Podcast | How Mount Rainier will tell us when it’s going to blow

By listening closely, scientists can tell us when to worry — but these mountain songs are more than just warning signs.

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Aerial view of Mt. Rainier

Mt. Rainier dominates the landscape around Seattle. (Ritu Shukla/AP)

Looming on the horizon like a holographic ice cream cone (when we can see it), Mount Rainier draws eyes skyward everywhere in Puget Sound. But fear mingles with our fascination: Is it going to blow? And if so, when?

Thankfully, “The Mountain” is one of the most monitored volcanoes in the world, and geologists can decode what’s happening with Rainier in part by isolating the unique sounds coming from within. Their findings can tell us when we should worry — but they also reveal that our entire region vibrates with an eerie music all its own. 

For this week’s episode, we’re joined on our trek to the edge of glaciers and deep within the rock by Kate Allstadt of the U.S. Geological Survey and Harold Tobin, director of the Pacific Northwest Seismic Network.

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Complete transcript:

Anonymous speaker: [00:00:00] This episode of Crosscut escapes is presented by Forterra. Land for good.

Ted Alvarez: [00:00:06] On a clear day in the Puget Sound region from almost any unobstructed high points, you can see Mount Rainier at 14,410 feet. It's the tallest mountain in the state and the fifth highest in the country, measured by prominence -- basically how much of the mountain you can see above the surrounding terrain.

It's actually the tallest in the lower 48. By area, it's 26 glaciers contain more than five times the ice of all the other Cascade volcanoes combined. Depending on the time of day, it glows on the horizon, like a holographic ice cream cone in flavors of blue, white, pink or purple.

And if you've climbed it, you know the view from the bottom is as good as the view from the top. We're lucky to have such a sight on the horizon, but it's also scary because it's still active. And at any time, it could blow.

Welcome to Crosscut Escapes. I'm your host, Ted Alvarez. And this week I'm heading to the mountain.

The last major eruption of Mount Rainier was in 1894. Early residents of Tacoma and Seattle reported seeing explosions on the summit, but it could get much worse. 5,000 years ago, a massive eruption blew several thousand feet off the top and superheated mudslides called lahar sped across the terrain.

They erased everything in their path until they were dowsed in the waters of Puget Sound over 50 miles away. If that happened again, well, we'd be in trouble. The good news is that geologists now can understand what kind of mood Mount Rainier is in. But to do that, we have to get up close, out onto the ice.

It's only out here that you can start to understand the world that is outside our everyday existence, but still shapes all of our lives. That's what we're doing with this podcast, escaping into the wild, with questions about the big and little things that make the Northwest tick. And by asking the right questions and listening, we can find the answers.

Here at the foot of Mount Rainier, for instance, you can actually hear what's happening inside the mountain. Actually, you probably can't hear it, but Kate Alstadt can. She's a geophysicist at the U.S. Geological Survey in Golden, Colorado. And one of her jobs is to record the voice of the volcano.

Kate Alstadt: [00:02:45] A lot of the signals that we actually study are lower frequency than what people can hear.

Part of my research that I do at the U.S.G.S. Involves looking at non-earthquake seismic signals in particular. I look at landslides and debris flows and sometimes glaciers. And I use those seismic signals to study processes and also the hazards related with those processes.

Ted Alvarez: [00:03:20] The U.S. Geological Survey has multiple seismic networks deployed throughout the U.S. And they're always recording.

Mount Rainier is one of the most monitored mountains in the world. There are 11 seismic stations on the peak. And they're recording all the time, a hundred samples per second. I wanted to know what happens when they hear something odd. When you think you might be listening to the beginning of something big.

Kate told me about one time back in 2010 when she was a grad student at the University of Washington and she and her colleagues noticed an unexpected signal coming from the mountain.

Kate Alstadt: [00:03:53] They were happening like every minute, the same thing. And they're just kind of worrisome because Rainier is a really dangerous volcano, obviously; we see these repeating earthquakes a lot related to volcanic activity. So that's why we really wanted to pay attention to like figure out what they were, 'cause we didn't see any other signs that there was volcanic activity going on at Rainier, except for these repeating earthquakes.

