Diffuse CO2 degassing and the origin of volcanic gas variability from Rincon de la Vieja, Miravalles and Tenorio volcanoes, Guanacaste province, Costa Rica

Volcanic gas emissions are an important key component for monitoring volcanic activity and magmatic input of carbon dioxide into the atmosphere as well as the assessment of geothermal potential in volcanic regions. Diffuse soil degassing of CO2 at Rincon de la Vieja and Miravalles volcanoes, assessed with the commonly accepted accumulation chamber method, showed the concentration of gas emissions in evident hydrothermal surface features in secondary gas emission zones of the volcanoes. Analyses of fumarolic gases were conducted to investigate similarities and differences between the volcanoes and the possibility of continued magma injection into their source(s). An output of 135 t/day over two degassing areas of together roughly 2 km2 was calculated at Miravalles and one area of 0.129 km2 at Rincon de la Vieja with 3.3 t/day. Comparatively low flux values and the particular soil flux distribution at the active Rincon de la Vieja volcano, suggests a different degassing behavior and stronger concentration of gas emissions at the active vent areas, compared to the dormant Miravalles volcano in case of a common hydrothermal reservoir. Similar chemical signatures of discharged fluids by the volcanoes of the Guanacaste region suggest a common hydrothermal reservoir fed by one or more magmatic source(s) with relatively primitive composition at Tenorio and Miravalles compared to Rincon de la Vieja.