In the early hours of June 13, a hydrothermal explosion in Yellowstone National Park’s Biscuit Basin sent several rocks flying into the air and formed cracks in the ground, one measuring over 60 feet long.

Several days later, a new boiling pool formed and was observed episodically spouting water 20 to 30 feet in the air, according to the Yellowstone Volcano Observatory.

The recent explosion follows a much larger explosion in 2024 that sent a cloud of debris nearly 200 feet in the air and tourists scurrying for shelter on the boardwalk. That blast led Yellowstone to close Biscuit Basin, and on June 13 when the most recent hydrothermal explosion happened, nobody was nearby or injured.

Because new instruments were installed following the 2024 explosion, scientists were able to study the recent event.

Yellowstone National Park, the world’s first national park, is home to roughly half of the world's geysers. The majority of them, including Grand Geyser and Old Faithful, reside in the Upper Geyser Basin. Biscuit Basin is part of that same geothermal feature, but it is isolated and a few miles away from Old Faithful.

“These are not uncommon events in Yellowstone. They probably happen a few times per year somewhere in the park, often completely unobserved,” said Michael Poland, the scientist in charge of the Yellowstone Volcano Observatory, which monitors the super volcano under the park’s surface.

“Biscuit Basin seems to be an area where there's more explosions than there are in other basins,” Poland added.

The recent explosion was a consequence of pressure changes in the shallow hydrothermal systems beneath the surface of the Biscuit Basin area, Poland said. In Biscuit Basin, as in other Yellowstone geyser basins, the subterranean plumbing that creates surface hydrothermal features is pressurized in part by boiling water and minerals. When minerals clog some of the plumbing, pressure builds.

“When that pressure suddenly drops, the boiling water will flash to steam, and that will drive an explosion,” Poland said.

The explosion opened several vent areas, holes in the surface connected to Yellowstone’s underground plumbing that are created by boiling water flashing to steam and creating pathways to the surface. Some individual vents spewed out rocks. The explosion also formed a number of cracks, with the largest spanning over 60 feet.

The new boiling pool of water is roughly 21-by-17 feet and was formed when the thin ground collapsed. The pool has shown some geyser-like activity since forming a few days ago, Poland said. 

It’s unclear why Biscuit Basin appears more prone to hydrothermal explosions than other areas in Yellowstone, Poland said. High water temperatures in the area could potentially contribute to events where subtle pressure changes cause the liquid water to turn to steam.

The event didn’t have a broader impact on Biscuit Basin itself, and Black Diamond Pool appears unaffected. Similarly, when Black Diamond Pool exploded in 2024, other features in the basin didn’t react, Poland said. 

Despite some online claims that “things are becoming more active” in the park, Poland said officials haven't seen an increase in hydrothermal activity in general throughout Yellowstone. 

“This is just Yellowstone being Yellowstone, this is how that hydrothermal system behaves,” said Poland. “Its just that we now have the technological ability to see these things that were happening all the time, but largely unobserved.”

The 2024 explosion, which took place at Black Diamond Pool, was a larger scale version of the recent event, Poland said. The event took place a couple hundred feet north of Black Diamond Pool.

Unlike the 2024 explosion, no one was present during the June 13 blast. 

“It’s hard to detect these things in general, just because most of the time there's no one around to see them happen,” said Poland. “That's why this monitoring is so important.”

After the 2024 explosion, Yellowstone Volcano Observatory installed several new hydrothermal monitoring tools in Biscuit Basin, including cameras; a seismometer that measures movement of the Earth’s surface; a GPS station that measures ground movements; and a new “infrasound array” that measures low-frequency acoustic energy made by geysers and volcanoes.

On the morning of June 13, scientists received alarms from these sensors suggesting increased activity. The infrasound technology allowed them to identify exactly where the event took place. A camera, which happened to be pointing directly at the explosion, recorded the exact location of the steam plume. 

In 2024 no instruments were installed in the basin, preventing scientists from studying the explosion.

In contrast, due to the new instruments’ proximity to the June event, scientists were able to collect “vast amounts of data” not only about the event but hydrothermal activity in the days prior. The second category of data may help the Volcano Observatory understand indicators of future explosions. 

“The real and ultimate goal is to identify some sort of precursors that might suggest that there are some warning signs before a hazardous hypothermal explosion,” said Poland. “That's really what we'd like to be able to detect, so that we can identify these hazards before they actually manifest and pose a danger to people.”