YELLOWSTONE NATIONAL PARK — A once well-known and rare acidic geyser in Yellowstone National Park came back to life in February. The Echinus Geyser used to be a popular attraction at the Norris Geyser Basin, with extra seats for viewing the geyser set in the nearby boardwalk.
“For decades, it was the one that people went down to watch because it was pretty reliable,” said Dr. Mike Poland, the chief scientist for the Yellowstone Volcano Observatory. He added, “There were a lot of descriptions of Echinus activity, especially in the second half of the 20th century, when it was really going up, especially in the 70s, 80s, 90s.”
WATCH: Yellowstone's rare Echinus Geyser is back
But, so far in this century, eruptions are rare, with just a few sporadic outbursts. Poland said, “There was a spate of activity that was similar to what happened back in February, back in the fall of 2017. And there was about a month-long period where the geyser was erupting like clockwork, almost every two to three hours. And then that too, just sort of suddenly stopped.”
That is exactly what appears to have happened this time as well. There have been no eruptions since late February, and the ones that did occur were smaller than in the past. “They haven't been as spectacular as previous eruptions. Instead of going up 75 feet as they could in decades past, they might go up 10, 20, 25 feet or so,” said Poland.
Echinus is the largest acidic geyser in the world. That description may be a bit confusing and even frightening. But the acid in Echinus is weak, more like what you would find in orange juice or vinegar. Still, it’s enough to erode the rocks around the geyser pool, giving those rocks an unusual, spiky appearance.
Scientists first noticed that Echinus was erupting again, thanks to instruments that showed a sudden surge in hot water flows. Poland explained that the surges, seen in the posted graphs, show both eruptions and what he calls surges. That’s when the water heats up, roils the surface, and surges up in the pool but does not erupt. In the charts, spikes that reach 70 degrees Celsius (158 Fahrenheit) are the eruptions. Spikes that only go to 40 to 50 degrees Celsius (104-122 Fahrenheit) are the surges.
“It's only about 600 feet or so from Steamboat,” noted Poland. Steamboat is the largest active geyser in the world, but it too has fallen mostly silent in recent years. After 50 years of dormancy, it erupted in 1961, remaining active for another three years before settling into an erratic, mostly dormant period until 2018, setting new eruption records through 2020. After that, it slowly tapered off, erupting just three times in 2025.
“No connections that we know of,” said Poland, adding, “It's fun to kind of play games with this, right? Because we had all that spate of activity at Echinus in 2017. That was just a few months before Steamboat became really active and started having a whole bunch of eruptions. And here we are, Steamboat sort of calming down, and we have another sequence of eruptions. And in fact, Steamboat erupted three days after Echinus last erupted.”
The reason for the sudden eruptions is still unknown, according to Poland.
“So whenever these geysers erupt, they make a lot of noise. And that also rattles the plumbing systems. And we can see where the noise is coming from. And that mapping has been done at Steamboat and Cistern Spring. And there you can see that the plumbing systems basically go straight down,” he said.
But, he added, after a couple of hundred feet, seismic equipment is unable to accurately map the underground cracks and fissures in the rock that feed these geysers.
A chance of seeing Echinus erupt if you visit the park exists, but it would be like winning the lottery.
“I want to see it, right? Like, like so many other people. It's still having these surges. So maybe it's not completely done. If it's anything like the 2017 to 2018 sequence, after we had a very repeatable sequence of eruptions, it settled down and then would have sort of a random one. So it really wouldn't surprise me if over the next year or maybe more, there's sort of a random eruption here or there. So it might be that if you're visiting Norris and you happen to be walking by Echinus one day, maybe you'll get lucky and see an eruption of that feature. But for Echinus, it seems like the really nice repeated sequence of eruptions might be over, or at least paused," Poland said.
