Surprise Yellowstone geyser eruption highlights little known hazard at popular park WPXI [Video]

BILLINGS, Mont. — (AP) — A surprise eruption of steam in a Yellowstone National Park geyser basin that sent people scrambling for safety as basketball-sized rocks flew overhead has highlighted a little-known hazard that scientists hope to be able to predict someday.

The hydrothermal explosion on Tuesday in Biscuit Basin caused no injuries as dozens of people fled down the boardwalk before the wooden walkway was destroyed. The blast sent rocks, steam, water and dirt high into the air, according to a witness and a scientist who reviewed video footage of the event.

It came in a park teeming with geysers, hot springs and other hydrothermal features that attracts millions of tourists annually. Some, like the famous Old Faithful, erupt like clockwork and are well understood by the scientists who monitor the park’s seismic activity.

But the type of explosion that happened this week is less common and understood, and potentially more hazardous given that they happen without …