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Our Past Favorites #7 - Not All Who Meander Are Lost · PlanetGeo: The Geology Podcast

• 0:02
  SPEAKER_00: Welcome to Planet Geo, the podcast where we talk about our amazing planet, how it works, and why it matters to you.
• 0:12
  SPEAKER_00: Chris, this episode, this is number four.
• 0:15
  SPEAKER_00: Well, number seven in our total list.
• 0:17
  SPEAKER_00: Your fourth one of your list of favorite episodes.
• 0:20
  SPEAKER_00: This was one of the one of the episodes where our title we didn't have a big title disagreement.
• 0:25
  SPEAKER_00: The title is kind of obvious for this one.
• 0:27
  SPEAKER_00: Do you remember?
• 0:28
  SPEAKER_01: I do.
• 0:28
  SPEAKER_01: I do.
• 0:29
  SPEAKER_01: I remember this.
• 0:34
  SPEAKER_01: No, I just more berated you over the title that you chose because I thought it was really bad.
• 0:39
  SPEAKER_01: This one I liked though.
• 0:40
  SPEAKER_01: Yes.
• 0:41
  SPEAKER_00: Usually would we disagree about an episode title?
• 0:44
  SPEAKER_00: It's because we both have bad ideas and we don't have any good ones.
• 0:47
  SPEAKER_00: But this one was like, I don't know who came up with it, but it's a pretty good one.
• 0:50
  SPEAKER_00: And we were like, oh yeah, that's clearly the one.
• 0:52
  SPEAKER_00: Uh, why are meandering streams in this episode in particular on meandering streams one of your favorites?
• 0:57
  SPEAKER_01: Because I love us I Jesse, I I don't know if I can actually contain my excitement with this, actually.
• 1:05
  SPEAKER_01: Seriously, when you look at the the dynamics of a stream and how it meanders back and forth, and how it's a for streams that do this, it's there are patterns in this.
• 1:17
  SPEAKER_01: And I love that.
• 1:19
  SPEAKER_01: Anytime you get patterns in geology, and the the how behind the why in this is just I think it's absolutely fascinating.
• 1:27
  SPEAKER_01: You know, Jenny and I go for walks almost every day along the Grand River.
• 1:32
  SPEAKER_01: We'll we'll take maple or puppy and we'll go for a walk along the river.
• 1:36
  SPEAKER_01: And it's a sweeping, meandering river.
• 1:38
  SPEAKER_01: And I love to think about okay, you know, you look at the width of the river, it's it's a pretty wide, impressive river.
• 1:44
  SPEAKER_01: You look at the width of it, and you're walking an apex of a meander, and then you think about where's the next one.
• 1:51
  SPEAKER_01: You can get really close by approximating the width of it and how much further you have to walk to get to the next bend.
• 1:58
  SPEAKER_01: I love it.
• 1:58
  SPEAKER_01: I I think it's amazing.
• 2:00
  SPEAKER_00: There's very few things in life I've moved to places where there are meandering rivers all over the place in Pennsylvania.
• 2:07
  SPEAKER_00: When we lived in eastern Pennsylvania, lots of meandering rivers.
• 2:10
  SPEAKER_00: We're kind of close to base level.
• 2:11
  SPEAKER_00: Same thing in in here in the Appalachian section and Alleghenies in in central Pennsylvania.
• 2:16
  SPEAKER_00: The rivers kind of just meander through the valleys, and then we have water gaps that cut the big rivers cut across the ridges, but between the ridges, you just have meandering streams.
• 2:24
  SPEAKER_00: There's very few things in life that are more pleasant than a walk on a path next to a meandering stream.
• 2:30
  SPEAKER_00: I just think it's a totally pleasant thing, and you can look at that stream and understand a ton about geology from this.
• 2:35
  SPEAKER_01: So I think our listeners, Jesse, can have that appreciation the next time they go for a walk.
• 2:41
  SPEAKER_01: So I think that this is appropriate and it's awesome to re-release to refresh people's minds about the beauty of how a stream works.
• 2:49
  SPEAKER_01: Because that's really what's going on.
• 2:50
  SPEAKER_00: I agree completely.
• 2:51
  SPEAKER_00: Absolutely.
• 2:52
  SPEAKER_00: Meandering streams, uh, not all who meander are lost was the title that we agreed on.
• 2:56
  SPEAKER_00: I like that.
• 2:56
  SPEAKER_00: That's a great one.
• 2:57
  SPEAKER_00: There's a there's a reason, there's a cause and effect for streams and how they meander.
• 3:01
  SPEAKER_00: So love this episode.
• 3:02
  SPEAKER_00: Let's get to it, Chris.
• 3:03
  SPEAKER_00: Let's go.
• 3:09
  SPEAKER_01: All right.
• 3:09
  SPEAKER_01: Hey, let's get going, Dr.
• 3:11
  SPEAKER_01: Rymink.
• 3:12
  SPEAKER_00: What are we doing today?
• 3:14
  SPEAKER_00: Stream meanders.
• 3:15
  SPEAKER_00: Really, really cool topic.
• 3:16
  SPEAKER_00: This, I think, is one of the topics that every like first year geology student who take the intro class, it's one of these mind-blowing things.
• 3:26
  SPEAKER_00: You know, like play tectonics is very cool.
• 3:28
  SPEAKER_00: Volcanoes are awesome, earthquakes are awesome.
• 3:31
  SPEAKER_00: This is awesome in a very, very different way, and it's sort of one of these mind-blowing things.
• 3:35
  SPEAKER_00: Everybody's seen stream meanders, and we're gonna explain them today, which is a really kind of a mind-blowing concept, I think, and very, very cool.
• 3:42
  SPEAKER_01: I agree, but we're gonna do something though today that explains meanders and they are not random.
• 3:50
  SPEAKER_01: And I don't talk about this in my classes.
• 3:52
  SPEAKER_01: Do you?
• 3:52
  SPEAKER_01: Do you get into the weeds on this?
• 3:54
  SPEAKER_00: No, I mean, usually the way my class is structured, Chris, I talk about minerals and I think you do the same thing.
• 4:00
  SPEAKER_01: Do you have structure in your class?
• 4:02
  SPEAKER_00: Yeah, it's a bit of whatever I want to talk about any given fall semester.
• 4:06
  SPEAKER_00: But you know, I usually so it starts with minerals and we go into rocks, and I obviously take way too long talking about igneous rocks and plate tectonics and things.
• 4:13
  SPEAKER_00: So by the end of the semester, I run out of time for glaciers and streams and all this kind of stuff.
• 4:18
  SPEAKER_00: I do hit streams because streams are super important in Pennsylvania, but sometimes I run out of time to talk about glaciers, for instance.
• 4:24
  SPEAKER_00: Right.
• 4:25
  SPEAKER_01: Yeah, yeah.
• 4:25
  SPEAKER_01: Oh, I never do that because I I'm in Michigan and we cannot neglect glaciers in Michigan.
• 4:30
  SPEAKER_01: That would be an injustice.
• 4:31
  SPEAKER_01: But what we're gonna do today, if I didn't know this and I listened to this, I would appreciate it much more.
• 4:36
  SPEAKER_01: And just like looking at rivers, because we're gonna talk about the geometry of meanders here, really.
• 4:41
  SPEAKER_01: I think it's such a cool topic.
• 4:43
  SPEAKER_00: Let's level set kind of what we're talking about here, is that there's a bunch of different types of rivers or streams.
• 4:48
  SPEAKER_00: We call them streams.
