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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 (CO<inf>2</inf>) 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 CO<inf>2</inf> diffuse degassing by employing standard methods for measuring CO<inf>2</inf> flux and temperature, and data processing. These methods were applied to map the spatial distribution of the measured parameters, investigate the origin of CO<inf>2</inf>, and quantify the volcanic CO<inf>2</inf> output within the surveyed area of Pululahua. We carried out a total of 350 soil CO<inf>2</inf> 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 CO<inf>2</inf> 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 CO<inf>2</inf>. Fluxes from each source are similar in magnitude, with approximately 90% of the measurements falling into an intermediate flux range. The occurrence of volcanic CO<inf>2</inf> emissions is supported by the carbon isotopic composition. Diffuse degassing distribution highlights a CO<inf>2</inf> anomaly surrounding the younger domes within the crater. We estimated the CO<inf>2</inf> 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 CO<inf>2</inf> emission from soil degassing, Pululahua's crater volcanic CO<inf>2</inf> contribution is estimated between 59 and 97 t d−1. Finally, the potential hazards associated with the release of cold CO<inf>2</inf> at Pululahua's crater are also discussed.