People travel from all over the world to see Yellowstone's famous geysers, colorful hot springs, burbling mud pots, and hissing fumaroles. The force that drives these amazing thermal features—a giant volcano—lies below much of the park. In this episode, we talk with scientists who monitor the volcano about misconceptions surrounding Yellowstone's volcanic past, present, and future.

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TRANSCRIPT:

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SCOTT CHRISTY: Imagine that you’re standing on a boardwalk in Yellowstone National Park. It is a sunny day in the height of summer.

(SOUND OF CROWD)

People around you look at their watches, and then back up, waiting for something to happen. And right then this starts…

(SOUND OF OLD FAITHFUL WITH CROWDS)

SCOTT CHRISTY: A stream of water shoots four or five feet out of a hole in the ground. It pulses up and down a few times and then jets over a hundred feet into the air.

(SOUND OF CLOSE OLD FAITHFUL)

SCOTT CHRISTY: And it continues to do this for a few minutes. This would be Old Faithful erupting next to you. The most famous of Yellowstone’s features. It does that all the time, with similar blasts coming from the ground at least every two hours.

MIKE POLAND – I don't know, I get caught up just like anyone else. When I am vising Old Faithful, I stop and I watch the eruptions.

SCOTT CHRISTY: That’s Mike Poland, the Scientist-in Charge at the Yellowstone Volcano Observatory.

MIKE POLAND - Doesn't matter how many times you see it. It's no less spectacular to me than the first time I saw it. And the more you know about what's driving this, I think the more spectacular it becomes. It's this heat engine that's beneath our feet that's made this possible. You're seeing the upper expression of this heat engine right at the surface. And I think it's a magical sort of thought to have as you're watching these geysers go off.

SCOTT CHRISTY: While there are geysers all over the world, Mike says that Yellowstone is famous for holding the greatest concentration of geysers anywhere.

MIKE POLAND: in order to get a geyser to really go, you need heat, you need water and heat. And of course we have plenty of water around here. The heat is supplied by a magma body that's underneath Yellowstone.

SCOTT CHRISTY: Which is basically a bunch of molten rock from the earth’s mantle rising up into the earth’s crust.

MIKE POLAND: The magma body is sometimes referred to as a supervolcano, or the Yellowstone system is called a supervolcano. It gets that name because it can be the source of some truly humongous eruptions. JAKE LOWENSTERN: Yeah, this is kind of a funny jargon sorts of stuff. SCOTT CHRISTY: That's Jake Lowenstern. He was Mike’s predecessor as the head of the Yellowstone Volcano Observatory. Jake says that what defines a volcano as a super volcano is a past super eruption. And that such eruptions are really, really big. JAKE LOWENSTERN: Super eruption is a meaningful term and that's when you have more than a thousand cubic kilometers of material that comes out in a single event. Let's kind of visualize that. A thousand cubic kilometers if you took the state of Texas and you buried it five feet deep in material.

SCOTT CHRISTY: These super-eruptions are much bigger than the largest volcanic eruptions of the 20th century, like Mt. St. Helens or Pinatubo. So much bigger that the amount of ash they put into the sky can change the climate of the entire earth. The closest we’ve come to one in modern history was in 1815, when an eruption of Mt. Tambora in Indonesia threw so much ash in the atmosphere that it was known as the ‘Year Without a Summer’. The eruption and following climate change caused crops to fail in both Europe and New England and even prompted Lord Byron to write a poem about that summer titled “Darkness.” And Tambora’s 1815 eruption? It is dwarfed in size by Yellowstone’s pre-historic super-eruptions— at least ten times smaller.

(MUSIC)

There are a number of volcanos other than Yellowstone that have produced a super-eruption in the past, but Jake says that in the earth’s history these big super-eruptions are pretty rare, with one going off every 100,000 years or so on average. And, much like Yellowstone, these other super-volcanoes are not usually the cone-shaped mountains we often associate with volcanoes—not that big triangle you might have drawn in grade school. Instead these super-volcanoes are essentially giant sink holes, surrounded by mountains. These sink holes or calderas, are what’s left after devastatingly large super eruptions take place, blowing up everything that used to be there. Just like with Yellowstone’s caldera—a caldera about the size of Rhode Island.

JAKE LOWENSTERN: It's had three very, very large volcanic eruptions. The most recent one was 640,000 years old so that seems incredibly old, and it is, but that was one of the largest eruptions in the last 20 million years in the United States and it's one of the big eruptions on earth that's well-recorded in a geologic record. And, um, Yellowstone is capable of doing that.

(MUSIC)

JAKE LOWENSTERN: So you have a lot of different things that happen here, yet because everybody has in their mind this one kind of big bad eruption, everybody assumes that if there is an eruption, it has to be the worse case scenario and that everybody is doomed. That's just wrong.

SCOTT CHRISTY: According to Jake, the kind of eruption most likely at Yellowstone would have a more regional impact. A small scale eruption that could come in a few forms. A giant belch of superheated gas and water from Yellowstone’s underground plumbing system or oozing lava flows like the ones in Hawaii.

JAKE LOWENSTERN: It'll affect the people in the park and it'll affect the park if something like that happens. There will be forest fires, when you bring lava out in the ground, it's hot. There is going to be road closures. You might dam up some rivers but it's not going to be a national event and that's the most likely kind of thing that can happen and even that, it's not very likely. One hasn't happened for 70,000 years.