So for the next couple of years, I was just so puzzled. Like, I wanted to get to the bottom of it. We knew that they were located somewhere right near the top of the mountain, but the seismic stations are part way down the mountain. And it's hard to understand what's going on when you're recording a small earthquake from far away, kind of like listening to your neighbors music through a wall, you know, you can't get the full story.

Ted Alvarez: [00:04:43] To get the whole story, kate and her colleagues needed to place temporary seismometers on the glaciers up above Camp Mirror, the spot where most climbers begin their ascent. So they roped in and climbed thousands of feet, lugging heavy equipment, batteries, a digitizer to record the data, solar panels and the seismometer itself, which kind of looks like a large metal coffee can. But despite their efforts, the mountain had other ideas.

Kate Alstadt: [00:05:08] I asked the lead climbing ranger at Mount Rainier National Park, where we should put this pretty expensive GPS instrument. He showed me the spot on Nisqually Glacier, where there weren't too many rockfalls and he thought it would be the safest place, but he warned me. He said that Mount Rainier does not reveal its secrets easily.

And he wasn't joking, because soon after we put that GPS instrument out, we had a series of rockfalls that happened on this glacier and they were the biggest landslides in decades.

Those took out this expensive GPS instrument that we had borrowed actually from the U.S.G.S.

Ted Alvarez: [00:05:52] We'll be back with more from the mountain after a message from our sponsor.

Anonymous speaker: [00:05:57] It takes work to sustain a place for all of us. For over 30 years Forterra has been doing that work, taking action to promote resilient communities and healthy ecosystems across our region, from planting thousands of trees each year to developing attainable housing to helping conserve over 250,000 acres of land.

The Washington based land trust has built programs and partnerships to advance conservation, restoration and community resiliency across the state. For more information, go to forterra.org. Okay. Back to the show.

Ted Alvarez: [00:06:39] So when we left Kate, she and her team were mourning the loss of some very expensive equipment.

Fortunately, the team had placed another sensor near the top of the mountain away from rockfall danger. But when they went to retrieve it, it had vanished, as if swallowed by Ranier itself, which in fact, was kind of what happened.

Kate Alstadt: [00:06:56] We just had no idea. And then a couple weeks later we got an email from some of the climbing rangers, who had actually dropped a sled down into a ravine to rescue somebody. And when they went down into the ravine, they actually found our seismic station with a solar panel and, you know, all the equipment just sitting there. They actually rescued our equipment and it was totally fine, except for the battery was a little smashed and it turns out we had a solar panel that was fabric. And so what we think happened, we can see it in the signal cause it recorded until it was yanked off the mountain ... there's this big signal of the wind kind of building up and it gets crazy windy at the top of the mountain. And so the wind's picking up and then all of a sudden you see these sharp electronic spikes of the instrument being ripped off the mountain. And then we think it parachuted down. Cause it had this fabric, we think it parachuted down into the ravine.

We were lucky that the climbing rangers actually happened to find it. And then we were able to get the data off of it and we can still, we can see it. So it was kind of like we were battling Mount Rainier to, you know, figure out what it was doing.

Ted Alvarez: [00:08:14] After collecting loads, more seismic data. Kate used an algorithm to identify whenever the quake occurred throughout time. She says it works kind of the way Shazam can identify a song in a noisy bar.

After cross-referencing that with other data like weather patterns, she found an answer to the source of the repeating earthquakes that might help everyone in Puget Sound breathe a sigh of relief.

Kate Alstadt: [00:08:36] They looked a lot like these ones that were related to a volcanic eruption, but they were actually from the glaciers and they were caused by big snowstorms, dropping a whole lot of snow on the mountain and the weight of the snow actually changed how the glaciers moved. So usually they just kind of glide along smoothly, but the weight of the snow actually caused some sticky spots to form. So as the glaciers slowly moved down the mountain, they would get stuck on these sticky spots and then kind of hang up for sometimes hours, sometimes minutes. And then as the glacier around it kept moving, then it would rupture that sticky spot over and over again. And you get these repeating earthquakes.

