Hydrothermal explosion surprises visitors at Yellowstone National Park

A surprise hydrothermal explosion that sent steam, water, rocks and dirt several meters (tens of feet) into the air has sent some visitors to Yellowstone National Park running for cover.

The hydrothermal explosion occurred around 10 a.m. at Biscuit Basin, a collection of hot springs located a couple of miles (3.2 kilometers) north of the famous Old Faithful geyser.

A video posted online showed about 20 people watching from a boardwalk as the eruption grew before their eyes and sprayed them. When water and debris began to fall, they ran away, some shouting “Get away!” and “Holy smokes!” People then turned to watch the spectacle beneath a huge cloud of steam.

The eruption damaged the boardwalk that keeps people away from Yellowstone’s fragile and often dangerous geothermal zones. Photos and videos of the aftermath showed damaged railings and boards covered in rocks and sediment near mud puddles.

There were no injuries, but the Biscuit Basin area was closed to ensure the safety of visitors, the U.S. Geological Survey (USGS) said in a statement.

A hydrothermal explosion occurs when water suddenly turns into steam underground. These explosions are relatively common in Yellowstone.

Similar explosions occurred in Biscuit Basin in 2009, 1991, and after the magnitude 7.2 Hebgen Lake earthquake, 40 miles (64 kilometers) away, in 1959.

As spectacular as it was, the latest one was small in scale, the statement said.

Scientists believe a series of hydrothermal explosions created Mary Bay on the northeast side of Yellowstone Lake about 13,800 years ago. At 1.5 miles (2.4 kilometers) wide, Mary Bay is the largest known hydrothermal explosion crater in the world.

Yellowstone sits on a massive dormant volcano. The hydrothermal explosion is not indicative of new activity in the volcanic system, which remains at normal levels, according to the USGS.

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Hanson reported from Helena, Montana.