Biscuit Basin Breaks Out Again, Not From Black Diamond

Early on Saturday, June 13, 2026, Biscuit Basin let loose again. Just after 5:09 in the morning, a small hydrothermal explosion pushed a plume of dark, muddy water and rock out of the ground in the Black Diamond Pool area. It was far smaller than the eruption that closed the basin in July 2024. But it happened in a spot I have been watching for two years.

New Vents First Showed in 2024

In the spring of 2024, before the major eruption, the new steam vents showed in an area beyond Black Diamond Pool. New energy like this can be a precursor to new vents opening up. In my repeat-photography project of the thermal features, this type of sign is a heads-up to document the area as best as possible from the boardwalks.

Expecting something to happen in this area, I certainly did not expect the large eruption from Black Diamond Pool. Taking a flight over the area in December 2024, after the Black Diamond eruption had closed the geyser basin, the colder temperatures showed the steam more clearly, making the area easier to read. The steam vents were in a line, with one much more pronounced than the others.

The energy was still there, and it would be interesting to see how it developed.

It developed.

Photo Courtesy USGS

The Breakout Caught on Camera

Monitoring equipment placed in the basin to keep an eye on Black Diamond Pool caught the initial breakout, registering both seismic energy and a low-frequency acoustic signal, called infrasound, coming from the direction of Black Diamond Pool. As the morning went on, park staff noticed the Firehole River running a light, milky grey for miles downstream, all the way to Midway Geyser Basin. Two new runoff channels from the basin into the river were visible from the road. All of these signs added up to “something happened.”

The obvious suspect was an eruption from Black Diamond. It had not. The temperature sensor on the pool showed only a small heat blip, not the sharp drop that follows a real eruption there. And the webcam that YVO installed in May 2025 happened to be pointed the right way and caught the whole thing: a dark steam plume jetting out of the ground to the north of Black Diamond, not from the pool itself.

Geologists were on the ground the next day. A few tens of yards north of the pool, they found three sets of brand new vents. The northern-most was still flowing, feeding a crack about 61 feet long and up to 5 feet wide, filled with 194-degree water. The middle group was five small vents, passively steaming at around 185 degrees by the next day. The southern group, closest to Black Diamond, was a linear vent about 49 feet long that had shoved a lot of water and sediment into the river before it stopped. Rocks were thrown out around all of it, but they did not go far, at most a few yards.

A New Geyser Showed Up

When the team returned two days later, they found a new pool of vigorously boiling, grey, silty water about 21 by 17 feet had formed near the middle vents. The ground geologists had walked on two days earlier was now an actively boiling pool, thumping as steam bubbles built and collapsed beneath it. This one didn’t form by explosion. It formed by collapse. By June 18, the webcam showed it spouting to perhaps 20 or 30 feet at intervals, and roiling hard the rest of the time.

Thanks to the camera on the boardwalk in the area, geologists will keep an eye on it. When new geysers break out, often their first eruptions are the largest, and they dwindle from there. But it’s very likely this area is not finished yet with its new look.

Normal Does Not Mean Safe

Biscuit Basin, and this stretch around Black Diamond Pool in particular, has been throwing rock and black, muddy water for well over a century. Black Diamond itself was likely created by explosions between about 1902 and 1912, with more events reshaping these pools in 1918, 1925, 1934, and 1953. It reactivated in 2006, went quiet again around 2012, then produced the enormous explosion of July 23, 2024. In between and since then, Black Diamond has continued to erupt to heights typically seen over the past couple of decades.

The original name for Black Diamond’s neighbor, now known as Black Opal Pool was “Black Boulder Geyser.” This tells us much. Thermal features are named for how they look, behave or to describe their location. This name likely came from the black, muddy eruptions that threw out boulders.

So, this behavior is truly normal for the area. That does not make it safe, but it is normal. The basin will remain closed indefinitely until the National Park Service gathers enough information to determine how to open it while still keeping the public safe. That’s something we can all appreciate.

The Upside of a Closed Basin

Having the basin closed has allowed the geology team to install monitoring equipment they couldn’t have done otherwise. This explosion happened about 330 feet from a monitoring station that YVO installed in the summer of 2025. No hydrothermal explosion has ever been recorded this close to instruments. Scientists now have seismic and infrasound data from right next to the event, and they are working through it to look for any precursors that might have signaled the explosion was coming. If these events give off a warning, this is the best chance yet to find it.

Given that the eruptions of Black Diamond have never really given any warning signs, having this data will hopefully give insights we can’t see from standing on the boardwalk watching a pool.

In the meantime, we are truly lucky that technology gives us a safe window to this ever-changing area, and that the geology team is doing such thorough work.

Janet has documented the thermal features through a personal passion project of repeat photography. She is in year 22 of this undertaking. Watching and tracking the energy shifts in the geyser basins in Yellowstone brings her back regularly to add to it her project each year. Information for this article was based on USGS articles, personal observations, and research throughout the years.

[Community Contributor]
📸 Header Image: Screenshot of USGS video

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