What is a hydrothermal explosion? Rare event rocks Yellowstone

A massive hydrothermal explosion rocked a well-known area of Yellowstone National Park on Tuesday, and authorities are surveying the extent of the damage.

The localized hydrothermal explosion took place at approximately 10:19 a.m. near Sapphire Pool in Biscuit Basin, located just north of Old Faithful, according to a statement released from the National Park Service.

“Biscuit Basin, including the parking lot and boardwalks, are temporarily closed for safety reasons,” park officials said. “The Grand Loop Road remains open.”

No injuries were reported and the extent of damage is unknown at this time.

Officials say that park staff from the United States Geological Survey (USGS) will now monitor conditions in the area and will open it up again once they deem it safe to do so.

“No other monitoring data show changes in the Yellowstone region,” officials said. “Today’s explosion does not reflect a change in the volcanic system, which remains at normal background levels of activity.”

Hydrothermal explosions are “violent and dramatic events resulting in the rapid ejection of boiling water, steam, mud, and rock fragments,” the USGS explains. “The explosions can reach heights of 2 km (1.2 miles) and leave craters that are from a few meters (tens of feet) up to more than 2 km (1.2 mi) in diameter. Ejected material, mostly breccia (angular rocks cemented by clay), can be found far as 3 to 4 km (1.8 to 2.5 mi) from the largest craters.”

Large hydrothermal explosions occur on average every 700 years, according to the USGS, and at least 25 explosion craters greater than 100 m (328 ft) wide have been identified.

“Although large hydrothermal explosions are rare events on a human time scale, the potential for additional future events of the sort in Yellowstone National Park is not insignificant,” said USGS. “Based on the occurrence of large hydrothermal explosion events over the past 16,000 years, an explosion large enough to create a 100-m- (328-ft-) wide crater might be expected every few hundred years.”