Dynamics of a geyser

Only about a thousand geysers are known to exist, and roughly half of them are found in Yellowstone National Park in the western US. Given a suitable—and rare—geology, underground liquid and vapor are heated and pressurized until turbulently vented to the atmosphere. To study an eruption jet’s dynamics, a multi-institutional team of geophysicists spent four days monitoring Yellowstone’s Lone Star Geyser, which has erupted reliably every three hours for many decades. Similar to other geysers, Lone Star had four distinct event stages. The main eruption stage has a notably unsteady flow with maximum velocities of 16–28 m/s, near the sound speed of the erupting bubbly mixture, and forms a fountain up to 13 m high, as seen in this IR image. The image also reveals some of the conduits within the 3-m-tall mineral-crusted cone. The other stages are relaxation to ambient conditions; recharging during which the plumbing refills; and a preplay period during which the geyser puffs and pulses. The team deployed high-quality visible and IR video cameras; acoustic, IR, and seismic sensors; and stream-discharge instruments. Among other things, the researchers saw flow oscillations with periods of roughly 30–70 seconds, likely due to boiling instabilities in the underground plumbing. They also learned that as the underground reservoir progressively emptied, the dominant discharge changed from mostly liquid to mostly steam. Chemical analysis of outflowing water revealed the reservoir temperature to be about 170 °C; water’s boiling point is 93 °C at Lone Star’s elevation. The geyser’s total heat output was about 1.4 MW. (L. Karlstrom et al., J. Geophys. Res. [Solid Earth], in press .)