Solve me a river

This week on Unexplainable or Not, Sally Helm, the newest member of our team, tries to figure out what's killing mussels, why rivers suddenly change course, and what the longest river in the world is. Guests: ⁠Douglas Edmonds⁠, professor at Indiana University; ⁠Neel Dhanesha⁠, science reporter For show transcripts, go to ⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠vox.com/unxtranscripts⁠⁠ ⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠For more, go to ⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠vox.com/unexplainable⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠ And please email us! ⁠⁠⁠⁠⁠⁠[email protected]⁠⁠ ⁠⁠⁠⁠⁠⁠⁠⁠We read every email. Support Unexplainable (and get ad-free episodes) by becoming a Vox Member today: ⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠vox.com/members⁠⁠ ⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠Thank you! Learn more about your ad choices. Visit podcastchoices.com/adchoices

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:01Speaker 00

  Support for the show comes from TikTok. If you listen to this show, you probably enjoy discovering new things. It is built into the DNA of the show that curiosity is its own reward and that there's always a deeper dive to do. And one place to explore some of the topics we've covered here is TikTok. Whether it's how to forecast volcanic eruptions, strange phenomena that the James Webb Space Telescope picked up near the beginning of time, or a literal deep dive on the ocean's deepest reefs, TikTok has a wealth of fascinating videos just waiting to be discovered. Your next discovery is waiting on TikTok. Learn more at tiktok.com/discovermore.

• 0:49Speaker 01

  Are you a pet owner? Every six seconds, a pet owner in the US gets hit with a vet bill over $1,000. Always an unwelcome surprise. That's where Fetch comes in. Fetch is the most complete pet insurance for dogs and cats, according to consumeradvocate.org. You get paid back up to 90% of vet bills at any vet in the US and Canada, with claims paid back in as little as two days. Go to fetchpet.com/save right now for your free quote. That's fetchpet.com/save.

• 1:29Noam Hassenfeld?

  This is Unexplainable or Not, the game show where we finally get some answers. Today, we wanted to introduce you to one of the newest members of our team, Sally Helm. Sally has worked on all kinds of shows you've probably listened to. She's the host of History This Week from the History Channel, and she's done tons of amazing reporting for Planet Money. Welcome, Sally.

• 1:52Speaker 00

  Hello, I'm so happy to be here. It's a delight, it's an honor, and I'm scared. It's a game show, so I'm in a hot seat.

• 1:58Noam Hassenfeld?

  Okay, Unexplainable or Not is a game show where you have to guess what we know and what we don't. You're gonna hear three scientific mysteries, and you're gonna hear them from me, from my co-host, Byrd Pinkerton.

• 2:10Speaker 00

  That's me.

• 2:11Noam Hassenfeld?

  And from longtime friend of the show, science reporter Neil Dineshia. Hello. Two of these mysteries are still unexplainable, but one of them has recently been solved. After you hear all three mysteries, you're going to get a chance to guess which one you think scientists have actually recently explained.

• 2:30Speaker 00

  OK.

• 2:31Noam Hassenfeld?

  And this week, I want to start with a question we got from a listener.

• 2:36Noam Hassenfeld?

  Hi, team. Love the podcast, but there's one thing that's been bothering me for a while now. Where does your cover art come from? I'm really excited we got this question because we do have new artwork, and we've been wanting to talk about it for a while on the show.

• 2:51Speaker 03

  New-ish.

• 2:51Noam Hassenfeld?

  Yeah, new-ish. Bird is right.

• 2:53Speaker 00

  OK, you're talking about like the podcast tile, the thing that shows up next to unexplainable.

• 2:57Noam Hassenfeld?

  Yeah, and it's a river map from 1944. And we figured the best way to explain why we chose a river map was with an entire game show all about rivers.

• 3:09Speaker 00

  Obviously, the easiest possible thing.

• 3:12Speaker 04

  What else would you do? Talk about it?

• 3:13Noam Hassenfeld?

  The least amount of work possible. So first up, you're going to hear a mystery from Bird.

• 3:21Speaker 03

  Sally, hello.

• 3:22Speaker 00

  Hi, Bird. Hello.

• 3:24Speaker 03

  Sally, we've known each other for a while at this point, ever since we were-

• 3:28Speaker 00

  Oh, these many years.

• 3:29Speaker 03

  -interns at NPR, the same intern class. But I realized I've never asked you an important question all this time, which is, are you a fan of mussels?

• 3:44Speaker 00

  Mussels. OK, since we're talking about rivers, I'm going to assume we mean the kind that has shells that come together.

• 3:51Speaker 03

  We are indeed talking about freshwater mussels.

