Climate and the Cryosphere with Dr. Caitlyn Florentine

Headwaters

A conversation with Dr. Caitlyn Florentine, research physical scientist with the US Geological Survey, who studies snow and ice in Glacier. This episode was recorded in May 2023.

Glacier Conservancy: https://glacier.org/headwaters Frank Waln music: https://www.instagram.com/frankwaln/ Stella Nall art: https://www.instagram.com/stella.nall/

Overview of the park’s glaciers: https://www.nps.gov/glac/learn/nature/glaciersoverview.htm

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TRANSCRIPT:

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Lacy Kowalski: Headwaters is supported by the Glacier National Park Conservancy.

Peri Sasnett: You're listening to Headwaters, a show from the icy mountains of northwest Montana about how Glacier National Park is connected to everything else. My name is Peri, and this episode is an interview that my co-host Daniel did with glaciologist Dr. Caitlyn Florentine—about how the U.S. Geological Survey studies the park's glaciers. This episode is part of a series of conversations we've been having with a wide variety of climate change experts. These episodes don't have to be listened to in any order. Each one stands on its own. And they all focus on a particular aspect of the way the world is being altered by the burning of fossil fuels. Over the past century and a half, human activity has released enough greenhouse gases to warm the Earth's climate over one degree Celsius, with only more warming on the way. Throughout 2023, Daniel sat down with experts to talk about how that warming is altering Glacier National Park, our lives and our futures.

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Peri: Glaciers are the park's namesake. So digging into the details of the science around them feels like the heart of the park's story. I will say this is a fairly wonky and detailed conversation about glacier science. I studied geology, so I loved it. But I think no matter your background, you'll find it thought provoking.

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Daniel Lombardi: Dr. Caitlyn Florentine, welcome to Headwaters.

Caitlyn Florentine: Hello. Thank you for having me.

Daniel: Can you introduce yourself? What's your job? What do you do?

Caitlyn: Yeah. My name is Caitlyn Florentine, and I work as a glaciologist for the U.S. Geological Survey. I'm a research scientist.

Daniel: So what have you been up to for the past couple of days?

Caitlyn: I've been here in the park doing fieldwork on Sperry Glacier.

Daniel: So you were up up in the mountains for the past couple of days?

Caitlyn: Yes.

Daniel: That's exciting.

Caitlyn: Yes, We had excellent weather.

Daniel: Do you think of yourself as a glaciologist or you study the cryosphere? How do you describe what you do?

Caitlyn: I consider myself a cryosphere scientist, and the cryosphere is the portion of the earth that is frozen. So anything involving frozen water: land, ice, sea ice, permafrost, seasonal snow. So I'm a glaciologist, and I think of it from sort of a geophysical perspective.

Daniel: You approach the study of the cryosphere, you approach glaciology from a very quantitative way. What does that mean?

Caitlyn: Correct. We are interested in being very sort of precise with the numbers. So quantifying the amount of water that's entering and exiting the glacier system, for example. So rather than having a sort of description of the quality of what's happening, we also strive to put numbers to that so that we can start to be a bit more precise and exact in our understanding, which then enables us to connect to other studies and sort of systems of the of the earth.

Daniel: So what made you want to get into this field? How did you get started in the study of the cryosphere?

Caitlyn: I really love the mountains and to be in the mountains and there is a plethora of snow and ice in mountain environments. So I studied geology as an undergrad at Colorado College, and I was really fascinated by earth processes and I knew I wanted to study something on timescales that were relevant to humans. And so I made a choice for graduate school between volcanology and glaciology. And then my sort of recreational interests led to me choosing glaciology ultimately.

Daniel: Oh, that's super interesting. Cool. Yeah, because you could have studied a geology that, you know, spans millions or even billions of years, but you had a desire to keep it on a human scale or closer to a human scale anyway.

Caitlyn: Exactly. My colleagues who study seasonal snow, for example, are inspecting processes that are happening over the timescale of seconds or or hours or days. And it's sort of that opportunity to toggle the window of time that we're considering, I think really captivated me and drew me to the cryosphere.

Daniel: Oh, that's okay. That plus you want to go be able to go up into the mountains for work. So it's a good fit. Well, what makes your work important? Like, why does the cryosphere matter? Why do glaciers matter?

