A photograph shows damage to the boardwalk near Black Diamond Pool, which erupted forcefully on the morning of July 23, 2024.
Yellowstone National Park has closed the Biscuit Basin area for the season after a hydrothermal explosion strewed boiling water and rocks skyward Tuesday morning, destroying a section of boardwalk and spurring frightened tourists to flee.
No one was injured in the blast at Black Diamond Pool, which was caused by hydrothermal conditions and not volcanic activity, the park said Wednesday. Geologists are monitoring conditions, mapping the debris field and sampling water to assess any changes in the hydrothermal system, according to the park.
Small explosions of boiling water from the area continue to be possible over the coming days to months, and it will be off-limits to visitors for the duration of the season.
A preliminary report, meanwhile, sheds light on what scientists understand so far about the explosion.
Grapefruit-sized rocks
The sudden transition of water to steam in the shallow hydrothermal system beneath Black Diamond Pool caused the explosion just before 10 a.m. on Tuesday, according to the park report. There were no detectable precursors to the event.
The blast was powerful enough to send a dark cloud of steam, mud and debris hundreds of feet into the air, destroy a nearby wooden boardwalk section and spew grapefruit-sized rocks up to hundreds of feet from the source, the report states.
"Some blocks closest to the explosion site are about 3 feet (1 meter) wide and weigh hundreds of pounds," the report reads.
The direction of the explosion concentrated northeast toward the Firehole River, and the largest blocks of debris fell in that direction. Along with Black Diamond Pool, adjacent Black Opal Pool was affected by the event. The pools remain distinct features, though the explosion has altered the shape of Black Diamond.
Just after the eruption, the park report says, minor water roiling and spouting continued in Black Diamond Pool. "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."
Not uncommon
Hydrothermal explosions typically occur in the park one to a few times per year, according to the report, but often in the backcountry where no one is around to witness them.
On Tuesday, however, roughly a dozen people were on the boardwalk when the eruption occurred, including Vlada March, a real estate agent from California whose video of the eruption went viral on social media.
Nobody was hurt, though March reported at least one member of her group was showered with debris.
Yellowstone has recorded similar hydrothermal explosions in the park, including one nearby in Biscuit Basin from Wall Pool in 2009, one in 1989 at Porkchop Geyser in Norris Geyser Basin, and on April 15 of this year at the Porcelain Terrace Area of Norris Geyser Basin. More significant hydrothermal explosions, probably similar in size to Tuesday's blast, occurred in the 1880s at Excelsior Geyser, in Midway Geyser Basin, the park reports.
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