• 3:57Speaker 00

  OK.

• 3:57Speaker 03

  So the unsung heroes of rivers, as some might say.

• 4:02Speaker 00

  I love an underdog. I'm already on board.

• 4:05Speaker 03

  So basically, freshwater mussels are in all kinds of rivers in the US. And this researcher, a professor at the University of Wisconsin-Madison, this guy named Tony Goldberg, he told me that the US is actually a hotspot of mussel diversity. So we have all kinds of amazing species. We have one called the heel splitter that looks, it looks kind of like a clam, but then it has this like really sharp edge. So the name is sort of-

• 4:36Speaker 00

  Ouch. So heel splitter are- When we stop on it.

• 4:39Speaker 03

  Yes. And then there's, there's like a kind of muscle that makes part of its little like fleshy bit essentially look like a tiny fish. And then like a bigger fish will come and try to eat the fake fish and the muscle will explode eggs at the big fish. So it like carries the eggs somewhere else. Pretty cool.

• 5:01Speaker 00

  Genius.

• 5:01Speaker 03

  And honestly, I just wanted to take a minute with some of the amazing names we've given to these muscles. So you have the purple wortyback. We got the pocketbook, the flat pig toe, the muckit, the golden riffle shell, the stirrup shell, and my favorite, the turgid blossom pearly muscle.

• 5:24Speaker 00

  That is a poem in itself.

• 5:26Speaker 04

  Such a good name.

• 5:26Speaker 03

  I agree. And I think like, these muscles are just delightful, right? Like in and of themselves. But Tony was telling me that they are also fairly vital for river ecology. So they essentially filter water like it is their job. They like suck in the water, right? They pull out particulates. So that can be food, but also pathogens like E. coli, herbicides, just like chemicals in the stream. And then whatever remains, they just kind of like poop out.

• 5:54Speaker 00

  Hmm. And are they doing this to like eat and get nutrients for themselves, but then as a byproduct, they clean the water?

• 6:00Speaker 03

  Yeah. And there's this, this video from like the, the Minnesota Department of, of Natural Resources. It's this like little time lapse. And so they start with like two containers of like dirty, kind of brownish, orangish muck. One has muscles in it, one doesn't. And over the course of literally like a few hours, you watch the dirty tank, right? It remains filthy, brown, and the muscle tank just like cleans up essentially. The water becomes see-through and probably not like lovely, but certainly more lovely than it was before. So these muscles, right? They are doing all this invisible work. And then on top of that, they're helping stabilize the riverbed, they're feeding animals, they're like dead shells, provide habitats. So they're

• 6:42Speaker 03

  just this like amazingly helpful, delightful creature that we have the privilege of having in our rivers. Except unfortunately, for a while now, some specific mussels have been struggling. So actually, some of the species that I told you about, like the flat pig toe, the stirrup shell, also unfortunately, the turgid blossom pearly mussel.

• 7:11Speaker 00

  No, bird.

• 7:12Speaker 03

  Yes, I am very sorry to say. They were all declared extinct, actually, in 2023 because I hadn't been seen for decades. Some other species are endangered. But also, Tony says, sort of more recently, researchers have started seeing these massive mussel die-offs. A whole bunch of mussels will just like die over the course of even just one season. So he calls it like a, an ecological emergency. And Tony is an epidemiologist, so he studies like pathogens in animals, everything from monkeys, robins, fish, mussels. And he joined like a whole team of people that wanted to

• 7:57Speaker 03

  investigate this. He said they called themselves the the Delta Strike Force of Mussel Interested Scientists. But in Tony's case, he's looking to see if the problem could be a pathogen of some kind, a bacteria, or a virus, or a parasite.

• 8:16Speaker 00

  Makes sense. Mussels dying, maybe they're getting sick from something in the water.

• 8:19Speaker 03

  Exactly. And so they kind of had to start from scratch, he told me, in in some ways. Like, he said they had to figure out how to identify even that a mussel was sick.

• 8:31Speaker 00

  Because if you just look at its shell, you're like, oh, that's a mussel. And you'd have to see it.

• 8:35Speaker 03

  Well, yeah, they they kind of just like open and close and like hang out. So they had to sort of figure out, like, how do you identify, like, sickness in a mussel? And there were a lot of viruses in these mussels, for example. But he had to figure out, like, were any of those a problem? Are there viruses or bacteria or parasites that are in the sick or dead mussels, but not in the healthy ones? And so basically, in order to kind of preserve our rivers as we know them, right, in order to keep these incredible animals in them that literally keep them clean for us. Researchers like Tony are still hunting for the culprit here,

• 9:18Speaker 03

  right? The, the smoking gun that is killing off these muscles in these big die-offs. And they have not found it yet.

