In short
A “game show” episode about river mysteries, plus a listener question about the show’s cover art.
Guests/backgrounds
Sally Helm, host of History This Week (History Channel) and former Planet Money reporter; co-hosts Bird Pinkerton and Neil Dinesha (science reporter).
Key claims
Freshwater mussels filter river water by removing particulates and contaminants (including E. coli, herbicides), stabilize riverbeds, and provide habitat; some species were declared extinct in 2023, and researchers are investigating “massive die-offs” but haven’t found the cause yet. River avulsions (course shifts by hundreds of miles) are explained by “gradient advantage” and “super elevation” from sediment; researchers used NASA satellite LIDAR to measure river surfaces and identify recent avulsions. The “longest river” question is treated as unanswerable due to measurement and source/end ambiguity.
Notable examples
“Heel splitter” mussel; 2010 Indus River shift in Pakistan (30–60 miles; ~20 million affected; ~2,000 deaths); Mississippi “Old River Control” floodgate; Montaro vs Marañon source debate for the Amazon.
Written by AI. May contain mistakes. Listen to the episode to check what was said.
Chapters
Tap a time to open that second in VOListener Question: Cover Art Origins
1:40 to 2:52
Discussion on the podcast's cover art and the choice of a river map.
“Okay, Unexplainable or Not is a game show where you have to guess what we know and what we don't.”
Freshwater Mussels: Unsung Heroes
2:52 to 6:34
Exploration of the role and issues surrounding freshwater mussels in rivers.
“So, first up, you're going to hear a mystery from Bird.”
The Mystery of River Avulsions
6:34 to 14:00
Examination of river avulsions, their impacts, and the ongoing mysteries surrounding them.
“But also, Tony says, sort of more recently, researchers have started seeing these massive muscle die-offs.”
Mysteries of River Avulsions
14:00 to 15:10
Exploring why river avulsions happen and the mystery surrounding it.
“like in Pakistan, the stakes are really high.”
The Longest River Debate
15:10 to 20:32
Discussing the complexities around measuring the longest river in the world.
“That is basically what everyone would say.”
Unanswerable Questions
20:32 to 21:19
Examining philosophical implications of measuring rivers and their lengths.
“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.”
Teasing the Mysteries
21:19 to 21:35
Introducing three mysteries related to rivers and mussels before a break.
“One of these mysteries has recently been figured out, and you're going to have a chance to make your final guess after the break.”
Teasing the Mysteries
22:42 to 23:55
Introducing three mysteries related to rivers and mussels before a break.
“The other day I was out shopping and picked up a cute dress, but I wasn't totally sure it was my style because I've been kind of moving away from sleeveless stuff lately.”
Teasing the Mysteries
25:06 to 25:29
Introducing three mysteries related to rivers and mussels before a break.
“This is a job for Indeed-sponsored jobs.”
Unraveling the River Mystery
28:01 to 28:46
Learn about the mystery of the disappearing river and its implications.
“It's almost as if you live in New Orleans, but over the course of a month, the river has disappeared.”
Show all 15 chapters
Understanding River Avulsions
28:47 to 31:08
Discover the scientific explanations behind why rivers change their courses.
“So the person you just heard is Doug Edmonds, who's a professor at Indiana University I mentioned earlier.”
Engineering Solutions for Avulsions
31:09 to 32:06
Explore potential engineering solutions for managing river avulsions amidst climate change.
“And similarly, in the Indus River in Pakistan, part of the reason that the avulsion happened is because a levy failed.”
The Significance of the Mississippi Map
32:07 to 34:46
Understand the historical significance of the avulsion map of the Mississippi River.
“When storms happen, they dump more water on things like rivers that then could flood in the way that the Indus River did.”
The Game Show Finale and Song
34:47 to 36:11
Experience the fun culmination of the game show with a humorous song.
“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.”
The Game Show Finale and Song
39:00 to 40:17
Experience the fun culmination of the game show with a humorous song.
“Unexplainable is part of the Vox Media Podcast Network, and we'll see you next time.”
