AN EXPERIMENTAL INVESTIGATION OF THE INFLUENCE OF GEYSER GEOMETRY ON ERUPTION DYNAMICS

Geyser eruptions, a source of fascination to millions of visitors at national parks and a useful analog to other erupting systems, are caused by thermodynamic and fluid mechanical instabilities that are coupled through the geometry of the subsurface plumbing system. Our understanding of geyser conduit systems has recently improved due to the identification of offset cavities (i.e., “bubble traps”), in many natural systems, which can trap steam and store energy that fuels eruptions. In bubble trap conduit geometries, there is a mechanical coupling between the eruption conduit and the offset reservoir, such that fluid flow in the eruption conduit can trigger thermodynamic changes in the bubble trap, and this is a likely mechanism for triggering eruptions. The nature of this coupled feedback, however, is poorly understood, and the situation is complicated by the fact that natural eruption conduits typically have complex geometries, including constrictions that accelerate fluids and may be able to choke flow.

We use a laboratory analog geyser to investigate the influence of eruption conduit constrictions on geyser dynamics. Our lab geyser includes a large (150 liters) water tank, electric heaters providing a total of 11kW, a steam injection system, and cold water and pressurized air supplies. Both the diameter and height of the eruption conduit can be varied, and one or more constrictions can be integrated along its length. Pressure-temperature conditions at six points within the bubble trap and eruption conduit, including within constrictions, are monitored at 10 kHz, and high-speed video cameras are used to observe flow dynamics within the transparent conduit system. We present these data and describe observed relationships between geometry and eruption dynamics. A notable result is that we commonly observed shock waves (3 to 4 bar amplitude), indicating choked flow, in eruption conduits with constrictions, demonstrating that this phenomenon, which has been hypothesized for some natural systems, is a normal consequence of the system dynamics.