Major Hydrothermal Explosion In Yellowstone National Park

Yellowstone National Park has not yet released a statement on the explosion. But Mike Poland, a research geophysicist and the scientist-in-charge of the Yellowstone Volcano Observatory, described the event as a "hydrothermal explosion" that happened near the Sapphire pool in Biscuit Basin.

Hydrothermal explosions happen multiple times a year in Yellowstone, Poland said.

Most explosions happen in the backcountry, but they are not unheard of in the front country. A similar explosion happened in May 2009 in Biscuit Basin, Poland said. Tuesday's appeared to be bigger.

"These things can happen somewhat randomly," Poland said Tuesday afternoon. "They are episodes of water flashing to steam underground. Sometimes they can be triggered by earthquakes. Often they are just the plumbing system underground. It's the randomness of the hydrothermal system."