• 4:49
  SPEAKER_00: Like the general classification for flowing water is streams.
• 4:53
  SPEAKER_00: And so there's a whole bunch of different types of streams.
• 4:55
  SPEAKER_00: You know, you can picture these in your head with us.
• 4:57
  SPEAKER_00: You can think of a mountain stream that's kind of going straight down the mountain valley, cascading over boulders and doing all this very interesting stuff.
• 5:04
  SPEAKER_00: It's usually frickin' cold water.
• 5:05
  SPEAKER_00: You can have streams that are a little bit quieter and they're in flat terrain and they kind of wind back and forth.
• 5:11
  SPEAKER_00: That's what we're talking about with meanders.
• 5:13
  SPEAKER_00: And so we're we're focusing on one specific subset of streams, which is meandering streams.
• 5:18
  SPEAKER_00: And where do these occur, Chris?
• 5:19
  SPEAKER_00: Like paint the visual for like where these occur.
• 5:23
  SPEAKER_01: First of all, you know, you and I, we tend to get a little off topic too.
• 5:27
  SPEAKER_01: So we're not just gonna focus on meanders.
• 5:30
  SPEAKER_01: So we'll we'll bring in some other things, we promise.
• 5:33
  SPEAKER_01: And also we're gonna end with entrenched meanders because those are a very, very cool thing and the dynamic of streams as well.
• 5:39
  SPEAKER_01: But meanders happen when rivers kind of flatten out.
• 5:44
  SPEAKER_01: You don't have meandering streams typically when you have they they tend to be much straighter when the gradient or slope is much steeper.
• 5:52
  SPEAKER_01: So when as soon as it flattens out, that's when rivers will will begin their meandering or looping process.
• 6:00
  SPEAKER_00: Totally, totally.
• 6:01
  SPEAKER_00: And so the places they flatten out are floodplains.
• 6:04
  SPEAKER_00: These are things where rivers hit their floodplain and they they kind of the the trajectory of the stream or the gradient of the stream from the start from the headwaters of the stream way up in the mountains to the mouth where it hits the ocean or hits some lake, it's kind of somewhere in there, the stream will start to become less steep.
• 6:20
  SPEAKER_00: And when it becomes less steep, this is what we're talking about.
• 6:23
  SPEAKER_00: So more flat land, basically.
• 6:25
  SPEAKER_00: And if you look at a map of Pennsylvania, that's a really kind of cool thing to do.
• 6:28
  SPEAKER_00: There's meandering streams everywhere, and they flow through the valleys.
• 6:32
  SPEAKER_00: So we are in the Ridge and Valley province, and we have these really long ridges that run for miles and miles and miles parallel to each other with a valley in between, and there'll be a stream meandering down the middle of that.
• 6:43
  SPEAKER_00: And it's really cool, you can just look at that.
• 6:45
  SPEAKER_01: Is your drainage pattern then what you just described?
• 6:47
  SPEAKER_01: Is that a trellis drainage pattern that you've got to do?
• 6:49
  SPEAKER_01: We have a trellis.
• 6:50
  SPEAKER_00: Yep, exactly.
• 6:50
  SPEAKER_01: Okay.
• 6:51
  SPEAKER_01: Yep.
• 6:51
  SPEAKER_01: Um, I was getting ready for this episode, and I came across a quote that I I don't think this is verbatim quote, but it's really, really good, and it it hit me.
• 7:00
  SPEAKER_01: It's something to the effect of you can never set foot in the same stream twice.
• 7:06
  SPEAKER_00: Love that one.
• 7:07
  SPEAKER_01: You know, where it's the water's not the same, the sediment's not the same, basically nothing is the same.
• 7:13
  SPEAKER_00: You know, Chris, I have this memory, and I think it was on a field trip with you when I was a TA, I think, in my senior year, when I was doing the independent study and I went along as a kind of a TA of your field trip, where there was cold up in the upper peninsula.
• 7:28
  SPEAKER_01: Where you had absolutely no responsibility and music?
• 7:30
  SPEAKER_00: Zero responsibilities.
• 7:31
  SPEAKER_00: We did a hike back along a stream.
• 7:34
  SPEAKER_00: Is this do you do that?
• 7:36
  SPEAKER_00: Did you do that in those days in the your trip, your spring trip to the upper peninsula?
• 7:40
  SPEAKER_00: We there was and it was one of these Did we go to a waterfall?
• 7:42
  SPEAKER_00: Yes, we went back to a waterfall and we sort of stopped halfway.
• 7:46
  SPEAKER_00: We weren't at the waterfall yet, or we were on our way back.
• 7:48
  SPEAKER_00: I'm not sure which one, but we stopped and had like a break, and I had zero responsibilities.
• 7:52
  SPEAKER_00: And that quote, I think you and I were discussing that quote, because it suddenly got sunny and warm, and we were just sitting next to a stream in the forest.
• 7:59
  SPEAKER_00: It was just glorious.
• 8:01
  SPEAKER_00: And uh I I love streams, they're so great.
• 8:04
  SPEAKER_01: I agree.
• 8:04
  SPEAKER_01: I think actually what you and I were talking about is I asked you, have you ever thought about where the water that's running in front of us right now, where it has been?
• 8:14
  SPEAKER_01: I think that's what we were contemplating.
• 8:16
  SPEAKER_01: Like following the life cycle of a water molecule.
• 8:19
  SPEAKER_00: Yeah, is really cool.
• 8:20
  SPEAKER_00: Totally crazy.
• 8:22
  SPEAKER_00: Really, really cool to do.
• 8:23
  SPEAKER_00: Streams are just thought-provoking.
• 8:25
  SPEAKER_00: I agree in all types of ways.
• 8:27
  SPEAKER_00: I agree.
• 8:28
  SPEAKER_00: Um, so that's the quote.
• 8:29
  SPEAKER_01: Okay, so basically, rivers in the mountains, they're governed by the slope, okay, their steepness, and they're confined by the valley, so they tend to be straighter.
• 8:38
  SPEAKER_01: As soon as they hit the broader, flatter floodplain, they begin to meander.
• 8:43
  SPEAKER_01: So in these meanders, let's start to get a little bit into the weeds on this a little bit.
• 8:48
  SPEAKER_01: That like these meanders uh have a function, they actually are managing the energy of the water, right?
• 8:55
  SPEAKER_01: I mean, if you think about what a meander does, at the basic, basic level, they're doing two things, right?
• 9:02
  SPEAKER_01: They increase the resistance because it's no longer flowing in a straight path.
• 9:07
  SPEAKER_01: So they increase the resistance and they decrease the gradient.
• 9:11
  SPEAKER_01: Chris, let me Which is the slope.
• 9:13
  SPEAKER_01: I'm sorry.
• 9:14
  SPEAKER_01: They decrease the steepness.
• 9:15
  SPEAKER_01: Yes.
• 9:16
  SPEAKER_00: The gradient is is kind of uh this is a term that's hard to understand.
• 9:19
  SPEAKER_00: So let's just visualize it really quickly.
• 9:21
  SPEAKER_00: So imagine you have there's an elevation when the stream comes out of the mountains and hits this floodplain, that's at an elevation, let's say it's like 300 feet above sea level.
• 9:29
  SPEAKER_00: And then the mouth of the stream is at sea level when it pours out in the ocean.
• 9:33
  SPEAKER_00: So there's 300 feet over that distance, right?
• 9:35
  SPEAKER_00: And if it's a straight stream and it's 10 miles, it's going 300 feet and 10 miles.
