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The awakened Yellowstone geyser is not a sign of impending explosion

A recent awakening of the world’s tallest geyser is not the harbinger of an impending volcanic eruption, according to a new study. And it is unlikely to predict a dangerous hydrothermal explosion, which can occur when overheated water turns to steam and violently comes out of the confined rock, researchers report in the January 12 National Academy of Sciences Proceedings.

The reasons for the sudden restart of the Steamboat Geyser, found in Yellowstone National Park in Wyoming, remain a mystery, 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 important.

After more than three years of inactivity, Steamboat abruptly fired a torrent of hot water into the sky on March 15, 2018. That event started a new active phase for the geyser, one of Yellowstone’s most famous features, and caused some observers of the park had wondered if the sudden eruption warned of greater dangers to come.

When it comes to potential threats in Yellowstone, the supervolcano itself receives most of the attention (SN: 1/2/18). But its deep magma deposit also heats groundwater flowing underground or pools on the surface, and that boiling water poses a much more immediate threat to park visitors. "Probably the biggest danger in Yellowstone is that people get off the trail and fall into boiling water. But there's always a risk of hydrothermal explosions," says Michael Manga, a geologist at the University of California, Berkeley.

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

So after Steamboat woke up again, the scientists thought it was "perfectly reasonable to consider the possibility that even more violent activity might occur," Manga says. To assess that potential threat, he and his colleagues collected a wide range of data from Steamboat (which exploded another 109 times between March 2018 and July 2020), as well as from other geysers in the region and surrounding environment.

Those data included seismic records dating back to 2003; Changes in ground shape determined by GPS that may be linked to moving magma; changes in the temperature in the subsoil, as well as in the amount of heat emitted into the air over the geyser basin; and changes in the volume and chemistry of water coming out of the steam.

The data revealed that just before the reactivation of Steamboat in 2018, seismic activity in the region increased slightly, the earth rose very slightly and increased the heat emanating from the atmosphere of the geyser basin, all of which could point to some kind of magmatic movement . But no other sleeping geyser in the region has woken up and subsoil temperatures have not changed. The team also found no other correlations between subsequent Steamboat eruptions and seismic activity, terrain deformation, or thermal emissions.

The steamboat also appeared to show a seasonal eruption cycle, which erupted more frequently during the summer than in the winter. That pattern suggests a possible relationship between eruption frequency and an increase in river flow due to snowmelt, the study suggests.

But the ultimate trigger for Steamboat's awakening is still unknown, says U.S. Geological Survey geophysicist Michael Poland, who is also the scientist in charge of the Yellowstone Volcano Observatory in Vancouver, Washington. The authors “did a very good job of taking all the possible variables they could and discarding them,” Poland says. "And while the answer is that we don't see any reason why Steamboat was launched, that's still valuable information."

The study also offers an insight into these mysterious and sometimes deadly hot springs. “Most geysers don’t behave in a predictable way,” Poland says. “Old Faithful is very unusual,” as 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 more than 100 meters into the air, while the Old Faithful fountain is perhaps a third of the height .

The new study gives a possible answer by noting that the hot water tank that feeds Steamboat is much deeper than other geysers. Water stored at the lower bottom is at higher pressure and can also reach higher temperatures, and that extra energy can cause those higher eruptions (SN: 21/03/16).

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