In situ observations of Old Faithful Geyser

In a series of experiments from 1983 to 1993, four probes were carefully lowered into Old Faithful Geyser, Yellowstone National Park, Wyoming. At different times, these probes variously recorded pressure-temperature-time conditions (to nearly 22 m depth), and video probes showed the conduit geometry and processes of recharge (to 13 m depth). Temperatures recorded were, within experimental error, the same as those recorded in 1942, with a peak bottom temperature (T) of 118 °C. Processes observed include fog formation in the upper levels of the conduit owing to wind and entrainment of cool air; “bank storage” of hot water that splashes to high levels, cools, and recharges; recharge of cooler ground water into the conduit; superheated steam expansion into the conduit (T = 129.5 °C); periodic temperature fluctuations; and exsolution of bubbles of noncondensable gas, which we propose are CO₂.