Temporal Variability in Gas Emissions at Bagana Volcano Revealed by Aerial, Ground, and Satellite Observations

Bagana is a remote, highly active volcano, located on Bougainville Island in southeastern Papua New Guinea. The volcano has exhibited sustained and prodigious sulfur dioxide gas emissions in recent decades, accompanied by frequent episodes of lava extrusion. The remote location of Bagana and its persistent activity have made it a valuable case study for satellite observations of active volcanism. This remoteness has also left many features of Bagana relatively unexplored. Here, we present the first measurements of volcanic gas composition, achieved by unoccupied aerial system (UAS) flights through the volcano's summit plume, and a payload comprising a miniaturized MultiGAS. We combine our measurements of the molar CO2/SO2 ratio in the plume with coincident remote sensing measurements (ground- and satellite-based) of SO2 emission rate to compute the first estimate of CO2 flux at Bagana. We report low SO2 and CO2 fluxes at Bagana from our fieldwork in September 2019, similar to 320 +/- 76 td(-1) and similar to 320 +/- 84 td(-1), respectively, which we attribute to the volcano's low level of activity at the time of our visit. We use satellite observations to demonstrate that Bagana's activity and emissions behavior are highly variable and advance the argument that such variability is likely an inherent feature of many volcanoes worldwide and yet is inadequately captured by our extant volcanic gas inventories, which are often biased to sporadic measurements. We argue that there is great value in the use of UAS combined with MultiGAS-type instruments for remote monitoring of gas emissions from other inaccessible volcanoes. Plain Language Summary Bagana is a remote and highly active volcano in southeastern Papua New Guinea (PNG). Historically, it has been among the most active volcanoes in PNG, notable for its long-lived eruptions and sustained gas emissions. Bagana has only been infrequently studied before now. We use unoccupied aerial systems (drones) along with ground- and satellite-based remote sensing data to characterize the chemical composition and flux of Bagana's gas emissions and place these in the context of global volcanic emissions. Owing to low activity during the time of our fieldwork, we report lower than anticipated emissions of carbon dioxide and sulfur dioxide from Bagana. We argue that characterizing highly variable volcanic emissions is challenging without long-term continuous observations and that, for remote volcanoes like Bagana, both drones and satellite observations are powerful tools to undertake these observations.