Transcript
Automatic transcript. May contain errors.0:00Sally Helm:Support for this show comes from Fetch Pet Insurance. Do you have a pet? Every six seconds, a pet owner in the U.S. gets hit with a vet bill of over$1 ,000. And it's almost always an unwelcome surprise. That's where Fetch Pet Insurance comes in. Fetch is the most complete pet insurance. Get paid back up to 90 % of vet bills. You can use any vet in the U.S. and Canada. All vets are in network. Go to FetchPet.com slash save right now for your free quote. That's FetchPet.com slash save. Support for this show comes from BetterHelp. Have you ever had so many tabs open that your computer starts slowing down?
0:44Sally Helm:Life can feel like that too. BetterHelp's 2026 State of Stigma report found that 74 % of Americans believe society still discourages asking for help. Therapy can help you sort through what's taking up space and quietly affecting you. With BetterHelp, connect with a licensed therapist online and switch anytime. Maybe it's time to close a few tabs. Visit betterhelp.com slash voxpods to get started.
1:12Neel Dhanesha: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 probably listen 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!
1:35Sally Helm: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 the hot seat.
1:41Neel Dhanesha:Okay, Unexplainable or Not is a game show where you have to guess what we know and what we don't. You're going to hear three scientific mysteries, and you're going to hear them from me, from my co-host, Bird Pinkerton. That's me. And from longtime friend of the show, science reporter Neil Dinesha. 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. Okay. And this week, I want to start with a question we got from a listener.
2:18Sally Helm: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?
2:26Neel Dhanesha: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.
2:33Sally Helm:New-ish.
2:34Neel Dhanesha:Yeah, new-ish. Bird is right.
2:36Sally Helm:Okay, you're talking about like the podcast tile, the thing that shows up next to Unexplainable.
2:40Neel Dhanesha:Yeah, and it's 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! Obviously. The easiest possible thing.
2:54Douglas Edmonds:What else would you do? Talk about it? The least amount of work possible.
2:59Neel Dhanesha:So, first up, you're going to hear a mystery from Bird.
3:03Sally Helm:Sally, hello.
3:05Neel Dhanesha:Hi, Bird.
3:06Sally Helm:Hello. Sally, we've known each other for a while at this point. I know. Ever since we were 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? Mussels. Okay, since we're talking about rivers, I'm going to assume we mean the kind that has shells that come together. We are indeed talking about freshwater mussels. Okay. So the unsung heroes of rivers, as some might say. I love an underdog. I'm already on board. So basically, freshwater mussels are in all kinds of rivers in the U.S. And this researcher, a professor at the University of Wisconsin-Madison, this guy named Tony Goldberg, He told me that the U.S.
4:02Sally Helm:is actually a hotspot of muscle diversity. So we have all kinds of amazing species. We have one called the heel splitter that looks kind of like a clam, but then it has this really sharp edge. So the name is sort of— Ooh, ouch. So heel splitter are heels when we step on it. Yes. And then 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 egg somewhere else. Pretty cool. Genius. And honestly, I just wanted to take a minute with some of the amazing names we've given to these muscles.
4:50Sally Helm:So you have the purple warty back. We got the pocketbook, the flat pig toe, the mucket, the golden riffle shell, the stirrup shell, and my favorite, the turgid blossom pearly mussel. That is a poem in itself. That's a good name. I agree. And I think, like, these mussels 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.
5:34Sally Helm:And then whatever remains, they just kind of like poop out. And are they doing this to like eat and get nutrients for themselves, but then as a byproduct, they clean the water? Yeah, and there's this video from like the Minnesota Department of Natural Resources. It's this like little time lapse. And so they start with like two containers of like dirty kind of brownish orange-ish muck. One has mussels 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 mussel tank just like cleans up, essentially. The water becomes see-through and probably not, like, lovely, but certainly more lovely than it was before.
6:13Sally Helm:So these mussels, 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 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 um like the flat pig toe the stirrup shell also unfortunately the turgid blossom pearly mussel no bird yes uh i am very sorry to say They were all declared extinct, actually, in 2023, because I hadn't been seen for decades.