• 9:28Speaker 00

  Okay.

• 9:28Speaker 03

  Unless they have.

• 9:35Speaker 00

  Please tell me that we know what is after our dear muscles.

• 9:41Noam Hassenfeld?

  What, what do you think, Sally? Do you think we know? Or do you think it's still a mystery?

• 9:47Speaker 00

  You know, I feel so much like I want us to know that I'm wondering if we don't, you know? Like, I'm wondering if I just have optimism and hope in my heart that we have figured it out. And it seems like we should be able to, but I'm intrigued that it's hard to even know what a sick muscle looks like. That makes me worry that maybe we don't know enough about muscles to really answer this question. So I'm gonna say, maybe as emotional self-protection, that we don't, we don't know.

• 10:17Noam Hassenfeld?

  I love the way you're thinking about it.

• 10:20Noam Hassenfeld?

  So no need to lock in your answer yet, just have it float around in the back for now.

• 10:24Speaker 00

  Great, as if on a river.

• 10:25Noam Hassenfeld?

  And Neil is up next. He's got another mystery for you about rivers.

• 10:30Speaker 00

  All right.

• 10:31Speaker 04

  Hello. We were not interns at NPR, and this is the first time I'm meeting you.

• 10:35Speaker 00

  I've never met you before. Hi.

• 10:37Speaker 04

  Hello. Well, since I've never met you, I also don't know where you live. Do you live near a river?

• 10:42Speaker 00

  You know, I live in Brooklyn, so kind of near the Hudson. And I grew up in Los Angeles, which is like, you know, ocean country. So rivers are a little less known to me overall.

• 10:52Speaker 04

  So I also live in Brooklyn. And I think one thing I've taken for granted in Brooklyn is that the East River and the Hudson River stay where they are. Like, the amount of water in them might change, like, there might be like a flood or a drought, and that could sort of affect how much water is in the river. But the course, for the most part, is pretty stable. And they're so stable that we build entire cities around them, right? Like, New York exists, and these two waterways have sort of been a major part of the shape of the city. But sometimes rivers can dramatically change course by as much as hundreds of miles. And it's not like just a river meandering one way or the other a little bit and then coming back to where it was before.

• 11:33Speaker 04

  It like fully moves and it leaves a dry channel behind where it was before.

• 11:39Speaker 00

  What?

• 11:40Speaker 04

  I know, right? So imagine if the Mississippi River, when it hit Louisiana, instead of going east and then down to Baton Rouge and New Orleans, it went west.

• 11:49Speaker 00

  Like zoink, different course.

• 11:51Speaker 04

  Exactly. And it would completely transform the cities. Like New Orleans would be in a lot of trouble. I mean, the entire state would. And this actually almost happened back in the 1960s. The Army Corps of Engineers built this huge floodgate on the Mississippi so that it wouldn't change course and join another river called the Atchafalaya.

• 12:13Speaker 00

  Okay, it was trying to change course and the Army Corps of Engineers was like, we can't allow this. And they were kept apart by the Army?

• 12:20Speaker 04

  They got kept apart by the Army Corps of Engineers. This tale of river love was stopped.

• 12:25Speaker 00

  Yeah, it's a star-crossed love story. I'm hooked.

• 12:29Speaker 03

  Question, would they have had to rename one or the other of the rivers if they merged?

• 12:35Speaker 04

  That's a good question.

• 12:36Speaker 03

  Do they hyphenate?

• 12:38Speaker 00

  But that just kicks the can down the road.

• 12:41Noam Hassenfeld?

  What if that river meets another river bird? Come on.

• 12:44Speaker 00

  Exactly.

• 12:45Speaker 03

  You know what? This is unimportant.

• 12:50Speaker 04

  So anyway, these like dramatic changes in course are called avulsions. And they can be pretty catastrophic. I talked to Douglas Edmonds, who's a professor at Indiana University. And he told me avulsions have caused some of the biggest river floods in the history of our planet. There's a really recent tragic example of this, when the Indus River in Pakistan moved west by 30 to 60 miles back in 2010. And that flooding affected about 20 million people and almost 2,000 people died.

• 13:20Speaker 00

  Wow.

• 13:21Speaker 04

  I know, it's really brutal.

• 13:23Speaker 00

  Right, because we don't expect rivers to change in this way. And like you said, we've built whole cities and whole neighborhoods, and people have their lives in a place where they didn't expect a river to be.

• 13:31Speaker 04

  Yeah.

• 13:32Noam Hassenfeld?

  And you want to be like right up against the river, right, to use it as best as you can.

