Collaborative Research: Violent Basaltic Explosive Volcanism II: Constraints and Conditions of Basaltic Plinian Eruptions

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Intellectual Merit: Basaltic volcanism most commonly produces effusion of lava, mildly explosive Strombolian activity or Hawaiian fire fountain eruptions. However, some basaltic eruptions are now recognized as extremely violent, i.e. generating widespread phreatomagmatic, subplinian and Plinian fall deposits, these include historical eruptions at Kilauea (Hawaii), Etna (Italy) and Tarawera (New Zealand). These eruptions are particularly dangerous because the ascent rate of basaltic magma prior to eruption can be very high (i.e., warning times as little as a few hours) and because their precursors may be ignored or misunderstood. We set out to constrain the conditions of pre-eruptive ascent and degassing that permitted basaltic magma to erupt at Plinian intensity, principally using the example of the 122 BC eruption of Mt Etna. Mechanisms to suppress or delay open-system behavior and promote extended coupling between gas and melt are essential to permit Plinian eruptions of basaltic magma. We will look to constrain conditions and rates of magma ascent and vesiculation by performingdecompression experiments on the 122 BC Etma melt at University of Texas and comparing experimental products with natural samples, texturally and chemically. We will quantify the range of vesicle and microlite populations in the erupted scoria and experimental charges using three different techniques, to ensure reliable data sets, and to allow critical comparison of the techniques. Finally we will measure pre- and post-eruptive volatile contents of the melt phases in the same pyroclasts. Broader impacts: Our goal is to understand the mechanisms for basaltic Plinian eruptions, with a long-term aim of applying such understanding to improve preparedness for future eruptions at large basaltic volcanoes. In particular there is evidence for several large subplinian to Plinian eruptions in Etna's recent history. It is likely that another large explosive eruption will happen and affect a large population. Because the modern population surrounding Etna is much greater and the inhabited area extends farther up the volcano's flanks, future eruptions pose significant potential hazards. We will present a summary of conclusions and impacts to emergency management agencies at a workshop in Italy followed by a focused workshop for students and researchers at Etna in 2007. Our results will also be widely disseminated via the Internet using linked web sites hosted by University of Hawaii, University of Texas and INGV, Italy and in the form of a DVD in Italian and English.