A hydrothermal explosion at Yellowstone National Park sent visitors running for cover Tuesday morning, according to park officials and footage taken by a witness. Thankfully, no injuries were reported.
The blast occurred around 10:20 a.m. local time near Sapphire Pool in Biscuit Basin, located about 3.5 kilometres northwest of the famous Old Faithful geyser, the U.S. National Park Service (NPS) said in a release. The entire area of Biscuit Basin, including the parking lot and boardwalks, has been closed until further notice for safety reasons.
Video of the explosion showed a huge column of grey smoke rising over the Biscuit Basin thermal area, raining down debris and rocks. Visitors, including numerous children, scrambled to run from the blast along the park’s wooden boardwalk.
Officials say the extent of the damage done by the explosion is unknown at this time. Photos of the aftermath showed the Biscuit Basin boardwalk covered in black dust and debris with extensive damage to some wooden guardrails. Planks of wood, seemingly from the boardwalk, lie littered on the ground.
Vlada March was on a tour in the basin when her guide said something unusual was happening. March started taking video.
“We saw more steam coming up and within seconds it became this huge thing,” said March, a California real estate agent who was with her mom, husband and their two kids. “It just exploded and became like a black cloud that covered the sun.”
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“I think our tour guide said ‘Run,’ and I started running and I started screaming at the kids, ‘Run, run, run,’ and I continued filming what I could,” she told The Associated Press.
Rocks that fell from the sky smashed the boardwalk they had been walking on. March’s mom, who had been sitting on a bench near the explosion, was shaken and dirty but otherwise fine, she said.
Walking back on the broken boardwalk “was a little scary,” she said, “but thankfully it didn’t break under us.”
Few details about where and how the explosion was triggered have been released by officials, but a joint statement from the NPS and the U.S. Geologic Survey (USGS) states that the “explosion appears to have originated near Black Diamond Pool.”
Black Diamond Pool is a large hot spring with a history of eruptions. The pool “erupted black murky water” after an earthquake in 2006 and continued to explosively erupt several more times in the following days. The last eruption at the pool was observed in 2016, according to park officials.
Hydrothermal explosions happen when water suddenly turns to steam underground. Liquid water takes up much less volume than water vapour, so when this heated water flashes to steam, it rapidly expands, causing an explosion.
“Hydrothermal explosions are violent and dramatic events resulting in the rapid ejection of boiling water, steam, mud, and rock fragments. The explosions can reach heights of 2 km and leave craters that are from a few meters up to more than 2 km in diameter,” according to a USGS fact page.
In fact, Black Diamond Pool likely formed due to a hydrothermal explosion. These kinds of blasts are not uncommon in the park.
Scientist Mike Poland with the Yellowstone Volcano Observatory said the explosion was “on the big side” of these periodic eruptions, and added that these blasts typically don’t happen around throngs of tourists. After viewing video from the event Poland estimated that the explosion sent material about 30 metres into the air. Park geologists are investigating what specifically happened in this case.
Officials say that the explosion “does not reflect a change in the volcanic system, which remains at normal background levels of activity.”
“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,” the NPS added.
Yellowstone National Park sits on top of one the world’s largest supervolcanoes. Yellowstone’s famous geysers and hot springs are heated by the volcano’s underground magma.
— with files from The Associated Press
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