Ultraviolet camera measurements of passive and explosive sulphur dioxide emissions at Yasur volcano, Vanuatu

Here, we present the first ultraviolet (UV) camera measurements of sulphur dioxide (SO2) flux from Yasur volcano, Vanuatu, for the period 6th – 9th July 2018. These data yield the first direct gas measurement-derived calculations of explosion gas masses at Yasur. Yasur typically exhibits persistent passive gas release interspersed with frequent strombolian explosions. We used compact forms of the ‘PiCam’ Raspberry Pi UV Camera system (Wilkes et al., 2017, 2016) powered through solar panels to collect images. Our daily median SO2 fluxes range from 4.0 – 5.1 kg s-1, with a measurement uncertainty of -12.2% to +14.7%, including errors from: gas cell calibration drift, uncertainties in plume direction and distance, as well as plume velocity. This work highlights the use of particle image velocimetry (PIV) for plume velocity determination, which was preferred over the typically used cross-correlation and optical flow methods because of the ability to function over a variety of plume conditions. We calculate SO2 masses for strombolian explosions of 8 – 81 kg (mean of 32 kg), which is, to our knowledge, the first budget of explosive gas masses from this target. Through the use of a simple statistical measure using the moving minimum, we estimate that passive degassing is the dominant mode of gas emission at Yasur, supplying an average of ~69% of the total gas released. Our work further highlights the utility of UV camera measurements in volcanology and, in particular, the benefit of the multiple camera approach in error characterisation. This work also adds to our inventory of gas-based data to characterise the spectrum of strombolian activity across the globe.