Phreatomagmatic volcanic eruptions involve interactions between magma and external water and are typically more explosive than otherwise similar magmatic eruptions that do not involve external water. Such magma-water interactions pose significant risks to society, agriculture, and the economy because they generate large volumes of fine-grained ash that can blanket nearby population centers, threaten livestock, and endanger air traffic, as demonstrated by the April 2010 and May 2011 eruptions in Iceland. Understanding the explosivity of magma-water interactions, therefore, is key to mitigating risk to society from volcanoes in wet environments. The proposed research will advance our understanding of how water enhances magma fragmentation in an explosive eruption, using a suite of case studies from Iceland in which varying amounts of water were involved. The results of this work will be disseminated broadly, through scientific publications and presentations, training of a new cadre of volcanologists, and the production of a series of short educational films designed to stimulate excitement in the processes of scientific inquiry and discovery in students of grades 9-12.
Understanding explosive magma-water interactions is complicated by the fact that the magma contains gases, which, in addition to external water, participate in driving the explosivity of the eruption. It is proposed to untangle the competing influences of magmatic gases and external water by comparing the explosive products of an end member eruption type ('rootless volcanic cones'), in which no magmatic gases participate, with ash from Icelandic eruptions in which magmatic gases were involved in the fragmentation process, and with particles produced experimentally under controlled laboratory conditions. Our comparisons will involve particle shape, size, and density analysis to quantify how water affects explosivity. Computer modeling of the explosion process, incorporating particle-scale and deposit-scale measurements, will allow refinement of our understanding of the physics of magma-water interactions. With validation using our case studies, the model will ultimately be useful for predicting patterns of ash dispersal from explosive lava-water interactions. The proposed work will allow quantification of the role of external water in a way that has not previously been possible, and as a consequence, it has the potential to impact hazards assessment and mitigation strategies for such eruptions.