Results of the CO2 diffuse degassing survey from the 2017 IAVCEI CCVG 13th volcanic gas workshop: Pululahua Dome Complex, Ecuador

Abstract

Pululahua is a potentially active andesite and dacite lava dome complex. This paper presents the results of a survey focused on carbon dioxide (CO₂) diffuse degassing at Pululahua, which was conducted during the 2017 International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) Commission of the Chemistry of Volcanic Gases (CCVG) 13th Gas Workshop. Our objective was to conduct a comprehensive investigation of CO₂ diffuse degassing by employing standard methods for measuring CO₂ flux and temperature, and data processing. These methods were applied to map the spatial distribution of the measured parameters, investigate the origin of CO₂, and quantify the volcanic CO₂ output within the surveyed area of Pululahua. We carried out a total of 350 soil CO₂ flux and 329 soil temperature measurements and collected 12 gas samples for carbon isotopic composition analysis, surrounding the three youngest domes in the complex. In addition, seventeen CO₂ flux measurements over a thermal water pool were performed. Our findings indicate that the diffuse emission at Pululahua's crater floor is fed by both biogenic and volcanic CO₂. Fluxes from each source are similar in magnitude, with approximately 90% of the measurements falling into an intermediate flux range. The occurrence of volcanic CO₂ emissions is supported by the carbon isotopic composition. Diffuse degassing distribution highlights a CO₂ anomaly surrounding the younger domes within the crater. We estimated the CO₂ diffuse emission using both statistical and geostatistical approaches over area of 3.36 km², resulting in values of 154.2 t d⁻¹ and 126.2 t d⁻¹ respectively. Based on the geostatistical quantification of the total CO₂ emission from soil degassing, Pululahua's crater volcanic CO₂ contribution is estimated between 59 and 97 t d⁻¹. Finally, the potential hazards associated with the release of cold CO₂ at Pululahua's crater are also discussed.