The geysers in Yellowstone National Park are as breathtakingly beautiful as they are mercurial. Old Faithful is famous in part because of its predictability, since most of these natural fonts are much more inscrutable.
That’s why geologists were excited when the Steamboat Geyser roared to life in 2018. Normally, this geyser has gaps between major fountaining episodes that can last anywhere from four days to half a century. But since last March, it’s been erupting as often as once a week.
The Yellowstone Volcano Observatory reports that Steamboat has now set a record by erupting a whopping 32 times in 2018, a personal best for the geyser for a single calendar year. Previously, this geyser made it as high as 29 paroxysms back in 1964.
Other nearby geysers have also been behaving fairly interestingly of late. Ear Spring Geyser, for example, has been pretty quiet since 1957, but it erupted spectacularly a few months back—and sprayed human garbage from the 1930s everywhere.
Is this all this hydrothermal hyperactivity unusual in any way, and if so, what’s driving it? We’ve got you covered.
Don’t stop me now
Although Yellowstone boasts a plethora of geysers to gawk at, Steamboat is a particular standout. It’s the world’s tallest active geyser, and at the best of times it can fire water 300 feet into the air. Recently, though, it’s significantly picked up the pace of its eruptions.
According to the U.S. Geological Survey, which keeps a record of all Steamboat’s water eruptions, the current theatrical sequence started on March 15, and the geyser has been pretty darn active ever since. So far, it’s erupted five times in 2019.
It’s eruptions, although frequent, aren’t what you would call predictable. There were only two in July, for example, but six in September. This erratic behavior is par for the course for geysers at the park, says Michael Poland, the scientist-in-charge at Yellowstone Volcano Observatory.
“It’s a good lesson in how geysers actually work,” he says. “As soon as you start to recognize a pattern, it changes.”
Steamboat is just one of many gurgling pools in the Norris Geyser Basin, which the National Park Service explains is the hottest and most changeable thermal area in Yellowstone.
“As geysers go, Steamboat is sort of typical in terms of having these sporadic, unpredictable eruptions,” Poland notes. “But because it’s this really tall geyser and it has this name recognition, it makes it that much more interesting.”
Giant Geyser, found in another part of the park, is another good example of the generally erratic nature of geysers. Giant has been erupting more frequently than it has in the recent historical past, too.
“But back in 2007 to 2008, Giant went bananas,” Poland says. “It erupted many, many more times than it had in the past year—and Steamboat didn’t do anything of the sort.”
The devil’s gnarly kettles
The science of how geysers work is well established. Three primary controlling factors are involved: the geothermal heat supply from an underlying magmatic source, the supply of rechargeable water, and the rocky plumbing system, says the University of Salford’s Philippa Demonte, an expert in acoustics, including those of volcanic systems. (Explore the inner workings of Yellowstone's caldera with our interactive graphic.)
A good way to think of it is like a stove kettle, she says. Sometimes you have groundwater with an unrestricted pathway to the surface, and like heating water in a shallow pan, this will take longer to boil. But if you have a constricted, rock-filled pathway, comparable to water in a kettle, it boils far quicker. More heat allows you to boil things quicker, and more water means longer boiling times, but you have more water for the eruption at the end.
You can’t generalize though, because each geyser is idiosyncratic. Lone Star Geyser is fairly predictable, erupting once every three hours. Others, like Sawmill Geyser, can be active for some time before dying down, Demonte says.
“The patterns of these systems defy description,” Poland adds. That’s one of the reasons why comprehending why geysers act as they do is so difficult.
Laboratory contraptions mimicking geysers also hint at how much we have left to understand. A 2014 study found that depending on how bubbles rise through the geological pipes, and depending on where the water actually boils, the same geyser can produce a weak eruption or a thoroughly effusive one, notes Helen Robinson, a geothermal expert and doctoral candidate at Glasgow University.
The water chemistry is pretty vital, too, Robinson says. If it’s able to break down rocks that are high in silica or calcium carbonate, for example, these minerals may precipitate out higher up in the system as the pressure and temperature of the plumbing network changes. This might seal up the fractures that had been letting water flow and lead to the potential death of a geyser.
With all this in mind, do we know what’s going on at Yellowstone? There’s been no change in the underlying heat source, and no major geological changes, Poland says.
However, the last few years have been exceptionally snowy, so a change in the supply of subsurface water may be a major factor. As it happens, the second-longest earthquake swarm in the park’s recorded history took place in 2017. Research tentatively suggests that the same heavy precipitation may have provided the faults involved with plenty of lubrication, allowing them to jut forward with reckless abandon.
In both cases, it’s difficult to make any definitive statements. There aren’t really any direct measurements of the subsurface water in the park, and such inferences are based on the records of surface water and precipitation. For now, Poland says, “we’re just speculating.”
What absolutely isn’t worth speculating about is the state of Yellowstone’s infamous volcanic system. Any uptick in any sort of activity at Yellowstone seems to spark fears about a catastrophic eruption of the park’s huge caldera, even though such worries are unfounded.
There has been no change to the underlying magma reservoir over the past few years, Poland emphasizes. Plus, the mischief of any of the park’s geysers—which operate at the very top of the crust—has no bearing whatsoever on that mostly solid magma cache many miles below the surface.