A hydrothermal explosion occurred on the morning of Tuesday, July 23, at Biscuit Basin near Sapphire Pool in Yellowstone National Park, resulting in significant disruptions and safety concerns. The explosion, which took place just before 10 AM, prompted the temporary closure of the Biscuit Basin area, including its boardwalks and parking lot, while the Grand Loop Road remains open.

The explosion was caused by a sudden transition of water to steam within the shallow hydrothermal system beneath Black Diamond Pool. This event sent steam and debris hundreds of feet into the air, damaging a nearby boardwalk and scattering rocks and mud over a wide area. Some rocks, measuring up to three feet in diameter, were propelled hundreds of feet from the explosion site. Despite the presence of visitors, no injuries were reported.

Following the explosion, National Park Service (NPS) and US Geological Survey (USGS) teams conducted a preliminary assessment. Black Diamond Pool and Black Opal Pool were significantly impacted, with debris causing murkiness and altering the shape of Black Diamond Pool. Initially, Black Diamond Pool exhibited minor roiling and water spouting, with bursts of hot water reaching up to eight feet. By Wednesday morning, both pools were overflowing, sending murky water into the Firehole River.

Hydrothermal explosions are not uncommon in Yellowstone, typically occurring one to a few times per year, though often in remote areas. Previous similar events include a 1989 explosion at Porkchop Geyser and a recent April 2024 explosion in the Porcelain Terrace Area of Norris Geyser Basin. Given the recent changes to the hydrothermal system, small explosions may continue in Biscuit Basin over the coming days to months.

For visitor safety, Biscuit Basin will remain closed for the rest of the 2024 season. Other nearby thermal areas, such as Black Sand Basin, remain open to visitors. Park staff, alongside USGS experts, will continue to monitor conditions and assess any further changes in the hydrothermal system. More information on visitor access and safety updates can be found on the Yellowstone National Park website.

For detailed information on Yellowstone’s volcanic and hydrothermal activity, visit the Yellowstone Volcano Observatory monitoring website or refer to recent USGS publications on the region’s hazards and monitoring plans.