THE ROLE OF NON-CONDENSABLE GASES IN GEYSER ERUPTIONS IN YELLOWSTONE NATIONAL PARK

Yellowstone National Park is home to the world’s greatest concentration of geysers. In order to ensure the safety of visitors, to address impacts on surface ecosystems by subsurface hydrothermal activity, and to protect these fragile features, it is increasingly important to accurately constrain the processes that give rise to geyser eruptions. Geysers are incompletely understood, largely thought to be driven by hot water and steam. Non-condensable gases, primarily magmatic CO₂, are present in Yellowstone hydrothermal waters, but to our knowledge no field-based research has directly addressed how such gases impact the geyser eruption mechanism. The goal of this study is to examine and determine if non-steam gases can play an important role in triggering and/or driving an eruption.

In November 2013, we sampled five hot water geysers and springs in Yellowstone. In order to understand the evolution of geyser waters and non-condensable gases on an eruption interval time-scale, we collected continuous in situ water quality data between eruptions and took time series water samples for major element chemistry, isotope, and dissolved gas analysis. Chemical geothermometry determined that the studied geyser and spring waters ascend from temperatures of 170 - 200°C. Subsurface steam separation is estimated to majorly contribute to the cooling of waters to their surface temperatures of around ~90°C, which concurrently strips dissolved CO₂ from the water. Using surface CO­₂ concentrations in Spouter Geyser, which increase leading up to an eruption, subsurface temperatures, and CO₂ partition coefficients, we calculated subsurface CO₂ concentrations in Spouter Geyser. Although dissolved gas analysis shows that CO₂ concentration is a minor component in surface waters of Spouter Geyser, subsurface concentrations may reach levels greater than solubility preceding an eruption at corresponding pressures and temperatures. We propose that ebullition of CO₂ may induce boiling to drive an eruption in hot water systems.