Sometime between June 14 and June 16, a boiling, gray pool opened up in the ground at Yellowstone‘s Biscuit Basin. Scientists can’t say exactly when—nobody was there. Two days earlier, they had been standing on that exact patch of ground.

Just after 5 a.m. on June 13, something blew in Biscuit Basin. By sunrise, the Firehole River had gone milky gray, a plume of suspended sediment running roughly 6 kilometers (about 3.7 miles) downstream. It was the second hydrothermal explosion in the same area in two years.

Black Diamond Pool blew in 2024, so it was the obvious first call. Temperature sensors at the pool showed almost nothing, though, and a monitoring camera told a different story—a dark plume of steam jetting north of the pool at 5:09:50 a.m., right when the seismic signals hit.

A New Boiling Pool Suddenly Appeared at Yellowstone. Scientists Are Investigating Why.

When geologists arrived the next day, they found three newly formed vents pushing near-boiling water into the Firehole River and an 18.5-meter-long crack still venting 90°C water. The USGS described the vents as pathways through which superheated groundwater suddenly reached the surface and flashed into steam. No pool yet.

When the team returned on June 16, the pool was there, 6.5 by 5.3 meters, filled with actively boiling, silty gray water that produced a thumping sound as steam bubbles formed and collapsed beneath the surface. No debris was found surrounding it, so the USGS suspects a collapse rather than an explosion. That’s why it never showed up on camera.

The June 13 explosion happened about 100 meters from a new Biscuit Basin monitoring station, installed in summer 2025. According to the USGS, no hydrothermal explosion has ever occurred that close to a monitoring system. Scientists are now reviewing data from both before and after the event in hopes of identifying precursors that nobody has managed to capture until now.

Biscuit Basin has been closed since the 2024 explosion, so nobody was at risk. The more pressing question now is whether anyone can learn to see these things coming—and for the first time, scientists actually have the data to try.