Caitlyn: The cryosphere right now is changing very quickly, relative to what we've observed in the last ten, twemty, fifty, a hundred years. And so that rate of change makes it really important that we not only document the changes that are occurring and understand the sort of pace of that change relative to the historical context, but also that we understand how these systems are working. Because with the rapid change of the cryosphere, so changes to seasonal snow and changes to glaciers, there are consequences downstream. So one sort of motivating example of why glaciers are important is the meltwater that glaciers provide. So a glacier sitting on the landscape will have some discharge of meltwater during the late summer months, at least in this part of the world. And that delivery of meltwater during a time of year that would otherwise be quite dry can be really critical for the aquatic habitats and for sort of broader water resources.

Daniel: I'm hearing you say kind of two things in particular there. One of them is that studying the cryosphere is important because it's changing and it's an indicator of change. So it's helpful in understanding how the world is changing. But you're also saying glaciers and the cryosphere is made of water, and water is important to people and wildlife and everything. They're valuable for that reason. Is that right?

Caitlyn: Yes, exactly.

Daniel: So I don't know if you know this, Caitlyn, but historians think that maybe one of the first euro-Americans to document a glacier here was this military guy John Van Austell, in the 1870s. But the complication is that he didn't realize he was looking at a glacier when he was. And so it wasn't until like ten years later, he came back to the same area inside what is now the park with a geologist. And they're like, oh, that's a glacier. And so then this area starts to be known as a place with glaciers. Of course, the Native Americans, the Kootenai people, the Blackfeet people, they had words describing the ice of this place. They they knew this place was full of snow and glaciers and ice for a long time before that. All of this is kind of me building up to ask you, you know, like some people might be surprised that glaciers are kind of hard to spot, surprisingly. What do you think? I mean, is that does that feel right?

Caitlyn: Yeah. So a glacier as it's now defined, it gets trickier when the ice masses get smaller. So if you're in a landscape where, there's, you're looking down a valley, and particularly at a time of year when the seasonal snow is absent. And so you're just looking at bare rock and bare ice, it will probably be quite evident what is a glacier versus what is not. Also, if you're looking at a glacier that has a lot of evidence of motion. So if you're looking at the terminus of a tidewater glacier and there are giant chunks of ice calving off into the ocean, then the sort of, all of the criteria for defining a glacier—ice that moves—is really in your face and really evident. In a landscape like Glacier National Park, the glaciers are much smaller and you have to hike a lot further into the mountains to observe them. And this has been true for the last last several centuries, if not last many thousands of years. This landscape did have big valley filling glaciers, but that was up to tens of thousands of years ago, maybe 12,000 years ago.

Daniel: So to put that another way, if you go to Alaska or if you came to this area 12,000 years ago, you're going to notice some glaciers, like they're pretty obvious because they're huge chunks of jagged moving ice. But these days in this place, glaciers are covered by seasonal snow. They're covered in rocks. They're they're smaller. It's a more complicated thing to discern. So it's not surprising that visitors today, when they come to the park or scientists a century ago maybe weren't sure at first when they were looking at a glacier.

Caitlyn: Precisely.

Daniel: Well, let's get a definition out of the way, then. Really simply what what is a glacier?

Caitlyn: A glacier is a body of ice that moves.

Daniel: Okay, simple enough.

Caitlyn: And when we talk about glaciers as moving bodies of ice, it's important to understand that, like most of us interact with ice when it's stagnant and it isn't under sufficient stress to deform and flow. But ice is actually a vicious material. So a comparable material would be honey or ketchup. So glacier ice will deform when it's under pressure. So same is how you have to hit a ketchup bottle to get the ketchup to come out of the bottle. So we sort of have two components of glacier motion. One is the ice deformation, the sort of vicious, fluid motion that I just described. And then one is the the sliding of the ice over its bed. When water gets to the bottom of a glacier, it can sort of pop the ice off its bed. And that decoupling and reduction of friction causes the glacier to move.

Daniel: Interesting. One of the things I'm taking away from what you're saying is that nature and glaciers, they don't really fit in a box. We say like this is a glacier, but in reality it's kind of a continuum or a spectrum of of movement of ice and water and rocks. Right?

