Search

Porkchop Geyser, in Yellowstone National Park, was the site of a small hydrothermal explosion on September 5, 1989. In the early 1960s, this was a quiescent spring with an intermittent seeping discharge. Infrequent geyser eruptions 3-5 m high started in 1971, and in 1985 the geyser began erupting as a perpetual spouter 6-9 m high. Perpetual spouting at the latter height continued until just before the catastrophic hydrothermal event when the geyser column suddenly rose to a height of 20-30 m, followed immediately by the explosive ejection of sinter blocks up to 1.88 m in maximum dimension and formation of an irregular crater 13.9 m long and 11.7 m wide. The ejected blocks show a variety of siliceous deposits indicative of changing environments of deposition with time, and possibly of prior hydrothermal explosive activity at this site. Water samples from Porkchop were collected and analyzed once in the 1920s, again in 1951, ten times between 1960 and mid-1989, and once in January 1990 after the explosion. Chemical geothermometry shows an increase in the temperature of last water-rock equilibration of about 60 to 70 °C from 1962 through 1989. This may have been the result of drawing water progressively from different and hotter regions of a single reservoir or mixing waters from two different reservoirs with a progressively larger proportion of water being drawn from the hotter reservoir from 1962 through 1989. Boiling of ascending fluids coming from hotter subsurface regions resulted in an increase in the proportion of steam to water discharged by the geyser. A constriction at the exit of the geyser tube throttled the flow of water and steam and allowed water in shallow cavities adjacent to the geyser tube to become heated to the boiling point at pressures greater than normal hydrostatic. We hypothesize that a sudden breaking loose of this constriction, likely triggered by a seasonal increase in subsurface boiling throughout Norris Basin, allowed water and steam to be discharged from Porkchop much more rapidly than previously. This resulted in a drop in pressure within the geyser tube, causing water in adjacent connected chambers to become superheated. An ensuing rapid flashing of superheated water to steam within relatively confined spaces resulted in the hydrothermal explosion.

A paper about thermal activity in Yellowstone National Park. It assesses impacts of geothermal, oil, gas, and other types of development adjacent to the park. It also relates these changes to magma under the park.

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 CO 2 .