Constraining the mechanisms and timing of magma ascent in plinian eruption through decompression experiments: a case study from the Pomici di Base eruption, Mt. Somma-Vesuvius (Naples, Italy)

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Worldwide about 800 million people live within 100 km of active volcanoes. As the ash emissions from the 2010 eruption of Eyjafjöll (Iceland) showed, volcanic eruptions can cause not only societal disruption trough the loss of life and livelihoods, but also a global economic crisis trough damage of critical infrastructure. The Campanian Volcanic District (Naples, Italy), counting up to 3 million inhabitants, is among the most dangerous volcanic areas worldwide and therefore deeply studied and monitored. Despite this, it is still impossible to predict if precursor activity, such as changes in volcanic gases, ground deformation or seismicity, may lead to low intensity or to catastrophic eruptions.Degassing processes related to magma rise in volcanic conduits are crucial issues as they control the style and intensity of volcanic eruptions. In fact, explosive eruptions are driven by the exsolution of volatile components to a separate fluid phase. This process is commonly caused by decreasing pressure after magma ascent into the conduit or after failure of rocks enclosing the magma chamber. However, the relations between magma decompression and vesiculation are still poorly investigated and understood.In this study, we plan to perform decompression experiments in high-pressure high-temperature apparatus on H2O-CO2 bearing latitic and trachitic melts from the plinian fallout of the Pomici di Base eruption (Mt.Somma-Vesuvius, Naples). Our aim is to understand how genetically related magmas with high to intermediate viscosity behave during magma uprising in terms of vesiculation and bubble growth. Furthermore, we aim to drive fast decompression experiments leading close to, or directly to magma fragmentation. Systematically changing the volatile compositions and contents and the decompression rates, this research will help to better characterize the relationship between the mechanism(s) and rate(s) of bubble vesiculation and growth, the fragmentation depth and the eruptive style. The obtained results will be useful to interpret late-stage, extensive magma vesiculation in natural systems leading to a shift of those systems towards apparently anomalous eruptive behavior. They will also provide key data to model degassing processes during magma ascent, to understand the evolution of eruptive style and to work out the volatile budget.