The excess gas paradox at volcanoes: does CO2 favor gas accumulation in mafic magmas?

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The forecasting of volcanic eruptions is vital for ~1.1 billion people living near volcanoes worldwide, and remains quite challenging. Volcanologists strive to forecast the likelihood, size, and style of eruptions. Many eruptions emit an excess amount of volcanic gases that is greater than the volume of erupted magma. We do not understand the factors that control the competition between gas retention and release in magmas, which, in turn, influence how volcanoes erupt. This team will seek answers by studying the potential link between the porosity of volcanic rocks erupted during explosive eruptions and the chemistry of volcanic gas emissions monitored via ground-based measurements at Mt Etna (Italy), the largest volcano in Europe. Around 1 million people live within 30 km of the volcanic vents. This project will support a PhD student and an undergraduate student. Research will be shared in publications and in public lectures, university-based websites, social media, and public mass media. This project aims to bridge the gap between the data and analysis collected by volcano observatories and a burgeoning understanding of magma physics, particularly in the context of the key role of volatile gas species in controlling eruption behavior. The project goal is to correlate the amount of pre- to syn-eruptive porosity in magmas during stages of unrest with gas emissions at active volcanoes. The PI plans to resolve the volume disparity between emitted volcanic gas and erupted magma at Mt Etna (Italy), one of the best monitored and studied volcanoes in the world, by testing two hypotheses: 1) CO2 concentration increase in gas favors porosity increase in mafic magmas, and 2) CO2 / SO2 in gas emissions used to determine mafic magma porosity at depth. The project includes three tasks to test the proposed hypotheses: a) a detailed microstructural and geochemical characterization of volcanic samples from representative eruptions of Mt Etna, b) a time-integrated analysis of magma porosity and volcanic parameters such as CO2 / SO2 ratio, and eruption style, intensity, and magnitude at Mt Etna, and c) modelling of H2O, CO2, and S partitioning between silicate melt and exsolved gas phase in mafic magma during pre-eruptive and syneruptive conditions using existing solubility models. The project includes the collaboration with scientists of the Osservatorio Etneo of the Istituto Nazionale di Geofisica e Vulcanologia (INGV) in (Italy) and from the DESY synchrotron facility in Hamburg (Germany).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.