• 9:39
  SPEAKER_00: That's the gradient.
• 9:40
  SPEAKER_00: However, if you add meanders in there, it's a lot longer path.
• 9:44
  SPEAKER_00: So the path the river takes, if you stretch the meanders out, is a lot longer than 10 miles.
• 9:49
  SPEAKER_00: And so the gradient is a lot less.
• 9:51
  SPEAKER_00: So that's what you mean by it decreases the gradient here.
• 9:54
  SPEAKER_00: And then the first thing you talked about, Chris, the resistance is if you've ever walked along a stream that's meandering or that's kind of has bends in it, you'll notice that the deeper parts are on the outside.
• 10:04
  SPEAKER_00: And that's because the the river is moving faster on the outside.
• 10:07
  SPEAKER_00: You'll often see this too.
• 10:08
  SPEAKER_00: Like there's faster water on the outside of the bend, it's cutting into there.
• 10:12
  SPEAKER_00: So there's a lot of energy being expended, cutting in.
• 10:16
  SPEAKER_00: There's erosion happening, which is using energy to kind of cut into that bank.
• 10:21
  SPEAKER_00: And so that's just the point about the resistance number one that you said.
• 10:25
  SPEAKER_01: So, you know, what the river is doing is it's just it's changing itself to minimize the energy that it's expending so it can maintain a state of equilibrium.
• 10:36
  SPEAKER_01: In and with a river where you talk about equilibrium, really then there's no net anything going on.
• 10:42
  SPEAKER_01: There's no net erosion, there's no net deposition.
• 10:45
  SPEAKER_01: That's a river that is in a state of equilibrium.
• 10:48
  SPEAKER_00: That's the key point here, Chris.
• 10:50
  SPEAKER_00: Because remember, when we just went back to that analogy of like 300 feet over 10 miles, and and that that's probably not enough height to for 10 miles of river.
• 10:58
  SPEAKER_00: But if you have a steep gradient, it's carrying sediment downstream a lot.
• 11:03
  SPEAKER_00: But it can only do that for so long until it runs out of sediment.
• 11:09
  SPEAKER_00: A straight stream at that gradient will carry a lot of sediment out, but you'll eventually run out of sediment upstream.
• 11:14
  SPEAKER_00: And so then your stream is kind of out of balance in a way.
• 11:17
  SPEAKER_00: And so when a meander is happening, there's not a lot of net transport of material downstream.
• 11:23
  SPEAKER_00: There is a little bit, but it's very, very, very slow.
• 11:25
  SPEAKER_00: And that's the thing that has to be balanced here.
• 11:27
  SPEAKER_00: The physics of like moving particles downstream has to be balanced with the gradient that it's going through.
• 11:33
  SPEAKER_01: A long time ago, Jesse, we talked about riffles, runs, pools, and glides.
• 11:37
  SPEAKER_01: Remember this episode a long time ago?
• 11:39
  SPEAKER_00: A long time ago.
• 11:40
  SPEAKER_01: It was a long no.
• 11:41
  SPEAKER_01: I don't well.
• 11:41
  SPEAKER_01: Let's throw back to that because this is a like classic example of this dynamic of rivers trying to reach the state of equilibrium.
• 11:50
  SPEAKER_01: I mean, rivers boiled down to their basic level.
• 11:54
  SPEAKER_01: They are transporting machines, right?
• 11:57
  SPEAKER_01: They're transporting water and sediment downstream.
• 12:01
  SPEAKER_01: When a river encounters a bend on the outside, you described it as this kind of cut bank thing, it's erosion.
• 12:07
  SPEAKER_01: You get a deeper pool on that outside of the bend.
• 12:10
  SPEAKER_01: If you looked at a profile, a cross-sectional profile of a river along this meander, you would see that the inside of the bend, it's very shallow and gentle sloping.
• 12:21
  SPEAKER_01: And as you approach the outside of the bend, the river gets much deeper.
• 12:25
  SPEAKER_01: It's gouged out into this thing that we call a pool.
• 12:28
  SPEAKER_01: I mean, it makes sense.
• 12:29
  SPEAKER_01: And it's actively then moving sediment out of that bend.
• 12:33
  SPEAKER_01: Well, then as it as the water comes out of the meander and the stream kind of straightens itself out, it's going to deposit the sediment now, which creates a riffle.
• 12:42
  SPEAKER_01: Or the water's more kind of more turbulent as it goes off over this deposited sediment.
• 12:47
  SPEAKER_01: And so it's just a throwback to this old episode a long time ago, the riffles runs pools.
• 12:53
  SPEAKER_00: And okay, I have an analogy that just popped into my head, which might be terrible.
• 12:56
  SPEAKER_00: So, but and you're the analogy, King.
• 12:58
  SPEAKER_00: Uh oh, I'll let you know.
• 12:59
  SPEAKER_00: So I want you to evaluate this one, Chris.
• 13:01
  SPEAKER_00: Okay.
• 13:01
  SPEAKER_00: So you just said that that streets are transporting machines, which is a great phrase.
• 13:06
  SPEAKER_00: I love that phrase.
• 13:07
  SPEAKER_00: Here's an analogy, okay?
• 13:08
  SPEAKER_00: Let's test this out and you can tell me how I did with this.
• 13:11
  SPEAKER_00: Let's put it into context of something everybody has seen, which is the conveyor belt at the grocery checkout, right?
• 13:16
  SPEAKER_00: You've got the conveyor belt.
• 13:17
  SPEAKER_00: Now, a mountain stream that has a gradient where it goes several thousand feet in a couple miles is a fast-moving conveyor.
• 13:24
  SPEAKER_00: It is the conveyor belt sped up really, really fast where you can just chuck a bunch of stuff on there and it'll take it away downstream, no problem, right?
• 13:32
  SPEAKER_00: It has that space.
• 13:33
  SPEAKER_00: What we're talking about demandering streams are streams that are slowing down that conveyor belt, like really slowing it down.
• 13:40
  SPEAKER_00: So you can't put many groceries on there.
• 13:41
  SPEAKER_00: The groceries kind of pile up and then fall off the sides because it's not moving fast enough.
• 13:46
  SPEAKER_00: The checkout person's really taking their time about it, or maybe they're new and they're not checking out fast enough.
• 13:50
  SPEAKER_00: And the sediment, the your groceries have to fall off the edges to maintain this balance.
• 13:54
  SPEAKER_00: You just can't pile them up very high.
• 13:55
  SPEAKER_00: That's the meandering stream.
• 13:57
  SPEAKER_00: And so this net transport has to slow down.
• 13:59
  SPEAKER_00: So instead of taking sediment downstream, down the conveyor belt really fast, instead of moving groceries down fast, they fall off the sides.
• 14:07
  SPEAKER_00: And that's what a meandering stream is doing is moving sediment laterally side to side instead of moving it downstream.
• 14:14
  SPEAKER_01: That works, Jesse.
• 14:15
  SPEAKER_01: Okay.
• 14:16
  SPEAKER_01: Well done, my young sage.
• 14:17
  SPEAKER_01: Um, let me go at it a different way a second.
• 14:20
  SPEAKER_01: Rivers move sediment.
• 14:22
  SPEAKER_01: Streams move sediment in three ways.
• 14:24
  SPEAKER_01: They they have what's called their dissolved load, which are like these molecules, their salts that are dissolved in the water, right?
• 14:31
  SPEAKER_01: This is again a throwback to way back when, when we talked about why the oceans are salty and so on, number five or something like that.
• 14:39
  SPEAKER_00: We're going back 140 episodes ago.