Ted Alvarez: [00:09:20] This time. Rainier's roiling insides. Weren't about to spew lava and smoke all over us. But still, living in the Pacific Northwest requires that we accept or ignore the fact that we're all floating on top of sea of hot magma.

Harold Tobin: [00:09:34] So, earthquakes of course are a hazard and we worry about them and we worry about the tsunamis and we worry about the volcanic eruptions, but there's no denying that the great natural beauty of the region is from exactly the same process. We wouldn't have the mountains, if it weren't for the earthquakes that have slowly produced them, one earthquake at a time over eons.

Ted Alvarez: [00:09:53] It helps if you can talk to someone like Harold Tobin.

Harold Tobin: [00:09:56] I'm a professor in the Department of Earth and Space Sciences at University of Washington. And I'm also the director of the Pacific Northwest Seismic Network. When you hear there's been an earthquake somewhere in our region, that's us. We are at the convergence of two tectonic plates.

The offshore part is called the Juan de Fuca Plate. It's actually crashing into North America or North America is running it over at very slow sort of inches per year kind of rates. The upshot of that is that we have a major earthquake fault system in between the two plates. That's the Cascadia Subduction Zone, big word, but all it really means is that it's a big fault.

The elements of the subduction zone include the mountain ranges from the coast inland, like the Olympics, but also when that plate gets deep enough underneath our feet, literally down below our feet by 50 miles or so, then melting starts to occur of the rock that's down there fueled by the fact that it's dragged water from the ocean down with it actually. And that is what fuels the volcanos of the Cascades.

So Mount Rainier and Mount St. Helens, Mount Baker and all the rest are all a line of volcanoes or a chain of volcanoes that we call arc volcanoes that are part of the subduction zone system. The entire zone is dominated by the crash of these plates. The interesting thing about the volcanoes is that the structure that you see itself, like the cone of Mount Rainier or Mount St Helen's, geologically is actually pretty young. Everything that you see at the surface is just, you know, hundreds of thousands of years old, or maybe a few million years old. And on the geologic time of thinking about things like the Cretaceous and stuff, many lifetimes of volcanoes goes into that length of time.

Ted Alvarez: [00:11:30] Understanding geologic time can be hard for our primate brains to process. An old trick is to imagine that all of Earth's history is one year long. If that were the case, humans wouldn't show up until 12 minutes before midnight on New Year's Eve. Of course, another way to wrap our heads around it was by listening to all the chaos going on under our feet.

Every rumble, crack and shift has its own signature sound. And through the magic of sound engineering, we can hear it all.

Harold Tobin: [00:11:56] Earthquakes normally are basically impulsive events. So they produce a kind of a bang or a crack and then a rumbling afterwards. It's probably more similar to lightning or maybe far away thunder and lightning than anything else. But a volcano often produces this stuff called harmonic tremor or harmonic rumbling. It's called harmonic because it actually does have tones and overtones. And so when you speed it up to the audio range, you know, you'll hear like a rising sound. It almost sounds like whale song at that point. right. And that's because it's doing similar things. It has, you know, a fundamental tone and then a bunch of overtone frequencies that give it a potentially, almost like a musical sound to it. It's unearthly or maybe it's very earthly would be a different way to put it.

Ted Alvarez: [00:12:44] A lot of the sounds coming from the guts of the earth sound erratic, strange, or even random, but sometimes a mountain can stumble into a rhythm or a pattern that borders on song. Sometimes that song can even tell us stories about an eruption as traumatic past. This is Mount St. Helens erupting in 1980. Scientists isolated repeating earthquakes that occurred at such even intervals that it almost sounds like someone beating a drum.

