Relationships Between Eruption Rate, Tephra Dispersal and Total Grain Size at Hekla and Askja volcanoes, Iceland: Enhancing the Source Term for Tephra Modeling

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The 2010 eruption of Eyjafjallajökull volcano demonstrated a vulnerability of global air traffic to even small eruptions from Icelandic (and other) volcanoes. The $3B economic impact via transport went well beyond the regional stranding of passengers to affect primary and manufacturing industry globally. Forecasts of ash concentrations that could have minimized the impact, were handicapped by a lack of key types of data. A key shortfall was a lack of distribution of ash particle sizes from past eruptions as input for forecasting models. the goal is to gather data from very young eruptions from two active Icelandic volcanoes to solve this problem. The target audience for this study is not merely volcanologists but meteorologists and decision makers for the global network of Volcanic Ash Advisory Centers. The researchers will work with an advisory group drawn from Volcanic Ash Advisory Centers and Meteorological Offices to ensure take-up of the results.Mass eruption rate, eruption column height, total grain size distribution (TGSD) and particle settling properties, like density and shape, are key contributions to understanding volcanic ash transport and dispersal models but globally very few eruptions are characterized for all these parameters. TGSD data is particularly lacking, e.g., of 25 eruptions with well constrained column height, volume and eruption rate listed by Mastin et al. (2009) only 5 have TGSD. We would acquire new and compile existing data for particle size and shape distributions for 4 Hekla eruptions (2000, 1991, 1970, H1 (1104)) and 2 phases of the 1875 Askja eruption. These range in eruption rate and volume over two orders of magnitude. The three 20th - 21st century eruptions, and Askja 1875 B, supply inputs to ?most plausible event? scenarios, for eruptive activity in the near future, whereas the H1, and 1875 phase D eruptions credibly constrain ?worst case? scenarios for a decadal time scale. We aim to (i) understand the relationships between tephra dispersal and eruption rate, TGSD, and pyroclast size, shape, density and crystallinity, and (ii) supply a set of robust field-derived source parameters to test models of tephra dispersal and transport.