| Summary: | Volcanic airfall (defined here as any material, such as volcanic ash, that falls from an eruption plume and cools before deposition) lands on glaciers, ice sheets, permafrost and snowfields worldwide. The interactions between these deposits and glaciated terrains have a range of possible outcomes, which can have consequences for life, resources and economy. If the deposit thickness exceeds a local ‘critical thickness’, the ice ablation rate will be reduced relative to the bare surface; conversely, thinner deposits enhance ablation of the underlying ice. We have compiled a volcano database known as the Supraglacial Volcanic Airfall Database, and a tool – the Supraglacial Volcanic Airfall Likelihood Index. The latter provides a framework for assessing the potential for deposition of volcanic airfall on glaciers and ice sheets based on eruption characteristics and the geographical location of the source volcano relative to the locations of glaciers/ice sheets. All of these characteristics have been incorporated into the database. This information has been put to use in the updated Eruption Source Parameter Database (Engwell et al., 2018) and within a case study on interactions of airfall and glaciers in the context of global volcanic hazards and risk (Hobbs et al., 2015). The Supraglacial Volcanic Airfall Database shows that a minimum of 208 (13.4%) of known active volcanoes host glaciers. The Supraglacial Volcanic Airfall Likelihood Index demonstrates that 428 (27.6%) of known active volcanoes have a high to extremely high likelihood of depositing supraglacial volcanic airfall should they erupt, with 102 (6.6%) having an extremely high likelihood. In order to test the validity of the Supraglacial Volcanic Airfall Likelihood Index, assessment of 895 eruptions which occurred over a 25-year period (1990-2014), from 233 source volcanoes, was carried out. The Supraglacial Volcanic Airfall Likelihood Index grading for volcanoes erupting during this period was found to accurately reflect those that were known sources, based on literature and imagery, of supraglacial volcanic airfall deposits. Within this 25-year period, the relative frequency of eruptions producing supraglacial airfall (n=163) to explosive eruptions (n=807) was 0.20, and there were 3 to 9 such eruptions per year. This indicates that a minimum of 20% of explosive eruptions are likely to generate supraglacial volcanic airfall. References Engwell S, Mastin L, the GVM eruption source parameter working group (2018) Eruption Source Parameter Database. Conjoint 6th WMO VAAC Best Practices Workshop (VAAC BP/6) and 8th WMO/IUGG Volcanic Ash Scientific Advisory Group Meeting (VASAG/8), Wellington, New Zealand, 5th-9th November 2018 Hobbs LK, Gilbert JS, Lane SJ, Loughlin S (2015). Interactions of volcanic airfall and glaciers: Supplementary Case Study 3. In: Loughlin SC, Sparks RSJ, Brown SK, Jenkins SF, Vye-Brown C (Eds). Global Volcanic Hazard and Risk. Cambridge University Press, 2015
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