Surprise Yellowstone geyser eruption highlights little known hazard at popular park

BILLINGS (AP) — A surprise eruption of steam in a Yellowstone National Park geyser basin that sent people scrambling for safety as large rocks shot into the air 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 steam, water and dark-colored rock and dirt an estimated 100 feet into the air.

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.