Seasonal and multi-year changes in CO2 degassing at Mammoth Mountain explained by solid-earth-driven fault valving

Changes in CO₂ emissions from volcanoes may evidence volcanic unrest. We use a multiyear time series of CO₂ flux collected at the Horseshoe Lake Tree Kill area on Mammoth Mountain, CA, to understand processes that cause variations in flux from this system. Seasonal variations are systematically lowest during the winter months and reach maximum values during the summer season. A persistent ∼20% reduction in CO₂ flux occurred during the Spring of 2017, coincident with the emergence of the area from drought and earthquake swarms in Long Valley Caldera. We used continuous GNSS measurements to calculate seasonal strains and stresses across the Mammoth Mountain area, and resolved resultant stresses onto the Mammoth Mountain Fault, which appears to facilitate gas transport to the surface. The normal stress changes are consistent with seasonal and multiyear changes in CO₂ flux, suggesting that fault valving by solid earth processes can alter surface gas fluxes.