Magnitude, intensity and impact of SO2 gas emissions from Nyiragongo volcano during 2004-2012

The activity of open-vent volcanoes with an active lava-lake, like Nyiragongo, is characterized by persistent degassing, thus continuous monitoring of the rate, volume and fate of their gas emissions is crucial to understand their volcanic geophysical state and potential impact. We report results of measurements of SO2 gas emissions from Nyiragongo conducted between 2004 and 2012 with a network of scanning-DOAS remote sensors. From these observations we found the typical distribution of the magnitude of emission events during passive degassing, which is found to be well-modeled by a Levy distribution. This finding indicates that quiescent emission events are independent and randomly distributed (markovian), which is compatible with a model of steady state degassing from convection of magma in the conduit, as supported by other observations. Major emission events should lie outside this distribution, thus, real-time continuous monitoring of the emission intensity can signal anomalous distributions related with non-passive degassing. Our measurements also provide important parameters to study the impact of the plumes of Nyiragongo, such as plume height and velocity, which are used to estimate the ground-concentration of SO2 based on atmospheric diffusion model. We conclude that long-term monitoring of gas emissions provides unique information on the dynamics and potential impact of eruptive activity at Nyiragongo.