First estimates of fumarolic SO 2 fluxes from Putana volcano, Chile, using an ultraviolet imaging camera

Putana is a stratovolcano in the central Andes volcanic zone in northern Chile on the border with Bolivia. Fumarolic activiy has been visible at its summit crater at 5890 m altitude from long distances since the early 1800s. However, due to its remote location neither detailed geological studies have been made nor gas fluxes have been monitored and therefore its evolution remains unknown. On November 28, 2012 an ultraviolet (UV) imaging camera was transported to Putana and for about 30 min images of the fumaroles were recorded at 12 Hz. These observations provide the first measurements of SO2 fluxes from the fumarolic field of Putana and demonstrate the applicability of the UV camera to detect such emissions. The measurement series was used to assess whether the sampling rate of the data influences the estimate of the gas flux. The results suggest that measurements made at 10 s and 1 min intervals capture the inherent (turbulent) variability in both the plume/wind speed and SO2 flux. Relatively high SO2 fluxes varying between 0.3 kg s− 1 and 1.4 kg s− 1, which translates to 26 t/day and 121 t/day assuming constant degassing throughout the day, were observed on November 28, 2012. Furthermore, we demonstrate how an optical flow algorithm can be integrated with the SO2 retrieval to calculate SO2 fluxes at pixel level. Average values of 0.64 kg s− 1 ± 0.20 kg s− 1 and 0.70 kg s− 1 ± 0.53 kg s− 1 were retrieved from a “classical” transect method and the “advanced” optical flow based retrieval, respectively. Assuming constant emissions throughout all times, these values would results in an average annual SO2 burden of 20–22 kT.