Kate Alstadt: [00:13:13] The signal here is from the Mount St. Helens eruption from when there were like fins of lava being extruded from the ground and there were sticky spots along the sides of that as it's being squeezed out of the earth that keep breaking over and over as the stress builds.

Ted Alvarez: [00:13:28] Earthquakes, tsunamis, fins of lava. It's all pretty scary stuff, as anyone who remembers the 1980 eruption will tell you. So how much should we worry that Rainier will surprise us with fire and fury?

Kate Alstadt: [00:13:39] I mean, it can. It has. You know, it happens. You can have eruptions with no warning, but it's not very common and especially Rainier which hasn't been active in such a long time, you know, it's kind of sealed up and old and creaky. So, yeah, we probably would have quite a bit of, you know, stuff happening that would alert us if it was waking up, but it's not guaranteed.

Harold Tobin: [00:14:04] The Cascade volcanoes, you know, they don't erupt all that often. Nobody really remembers a major abruption of Mount Rainier, 'cause it's been hundreds of years since there was one. And for them to stay quiet for even thousands of years, then having eruptive phase is perfectly normal for a volcano. So geologic time just encompasses a timescale that us humans are not so good at thinking in, but the reality is, again, that, that on geologic timescales, those are active volcanoes.

2020 has been a pretty rough year for all kinds of reasons, but in the Northwest it's been a pretty good quiet year from the point of view of earthquakes. We haven't had a lot of even small-scale felt ones, but on the other hand, it is kind of important for us to get those reminders. Now, everybody's kind of aware now that there's the possibility of a, of a giant earthquake off our coast.

What people may forget also is that coming up in February, 20 years ago, the Nisqually Earthquake was a pretty good shake and caused some real damage in our region. Another Nisqually-like earthquake is actually the most likely next damaging scale earthquake that we might experience.

It's just an important reminder that they don't come regularly spaced in time. They're random events and we always have the possibility that one could pop up without any advanced notice. It doesn't make us overdue, but the essence of randomness is that it can still have clusters and long periods in between events. You know, earthquakes are nefarious in a sense because the stress builds up silently over decades or even hundreds of years and then all the action happens in a few seconds or a few minutes with maybe aftershocks after that. But that's just the nature of earthquakes. That's what we struggle to understand.

Ted Alvarez: [00:15:44] That might not sound exactly reassuring to some of you out there, but I like to think our mountains are made just a little sharper and that much more beautiful simply because they are alive and dangerous on the inside. And I think it's comforting to know that whenever you see them, either out here on this glacier or while stuck in traffic on I-5, Ranier and all the other volcanoes are singing to us and we're listening.

Geology's not just a hundred million year old rocks and dinosaur bones it's like happening now. You know, that's kind of why I got into this field and why went to the Pacific Northwest to do my graduate studies is because there's all sorts of things that happen that maybe we can't see with the naked eye, but when we use scientific instruments, then we can really understand that, you know, we live on a dynamic planet that's continuously changing and you know, there are these hazards that seem far off, but they're not necessarily always abstract.

Harold Tobin: [00:16:54] I think the idea, you know, that most people have about geology is it's kind of, it's about the remote distant past, these unfathomable times, like 65 million years ago and the dinosaurs or something, but geology is equally something that's actually going on as an active process on the planet. It's hard to see it. You know, changing day to day, except that once in a while, we really do see it on that kind of human timescale when a landslide occurs or an earthquake or the volcano does something.

So I'm just tremendously excited by the fact that the earth is kind of in motion and alive around us all the time in ways that we can only detect by, by doing this kind of scientific sleuthing.

Ted Alvarez: [00:17:34] That's it for this week's episode. Many thanks again to Kate Alstadt and Harold Tobin. Music and mixing by the Explorerist. You can subscribe to Crosscut Escapes on Apple podcasts, Stitcher, Spotify or wherever you listen. For more on Crosscut Escapes. Go to crosscut.com/escapes. And if you like the show, please review us; it helps other people find us.

Crosscut Escapes is a product of Cascade Public Media. I'm Ted Alvarez and we'll be back with another episode next week.