• 13:37Speaker 04

  Right, there have historically been so many benefits to being on a river, right? It's great for trade, it's also a good water source. If it's not super polluted, it's also just kind of nice to be by a river. And so, you know, that particular instance in Pakistan, it happened during a really heavy monsoon storm. So it was especially quick. But most avalions, Doug told me, are slower. They take decades or even centuries. So if we notice it in time, we can build things like that floodgate in Louisiana, which is called Old River Control. And if anyone's interested in reading more about that, there's a great essay by John McPhee called Atchafalaya. I love it so much that I talk to people about it unbitten all the time. But the point is that, you know, in either case, whether it's the slow gradual avulsion or the fast moving one caused by a storm like in Pakistan, the stakes are really high.

• 14:23Speaker 04

  But it's still kind of a mystery. Like, we don't really know what causes these avalions to happen. Unless we do, and we can do something about it.

• 14:36Speaker 00

  Um, um, um. On this one, I'm gonna say we do. I just feel like we know. I feel like rivers are so big, the stakes are so high. I mean, it is crazy that this happens. Like, imagining the zoink, the turning left instead of right, or right instead of left. It does feel like a magical thing. Yeah, I'm gonna say we figured this one out. I'm gonna say someone knows why.

• 15:03Noam Hassenfeld?

  Okay.

• 15:04Speaker 03

  But you do have to remember that this was unexplained for a long time.

• 15:09Speaker 00

  No, it's so true. As I was saying that, I was like, we've had rivers, we've had rivers all the time.

• 15:14Speaker 04

  Like, the end of this one was like, not that long ago, you know?

• 15:17Speaker 00

  Yeah.

• 15:18Noam Hassenfeld?

  Hold your thought for now. There might be another mystery coming, or actually, there is another mystery coming from me right now. And mine starts with a seemingly simple question. What is the longest river in the world?

• 15:35Speaker 00

  Uh, I don't, I don't, the Nile.

• 15:39Noam Hassenfeld?

  The Nile, great answer. That is basically what everyone would say. It's what the US government says. It's what the Guinness Book of World Records says. It's what Wikipedia says. But scientists are starting to wonder whether the Amazon might actually be longer.

• 15:55Speaker 00

  Hmm, that was my number two.

• 15:57Noam Hassenfeld?

  I, it's, it's, you're, you're very good on river length, just intuitive river length.

• 16:02Speaker 00

  I have a deep intuition of that.

• 16:03Noam Hassenfeld?

  So when I heard about this, I was sort of surprised that it was even a question.

• 16:08Speaker 00

  Right, right. Because like, can't we just measure?

• 16:10Noam Hassenfeld?

  Can't you just measure the river, right?

• 16:12Speaker 00

  Very big tape measure to the Amazon.

• 16:13Noam Hassenfeld?

  Yes, we see where the river is, just measure it. So I called up this explorer, Yuri Sanata.

• 16:20Speaker 00

  An explorer?

• 16:21Noam Hassenfeld?

  An explorer. I, I'm so excited to just like interview an explorer, especially because he has this expedition that he is planning to go the entire length of the Amazon on a boat.

• 16:33Speaker 00

  Wow.

• 16:34Noam Hassenfeld?

  And.

• 16:35Speaker 04

  And it has a really big tape measure on it.

• 16:36Noam Hassenfeld?

  Yes, it's gonna just leave one end at the beginning of the Amazon. And then the snapback is just really dangerous. But he told me there's two things that make answering this question really hard. So one is deciding how to measure it. And two is deciding where it starts and ends. So let's just start with how to measure it.

• 16:58Speaker 00

  Yeah, do you mean like what tool to use? Or like, do we go with meters or feet?

• 17:02Noam Hassenfeld?

  So it's related to something called the coastline paradox. Basically, like rivers, coastlines are really tough to measure. So if you look at Norway and compare it to Russia on a map, Russia looks like it has this huge coastline. Norway is just this little country hanging out at the top of Europe. But when you zoom in, you'll see that Norway has all of these things kind of etching into the land, these fjords. And when you follow every little nook and cranny into Norway, turns out Norway actually has the second longest coastline in the world, much longer than Russia, longer than the entire European Union. And it's because when you zoom in, these squiggly lines get longer.

• 17:45Noam Hassenfeld?

  And it's the same thing with rivers. So from above, the twists and turns, they get smoothed out. You see like, okay, the river is just this kind of line. But when you zoom in, you see it takes all of these little twists and turns. And the question is, how far should you keep zooming in? Should you zoom in to where you'll be measuring every twist and turn with a ruler? Or whether you'll be measuring every twist and turn with a microscope? The further you zoom in, the longer the river gets. It's honestly almost like a fractal. You could zoom in to the point that this question becomes absurd, and there's a situation where it could become like an infinitely long river. That's probably beyond where we need to go. All rivers are actually the same length. All rivers are the same. Trick question.

