CH4 and CO2 diffuse gas emissions before, during and after a Steamboat Geyser eruption

Abstract

Steamboat Geyser in Norris Geyser Basin in the northwestern part of Yellowstone National Park is the highest erupting active geyser in the world with jets of fluids observed to be as high as 115 m. Steamboat eruptions increased from 11 between 2000 and 2017 to 131 between 19 April 2018 and 21 February 2021. Recurrence intervals are now irregular, averaging 8 ± 4 (1σ) days between each event. To examine whether changes in gas emissions could serve as eruption precursors for Steamboat, on June 12, 2019 we made continuous measurements of the diffuse emissions of methane (CH4) and carbon dioxide (CO2) ~30 m from the geyser before and after a single eruption event. These results showed steady fluxes during the 2.5 h, except for a sharp decrease of 58% for CH4 and 50% for CO2 10–25 min before the eruption. These precursor measurements were followed by the eruption and 3.5 h of measurements that showed fluxes quickly returning to previously measured values. Similarly, precursor carbon isotope measurements of CH4 (δ13C-CH4) and CO2 (δ13C-CO2) were both distinctly lighter (−35.7 ± 2.1‰ and −6.2 ± 0.4‰, respectively) than the non-precursor measurements (−27.5 ± 0.3‰; −3.9 ± 0.1‰, respectively) that reflected a deep source. This suggests that the diffuse emissions of deeply sourced gas was interrupted near the commencement of this one observed eruption at Steamboat.