Visitors and scientists in Yellowstone National Park noticed a few changes when gazing into the abyss this summer. One of the park’s deepest hot springs has lost its (relative) cool, suggesting it could soon have a violent outburst.
Then again, maybe it won’t.
The Abyss Pool in the West Thumb Geyser Basin cranked up the heat and changed its color over the last few months. It’s another example of Yellowstone’s dynamic, ever-changing landscape.
“This is Yellowstone being Yellowstone,” said Mike Poland, the scientist in charge of the Yellowstone Volcano Observatory. “They’re some of the most dynamic features on the planet, and Abyss Pool is demonstrating that.”
Eruptive Abyss
The Abyss Pool is one of the deepest hot springs in the park, reaching a depth of 53 feet. Its name is believed to have come from Gustavus Cheyney Doane, who described its “deep abysses” during the Washburn-Langford-Doane Expedition of Yellowstone in 1870.
The name also evokes mystery, and the Abyss Pool has had its share. In August 2022, a human foot was found floating in Abyss Pool DNA analysis identified the remains as belonging to Il Hun Ro, 70, who was last seen in Yellowstone.
Despite being called a pool, the Abyss Pool has a history of violent eruptions. It can send hot thermal water up to 100 feet high and throw out pieces of sinter, siliceous mud and rock formed around hot springs.
Poland said previous eruptions of Abyss Pool occurred when the pool was “running hotter.” Between September 1991 and May 1992, several eruptions occurred weeks, days, and even hours apart.
“It's possible that this will have some eruptions,” he said. “It’s also possible that the temperature will start to go down. It's impossible to say how these things will come out.”
Going Through Changes
Over the summer, there were noticeable changes in the behavior and appearance of Abyss Pool. Scientists have been monitoring the hot spring ever since.
First, the pool’s water level slowly rose between one and two feet. The water level rose so much that the pool was overflowing, which might have sent a surge downhill into Yellowstone Lake.
Then, Abyss Pool changed its color. The dark greenish-black water transitioned to “a brilliant blue,” as Poland described it.
Color change is a definite sign of temperature change in thermal pools. Morning Glory Pool in the Upper Geyser Basin near Old Faithful had a similarly brilliant blue color until its conduit was blocked by coins and other trash, reducing its temperature and changing its color.
“The temperature of Abyss Pool is somewhere in the range of about 180 degrees Fahrenheit right now,” Poland said. “Why that's happening? We don’t know.”
Poland is skeptical that the changes at Abyss Pool are signs that the West Thumb Geyser Basin is becoming “more active.” He thinks it has to do with the subterranean plumbing system that feeds water to the features.
“It's more likely to do with the shallow plumbing system and how heat is being distributed in the area,” he said. “Water is constantly moving around in the area, and that sort of activity changes all the time.”
There’s no timetable to follow, but it’s possible that Abyss Pool could already have cooled down and gone dark again. If it hasn’t, Poland believes the pool could change again as the seasons change in the park.
“The temperature could plateau and start to go down as snow melts and starts to inundate the area in the spring,” he said. “It's very interesting and something that certainly bears watching, but we don’t really know what the outcome of this will be.”
Abyss Pool in the West Thumb Geyser Basin of Yellowstone National Park is getting hotter and changing colors, which scientists say may indicate it's building up to violently erupt. Then again, it may not. (Getty Images) 
Abyss Pool in the West Thumb Geyser Basin of Yellowstone National Park is getting hotter and changing colors, which scientists say may indicate it's building up to violently erupt. Then again, it may not. (Getty Images)
Dynamic Landscape
The West Thumb Geyser Basin isn’t the largest or most popular thermal basin in Yellowstone National Park, but Poland believes it’s overlooked and underrated for what it is. One reason is that several of the basin’s thermal features aren’t visible without a snorkel or a scuba tank.
“There are a lot of features that are submarine, just off the shore,” he said. “That whole area is an incredibly active thermal basin, but part of it is in Yellowstone Lake.”
The visible features, like Abyss Pool and the Occasional, Lakeshore, and Twin Geysers have unique and erratic eruptive behaviors. When Twin Geysers erupted in 1934, it sent boiling water, mud and sticks 120 feet into the air.
Poland and other Yellowstone scientists are monitoring Abyss Pool to see if the deep hot spring will erupt while it’s still hot. Even if it doesn’t, Poland sees it as another example of what makes Yellowstone National Park one of the most dynamic landscapes in the world.
“This is the nature of Yellowstone’s thermal basins,” he said. “They are incredibly dynamic. They're always changing. They're supposed to be some of the most dynamic features on the planet, and this is precisely what those features are supposed to do.”
Andrew Rossi can be reached at arossi@cowboystatedaily.com.