• 18:28Noam Hassenfeld?

  And then also, like, rivers are changing, they're moving. It's tough to get a consistent measurement, just like Neil was saying.

• 18:33Speaker 00

  It's like, you're gonna have to approximate, like, what level are you approximating?

• 18:37Noam Hassenfeld?

  Exactly. Any, any way you measure it is an approximation, right? You just have to decide what approximation you're comfortable with. But that's only one of the big issues. The next one is where are you measuring from? So you might think, okay, just go to the beginning of the Amazon, right? But there's no one beginning. There's a bunch of little rivers that come out of the Andes and feed into the Amazon. You know, people used to think the furthest was the Maranyon River in northern Peru. But then, a few years ago, explorers followed another tiny river from the Amazon, and they realized it went further away. This was the Montaro River. And Yuri says that at the source of the Montaro River, it just looks like some water dripping from a rock in the mountain.

• 19:21Speaker 00

  That feels like the beginning.

• 19:22Noam Hassenfeld?

  I mean, it could be, but this is just the furthest source they've got so far. There could be another river that they haven't found that's just really tiny and twisty that could actually go longer and start even further away. But it's so remote, it's so high up, we're talking like 15,000 feet up in the Andes. It's so high up that Yuri said that for the entire first month of his expedition, he's gonna be whitewater rafting down the mountain for a month.

• 19:49Speaker 00

  This is why we get to have explorers.

• 19:51Noam Hassenfeld?

  Yes, this is why we still, in 2025, we need explorers. And then, the same issue happens at the end of the Amazon. It's less complicated, but when the Amazon hits the Atlantic, it runs through a series of islands right at the Atlantic where the land kind of starts to break up. And there's this question, does the river follow along the side of the islands? Or does the river end when the islands start? And so we're left with this situation where right now, most people think the Nile is the longest. One African scientist got in touch with Yuri because he heard about his expedition was like, please, please don't take the record from us. But Yuri is plowing ahead on his expedition unless he's already done his expedition and we do know what is the longest river and I am pulling a fast one on you.

• 20:37Speaker 00

  I'm gonna say, and I don't think Yuri would agree with me, but I'm gonna say this is not an answerable question at all. You've convinced me that all rivers are the length infinity. It's all an approximation anyway.

• 20:48Noam Hassenfeld?

  Oh, so your answer is there's no longest river?

• 20:51Speaker 00

  My answer is there's no longest river. Yeah, I mean, one of my high school teachers once told me the difference between physics and math is if you're walking towards a wall in math, you never get there. Like if you're going halfway towards the wall, you just always go halfway again. But, you know, in physics, eventually you get there.

• 21:09Speaker 03

  Zeno's River.

• 21:10Speaker 00

  Zeno's River. Exactly. They're all Zeno's River.

• 21:13Noam Hassenfeld?

  I mean, it's a creative explanation. You will have to ask yourself, did we choose to answer this question with math or with physics?

• 21:21Speaker 00

  Yeah, exactly. I mean, I think we don't know. I think we don't know this one.

• 21:25Noam Hassenfeld?

  Okay, you got three mysteries. You got the mystery of muscles. You got the mystery of rivers changing course. And then you got the mystery of the longest river. They're all unexplainable, or at least they all were unexplainable at one point. One of these mysteries has recently been figured out. And you're gonna have a chance to make your final guess after the break.

• 21:52Noam Hassenfeld?

  Support for the show comes from Sonos. Hey, Sonos, give me some music.

• 21:58Noam Hassenfeld?

  All right, one of life's great mysteries. You're listening to music in the living room, but you gotta grab something from the kitchen. You don't want to take the speaker with you, but you also don't want to miss that beat drop. And this is where I introduce you to the magic of Sonos. Sonos sent me a couple of speakers to try out, so I've got to move two here in the living room. And then I walk down the hall.

• 22:23Noam Hassenfeld?

  I get in here to the kitchen and I got a brand new Sonos Play right here on the counter. I can open the fridge, grab a seltzer.

• 22:41Noam Hassenfeld?

  And yeah, I didn't miss a second. And I can make each speaker louder or softer in the Sonos app, or if I'm using AirPlay, so I can make it louder in the kitchen without blasting whoever is still in the living room. It's all just easy and it sounds amazing. These speakers are crisp. They've got great bass. And I'm especially impressed with the new Sonos Play. It packs this like truly awesome sound in a much smaller size. So I don't know, if I want to head outside for a minute. It's super easy and yeah, pretty nice out. Visit sonos.com and build your system.

