Aggie Geologists say Yellowstone Steam Blast Among Park's Significant Hazards

A hydrothermal explosion July 23 at Yellowstone National Park sent visitors running for cover, as steam shot into the air and rocks rained down on a popular viewing area. The blast occurred about 10 a.m. local time near the Black Diamond Pool in Biscuit Basin, about two miles northwest of Old Faithful. No injuries were reported.

“Steam explosions like Tuesday’s incident have long been considered one of the most significant hazards posed to Yellowstone visitors,” says Tony Lowry, associate professor in Utah State University’s Department of Geosciences. “Biscuit Basin has had smaller, but still dangerous, events in the recent past.”

USU alum Jamie Farrell, research associate professor in the University of Utah’s Department of Geology and Geophysics and chief seismologist of the U.S. Geological Survey’s Yellowstone Volcano Observatory, says it was “very lucky” no one was hurt in today’s blast.

“Hydrothermal explosions happen quite frequently in the park, though they often occur in the uninhabited back country," says Farrell, who earned a bachelor’s degree in geology from Utah State in 2001.

Farrell says the blasts aren’t volcanic eruptions and no magma is involved.

“These incidents occur when very hot, mineral-laden water builds up and clogs the plumbing, so to speak; pressure builds up and is forced upward through pre-existing fractures to erupt at the surface,” he says.

USU Geosciences Emeritus Professor John Shervais says hydrothermal explosions differ from geysers in that the super-heated water is confined in the subsurface by debris or silica deposits choking the fracture system.

“At some point, this blockage fails under the increasing pressure, releasing not just super-heated water and steam, but also rock debris ripped from the conduit walls as it forces its way to the surface,” Shervais says. “The ejected rock debris and mud are typically highly altered volcanic rocks, weakened by the formation of clay.”

Shervais and Farrell, incidentally, jointly witnessed a similar, though smaller, explosion near today’s blast site in 2009, while participating in a National Science Foundation-funded Earthscope Consortium field trip.

“There was a big boom with water and the blast threw laptop-sized rocks,” Farrell says.

“We heard a rumble, then blocks of rock and mud were falling everywhere,” Shervais says. “By the time I got my camera out, it was over.”

Farrell says such explosions are an under-appreciated hazard in Yellowstone and, to that end, he, University of Utah colleagues and park officials, along with the USGS, are working on installation of a monitoring system to warn of future explosions.

“Tuesday’s incident, I suppose, will be an impetus to advance that project,” he says.

According to a July 24 news release, Yellowstone National Park has closed Biscuit Basin for the remainder of the 2024 season for visitor safety. Grand Loop Road remains open to vehicles and other nearby thermal basins, including Black Sand Basin, are open.