Latest / PlanetGeo: The Geology Podcast / Great Smoky Mountain National Park

Transcript

Great Smoky Mountain National Park · PlanetGeo: The Geology Podcast

0:01
SPEAKER_00: Welcome to Planet Geo, the podcast where we talk about our amazing planet, how it works, and why it matters to you.
0:14
SPEAKER_01: How are we doing, Jesse Remink?
0:16
SPEAKER_00: Good, Chris.
0:17
SPEAKER_00: How about you?
0:18
SPEAKER_01: I'm great, actually.
0:19
SPEAKER_01: Yeah.
0:20
SPEAKER_01: I'm feeling especially smart today.
0:22
SPEAKER_00: Especially smart.
0:23
SPEAKER_00: That's good because you were telling me how I should be so lucky to get the chance to work with you before we hit record.
0:28
SPEAKER_00: You're just, you know, I'm feeling lucky.
0:31
SPEAKER_00: Well, you should.
0:32
SPEAKER_00: And I need to do a better job of reminding you of how lucky you are.
0:35
SPEAKER_00: I mean, look at you sitting in there with your hoodie flannel.
0:38
SPEAKER_00: I mean, what is the weather in Michigan right now?
0:40
SPEAKER_00: Is it super cold or what's going on?
0:41
SPEAKER_01: It is.
0:42
SPEAKER_01: Oh man, it's cold.
0:43
SPEAKER_01: Yeah.
0:43
SPEAKER_01: I'm not not liking this very much at all.
0:46
SPEAKER_01: But I'm cozy.
0:47
SPEAKER_01: I'm in my in the basement in the cave.
0:49
SPEAKER_01: In the cave.
0:50
SPEAKER_01: In the recording cave.
0:51
SPEAKER_01: Good to go.
0:52
SPEAKER_00: All right.
0:53
SPEAKER_00: Today, this is a you one, man.
0:55
SPEAKER_00: This is uh this is something you put together.
0:57
SPEAKER_00: You've been to Great Smoky Mountain National Park.
0:59
SPEAKER_00: How many times now?
1:00
SPEAKER_01: Oh, I don't know.
1:01
SPEAKER_01: I have absolutely no idea.
1:03
SPEAKER_01: We go all the time, right?
1:04
SPEAKER_01: We do, yeah.
1:05
SPEAKER_01: Yeah, we do.
1:06
SPEAKER_01: And so, yeah, we've been kind of neglectful, right?
1:09
SPEAKER_01: Uh.
1:10
SPEAKER_01: We've done a lot of episodes on the western mountains, and you know, we've done some things in the southwest, and we've kind of neglected the eastern mountains in the United States, and we can't do that.
1:20
SPEAKER_01: No, we can't be doing that.
1:21
SPEAKER_00: No, definitely not.
1:22
SPEAKER_00: And I live now in the Appalachians, the Central Appalachians, which is a different geology, different rocks, but broadly similar tectonics.
1:30
SPEAKER_00: We just don't get the exposure of the Great Smoky Mountain.
1:32
SPEAKER_00: So I agree.
1:33
SPEAKER_00: We've completely been missing the East Coast, cool East Coast parks and rocks so far in Planet Geo.
1:41
SPEAKER_01: Well, it's why I keep going back to them.
1:43
SPEAKER_01: I love them.
1:43
SPEAKER_01: It's uh not very far away.
1:45
SPEAKER_01: You know, it's like a 10-hour drive, and I love that doable thing.
1:49
SPEAKER_00: That's nothing.
1:49
SPEAKER_01: Um, because to get out west is much, much further.
1:52
SPEAKER_01: So yeah, we go there a lot, and I absolutely love them.
1:56
SPEAKER_00: So we're gonna chunk this up into kind of three general parts.
2:00
SPEAKER_00: We're gonna talk about the bedrock geology, the deformation in mountain building, and then erosion, which kind of sets the smoky mountains or the Appalachians apart from other more modern mountain belts.
2:11
SPEAKER_00: But we need to start out, unfortunately, talking about biology a little bit and why the smokies, why are they smoky?
2:20
SPEAKER_00: So, Chris, why are the smoky mountains smoky?
2:23
SPEAKER_01: Uh yeah.
2:24
SPEAKER_01: Well, if you've ever seen the Smoky Mountains, they have this kind of they have a hue to them for sure.
2:31
SPEAKER_01: Um, a lot of people think the Smoky Mountains are called this because it's got this kind of like smog look to it, but it's actually not, it has a bluish hue to it, which is what sets it apart from a human problem versus like this natural kind of thing that's going on, and that's what is happening in the smokies.
2:50
SPEAKER_01: It comes down to a biological thing that's going on.
2:53
SPEAKER_00: There's one time I remember it wasn't in the Smoky Mountain National Park, but it was in the in the Blue Ridge, and we were sitting, I was with a couple friends, and we're in a national park in Shenandoah National Park, and we were like facing west, and it was at sunset, and we went out and had kind of been raining for a lot of the day, and we had the whiskey sitting on this rock ledge looking out over the valleys.
3:14
SPEAKER_00: And you know what I'm talking about, Chris.
3:15
SPEAKER_00: You have many experiences with Jenny, I'm sure.
3:17
SPEAKER_00: But the clouds were just rolling over the hills, the mountains, and it was just you see these clouds, these really blue clouds, but then there's this haze to it.
3:27
SPEAKER_00: I mean, distances look huge in this region, like it looks like you you can see forever when it's really not that far.
3:34
SPEAKER_00: I think because of this kind of blue haziness to it, right?
3:37
SPEAKER_01: Yeah, and and so you've you've seen that then, right?
3:40
SPEAKER_00: Oh, yeah.
3:41
SPEAKER_00: I just have this really distinct memory.
3:43
SPEAKER_00: We're sitting on this rock ledge, it's kind of cold, it had been raining, like the water's dripping down from the leaves, and there's this like blue fog rolling over the mountains.
3:53
SPEAKER_00: It's just stunningly beautiful as a sunset.
3:55
SPEAKER_00: Beautiful.