• 23:25Noam Hassenfeld?

  Sonos, love the sound, feel the system.

• 23:32Speaker 00

  Support for the show comes from Quince. Fall is my absolute favorite season. I love fall colors. I love fall leather. I love the specific light you sometimes get on a fall afternoon. And I really love fall clothes, which Quince has. This fall, Quince is offering pieces with premium materials like 100% Mongolian cashmere, organic cotton and merino wool. The styles are timeless, versatile, and designed to become the dependable pieces you reach for day after day. Their 100% Mongolian cashmere sweaters start at just $60, giving you the softness and quality you'd expect from a luxury brand without the luxury price tag.

• 24:15Speaker 00

  I think my favorite thing about Quince clothes is that they're just good wardrobe staples. I got three black shirts from them, each in a slightly different style, and they are just correct. They fit the way they are supposed to. They look nice. They feel nice. And they go well with the rest of my closet. Find your next fall favorites at Quince. Download the Quince app for app exclusive offers or go to quince.com. Get free shipping on your order and 365 day returns, now available in Canada and the UK too. And when Quince asks you where you heard about them, please let them know it was unexplainable. It's a great way to support the show.

• 24:57Speaker 01

  Are you a pet owner? Every six seconds, a pet owner in the US gets hit with a vet bill over $1,000. Always an unwelcome surprise. That's where Fetch comes in. Fetch is the most complete pet insurance for dogs and cats. According to consumeradvocate.org, you get paid back up to 90% of vet bills at any vet in the US and Canada with claims paid back in as little as two days. Go to fetchpet.com/save right now for your free quote. That's fetchpet.com/save.

• 25:46Noam Hassenfeld?

  Okay, it's unexplainable or not. Sally, welcome back.

• 25:49Speaker 00

  Hello.

• 25:51Noam Hassenfeld?

  Businesslike. One word.

• 25:56Speaker 03

  So happy to be here.

• 26:00Noam Hassenfeld?

  No, Sally, I feel like Sally's got her game face on, you know? She's ready.

• 26:04Speaker 03

  Sally is the person who you're playing Parcheesi. And she's like, this is actually not a joke. And I am mad at you.

• 26:12Noam Hassenfeld?

  I thought your go to game there was Parcheesi. I don't even think I've ever played Parcheesi. What is Parcheesi?

• 26:19Speaker 03

  No, it's like one of the most fit. If you go, I went to like a board game exhibit and like half the board games were Parcheesi.

• 26:26Speaker 00

  I think it is the most classic game and also I've never seen it.

• 26:29Noam Hassenfeld?

  This is what I'm saying, Sally.

• 26:31Speaker 03

  All right, well, later as team bonding, we're all playing Parcheesi. And it will probably start a fight, presumably with Sally, because she takes games very seriously, apparently.

• 26:44Noam Hassenfeld?

  Anyway, so we've got three mysteries for you to choose from. Only one of them has been solved.

• 26:51Noam Hassenfeld?

  Mystery one, what is killing freshwater mussels? Mystery two, why do rivers change course, sometimes by hundreds of miles? And mystery three, what is the longest river in the world? So Sally, without making your final guess just yet, what are you thinking? What's going on in your head?

• 27:13Speaker 00

  I mean, as we know, my initial impression was we know about the rivers. We don't know about the mussels. We know about the avults. We don't know about the muscle killer. And the question of the longest river has become a philosophical one in my mind that is unanswerable. I think what I'm feeling now is that maybe actually we know about the mussels. Because Bird is right. The river question has been unsolved for so long that maybe it's still unsolved. Maybe it's still just like a giant geological mystery.

• 27:45Noam Hassenfeld?

  I would say that when you're playing a game show, you might not want to take advice from the person trying to trick you.

• 27:53Speaker 00

  That's a great point.

• 27:56Speaker 04

  This is high level Partizzi.

• 27:58Speaker 00

  I'm playing checkers. Bird's playing Partizzi.

• 28:03Speaker 03

  I'm playing four dimensional Partizzi.

• 28:05Speaker 00

  OK, I'm gonna say that we have found why the mussels are dying. We know the answer to that.

• 28:15Noam Hassenfeld?

  OK, mussels dying, final answer?

• 28:20Speaker 00

  Yes.

• 28:22Noam Hassenfeld?

  OK, here's the answer.

• 28:26Speaker 05

  It's almost as if you live in New Orleans, but over the course of a month, the river has disappeared. It's run dry. The river channel is still there, but the water is gone.

