Hydrothermal explosion at Yellowstone sends up geyser of rock and ...

Visitors ran for safety at Yellowstone National Park after a hydrothermal explosion sent rock and steam spewing into the air north of the Old Faithful geyser Tuesday, park officials said.

There were no injuries, and the extent of the damage from the blast, which occurred in Biscuit Basin, about 2 miles northwest of Old Faithful, at around 10:19 a.m., was unknown, the National Park Service said in a statement.

The type of explosion that happened Tuesday involves hot water and results in “the rapid ejection of boiling water, steam, mud, and rock fragments,” according to the U.S. Geological Survey.

Video of the eruption showed people, including children, running as a column of black and gray material and vapor launched into the air.

Yellowstone is famed for its thermal features and hot pools.

Hydrothermal explosions happen when water at or near boiling point beneath the ground rapidly turns into stream because of a drop in pressure, the USGS says.

Explosions like Tuesday’s “are relatively common in Yellowstone,” the USGS said in a statement. A small one happened in Norris Geyser Basin in April, and there was an explosion in Biscuit Basin in 2009, it said.

Photos posted by Yellowstone National Park show the nearby boardwalk covered in dirt, rocks and debris.

The boardwalk and a parking lot were closed for the time being because of safety concerns, the park service said. The explosion has nothing to do with volcanic activity, it noted.

Park and USGS staff members are monitoring the situation and will decide when the area can be reopened, officials said.