Caitlyn: Precisely. And that's where science can be helpful for clarifying this complexity and ambiguity that would otherwise be difficult to navigate or interact with. So when we assign a scientific definition for what is a glacier, then we can start to categorize nature and put a more precise understanding to how much water is frozen in the landscape, for example.

Daniel: Mm hmm. All right. Well, can you give me some more basic facts about the park's glaciers? How old are they? When, when did they form?

Caitlyn: Yeah, that's an interesting question. And I think it's important when we ponder that question to understand that because the glacier is moving, it's sort of cycling ice through itself.

Daniel: Hmm.

Caitlyn: Every every year at all times.

Daniel: So because a glacier is moving ice and it's ice that's, you know, cycling through, any piece of individual ice is going to be less old than the footprint or the existence of a glacier in that area.

Caitlyn: Exactly.

Daniel: Okay. Interesting. And so let's describe that process now. I guess simply glaciers, you say, are a mass of ice that's moving. How that happens is you get a lot of snow in the winter. It compresses into ice and then it flows under its weight and melts out the other end. So it's this like conveyor belt of moving ice. How do you define or how do you describe that process, like the glacier anatomy 101.

Caitlyn: Yeah. So traditionally and sort of in our most well behaved, textbook understanding of a glacier, we have this body of ice that stretches from some high elevation zone to a lower elevation zone. And the high elevation zone typically can be described as the accumulation zone. So there's actively mass accumulating every year in that zone. So there's more snow that accumulates, then melts in the accumulation zone at high cold elevations. And so you have this conveyor belt motion and the snow that's accumulating, up high is compressing and eventually densifying into ice, which then is flowing towards the ablation zone.

Daniel: Okay, so basically it's colder up higher and it's warmer, down lower. So the higher zones, you get a lot more snow, it compresses into ice and then the glacier flows and if it's growing, it's going to keep flowing until it reaches a place that's warm enough that it melts.

Caitlyn: Precisely.

Daniel: And that's happening kind of on a seasonal basis, but it's also happening on a really much larger timescale, too.

Caitlyn: Yeah. However long it takes, those particles that are deposited in the high accumulation zone. The sort of timescale of their residence time, if you will, within the glacier will be defined by how fast the glacier is moving. So there are places on the Greenland ice sheet where it takes thousands of years for a snowflake that falls at the top of the ice sheet to make its way all the way to the margin and melt out. The glaciers here in Glacier National Park are much smaller, so the residence times would be much shorter.

Daniel: Like, it might take a snowflake that lands at the top of Sperry Glacier a few decades to reach the melt zone or the ablation zone?

Caitlyn: Precisely. And we have evidence of materials, you know, materials from the human system being deposited up high on Sperry Glacier, for example, and then melting out several decades later. So that's an indicator of the residence time.

Daniel: Yeah. So the evidence we have on Sperry Glacier for that residence time, was there a a ski? That like, got lost up on Upper Sperry Glacier and then eventually melted out?

Caitlyn: Yes.

Daniel: Okay. So do we know like, oh, this ski is from the seventies or something?

Caitlyn: Precisely.

Daniel: So you can say, okay, it takes a few decades for the for a snowflake or a ski to move through the glacier.

Caitlyn: Yes.

Daniel: Interesting. Now, we should explain that moraines are—all the little crumbs of the mountain that the glacier is like scraping off, they pile up around the edge of the glacier, and that's called a moraine. So there's. Yeah. Do you have a good way to explain what a moraine is?

Caitlyn: Yeah. So a moraine is a hill of poorly-sorted rock that's deposited on the edge of a glacier. So it's sort of a sharply crusted hill that hugs the edge of the glacier. And so it will form as those crumbs of rock and sediment are deposited along the margin of the glacier. When the glacier occupies the same position for a long period of time. However, when the glacier starts to retreat, that moraine will persist, so it acts as evidence and demarcating the stamp that of land that the ice occupied for some long period of time.

Daniel: So that's helpful. If you're a scientist without a whole lot of fancy technology a century ago, you can just like hike around in the park and you can see a glacier, but then you can see like, Oh, there's a moraine, and I can see where the glacier used to be because the dirt pile or the moraine surrounding it is far away from the ice now. So I can tell that the glacier is retreating away from where it used to be.

Caitlyn: Exactly.

