Since Yellowstone’s Steamboat Geyser made headlines in 2018 with a sudden trio of eruptions, it has spouted over 100 times and set new records for annual activity, Laura Geggel reports for Live Science. The burst of activity by the national park’s tallest geyser followed more than three years of silence, so scientists set off to research why it awoke and what’s made it so active.
Now, new research published on Monday in the Proceedings of the National Academy of Sciences sheds light on the mystery. The height of geyser eruptions seems to depend on the depth of a geyser’s water source, the researchers found. While it didn’t conclusively identify what sparked Steamboat Geyser’s new activity, the study did rule out several theories, including the idea that the geyser might have been a sign that Yellowstone was ready to blow. The data didn’t support that theory: other geysers around Steamboat haven’t reactivated, and the groundwater temperature did not go up.
“This study does an excellent job of assessing a wide range of factors, and perhaps not surprisingly, there's no easy answer to why the geyser is now in a phase of increased activity,” says Michael Poland, who leads the Yellowstone Volcano Observatory and reviewed the new paper, to Brett French at the Billings Gazette. “Why Steamboat came back to life, and why many geysers have unpredictable behavior, the answer remains elusive.”
Yellowstone National Park is home to more than 500 geysers. The most iconic is Old Faithful, which erupts about 20 times per day or every 90 minutes. Old Faithful’s eruptions reach about 106 to 184 feet tall, Tara Yarlagadda writes for Inverse. The Steamboat Geyser blows that out of the water with eruptions reaching over 300 feet tall, making it the largest geyser in the park. It’s far less reliable than Old Faithful, though. Over the last three years of activity, Steamboat Geyser’s eruptions have had as few as three days between them, and as many as 35.
In the new study, the researchers wanted to understand why the geyser reactivated, why its eruptions are so tall, and why they are so irregular. They came up with answers to two of their three questions.
As for the period between eruptions, the data show that the geyser is most active in the spring and summer, and less active in the colder months. That may be because water from rain and melting snow in the spring forces groundwater to refill the geyser’s reservoir more quickly than in the fall and winter.
“I found it interesting that there is a correlation between eruption interval and season, which does argue that the amount of water in the subsurface can control how frequently it is active,” says Poland to the Billings Gazette.
The researchers also found that the Steamboat Geyser’s reservoir reaches much deeper underground than other geysers. This explains why the eruptions reach such impressive heights.
"Its water erupts from deeper where it is hotter and has more energy," says lead author Michael Manga, a geoscientist at the University of California, Berkeley, to Inverse.
The reservoir is about 82 feet deep, which means the water is under more pressure the same way that when a diver swims deeper underwater, they are under more water pressure, per the Billings Gazette.
When water is under a lot of pressure, it can reach a higher temperature before starting to boil compared to water at ground level. (This is the opposite of water having a lower boiling point at higher altitudes, where it’s under less air pressure.) The higher pressure and temperature mean the water builds up a lot of energy before bursting up to the surface, giving the eruptions their impressive height.
But why was the Steamboat Geyser quiet for over three years and then become unusually active? The new study couldn’t provide a conclusive answer, but they did rule out the possibility that Yellowstone’s volcano might be ready to erupt. No other geysers in Steamboat’s neighborhood, Norris Geyser Basin, reactivated as they would if magma was moving toward the surface. And the groundwater feeding Steamboat Geyser has not increased in temperature.
“We don’t find any evidence that there is a big eruption coming. I think that is an important takeaway,” Manga says in a statement.
The study also ruled out the theory that the geyser was activated by seismic swarms in 2017 and 2018, and the theory that ground deformation in Norris Geyser Basin had a role. They found that the ground around Steamboat Geyser rose before the geyser burst, and the air temperature around the geyser has increased slightly, per the statement. The new activity might be related to a rearrangement of the underground plumbing leading to the geyser, but the data was inconclusive.