YELLOWSTONE NATIONAL PARK, Wyoming – Just before 10am on Tuesday, July 23, a large hydrothermal explosion shot rocks and debris hundreds of feet into the air at the Black Diamond Pool in Yellowstone National Park’s Biscuit Basin. Information on the explosion was fairly scarce in the moment, but the National Park has been releasing more and more information since.
A press release from the park explains that, while most of the chunks blown into the sky were grapefruit sized, some 3-foot-wide blocks that weighed hundreds of pounds were launched close to the explosion site. Debris was largely directed northeast of the explosion site, with the largest of blocks falling towards the Firehole River.
“Black Diamond Pool and Black Opal Pool were affected by Tuesday’s explosion, and while they remain distinct features, the shape of Black Diamond has changed somewhat. Both pools are murky due to debris, and the unstable ground around their edges occasionally slides into the water. Just after the eruption, Black Diamond Pool exhibited minor roiling and water spouting. The water level in the pool rose over the course of the day, and by Tuesday afternoon the roiling transitioned to occasional bursts of hot water that reached about 8 feet (2.4 meters) in height.“
According to the United States Geological Survey, a hydrothermal explosion occurs when fluids at or near boiling point in shallow interconnected reservoirs rapidly transition to steam due to a sudden pressure drop. As the vapor takes up more space than the fluid, the sudden transition quickly blows apart rocks and launches debris.
While the July 23 explosion seemed quite large, Yellowstone’s largest hydrothermal explosions are much more devastating. 25 explosion craters larger than 328 feet (100 meters) wide have been identified in the park, with one of these large explosions taking place on average every 700 years. The largest hydrothermal explosions can reach heights of 1.2 miles (2km), with debris flying as far as 2.5 miles from the crater site.
“Although large hydrothermal explosions are rare events on a human time scale, the potential for additional future events of the sort in Yellowstone National Park is not insignificant. Based on the occurrence of large hydrothermal explosion events over the past 16,000 years, an explosion large enough to create a 100-m- (328-ft-) wide crater might be expected every few hundred years.” – USGS
Yellowstone National Park:
Given the recent changes to the hydrothermal plumbing system, small explosions of boiling water from this area in Biscuit Basin continue to be possible over the coming days to months. USGS and NPS geologists will be monitoring conditions, mapping the debris field, and sampling water to assess any changes in the shallow hydrothermal system over the next several days.
Hydrothermal explosions typically occur in the park one to a few times per year, but often in the back country where they may not be immediately detected.
Similar, although smaller, hydrothermal explosions took place in 1989 at Porkchop Geyser in Norris Geyser Basin, and on April 15, 2024, from the Porcelain Terrace Area of Norris Geyser Basin. A small hydrothermal explosion occurred from Wall Pool, in Biscuit Basin, in 2009. Significant hydrothermal explosions, probably similar in size to that of July 23, 2024, occurred in the 1880s at Excelsior Geyser, in Midway Geyser Basin.
Yellowstone National Park has closed Biscuit Basin for the remainder of the 2024 season for visitor safety. Grand Loop Road remains open to vehicles, and other nearby thermal basins, like Black Sand Basin, are open. Additional Yellowstone National Park information about visitor access can be found at https://www.nps.gov/yell/index.htm.
