Scientists know there is a reservoir of water deep beneath Yellowstone National Park. Somehow, that water rises through the earth, creating the features that make Yellowstone unique. Researchers at the University of Wyoming and Montana State University are trying to figure out what's going on beneath the surface and what that means for life in the park and beyond.
If you've visited Yellowstone National Park, you've seen the brightly colored pools and geysers shooting water sky-high. UW Geology and Geophysics professor Ken Sims said we only have a 2-D image of the park. In other words, we only get to see the surface. His team is trying to find out how water moves from below ground to get to the point where it sprays out of a geyser.
"Everything you look at at Old Faithful is a cartoon, essentially," said Sims. "At some point the idea is that you'll see a real image of what it looks like down there, what the pathways are down beneath there, and then how that water is reacting with the rock to make the chemistry."
To make the underground pathways, Sims said rainwater and melted snow seep down to the reservoir, then plow a path back up to the surface.
"Water goes down, interacts with deep rock and magmatic gases, and it comes back up," he said. "As it comes back up, it's probably finding sort of the easiest pathways for it to come through."
Associate Research Scientist Brad Carr said there are two main theories for how the water comes back up.
"Imagine in a real simplistic way there's sort of the anthill scenario," he said. "Then there's the other fundamental idea that these things are just shotguns."
Carr said in the anthill scenario, the water carves out complicated passageways up to the surface where it shoots out. In the shotgun model, water builds up beneath the opening and shoots straight up. To look at what might actually be the case, he said they measure properties of the underground material that change when it gets wet.
Carr said both the anthill and the shotgun model might be at play.
"There's kind of two types of geysers that are most prevalent in the Upper Geyser Basin," he said. "One is the pool geysers: they sort of look like pools, they fill up, they burp, essentially. They throw water, but not like hundreds of feet. It's tens of feet maybe."
The pool geysers may have different underground pathways for the water than cone geysers, which may explain why the geysers shoot water so differently.
"The cone geysers, very much like Old Faithful, have the same chemistry, but their system is different," said Carr. "They can throw water hundreds of feet, or in the case of Steamboat at Norris, you know three hundred feet."
Yellowstone's features might have different structures, but they can also have different chemistries. As water moves toward the surface, pressure increases. It reaches a high enough point that the water flash-boils, separating into liquid and steam.
Sims said the steam is acidic, and gets even more acidic as it rises.
"When it does that then it just starts chewing up the rock and eats it up," he said. "It chemically erodes the rock and makes these mud pools."
Sims said some features are formed by the other liquid.
"You can have two pools right next to each other and they can have completely different signatures," he said. "The model is that the acid one is chewing up the rock that's shallow, whereas the other stuff the water-rock interaction is old and it occurred deep."
By looking at the chemistry in pools, Sims said scientists can determine how old and how deep the rock is that interacted with the water. That gives them more information about the structure underground.
Understanding the chemistry and pathways under Yellowstone is also important for understanding the life that forms in its springs. Montana State University Associate Professor Eric Boyd said the team is also studying the tiny microbes that live in Yellowstone's hot water.
"What we're specifically interested in are systems that host what we call rock-powered life," he said. "By that, I mean life that is dependent on chemical sources of energy, not light sources of energy."
Boyd said rock-powered life is important because it's the first kind of life that formed on Earth. He said photosynthesis and complex organisms came much later and would be harder to find on other planets.
"One of NASA's major goals, you know in exploring our solar system, is to ask the question 'could life exist on another planet?'" said Boyd. "Well, all life on Earth, from you to your cat to your dog, your ancestor is a microbe and a very primitive microbe."
By studying microbes' living conditions in Yellowstone, Boyd said researchers can learn about what it takes for life to form. That can be applied in space.
"If you wanna start looking for life on another planet, you're not going to go so far as to say 'oh, i'm going to look for humans'," he said. "What you're going to do is look for the primitive forms of life."
The team has plans to study sites across the park in order to learn more about Yellowstone, life on Earth and life beyond.
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