The area of Yellowstone National Park where a hydrothermal explosion sent visitors scrambling for cover from rocks and steam will remain closed for the remainder of the summer, the National Parks Service said.
No one was injured in the eruption on Tuesday in Biscuit Basin, which is about two miles away from Old Faithful.
It destroyed a nearby boardwalk, sent steam into the air and propelled "grapefruit-sized rocks" hundreds of feet away, the NPS said.
The hydrothermal explosion was caused by water suddenly "transitioning to steam in the shallow hydrothermal system beneath Black Diamond Pool and was not caused by volcanic activity."
The NPS said such explosions "typically occur" in the park a few times a year, but usually in the back country where they may not be detected.
