existing catalogue and generate updated single- or multi-volcano hazard maps without having to rerun the simulations whenever eruption probabilities or monitoring information change.
The authors demonstrate the approach using 53,016 simulations for 12 European volcanoes in the Azores, the Canary Islands, Iceland and Italy. The simulations cover both regional tephra fallout, using 2 km nests, and continental-scale airborne ash relevant to aviation, using a 10 km European domain. The data are openly available through a Simulation Data Lake, supported by a workflow that also allows the catalogue to be expanded to include other volcanoes.
I consider this a strong and useful contribution. The catalogue-based approach provides a flexible way to develop and update probabilistic tephra hazard maps as scientific knowledge, eruption probabilities or monitoring information change, without the need to rerun the full set of simulations. This is relevant for both research and operational applications. I recommend minor revisions. My comments are mainly aimed at clarifying some methodological aspects and the interpretation and potential use of the resulting hazard maps.
L20–23: Could the authors briefly explain how the exposed elements mentioned here may be affected by tephra fallout, and whether there are established impact thresholds or accumulation loads associated with these impacts? A brief reference to relevant impact or vulnerability studies would help readers understand how the hazard outputs relate to potential consequences.
L80–82: Could the authors clarify how the cited studies support the combination of overlapping footprints from different volcanoes? In particular, what assumptions are made when combining the contributions from multiple volcanoes? For example, does this approach assume independence between volcanoes, and how is the potential temporal coincidence of eruptions addressed in the resulting multi-volcano hazard maps?
L89: Have these values or criteria been evaluated or validated, for example through expert elicitation or comparison with past eruptions? A brief explanation of their basis, along with any relevant limitations, would help readers understand how they should be interpreted.
L98–99: Could the authors clarify what is meant by “homogeneous” footprints and in what sense they are directly comparable? In particular, can users compare individual footprints across volcanoes, and what conditions are required for this comparison, such as a common grid, consistent thresholds or the use of the same meteorological wind period?
L107–108: How are unrest signals incorporated into the catalogue? Are they represented through specific source parameters or eruption scenarios, or are they used only to update the PDFs assigned to the existing footprints? Clarifying this point would help readers understand how short-term monitoring information is incorporated into the framework and whether it can modify the physical scenarios considered.
L120–121: Has the catalogue or the proposed workflow been evaluated by potential end users? If so, could the authors briefly describe how this evaluation was conducted and summarise the main feedback? This would help clarify the framework's readiness for operational applications.
L194–195: I understand that the study focuses on continental-scale hazard assessment. However, excluding eruption columns below 2 km could lead users to overlook the relevance of smaller eruptions, which are generally more frequent and may still produce significant local impacts. I suggest explicitly stating that the resulting hazard maps are conditional on eruption columns reaching at least 2 km above the vent. It would also be useful to briefly discuss whether smaller eruptions could still produce relevant impacts in proximal areas, for example on agriculture, infrastructure or local aviation, and how these are addressed, if at all, by the proposed framework.