3:56
SPEAKER_01: I mean, this actually goes back to Native Americans with the with the Cherokee.
3:59
SPEAKER_01: You know, these mountains have been sacred to the Cherokee, and they refer to them as the Shikanahe.
4:04
SPEAKER_01: That means the land of blue smoke.
4:07
SPEAKER_01: It's really uh an obvious apparent thing.
4:10
SPEAKER_01: So, what is going on with this is actually because of biology.
4:15
SPEAKER_01: The pine trees are shucks.
4:17
SPEAKER_00: Biology actually serves a purpose here.
4:20
SPEAKER_01: Yeah, and it has to do with photosynthesis.
4:23
SPEAKER_01: And you know, I think like on a very general level, most people think of photosynthesis as it takes in carbon dioxide, uses water, and recombines these compounds to create oxygen and sugar, right?
4:36
SPEAKER_01: Um, one of the things that is also given off due to photosynthesis are what are called these volatile organic compounds, or what we refer to all the time as VOCs.
4:46
SPEAKER_01: And it's natural you're smelling it when you smell the scent of a pine forest, for instance.
4:53
SPEAKER_01: That scent is the volatile organic compounds.
4:57
SPEAKER_01: Um, and that's kind of a it's an interesting thing, right?
4:59
SPEAKER_01: Volatile organic compounds sounds horrible.
5:01
SPEAKER_00: And in many ways, they they are kind of bad to breathe in.
5:05
SPEAKER_00: Like, what do you mean?
5:06
SPEAKER_00: I mean, in the lab we talk about VOCs and they're given off with chemical reactions that you really don't want to breathe in VOCs.
5:13
SPEAKER_00: But in this case, they're natural and not harmful to humans, they're in relatively low proportions.
5:19
SPEAKER_01: Right.
5:19
SPEAKER_01: And these VOCs, these volatile organic compounds, they have a very high vapor pressure, which means that they can form vapors at room temperature.
5:28
SPEAKER_01: What happens essentially, I'm just gonna kind of boil this down real quick.
5:32
SPEAKER_01: It's a lot like why our sky is blue.
5:34
SPEAKER_01: It's the same reason.
5:36
SPEAKER_01: When sunlight comes in, the particles that are in our atmosphere, the molecules and so on, they scatter blue light more than the other wavelengths of the visible light spectrum.
5:48
SPEAKER_01: And so because they're they're scattered in random directions and they're scattered towards our eyes, that's what we see is blue.
5:55
SPEAKER_01: Throw into this then all these volatile organic compounds, and they do the same thing.
6:00
SPEAKER_01: They scatter the blue light preferentially, which makes it hazy, and it's bluish because of the blue light getting scattered more than like the reds and the oranges and the yellows, the Roy part of the visible spectrum.
6:12
SPEAKER_01: So it really comes down to the the fact that the smokies have a lot of pinching.
6:21
SPEAKER_00: You know, I was thinking about this as we were putting this script together.
6:24
SPEAKER_00: I was driving back across the Appalachians in Pennsylvania from State College, New York, and yeah, it was this blue haze kind of around, and it was beautiful.
6:31
SPEAKER_00: I mean, it's stunningly beautiful to see.
6:34
SPEAKER_00: And, you know, we have to note that the Great Smoky Mountains are actually the most biodiverse national park in the United States national park system.
6:43
SPEAKER_00: And depending on your definition, could be defined as a temperate rainforest.
6:46
SPEAKER_00: There's a lot of plants, so many trees, a lot of different animal life.
6:50
SPEAKER_00: Over 19,000 species have been documented there, and way more probably live there that have been undocumented, but it's a really biodiverse place, which plays into this.
7:00
SPEAKER_00: Why are they smoky, as you've been talking about, Chris?
7:03
SPEAKER_01: Exactly.
7:04
SPEAKER_01: And I think also it's important to note that they're not the only mountains that are smoky like this.
7:09
SPEAKER_01: Um, you and I have both been to Acadia.
7:12
SPEAKER_01: We we went on a rock collecting trip, not in Acadia, but we were in the vicinity, and so we took a day and just, oh man, we did a ton of hiking on that day in Acadia.
7:22
SPEAKER_01: And they are known for that too.
7:25
SPEAKER_01: They have extensive pine forests, and it get for the same reason they give off these volatile organic compounds and often gives them this kind of bluish haze as well.
7:34
SPEAKER_01: So it's not exclusive to Great Smoky Mountain National Park, but that's what it's known for for sure.
7:40
SPEAKER_01: If you've ever been there, then you know exactly what we're talking about.
7:43
SPEAKER_01: And I I think it's also important to note that like 80% of this uh haze that give the smokies their name comes from this natural thing, this photosynthesis and volatile organic compounds.
7:56
SPEAKER_01: Um 20% of it is coming from burning of like coal and the human-induced emissions, which changes the hue from a bluish to a white kind of thing.
8:07
SPEAKER_01: But the vast majority of the smokies being smoky is totally natural.
8:11
SPEAKER_01: And that's something that a lot of people don't realize.
8:13
SPEAKER_01: They think uh they have this haze, and everybody automatically reverts to oh, it's human smog.
8:18
SPEAKER_00: And that's really typically the natural one tends to give this blue hue, as you mentioned before, whereas unnatural or human-induced or sort of burning coal, those sulfate particles is what they typically are, give a like a whiter, grayish haze and not really this blue tinge to it.
8:35
SPEAKER_00: This blueness is definitely entrenched in Great Smoky Mountain National Park.
8:39
SPEAKER_00: Yeah.
8:39
SPEAKER_01: But on a positive note, they think it's getting better.
8:41
SPEAKER_01: Oh, that's good.
8:42
SPEAKER_01: You know, the with the burning of less coal for electricity primarily, the human-induced side of the smokies is getting better.
8:50
SPEAKER_00: So that's good.
8:51
SPEAKER_00: All right, Chris.
8:52
SPEAKER_00: Uh, I don't know.
8:52
SPEAKER_00: That's enough about biology for me.
