The Cold Case of What’s Heating Up Yellowstone’s Steamboat Geyser

Yellowstone National Park is an excess of geologic riches, from sweeping volcanic vistas to bubbling caldrons with multicolored irises. But one of its 10,000 thermal features has been capturing everyone’s attention recently: Steamboat Geyser.

Steamboat, the world’s tallest active geyser, can launch superheated water almost 400 feet into the sky. These eruptions have been erratic, with gaps between each major outburst lasting anywhere from four days to 50 years. But in March 2018, it began a showstopping performance that shows no sign of petering out. The geyser’s 129 eruptions from the moment of its awakening to the present date exceed the total number seen gushing from Steamboat in the preceding half-century.

Naturally, scientists want to know what kicked off this display of flamboyant fluidity.

And a study, published Monday in the Proceedings of the National Academy of Sciences, has at least ruled out certain culprits, such as earthquakes or snowfall. Even though scientists couldn’t pin down a prime suspect, the finding extends scientific knowledge of the natural engineering underlying geysers, which remains fuzzy at best.

“We still can’t explain simple things about how they work,” said Mara Reed, a graduate student at the University of California, Berkeley, and the study’s lead author. “There’s just so much more to learn.”

Her co-author, Michael Manga, a geoscientist at the University of California, Berkeley, agreed, framing geysers as simplified volcanoes. “If we can’t understand a geyser, our prospects for understanding magmatic volcanoes are much lower,” he said.

Geysers are volcanically powered water cannons. Magma deep underground heats the rocks above, which in turn heat a shallow rechargeable water supply stored under pressure. Change the water or heat supply, or alter the pathways to the surface — say, through minerals crystallizing out of the fluid and forming a plug — and the geyser’s behavior changes.

Change is the norm for Yellowstone’s thermal features. Since detailed observations of the park’s underlying supervolcano’s mercurial hydrothermal system began more than a century ago, watchers have seen countless warm patches, hot springs and geysers come and go. That means Steamboat’s dramatic switch isn’t out of place, said Michael Poland, the scientist-in-charge at the U.S. Geological Survey’s Yellowstone Volcano Observatory and who wasn’t involved with the new work.

But Steamboat’s prolific eruptions, along with the plethora of modern scientific sensors scattered around the park and observations by citizen scientists, have given researchers a great opportunity to study what makes it tick, and allowed Ms. Reed’s team to seek explanations for the geyser’s dramatic 2018 activation.

Could earthquakes be to blame? A swarm of earthquakes did precede Steamboat’s activation, but such tremors failed to shake the ground with enough vigor to rearrange the geologic plumbing below ground and change the geyser’s behavior.

A sufficient supply of precipitation could, however, contribute to Steamboat’s hyperactivity: Eruptions were seen to happen more often between late spring and midsummer, when melting snow enters the ground. But, Dr. Manga said, the fountains’ chemistry suggests it’s not fresh snowmelt that’s erupting. Instead, the rainwater may be piling on pressure and driving the eruption of older hot water pockets.

Still, snowmelt wasn’t the initial trigger. There was no correlation between the amount of precipitation estimated to have fallen on Norris Geyser Basin, in which Steamboat sits, and Steamboat’s awakening.

A Chicago-size section of that basin has been rising and falling in elevation lately, and a recent study suggested this was driven by pockets of hydrothermal fluids moving about and ultimately gathering just below the surface. This was also mooted as a possible explanation for Steamboat’s recent activation.

But, said Dr. Manga, a newly arrived shallow pool of hot fluids should have jump-started multiple dormant geysers in the region, not just Steamboat. The local hydrothermal features should have also become noticeably hotter, but no unambiguous temperature spike was detected.

The lack of definitive answers may frustrate some. But for Ms. Reed, playing detective with Steamboat is a dream fulfilled. The last major eruptive period was in the 1980s, before her time. She thought she had missed her chance to see one of its spectacular shows. “Now I’ve gotten to see it,” she said, “and it blew my mind every time.”

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