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 anddacite lava dome complex. This paper presents the results of a survey focusedon carbon dioxide (CO2) diffuse degassing at Pululahua, which wasconducted during the 2017 International Association of Volcanology andChemistry of the Earth´s Interior (IAVCEI) Commission of the Chemistry ofVolcanic Gases (CCVG) 13th Gas Workshop. Our objective was toconduct a comprehensive investigation of CO2 diffuse degassing byemploying standard methods for measuring CO2 flux and temperature,and data processing. These methods were applied to map the spatial distributionof the measured parameters, investigate the origin of CO2, andquantify the volcanic CO2 output within the surveyed area ofPululahua. We carried out a total of 350 soil CO2 flux and 329 soiltemperature measurements and collected 12 gas samples for carbon isotopiccomposition analysis, surrounding the three youngest domes in the complex. Inaddition, seventeen CO2 flux measurements over a thermal water poolwere performed. Our findings indicate that the diffuse emission at Pululahua´scrater floor is fed by both biogenic and volcanic CO2. Fluxes fromeach source are similar in magnitude, with approximately 90% of themeasurements falling into an intermediate flux range. The occurrence ofvolcanic CO2 emissions is supported by the carbon isotopiccomposition. Diffuse degassing distribution highlights a CO2 anomalysurrounding the younger domes within the crater. We estimated the CO2 diffuseemission using both statistical and geostatistical approaches over area of 3.36km2, resulting in values of 154.2 t d-1 and 126.2 t d-1respectively. Based on the geostatistical quantification of the total CO2emission from soil degassing, Pululahu´s crater volcanic CO2contribution is estimated between 59 and 97 t d-1. Finally, thepotential hazards associated with the release of cold CO2 atPululahua´s crater are also discussed.