7:05Sally Helm:Some other species are endangered. But also, Tony says, sort of more recently, researchers have started seeing these massive muscle die-offs. A whole bunch of muscles will just, like, die over the course of even just one season. So he calls it, like, an ecological emergency. And Tony is an epidemiologist. So he studies like pathogens and animals, everything from monkeys, robins, fish, mussels. And he joined like a whole team of people that wanted to investigate this. He said they called themselves the Delta Strike Force of muscle-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.
7:58Sally Helm:Makes sense. Muscles dying. Maybe they're getting sick from something in the water. Exactly. And so they kind of had to start from scratch, he told me, in some ways. Like, he said they had to figure out how to identify even that a muscle was sick. Because if you just look at its shell, you're like, oh, that's a muscle. And you'd have to see its inside. Well, yeah, 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 muscle? And there were a lot of viruses in these muscles, for example. But he had to figure out, like, were any of those a problem?
8:35Sally Helm:Are there viruses or bacteria or parasites that are in the sick or dead muscles, 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, right? The smoking gun that is killing off these mussels in these big die-offs. And they have not found it yet. Okay. Unless they have.
9:17Sally Helm:Please tell me that we know what is after our dear muscles.
9:23Neel Dhanesha:What do you think, Sally? Do you think we know or do you think it's still a mystery?
9:29Sally Helm: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 going to say, maybe as emotional self-protection, that we don't. We don't know. I love the way you're thinking about it.
10:02Neel Dhanesha:So no need to lock in your answer yet. Just have it float around in the back for now.
10:07Sally Helm:Great. As if on a river.
10:09Neel Dhanesha:And Neil is up next. He's got another mystery for you about rivers. All right.
10:14Douglas Edmonds:Hello. We were not interns at NPR, and this is the first time I'm meeting you. I've never met you before.
10:19Sally Helm:Hi. Hello.
10:21Douglas Edmonds:Well, since I've never met you, I also don't know where you live. Do you live near a river?
10:25Sally Helm: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.
10:34Douglas Edmonds: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.
11:09Douglas Edmonds: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. It like fully moves and it leaves a dry channel behind where it was before. 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.
11:32Sally Helm:Just like zoink, different course.
11:34Douglas Edmonds:Exactly. And it would completely transform these 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 Atchvalia.
11:56Sally Helm: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?
12:03Douglas Edmonds:They got kept apart by the Army Corps of Engineers. This tale of river love was stopped.
12:08Sally Helm:Okay, yeah. It's a Starcross love story. I'm hooked. Question, would they have had to rename one or the other of the rivers if they merged?
Read the full transcript
12:18Douglas Edmonds:That's a good question.
12:19Sally Helm:Do they hyphenate? But that just kicks the can down the road.
12:24Neel Dhanesha:What if that river meets another river bird? Come on. Exactly. Right.
12:27Sally Helm:You know what? This is unimportant.
12:32Douglas Edmonds: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.
13:03Sally Helm:Wow.
13:04Douglas Edmonds:I know. It's really brutal.
13:06Sally Helm: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.
13:14Neel Dhanesha:Yeah, exactly. And you want to be like right up against the river, right, to use it as best as you can.
13:19Douglas Edmonds: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 of Uljun's, Doug told me, are slower. They take decades or even centuries. So if you 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.
13:50Douglas Edmonds:I love it so much that I talk to people about it unbidden 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. But it's still kind of a mystery. Like, we don't really know what causes these avulsions to happen unless we do and we can do something about it.
14:19Sally Helm:On this one, I'm going to 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 going to say we figured this one out. I'm going to say someone knows why. Okay. But you do have to remember that this was unexplained for a long time. No, it's so true. As I was saying that, I was like, we've had rivers. We've had rivers the whole time.
14:56Douglas Edmonds:Like the Indus one was like not that long ago, you know? Yeah.
15:01Neel Dhanesha:Hold your thought for now. There might be another mystery coming. Well, 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?
15:20Sally Helm:The Nile.
