Can CO2trigger a thermal geyser eruption?

Abstract

Geyser eruptions are produced by a complex and poorly understood set of subsurface processes and conditions. They typically have an abundant supply of water, relatively permeable and competent subsurface material, a conduit to the surface, a driving mechanism (commonly believed to be the initiation of gas lift pumping by steam formation in the conduit), and a trigger. Here we present time series of dissolved CO 2 concentrations in near-surface discharge waters of a thermal geyser in Yellowstone National Park (northwestern United States) that vary systematically over several eruption cycles. Chemical geothermometry, combined with a temperature profile in a nearby well, suggests that the geyser water ascends from non-boiling conditions (∼153–171 °C at a depth of 57–65 m). When the time series of near-surface measured CO 2 concentrations are extrapolated to these subsurface conditions assuming dominantly adiabatic cooling, the additional gas pressure from dissolved CO 2 is large enough to cause the total dissolved gas pressure to exceed bubbling pressure, inducing bubble formation. We postulate that CO 2 is a necessary component to triggering eruptions in the geyser studied. Furthermore, unlike steam, CO 2 bubbles do not completely re-condense during cooling in the geyser conduit, hence providing better sustenance for gas lift pumping than pure H 2 O boiling.