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

Issues of eruption forecasting during the 2010 eruption of Eyjafjallajökull volcano in Iceland, and its $3B economic impact, highlighted the need for a larger global dataset of total grain size distributions (TGSD) as critical source-term parameters for models for volcanic ash transport and dispersal, such as the models used by the Volcanic Ash Advisory Centers (VAACs) for ash forecasts. We present TGSD data for 2 more frequently active Icelandic central volcanos: namely 4 historical eruptions of Hekla volcano (in 1104, 1300, 1693, and 1766) and two phases (B and D) of the 1875 Askja eruption, determined using the Voronoi Tessellation technique. These eruptions cover a range in magma composition (andesite to rhyolite), eruptive volume (0.01 to 2.0 km3; 0.004 to 0.6 km3 DRE), and inferred mass eruption rate (MER, 106 to 108 kg/s). These data more than doubles the global dataset of internally consistent TGSD and offer more extensive comparison of the relationship between MER and TGSD.