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

Abstract

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 SO 2 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 SO 2 flux. Relatively high SO 2 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 SO 2 retrieval to calculate SO 2 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 SO 2 burden of 20-22 kT.

Improved optical flow velocity analysis in SO<sub>2</sub> camera images of volcanic plumes – implications for emission-rate retrievals investigated at Mt Etna, Italy and Guallatiri, Chile

“…This allows us to study high-frequency variations in the emission signals or to investigate individual sources separately (e.g. Tamburello et al, 2013, D'Aleo et al, 2016. As a result, the cameras are often pointed at the vicinity of the source, where the plumes can show turbulent behaviour, mostly as a result of aerodynamic effects and buoyancy.…”

“…Luckily, the high resolution of the imaging systems allows us to account for these spatial and temporal fluctuations by directly measuring the projected 2-D velocity fields using optical flow (OF) algorithms (e.g. Krueger et al, 2013, Bjornsson et al, 2013, Peters et al, 2015, Lopez et al, 2015, Stebel et al, 2015, Kern et al, 2015.…”

Ultraviolet Imaging of Volcanic Plumes: A New Paradigm in Volcanology

“…The cameras have now been deployed on a significant number of volcanoes worldwide, due in part to the convenience of being able to set up and operate from fixed positions during discrete field campaigns (e.g., [31,32]). To date, the targets covered by permanent network installations have been rather few, e.g., Etna and Stromboli in Italy and Kīlauea in Hawaii [33][34][35][36][37], potentially as a consequence of the requirement to image the plume, e.g., without cloud cover between the camera and summit area.…”

Ultraviolet Imaging of Volcanic Plumes: A New Paradigm in Volcanology

“…The cameras have now been deployed on a significant number of volcanoes worldwide, due in part to the convenience of being able to set up and operate from fixed positions during discrete field campaigns [e.g., 28,29]. To date, the targets covered by permanent network installations have been rather fewer, e.g., Etna, Stromboli and Kīlauea [30][31][32][33][34], potentially as a consequence of the large cost of the scientific grade cameras, typically used in these deployments, as well as the requirement to image the plume, e.g., without cloud cover between the camera and summit area.…”