Watch: Hydrothermal explosion at Yellowstone sends tourists racing for safety

A hydrothermal explosion sent a towering column of boiling water, mud and rock shooting into the air at Yellowstone National Park in Wyoming on Tuesday morning, destroying a section of boardwalk and sending dozens of tourists running for safety, officials said. No injuries were reported, according to the United States Geological Survey, but the area remained closed to the public.

The explosion occurred around 10 a.m. in the Biscuit Basin area of the park. Several tourists captured video of the event, and in some footage an adult can be heard shouting at children to run.

The explosion was a couple of miles north of the Old Faithful Geyser, which regularly shoots steam into the sky. "This is quite a bit different than Old Faithful," said Michael Poland, the scientist in charge at the Yellowstone Volcano Observatory, who said the hydrothermal event took place near Black Diamond Pool in Biscuit Basin.

Explosions like the one Tuesday happen when water suddenly turns to steam in the underground "plumbing" beneath the park's hydrothermal system, Poland said. The change can be caused by a major event like an earthquake. "That's not the case here," he said. "Instead, what we had was a very localized change in this plumbing system. Pressure can build and you can get an explosion like this."

Similar explosions took place in the Norris Geyser Basin this year and at Biscuit Basin in 2009.

In a statement, US Geological Survey officials assured that the episode was not connected to a change in volcanic activity, either. (Yes, Yellowstone also has volcanic activity).

Hydrothermal explosions in the park are fairly common -- taking place as often as twice a year, frequently in the backcountry -- but can go undetected other than by monitoring equipment, according to Poland. This explosion, however, was fully documented by tourists with smartphones. "It's really quite dramatic," Poland said of the footage.

More than a dozen miles of wooden boardwalk allow tourists to view the park's vaunted thermal features, such as geysers, hot springs and mudpots. The thermal features attract crowds despite -- or because of -- their sharp sulfuric smell and their otherworldly bubbling and spouting.

Since Yellowstone opened in 1872, around two dozen people have been injured or killed by scalding thermal features, more than double the number harmed in encounters with wildlife, according to the U.S. Geological Survey. But none of the episodes were connected to unexpected activity like what took place at Biscuit Basin.

"There hasn't been anyone killed by explosions like these," Poland said.

Most incidents are caused by burns; many of the hot springs in the park are hotter than 150 degrees Fahrenheit. In 2022, a human foot was found in the Abyss Pool in the southern part of the park; officials linked it to the accidental death of a 70-year-old man who had been visiting the park.

Last month, a 21-year-old tourist was sentenced to a week in jail for walking off a path near Steamboat Geyser, the world's tallest active geyser, which can shoot water more than 300 feet into the air, far higher than Old Faithful. A park employee had seen the tourist ignore signs that it was illegal to stray from the path.