• 28:41Speaker 00

  Hey.

• 28:47Noam Hassenfeld?

  Oh, I'm sorry. I wish people could see Sally's face looking like just and Bird just dancing like.

• 28:58Speaker 00

  Wow. Okay, so we've solved this long running geologic mystery that we've been struggling with for centuries. Neil, what do we know?

• 29:07Speaker 04

  Yeah.

• 29:08Speaker 00

  Why does this happen?

• 29:09Speaker 04

  So the person you just heard is Doug Edmonds, who's that professor at Indiana University I mentioned earlier. He's one of the co-authors of a paper about why avalions happen.

• 29:17Speaker 05

  So there are really two competing ideas for why river avalions occur. One is simple and one is a little more complex.

• 29:27Speaker 04

  The simple idea is that water likes to go downhill. And so if the water finds a steeper slope than the one it's currently on, it'll go that way instead. Doug calls that gradient advantage.

• 29:39Speaker 05

  So the more complex explanation has to do with the fact that especially near coastlines, where a lot of avalions tend to occur, rivers are depositing sediment on their beds.

• 29:50Speaker 04

  They're full of sediment, they're carrying it downstream, some of it settles at the bottom of the river as it goes along.

• 29:56Speaker 05

  If you imagine, just like you jack up a car with a jack, that sediment kind of brings the river up above its surrounding floodplain.

• 30:05Speaker 04

  That is what Doug calls super elevation, which is just one of those fantastic scientific names that everything should have. And we've known for a while that sediment can cause super elevation. We've known that since, I think, the 1940s or so. But it's been historically really hard to measure super elevation. Kind of related to what Noam was talking about earlier, there's like all kinds of factors that makes it hard to measure what the surface of a river actually is like. But that is exactly what Doug and his team did. And they did it with space lasers.

• 30:38Speaker 05

  Yep, space lasers.

• 30:40Speaker 00

  I did not know space lasers were coming.

• 30:43Speaker 04

  I, you know, I didn't either. But yeah, they used LiDAR from these NASA satellites to do two things. First, they actually measured the surface of rivers as they are now all over the world. But they also used the satellites to find evidence of avalions that happened over the past 30 years. And they found a bunch that they had no idea existed before.

• 31:03Speaker 05

  We ended up realizing that both super elevation and gradient advantage actually work together to create the best predictor we now have of when a river avulsion will occur.

• 31:15Speaker 00

  Wow.

• 31:16Speaker 04

  And, you know, I think like in, in a lot of the US and Europe, our rivers are really engineered. We have things like dams and levees and that floodgate I mentioned earlier. But we also have seen how they fail. You know, 20 years ago, very famously, the levees on the Mississippi failed when Hurricane Katrina hit New Orleans. And similarly, in the Indus River in Pakistan, part of the reason that the avulsion happened is because a levee failed. So what Doug says actually is that the best sort of solve for avalions, if you're going to go down the engineering route, is making spillways, which essentially divert the flow of the river when it's in flood and sort of send some of that water and sediment into like a floodplain or somewhere else that like, you know, you can safely sort

• 31:59Speaker 04

  of just dissipate some of the force. But, you know, that kind of infrastructure is expensive. And for most of the rest of the world, which might not have the capacity to build that infrastructure, or the time, frankly, these hazard maps could help people figure out where the most urgent places to build the most targeted kinds of infrastructure could be. Or at the very least, educate them on the risks, which is especially relevant now, because climate change is making flooding worse. There's more water in the atmosphere. When storms happen, they dump more water on things like rivers that then could flood in the way that the Indus River did. And so that data could just save a whole lot of lives.

• 32:36Speaker 00

  Well, so we know why rivers change course and we can do something about it. This is good news, Neil.

• 32:41Speaker 04

  Hmm.

• 32:43Noam Hassenfeld?

  So just to just to circle back to that initial question we got at the beginning. We started the show with this question from a listener about why did we pick our cover art? And our cover art is a map from 1944 of all the courses that Mississippi River has taken over thousands of years.

• 33:05Speaker 00

  Wow, it's an evolution map.

• 33:07Noam Hassenfeld?

  It's called something like the Mississippi Meander Map. It's basically the map of Neil's mystery. And the basic reason I wanted to do a game show just to answer this question is to show how many mysteries there are in rivers, these things that maybe we take for granted, how much we still don't know. But Bird, you were the one who found this specific 1944 river map. And I wonder if you could say a bit about what got you so excited about it?

