Understanding Yellowstone as a volcano

Adam Del Rosso interviewed Michael Poland, a researcher at the Yellowstone Volcano Observatory, to understand how Yellowstone is a volcano, and if we should be worried about it erupting.

Video Transcript

ADAM DEL ROSSO: Michael Poland, the scientist in charge at the Yellowstone Volcano Observatory, joins us this evening. Mike, thank you so much for being here.

MICHAEL POLAND: My pleasure.

ADAM DEL ROSSO: So we know Yellowstone is a beautiful national park, but some might not know that it's also a caldera volcano. Can you tell us exactly what that means?

MICHAEL POLAND: Yeah. A caldera volcano is a system-- it's not a pointy mountain like Mount Fuji or Mount St. Helens, what most people think of as a volcano. It's sort of a large volcanic field that's experienced a major collapse, meaning that it's had a large eruption and the ground has collapsed into the space that was evacuated when the magma chamber emptied. And so they tend to be very large depressions, large, large craters.

The Yellowstone system has subsequently largely filled up due to lava flow activity. So you can't really see that crater anymore, but it's a huge one. It's tens of miles across. So that's kind of what we mean, when we say caldera system.

ADAM DEL ROSSO: Now I read your April report that says that there were 43 earthquakes in the region throughout the month. That sounds like a lot. Is it? Should we be worried?

MICHAEL POLAND: Actually, 43 earthquakes in a month is well below average. The Yellowstone system is really active as a tectonic system, so we see anywhere in the neighborhood of about 1,500 to 2,500 earthquakes per year on average. So typically, there's 100 or 200 earthquakes every month at Yellowstone. And these are mostly caused by very small faults that are going-- the earthquakes are in the magnitude one, two range. Every year, there's a few magnitude three events-- typically, four or five events, perhaps.

But they're very small events caused by all of the water that's moving around in the subsurface, and the area is chock full of faults because it's in a very tectonically active part of the Western US. And it's also weak because of the heat that's being input to the system by the Yellowstone volcanic system. So that combination of the weak crust due to the heat and all the faults and all the water moving around in the subsurface just creates the perfect conditions for lots and lots of small earthquakes.

ADAM DEL ROSSO: So how closely related is the seismic activity with the volcanic activity?

MICHAEL POLAND: Well, they're definitely interrelated in that you wouldn't have so much seismic activity if this also weren't an active volcanic system. And that provides that heat that weakens the crust. And you can look at areas to the north and south of Yellowstone and they're not as seismically active, even though there are faults in the region and there are earthquakes in the region.

So they are interrelated, but it's not like you might expect at some other volcanoes where the earthquakes are directly related to volcanic activity. So when you see swarms of earthquakes at some volcanoes, that's a sign that the volcano may be coming back to life. Whereas at Yellowstone, swarms of earthquakes are sort of-- that's normal. We see typically a couple of swarms of earthquakes every month. And that's been happening as long as people have recorded measurements at Yellowstone. Back in the 1870s, when explorers were mapping Yellowstone for the first time, they recorded feeling earthquakes.

So this is the way Yellowstone has always been. Yellowstone is a seismically active place. That's-- that's normal for this area.

ADAM DEL ROSSO: It's good to know. I've heard talk-- and I'm sure some of our viewers have as well-- that a major eruption is overdue. Being in the business of predictions, is an eruption something that you can predict? And how do you monitor its status?

MICHAEL POLAND: We can definitely forecast eruptions. We look for indicators, and those are deviations from background. Now background at Yellowstone is sort of a high level of earthquake activity. Now if we saw that earthquake activity begin to pick up in very significant ways, where we, instead of seeing thousands of earthquakes every year, we were maybe seeing tens of thousands of measurable earthquakes, magnitude one, two, three. If we were seeing much stronger events, magnitude fours and fives, very regularly, then that might be an indication that the volcanic system was starting to come back to life.

But we would also see ground deformation. The ground at Yellowstone rises and falls. It goes up and down at rates of an inch or two per year, typically. Sometimes it's going up, sometimes it's going down. And right now, it's going down. Has been since 2015. But if it were to suddenly start rising very quickly, much more than this kind of background breathing that it does, that might be another indicator.

Changes in thermal emissions-- the temperature of the ground. Changes in gas emissions could also be a sign of changes in magmatic activity beneath the surface. So there are these signs that we've learned to recognize. But the key is knowing what the background is, knowing what normal is. And then we find deviations from normal, and that can help us forecast whether or not a volcano is becoming more active.

ADAM DEL ROSSO: Now is this something that we need to worry about in our lifetime? Is there a way to even know that?

MICHAEL POLAND: Well, we've done a lot of probing of the subsurface using various techniques, not just-- not drilling. There's been a little bit of that, but that really can't tell us as much about the subsurface as, say, looking at seismic imaging. That's almost like taking an MRI of the surface, the subsurface. And from those sorts of measurements, we know that the Yellowstone magma system is mostly solid. It's only about 5% to 15% molten. The rest of it is just hot, kind of plasticky solid rock.

So there's no indication that the Yellowstone magmatic system is really going to be waking up any time soon. In order to mobilize all of that hot, sticky rock down there, you'd have to have a large input of heat. And that would be the kind of thing that was accompanied by really unmistakable changes that we can measure at the surface in seismicity and ground deformation, gas emissions, and so forth.

So there's no sign of that happening. And then it takes a while to rejuvenate a system, so it's not something that typically we would need to worry about in a scale of a human lifetime.

ADAM DEL ROSSO: Good, good. Now given the size of the volcano, how impactful would a major eruption be? And is there anything that can be done to prepare?

MICHAEL POLAND: Well, there's a lot of different types of eruptions that could happen from Yellowstone. And the most common is sort of a steam explosion, a hydrothermal explosion. Those can be pretty significant. And you know, if there are people around, people nearby, then they can be damaging. It can be deadly. We've seen examples of small explosions in Japan in 2014, in New Zealand in 2019 that resulted in deaths, even though they were relatively small events. So looking at the subsurface-- that doesn't even have to involve magma, just water flashing to steam. So looking at that hydrothermal system, monitoring that is important.

Lava flows are also relatively common at Yellowstone, although not common on human timescales. The last lava flow was 70,000 years ago. But those are things that really won't impact people so much because you can more or less walk out of the way of those. It could impact infrastructure though, of course-- some roads and and facilities in the park.

And then, of course, there's the large explosions, which Yellowstone is well known for. Those happen maybe once, maybe twice every million years or so. And those would be significant if they were to-- anything like that were to happen in the future. Not just for the region, which would see a lot of ash fall, but there would be so much ash and gas put into the atmosphere that it would have an impact on global climate. It would cause cooling by reflecting a lot of the sun's energy. So these sorts of big, catastrophic eruptions, whether they happen in Yellowstone or other places on Earth-- these kinds of caldera system volcanoes exist in many other places. They can have global implications.

ADAM DEL ROSSO: Mike, that's a lot of great information. Thank you so much. I wish we had more time to keep on talking, but I think we're already getting the wrap here. So we're going to do that, wrap this up. And we're going to keep our fingers crossed that we stay eruption free.

MICHAEL POLAND: My pleasure. I hope everyone out there has a chance to come and see Yellowstone. It's an amazing place.