Origin and Quantification of Diffuse CO2 and H2S emission at Crater Hills, Yellowstone National Park

Abstract:

At Crater Hills, a thermally-altered area adjoining the Sour Creek resurgent dome that is located within the Yellowstone Caldera, we characterized volatile emissions based upon our soil degassing measurements and soil gas chemistry in 2014 and fumarole gas chemistry in 2007 (Bergfeld et al., 2011). The investigation at Crater Hills on its diffuse gases isotopes and CO₂, H₂S emission improve our understanding on its gas emission mode – including total emission and spatial distribution, and contribute to a more accurate estimation of total CO₂ emission at Yellowstone volcanic system. The total emission of CO₂ interpolated by sequential Gaussian simulation method (sGs) was 66 to 109 t d^-1 with 95% confidence, which is an underestimation due to the inability to measure a high flux area on a slope as well as the absence of fumarole and pool emissions[CAW1] [CAW2] [CAW3] . Indicated by gas chemistry data of the fumarole at Crater Hills in 2007, the proportion of CO₂ derived from magma would be at least 38% if considering the worst and unreasonable scenario; other scenarios give a much higher proportion of magma component, which would be over 50%. Faults or fractures covered by overlying alluvium are very likely to exist at Crater Hills, based on the similarity between the connection of high flux areas and the trend of the regional faults. The estimated emission of H₂S was 0.39 t d^-1, based on the linear correlation between H₂S and CO₂. The heat output was also estimated to be ~35MW with a[CAW4] verage heat flux of ~100 W m^-2 based upon CO₂-H₂O-heat relations. The temperature of liquid-dominated reservoir was estimated to be 270-300 ⁰C estimated by Fournier (1989), and was 213 ºC to 217 ºC for the vapor-dominated reservoir which is the source for the sampled fumarole gas in 2007.