Daniel: Interesting. Yeah. So there's all these clues of what the glaciers have done in the past using those clues. Do we know how? How old are the park's glaciers?

Caitlyn: Interesting question. There's been a sort of waxing and waning of glaciers in their present configuration. Now, 12,000 years ago, we have evidence, we know that this entire mountain range was encased in ice when we go further back in time. But the sort of predominant thinking and understanding, piecing together other geologic evidence is that these mountains were relatively ice free, roughly 7,000, 6,500 years ago. And then the the present modern glaciers sort of formed and have persisted. So it's it's an interesting, like the question of how old are the glaciers is actually sort of more interesting than one might think because it's not just a stagnant patch of ice sitting on the landscape. It's dynamic and it's interacting with the climate system and then it's physically flowing.

Daniel: That's super interesting. And I think that's like my take away from this whole conversation and is that these questions that seem simple, like what is a glacier? How old are the glaciers? They seem simple, but they actually have a lot of layers. And the more you dig in to it, the more complicated it gets.

Caitlyn: There are physical constraints over how fast a landscape can evolve, and that's what makes the current moment in time that we're living in right now so sort of fascinating. And what really underscores Earth science in general is we can't always look to the past for analogs of how the Earth's system responds to the sort of radiative forcing, or the mismatch between how much heat we're keeping in the Earth's system versus how much is being radiate, like vented back into space.

Daniel: Okay, I really like that because in climate change thinking and sciences, there's a lot of understanding that because we're changing the climate so fast, we can't necessarily look at the past and how the climate has changed in the past to understand how it's going to change in the future. And yet, because we can't see into the future, but we have some tools to see into the past, we end up kind of relying on inevitably and maybe over relying on evidence from the past to make guesses about the future. One thing I know that glaciologists or scientists, geologists were doing here in Glacier National Park a century ago is they're they're taking the cutting edge technology that they had a camera and they're going out near and on the glaciers and they're taking pictures. How does that come back up today? Like, what is the these historic photos? What does that allow for today?

Caitlyn: So if you have a camera today and go back to the exact same location, you can take the same picture. And the only thing that has changed is whatever's changed on the landscape. And so that repeat photography exercise provides a really objective qualitative documentation of how the landscape has changed.

Daniel: And so that was kind of a sub-project that your team at the U.S. Geological Survey started doing in the nineties as a way, Oh, let's collect up these historic photos that scientists took a century ago, and let's take the same pictures from the same vantage point. Let's take it again. We can even try and take it on the same day or about the same time of year time a month and see how how things have changed. So it's it's a very intuitive kind of science. Just what did it look like 100 years ago with a photo? And what does it look like today?

Caitlyn: Exactly. So it provides the starting point for understanding the character of landscape change. And then with our modern techniques, we can start to dig into, you know, addressing questions of what exactly is driving that change? What does that change say about what's going to happen in the future?

Daniel: The repeat photos are cool because they I mean, they answer the most very basic question: are things changing? But it's it's very qualitative. As you say, it's it's not super measurable. We can see that oh, yes, Sperry Glacier is a lot smaller now, but it's hard to measure that. Which shifts us then to the science and the approach to studying the cryosphere that your team has had for the past couple of decades. Where repeat photography is a nice communication tool and a good, you know, starting point to understand the the quality of the change. But now you're bringing Newtonian physics and really measurable science to the glaciers.

Caitlyn: Yeah, and I would say the repeat photography project is a precise scientific exercise. So it is providing a very objective, repeatable, you know, it's reproducible. And it's not, there's no sort of manipulation or prerogative or agenda that's influencing the outcome of that photograph. So it still is applying the scientific method of the objective to capture the same image from the same exact location.

Daniel: Yeah, that's important to remember that the repeat photos aren't just, you know, 100 years ago and today there's actually a lot of intervals in there. And we can repeat photos now that were taken in the eighties or the nineties. And so I think that's important. What you say about, it is a very scientific approach, but it's also a very powerful communication tool to see how things change.

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Daniel: So you mentioned this at the start, but the past few days you've been up in the park, you've been in the mountains, you've been at Sperry Glacier. So you're still venturing into the field, just like the scientists and the glaciologists a century ago. But it's a little different. Let's talk about about your past few days. What were you trying to do up there and what was it like?