• 14:41
  SPEAKER_01: I can't believe I actually remember it.
• 14:43
  SPEAKER_01: Um, anyway, that's the dissolved load.
• 14:46
  SPEAKER_01: It's a pretty small amount in terms of the overall load that a river carries.
• 14:50
  SPEAKER_01: But the next one is the suspended load.
• 14:52
  SPEAKER_01: And these are particles that are they're carried in the column of water, they're carried in suspension.
• 14:58
  SPEAKER_01: This includes particles like dust-sized particles and silt-sized particles, and even sand if it's moving fast enough.
• 15:05
  SPEAKER_01: So if you can imagine sand moving in the suspended load of a river, as soon as that water slows down just a little bit, it doesn't have enough energy now to carry that sand, and the sand is deposited.
• 15:18
  SPEAKER_01: And that's what happens when a river comes out of the pool and it straightens out.
• 15:22
  SPEAKER_01: There's a little bit of lower energy, a little slower movement, and some of the suspended material now is going to be deposited.
• 15:30
  SPEAKER_01: And then the third way that rivers move sediment is along the bed of the river where they roll and they slide and they kind of bounce or saltate along the bottom.
• 15:38
  SPEAKER_01: And the same thing is if the river slows down just a little bit, those things stop moving.
• 15:43
  SPEAKER_01: So it's the a combination of the bed load and the suspended load that create the riffles then coming out of the pool.
• 15:50
  SPEAKER_00: Let's move into that pool dynamic or the bend, the actual meander part.
• 15:53
  SPEAKER_00: Maybe I'll just cover the the names that we're going to use, then we can start talking about the physics of these meanders.
• 15:58
  SPEAKER_00: Um I can't wait.
• 16:00
  SPEAKER_00: Okay.
• 16:01
  SPEAKER_00: So if you're looking at a meandering stream, you're walking along a path, and the stream is winding to the path and then away from the path, and then to the path.
• 16:08
  SPEAKER_00: Now let's get in a kayak.
• 16:09
  SPEAKER_01: Let's get in a kayak.
• 16:10
  SPEAKER_00: Well, okay, we could get in a kayak, but you know, uh in Pennsylvania we don't have that many.
• 16:14
  SPEAKER_00: There's some you can kayak, but the streams are small, these meandering ones.
• 16:17
  SPEAKER_00: So I'm usually by a path, but you can be in a kayak.
• 16:20
  SPEAKER_00: Chris is in a kayak, I'm by the path.
• 16:22
  SPEAKER_00: Chris and Jenny are in kayaks, and maybe you got a dual kayak, and you know, Chris is in front and Jenny's got her legs up.
• 16:28
  SPEAKER_00: We have those sometimes.
• 16:29
  SPEAKER_00: Jenny's got her legs kicking her legs up front with her beer, and you're doing all the paddling in the back.
• 16:32
  SPEAKER_00: Is that what happens here?
• 16:34
  SPEAKER_00: Chris, bring me over there.
• 16:35
  SPEAKER_00: Chris, bring me over here.
• 16:36
  SPEAKER_00: Usually it's the other way around, my friend.
• 16:38
  SPEAKER_00: Okay, so if actually, this is a good visual.
• 16:40
  SPEAKER_00: If I'm walking down the path, straight path, and the the river where that you guys are kayaking in, you're kind of meandering towards me where the river will be right next to the path, and then you meander away.
• 16:48
  SPEAKER_00: You sort of bend away, you go around another bend, and then you come back close to the path, right?
• 16:53
  SPEAKER_00: And so if we look at that lateral variation inside of the bends, the water is slow, and you can see this.
• 17:00
  SPEAKER_00: You can look at this from the path or from your kayak, and you can see that it's slow water, it's sandy there.
• 17:05
  SPEAKER_00: And you can look on the outside of the bend and the water's fast and the the riverbed is deep.
• 17:09
  SPEAKER_00: And what's happening here is on the outside of the bend, because the water's faster, it's deeper, the water at the top is moving faster because the water's deeper, it's cutting.
• 17:19
  SPEAKER_00: And so on the outside is where the erosion happens.
• 17:22
  SPEAKER_00: As the water is scraping along that outside of the bend, it's eroding.
• 17:25
  SPEAKER_00: It's cutting in, it's forming what we call cut banks.
• 17:28
  SPEAKER_00: And us trout fishermen really like cut banks because the big trout like to hide underneath of the cut bank there.
• 17:34
  SPEAKER_00: They're if they're safe from eagles and ospreys and all that stuff.
• 17:37
  SPEAKER_00: And then on the inside of the bend, it's this shallow sloping thing that we call a point bar, which is this shallow sloping.
• 17:44
  SPEAKER_00: The bank is sandy usually and it slopes gradually towards the outside of the bend in the river.
• 17:50
  SPEAKER_00: And that is where deposition is happening.
• 17:52
  SPEAKER_00: So sediment is being deposited on the inside.
• 17:55
  SPEAKER_00: Again, because Chris, you described this beautifully, coming out of the riffles.
• 17:58
  SPEAKER_00: There's sediment being dumped off, and when the river is flowing straight, it hits the inside of the curve and it slows down, it hits the outside of the curve and it speeds up.
• 18:06
  SPEAKER_00: So the outside is quote unquote hungry, the inside is not hungry, is regurgitating some sediment and dropping it off right there.
• 18:14
  SPEAKER_00: And so this causes that meander to keep cutting further to the outside and keep depositing on the inside.
• 18:21
  SPEAKER_00: And so obviously, if you speed this up, the river keeps meandering or keeps cutting away the outside and cutting away the outside and depositing the inside, depositing the inside, and that loop keeps getting more and more exaggerated.
• 18:34
  SPEAKER_00: And eventually you on your kayaks will cut into my path and the path will have to change.
• 18:38
  SPEAKER_01: Good.
• 18:39
  SPEAKER_01: I want to put a pin in something because I want to come back to it.
• 18:41
  SPEAKER_01: So remind me, all right?
• 18:42
  SPEAKER_01: I want to put a pin in the path of Jenny and I and the kayak as we come out of the meander.
• 18:48
  SPEAKER_01: Okay, so let's let's come back to that later on.
• 18:51
  SPEAKER_01: But before we do that, we need to get into some of the weeds.
• 18:54
  SPEAKER_01: And this is the cool part about I think this episode that I think most people that are not like fluvial geomorphologists don't really know.
• 19:03
  SPEAKER_01: And I think it's a very, very awesome aspect to river dynamics and meanders in particular.
• 19:09
  SPEAKER_01: So let's get into the detail.
• 19:10
  SPEAKER_01: The geometry of meanders is not random, it's specific and it's amazing.
• 19:16
  SPEAKER_01: I love this stuff.
• 19:17
  SPEAKER_01: But we have to introduce some terminology a second.
• 19:20
  SPEAKER_01: So let's introduce first the wavelength of meanders.
• 19:24
  SPEAKER_01: And what we're talking about is let's say the crest of one meander to the crest of another meander further downstream.
• 19:33
  SPEAKER_00: Chris, let me just double-click on this a minute.
• 19:35
  SPEAKER_00: This is done with like satellite imagery.
• 19:36
  SPEAKER_00: This is done top down.
• 19:38
  SPEAKER_00: You're we're looking at an airplane view or a satellite image of the river, and you're seeing it meander up and down, back and forth on your map.
• 19:44
  SPEAKER_00: And this is actually how scientists who study these things look at these things.
• 19:47
  SPEAKER_00: They take satellite imagery and measure the distances between these bends.
