The bomblike steam eruption produced a mushroom cloud that, as it collapsed, sent rocky debris flowing out sideways at 200 miles an hour (320 kilometers an hour) to a distance of a few kilometers, according to a geologic analysis of rock deposits at the site, study co-author Brent Geohring said.
The question is, when?
Scientists had assumed the explosion occurred comfortably in the past, most likely several thousand years ago, when the Death Valley area was wetter.
The explosive mixing of magma and water, they thought, could be explained by the presence of lakes that have long since disappeared.
The new study, though, suggests the massive blast occurred more recently, when Death Valley was very much as it is today—which could mean that conditions are still ripe for an eruption.
"Very Young" Volcano
In 2008 Goehring, then with Columbia University's Lamont-Doherty Earth Observatory, and study co-author Peri Sasnett, then a Columbia undergrad, visited Death Valley on a geology field trip.
The two got to wondering exactly how old Ubehebe (YOU-bee-hee-bee) Crater really is. "It looks very young," Goehring said.
With permission from the Park Service, they collected samples from the crater for lab analysis. The specimens in question, he added, aren't lava, but are instead rocks from surface layers that were blown out of the crater by the explosion.
The samples, they discovered, contain rare isotopes created when rocks are bombarded by cosmic rays. Because this radiation doesn't penetrate deeply into the Earth, the isotopes can reveal how long a rock has been on the surface.
"We weren't dating the formation of the rock itself," Goehring emphasized—but rather the date when the rock had been thrust from the depths.
"We were literally atom counting," he said. "These [isotopes] are only produced at 10 to 15 atoms per year in a gram of rock. So they're at very, very low concentrations."
The Awkward Years
The study backed up the scientists' hunch that Ubehebe Crater was a relative newborn.
Rather than being several thousand years old, it and nearby smaller craters appear to have been the result of a series of explosions, the largest and most recent of which was 800 years ago.
The dating method "is very cool," said Kelly Russell, a volcanologist from the University of British Columbia in Vancouver, Canada, who was not part of the study team.
"To be able to date young volcanic events that precisely is something we're always seeking to do," Russell said. "That's the awkward period—these prehistoric events that are very young."
Conditions Right for Eruption?
According to the new data, the eruption was recent enough to suggest that the area might become volcanically active again.
"A volcano that young has to be considered potentially active," Russell said. And if there's still water around, he added, there is the potential for another explosion.
Goehring believes that it's quite likely that enough water still exists. The 800-year-old explosion, he said, came at a time when Death Valley was even drier than today, he noted.
If fact, he said, "there's actually water underneath the crater today. There are springs nearby."
Nor does it take a gargantuan of water to create a giant eruption. "You need about a hundred Olympic-size swimming pools to generate enough steam to [produce] Ubehebe Crater," Goehring said.
Beyond that volume, in fact, the water could actually damp down a potential explosion. "You get the highest degree of explosivity with sort of a sweet spot, mixing water to magma," Russell said.
As for the other main ingredient—magma—there's no telling when some could begin rising toward the surface, and the groundwater.
Luckily, though, the popular tourist attraction probably won't explode without warning.
"You would expect to see some hydrothermal activity and seismic activity, much like you do at Mount St. Helens," Goehring said. (See pictures of the Mount St. Helens volcano before and after its 1980 blast.)
National Park Service education specialist Stephanie Kyriazis agrees. "Right now, we're not planning to issue an orange alert or anything like that," Kyriazis said in a statement.
If the Ubehebe volcano were to explode, however, the eruption would be spectacular—and hot—if the ancient mushroom cloud is any indication.
The rock "probably would have been a few hundred degrees C," study co-author Goehring said. "It wouldn't have been molten, but it would have been quite hot.
"It would be fun to see," he added, "But I wouldn't want to be nearby."
The Death Valley volcano study was published January 18 in the journal Geophysical Research Letters.