Caitlyn: Yeah. So this week we approached Sperry Glacier to measure the winter mass balance. So we visit Sperry Glacier twice a year: in the fall, and in the spring. And in the fall, we're measuring how much ice the glacier has lost during the mount season. And in the spring, we're measuring how much snow has accumulated on the glacier during the winter season. And so these two measurements give us an understanding of the mass balance, or the mass budget of the glacier. So mass balance is basically the checking account for water mass on the glacier every year. And here in Glacier National Park, we started taking these measurements in 2005 on Sperry Glacier. However, the U.S. Geological Survey has been conducting this mass balance research on glaciers in North America since as early as the 1950s. So the mass balance measurements involve installing stakes on the glacier surface, were measuring snow depth and also snow density. So we're measuring how deep the snow is, and then we're measuring the the mass of the snow. And this year, we've seen a very precipitous decline of the seasonal snowpack. And so we were measuring snow densities that were quite high for this time of year. So usually spring snow densities are maybe 500, 550 grams per cubic centimeter. In the wintertime, lighter, fluffier snow. I mean, at Bridger Bowl, the sort of coldsmoke, as it's referred to, is about 10% water mass. And in a more typical winter snow pack around here, in the sort of wetter climate of Glacier National Park is maybe 30, 40% water mass. And so we were in the springtime, it's maybe 50% water mass. And this week, on Monday, we were measuring 60%. So that's quite dense. And we also were measuring snow depths that were quite shallow relative to what we've measured in the past 18 years. So it was pretty bony. The snow cover is thin,.

Daniel: Pretty bony.

Caitlyn: Probably about a month ahead in the melt season relative to sort of the typical progression.

Daniel: Let me go back to the start of this. So this has been going on since 2005 here on Sperry Glacier, but it's been going on a lot longer around the country and around the world. And when you actually go to do it, it sounds like it gets pretty complicated, but the concepts kind of simple. Basically, you're going up and you're measuring the glacier. How thick is it? How dense is it in the spring and in the fall? And then you can if you do that over time, you can see how the mass of the glacier is changing from winter to summer and over time.

Caitlyn: And it's even simpler than that because we're just measuring the surface. So we're just measuring how much mass is added and how much is subtracted. So we don't actually measure how thick and dense the glacier writ large is. We're just sampling how much mass is entering and exiting the system. So we have these little dip sticks, basically point measurements at stakes around the glacier, and that gives us the starting point for understanding that seasonal rhythm. And then we take those measurements back to the office and we then extrapolate from those points to get a glacier-wide balance. We then calibrate those measurements against measurements from space in order to account for the fact that we're not going to install stakes where there are locations that we can't access on foot. So we're not going to install them in crevasse zones, we're not going to install them at the base of avalanche paths. And so knowing that we have this bias, this sort of systematic bias that we need to correct, we calibrate against different representations of the surface mass balance. So these stake measurements, though, that I'm describing that we just collected this week for field measurements are very powerful because they provide direct measurements of the seasonal rhythm of mass accumulation and ablation.

Daniel: So some years I suppose you're seeing the glacier grow, right?

Caitlyn: So this will be the 18th year of glacial logical measurements on Sperry Glacier. And I think there's only been one year that we've seen a positive balance. And so overall, Sperry has lost more mass than it has gained in the past 18 years.

Daniel: Interesting. So you're taking these measurements of Sperry Glacier and you can see, you can graph it then and you can see it like, oh, it held kind of steady this year. Oh, it dipped a little Oh, it maybe went up a little. But overall, you're watching it trend downward.

Caitlyn: Yes.

Daniel: Now, that seems like a great system, but it also seems like a lot of physical work. You have to get up to the glacier. You have to drill these holes. You have to put in all these stakes and everything. So you're this is really only happening at Sperry Glacier. It's happening a lot of places around the world and around the country. But here in the park, you're only doing it at one glacier. And I'm guessing that that's just because because it's a lot of work.

Caitlyn: Yes, it is logistically demanding. And for that reason, continuous records like this are very rare on our planet. So of the 200,000 glaciers on Earth, only one in every 10,000 has a continuous decades long mass balance record. So it really requires a commitment to repeat these measurements in a systematic way such that there is a cohesive, uninterrupted record. Which is really powerful scientifically, because then it allows us to understand those that seasonal rhythm.

