Hydrothermal explosion in Yellowstone National Park sends rocks and debris flying towards visitors

Biscuit Basin debris on boardwalks Park staff assess the damage to Biscuit Basin boardwalks after hydrothermal explosion Photo: NPS

Park officials say that hydrothermal explosions like this are not a sign of impending volcanic eruptions, and they are not caused by magma rising towards the surface.

YELLOWSTONE NATIONAL PARK, Mont. — On Tuesday, July 23, at approximately 10:19 a.m., a hydrothermal explosion occurred near Sapphire Pool in Biscuit Basin, north of Old Faithful. The explosion shot hot-water and large chunks of rock and debris hundreds of feet in the air that then rain down on visitors and the board walk.

No injuries were reported in the incident however the board walk was badly damaged and the full extent of damage is currently unknown.

Park officials say that today’s explosion does not reflect activity within the volcanic system, which remains at normal background levels of activity.  Hydrothermal explosions like that of today are not a sign of impending volcanic eruptions, and they are not caused by magma rising towards the surface.

Park officials have temporarily closed Biscuit Basin, including the parking lot and boardwalks, for safety reasons. The Grand Loop Road remains open.

The explosion, which was recorded by numerous visitors, appears to have originated near Black Diamond Pool and caused damage to the boardwalk. Yellowstone National Park geologists and USGS staff are monitoring the situation and will reopen the area once it is deemed safe.

Hydrothermal explosions occur when underground water suddenly flashes to steam. Previous explosions include Porkchop Geyser in 1989 and a similar event in Biscuit Basin on May 17, 2009.