8:54
SPEAKER_00: I'm I'm kind of I've had my daily allotment of biology stuff now.
8:58
SPEAKER_00: So let's get into some rocks, shall we?
9:00
SPEAKER_01: Okay, let's do it.
9:01
SPEAKER_00: Like you said, three chunks.
9:02
SPEAKER_00: This is the bedrock geology.
9:04
SPEAKER_00: We're talking about really the basement rocks.
9:07
SPEAKER_00: We term these metamorphic and igneous rocks at the deep roots of the continents bedrock or basement rocks, typically.
9:15
SPEAKER_00: So the smokies are some of one of the oldest mountain chains in the world.
9:20
SPEAKER_00: And we'll kind of end talking about this aspect as well because it shapes how we see the landscape, what the landscape looks like.
9:27
SPEAKER_00: But the oldest rocks in the smokies are really old, over a billion years old.
9:31
SPEAKER_00: The earth again is 4.5 billion years old, 4.5682 billion years old.
9:36
SPEAKER_00: And the oldest rocks here are dated back to ancient supercontinents or ancient continental collision zones where the crust was buried really deeply and heated up and metamorphosed, high pressures, high temperatures, and was buried in these ancient mountain belts, even more ancient than the smokies.
9:56
SPEAKER_00: The smokies are ancient, but we're talking about one step further back than the smokies.
10:00
SPEAKER_01: I want to ask you a question with something that you said.
10:03
SPEAKER_01: You said that these are one of the oldest mountain chains.
10:05
SPEAKER_01: Uh and the rocks, some of the rocks are super old.
10:09
SPEAKER_01: However, they're not as old as the rocks that are exposed in the core of the Tetons, for instance, or the rocks that are exposed in parts of the Rockies.
10:18
SPEAKER_01: All right.
10:20
SPEAKER_01: So what we're talking about is really two different things, right?
10:24
SPEAKER_01: We talk about these this is the oldest mountain chain.
10:27
SPEAKER_01: What we're referring to is uh that the actual like mountain building events that took place are super, super old.
10:36
SPEAKER_01: The rocks that are exposed are not necessarily the oldest rocks that you know that we've discussed in previous episodes, right?
10:44
SPEAKER_00: That's right.
10:44
SPEAKER_00: So we talk about kind of two different things here.
10:47
SPEAKER_00: We're exactly we're talking about when did the mountains, the topographic feature of the mountains form, and when did the rocks form?
10:54
SPEAKER_00: And those are two distinct events, right?
10:58
SPEAKER_00: And so we're talking right now about the rocks that are exposed, which could be have been formed and metamorphosed during the most recent mountain building event, but in this case, they were formed during a prior mountain building event, so before the smoky mountains were formed, before the topographic feature of the smoky mountains was formed.
11:16
SPEAKER_00: I think another way to explain it, which hopefully makes a little bit more sense, is that there have been several continental collisions throughout Earth history.
11:27
SPEAKER_01: Well, I think what you mean is like supercontinents, right?
11:31
SPEAKER_01: Supercontinents, exactly.
11:32
SPEAKER_01: Most people, most of our audience is familiar with the term Pangaea, which is the last time that the world, the earth, had a supercontinent on it, right?
11:44
SPEAKER_01: But what a lot of people don't realize is that that's just the last time that happened.
11:50
SPEAKER_01: And in order to talk about the smokies, we have to talk about an earlier supercontinent.
11:55
SPEAKER_01: And I want to throw this back to you, Jesse, because this is kind of right up your alley because you deal with all things old.
12:02
SPEAKER_01: So what are we talking about?
12:04
SPEAKER_01: What's this supercontinent and when did this happen?
12:06
SPEAKER_00: So supercontinents are times in Earth history when most of the continental land masses were all one single unit.
12:13
SPEAKER_00: They were all aggregated together into one package, hence supercontinent.
12:17
SPEAKER_00: You have one or two supercontinents on Earth during a supercontinent cycle.
12:22
SPEAKER_00: So basically, you take North America, you take Africa, you take Europe, you smash them together, that's a supercontinent.
12:28
SPEAKER_00: And that has happened multiple times.
12:30
SPEAKER_00: You said Pangea.
12:31
SPEAKER_00: Pangea existed the last couple hundred million years, so 330 million years to about 170 million years ago.
12:40
SPEAKER_00: That was Pangea.
12:41
SPEAKER_00: That's prior to the Atlantic Ocean opening up.
12:44
SPEAKER_00: So Europe, Africa, the Americas, North and South America, smash them together, supercontinent Pangea.
12:50
SPEAKER_00: There have been older ones.
12:52
SPEAKER_00: There's some like Gondwana, there's some like Rhodinia, and that's the one that we're going to talk about.
12:57
SPEAKER_00: Rhodinia, R-O-D-I-N-I-A.
13:00
SPEAKER_00: That is a supercontinent that existed between 1.1 billion years ago and 750 million years ago.
13:07
SPEAKER_00: So between that time interval for that 400 million year cycle, the continents were grouped together.
13:14
SPEAKER_00: So I think to kind of bring it back to mountain building events, when you smash continents together, when you aggregate continents, that is a very violent event that builds mountains and that creates metamorphism.
13:24
SPEAKER_00: That metamorphoses rocks.
13:26
SPEAKER_00: The rocks caught up in that collision or that aggregation of continents together get deformed, altered, metamorphosed.
13:35
SPEAKER_00: And that's what we are seeing in the basement of the Great Smoky Mountains is 1.1 billion year old rocks that were formed and metamorphosed during the formation of Rhodinia, this ancient supercontinent.
13:49
SPEAKER_01: Right.
13:49
SPEAKER_01: And so we refer to that as a continent-to-continent convergent boundary.
13:53
SPEAKER_01: We have a modern-day analogy of that actually.
13:55
SPEAKER_01: We can point to you know the Himalayas, where the subcontinent of India is colliding with Eurasia.
14:01
SPEAKER_01: And what happens with continent-to-continent convergence is a little bit different than what happens when, let's say, an oceanic plate collides with a continental plate or converges with it, right?
