- Yellowstone scientists now have evidence that explains a massive eruption at Black Diamond Pool last year.
- The Biscuit Basin, where the pool is located, has been closed since July 2024 while a cause was determined.
- The eruption destroyed the underground "plumbing" of the region, causing a series of smaller random explosions.
The Black Diamond pool in Yellowstone National Park’s Biscuit Basin erupted a year ago last week, sending debris 400 feet into the air. Visitors scattered as mud, rock and hot water rained down from the sky. Large sections of the boardwalks were destroyed and the area has been closed ever since.
“There were a lot of questions about what happened after the large hydrothermal explosion,” said Michael Poland, the scientist-in-charge of Yellowstone Volcano Observatory. And, “there were some indications that probably the pool was still very active.”
But active in what way, was the question and scientists have spent the past year trying to find out.
The area is only two miles north of Old Faithful and includes beloved visitor attractions like the Sapphire Pool. The park needs to understand what happened before it can rebuild or allow visitors to return, and Poland and other researchers were not sure if it was an isolated event or something greater.
“Hazards associated with hydrothermal events cannot be understated,” wrote Poland in his weekly newsletter, Yellowstone Caldera Chronicles. “The July 2024 event at Biscuit Basin expelled boulders large enough to smash through boardwalks as visitors ran for safety. ”
Taking the temperature
Since the eruption, a series of events kept popping up in the area that indicated there was likely more instability, but none were conclusive on their own.
“Trail cams would catch ... that some rocks had moved, the shoreline was wetter, the water was agitated,” Poland said.
In some instances, unknown events “toppled small seismometers, buried temperature sensors in mud, and in one case washed a temperature sensor down into the Firehole River,” Poland wrote.
The pool’s temperature readings would spike at various times and then there were two different eyewitness accounts — not always the most reliable source for geologists — that claimed to have seen parts of small eruptions, too.
All of this together, Poland wrote, suggested that “something was going on.“ (Italics his). Due to the “mysterious nature” of the events, Poland wrote that he and his colleagues started to call them “Sasquatch” sightings.
Getting a clearer picture
The team installed a webcam video recorder in May, in an attempt to confirm what exactly was going on in Biscuit Basin.
Two weeks later, the Yellowstone Volcano Observatory finally recorded video of its “Sasquatch.”
In the footage, the Black Diamond Pool sends off a 30 foot high eruption of steam and debris into the air for a four-second period. Since that first video, they’ve now caught three or four more eruptions.
“That’s allowed us — because we’re also recording other data sets at the same time — to associate everything,“ Poland said. ”Now we know what these temperature fluctuations are associated with. We know what they mean because we now have a visual record of the activity."
As the video correlated to other evidence that the Yellowstone Volcano Observatory recorded from its other nearby equipment, such as sound recorders and temperature gauges, they can confirm the full spectrum of activity since last July’s eruption.
There have been at least eight eruptions to the Black Diamond pool since the big one in 2024. Knowing about those previous events paints a clear picture of the hydrothermal activity under Biscuit Basin.
“The plumbing system was blown up in 2024 by that explosion. In fact, when we look at the rocks that are scattered around the surface from that event, you can see these very silica rich rocks that clearly have lined the inside of the hot water conduits,” Poland said.
Those “Sasquatch” sightings are actually just part of nature’s healing process as it re-plumbs the heat and water pathways underneath the basin.
“(The) system is sort of trying to rebuild itself and pressure can build in places because it’s all been badly disrupted,” Poland said. “When pressure builds to a point where it’s going to overcome the strength of the rock then you get these small eruptions.”
Geothermal detectives
This last and necessary piece of evidence was what the scientists needed to combine all the other strands of information. While it does not answer for how long these eruptions might continue, at least the scientists can conclude that there is not some larger issue developing under the surface.
“It’s sort of like detective work. You approach a scene and something happened. It could have been a hydrothermal explosion that you didn’t observe, or it could have been a volcanic eruption that occurred a million years ago,” Poland said about geology.
“There’s evidence in the rocks and various data sets you can collect. You’ve got to piece together the story of what happened based on the evidence you have available to you. It’s not too different from solving a crime.”
As Yellowstone is one of the largest supervolcanoes on the planet, Poland did make sure that there was no concern that the event was linked to any larger, more nefarious activity. There may be fires, floods, earthquakes and tsunamis occurring all at the same time this summer, but — for now — we do not need to worry about a volcanic eruption on U.S. soil.
“It’s really no surprise that occasionally (Yellowstone’s geothermal features) sort of fail,” Poland said. “It’s not reflecting a change in the magmatic system that’s a few miles beneath the surface. This is really just reflecting what’s happening 100 feet below.”