A hydrothermal explosion violently shook part of Yellowstone National Park's Biscuit Basin Tuesday, damaging a boardwalk as several park guests ran to safety.

The explosion occurred at the Biscuit Basin thermal area around 10 a.m. local time, appearing to originate near the Black Diamond Pool, according to the U.S. Geological Survey. There were no injuries immediately reported.

Biscuit Basin as well as its boardwalks and parking lots are closed for visitor safety as park geologists investigate what occurred, USGS reported. The popular tourist spot is located roughly two miles northwest of Old Faithful.

Volcanic activity for the Yellowstone region remains at normal levels, according to USGS.

Video captures explosion

Video shared on Facebook captured the eruption that sent people running away as it created a massive fume in its wake.

Facebook user Vlada March, who posted the video, wrote on platform that the explosion occurred right in front of her and her family.

"Boardwalk destroyed, my mom got some of the debris but everyone is safe. Unbelievable and grateful to be alive," March wrote.

"Hydrothermal explosions like that of today are not a sign of impending volcanic eruptions, and they are not caused by magma rising towards the surface," USGC wrote.

What are hydrothermal explosions?

Hydrothermal explosions happen when hot water in a volcano system flashes into steam in a confined area, Lisa Morgan, an emeritus USGS research geologist, wrote for the Yellowstone Caldera Chronicles, a Yellowstone Volcano Observatory publication.

The explosions are “one of the most important and least understood geologic hazards,” Morgan said. Sudden drops in pressure lead to rapid expansion of the high-temperature fluids or vapors and result in a crater-forming eruption.

Yellowstone is the hotbed for the geologic hazard worldwide and explosions occur as many as a couple times a year, Michael Poland, the scientist-in-charge at the observatory, told USA TODAY.

The area northeast of Yellowstone Lake is home to the three largest-known hydrothermal explosion craters on earth. Mary Bay, a crater formed 13,000 years ago, is the biggest at a mile and a half wide; Turbid Lake is a mile across and was formed 9,400 years ago; and Elliott’s Crater is nearly half a mile wide and was formed 8,000 years ago.

An explosion big enough to leave a crater the size of a football field can be expected every few hundred years, according to the observatory.

The explosions can happen anywhere there is hydrothermal activity, according to Poland. Other hotbeds are New Zealand, Iceland and Chile.

Has a hydrothermal explosion hurt anybody?

Compared to volcano eruptions and earthquakes, hydrothermal explosions are “an underappreciated geologic hazard,” said Poland.

Most explosions are small and go unobserved, according to Poland. For example, geologists this spring discovered a crater several feet wide in Yellowstone's Norris Geyser Basin from an explosion on April 15, 2024.

No one has been killed or injured by a hydrothermal explosion, although between "blowing out rock, mud and boiling water, it's not something you want to be close to," Poland said.

But some recent explosions have produced awesome results.

Ear Spring, near Old Faithful, exploded in 2018, sending not only rocks flying but garbage dating back to the 1930s, including a Hamm's beer can, a vintage pacifier, a shoe heel and dozens of coins.

In 1989, eight observers watched Porkchop Geyser grow from a 30-foot water spout to 100 feet before blowing up. The explosion created a 30-foot crater and destroyed the porkchop shape of the hydrothermal pool, according to Poland. No one was hurt. 

Another explosion in Biscuit Basin happened on May 17, 2009, per USGS.

Scientists are researching how to predict hydrothermal explosions, but some are skeptical it can even be done, according to Poland.

"One of the things we don't fully know right now is whether these things can be forecast," he said. "It's still an open question."

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