14:11
SPEAKER_00: What is the main difference?
14:12
SPEAKER_00: Well, the main difference is that an oceanic plate is more dense and thinner, so it subducts, it gets recycled into the mantle.
14:18
SPEAKER_00: Continents are too buoyant and too thick to be subducted.
14:23
SPEAKER_00: So they just smash together.
14:25
SPEAKER_00: And you create doubly thick continental crust, which causes a lot of metamorphism.
14:30
SPEAKER_00: The Himalayas are about 70 kilometers thick, the continental crust is, whereas in most continental crusts it's more like 35 or 40 kilometers thick.
14:39
SPEAKER_00: And so these supercontinents, as we go back in time, there have been more supercontinent cycles proposed.
14:45
SPEAKER_00: You know, rocks that I study that are about 2.7 billion years old, which you mentioned at the base of the Tetons.
14:51
SPEAKER_00: There's a supercontinent proposed that would have been Kenorland, or there's some various other proposals for a possible supercontinent that long ago, back in Earth history, but we just have less information from that far back in time.
15:04
SPEAKER_01: Okay, so let's get back on track then.
15:06
SPEAKER_01: Rhodinia, this supercontinent that began happening about 1.1 billion years ago.
15:13
SPEAKER_01: Why is that important?
15:15
SPEAKER_01: That's what happened.
15:17
SPEAKER_01: But how does that play into the beginning, anyway, of the story of the great Smoky Mountain Ash?
15:23
SPEAKER_00: Well, so we have to consider that the rocks themselves, these deep-rooted rocks, were metamorphosed during that mountain building event.
15:30
SPEAKER_00: So those rocks contain a record of this supercontinent cycle.
15:34
SPEAKER_00: And then after that, at some point, that supercontinent broke apart and formed another ocean.
15:41
SPEAKER_00: So you imagine when about 175 million years ago the Atlantic Ocean started forming.
15:49
SPEAKER_00: When you had a supercontinent, you had Africa and South America and Europe and North America all smashed together, the continent started to break apart, and you formed a big ocean basin in there, and it's still getting bigger and bigger and bigger today.
16:04
SPEAKER_00: That process has happened before.
16:06
SPEAKER_00: And so this breakup of Rhodinia formed this ocean basin.
16:11
SPEAKER_00: And that formed a lot of the younger rocks that we see in the Smoky Mountains.
16:14
SPEAKER_00: So that's kind of why we have to worry about this event.
16:17
SPEAKER_01: So this continental convergence created these massive mountains, and then it began to break apart.
16:24
SPEAKER_01: And what happens when you take these continental convergence and then begin to split them apart is you have the highlands, you also have these immense basins that are created by this divergence, right?
16:35
SPEAKER_01: So you have the sediment then from the highlands, these rocks that are being weathered and eroded and carried down into this newly created basin that is just continuing to open up and get bigger and bigger and bigger, and more and more sedimentary rocks are being deposited there.
16:54
SPEAKER_01: And there's this one basin that's important in Great Smoky Mountain National Park because the Okoe Basin is where Great Smoky Mountain National Park sits today.
17:07
SPEAKER_01: And what was going on in the Okoe Basin?
17:09
SPEAKER_00: In this time period, this supercontinent is breaking apart.
17:13
SPEAKER_00: And there's a few modern analogies for this.
17:16
SPEAKER_00: One is the East African Rift in Africa, where you have segments of continental crust that are separating.
17:23
SPEAKER_00: There's a lot of volcanic activity.
17:25
SPEAKER_00: There's actually sediments being deposited.
17:27
SPEAKER_00: Because if you think if you pull apart something, you stretch it and you pull it apart, you're going to get cracks forming in it.
17:33
SPEAKER_00: And the stuff that's being pulled apart is thinned, which means that you have a topographic relief generated.
17:39
SPEAKER_00: Now you have thick crust on the edges, you have thin crust in the middle where it's being stretched and broken apart, which means that erosion starts to happen.
17:47
SPEAKER_00: And you pull sediments from the high parts, from the thick parts, and you erode those into the basin that you're forming.
17:53
SPEAKER_00: So that's still ongoing right now.
17:57
SPEAKER_00: The Appalachian Mountains are being eroded into the Atlantic Ocean and being deposited there because that's a thinner area.
18:03
SPEAKER_00: We have topography, so erosion happens.
18:06
SPEAKER_00: So this basin that's been forming, it's formed as you stretch apart continental crust and you break it, you get sedimentation, you get sediments being formed.
18:15
SPEAKER_00: And that eventually forms rocks, which we see today.
18:18
SPEAKER_00: And they're forming the rocks that we see now in the Great Smoky Mountain National Park.
18:22
SPEAKER_01: So rivers were carrying massive amounts of sediment to this basin where the smokies sit today.
18:28
SPEAKER_01: And this is an amazing thing, to me, anyway.
18:32
SPEAKER_01: There are nine miles of vertically accumulated sedimentary rocks in this Okoe basin.
18:41
SPEAKER_01: Nine miles.
18:42
SPEAKER_00: It's amazing.
18:43
SPEAKER_01: It is.
18:44
SPEAKER_01: So how does that happen?
18:45
SPEAKER_01: Like I think we need to talk about this a second and paint a picture of wait a minute, how can you get nine miles of vertically accumulated rocks?
18:53
SPEAKER_01: Because you know, I'm looking outside right now, it's kind of cloudy out.
18:55
SPEAKER_01: The clouds are maybe a mile high.
18:57
SPEAKER_00: I know.
18:57
SPEAKER_00: Nine miles is incredible.
18:59
SPEAKER_01: How does that happen?
19:00
SPEAKER_00: Yeah, so there's this term called isostasy.
19:05
SPEAKER_00: And isostasy is how high does the crust float?
19:10
SPEAKER_00: You can think of it like floating on the mantle.
19:13
SPEAKER_00: So the crust is floating on the mantle and thicker crust.
19:18
SPEAKER_00: You have this analogy, Chris, of a shipping container, a cargo ship with shipping containers on it.
