A multi-scale risk assessment for tephra fallout and airborne concentration from multiple Icelandic volcanoes – Part 1: Hazard assessment

Abstract

Abstract. In order to assist the elaboration of proactive measures for the management of future volcanic eruptions in Iceland, we developed a new scenario-based approach to assess the hazard associated with tephra dispersal and sedimentation at various scales and for multiple sources. The target volcanoes are Hekla, Katla, Eyjafjallajökull and Askja, selected either for their high probabilities of eruption and/or their high potential impact. By coupling tephrostratigraphic studies, probabilistic techniques and modelling, we developed comprehensive eruption scenarios for both short- and long-lasting eruptions and compiled hazard maps for tephra ground deposition at a national scale and air concentration at a European scale using the TEPHRA2 and FALL3D models, respectively. New algorithms for the identification of realistic sets of eruptive source parameters are investigated, which assist the generation of probability density functions of eruption source parameters for the selected scenarios. Aggregation processes were accounted for using various empirical models. Outcomes, i.e. probabilities conditioned to the occurrence of an eruption, help the assessment and comparison of hazard levels at different scales. For example, at a national scale Askja has a 5–10% probability of blanketing the easternmost half of the country with a tephra accumulation of at least 1 kg m−2. At a continental scale, Katla has a 5–10% probability of producing ash clouds with concentrations of 2 mg m−3 over the UK, Scandinavia and northern Europe with a mean arrival time of 48–72 h and a mean persistence time of 6–18 h. In a companion paper, Scaini et al. (2014) present a vulnerability assessment for Iceland to ground deposition of tephra and for the European air traffic to airborne ash which, combined with the outcomes of the present paper, constitute one of the first comprehensive multi-scale risk assessment associated with tephra dispersal and sedimentation.

Chronology and impact of the 2011 Cordón Caulle eruption, Chile

“…In particular, we applied the analytical model TEPHRA2 (Bonadonna et al, 2005) coupled with probabilistic approaches developed to model long-lasting eruptions (Bonadonna, 2006;Biass et al, 2014). We focus only on the most vigorous initial phase (layer A-F, 4-5 June 2011; Pistolesi et al, 2015), characterized by plume heights of 11-14 km a.s.l.…”

“…8, Appendix B). 1000 eruptions were simulated following the long-lasting eruption range scenario of Biass et al (2014). For each simulation, eruption dates and durations were stochastically sampled within the predefined ranges in order to retrieve the corresponding wind profiles.…”

“…For each simulation, eruption dates and durations were stochastically sampled within the predefined ranges in order to retrieve the corresponding wind profiles. The median and sigma values of a Gaussian total grain-size distribution were sampled (Table 8), and aggregation is accounted for using the method of (see Biass et al, 2014 for more details). The entire eruption duration was split into 6 h long intervals, for which a plume height was sampled and converted into an erupted mass using the formulation of mass eruption rate of Degruyter and Bonadonna (2012).…”

Dynamics and tephra dispersal of Violent Strombolian eruptions at Vesuvius: insights from field data, wind reconstruction and numerical simulation of the 1906 event

“…Based on these new volcanological data and reconstruction of wind field direction and intensity, partially derived from historical sources, the 1906 event was numerically simulated and results compared to deposit distributions. The modelling outcomes for the ash emission phase provide a better agreement with the measured tephra mass load for a simulation run in which ash aggregation (described by the models of Cornell et al J Volcanol Geotherm Res 17:89-109, 1983, and Biass et al Nat Hazard Earth Syst Sci 14:2265-2287, 2014) is specifically taken into account, confirming the importance of this process during tephra dispersal. The aggregation model that best fits the simulated results to the measured ground loadings has 80 % of particles Φ≥4 that aggregate uniformly in the range Φ=−1 to 3.…”

“…For this reason, to take into account particle aggregation, assumptions must be made about the grain size of the aggregating ash and of the resulting aggregates. To investigate the effects of different assumptions, we used both the Cornell et al (1983) and Biass et al (2014) models. The first one assumes that all particles smaller than 32 μm, 75 % of those between 32 and 45 μm, and 50 % of those between 45 and 64 μm, aggregate to form 200-μm diameter particles.…”