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

Abstract:

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 CO₂ budget estimates along the CAVA.