19:24
SPEAKER_00: If you load up shipping containers, heavy, full shipping containers on the ship, the bottom of the ship is gonna sink down.
19:32
SPEAKER_00: The top is still gonna float high, though.
19:35
SPEAKER_00: But as you put your first layer on, the ship's floating pretty high.
19:38
SPEAKER_00: It's you don't have a deep draft in the ship.
19:41
SPEAKER_00: Put your second layer of shipping container ships on it, it's gonna sink down, third layer sink down, fourth layer.
19:47
SPEAKER_00: I mean, maybe these things go up 15 layers.
19:49
SPEAKER_00: I don't really know.
19:49
SPEAKER_00: How high do shipping container layers go?
19:51
SPEAKER_00: 15, let's say.
19:54
SPEAKER_00: And so as you layer these things on, the ship sinks down.
19:58
SPEAKER_00: That's what's going on here to accumulate nine miles of sediments, is that as you pile sediments into the basin, the basin sinks down and you can put more sediments in there.
20:10
SPEAKER_00: You're creating room.
20:12
SPEAKER_01: Right.
20:12
SPEAKER_01: It allows for more deposition, and that's exactly what's going on.
20:15
SPEAKER_01: You said you referred to it earlier about the sediment getting shed off from the Appalachians today, is getting carried to the Mississippi Delta.
20:23
SPEAKER_01: Well, it's the exact same process.
20:26
SPEAKER_01: If you don't have this process going on, then the deposition gets spread out over this vast area.
20:32
SPEAKER_01: But instead, what happens is it deposits sediment, that sediment weighs a lot, it causes it to sink, which allows for more sediment to be deposited, which sinks and it just repeats again and again and again.
20:42
SPEAKER_00: And this term is called accommodation space.
20:45
SPEAKER_00: How much sediment can you pack in there before it fills up?
20:48
SPEAKER_00: Because once it fills up, you can't put any more sediments in there and there's no more erosion.
20:52
SPEAKER_00: But the subsidence creates more accommodation space.
20:55
SPEAKER_00: The weight of the sediments causes it to sink down, it creates more space to put more sediments in.
21:00
SPEAKER_01: That's cool.
21:01
SPEAKER_01: Now we got nine miles of sediment, which is an amazing scientific fact.
21:06
SPEAKER_01: But what does it look like?
21:07
SPEAKER_01: Well, it's relatively flat, vertically accumulated, sedimentary rocks, so it looks nothing like the mountains we see today.
21:16
SPEAKER_01: We're gonna get to that point, but we need other steps in there.
21:19
SPEAKER_01: But there's one other thing that happened with this host of rocks, too, right?
21:24
SPEAKER_01: That we have much younger sedimentary rocks, you know, 540 to ish 450 million years old.
21:32
SPEAKER_01: That's much younger than these rocks we just got done talking about.
21:36
SPEAKER_01: And this was a little bit different in the sense that it transitioned to this shallow continental margin kind of deposition where we had rocks like limestones being deposited then and other you know shallow marine, typical shallow marine sedimenture rocks.
21:53
SPEAKER_00: Absolutely.
21:54
SPEAKER_00: And so it basically transitions from a lot of sedimentation, a lot of deposition, a lot of this isostatic.
22:00
SPEAKER_00: Sinking and accommodation space buildup to a more passive environment where there's not a lot of erosion happening.
22:05
SPEAKER_00: There's not a lot of topography that creates this accommodation space.
22:10
SPEAKER_00: So it becomes a little bit more passive, but it continues forming rocks.
22:13
SPEAKER_00: You're exactly right, Chris.
22:14
SPEAKER_00: And these early phases are very active.
22:17
SPEAKER_00: There's a lot of copper deposits formed in this Echoe basin, but it kind of calls everything kind of calms down and becomes a passive margin, which deposits these background sediments.
22:27
SPEAKER_01: And some of these younger rocks have some really cool fossils in them.
22:30
SPEAKER_01: The fossils, they they're like from burrowing organisms, filter feeders, things like this.
22:35
SPEAKER_01: And so you have fossils in and of themselves, but you also have trace fossils where you have these like burrows where these organisms were going.
22:43
SPEAKER_00: And it's super this time period is the this sort of 570 to 450 million year time period, is really the onset of multicellular life on Earth.
22:52
SPEAKER_00: So there's this a big explosion in biodiversity for the first time in Earth history.
22:56
SPEAKER_00: And so the trace fossils are crazy in here sometimes.
22:59
SPEAKER_01: Yeah.
23:00
SPEAKER_01: All right.
23:00
SPEAKER_01: Let's move on, Jesse, to the next phase then, which is the deformation and mountain building.
23:07
SPEAKER_01: We're going to get closer then to how do we get to these mountains looking like.
23:11
SPEAKER_00: Absolutely, let's do it.
23:12
SPEAKER_00: So we've arrived at the point where these continents are spreading apart.
23:15
SPEAKER_00: We have this passive margin, sedimentation's happening, but eventually they start to come back together.
23:20
SPEAKER_00: We talked about this supercontinent cycle and how we have multiple supercontinents in history.
23:24
SPEAKER_00: We need to build Pangaea now.
23:26
SPEAKER_00: So what happens is these continents start to come back together.
23:30
SPEAKER_00: And there's multiple collisional events that happen during this process.
23:35
SPEAKER_00: It takes a while to add a bunch of stuff to the continents.
23:38
SPEAKER_01: This is just a random process, right?
23:40
SPEAKER_01: I mean, continents coming together, it's totally a random thing.
23:43
SPEAKER_00: That's it's up for debate whether it's a random thing or not.
23:46
SPEAKER_00: I mean, where they occur, but it basically imagined continents.
23:49
SPEAKER_00: Really?
23:50
SPEAKER_01: I always thought that it was just a given that when supercontinents form, it's kind of just this random thing that happened.
23:59
SPEAKER_00: Well, I think it's a little bit up for debate.
24:01
SPEAKER_00: There's this old idea named after Tuzo Wilson of plate tectonics fame, uh, that is called the Wilson cycle, which is jumping Tuzo Wilson.