• 19:51
  SPEAKER_00: So think of it like a wave where the wavelength and the amplitude is you know how far the wave goes up and down.
• 19:57
  SPEAKER_00: This is the same thing, except this the map view of this stream.
• 20:02
  SPEAKER_01: That's right.
• 20:02
  SPEAKER_01: So we're looking at two identical spots on consecutive meanders.
• 20:08
  SPEAKER_01: Perfect.
• 20:08
  SPEAKER_01: So like crest to crest or the same, we're trying to find the same point in two consecutive meanders.
• 20:14
  SPEAKER_01: We call that the wavelength of the meander because it it kind of looks like that, like you just said.
• 20:20
  SPEAKER_01: And so that's called the wavelength.
• 20:22
  SPEAKER_01: And the beauty of this is that regardless of the stream, regardless of the size of the river, this can be a small thing like in your lab, like a stream table in your lab, or a massive river like the Mississippi or the Missouri.
• 20:36
  SPEAKER_01: It doesn't matter.
• 20:38
  SPEAKER_01: The wavelength is gonna be about eleven times the width of the river channel.
• 20:46
  SPEAKER_01: Now that's like I find that to be very exciting.
• 20:49
  SPEAKER_01: I I don't know why.
• 20:50
  SPEAKER_01: It just be but I think it's because it just makes perfect sense.
• 20:53
  SPEAKER_01: Like when you kayak a river, when you're walking along a path and you're looking at these bends, these oppositely looping bends back and forth they go, they're not random.
• 21:02
  SPEAKER_01: And I just think that when you understand that, that there's a reason to this madness, that it just makes it I can appreciate then that so much more.
• 21:13
  SPEAKER_01: I I don't know.
• 21:14
  SPEAKER_01: I just find it to be very exciting.
• 21:15
  SPEAKER_01: And I don't know why.
• 21:16
  SPEAKER_01: I really need to do a better job of this in my classes because I don't talk about this with my students.
• 21:21
  SPEAKER_01: It's and again, it's the same reason.
• 21:22
  SPEAKER_01: I'm running out of time.
• 21:23
  SPEAKER_01: My exam for my students from Grand Valley is coming up next week, Tuesday.
• 21:27
  SPEAKER_01: I'm out of time.
• 21:28
  SPEAKER_00: And I think that you know, this is you know, we live in an ordered system, really.
• 21:32
  SPEAKER_00: This is like an ordered environment.
• 21:34
  SPEAKER_00: And the reason that it's like 11 times or you know, 10 to 14 times the width, there's obviously variation.
• 21:39
  SPEAKER_00: There's like natural Can I finish that real quick?
• 21:41
  SPEAKER_01: Sure, go for it.
• 21:42
  SPEAKER_01: So it's usually 11 times the width of the river.
• 21:45
  SPEAKER_01: So the wavelength is eleven times greater than the width of the river, no matter what the width of the river happens to be.
• 21:51
  SPEAKER_01: And it is always ten to fourteen times the width of the river.
• 21:57
  SPEAKER_00: And this is, I think, you know, it's very complicated.
• 22:00
  SPEAKER_00: In detail.
• 22:00
  SPEAKER_00: And it's very hard for people to accurately model the details here.
• 22:05
  SPEAKER_00: So if people say, okay, I'm going to create a stream, I've got a stream out there in the world.
• 22:08
  SPEAKER_00: I'm going to look at it.
• 22:09
  SPEAKER_00: I'm going to create a physical model of this stream and sort of forward model it.
• 22:12
  SPEAKER_00: So look at satellite imagery from 1980 of this meandering stream and then say, I'm going to model it forward to 2023 with some physics.
• 22:20
  SPEAKER_00: They don't do a great job of matching up perfectly, but they get some of the main principles right.
• 22:25
  SPEAKER_00: So it's really hard.
• 22:26
  SPEAKER_00: My point is it's really hard to model the detailed physics of this, but the broad scale physics makes sense.
• 22:32
  SPEAKER_00: Like the width of the stream, that's amount of water.
• 22:35
  SPEAKER_00: And amount of water moving downstream is energy.
• 22:38
  SPEAKER_00: And so the wider the stream, the more energy that's expended, and the more energy is available to cut these meanders.
• 22:45
  SPEAKER_00: And so you get wider, broader meanders that have a greater wavelength when you have a wider stream, because there's just more energy, more water flowing, more energy to do this erosion and deposition in a broader wavelength pattern.
• 22:59
  SPEAKER_00: So that's why there's this relationship between stream width and wavelength of the meanders.
• 23:03
  SPEAKER_01: Let me try to simplify what you just said a little bit, if I could.
• 23:08
  SPEAKER_01: And that's where I want to come back to me and my kayak is if I get Jenny and I into the swift part of the river, and we're just drifting with very little direction, maybe a little bit of direction, but I'm just basically gonna drift.
• 23:20
  SPEAKER_01: I'm gonna drift.
• 23:21
  SPEAKER_00: Let me interrupt and say it wouldn't be by your choice.
• 23:23
  SPEAKER_00: This would be at Jenny's direction.
• 23:24
  SPEAKER_00: I mean, Jenny Jenny is controlling the situation here.
• 23:27
  SPEAKER_00: Let's not say Chris I did this.
• 23:28
  SPEAKER_00: It's Jenny directed you to do this.
• 23:30
  SPEAKER_00: So okay, continue.
• 23:33
  SPEAKER_01: True.
• 23:33
  SPEAKER_01: Okay, so we're just drifting in the swift part of the river.
• 23:36
  SPEAKER_01: So it's gonna naturally then take us to the outside of this meander, right?
• 23:40
  SPEAKER_01: Yep.
• 23:40
  SPEAKER_01: And I'm gonna go around the meander, and my kayak is basically gonna stay in that swift part of the river.
• 23:46
  SPEAKER_00: No, you're gonna try the the important thing, you're you're gonna have to work hard to stay out of like the brambles and the branches because you're gonna be like, if you just let it go, that cock would nose into the bank, and you know, there'd be a branch falling on Jenny, and you know, it'd be really hard.
• 23:58
  SPEAKER_00: So you're working at hard.
• 24:02
  SPEAKER_01: But as I come out of that meander, the waters as it slams into that bank kind of gets swept then across the channel.
• 24:10
  SPEAKER_01: It's it's almost like a a slingshot effect, if you will.
• 24:14
  SPEAKER_01: And so my kayak, if I keep it in that swift part of the river, is now gonna drift me slowly across the other side of the river.
• 24:22
  SPEAKER_01: Yep.
• 24:23
  SPEAKER_01: So the the wider that river is, the longer it's gonna take me to slingshot or sweep across to the other side of the river.
• 24:32
  SPEAKER_01: And that's where when the river then slams into that other side, that's the beginning of the other meander.
• 24:39
  SPEAKER_00: Let me just double-click on something you said there.
• 24:41
  SPEAKER_00: I'm kind of imagining this with a left-handed bank.
• 24:43
  SPEAKER_00: So you're coming and you're kind of the fast parts on the left side of the river.
• 24:47
  SPEAKER_00: You're trying fighting to keep off that bank.
• 24:49
  SPEAKER_00: And then when you come out and the river straightens out into a riffle section, you're gonna have a bit of a rightward momentum.
• 24:56
  SPEAKER_00: Like you're coming out of this curve that's curving from left to right, and you're gonna still be curving from left to right, and you're gonna cross that riffle section, not straight down the river, but going from left to right, and you're following the water, like you said.
