Preparations for Yellowstone National Park’s summer season are underway. A convoy of construction vehicles equipped with snow removal tools is slowly plowing through the thick layers of snow on the Grand Loop Road in preparation for tourists in May.
One area of Yellowstone that the park’s managers and scientists are monitoring closely is Biscuit Basin. The thermal area near Old Faithful has been closed since July 23, 2024, after a massive hydrothermal explosion of Black Diamond Pool destroyed the boardwalk, scattering tourists and sending refrigerator-sized rocks hurtling through the air.
The thermal feature has been closed since, and will remain closed for now because it’s still active and could erupt violently again.
“Biscuit Basin remains closed until further notice, and we are continuing to monitor geologic activity in the area,” Yellowstone National Park Information Specialist Linda Veress told Cowboy State Daily.
The park’s official website says Biscuit Basin is closed “due to the possibility of another event at the site.”
Mike Poland, scientist-in-charge of the Yellowstone Volcano Observatory, said that’s within the realm of possibility since there’s been a lot of activity since last July.
“Biscuit basin is continuing to have several explosions, sending mud, water and debris up a few tens of feet,” he said. “And something we're trying to keep track of right now.”
Finding The New Normal
The July 23 hydrothermal explosion at Black Diamond Pool sent 148.5-degree water more than 100 feet into the air. It left a 30-foot crater in its aftermath, and debris from the explosion was found more than 200 feet away from the pool.
Black Diamond Pool has remained active since. Poland said monitoring equipment installed in the area has detected several smaller explosions since July, which makes the area potentially hazardous for tourists.
“Some explosions have been witnessed by tour guides driving past Biscuit Basin,” he said. “There's still a lot of hot water down there that's flashing the steam from time to time.”
Hydrothermal explosions are caused by the force of water rapidly changing to steam. They can theoretically happen anywhere at any time in Yellowstone, but Poland believes the ongoing activity at Black Diamond Pool is a sign that the thermal feature is “readjusting” to the aftermath of the July 23 event.
“When the explosion occurred, it probably created confinements in the plumbing system that can lead to unpredictable, small-level hydrothermal explosions,” he said. “This isn’t anything out of the ordinary. Everything needs to adjust to its new normal, establish new conduits, and so forth.”
There haven’t been any eruptions on the scale of the July 23 explosion. Still, Poland said ongoing activity is enough to make park managers wary of allowing visitors to return to Biscuit Basin.
“I think the park’s staff are being cautious about what’s going on in the area because Black Diamond Pool is still a very unstable feature,” he said. “We don’t know how things will turn out at Black Diamond Pool. These small explosions will continue, but we can’t say if it will culminate into something bigger.”
Biscuit Basin as it appeared in December 2024. The thermal area near Old Faithful has been closed since July 23, when a hydrothermal explosion under Black Diamond Pool sent water, mud, and debris hundreds of feet into the air. Several smaller explosions at Black Diamond Pool have been documented since then. (Andrew Rossi, Cowboy State Daily) 
Biscuit Basin as it appeared in December 2024. The thermal area near Old Faithful has been closed since July 23, when a hydrothermal explosion under Black Diamond Pool sent water, mud, and debris hundreds of feet into the air. Several smaller explosions at Black Diamond Pool have been documented since then. (Andrew Rossi, Cowboy State Daily) 
A dramatic video of the aftermath of the Black Diamond Pool explosion July 23, 2024, resembles a war zone. The event also is an opportunity for research, and the park has put out a call for help in studying what happened. (National Park Service)
Safety First
Black Diamond Pool has an erratic history. After an earthquake in July 2006, the pool had several eruptive explosions. The July 23 explosion was the second one that occurred in 2024, even though the pool had been quiet since 2016.
Poland said the intensity of last year’s explosion might have permanently changed the behavior of Black Diamond Pool. Until he and other park scientists can understand the extent of that change, Biscuit Basin will probably remain closed to tourists.
“The park's main concern is safety,” he said. “It's important to characterize the activity we're seeing, understand it, and understand its likely future course. With that information, then the park can make an informed decision about access for the public.”
The explosion destroyed a significant portion of the Biscuit Basin boardwalk. The damage has yet to be addressed because of the ongoing unknowns surrounding Black Diamond Pool.
“They have to repair a bunch of boardwalks in the area,” Poland said. “It's a big operation for the park to handle, especially when we aren’t sure if we’ve entered a new pattern of (hydrothermal) activity for the area. It’s a bit early to say when Biscuit Basin will reopen.”
Scientific Scrutiny
Since the big explosion of Black Diamond Pool, scientists have been scurrying in and out of Biscuit Basin to install new equipment to monitor Biscuit Basin. Poland said more equipment will be installed this summer once the area is more accessible.
“It's been absolutely fascinating to collect these sorts of data sets,” he said. “We're hoping to characterize some of these explosions in detail and, potentially, any changes that lead up to them. Ultimately, we would like to forecast these hazardous events.”
There is currently no way to forecast hydrothermal explosions in Yellowstone or anywhere else in the world. However, the ongoing activity at Black Diamond Pool could reveal patterns and signs of an imminent explosion, which could potentially save lives.
Poland previously described the July 23 event as “small.” The largest known hydrothermal explosion occurred 14,000 years ago, evidenced by a 1.5-mile-wide crater on the northern edge of Yellowstone Lake.
"As dramatic and as hazardous as the Black Diamond Pool event was, it was relatively small in the context of the steam explosions in Yellowstone's geologic history,” he said.
There’s a lot of uncertainty in the shattered landscape and debris field of Black Diamond Pool. It’ll take a lot of scientific scrutiny and elbow grease from the National Park Service before it’s deemed safe enough for tourists to return to Biscuit Basin.
“Everything’s focused on Black Diamond Pool right now,” Poland said. “We can't rule out that things are happening in the other features of Biscuit Basin, but Black Diamond has been the focus of all the activities since July. We’re trying to keep track of everything.”
Contact Andrew Rossi at arossi@cowboystatedaily.com
Andrew Rossi can be reached at arossi@cowboystatedaily.com.