Daniel: Right, because we have repeat photos. The repeat photos can tell us, Oh, look, the glacier got smaller over the past 50 years or 100 years, but it doesn't really tell us what happened in between and these measurements. You're doing the mass balance measurements. They tell you what happened in between.

Caitlyn: Exactly. And they help us to understand how the glacier responds to years where there may have been a big melt season. So a very hot, dry summer. But if there was also a big snow season preceding that, then the glacier may actually be in balance for the year or close to balance, whereas there could be years where the summer melts And sort of the lived experience of being in these mountains in the summer isn't that noteworthy. And then when we look at the cumulative record, we can start to really sort of understand the precise connection between the glacier and the ambient climate.

Daniel: So this is a fairly simple concept. You're measuring the the snow in the spring and measuring how much it melts in the fall. In my head, one of the big changes, one of the big shifts in glaciology happens with airplanes and aerial photography. Can you explain what changes? What does that allow for?

Caitlyn: When you can view the glaciers and the mountains from an aerial perspective, you gain an understanding of how the glaciers are changing across the region.

Daniel: It's too much work to go hike up to every glacier and measure how its mass balance is changing. But once you start being able to take pictures from the air, you don't know how how the mass is changing, but you could start measuring how the area of the glaciers are changing. So in my head, tell me if this is right, aerial photography or even from satellites, I guess—that's a big shift in the study of the cryosphere.

Caitlyn: Yeah, and I'd say it's true not just for the cryosphere, but for Earth sciences in general. Our ability to view our planet from a distance. We have a time series of glacier area at various snapshots starting in 1966, and that was generated by tracing the area of the glacier from aerial images. So pictures taken from airplanes provide that baseline imagery that we can then use to trace the extent of the glaciers. And then if we have aerial or satellite imagery from the modern era, we can do the same thing and then we can quantify the area change.

Daniel: The disadvantage is you don't know how much snow is falling on the glacier in the spring and you don't know how much is melting in the fall. But the advantage is you can look at all of the glaciers in the park at once. You can take pictures of them all. So that that's a huge advantage. So I guess the basis for glacier science in this area, as I understand it, is these aerial images. You have pictures of the glaciers from above. And then that coupled with the mass balance measurements that's just happening at Sperry Glacier, but happening over eighteen years. So those two things together, you start to get a pretty good picture of how things are changing.

Caitlyn: Definitely.

Daniel: And I guess the change that we're seeing is you have these pictures from 1966, and the area is getting smaller and all the glaciers. So that doesn't tell us if they're getting thinner necessarily or thicker or whatever. But it it does tell us that the area is getting smaller. So that's by area. We're talking about a measurement squared. So like square acres or square kilometers, right?

Caitlyn: Yes.

Daniel: So another thing I want to ask you about then, aerial images, that, that starts to unlock a new way of understanding the cryosphere on earth. But with satellites, it also starts unlocking, studying the cryosphere on other planets. So as a fun piece of trivia, like other planets have glaciers, right?

Caitlyn: Yes, Other planets have ice. And it's something that is definitely a point of interest, especially for the search for life on other planets.

Daniel: Oh of course

Caitlyn: There's sort of this tagline, follow the water.

Daniel: Yeah. Which is super interesting and interesting that glaciers on earth are made of rocks and water, but in other places in the solar system, they could be made of, I don't know, nitrogen or carbon dioxide.

Caitlyn: Well, and another factor to consider is like a glacier on Mars will have different dimensions than a glacier on earth because the gravitational force on Mars is different.

Daniel: I mean, the fundamental principles are still the same. But some of the numbers are going to shift because you have different gravity and. Interesting.

Caitlyn: Exactly.

Daniel: Okay. So all of that to me reinforces the importance of of approaching the science in a really quantitative way, having like, ways to really measure the glaciers.

Caitlyn: Exactly.

Daniel: Your research is on the cutting edge of those quantitative methods.

