NSFGEO-NERC: Physical and Chemical Constraints on Large-volume Pyroclastic Blasts: The Campanian Ignimbrite Eruption, Italy

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Overview:The Campanian Ignimbrite was emplaced from a dilute pyroclastic density current that accompanied caldera collapse of the Campi Flegrei. The currents reached over 80 km from the vent area and the fallout covers 3.5 million km2, reaching at least 2500 km from the vent. Abundant gas is needed to produce a current that was apparently more than a kilometer thick, but where did this gas come from? Recent work by the proposing team found that emplacement temperatures of the Campanian Ignimbrite were above 580oC, indicating that the current did not cool off very much during transport, which in turn implies minimal entrainment of atmospheric gases and a very short eruption duration. Magmatic gases are likely important, but very high levels of dissolved gas prior to eruption would be needed if that is the only source. Superheated hydrothermal water (estimated at 500oC at 5 km depth today) may be an additional gas source. We propose 1) detailed field investigations to better characterize the Campanian Ignimbrite stratigraphy, in order to link distal and proximal deposits and to define the relative timing of volcanic events; 2) a detailed petrologic study of Campanian Ignimbrite products, notably by performing complete volatile analysis (H2O, CO2, S, F and Cl) of melt inclusions and apatite microphenocrysts via Fourier Transform Infrared (FTIR) spectroscopy, ion probe, and electron microprobe; and 3) an experimental investigation of the cooling rates of Campanian Ignimbrite eruptive products, using a technique that studies the glass transition temperature atvarying strain rates and residual water contents.Intellectual Merit:We propose to test the hypothesis that sustained dilute PDCs may be driven by gas sourced from the magmatic and/or hydrothermal systems, rather than dominantly from atmospheric gases incorporated into the column and flow. This would extend our ability to forecast volcanic hazards by linking field observations and measurements to internal magmatic processes. The Campanian Ignimbrite has proximal and medial/distal deposits that are difficult to correlate. Recent advances in geochemical and magnetic techniques used to correlate the distal fallout will be applied to the ignimbrite and proximal deposits. Cooling histories of clasts will be traced using recently developed methods to analyze glass transition temperatures and rheological changes. Back-calculating volatile concentrations during open-system degassing is a new technique that should reveal much about the Campanian Ignimbrite magma history. Understanding the potential role of hydrothermal fluids in ?supercharging? an eruption would require some re-thinking of current models and interpretations of datasets, as hydrothermal water may not appear in many petrologic measurements of gases.Broader Impacts:The Naples area has one of the highest volcanic risks in the world, with about 4 million people living in the area that was affected by the Campanian Ignimbrite (ignoring the people living in the fallout zone - >100 million). Understanding the magmatic/hydrothermal conditions that led to such a high-mobility current would allow a better assessment of the risks as current conditions change. We will be working with personnel from the Osservatorio Vesuviano, so our results will be incorporated into their risk assessments. This proposed NSF/NERC project will foster a significant international collaboration between the US, UK, and Italy and will incorporate the education of underrepresented groups in the form of PhD/MS students and post-doctoral researchers.