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How did historic flooding impact earthquakes and eruptions? Turns out not that much.

old faithful erupts.
Jacob W. Frank
Old Faithful in Yellowstone National Park

Yellowstone National Park received historic flooding earlier this summer. There have been a lot of effects on things like roads, tourism, and infrastructure, causing the landscape to change dramatically. But what about other things - like earthquakes and eruptions? Yellowstone is one of the most seismically active areas in the country.

Wyoming Public Radio's Caitlin Tan spoke with Mike Poland, the scientist-in-charge for the Yellowstone Volcano Observatory, to find out.

Caitlin Tan: So what I wanted to get into with you is the seismic activity, and how maybe that has been affected by flooding. With Yellowstone, I feel like there's always this standing question of 'When is it going to erupt?' Do you think the flooding event from the summer could trigger more seismic activity?

Mike Poland: It's pretty unlikely to trigger any more seismicity, or really any activity at all in Yellowstone. There's a couple of reasons for this.

First off, the rates of groundwater infiltration, the water getting into the subsurface, are relatively slow compared to how fast the rivers were carrying the water away. So it's not as if all of that water just went straight into the ground and disappeared. Of course, most of it ended up in the rivers and ultimately out in the Gulf of Mexico as it went down the Yellowstone and Missouri and Mississippi.

Another reason is that a lot of the seismicity in Yellowstone is driven by water that interacts with existing tectonic faults. It doesn't have much to do with the volcanic system there - that's one of the bigger misconceptions about the area. But a lot of that water is already in the ground, and it's coming from below. So this is water that has fallen as rain or snow a long time ago, and it's percolated way down into the ground and been heated by the hot ground and the magmatic system that is down there many miles deep. And then it starts to rise back up. And that's the water that sort of gets into the faults and helps to cause some of those faults to slip with these very small magnitude earthquakes.

So rainfall, in the context of Yellowstone, probably isn't going to cause that much of an impact on seismicity. We have seen a few places in the world where rainfall may have an impact on seismicity. But in Yellowstone, we've never noted those sorts of correlations. So it's not something that I'd expect we'd see any changes.

CT: So you make these monthly videos kind of updating people on geological activity in the park. And in one of your videos, you mentioned there were 149 earthquakes in June, which you said is actually normal, which is wild to me. I think maybe a lot of us didn't realize how many little earthquakes are happening. Can you kind of just elaborate on that? Can we feel these earthquakes?

MP: It's funny, isn't it, that Yellowstone is really one of the most seismically active places in the country. There are, on average, somewhere between 1,500 and 2,500 earthquakes every year, but 99 percent of them are magnitude two and lower. And those really aren't felt. That kind of seismicity is normal. I like to just say that it's Yellowstone being Yellowstone. That's what the place does.

CT: Well, what about geysers, were those affected at all from the flooding?

MP: Well, it's possible that geysers will be affected, although it will take us a while to really see. And this is because there is a correlation between overall precipitation, rainfall, and geyser activity. In years where we see more precipitation, there can be a decrease in the interval between geyser eruptions. And then when there's less precipitation, there can be an increase in that time. This is not something that would be necessarily perceptible by most people, but it becomes statistically significant.

So for example, if you track eruptions of Old Faithful, you might see that on average in a wet year, they were a couple of minutes closer together than during a dry year, when they're a couple of minutes further apart.

So it's not really something that you'd notice if you were hanging out at Old Faithful, but statistically, we can see that when we look at large datasets. So it's a bit early to say whether the flood event would have that kind of effect. And, in fact, it's probably the only real effects that the flood might have on Yellowstone's hydrothermal system would be possibly a slight change in the interval between eruptions at some geysers.

A damaged road in Yellowstone National Park
Jacob W. Frank
Flood damage in Yellowstone National Park.

CT: Also in one of your recent videos, you talked about the Steamboat Geyser. It's the most active geyser in the world. But you mentioned that it hasn't been quite as active as previous years. And I'm wondering, why is that?

MP: I wish we knew why. This is one of the real neat mysteries of Yellowstone. I think many people have this perception that geysers behave in a predictable way. And some of them do; Old Faithful is kind of the classic example of that. But there are an awful lot of geysers as well that behave randomly. They don't erupt on any set schedule. They don't really have recurrence intervals. They change quite a lot over time.

Steamboat is a wonderful example of that. It will go through phases where it can go years without a major eruption. It can splash water and have minor eruptions, but there might be years between major eruptions. And then it will go into a period where there are many major eruptions in a few year time period. It did that in the 1960s. It did that in the 1980s. And it's doing that right now with a really impressive number of major eruptions since 2018.

But as to why it becomes active and then goes dormant? We really don't have a handle on that. We can say what it's not. It's not related to, as near as we can tell, precipitation. It's not related to earthquake activity or the temperature of the ground. And so the best guess is that it has something to do with the geyser's plumbing system. I like to think of these geysers as sort of like having the plumbing systems that you'd have in an old house. It simply springs a leak, then your whole plumbing system is messed up. And geysers are just sort of that way - they're fragile. There's a lot of minerals that precipitate on the conduits that carry the water to the geysers. And so they're really subject to a lot of change.

CT: So Mike, is there any other notable geological activity from the summer that you're looking for going forward that you could share with us?

MP: We are hoping to mount a neat, comprehensive expedition to this new thermal area. There is an area called Turn Lake, which is sort of off to the east of the Grand Canyon area. And a few years ago, looking at satellite data, there were some scientists who work for the Volcano Observatory that noted that there was a hot area there where there hadn't been a hot area before. In sort of diving into this and looking at it, they found that it's a new thermal area.

It had been a healthy forest in the early 2000s, late 90s. But over the last 20 years, trees have started dying, the ground has turned that chalky white that we see in a lot of thermal areas, and it's heated up to where you've got boiling temperatures just a few inches below the ground. And that really provides a neat opportunity to understand the lifecycle of these thermal areas. We've seen some of them go dormant, but we've never really seen one be born.

Caitlin Tan is the Energy and Natural Resources reporter based in Sublette County, Wyoming. Since graduating from the University of Wyoming in 2017, she’s reported on salmon in Alaska, folkways in Appalachia and helped produce 'All Things Considered' in Washington D.C. She formerly co-hosted the podcast ‘Inside Appalachia.' You can typically find her outside in the mountains with her two dogs.
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