24:10
SPEAKER_00: Yeah, just uh Oh my god.
24:16
SPEAKER_00: I need a new podcast partner.
24:17
SPEAKER_00: Uh so there's a there's this idea that supercontinents have existed on kind of a 400, 450 year cycle throughout history.
24:26
SPEAKER_00: If you compare Pangaea to Rhodinia, it's about 450 million years apart, and that goes back further in time.
24:32
SPEAKER_00: And the thinking is that if you break apart a continent, a supercontinent, as it spreads out, it only has a certain amount of distance to go till it gets all the way around the earth and they run back into each other.
24:43
SPEAKER_00: I mean, that's that's a gross oversimplification, but basically, like continents will drift apart and then they'll hit each other on the other side.
24:49
SPEAKER_00: That cycle is around about 450 million years.
24:52
SPEAKER_00: Again, very oversimplified, but that's a good way to kind of picture it, I think, this time period.
24:57
SPEAKER_01: That's awesome.
24:57
SPEAKER_01: I yeah, I'm gonna look into this then more.
25:00
SPEAKER_01: I've got I've got work to do.
25:01
SPEAKER_00: It's not quite right that they drift around and and hit each other, but they kind of spread apart till they don't spread anymore, and then they come back together.
25:08
SPEAKER_00: So ocean basins open up and close.
25:10
SPEAKER_00: And so that's what's happening.
25:13
SPEAKER_00: Now we're starting the continents kind of drift back towards each other.
25:16
SPEAKER_00: They're moving via plate tectonics, and they eventually run into each other.
25:20
SPEAKER_00: There's some island arc accretionary events that happen that are relatively minor.
25:24
SPEAKER_00: They create little mountains, but not on the scale of continent-continent collision.
25:29
SPEAKER_00: That's a big event.
25:30
SPEAKER_00: And so, Chris, what happens to the rocks when that happens?
25:34
SPEAKER_01: So before the continents come together, we have nine miles of rather boring, flat, vertically accumulated sedimentary rocks.
25:42
SPEAKER_01: Now I say boring, it's amazing that there's that much, but that's what we have.
25:46
SPEAKER_01: When you take then these continental land masses and they collide together then to form Pangaea.
25:54
SPEAKER_01: So we're talking about North America colliding with Europe and and Africa.
25:58
SPEAKER_01: So this continent to continent convergent boundary takes these flat-line sedimentary rocks and it throws them into massive folds like anaclines and synclines, and there were earthquakes and faults and things like this going on.
26:12
SPEAKER_01: Because if you bend rocks too far too fast, they break.
26:15
SPEAKER_01: Okay.
26:16
SPEAKER_01: And so some of these earthquakes were violent earthquakes.
26:20
SPEAKER_01: It began to now really get interesting.
26:22
SPEAKER_00: And it deforms the rocks that we see.
26:24
SPEAKER_00: So the pressures and temperatures are pretty high.
26:28
SPEAKER_00: In the Smoky Mountain National Park, we get to, I've seen numbers that are around 700 degrees and nine kilobars, which is basically about 27 kilometers deep.
26:40
SPEAKER_00: So pretty thick and pretty deep, the metamorphosis.
26:43
SPEAKER_00: So you're taking these sediments and putting them down, not just nine miles deep, but 27 kilometers deep.
26:48
SPEAKER_00: That's a big difference.
26:50
SPEAKER_00: So we're burying them even further, heating them up and metamorphosing them during this time.
26:54
SPEAKER_01: And we're talking about the entire Appalachian mountain region that's being uplifted and affected this way.
27:01
SPEAKER_01: So that we're not just talking about the smokies here.
27:03
SPEAKER_01: We're talking about the entire range that goes through the you know, the Blue Ridge Parkways, Shenandoah National Park, Great Smokies up to Acadia.
27:12
SPEAKER_01: It's this entire mountain range that's being affected.
27:16
SPEAKER_01: And it didn't all happen at the same time.
27:18
SPEAKER_01: It was kind of like a you know, a swinging door.
27:22
SPEAKER_00: That's a perfect analogy, Chris.
27:23
SPEAKER_00: I love the swinging gate, swinging door kind of analogy.
27:26
SPEAKER_00: That that's great.
27:27
SPEAKER_00: So, Chris, during this phenomenon, you you take sandstones, you turn them into quartzites, you take shales, you turn them into slates, or schifs, or something even higher grade.
27:37
SPEAKER_01: I want to just say, Jesse, that these mountains they were much larger during this time at the peak of this mountain building event, they were bigger than the Rockies today.
27:49
SPEAKER_01: I mean, these were mountains that were more like the Himalayas than the Rockies, right?
27:54
SPEAKER_01: I mean, these these were massive mountains at the time.
27:57
SPEAKER_01: So where did this heat and pressure, obviously the pressure, I think, but where did this all come from?
28:04
SPEAKER_01: What's the source of this?
28:05
SPEAKER_01: What's going on?
28:06
SPEAKER_00: Well, the heat, well, the pressure, yeah, you're right.
28:08
SPEAKER_00: It's it's just burial, so it's higher pressure.
28:10
SPEAKER_00: The heat is the same kind of thing, basically.
28:12
SPEAKER_00: You know, as you bury stuff, the interior of the earth is hotter, and so you're both putting rocks down deep, and it's also harder to get that heat out.
28:20
SPEAKER_00: So the rocks have this internal radiogenic heat production.
28:23
SPEAKER_00: We've talked about uranium in rocks before.
28:25
SPEAKER_00: They're producing heat internally, and so if you bury them, it's harder to get that heat out.
28:29
SPEAKER_00: It's like putting them under a big blanket, and so they kind of internally heat up as well.
28:33
SPEAKER_00: So there's two kind of two sources of heat.
28:35
SPEAKER_00: Uh, but but really it comes down to this radiogenic heating.
28:38
SPEAKER_00: So it's thick, the heat is under this blanket, and so they heat up and they get pretty hot.