• 25:09
  SPEAKER_00: By the time you hit the the next curve, you're on the right side and you're impacting the right side of the stream.
• 25:14
  SPEAKER_00: Hence, that's where the erosion happens and it starts to curve back towards the left.
• 25:18
  SPEAKER_00: Like that's what we're talking about, this slingshot thing you're describing.
• 25:21
  SPEAKER_00: You get slingshotted out of one curve into the next one, and that exaggerates, that creates exaggerated loops and exaggerated loops.
• 25:29
  SPEAKER_00: And the eventual thing, which we didn't actually talk about, is that the eventual outcome of this is that these loops get bigger and bigger and bigger until they become circles, the stream cuts itself off and will cut off a meander, and then that cut-off meander is no longer connected to the river, so it becomes this big horseshoe bend, and then eventually it'll cut across the horseshoe part, and so it cuts off that meander, and that becomes an oxbow lake, and then the river will straighten out for a section, gain speed, and then start this meandering process over again.
• 26:01
  SPEAKER_00: So these meanders happen progressively over and over and over and over.
• 26:05
  SPEAKER_00: And if you ever want to see something really cool, look at a lidar map of a meandering stream.
• 26:10
  SPEAKER_00: So these really high-resolution laser maps, topographic maps, you can see generations of meanders in these floodplains, and they're really beautiful.
• 26:18
  SPEAKER_00: People make artwork out of them, and then they're really, really cool.
• 26:20
  SPEAKER_01: That's that's a really good point.
• 26:22
  SPEAKER_01: Meanders, oxbows, they are I don't know, they get me.
• 26:27
  SPEAKER_01: Yeah, they they just they grab me at my emotions when you see them.
• 26:31
  SPEAKER_01: Like I I think of one of my favorite places to see this is in the Appalachian Mountains looking at the Cumberland River, and it's just broad, sweeping, meandering, dirty looking river because it's got a lot of suspended load in it, and it just oxbows all over the place.
• 26:46
  SPEAKER_01: And it's just one of the best examples on the planet to see this kind of looping, curving, but yet it's not random.
• 26:54
  SPEAKER_01: And you know, again, to come back to this point, and and really what I want our all of our listeners to do is look at meandering rivers a little bit differently and see if that makes sense.
• 27:04
  SPEAKER_01: You can look at the width of the river, multiply that by about 11, and that's where the next meander is gonna be.
• 27:12
  SPEAKER_01: And it just keeps doing this again and again and again with regularity.
• 27:15
  SPEAKER_01: It's just such an awesome thing.
• 27:17
  SPEAKER_00: So let's just tidy up this physics part here, Chris, or the the sort of regularity here.
• 27:21
  SPEAKER_00: So we described wavelength, which is the distance between meanders in the same direction.
• 27:26
  SPEAKER_00: So these right hand bends, the distance between two right hand bends is the wavelength.
• 27:31
  SPEAKER_00: There's the radius of curvature, so like as this horseshoe develops, the size of that horseshoe is also a function of the physics of the river, and it's usually about one-fifth the wavelength.
• 27:41
  SPEAKER_00: So smaller rivers have tighter loops, larger rivers have much broader loops.
• 27:46
  SPEAKER_00: This is proportional to the width of the river and to the wavelength of these meanders.
• 27:51
  SPEAKER_00: And I think this brings up like why these happen, like why do meanders happen or how do they start in the first place?
• 27:58
  SPEAKER_00: I want you to answer this, Chris, but I just want to say one thing that the people who study these things in the lab, I saw one of these.
• 28:04
  SPEAKER_00: I went and gave a talk at Lafayette College up in northeastern Pennsylvania, and they have a flume, which is a huge room with basically a big tank in it that sits on pistons.
• 28:16
  SPEAKER_00: And so this tank is it's like the size of a semi-truck trailer, probably, of this clear glass tank that has tons of sand in it.
• 28:25
  SPEAKER_00: It has water, a big water tank upstream.
• 28:28
  SPEAKER_00: There's like viewing sides to it, and you can change the pitch of this thing.
• 28:32
  SPEAKER_00: So you can like turn you can tilt it, you can put one side up and one side down, and there's a ton of sand in this thing.
• 28:37
  SPEAKER_00: And so you can put whatever sediment you want in there.
• 28:39
  SPEAKER_00: You can start a stream by just dumping water into one side of it and watch how the stream changes.
• 28:44
  SPEAKER_00: And so people see these meanders occur, start with a straight path, turn it on, and then within hours to days, you have a meandering stream.
• 28:53
  SPEAKER_00: And so we can see this in the lab.
• 28:54
  SPEAKER_00: This people do experiments like this in the lab in these big flumes.
• 28:58
  SPEAKER_00: They're really cool.
• 28:59
  SPEAKER_01: I have one.
• 28:59
  SPEAKER_01: It's not the size of a semi.
• 29:01
  SPEAKER_01: It is instead, it is the size uh it's about six feet long and three feet wide.
• 29:08
  SPEAKER_01: It it circulates its own water back and forth, so it's kind of cool that way.
• 29:11
  SPEAKER_01: It's got a pump in it, you know.
• 29:13
  SPEAKER_01: So I have on one end of it where water, I can control the outflow of the water.
• 29:17
  SPEAKER_01: I can have it a trickle, I can flood it, I could, you know, I can control that.
• 29:21
  SPEAKER_01: And then it goes down into a lake and it creates a delta and so on.
• 29:24
  SPEAKER_01: It's it I'd like to just turn it on and let it run, and then just students will just migrate into your class then and just stand in front of it, and they're mesmerized by this dynamic going on in front of them.
• 29:36
  SPEAKER_01: It's really a really a cool thing.
• 29:38
  SPEAKER_01: But that you got man, I have an idea.
• 29:40
  SPEAKER_01: I think I want to build a sandbox outside of my room, like a big, big sandbox outside of my classroom.
• 29:46
  SPEAKER_01: And then I I have a water source nearby.
• 29:49
  SPEAKER_00: I can just, you know, turn it on and let it go.
• 29:51
  SPEAKER_01: I can create my own.
• 29:52
  SPEAKER_01: Yeah.
• 29:52
  SPEAKER_00: Sounds great.
• 29:53
  SPEAKER_01: Man, done.
• 29:54
  SPEAKER_01: Yeah, I'm I'm gonna make this happen.
• 29:55
  SPEAKER_01: This is I need another TA, Jesse.
• 29:58
  SPEAKER_00: Maybe someone more productive.
• 30:00
  SPEAKER_00: I need a TA that's actually gonna do something.
• 30:01
  SPEAKER_00: Yeah, more productive than I was.
• 30:03
  SPEAKER_00: Um, you were such a piece of work.
• 30:05
  SPEAKER_00: All right.
• 30:05
  SPEAKER_00: So, Chris, I you know, I just described how we can do experiments with this.
• 30:08
  SPEAKER_00: Why do meanders happen?
• 30:09
  SPEAKER_00: Like what starts at the rivers, let's assume it's straight to start with.
• 30:12
  SPEAKER_00: Why does it start to meander?
• 30:13
  SPEAKER_01: There are so many things that can cause meanders to begin.
• 30:16
  SPEAKER_01: And once they begin, then they take on this regularity that we talked about just a few minutes ago.
• 30:22
  SPEAKER_01: It could be a log falling across the river, it can be a bridge with pilings in the middle of the river.
• 30:28
  SPEAKER_01: It can be a muskrat digging a tunnel underneath the river into the bank on one side of the river, and that tunnel weakens that part of the river, erosion begins, and it creates a pool.