Caitlyn: Yes. So as we've described, we have this glacialogical approach. Which is very logistically demanding and time consuming, but it provides us the advantage of having seasonal information0ù so precise, a precise understanding of winter accumulation and summer ablation. But it's for one single glacier within the mountain range. And then we have the advantage of aerial photography and aerial imagery which provides information about the aerial extent of the glacier for the entire mountain range. And so photogrammetry is a technique that sort of marries the advantage of both approaches. And so photogrammetry is basically leveraging the same sort of phenomena that happens with our eyeballs, where there are two images that are offset. And if there are offset and overlapping, we can use that two dimensional information from the aerial image to sort of recreate the third dimension. And then if we repeat that exercise, say, with aerial imagery from the 1960s and satellite imagery from 2023, we have elevation information from both those years and we can difference the elevations to calculate the vertical change. And then we have a measurement of mass change across the landscape using photogrammetry. And we can compare that to our glacialogical measurements that give us the really fine tune seasonal information.

Daniel: This is kind of blowing my mind. So so basically, by taking two offset pictures of the glaciers from the air, you can use math, geometry I guess, to make a lot of different calculations about the shape, the three dimensional shape of the glaciers.

Caitlyn: Precisely.

Daniel: That's incredible. It sounds difficult to calculate.

Caitlyn: It involves specialized expertise, and actually the technology that, and the sort of workflows that the USGS Glacier Group leverages were originally developed for NASA's missions, for the Apollo missions. So for surveying the surface of the moon.

Daniel: There's all kinds of ways that studying the glaciers is being approached. We've hinted that mostly what you're observing is that glaciers are getting smaller. But let's let's talk about that. So is that true? All the lines of evidence point towards the glaciers are shrinking.

Caitlyn: Yes.

Daniel: Hmm.

Caitlyn: It's important, though, to understand that there can also be situations. Not so much for the glaciers here in Glacier National Park, but glaciers elsewhere where the dynamics aren't necessarily so sort of the flow of the ice isn't always directly coupled to what's happening with weather and snow accumulation and ice melt in any given year.

Daniel: The simple equation is like, well, it's hot in the summer so the glacier melts. If it's not super snowy in the winter, then the summer is stronger than the winter and the glacier gets smaller. But what you're saying is, yeah, that's that's generally very true. But there's there's some real nuances happening on specific glaciers that have more to do with water under the glacier, how steep is the glacier? One I've heard about is wind, right, and drifting. That's a big thing here in Glacier National Park, right?

Caitlyn: Exactly. And so one of those local processes that you just described is the wind drifting and wind scour of snow. Snow, snow, avalanche accumulation is another example. The shading of the surface from the topographic relief.

Daniel: It's not just how much snow falls in the winter. It's also like how much snow falls and then blows onto the glacier.

Caitlyn: Exactly. That redistribution of snow is a big important process for controlling the spatial variability of snow accumulation. And and so it becomes a relatively major influence on the mass balance of these small glaciers.

Daniel: Do you know off the top of your head, kind of the ballpark numbers that we're talking about, how much snow falls in the mountains of glacier versus how much drifts on top of Sperry Glacier?

Caitlyn: That's an open question. We have some ongoing studies that have quantified those different processes, like sort of the direct accumulation versus the relative accumulation, according to, or driven by wind drifts.

Daniel: Is it something like, you know, a high elevation forest in Glacier National Park is going to get a a couple of meters of snow over the winter. But the top of Sperry Glacier, where the wind's blowing, it's going to get like dozens of meters of snow, is that?

Caitlyn: One way I like to think about this topic is there is a glacier there for a reason. So, yeah, it's been favoring snow accumulation and the persistence of that frozen water mass. And that's how the ice forms to begin with. So generally, the, the location of the glaciers particularly now in a time when I mean, this the mountain range here in Glacier National Park is sparsely glacier ice to begin with. And when I say to begin with, I mean, like since 200 years ago.

Daniel: Mm hmm.

Caitlyn: And then with climate warming and conditions trending towards a climate that's less and less favorable to maintaining glacier ice on the landscape, those local processes become increasingly influential in terms of the persistence of ice.

Daniel: One thing that people think a lot about the park's glaciers is like, Oh, they're getting smaller. So as they get smaller, they're going to melt faster and faster. Like that's intuitive. Like, we think that's common sense. But your research has found that's not really quite true, that as they get smaller, they also become more shaded, they become more sheltered and they become relatively more snowdrift, you know—and wind blown snow lands on more of the glacier. So they're almost becoming more resilient as they get smaller.

