Dozens Dash for Safety From Surprise Yellowstone Eruption

A surprise eruption in Yellowstone National Park shot steam, water and dark-colored rock and dirt high into the sky Tuesday and sent sightseers running for safety, the AP reports. The hydrothermal explosion happened around 10am in Biscuit Basin, a collection of hot springs a couple miles north of the famous Old Faithful Geyser. Video posted online showed a couple dozen people watching from a boardwalk as the eruption sprayed and grew in front of them. As water and debris began to fall, they ran to keep clear, some yelling "Back up!" and "Holy cow!" People then turned to watch the spectacle under a huge cloud of steam. A hydrothermal explosion happens when water suddenly flashes to steam underground. Such blasts are relatively common in Yellowstone.

No injuries were reported, but the Biscuit Basin area was closed for visitor safety. The eruption damaged a boardwalk that keeps people off Yellowstone's fragile and often dangerous geothermal areas. "We saw more steam coming up and within seconds it became this huge thing," says one woman who was on a tour at the time. "It just exploded and became like a black cloud that covered the sun." An expert estimates the explosion sent material about 100 feet into the air. 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.

The explosion could have resulted from a clogged passageway in the extensive natural plumbing network that underlies Yellowstone's world-famous geysers, hot springs and other thermal features, said scientist Mike Poland with the Yellowstone Volcano Observatory. A clog would have caused a buildup of heat and pressure such as happens inside a pressure cooker, he said, until the water suddenly flashed to steam, causing an instantaneous and huge expansion in volume and triggering the explosion. Park geologists were investigating what specifically happened in this case. Yellowstone is centered on a huge, dormant volcano, but the explosion did not indicate new activity within the volcanic system, per USGS. (More Yellowstone National Park stories.)