15:21Neel Dhanesha:The Nile. Great answer. That is basically what everyone would say. It's what the U.S. 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.
15:38Sally Helm:That was my number two.
15:40Neel Dhanesha:I, it's, you're, you're very good on river length, just intuitive river length. I have a deep intuition of that. So when I heard about this, I was sort of surprised that it was even a question.
15:51Sally Helm:Right.
15:51Neel Dhanesha:Like, can't we just measure?
15:53Sally Helm:Can't you just measure the river, right? Very big tape measure to the Amazon.
15:56Neel Dhanesha:We see where the river is, just measure it. So I called up this explorer, Yuri Sonata. An explorer? 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. Wow. And it has really big tape measure on it. Yes. It's going to 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.
16:38Neel Dhanesha:So let's just start with how to measure it.
16:40Sally Helm:Yeah, do you mean like what tool to use or like do we go with meters or feet?
16:44Neel Dhanesha: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.
17:22Neel Dhanesha:And it's because when you zoom in, these squiggly lines get longer. 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.
18:02Neel Dhanesha:That's probably beyond where we need to go.
18:05Sally Helm:All rivers are actually the same length. All rivers are the same. Trick question.
18:11Neel Dhanesha:And then also like rivers are changing, they're moving. It's tough to get a consistent measurement, just like Neil was saying.
18:16Sally Helm:It's like you're going to have to approximate like what level are you approximating?
18:19Neel Dhanesha:Exactly. 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 Marañon 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.
18:54Neel Dhanesha: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.
19:03Sally Helm:That feels like the beginning.
19:05Neel Dhanesha: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 going to be whitewater rafting down the mountain for a month.
19:31Sally Helm:This is why we get to have explorers.
19:34Neel Dhanesha: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 and was like, please, please don't take the record from us.
20:07But 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.
20:20Sally Helm:I'm going to say, and I don't think Yuri would agree with me, but I'm going to 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.
20:31Neel Dhanesha:Oh, so your answer is there's no longest river.
20:33Sally Helm: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. Zeno's River. Zeno's River. Exactly. They're all Zeno's River.
20:56Neel Dhanesha: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?
21:03Sally Helm:Yeah, exactly. I mean, I think we don't know. I think we don't know this one. Okay, you got three mysteries.
21:10Neel Dhanesha:You got the mystery of mussels, 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 going to have a chance to make your final guess after the break.
21:35Sally Helm:Support for this show comes from Shopify. Starting a business is not easy. It can come with a lot of self-doubt and questions like, what if I fail? Or what if nobody buys what I have to sell? But if you are a small business owner pushing through that self-doubt, Shopify wants you to know that it is there to help along the way. Shopify is the commerce platform behind millions of businesses around the world and, according to their numbers, 10 % of all e-commerce in the U.S., from household names like Magic Spoon to brands just getting started. Their design studio lets you build a beautiful online store that matches your brand style.
22:14Sally Helm:They offer a host of helpful AI tools, plus built-in marketing tools to help you create effective email and social media campaigns. And if you ever get stuck, their award-winning 24-7 customer support has your back. It is time to turn those what-ifs into Shopify today. Sign up for your$1 per month trial today at shopify.com slash unexplainable. Go to shopify.com slash unexplainable. That is shopify.com slash unexplainable.
22:50Sally Helm:Support for the show comes from Quince. The other day I was out shopping and picked up a cute dress, but I wasn't totally sure it was my style because I've been kind of moving away from sleeveless stuff lately. Then I brought it home and tried it on over a little lightweight black t-shirt that I got from Quince. And I am literally wearing the whole outfit right now as I record this ad. The shirt from Quince was just the perfect thing to pair with the dress to give it sleeves and the shirt is light and breathable enough that I'm not like sitting in the studio too warm. So as a person who loves to layer clothing, I really, really appreciate that Quince has a wide array of shirts and a whole bunch of different cuts, lots of options for people like me.