Caitlyn: Yes. This question of relative vulnerability is really interesting and we're really keen to address that very question of do we see enhanced ice loss through time as the summers get warmer and warmer, or do we see more resilience as the glaciers are relegated to these shady wind-loaded spots? And what we're finding is that that resilience and that sort of niche like refugial setting has a buffering capacity that only can go so far.

Daniel: Mmhmm.

Caitlyn: So then if we once the glaciers experience sufficient melt, it just can't keep up even with that refugial setting.

Daniel: Okay, it helps the glaciers to be shaded and snow drifted and and tucked into their little cirques. But at a certain point, if the climate gets hot enough, it doesn't matter.

Caitlyn: Exactly.

Daniel: But it does seem like it would make predicting when the glaciers are going to be gone, quote, unquote. You know, that that starts to become pretty tricky when you start realizing that it's not just a uniform rate of retreat.

Caitlyn: Exactly. And that I mean, that hits the nail on the head. It's really important to understand how much ice is there to begin with, not just in the footprint, but also in the thickness. Like we do our best to represent these spatially variable processes and models, but having direct measurements of how much where actually—how much snow is actually accumulating at a location really helps us to at least start to constrain that margin of uncertainty.

Daniel: Right. Right. So we we know through a lot of lines of evidence that all of the glaciers are generally retreating and getting smaller. But saying or predicting when they'll be gone is pretty hard to calculate precisely at this point. And it also kind of depends on how you define gone and a whole bunch of other things.

Caitlyn: That's where some of these details really start to start to matter. But every sort of scientifically sophisticated, well constrained, physically informed model of the progression of glacier ice in Glacier National Park portends the continued demise of this frozen water.

Daniel: Well, to wrap up, you were just up at Sperry Glacier. What was it like up there after a winter in the office?

Caitlyn: The snowpack at Sperry Glacier this year was lower than it has been in past years, and we were struck by how much bare ice was exposed. There's this scour spot on Sperry Glacier, where we often see bare ice even in and throughout the winter. But certainly in the spring, once the melt season has started. However, the amount of bare ice that was exposed was definitely noticeably larger than it has been in the past. The other thing that was striking is that we could hear meltwater, which isn't common for the spring trip so often the spring trip, it feels more like winter still in the Sperry Glacier Basin and it definitely felt like spring. And obviously those sort of qualitative descriptions and the experience of being a human being on the landscape, that informs our sensibility of what's happening this year on Sperry Glacier with this winter mass balance. But the measurements of snow, depth and density will help us to really quantify how much snow has accumulated on the glacier. But it really seems like this melt season is proceeding a lot faster than a sort of a typical melt season.

Daniel: Sperry Glacier's melting out fast. Wow. A lot of your job is very quantitative. A lot of these complex Newtonian physics and first principles that we're talking about, programing out computer models. But it's special. And nice to catch you today right after you're coming out of the field and just having kind of the human experience on Sperry Glacier and on a on a year when it's changing particularly fast.

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Caitlyn: Yeah, we'll see. We'll have to compare it to other years where we've seen a relatively stout winter snowpack and mild, cloudy summer. So that's the beauty of having these measurements and this record all the way back to 2005. We can really put what we're seeing this year into into context. But thank you for the opportunity to speak with you. It's really nice to catch up.

Daniel: Yeah, this was a good conversation. Thanks for coming, Caitlyn.

Caitlyn: Yeah, you're welcome.

Peri: Headwaters is funded by donations to the Glacier National Park Conservancy. As an organization dedicated to supporting the park, the Conservancy funds a lot of sustainability initiatives from solar panels on park buildings to storytelling projects like this one, the Conservancy is doing critical work to prevent the worst impacts of climate change. You can learn more about what they do and about how to get involved at Glacier.org. This show is created by Daniel Lombardi. Michael Faist, Gaby Eseverri, and me, Peri Sasnett. We get critical support from Lacy Kowalski, Melissa Sladek, Kristen Friesen, and so many good people with Glacier's natural and cultural resource teams. Our music was made by the brilliant Frank Waln, and the show's cover art is by our sweet friend Stella Nall. Check out Frank and Stella's work at the links in the show notes. Besides sharing this episode with a friend who might appreciate it, you can help us out by leaving a rating and review in your podcast app. Thanks for listening.