IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4A1_4D-O2Room A6

Date/Time: July 24 9:00-9:15

A multi-scale risk assessment for tephra fallout and airborne concentration from multiple
Icelandic volcanoes - Part I: hazard assessment
Sebastien Biass1 , Chiara Scaini2 , Costanza Bonadonna1 , Kate Smith3 , Arnau Folch2 , Armann
Höskuldsson4 , Adriana Galderisi5
1Section of Earth and Environmental Sciences, University of Geneva, Switzerland, 2 CASE Department,Barcelona Supercomputing Center (BSC-CNS), Spain, 3 University of Exeter, UK, 4 Nordic VolcanologicalCenter, University of Iceland, Iceland, 5 Universita Federico II di Napoli, Italy
E-mail: sebastien.biasse@unige.chIn order to assist the elaboration of proactive measures for the management of future volcanic eruptions inIceland, we developed a new approach to assess the medium- to long-term hazard related to tephra fallout atvarious scales and for multiple sources. We coupled field studies with numerical modelling to compile a local
ground deposition assessment using the advection-diffusion model TEPHRA2 and a regional atmospheric ash
concentration assessment using the numerical model FALL3D.
This study focuses on four volcanoes – Hekla, Katla, Askja and Eyjafjallajökull – selected for their high probabilityof eruption in a near future or their high potential impacts. Due to their different eruptive behaviours and different
degrees of knowledge of past eruptions, separate schemes for the quantification of the hazard were developed.
All scenarios are a combination of 1000 runs of each model, varying Eruption Source Parameters (EPS) and/or
meteorological conditions (in 10 years of Reanalysis data). EPS (plume height, erupted mass, eruption duration)
were defined for each scenario based on field and literature studies.
Two scenarios were considered for Hekla volcano (based on the 1947 and on the 2000 eruptions as references)using the Eruption Range Scenarios approach (ERS), where wind conditions and EPS are stochastically sampled.
Eruptions at Katla are numerous and heterogeneous in eruptive styles, including basaltic, silicic and long-lasting
eruptions. One ERS was produced for the VEI 2-3 classes to account for the basaltic activity. At Askja, two OneEruption Scenarios were considered to account for both the phreatomagmatic and the magmatic phase of the 1875
eruption, with varying wind conditions and EPS fixed deterministically. We also produced an ERS for VEI 5, basedon field evidences of deposits larger than the 1875 eruption. At Eyjafjallajökull, we modelled possible patternsof tephra dispersal associated with a long-lasting eruption similar to 2010. Outputs are produced in a variety ofshapes such as probability maps of ground tephra accumulation and airborne concentration, isomass maps for agiven probability, hazard curves and atmospheric travel and residence times. At a local scale, results show a strong
prevailing pattern of tephra deposition and transportation towards the E and NE part of the island, leaving a very
low probability of Reykjavik to be impacted. At regional scale, there is a low to medium probability of having criticalash concentration in Northern Europe and UK airspaces.
This method combines field and numerical approaches and provides a multi-scale hazard assessment to describe
both the local hazard associated with ground deposition of tephra and the hazard at a regional scale associatedwith the long residence time of volcanic particles in the atmosphere, which is the first step to the compilation ofcomprehensive risk assessments. The vulnerability and impact are presented in Part II.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

1138