23:39Sally Helm:But if you are looking for not just shirts, but a whole range of lighter, cooler wardrobe pieces as part of a summer refresh, Quince also has you covered. Quince can help you find some new, breathable outfits that are easy to wear and still look put together. Elevate your summer wardrobe. Go to quince.com slash unexplainable for free shipping on your order and 365-day returns. Now available in Canada, too. So that is quince.com slash unexplainable for free shipping and 365-day returns. quince.com slash unexplainable.
24:18Sally Helm:Support for this show comes from Indeed. When the pressure's on and you need to hire the right person for the job, Indeed Sponsored Jobs has your back. Sponsored jobs posted directly on Indeed are 95 % more likely to report a hire than non-sponsored jobs. Join the 3.3 million employers worldwide that use Indeed to connect with quality talent that fits their needs. Spend less time searching and more time actually interviewing candidates who check all your boxes. Less stress, less time, more results. When you need the right person to cut through the chaos, this is a job for Indeed-sponsored jobs.
24:52Sally Helm:And listeners of this show will get a$75 sponsored job credit to help your job get the premium status it deserves at Indeed.com slash podcast. Just go to Indeed.com slash podcast right now and support the show by saying you heard about Indeed on this podcast. That's Indeed.com slash podcast. Terms and conditions apply. Need to hire? This is a job for Indeed-sponsored jobs.
25:26Neel Dhanesha:okay it's unexplainable or not sally welcome back hello business like one word
25:41Neel Dhanesha:no sally i feel like sally's got her game face on you know she's ready She's ready to go.
25:46Sally Helm: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.
25:53Douglas Edmonds:Your go-to game there was Parcheesi.
25:56Neel Dhanesha:I don't even think I've ever played Parcheesi. What is Parcheesi?
26:00Sally Helm:No, it was like one of the most – if you go – I went to like a board game exhibit, and like half the board games were Parcheesi. I think it is the most classic game, and also I've never seen it. This is what I'm saying, Sally. All right. Well, later as team bonding, we're all playing Parcheesi. Okay. And it will probably start a fight, presumably with Sally, because she takes games very seriously, apparently.
26:24Neel Dhanesha:Anyway, so we've got three mysteries for you to choose from. Only one of them has been solved. 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?
26:54Sally Helm: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 avulsions, 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.
27:26Neel Dhanesha: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. That's true.
27:35Sally Helm:That's a great point.
27:36Douglas Edmonds:This is high-level Parcheesi. This is...
27:39Sally Helm:I'm playing checkers. Bird's playing Parcheesi. I'm playing four-dimensional Parcheesi. Okay, I'm going to say that we have found why the muscles are dying. We know the answer to that.
27:56Neel Dhanesha:Okay. Muscles dying. Final answer? Yes.
28:03Douglas Edmonds:Okay, here's the answer. 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.
28:21Sally Helm:Okay!
28:25Bird! Bird!
28:28Sally Helm:Oh, I'm sorry!
28:30Neel Dhanesha:I wish people could see Sally's face looking like just, and Bird just dancing like, Ho, ho, ho, ho, ho.
28:38Sally Helm:Wow. Okay, so we've solved this long-running geologic mystery that we've been struggling with for centuries. Neil, what do we know?
28:48Douglas Edmonds:Yeah.
28:49Sally Helm:Why does this happen?
28:50Douglas Edmonds:So the person you just heard is Doug Edmonds, who's a professor at Indiana University I mentioned earlier. He's one of the co-authors of a paper about why avulsions happen. So there are really two competing ideas for why river avulsions occur. One is simple when one is a little more complex. 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. So the more complex explanation has to do with the fact that, especially near the coastlines where a lot of avulsions tend to occur, rivers are depositing sediment on their beds.
29:31Douglas Edmonds:They're full of sediment. They're carrying it downstream. Some of it settles to the bottom of the river as it goes along. 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. 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 superelevation. Kind of related to what Noam was talking about earlier.
30:07Douglas Edmonds: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. Yeah, space lasers. No.
30:21Sally Helm:Yes. I did not know space lasers were coming.
30:24Douglas Edmonds: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 avulsions that happened over the past 30 years. And they found a bunch that they had no idea existed before. 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.
