| Summary: | Ph.D. University of Hawaii at Manoa 2016. Includes bibliographical references. Among Icelandic volcanoes, Hekla is one of the most frequently active, with multiple pre-historic large Plinian eruptions and 18 historical subplinian–Plinian eruptions, whereas Askja is one of the largest volcanic systems and the 1875 eruption was one the largest historical eruptions. Future eruptions, especially from Hekla, are likely to pose a hazard to international air traffic. For example, the 2010 eruption of Eyjafjallajökull volcano in Iceland caused unprecedented economic impact and demonstrated a vulnerability of global air traffic to even small eruptions from Icelandic, and other, volcanoes. It also highlighted the need for better constraints of eruption source parameters, especially total grain size distribution data (TGSD), that are used as inputs for real-time ash dispersal forecast models. Source parameters (excluding TGSD) have previously been determined only for eruptions covering a small range of the possible eruptive behaviour of Hekla. This dissertation provides eruption source parameters (volume, plume height, and mass eruption rate) for five of the largest historical Hekla eruptions, as well as new TGSD data for four of the Hekla eruptions and two phases of the 1875 Askja eruption. TGSDs were determined using a consistent methodology, thereby significantly expanding the global data set of internally consistent TGSDs. This enables the relationship between eruption intensity and TGSD to be better investigated as well as provides a set of robust source parameters for future real-time models that forecast volcanic ash dispersal and transport, and influence decisions concerning closure of air space.
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