A churning pool of water has opened up in Yellowstone National Park – just two days after scientists were walking around on the exact patch of ground.
The spot where they were standing was replaced by a silt-gray pit the size of a small swimming pool, hissing and thumping with boiling water.
The weird part? Nobody saw it happen.
The new pool appeared in the Biscuit Basin sometime between June 14 and 16 – shortly after the area was rocked by a small hydrothermal explosion on June 13.
It's the second such event in Biscuit Basin in two years.
This latest incident "emphasizes the dynamic and hazardous nature of hydrothermal activity in the region," according to the US Geological Survey (USGS) team.
The last explosion in July 2024 sent rocks and scalding water blasting into the air, causing significant damage to the boardwalk and visitor area.
This recent event was smaller, and thankfully, no one was hurt on either occasion.
But what's incredibly cool is that, this time, scientists were able to capture the eruption on camera (see video below).
So what's going on in Biscuit Basin?
"Just after 5:09 am MDT on Saturday, June 13, 2026, monitoring equipment in Biscuit Basin registered anomalous activity, including seismic energy and a low-frequency acoustic signal, called infrasound, that was coming from the general direction of Black Diamond Pool," the USGS team writes.
Once the Sun came up, they noticed something else weird – the downstream Firehole River was filled with a light-grey, milky plume.
The Yellowstone National Park Geology team immediately assumed that nearby Black Diamond Pool had erupted once again.
But their sensors only showed a small heat blip at the time of the geothermal event, indicating the real explosion happened elsewhere.
So if it wasn't Black Diamond Pool, what was it?
Their main clue came from the footage below, captured by a Yellowstone Volcano Observatory camera.
If you look to the top right of the screen, at 5:09:50 am, you can see a plume of dark steam spewing from the area north of the Black Diamond Pool.
That was the same time as the seismic and infrasound anomalies.
A visit to the site the next day revealed evidence that large amounts of boiling hot hydrothermal water had surged into the Firehold River from three newly formed vents.
"These vents represent pathways where water at or even slightly above boiling temperatures beneath the ground suddenly found a pathway to the surface and flashed to steam, driving a hydrothermal explosion," the team writes.
By the time the team was on site, the water had cooled to around 85 °C (185 °F).
But they could clearly see a crack 18.5 meters (61 feet) long and up to 1.5 meters (5 feet) wide, which was still sending near-boiling water into the river.
The crack was surrounded by rocks that had been ejected during the explosion, but they appeared to have only traveled a few meters, so the explosion likely wasn't as large as the 2024 event.
You can see the locations of the new vents below.
At that point, however, there was no sign of the new pool.
It wasn't until the researchers returned on June 16 that they were shocked to find an actively boiling, gray, silty pool measuring 6.5 meters by 5.3 meters.
The pool was producing a thumping sound caused by steam bubbles forming and collapsing (which is a little terrifying, given their recent visit).
They're still not sure when it opened up.
Based on the lack of debris around the new pool, the USGS team suggests it formed by collapse rather than explosion, meaning it wasn't captured on camera the way the earlier eruption was.
However, later footage captured on June 18 showed jets of water intermittently spouting to heights of 6–9 meters, suggesting the area is still active.
You can see these spurting up in the distance behind the Black Diamond Pool between 10:24:30 am and 10:25:00 am.
Of course, this is far from the first time new features have appeared in front of our eyes in Yellowstone.
Just last summer, we saw another milky blue pool form in the Porcelain Basin area. And there has been plenty of geyser action over the years.
One very special thing about this event is that it's the closest a hydrothermal explosion has ever occurred to a monitoring system.
So the team has plenty of recorded data to review from both before and after the event to gain more insight into exactly what happened, and whether there were any warning signs.
Related: Scientists Found The 'Lid' Keeping The Yellowstone Supervolcano From Erupting
While there's a lot we still don't know, this event is a pretty cool reminder that our planet is still full of surprises.