• 30:41
  SPEAKER_01: And once you get a pool, then you have faster flowing water, and the process is on.
• 30:46
  SPEAKER_01: And so there are so many things that can cause meandering to begin.
• 30:54
  SPEAKER_01: Anything that diverts water to one side of the channel is is a is enough.
• 30:58
  SPEAKER_00: And you know this from your your flume in your classroom and people who do these experiments, you take completely homogenous sand, you completely homogenize it, have a s perfectly straight stream starting, this will naturally happen.
• 31:11
  SPEAKER_00: Meanders will naturally happen because there's very subtle variations.
• 31:14
  SPEAKER_00: Any little tiny pebble difference can shift the water intensity to one side of the stream, and then because the slingshot effect, it just starts happening.
• 31:22
  SPEAKER_00: So this is like unavoidable almost, and very, very slight perturbations, like you described a muskrat drilling into the side or digging into the side.
• 31:30
  SPEAKER_00: You know, that's a pretty small perturbation, but it can cause massive meanders to sort of initiate.
• 31:35
  SPEAKER_00: So it's kind of a natural outcome of rivers in this uh type of setting.
• 31:40
  SPEAKER_01: All right.
• 31:40
  SPEAKER_01: So, Jesse, I think next, you want to did you want to talk about this this kind of paper that you know meanders and river dynamics are tied to vegetation a little bit?
• 31:49
  SPEAKER_00: Like, do you want to just a little summary on this?
• 31:53
  SPEAKER_00: You know me.
• 31:53
  SPEAKER_00: I I I kind of I always like to highlight that the early earth was different than the modern earth in some way or shape or form.
• 32:00
  SPEAKER_00: And a colleague of mine has been focusing a fair bit of research on this, looking at how plants affect meandering streams, really.
• 32:08
  SPEAKER_00: And there's a couple different aspects to this, but if we think of like Earth history, plants have been plants have been on land and have colonized the land for the last 350, 450 million years.
• 32:20
  SPEAKER_00: Before that, there weren't many land plants, and so a lot of the rivers did not have plants anchoring the banks of the rivers and things like that.
• 32:27
  SPEAKER_00: So so river systems on the early earth before 450 million years ago might have been very, very different.
• 32:33
  SPEAKER_01: Um and so what Yeah, weathering and erosion must have looked way different.
• 32:36
  SPEAKER_00: Totally different, right?
• 32:37
  SPEAKER_00: Just completely different stuff.
• 32:39
  SPEAKER_00: And so people who study vegetated rivers and unvegetated rivers, like think about a meander in a desert versus a meander in a lush jungle environment, those are very different.
• 32:50
  SPEAKER_00: And actually the plants do a lot.
• 32:52
  SPEAKER_00: The plants impact how much energy it takes to erode the stream bank, really, is the key thing.
• 32:57
  SPEAKER_00: More plants equals more energy required to make meanders.
• 33:01
  SPEAKER_00: And so I think that the important highlights here, Chris, are that the channel width of unvegetated rivers, so rivers in arid environments or in, you know, without vegetation on the banks, those usually have a smaller channel width and they migrate a lot faster.
• 33:17
  SPEAKER_00: The migration rate in meters per year is like an order of magnitude faster than vegetated rivers.
• 33:23
  SPEAKER_00: So the stream that we were describing through the forest of Pennsylvania is moving slower than if there were not trees there, like the lateral migration here.
• 33:33
  SPEAKER_00: Just because it's got to fight through all the roots and the biology, I think.
• 33:36
  SPEAKER_00: You know, that's the the sort of take-home physics.
• 33:38
  SPEAKER_01: Okay, interesting.
• 33:39
  SPEAKER_01: I have an idea.
• 33:40
  SPEAKER_01: We have been throwing around this idea of doing a topic for an episode on how to read a scientific paper.
• 33:47
  SPEAKER_01: And this is you, and it's basically me talking to you about this.
• 33:51
  SPEAKER_01: What do you say we put together a little series then following this episode up with we can use that and talk more about river dynamics and also talk about how to read a scientific paper because I think that's something that's an important topic.
• 34:06
  SPEAKER_00: I like that.
• 34:07
  SPEAKER_00: That's a really good one.
• 34:08
  SPEAKER_00: That's a good idea, Chris.
• 34:09
  SPEAKER_00: This would be a great one.
• 34:09
  SPEAKER_00: It's sort of a review of stream meanders and vegetated, unvegetated.
• 34:13
  SPEAKER_00: And it's a it's a learned skill, this reading a scientific paper, because it's not easy to start with.
• 34:18
  SPEAKER_00: So yeah, I like that.
• 34:19
  SPEAKER_00: That's a great idea.
• 34:19
  SPEAKER_00: Good idea.
• 34:20
  SPEAKER_00: Let's let's do that in a in a coming episode here for sure.
• 34:22
  SPEAKER_01: Okay, good.
• 34:23
  SPEAKER_01: Well, hey, let's wrap today's episode up with one final thing that I I don't know.
• 34:27
  SPEAKER_01: I don't want to gloss over too much, but I think we've covered meanders well enough.
• 34:32
  SPEAKER_01: Uh, what I want to talk about are entrenched meanders, because these are some of the most beautiful geologic features that exist.
• 34:40
  SPEAKER_01: Famous examples of entrenched meanders are Horseshoe Canyon in Canyonlands National Park.
• 34:46
  SPEAKER_01: Both you and I have seen this.
• 34:47
  SPEAKER_01: The goosenecks in Gooseneck State Park in Utah.
• 34:51
  SPEAKER_01: These are just a couple of like examples of very, very famous entrenched meanders.
• 34:56
  SPEAKER_00: And if you don't know what those look like, the visual in your head here is a big bend in a river, a horseshoe bend in a river that's cut through rock where there's cliffs on either side of that river.
• 35:07
  SPEAKER_00: So very different from the floodplain that you and I were just talking about, Chris, that you and Jenny were casually kayaking through.
• 35:13
  SPEAKER_00: This would not be a casual kayak in this river system.
• 35:16
  SPEAKER_00: You know, this is class four rapids on these types of rivers, but that's the visual we're painting here.
• 35:21
  SPEAKER_00: That's what an entrenched meander is, it's entrenched in cliffs, basically, rock.
• 35:26
  SPEAKER_01: And they have very little migration, they're not going to move much because they are confined now by the valley walls.
• 35:32
  SPEAKER_00: That's a key point, Chris.
• 35:34
  SPEAKER_00: So, okay, that's a really key point because I think these entrenched meanders are very commonly misunderstood because people look at it and think, oh, it cut through the rock.
• 35:42
  SPEAKER_00: Like the meanders are cutting through the rock.
• 35:45
  SPEAKER_00: But you just said that there's very little lateral migration.
• 35:48
  SPEAKER_00: And if you look at these rivers, you can see that there's no like undercut bank.
• 35:52
  SPEAKER_00: There's no like uh, well, maybe there's a little bit of undercut bank, but there's a little bit of deposition on the inside of the bends, but not a lot.
• 35:58
  SPEAKER_00: Like it's it's not the same dynamics, and the stream is not cutting outward as much.
• 36:03
  SPEAKER_00: And that's a key part of how these things form.
• 36:07
  SPEAKER_00: The question I think that people get confused about is when did the meanders happen?
• 36:12
  SPEAKER_00: And what's the answer, Chris?
• 36:14
  SPEAKER_01: The meanders happen first.
