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Sulfur scrubbing and remobilization at Poás: Implications for gas monitoring at volcanic lakes

Maarten de Moor 1,2, Alejandro Rodríguez1, Jaime Barnes3, Geoffroy Avard1, Jeff Cullen3, Alessandro Aiuppa4

  • Affiliations: 1Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional, Heredia, Costa Rica 2Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM, USA 3Department of Earth and Planetary Sciences, University of Texas, Austin, TX, USA 4Dipartimento DiSTeM, Università di Palermo, Palermo, Italy

  • Presentation type: Poster

  • Presentation time: Friday 16:30 - 18:00, Room Poster Hall

  • Poster Board Number: 82

  • Programme No: 6.8.8

  • Theme 6 > Session 8

Abstract

Gas monitoring using in-situ MultiGAS stations at Poás volcano has shown that key gas ratios (SO2/CO2 and H2S/SO2) change with eruptive activity and geophysical signals. However, interpreting these correlations requires understanding of complex sulfur dynamics in hydrothermal-magmatic systems. The latest cycle of lake growth and disappearance between 2019 and 2024 at Poás provides an opportunity to investigate sulfur scrubbing. During this period we estimate that ~118 ktons S was degassed to the atmosphere as SO2, compared to ~68 ktons of elemental S deposited by the lake, and ~65 ktons emitted by flank springs as dissolved sulfate. The lake itself is an ephemeral S sink containing <15 ktons S as dissolved bisulfate. Therefore, at least half of the SO2 released from the magma is scrubbed by the hydrothermal system. Elemental S is likely generated by both H2S oxidation and SO2 disproportionation, as evidenced by decreasing H2S/SO2 and decreasing SO2/CO2 during lake growth.  Eruptive episodes at Poás are associated with high SO2/CO2 , likely due to increased magmatic SO2 input. However, CO2- SO2-H2S systematics suggest that revolatilization of elemental S and dissolved bisulfate could be significant processes during eruptive degassing. Sulfur isotopes should be a powerful tool for distinguishing between magmatic gas and secondary gases produced by scrubbing/remobilization processes. To this end we have collected time-series plume and fumarole samples to determine the sulfur isotope compositions of both SO2 and H2S, as well as samples of secondary products, which we will present to further investigate dynamic changes in sulfur processing at Poás.