30:56Sally Helm:Wow.
30:57Douglas Edmonds:And, you know, I think like in a lot of the U.S. 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 levy failed. So what Doug says actually is that the best sort of solve for avulsions, 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 of just dissipate some of the force.
31:42Douglas Edmonds: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.
32:13Douglas Edmonds:And so that data could just save a whole lot of lives. Wow.
32:17Sally Helm:So we know why rivers change course and we can do something about it. This is good news, Neil.
32:23Neel Dhanesha:So 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.
32:46Sally Helm:Wow, it's an avulsion map.
32:47Neel Dhanesha: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.
33:15Sally Helm: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. And so this particular image just sort of felt really representative of just some of the themes of our show.
34:05I don't know.
34:05Neel Dhanesha: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.
34:41Neel Dhanesha:And it also tells me that like so many of the things that we for granted are not written in stone and are kind of always evolving.
34:51Sally Helm: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...
35:01Neel Dhanesha:We do like worms.
35:03Sally Helm:Theoretically advanced take on the logo. Okay.
35:09Neel Dhanesha:One last thing before we leave. Sally.
35:12Sally Helm:Yes. Even though you didn't win, you were so close, though. I was so close. Until Bird sabotaged you.
35:21Neel Dhanesha: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, River's Changing Course. So I'm going to play it for you.
35:40Neel Dhanesha:When I was young, it was paradise Growing upright by the riverside By the riverside
35:57Neel Dhanesha:But one day I looked for tilapia And I couldn't find where the river was, where the river was
36:17Neel Dhanesha:How'd my river abandon me? Maybe lasers from space will see the avulsions of yesterday How my river curved away When I was young it was paradise But I've made my tilapia sacrifice No tilapia
37:08Anymore
37:09Neel Dhanesha:What?
37:11Douglas Edmonds:I love this so much.
37:14Sally Helm:Noam, were you like, did you write this while waiting for dinner? What is the tilapia?
37:20Neel Dhanesha:I call it no tilapia.
37:24Sally Helm:Into the canon of river songs it goes.
37:28Neel Dhanesha:That's it for Unexplainable or Not. Thank you to our guest, Sally Helm. Thank you. To our presenters, Bird Pinkerton. That's me. And Neil Dinesha. That's me. 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 unexplainable at vox.com. We read all the emails. And that is it for Unexplainable or Not. Goodbye.
37:54Sally Helm:Woo-hoo!
38:03Neel Dhanesha:This episode was reported by Byrd Pinkerton, Meredith Hodnott, and me, Noam Hassenfeld. I also wrote the music. Production from Meredith, who also runs the show. Editing from Joanna Solitaroff. Guessing from Sally Helm. Thank you, Sally. Mixing and sound design from Christian Ayala. 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 onto freshwater mussels 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.
38:42Neel Dhanesha:We're at unexplainable at vox.com. You can also leave us a review or a rating wherever you listen, which really 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 slash 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.
39:13Neel Dhanesha:When I was young, it was paradise. But I've made my tilapia sacrifice. No tilapia anymore.
39:51Sally Helm:created agents that can do the work from end to end. They build a plan, pull from secure data sources, run sub-agents in parallel, and draft the work product ready for your review. So you delegate the work and own the judgment. Trusted by more than 60 % of the Amlaw 100 and leading Fortune 500 legal teams, Harvey is the AI operating system designed specifically for legal work. Harvey. AI tailored for law. Learn more at Harvey.ai. Support for this show comes from Fetch Pet Insurance. Do you have a pet? Every six seconds, a pet owner in the U.S. gets hit with a vet bill of over$1 ,000. And it's almost always an unwelcome surprise.
40:36Sally Helm:That's where Fetch Pet Insurance comes in. Fetch is the most complete pet insurance. Get paid back up to 90 % of vet bills. You can use any vet in the U.S. and Canada. All vets are in network. Go to FetchPet.com slash save right now for your free quote. That's FetchPet.com slash save.
From the publisher
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! unexplainable@vox.com
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