SCOTT CHRISTY: You can still see evidence of pre-historic lava-flows throughout the park. Flows that birthed the main plateaus of rock across Yellowstone. But again Jake really isn’t too worried about new lava flows or other events popping up any time soon.

JAKE LOWENSTERN: if I were offered a job here and if I were at the right time of life, I would certainly live here in a second.

SCOTT CHRISTY: Learning more about the Yellowstone volcano’s past and paying attention to its present is what scientists like Mike and Jake do as members of the Yellowstone Volcano Observatory. Scientists at the observatory come from groups like the United States Geological Survey, the National Park Service, and Universities of the states surrounding the park. Again, Mike Poland,

MIKE POLAND: Some of us are geophysicists. Some of us are geochemists. Some of us specialize in gas emissions or rock compositions. Other people specialize in locating earthquakes. It's a unique group of scientists. And it's all really getting at ways of better understanding the current activity and the processes that are happening now beneath our feet.

SCOTT CHRISTY: Research trying to understand the volcano can lead scientists in unexpected directions. Mike and fellow researcher Elske de Zeeuw-van Dalfsen are standing in the middle of a lodgepole pine forest as heavy wind whips the trees back and forth.

MIKE POLAND: My goodness. I know they're designed to do this but it's a little unnerving to be, okay.

SCOTT CHRISTY: As Mike and Elska deploy a sensitive piece of equipment to measure gravity at the site. A pine maybe 30 feet tall breaks and falls to the ground while the rest of the trees continue to crack and whine.

MIKE POLAND: That would be an interesting manifestation in the gravity record if we had it running when that tree fell. Because we’d detect the vibrations from that.

MIKE POLAND: We're doing a gravity survey throughout the park right now and the idea is that gravity actually isn't a constant. It varies depending on what's beneath your feet. It will especially vary over time if there's an influx in mass beneath the ground, say or water or magma. If there's more or water or magma beneath the ground, gravity actually pulls a little stronger and we can record that with these instruments.

SCOTT CHRISTY: These measurements of gravity could provide a better understanding of changes in the magma chamber below the park, and are one example of ongoing research at the Observatory. Scientists are also studying the age of gases released by geysers and fumaroles to understand how old the molten rocks below the surface are, and where in the earth’s crust they are being melted from. Other researchers are measuring recent ground deformation, which means the changing shape of the earth’s surface caused from below. In 2014, in the park near Norris,

MIKE POLAND: the ground began to uplift by several centimeters a year, which is extraordinary by geologic standards. This is something that of course you wouldn't notice, but measuring with GPS and with radar satellites we could see this uplift.

MIKE POLAND: Then there was an earthquake.

MIKE POLAND: And right after this magnitude 4 or so earthquake, the ground started to subside by about the same rate, several centimeters a year.

SCOTT CHRISTY: Researchers think that earthquake was caused by pressure releasing. Heated water accumulating behind a seal and the seal breaking. Afterwards the ground started falling as the water drained out from behind the barrier. And while all this research helps scientists better understand whats going on under the park, Yellowstone’s past of large eruptions can add a dramatic flair to current events surrounding the volcano. In 2017 thousands of earthquakes were detected occurring in just over three months near West Yellowstone. Major news outlets often covered the story of the earthquake swarms and were quick to cite the potential for disaster.

MIKE POLAND: It seems that whenever there's an earthquake swarm at Yellowstone this idea that the volcano is about to erupt comes up. And there are swarms all the time. If it were true that Yellowstone swarms were indicating an eruption was imminent, then eruption is likely to be imminent every year. So this is just the way Yellowstone works. Yellowstone releases seismic energy in swarms. Some swarms are big. Some swarms are small.

MIKE POLAND: It's what Yellowstone does. So they're not anything to get worried about. In my opinion, they're more something to get interested by. MIKE POLAND: the rocks that are around tell a heck of a story. There are lava flows all over the interior of the caldera. Outside the caldera there are tufts, welded ash deposits, thick ash deposits from the large eruptions that have occurred over the last two million years. MIKE POLAND: Obsidians and ash flows and basalt lava flows all mingled together to tell this story. MIKE POLAND: So there's a story recorded in the rocks, which tells the geologic history of Yellowstone, and it's an interesting story. (MUSIC)

SCOTT CHRISTY: And this story, the story of the volcano, can be seen everywhere in Yellowstone. It’s one of the things that makes Yellowstone so unique. The shapes of land, the courses of the rivers, and all of the amazing thermal features. They are all dictated by the volcano. Even plant and animal habitats in the park are defined by volcanic rock types. The volcano isn’t just written across the landscape, it is the landscape. And this is something special to see, even for a scientist studying it.

MIKE POLAND: Not only is there a lot of activity to measure, a lot of things to observe, but it's a spectacular place. Period. (SOUND OF OLD FAITHFUL COMING BACK IN FADED IN UNDER)

MIKE POLAND: There's a reason that there are millions of people a year that come to visit. It's really a privilege to work in such a spectacular place, not just geologically and vulcanologically, but also in terms of its ecology, in terms of its landscapes. It's a real wonderland.

GEYSER GOING BIGGER SOUND

MIKE POLAND: So come to Yellowstone and look at the landscape and explore the geology.

SCOTT CHRISTY: For Yellowstone National Park, I’m Scott Christy

MUSIC FADE AND OLD FAITHFUL OUTRO