YELLOWSTONE NATIONAL PARK — Scientists at the Yellowstone Volcano Observatory (YVO) are studying the habits of Black Diamond Pool in Biscuit Basin. The YVO scientists believed that the still-closed area where a hydrothermal explosion occurred last summer was still active after the explosion, but data and evidence could not prove it.
This week’s Caldera Chronicles is written by Mara H. Reed, Samantha R. Hilburn and Margery B. Price, all physical science technicians in the Geology Program at Yellowstone National Park (YNP). They explain that two eruptions were witnessed by people, in November 2024 and in January 2025, but more seemed to be going on.
The authors discuss the signs that led them to believe the Black Diamond Pool was active, such as new sediment and rock debris appearing, small seismometers falling over, temperature sensors getting buried in the mud and one sensor even getting swept down the Firehole River. Temperature records from sensors also revealed that at least eight events had occurred between January and April 2025.
“But scientists could not determine the size or duration of eruptions from available data,” the column reads. “Due to the mysterious nature, scientists started to call the events ‘Sasquatch’ eruptions, referencing a creature from North American folklore (also called Bigfoot).”
In May, YVO installed a webcam at Biscuit Basin to keep tabs on the thermal pool. The webcam finally caught a four-second explosion of water, steam and sediment on May 31 at 8:39 p.m.
“At last, a Sasquatch sighting!”
Temperature sensors increased from 125°F to 146°F and back down to 125°F over the course of four minutes. The webcam captured similar hydrothermal events on June 12, July 3 and July 14. The footage combined with infrasound sensors and temperature records provide extra data in learning the size and duration of eruptions.
According to the column, hydrothermal explosions are caused by pressure changes that result from water changing to steam in a confined space. The expanding steam bubbles build up pressure until eventually the explosion breaks through the sealed rock.
“The July 23, 2024, explosion at Black Diamond Pool clearly changed the shallow hot water and steam plumbing system of the feature,” the authors wrote, “so that now it seems to favor small eruptions every few days to weeks.”
