The puzzling science behind the awakening of a powerful Yellowstone geyser

Yellowstone may be one of America's most enduring — and popular — symbols of rugged wilderness. This is for good reason: Due to its famous volcanic activity, Yellowstone boasts more geysers than anywhere else in the world, attracting 4 million visitors in 2019.

But despite the popularity of Yellowstone, we still know relatively little about the science behind these geysers — especially the Steamboat Geyser, which began intensely and regularly erupting in 2018 after 34 years of sporadic eruptions.

Scientists wanted to know why the once-dormant geyser awakened — and whether it had anything to do with weather, earthquakes, or future volcanic eruptions. Following the publication of research released Monday in the journal Proceedings of the National Academy of Sciences, we're one step closer to figuring out those answers.

The big idea — The scientists laid out three key questions that would guide their experiments.

The team tested out their hypotheses for each question but ultimately raised more questions than answers in the course of their research.

Why did Steamboat become active again?

Compared to Old Faithful, which regularly erupts 20 times a day, Steamboat had only sporadically erupted prior to 2015. By 2018, the geyser had been dormant for more than three years.

But in March 2018, the geyser mysteriously erupted once more, exciting tourists and geologists around the world. Between March 2018 and July 2020, the geyser erupted 109 times — more than any other time in Steamboat's active history.

When Steamboat became reactive in 2018, all kinds of scientific speculation abounded over the reason for its return. Most focused on the possibility of volcanic magma intruding in from the underground

Michael Manga, a co-author on the study and chair of the Earth and Planetary Science department at UC Berkeley, tells Inverse: "When Steamboat started erupting again there were suggestions that its reactivation was the result of magma intrusion (magma underground)."

Scientists were excited about this magma hypothesis for another reason: If true, it "may foretell volcanic eruptions" according to Manga. And Yellowstone's volcanoes are no joke.

The researchers began digging into possible evidence to support their hypothesis, particularly evidence related to hydrothermal activity.

"We looked for evidence that gases and fluids from intruded magmas caused Steamboat to start erupting," Manga says.

But despite an increase in both seismic activity and heat to the geyser area prior to the 2018 eruption, the researchers' results were ultimately inconclusive about a cause. Correlation doesn't equal causation, after all.

"These may be signals of magma influencing the surface," Manga says. "However, we did not find any evidence for temperature changes in the water that erupts, no other dormant geysers erupted, and there were no changes in the amount of magmatic fluids being discharged."

That's good news when it comes to the future of Yellowstone's supervolcano, which hasn't majorly erupted in the past 70,000 years. For an eruption to happen, there would need to be underground magma movement.

What controls how often Steamboat geyser erupts?

Steamboat erupts an average of every seven days, though its eruptions can range from 3 to 35 days. The researchers wanted to better understand the mechanisms behind these variations in eruption times.

From the data gathered, researchers observed that Steamboat had shorter intervals between eruptions in the summer and longer intervals in the winter months, with the average number of eruptions peaking in May.

Therefore, Steamboat's intervals weren't random — there was some seasonal method to the madness.

Using seismic spectral amplitude measurements (SSAM) — also used in monitoring volcanoes — the scientists found seismic activity in underground hydrothermal systems sharply declined by 50 percent following Steamboat's big 2018 eruption.

As with the first question, the key may lie in nearby hydrothermal activity, such as water coming in from the nearby Gibbon River, which may affect the geyser's eruptions. Yellowstone's hydrothermal system is the visible expression of its volcano.

Through their seismic measurements, the researchers concluded that "abnormally long intervals coincide with weakening of a shallow seismic source in the geyser basin’s hydrothermal system."

But, ultimately, the study team wasn't able to draw any connections between intervals and the volume of water that erupted. Simply knowing the interval between eruptions doesn't mean that you can predict whether the next eruption will be big or not.

Why are Steamboat’s eruptions so tall compared to other geysers?

With eruptions exceeding heights of 300 feet, the Steamboat geyser is the tallest of all active geysers in the world. By contrast, Old Faithful reaches heights of 106 to 184 feet during major eruptions

Research related to this third question yielded the most conclusive and helpful answers — not only for the scientists but for curious tourists too.

The study states that "Steamboat’s erupted water is stored deeper than at other geysers." These deeper waters contain more thermal energy, which drives more powerful and bigger eruptions.

"We explained why Steamboat is so tall — its water erupts from deeper where it is hotter and has more energy," Manga says.

But the researchers concede there is still much we don't know about Steamboat's spectacular eruptions, particularly the correlation between the water's depth and the exact height of the eruptions.

Why it matters — Although the scientists came away with some inconclusive results, the implications of their geyser research goes beyond Steamboat or even Yellowstone.

The scientist's discoveries don't just tell us about how geysers work. They also help us better understand volcanic processes around the world — and possibly around the galaxy.

But, first, they need to gather more data in and around the geyser.

The study predicts:

"Such data would help answer fundamental questions about how geysers work and provide insight into similar multiphase processes and associated geophysical signals that occur at volcanoes and on other planetary bodies, such as Saturn’s moon Enceladus."

What's next — While the researchers were able to gather a fair amount of data, a small sample size hindered their efforts.

Surprisingly, despite the considerable tourist attention devoted to Yellowstone's geysers, we're still lacking sufficient data to fully understand them. Hopefully, future data-gathering efforts will focus on Yellowstone's geysers, so that we can not only marvel at their splendor but understand them, too.

Abstract: Steamboat Geyser in Yellowstone National Park’s Norris GeyserBasin began a prolific sequence of eruptions in March 2018 after 34 y of sporadic activity. We analyze a wide range of datasets to explore triggering mechanisms for Steamboat’s reactivation and controls on eruption intervals and height. Prior to Steamboat’srenewed activity, Norris Geyser Basin experienced uplift, a slight increase in radiant temperature, and increased regional seismicity, which may indicate that magmatic processes promoted reactivation. However, because the geothermal reservoir temperature did not change, no other dormant geysers became active, and previous periods with greater seismic moment release did not reawaken Steamboat, the reason for reactivation remains ambiguous. Eruption intervals since 2018 (3.16 to 35.45 d) modulate seasonally, with shorter intervals in the summer. Abnormally long intervals coincide with weakening of a shallow seismic source in the geyser basin’s hydrothermal system. We find no relation between interval and erupted volume, implying unsteady heat and mass discharge. Finally, using data from geysers worldwide, we find a correlation between eruption height and inferred depth to the shallow reservoir supplying water to eruptions. Steamboat is taller because water is stored deeper there than at other geysers, and, hence, more energy is available to power the eruptions.