Surprise blast of rock, water and steam in Yellowstone sends dozens running for safety

The hydrothermal explosion happened around 10 a.m. in Biscuit Basin, a collection of hot springs a couple miles north of the famous Old Faithful Geyser.

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.

On occasion they get much bigger: The largest known crater from a hydrothermal explosion on Earth is in Yellowstone and measures 1.5 miles (2.4 kilometers) across, Poland said. Scientists theorize that a series of hydrothermal explosions created that crater some 13,800 years ago in the Mary Bay area on the northeastern side of Yellowstone Lake.

By comparison, the crater from Tuesday’s explosion will likely be measured in feet, Poland said.

“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,” he said. “It’s a very good reminder of an underappreciated hazard in Yellowstone.”

The hydrothermal explosion did not indicate new activity within the volcanic system, which remains at normal levels, according to the U.S. Geological Survey.