• 36:16
  SPEAKER_01: You have this river that was doing what we've described for the last half hour is they're establishing this equilibrium.
• 36:23
  SPEAKER_01: It was broad, it was flat, and it began to you know minimize energy and deposit and erode at the same time and establish a state of equilibrium.
• 36:34
  SPEAKER_01: And the meanders developed.
• 36:37
  SPEAKER_01: And then then geology happened.
• 36:41
  SPEAKER_01: Uplift probably happened where the land began to elevate and the river now is gonna accelerate and it's gonna try to keep up with the rate of uplift.
• 36:54
  SPEAKER_01: And it's gonna down cut as the uplift is happening.
• 36:57
  SPEAKER_01: So this is very different than what I think a lot of people think when they look at this.
• 37:01
  SPEAKER_01: They think that it downcut through the rock like you described.
• 37:04
  SPEAKER_01: Instead, we had the meanders that were established.
• 37:08
  SPEAKER_00: Uplift began and the river just kept up.
• 37:10
  SPEAKER_00: Can I kind of summarize that a minute, Chris?
• 37:12
  SPEAKER_00: And and and correct me if I get this wrong, if I miss something key here, but I want to just summarize it.
• 37:16
  SPEAKER_00: The meander pattern is inherited by a previous generation of river, by the ancient river system that was actually meandering and cutting out side to side, right?
• 37:27
  SPEAKER_00: That the meander shape is inherited.
• 37:30
  SPEAKER_00: And the way I like to describe this in class is that a river, when it's at high elevation in the mountains, when it has a lot of distance to go high gradient, it wants to cut down.
• 37:40
  SPEAKER_00: So if it has to go down 3,000 feet in a mile, it is cutting down first.
• 37:45
  SPEAKER_00: And when it doesn't have anywhere to cut down, it'll cut out side to side, i.e., it'll start to meander side to side.
• 37:52
  SPEAKER_00: So when it has a shallow gradient, it's cutting out to side to side, it's meandering.
• 37:56
  SPEAKER_00: And so we've kind of reversed this.
• 37:58
  SPEAKER_00: We've taken a meandering stream that had a low gradient, and all of a sudden we made it want to cut down, and it just cut straight down, it kept the same stream profile and just went straight down very fast, which means it inherited that shape, uh that sinuosity, whereas it would have normally been a straight stream if you kind of started from scratch.
• 38:18
  SPEAKER_01: No, I like the way you put that.
• 38:20
  SPEAKER_01: In fact, I'm gonna steal that.
• 38:21
  SPEAKER_01: That's the way I'm gonna use it from now on, is the shape of the meanders is inherited because they came first.
• 38:27
  SPEAKER_01: So I like that.
• 38:27
  SPEAKER_01: It's a good way of putting it.
• 38:29
  SPEAKER_00: I think this highlights an important concept here and an important thing about meandering streams is that there's a couple ways to force this, to want to make the river like cut down.
• 38:37
  SPEAKER_00: The first is to uplift the land.
• 38:39
  SPEAKER_00: You force the stream to be at higher elevations and it wants to cut down to the same like sea level gradient.
• 38:44
  SPEAKER_00: The other thing to do is change what we call base level, like where the mouth of the stream is.
• 38:49
  SPEAKER_00: And so we can if we put a dam somewhere, that changes base level.
• 38:52
  SPEAKER_00: If we remove a dam, if we drain a lake, if we change the base level where the stream is ending, it changes that gradient and how the stream is cutting in and out.
• 39:02
  SPEAKER_00: And meanders are really important mostly because in society we have built up a lot of industry and we've built our society around a meandering stream's current profile, and which means we don't want to let it naturally meander like it should be doing.
• 39:21
  SPEAKER_00: Like the Mississippi River is a classic example.
• 39:24
  SPEAKER_00: There's a bunch of little rivers in Pennsylvania that are great examples of this.
• 39:27
  SPEAKER_00: We build a little town around a meandering stream, and all of a sudden we put concrete embankments all the way around that stream because we don't want it to change its profile anymore.
• 39:35
  SPEAKER_00: So we're changing the behavior of that stream because we've sort of built up our civilization around a profile that is changing, right?
• 39:42
  SPEAKER_00: It's kind of like uh we talked about barrier islands and how they're changing all the time.
• 39:47
  SPEAKER_00: Meandering streams are are very similar to that.
• 39:49
  SPEAKER_00: They meander pretty quickly, and we're kind of locking them in.
• 39:53
  SPEAKER_01: That's a great idea for another episode in a series of what is the effect on the river when we levy a river?
• 40:01
  SPEAKER_01: We try to control the Mississippi by levying it.
• 40:04
  SPEAKER_01: What are the pros to that?
• 40:06
  SPEAKER_01: What's good about it, and what's bad about it?
• 40:08
  SPEAKER_01: Because whenever you try to affect a river, you're gonna affect the geology.
• 40:11
  SPEAKER_01: I mean, what's what's going on?
• 40:13
  SPEAKER_01: You know, it's I think that's a you know really good idea for an episode.
• 40:16
  SPEAKER_00: We're kind of I think we should we should tidy these all together and make a you know something about ephemeral geological features, you know, like barrier islands and meandering streams, these things that change a lot, and we're sort of forcing them to not change, or we're not wanting them to change because we've built stuff around them, you know.
• 40:31
  SPEAKER_00: Like that's a that's a good episode.
• 40:34
  SPEAKER_00: Um okay.
• 40:35
  SPEAKER_00: Well, Chris, did we cover entrenched meanders?
• 40:38
  SPEAKER_00: I think we got the main point across.
• 40:40
  SPEAKER_00: That's a whole big I mean, that and water gaps and all these interesting morphological features, those are long episodes in and of themselves.
• 40:48
  SPEAKER_00: But did we hit the highlights?
• 40:49
  SPEAKER_01: I think it's a good idea, good suggestion.
• 40:52
  SPEAKER_01: Just push pause and Google image an entrenched meander or Google Horseshoe Canyon, and you'll get it, you'll see exactly what we're talking about if you have that visual.
• 41:02
  SPEAKER_00: Hey, Chris, you know, we haven't done a stream chapter.
• 41:05
  SPEAKER_00: We've got it on our docket of things to do for Camp Geo.
• 41:08
  SPEAKER_00: But if you want all of the other basics of geoscience, we've got most of our content up on Camp Geo now.
• 41:14
  SPEAKER_00: We've got eight or nine chapters.
• 41:16
  SPEAKER_00: If you want to learn all the basics of geoscience with images, the way we think you really need to understand it with Chris and I, you can go to geo.campcourses.com, the first link in your show notes.
• 41:25
  SPEAKER_00: Check that out.
• 41:25
  SPEAKER_00: Leave us a rating and review on your podcast platform.
• 41:28
  SPEAKER_00: Send us an email, planetgeocast at gmail.com.
• 41:32
  SPEAKER_00: That's super useful.
• 41:33
  SPEAKER_00: We're building office hours episodes always in the background here.
• 41:36
  SPEAKER_00: We got a lot of good suggestions and questions, and we're putting those together in office hours episodes as we speak here.
• 41:42
  SPEAKER_00: Go to our website, planetgeocast.com.
• 41:44
  SPEAKER_00: There you can subscribe, support us.
• 41:46
  SPEAKER_00: We always love that and appreciate those of you who have supported us so far.
• 41:50
  SPEAKER_00: Streams are beautiful.
• 41:52
  SPEAKER_00: There.
• 41:53
  SPEAKER_00: Cheers, peace.