• 33:34Speaker 03

  Yeah, I think we were looking at a lot of really beautiful, old scientific imagery that is just, you know, at the crux of sort of science and art, which is where I would like to hope that our show is. But I think what I really loved about this, as we were all talking about it, was this idea of like, science too, is this thing that is constantly sort of carving new channels for itself and finding new directions and new spaces and is like both shaped by the environment around it and shaping the environment around it.

• 34:13Speaker 03

  And so this particular image just sort of felt really representative of just some of the themes of our show.

• 34:24Noam Hassenfeld?

  I don't know, for me, I guess it reminds me that all the stuff that we take for granted, all of these things that you just, you look in the world and you see a river there and you think that that just must be where it's always been. And it's kind of like the scientific knowledge we tend to take for granted, that it's just that way because we figured out the right thing. And when you see the map that the Mississippi River has taken over thousands of years and you see that it's sort of gone in different ways and traced different patterns. To me, it tells you how hard it is to get to where we are today in terms of scientific knowledge and also Rivers. And it also tells me that like so many of the things that we take for granted are not

• 35:06Noam Hassenfeld?

  written in stone and are kind of always evolving.

• 35:10Speaker 03

  I also like that Joey, the graphic designer we were working with, changed the colors such that it sort of also looks like guts and worms. But that is perhaps the last.

• 35:21Noam Hassenfeld?

  We do, we do like worms.

• 35:22Speaker 03

  Theoretically advanced take on the logo.

• 35:28Noam Hassenfeld?

  Okay. One last thing before we leave. Sally.

• 35:31Speaker 00

  Yes.

• 35:32Noam Hassenfeld?

  Even though you didn't win, you were so close, though.

• 35:35Speaker 00

  I was so close.

• 35:35Noam Hassenfeld?

  Until Bird sabotaged you.

• 35:40Noam Hassenfeld?

  Even though you didn't win, we do have a consolation prize for you. We have a tradition on our game shows that I write a song about the revealed mystery. In this case, Rivers changing course. So I'm gonna play it for you.

• 36:00Noam Hassenfeld?

  When I was young, it was paradise. Growing upright by the riverside, by the riverside.

• 36:18Noam Hassenfeld?

  But one day I looked for tilapia and I couldn't find where the river was, where the river was.

• 36:37Noam Hassenfeld?

  How'd my river abandon me? Maybe lasers from space will see the evulsions of yesterday. How my river curved away.

• 37:13Noam Hassenfeld?

  When I was young, it was paradise. But I've made my tilapia sacrifice. No tilapia. Like. Anymore. What? I love this so much. Noam, were you like, did you write this while waiting for dinner? What is this? What is the tilapia? I call it no tilapia.

• 37:43Speaker 00

  Into the canon of River Songs it goes.

• 37:47Noam Hassenfeld?

  That's it for Unexplainable or Not. Thank you to our guest Sally Helm.

• 37:52Speaker 00

  You.

• 37:52Noam Hassenfeld?

  To our presenters, Byrd Pinkerton.

• 37:54Speaker 00

  That's me.

• 37:55Noam Hassenfeld?

  And Neil Dinesha.

• 37:56Speaker 04

  That's me.

• 37:57Noam Hassenfeld?

  And thanks to our audience for joining us. If you have a mystery or a solved mystery you want us to tell on an upcoming game show, let us know. You can write us at [email protected]. We read all the emails. And that is it for Unexplainable or Not. Goodbye.

• 38:13Speaker 00

  Woohoo.

• 38:22Noam Hassenfeld?

  This episode was reported by Byrd Pinkerton, Meredith Hadnot, and me, Noam Hassenfeld. I also wrote the music. Production from Meredith, who also runs the show. Editing from Joanna Solotaroff. Guessing from Sally Helm. Thank you, Sally. Mixing and sound design from Christiane Yala. Fact checking from Melissa Hirsch. And Jorge Just and Julia Longoria are our editorial directors. Special thanks this week to Kim Moss for turning Bird on to freshwater muscles and to Joey Sendai Diego for designing our artwork. Thanks, as always, to Brian Resnick for co-creating the show, along with me and Bird. And if any of you out there have thoughts about the show, send us an email. We're at [email protected].

• 39:04Noam Hassenfeld?

  You can also leave us a review or a rating wherever you listen. It truly helps us out. And if you're into supporting the show even more, and all of Vox in general, you can join our membership program. You can go to vox.com/members to sign up. And right now, there's a sale, 30% off on an annual membership. Check it out. Unexplainable is part of the Vox Media Podcast Network, and we'll see you next time.

• 39:32Noam Hassenfeld?

  When I was young, it was paradise. But I've made my tilapia sacrifice. No tilapia anymore.

• 40:00Speaker 00

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