Reawakened Yellowstone geyser isn’t a sign of imminent explosion

A recent reawakening of the tallest geyser in the world is not a harbinger of an imminent volcanic eruption, a new study reports. And it isn’t likely to portend a dangerous hydrothermal explosion either, which can occur when superheated water turns to steam and bursts violently out of the confining rock, researchers report in the Jan. 12 Proceedings of the National Academy of Sciences.

The reason for the sudden restart of Steamboat Geyser, found at Yellowstone National Park in Wyoming, remains a mystery, the scientists say. But the study, which examines a wealth of seismic, environmental and other data from the Yellowstone region, is helping scientists better understand what makes Steamboat, and other geysers, tick.

After over three years of dormancy, Steamboat abruptly shot a towering stream of hot water into the sky on March 15, 2018. That event kicked off a new active phase for the geyser, one of Yellowstone’s most famous features — and made some park watchers wonder if the sudden eruption warned of greater dangers yet to come.

When it comes to potential threats at Yellowstone, the supervolcano itself gets most of the attention (SN: 1/2/18). But its deep reservoir of magma also heats groundwater that circulates underground or pools on the surface — and those boiling waters pose a far more immediate threat to park visitors. “Probably the biggest hazard in Yellowstone is people going off trail and falling in the boiling water. But there’s always a risk of hydrothermal explosions,” says Michael Manga, a geologist at the University of California, Berkeley.

Such explosions are little understood and therefore difficult to anticipate. But they can be deadly: In December 2019, for example, a sudden hydrothermal explosion at Whakaari, or White Island, in New Zealand killed 22 people.

So after Steamboat reawakened, scientists thought it was “perfectly reasonable to consider the possibility that maybe even more violent activity might be coming along,” Manga says. To assess that potential threat, he and colleagues collected a wide range of data from Steamboat — which erupted another 109 times between March 2018 and July 2020 — as well as from other geysers in the region and from the surrounding environment.

Those data included seismic records going back to 2003; GPS-determined changes in the shape of the ground that might be linked to moving magma; changes in temperature underground as well as in how much heat was emitted to the air over the geyser basin; and changes in the volume and chemistry of the water erupting out of Steamboat.

The data revealed that, just before Steamboat’s 2018 reactivation, seismic activity in the region was slightly heightened, the land rose very slightly and the heat emanating to the atmosphere from the geyser basin increased — all of which might point to some sort of magmatic movement. But no other dormant geyser in the region awoke, and temperatures underground didn’t change. The team also found no other correlations between subsequent Steamboat eruptions and seismic activity, land deformation or thermal emissions.

Steamboat also seemed to show a seasonal eruption cycle, bursting forth more often during the summer than in the winter. That pattern suggests a possible relationship between eruption frequency and an increase in river flow due to melting snow, the study suggests.

But the ultimate trigger for Steamboat’s reawakening is still unknown, says U.S. Geological Survey geophysicist Michael Poland, who is also the scientist-in-charge at the Yellowstone Volcano Observatory in Vancouver, Wash. The authors “did a really nice job of taking every possible variable that they could and ruling them out,” Poland says. “And even though the answer is we don’t see any reason why Steamboat became active, that’s still valuable information.”

The study also gives some insight into these mysterious, and sometimes deadly, hot-water fountains. “Most geysers don’t behave in a predictable way,” Poland says. “Old Faithful is very unusual” in that it erupts on a regular schedule. One of the most fundamental questions about geysers is why they erupt to certain heights, he adds — and why, for example, Steamboat can shoot water over 100 meters into the air, while Old Faithful’s fountain is perhaps a third as high.

The new study gives a possible answer, by noting that the reservoir of hot water that feeds Steamboat is much deeper than other geysers. Water stored deeper underground is under higher pressure and can also get to higher temperatures — and that extra energy may drive those taller eruptions (SN: 3/21/16).