The largest geyser in Yellowstone National Park has been more active in the past two years than ever before.
In a study recently published in the Proceedings of the National Academy of Sciences, scientists have ruled out many of the theories about why Steamboat geyser has been so explosive, erupting more than 120 times since March 2018.
“The question of why Steamboat geyser started to erupt is an important question even if we come up with an inconclusive answer,” said Michael Manga, a geoscientist and professor at the University of California, Berkley, who co-authored the research paper. The lead author was graduate student Mara Reed of the University of Wisconsin-Eau Claire.
“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,” said Michael Poland, scientist-in-charge of the Yellowstone Volcano Observatory.
“Why Steamboat came back to life, and why many geysers have unpredictable behavior, the answer remains elusive,” he added.
The theory going into the research project was that Steamboat began erupting because of underground magmatic activity, the molten rock that reaches close to the surface in the ancient Yellowstone volcano crater.
“If that was correct, that means there’s a risk of a future eruption, or some kind of hydrothermal explosion,” Manga said. “So coming up with an inconclusive answer means the volcano’s probably not going to erupt, at least not anytime soon.”
Instead, the study suggests the geyser’s activity may be driven by hot water circulating deep underground. This water, however, “has been isolated from the surface for many, many decades,” Manga noted.
What the study was able to answer is why Steamboat geyser shoots water so high, more than 115 meters into the sky, taller than any other geyser in the world.
“Water in Steamboat is stored deeper than in other geysers, resulting in increased energy to power taller eruption plumes,” the study found.
That’s because the deeper underground the water is stored, the hotter the water. The hotter the water, the more energy it has to drive eruptions, Manga said. Pressure also increases with depth. As an example, think of how water pressure increases with depth as a submarine dives into the ocean.
Because the geyser has been so active, the scientists were also able to chart the intervals between eruptions, which are shorter in the summer and longer in the winter.
“What varies over the years is how much water is available in the shallow subsurface,” Manga said.
“The median interval for the 108 eruptions analyzed between April 2018 and July 2020 was 7.17 days, with a range of 3.16 to 35.45 days,” the study found. “Most (86 percent) of the intervals are under 10 days.”
So anyone hoping to see the geyser should come in the summer and plan their visit about a week after the previous eruption. Old Faithful, on the other hand, erupts about 20 times a day — a much more predictable and reliable occurrence for time-constrained tourists.
“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,” Poland said.
The scientists were also able to categorize how much water Steamboat is capable of shooting out — as much as 500 cubic meters, almost one-quarter of an Olympic-size swimming pool. “Few geysers have estimates of erupted volumes because water discharge is challenging to measure, but those with estimates erupt less water: 8 to 11 cubic meters during major eruptions at Lone Star; uncertain estimates of 38 to 45 cubic meters and 14 to 32 cubic meters for Old Faithful; 31 to 38 m3 for Echinus in Norris Geyser Basin ...”
However, “many other geysers erupt more water when averaged over time.”
Going into the study, there were several theories about why Steamboat geyser became active and has remained so. These included aftershocks from the destructive 1959 Hebgen Lake earthquake and seismic swarms that swept through the area in 2017 and 2018. The idea was that the activity had altered fluid flow in the earth’s crust.
Also ruled out was ground deformation in the Norris Geyser Basin as magma underneath raised and lowered the shallow crust.
“Out of a small sample of seven other geysers within the Yellowstone Caldera chosen for their relatively complete records, none have active periods that correlate with caldera uplift between 1996-2020,” the study reported.
Likewise, changes in the geyser’s water temperature were discarded as a reason. Temperatures varied little in the geyser’s reservoir between 2000 and 2019.
“Steamboat’s reactivation at a time when the area is very well monitored, both in terms of geophysical factors (like earthquakes) and environmental parameters (like rainfall), allows us to finally start exploring some of the factors that might influence its activity, and that of similar geysers,” Poland said.
“One of the things I enjoyed about this study is the huge range and types of observations we had to pull together,” Manga said.
That required a large group of people with different scientific skills, many of them graduate students. They met at a summer school and identified understanding Steamboat as an important question. Together they were able to look at satellite data, seismic data, ground vibrations, GPS info, water samples, water chemistry, the climate record, geological mapping and theoretical fluid mechanics.
“It was really the integration of all these different data sets and approaches that made it possible to answer all those questions,” Manga said.
“If you don’t have data you can’t answer questions,” he added. “And so few geysers have good data or much data at all.”
With that in mind, he’s hoping the study may encourage other scientists and citizens to collect data.
When will Steamboat stop? In its two previous active periods, the time between eruptions grew longer and longer before finally halting.
“There’s no evidence yet for any change in behavior that suggests it’s going to stop,” Manga said.
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The recently published study examining Steamboat geyser in Yellowstone National Park points out many interesting features that make it unique.
l “Unlike cone-type geysers in Yellowstone’s Upper Geyser Basin that have existed for thousands of years — such as Old Faithful, Giant, and Castle geysers — Steamboat is probably a relatively young geyser that broke out or significantly enlarged itself in August 1878.”
l Present-day Steamboat geyser consists of two vents.
l The main liquid phase of a Steamboat eruption can last anywhere from 3 to 90 minutes.
l The geyser has had three other active periods that scientists are aware of: The first is between early September 1961 and early 1969; the second was between Jan. 13, 1982, and Sept. 26, 1984, and the current episode, which began March 15, 2018.
l Cistern Spring, located about 100 yards to the southwest of Steamboat, “is the only thermal feature with documented evidence for a subsurface hydraulic connection to Steamboat. In the summer of 1966, Cistern’s water level began draining several meters after every major eruption of Steamboat. This relationship continues.”
l Norris Geyser Basin, where Steamboat is located, “is the hottest and most dynamic of Yellowstone’s active hydrothermal areas,” according to the National Park Service. “Norris is so hot (a 1,000-foot-deep drill hole recorded a temperature of 459 degrees) and dynamic because it sits at the intersection of three major faults, two of which intersect with a ring fracture zone from the Yellowstone caldera eruption of 640,000 years ago.”
l A ring fracture zone roughly marks the edges of an underlying magma chamber.