US: Surprise hydrothermal blast shoots steam, rocks in sky, scaring tourists

A sudden hydrothermal explosion erupted in Yellowstone National Park’s Biscuit Basin, sending steam, water, and dark rock skyward around 10 am on Tuesday.

The unexpected event caught tourists off guard, forcing them to flee for safety as debris rained down.

Video footage shared online captured the moment, showing dozens of visitors on a boardwalk as the explosion grew.

Amid shouts of “Back up!” and “Holy cow!” tourists scrambled to avoid the falling debris and to witness the dramatic event under a massive steam cloud.

“It just exploded”: Witnesses recall the incident

Vlada March, a California real estate agent on a tour with her family, described the scene as surreal, CBS News reported . “We saw more steam coming up and within seconds it became this huge thing,” March recounted. “It just exploded and became like a black cloud that covered the sun.”

March managed to film parts of the eruption while urging her children to run for safety.

The explosion shattered the boardwalk, leaving rocks and debris scattered. March’s mother, sitting on a nearby bench, was unharmed but visibly shaken.

“Walking back on the broken boardwalk was a little scary,” March added, “but thankfully it didn’t break under us.”

Photos and videos from the aftermath revealed damaged guardrails and boards covered in rock and silt near muddy pools. Park officials promptly closed the Biscuit Basin area to ensure visitor safety.

Understanding the explosion: Insights from scientists

As reported by AP News , Mike Poland of the Yellowstone Volcano Observatory offered an explanation for the dramatic event. The explosion likely resulted from a clogged passageway in Yellowstone’s geothermal plumbing system, causing heat and pressure buildup.

It’s like a pressure cooker, Poland explained, “until the water suddenly flashed to steam, causing an instantaneous and huge expansion in volume and triggering the explosion.”

Poland estimated that the explosion sent material about 100 feet into the air, describing it as “on the big side” of such eruptions. However, he noted that these explosions occur periodically, often unnoticed by tourists. The largest known hydrothermal explosion crater in Yellowstone, created around 13,800 years ago, measures 1.5 miles across.

“What we saw today was spectacular and definitely hazardous. But on the scale of what the Yellowstone system has done in the past, it was relatively small,” Poland emphasized. “It’s a very good reminder of an underappreciated hazard in Yellowstone.”

The unpredictable nature of hydrothermal explosions

Hydrothermal explosions are notoriously hard to predict. The U.S. Geological Survey (USGS) also likened these eruptions to a pressure cooker, noting that they may not give warning signs at all. Unlike volcanoes , which typically emit warning signs before erupting, hydrothermal explosions can occur without any prior indication.

The USGS confirmed that there were no signs of volcanic activity in the Yellowstone region following the explosion, and volcanic activity remained “at normal background levels.”

The agency added, “This sort of thing happens 1-2 times per year somewhere in Yellowstone (often in the backcountry, so it goes unnoticed). It’s an underappreciated hazard that we’ve been emphasizing for years.”

Aerial photos showed the pool near the boardwalk somewhat enlarged, with its water turned a muddy beige. Despite the dramatic event, the nearby Sapphire Pool retained its usual blue hues. Park geologists are investigating the specifics of the explosion.

Yellowstone is centered on a massive dormant volcano. The recent hydrothermal explosion did not indicate new volcanic activity , and the area remains safe for visitors who adhere to park guidelines. Since 1890, at least 22 people have died from injuries related to thermal features in Yellowstone.

Visitors are always warned to stay on marked paths and trails in thermal areas because the ground can be thin and breakable, hiding hot and sometimes acidic water. This recent event shows just how unpredictable and dangerous Yellowstone’s geothermal features can be.