Joint Inversions of Gas Emissions and Ground Deformation During and Following Volcanic Eruptions

Abstract:

Volcanic eruptions are associated with complex, time-dependent gas emissions and ground deformation. Observations of such signals are a primary gauge of eruption mechanisms, progress and cessation and as such, are critical for hazard assessment. It is often the case that gas emissions and deformation continue for months to years after the end of an eruption. Interpretation of such signals are critical for making decisions about whether an eruption may be considered over or not, yet very little is understood about the processes behind them and how they are coupled. However, the link between the deformation measured and the gases emitted during and after eruptions is fundamental. It has long been recognised that the presence of exsolved fluids enhances magma compressibility, leading to smaller-than-expected syn-eruptive volume changes observed at the surface (by InSAR or by GPS networks). The fluid phase present in the magma prior to eruption contains an assemblage of volatile species, most of which we are able to measure at the surface. Our improved understanding of volatile saturation in silicate melts and the availability of thermodynamic models to predict the partitioning of sulfur between fluid and melt means that coupled interpretations of gas emissions and deformation are now possible, given independent estimates of erupted volumes and other intrinsic parameters such as pressure, temperature and oxygen fugacity. We illustrate, using a well constrained example of a prolonged, multi-episode eruption, the utility in developing coupled models to describe volume changes and outgassing processes with a view to enhancing our ability to interpret these critical monitoring data streams.