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Publisher's version (útgefin grein) ; Mt. Öræfajökull is one of the most dangerous volcanoes in Iceland with potential for a VEI6 eruption and the generation of many severe associated hazards. It is not a frequently erupting volcano with two eruptions in the last 1100 years, in 1362 and 1727–28. During the 1362 eruption 10 km3 of freshly fallen tephra was emitted, the eruption plume reached the stratosphere and was dispersed offshore toward mainland Europe. In this study we investigate the possible impact due to tephra fallout to critical infrastructures in Iceland namely – roads, airports, electrical power-lines – in case of a new eruption at Öræfajökull of similar intensity as in 1362. The analysis is done by running several times the VOL-CALPUFF dispersal model to simulate the dispersal of ash in the atmosphere and its deposition on the ground. The resulting maps show the probability of exceeding critical thickness of the tephra fall. Critical infrastructures have been added to the analysis to get a quantitative assessment of the potential impact. The results indicate that in case of an event similar to the 1362 eruption, the tephra fallout could be expected over most of the country, with higher likelihood on the eastern side. The tephra fallout is likely to have a severe impact in the proximity of the volcano, generating a deposit with a load of up to 1000 kg/m2. The likelihood of failure for more than 160 km of the electrical power-line and for critical driving conditions on about 900 km of the main ring road is between 50 and 100%. The probability that the tephra fall will affect three of the main domestic airports is higher than 50%. An eruption of this magnitude is likely to affect commuting and communication between the greater Reykjavík area, where the government resides, and the rest of the country. Our analysis also reveals the limitations of current knowledge and understanding of the Öræfajökull volcano and highlights the need for further studies on past activity to better characterize its future behavior. ; This study has been benefiting from the GOSVÁ project (2012–2018) funded by the Icelandic Government together with the International Civil Aviation Organization (ICAO). ; Peer Reviewed

The effusive six months long 2014-2015 Bárðarbunga eruption (31 August-27 February) was the largest in Iceland for more than 200 years, producing 1.6 ± 0.3 km3 of lava. The total SO2 emission was 11 ± 5 Mt, more than the amount emitted from Europe in 2011. The ground level concentration of SO2 exceeded the 350 µg m−3 hourly average health limit over much of Iceland for days to weeks. Anomalously high SO2 concentrations were also measured at several locations in Europe in September. The lowest pH of fresh snowmelt at the eruption site was 3.3, and 3.2 in precipitation 105 km away from the source. Elevated dissolved H2SO4, HCl, HF, and metal concentrations were measured in snow and precipitation. Environmental pressures from the eruption and impacts on populated areas were reduced by its remoteness, timing, and the weather. The anticipated primary environmental pressure is on the surface waters, soils, and vegetation of Iceland. ; Funding for the research came from the Icelandic government via the Icelandic Civil Protection Agency, the EC FP7 Framework programme via the Futurevolc project, the Swedish Research Council FORMAS supported the DOAS measurements Geochemical Perspectives Letters Letter Letter Geochemical Perspectives Letters 92 Geochem. Persp. Let. (2015) 1, 84-93 | doi:10.7185/geochemlet.1509 Geochem. Persp. Let. (2015) 1, 84-93 | doi:10.7185/geochemlet.1509 93 and The French centre of excellence "Clervolc" programme financed the microprobe analysis. We are grateful to the Environmental Protection Agency in Ireland, the National Institute for Public Health and the Environment in the Netherlands, the Belgian Interregional Environment Agency, the Department for Environment Food & Rural Affairs in UK, and the Environment Agency of Austria for ground–level SO2 concentration data in air in the respective countries. ; Peer Reviewed