Open-Vent Degassing of CO2 from Typical Andesitic Volcanoes in the Central American Volcanic Arc

Monday, 15 December 2014: 11:35 AM
Philippe Robidoux1,2, Alessandro Aiuppa1,2, Silvio Rotolo2, Gaetano Giudice1, Roberto Moretti3, Vladimir Conde4, Bo Galle4 and Giancarlo Tamburello2, (1)National Institute of Geophysics and Volcanology, Palermo, Rome, Italy, (2)University of Palermo, Palermo, Italy, (3)Department of Civil Engineering, The Second University of Naples, INGV, Naples, Italy, (4)Chalmers University of Technology, Gothenburg, Sweden
The collection of H2O-CO2-SO2 volcanic gas datasets at open-vent basaltic volcanoes has increased since the introduction of electrochemical/NDIR (Multi-GAS) instruments in the field. An open problem remains to understand the degassing regime of volcanoes of intermediate compositions, which is complicated by wide range of eruption styles. We propose here to initiate the study of the degassing regime of Telica and San Cristobal (Nicaragua), two constantly monitored volcanoes in the Central American Volcanic Arc (CAVA). We calculated the CO2 flux sustained by summit plume degassing at Telica and San Cristobal as the product of the CO2/SO2 ratio of Multi-GAS technique with parallel SO2 flux measurements, made by using scanning UV-DOAS instruments in 2013. At Telica, the CO2 flux was evaluated at 166±76 t/d and at San Cristobal we measured 520±260 t/d. Degassing activity at Telica volcano consists in surface gas discharges dominated by H2O (70-98 mol%; mean of 92 mol%), and by CO2 (1-23 mol%; mean of 6 mol%) and SO2 (0.5-7.4 mol%; mean of 2.9 mol%). San Cristobal gas is dominated by H2O (85-97 mol%; mean of 92 mol%), and by CO2 (2-12 mol%; mean of 6 mol%) and SO2 (3-5 mol%; mean of 3.8 mol%). These values are typical of volcanic arc regions and the volcanoes were in a stage of quiescent degassing without excess of CO2 output relatively to the other major gases. By interpreting our recent gas measurements in tandem with preliminary melt inclusion records of pre-eruptive dissolved volatile abundances, we hope to build a conceptual degassing model taking into account the active degassing regimes during past volcanic eruptions. Finally, we hope to refine the CObudget estimates along the CAVA.