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.The new pool, which opened up in the ground the scientists were walking on two days earlier. (USGS)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.An aerial shot from July 2024 showing the damage caused by the previous geothermal explosion. (USGS)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.