28:42
SPEAKER_01: One thing I love about like that burial metamorphism, that process is that if there were any sedimentary structures in the rocks, trace fossils, ripple marks, mud cracks, things like this, burial metamorphism preserves those.
28:56
SPEAKER_01: It changes the rocks to a different rock.
28:59
SPEAKER_01: You know, quart sandstone gets changed into quartzite and things like that, but it'll preserve those structures, which I think is is super, super cool.
29:07
SPEAKER_01: This massive amount of folding that we're talking about and faulting going on.
29:12
SPEAKER_01: You see this.
29:12
SPEAKER_01: These are no longer flat line sedimentary rocks.
29:15
SPEAKER_01: You drive through any part of the Appalachian region and you look out the window and these road cuts and you see rocks that are sometimes they're folded to the point where they're straight up and down.
29:25
SPEAKER_01: That's just I I never get tired of that.
29:28
SPEAKER_01: Looking at the amount and the and the power behind this kind of deformation is mind-boggling to me.
29:35
SPEAKER_00: Yeah, it's a super powerful event, super aggressive, really.
29:40
SPEAKER_00: I like the way you said that, Chris.
29:41
SPEAKER_00: Sandstones were turned into quartzites, shales were turned into slates and even higher grade rocks during this metamorphism, and and so some of the structures are preserved and and some of them are overprinted because of higher temperature, higher grade metamorphism.
29:55
SPEAKER_00: So Chris, then we have to move on.
29:58
SPEAKER_00: We've got this big, high, really high mountain belt.
30:02
SPEAKER_00: We're not yet at the current version of the Smoky Mountains.
30:05
SPEAKER_00: We have to get there, and so that's erosion.
30:08
SPEAKER_00: So that's the third part of what we're gonna talk about is erosion.
30:13
SPEAKER_00: What happens to this mountain belt after the last 250 million years?
30:18
SPEAKER_01: Right.
30:18
SPEAKER_01: And I I like the saying erosion happens.
30:21
SPEAKER_01: You know, like shit happens, erosion happens.
30:24
SPEAKER_01: That's good.
30:25
SPEAKER_01: It uh it does.
30:27
SPEAKER_01: It should be a t-shirt, right?
30:28
SPEAKER_01: It should be a t-shirt.
30:29
SPEAKER_01: Just erosion happens.
30:30
SPEAKER_00: You could make a t-shirt, erosion happens, and put the little Planet Geo logo on it.
30:34
SPEAKER_00: That'd be good.
30:35
SPEAKER_00: A good idea.
30:36
SPEAKER_01: Yeah, I know.
30:36
SPEAKER_00: I so Chris, what happens?
30:39
SPEAKER_00: You know, that we're talking about erosion, breaking things down.
30:41
SPEAKER_00: What happens during this process?
30:43
SPEAKER_00: Where are we at?
30:44
SPEAKER_01: Where we're at now is that the continental convergence, this massive mountain range that was formed by this, it transitions now to breaking apart.
30:55
SPEAKER_01: Now we're gonna take Pangaea and we're gonna begin to split it apart into something that, well, eventually it looks like where we're at today, because that's that's what happens.
31:04
SPEAKER_01: So around 240 million years ago, Pangaea began to break apart.
31:09
SPEAKER_01: The Atlantic Ocean is a result of that uh divergence, and it's still going on today.
31:15
SPEAKER_01: The Atlantic Ocean's getting bigger and bigger and bigger from the same event okay that broke apart Pangaea.
31:22
SPEAKER_01: So there are I like this uh in geology, there are patterns in geology.
31:27
SPEAKER_01: I think that's helpful to recognize that kind of thing and to to point that out.
31:31
SPEAKER_01: So we have this mountain building event, right?
31:34
SPEAKER_01: And when the mountain building event ends, and when any mountain building event ends, what takes over?
31:39
SPEAKER_00: Well, erosion happens, I think.
31:41
SPEAKER_01: That's right, erosion happens.
31:43
SPEAKER_01: My new shirt idea.
31:44
SPEAKER_01: And so that's a pattern, right?
31:46
SPEAKER_01: If you want to boil geology down really, really to simple terms, you have two forces at play forces that lift things up, that's plate tectonics, and forces that wear things down, and that's weather and erosion.
32:00
SPEAKER_01: Right.
32:00
SPEAKER_01: And so the mountain building event is now done, and now divergence pulling apart begins to take over, and erosion then begins to be the dominant process.
32:12
SPEAKER_01: And so the mountains we see today is the core that existed a hundred million years ago from this mountain building event.
32:20
SPEAKER_01: So we're exposing as erosion happens, you're exposing older and older and older rocks.
32:27
SPEAKER_01: And so the sediment gets carried away, it's now being deposited in the Gulf of Mexico.
32:31
SPEAKER_01: All these rivers bring it to the Mississippi and down it goes.
32:34
SPEAKER_01: I think of it this way.
32:35
SPEAKER_01: I I got I got a little joke here, okay?
32:38
SPEAKER_01: I think because I'm proud of myself.
32:40
SPEAKER_01: You have this like what used to be this really muscular mountain range, okay?
32:46
SPEAKER_01: And it now it's losing its physique and it's developing a bit of a punch.
32:51
SPEAKER_01: It's it's kind of like you.
32:53
SPEAKER_01: You know, like you not that you were not that you were ever not that you were ever muscular or anything like that.
33:00
SPEAKER_01: That's a good one.
33:01
SPEAKER_00: That's one of your better jokes.
33:02
SPEAKER_00: You're deteriorating.
33:05
SPEAKER_00: Well done.
33:05
SPEAKER_00: I uh I applaud you for that one.
33:07
SPEAKER_00: That was a good one.
33:08
SPEAKER_00: That was a good one.
33:09
SPEAKER_00: And then, you know, not far off.
33:10
SPEAKER_00: Uh not far off.
33:12
SPEAKER_00: You know, this lack of going to the gym during COVID.
33:14
SPEAKER_00: I was actually, I've tried to, I think I was talking to you about this before.
33:17
SPEAKER_00: I've been you know playing basketball and mountain biking again.
