A Canary in an Ice-Rich, Slumping Rock Glacier in Alaska

Emily Schwing: This is Scientific American’s 60-Second Science. I’m Emily Schwing.

How do you fight an uphill battle when the problem is moving downhill? That’s exactly what Denali National Park’s resident geologist Denny Capps is trying to figure out.

Caps: In recent years, the Pretty Rocks landslide transformed from a minor maintenance concern to really our foremost challenge.

Schwing: On a crisp fall day in September, just inside the park entrance, not much is happening inside the offices. Staff here are a week out from buttoning up the park for winter. But more than 40 miles down the park’s only road, at a place known as Pretty Rocks, things are really moving downhill, at up to a half an inch an hour.

Paul Ollig: The Pretty Rocks landslide acts much more like a glacier than it does what most people consider to be a landslide.

Time-lapse image of the Pretty Rocks slump from July 21 to August 25, 2021. During this time, the road was displaced by 21 feet. Credit: National Park Service Geology Team

Schwing: Paul Ollig is the director of interpretation and education at Denali.

Ollig: In that it is this very ice-rich material that responds to fluctuations in temperature and will speed up and slow down based on a lot of different factors, regarding the level of the ice, the temperature of the ice. And so we tend to consider the Pretty Rocks landslide to be more like a rock glacier than what we would typically consider to be a landslide.

Schwing: Ollig says the landslide is a harbinger of what else may come for the entire U.S. National Park System.

Ollig: This is, in my perspective, kind of a “canary in the coal mine” type of situation, where we’re on the front lines of these climate change impacts. But as we see more and more of these, more parks are going to be faced with other challenges that may be just as, or even more, difficult to figure out.

Schwing: Here in the heart of Alaska, much of the ground is supposed to be semi-permanently frozen for most of the year. But Denny Capps says the signs of a changing climate here have been evident for years.

Caps: Denali is a really great place to understand what that future looks like. And also, with the temperatures that we’ve had over the last few years, we’re already hitting the predictions for 2040 for here and places in the park. So we’re well ahead of the existing forecast for climate change here in the park. So that’s really got our attention.

Schwing: At Pretty Rocks, the road conditions were changing so much by the end of this summer season that park officials finally had to close it, cutting off access to a visitor’s center that offers direct views of North America’s tallest mountain and a wilderness lodge. And Pretty Rocks isn’t the only spot that’s keeping Denny Capps busy.

Caps: Yeah, certainly not. It’s all up and down the park road we’re having challenges with with permafrost. We do have a system that we refer to as the Unstable Slope Management Program, where we’re tracking over 140 unstable slopes all up and down the park road. Now, not all those are necessarily being conditioned by permafrost, but many of them are.

Schwing: When you say 140, it seems like quite a high number of places for the park to have eyes on.

Caps: It is a relatively high number, but we want to make sure and not always be in a reactive position. And some of those sites are very minor maintenance concerns—you know, things that we’ve maybe had to do a little bit of dirt work on in the past. And we’re just watching all the way up to Pretty Rocks. We’ve got like major mass turnover that is causing road closures—so a whole range of severity and kind of magnitude and frequency of impacts across the board there.

Schwing: So what’s causing all this movement? Warmer year-round temperatures combined with increased summer rainfall—it all adds up to melting what was once frozen ground.

Caps: I know that I’ve seen more intense rainfalls and flooding. We’ve had a number of rainfall records that have been set in those 10 years that I’ve been here, including some very intense rainfalls. We had what long-term Alaskan meteorologists described as the highest daily rainfall amount for a noncoastal site and in recorded history here last year. Here on the north side of the mountains, where it’s relatively dry, and we have a lot of topographic relief, we have thawing permafrost. Having rain at that level could be catastrophic for us.

Schwing: It’s kind of like pouring hot water on an ice cube.

Caps: It really is. And that’s one of the things we’ve come to recognize is—it’s really important—is this rain and, specifically, the temperature of that rain, because I think we all know that, you know, if you have warm air, that can certainly warm things up. But if you have warm water, it actually carries more heat with it, and it brings that heat down into the ground. So we’re really coming to recognize the importance of the amount and the temperature of rainfall coming down on these sensitive areas.

Schwing: Because much of Denali National Park is designated wilderness, long-term solutions are limited.

Caps: Unfortunately, we don’t want to experiment too much here. You know, this is a sensitive place. So, for example, in other locations, instead of filling it in with gravel to build up the road, you might put in Styrofoam underneath because that insulates the ground, and it’s much lighter. However, we don’t want Styrofoam coming out into our environment here and raining plastic down our rivers forever.

So, you know, we are in the process of determining exactly what it is that we’re going to do at these locations. But in general, we at Pretty Rocks are probably going to end up bridging the landslide there. It’s one of the classic ways that you deal with any type of geologic hazard like this. If you have a bull charging at you, you step aside and let it go by. You don’t square your shoulders and try to stop it. And so that’s essentially what we’re going to do—to try to do—at Pretty Rocks. 

Schwing: Denali is America’s third largest National Park. The two that surpass it in size are also located in Alaska: Gates of the Arctic and Wrangell–St. Elias. And there, too, large swaths of permafrost are at risk of melting. From Paul Ollig’s perspective, with a focus on educating and informing the public, he says there might be a silver lining.

Ollig: Having specific infrastructure, like a potential bridge over a landslide like Pretty Rocks, is a great tool for us to use. As challenging as it is, it does give us a very tangible item in which to frame the conversation about climate change impacts and to talk about solutions, to talk about what is going to be required of parks in order to adapt to changing conditions.

Schwing: Park officials are working on plans for a $55-million bridge over the slumping section of road at Pretty Rocks. Construction could begin as early as next summer. Now that fall has set in, and the park has received its first snowfall, there’s not much left to be done other than watch and wait.

Caps: We’re really curious to see how it’s going to respond through the wintertime. So last spring, when we got out with spring road opening in late March, we had about an 18-vertical-foot scarp that dropped down. So we already have an 18-foot vertical scarp at that location. So we’re certainly expecting major challenges next spring.

Schwing: As is normally the case in Alaska, it’s never quite clear what melting snow might reveal when warmer weather returns the next year.

For 60-Second Science, I’m Emily Schwing. 

[The above text is a transcript of this podcast.]

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