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 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 impacts. 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 help assessing and comparing 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 1kg 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 multi-scale risk assessment associated with tephra dispersal and sedimentation.

The importance of grain size and shape in controlling the dispersion of the Vedde cryptotephra

“…Maximum plume height estimates for recent Icelandic eruptions range from 10 to 20 km (e.g. Biass et al ., ; Leadbetter and Hort, ), but our initial analysis (Supporting Information) indicated a plume 20 km was needed. Carey et al .…”

A GIS-based tool to support air traffic management during explosive volcanic eruptions

“…Previous studies (e.g. Leadbetter and Hort, 2011;Biass et al, 2014) have estimated that the probability of having ''unfavorable'' wind conditions is of about 8-10% according to wind statistics for the 2000-2010 period, but this percentage increases during the winter season. In this particular example, we assume a ''worst-case'' meteorological scenario, that is, a synoptic weather situation is selected in which winds at altitude blow towards U.K and Central Europe.…”

“…This approach is similar to existing tephra dispersal hazard assessment (Papp et al, 2005;Barsotti et al, 2010;Folch and Sulpizio, 2010;Leadbetter and Hort, 2011). In the default setup, the tool considers three concentration values (or thresholds) of 0 tolerance, 0.2 and 2 mg/m 3 , already adopted in recent quantitative hazard assessments in order to produce probabilistic hazard maps for ash dispersal Sulpizio et al, 2012;Bonasia et al, 2013;Biass et al, 2014). Each contour (one for each threshold) delineates an area in which ash concentration is higher than the corresponding threshold and is stored in a spatial database as a polygon.…”

“…The eruptive scenario is selected from the Eruption Range Scenario (ERS, Bonadonna, 2006) defined by Biass et al (2014) for Katla volcano. Explosive activity in Iceland is likely to impact the European air traffic network in case of winds blowing towards the continent.…”

“…For the longterm, ash dispersal modeling is also better tailored to civil aviation, and probabilistic hazard assessments already exist for several volcanoes worldwide (e.g. Papp et al, 2005;Barsotti et al, 2010;Folch and Sulpizio, 2010;Leadbetter and Hort, 2011;Scaini et al, 2012Scaini et al, , 2013Sulpizio et al, 2012;Bonasia et al, 2013;Biass et al, 2014). The second key element regards impact assessment, necessary to manage emergencies and improve long-term preparedness.…”