33:20
SPEAKER_00: And oh my god, I am so out of shape.
33:23
SPEAKER_00: I'm so unfit.
33:24
SPEAKER_00: It's unbelievable.
33:25
SPEAKER_00: Man, it goes away pretty quick.
33:27
SPEAKER_01: I know.
33:27
SPEAKER_01: I gosh.
33:28
SPEAKER_01: Well, Jesse, I have to look at you when we record this.
33:32
SPEAKER_00: We're looking at each other and like I'm looking a bit, am I looking a bit heavy right now?
33:36
SPEAKER_00: Oh, that's no good.
33:37
SPEAKER_00: All right, I gotta black it.
33:40
SPEAKER_00: That's a funny joke and uh uh quite a good analogy, actually.
33:44
SPEAKER_00: Yeah, the mountains lose their physique and develop a paunch.
33:47
SPEAKER_00: That's a good one.
33:47
SPEAKER_00: I like that.
33:49
SPEAKER_00: So I mean, but you're absolutely right.
33:51
SPEAKER_00: I mean, this is this is a great analogy, and uh you look at the Rockies, you look at the Himalayas, you look at any of these more modern active mountain belts, and they look aggressive, right?
34:02
SPEAKER_00: They look like, oh, that's a dangerous mountain belt.
34:05
SPEAKER_00: You look at the Appalachians, uh, it's not quite that way, right?
34:09
SPEAKER_00: It just doesn't have that raw power behind it, that you just don't have that raw power and aggression in the mountain belt.
34:16
SPEAKER_00: And the weathering process happens differently too, right?
34:19
SPEAKER_00: There's way more time for what we call differential weathering and erosion to take place, which means that some rocks are harder to weather than others.
34:26
SPEAKER_00: That's all that means.
34:27
SPEAKER_00: And so over time, hard rocks will remain as hills and peaks and mountains, and soft rocks will be made into valleys.
34:36
SPEAKER_00: And we can see this all throughout the eastern United States.
34:40
SPEAKER_00: Where I'm at in York is this really rolling countryside, and the hills are all resistant rock layers that are slightly more resistant than the valley layers.
34:50
SPEAKER_00: And so all the ridges and valleys formed by this differential weather and erosion where ridges are tough stuff, valleys are weak stuff, usually tough stuff like quartzite or metamorphic rocks, and the weak stuff is shale or slates, and those things get knocked down eroded into deeper valleys.
35:08
SPEAKER_00: And this also forms a lot of the water features that you see in Smoky Mountain National Park, right, Chris?
35:13
SPEAKER_01: That's right.
35:14
SPEAKER_01: Lots of waterfalls.
35:16
SPEAKER_01: This gives us an opportunity then to talk a little bit about how well how do waterfalls often develop, right?
35:20
SPEAKER_01: Well, as as a river is down cutting through, let's say, a resistant rock type, and it downcuts the down cuts, but below that resistant rock type is a softer, weaker, kind of a wimpy rock.
35:34
SPEAKER_01: When it gets down to the point that erodes through the hard rock and starts to encounter the soft rock beneath it, it'll erode the soft rock much faster at that point, and that's what's going to begin to develop into then a waterfall.
35:48
SPEAKER_01: It forms this what we call in geology a nick point, where you go from hard rock to soft rock.
35:54
SPEAKER_01: The nick point is where the soft rock gets exploited much faster than the hard rock does, and it forms a waterfall.
36:03
SPEAKER_00: And so And uh you've got a couple I have not actually been to Smoky Mountain National Park.
36:09
SPEAKER_00: You've been there, like we said, many times.
36:11
SPEAKER_00: And so our Geo Short next week, we are going to talk about various places you can go to see this really cool geology, many of them waterfalls, in the Great Smoky Mountain National Park.
36:23
SPEAKER_00: And so tune in next week for some specific places when you're planning your summer trip to Smoky Mountain National Park to go see the cool geology there, right, Chris?
36:32
SPEAKER_00: So I think that's kind of a wrap, right?
36:35
SPEAKER_00: On our we've covered our three things here, and you want to just quickly summarize them and and uh we can call it uh an episode?
36:41
SPEAKER_01: Yeah, sure.
36:41
SPEAKER_01: Uh so we started with the basement rocks, the bedrock geology of the old core of the mountain range, and then we got into this massive accumulation of sedimentary rocks that then got deformed when Pangaea formed.
36:56
SPEAKER_01: When Pangea came together, it took these rocks and folded them and faulted them and just made them spectacular.
37:04
SPEAKER_01: And then when Pangea began to break apart, the mountain building is done, and the pattern in geology, when the mountain building's done, erosion takes over, and that's where we're at right now.
37:13
SPEAKER_01: So erosion has been going on now since the breakup of Pangea, and I want to be really clear about this.
37:22
SPEAKER_01: I I love the smokies, I love the Appalachians.
37:26
SPEAKER_01: We said that they're not a muscular range anymore.
37:28
SPEAKER_01: They used to be, they're not anymore, but not to take away from them, they're just different.
37:33
SPEAKER_01: These mountains look different, but I absolutely love them.
37:38
SPEAKER_01: They're absolutely leader.
37:39
SPEAKER_01: So go there.
37:40
SPEAKER_00: They're beautiful, they're really, really, really spectacular, and there's really cool geoscience to be seen and learned in the region for sure.
37:48
SPEAKER_00: Um, so Chris, that's a great one.
37:50
SPEAKER_00: We'll wrap up by saying, as usual, if you like Planet Geo, follow us on all the social medias, give us a rating and a review, those help the algorithm.
37:57
SPEAKER_00: Visit our new website, planetgeocast.com, send us an email, planetgeocast at gmail.com, and our social media intern is Livy Leone.
38:06
SPEAKER_00: She's been doing a great job.
38:07
SPEAKER_00: Check out all the social medias at Planet Geocast.
38:10
SPEAKER_01: And most importantly, share this with somebody that you think would like it.
38:15
SPEAKER_00: Absolutely.
38:16
SPEAKER_00: Cheers.
38:16
SPEAKER_00: Cheers.