PlanetGeo: The Geology Podcast
PlanetGeo: The Geology Podcast
The Grand Canyon National Park
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“Crying: acceptable at funerals and the Grand Canyon” - Ron Swanson
Today, we talk about the Grand Canyon. The scenery and geology combine to create one of the Natural Wonders of the World. If you are planning a trip, or would like to learn more about this spectacular location, listen to this episode!
It’s hard to show the principles of stratigraphy better than what’s on display in the Grand Canyon. Each layer gives clues to the environment of deposition and what the Earth was like at the time the sediment was laid down. It’s one of the best example of the geological Laws of Superposition and Original Horizontality on the planet. Other relative dating principles, that are also amazing textbook examples, include the principles of lateral continuity and cross cutting relations.
In this episode you will learn about the three main groups of rock formations on display in the Canyon. Really the only way to talk about them is from oldest to youngest - start at the beginning and work to last page in the book. The three formations are:
1- The Metamorphic Basement Rocks (up to 1.7 BILLION years old!)
2- The Precambrian Grand Canyon Supergroup - all sedimentary rocks with a billion years of missing time.
3- Paleozoic Strata - a continuous record of Earth for ~300 million years.
The bottom line is that the rocks are old, and the canyon is young. We end this podcast with a discussion of the very young volcanic rocks around the Grand Canyon like Sunset Crater, and we also discuss some scientific ideas about how the Canyon formed, a process that started about five million years ago.
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Welcome to Planet Geo, the podcast where we talk about our amazing planet, how it works, and why it matters to you. All right, Chris, how are we doing today? I'm doing great. How are you doing, Jess? I yeah, I'm doing pretty well. Doing pretty well. This is fun.
SPEAKER_00You had to think about that, right?
SPEAKER_02Yeah, well, you know, this week, you know, it's been a week, but we're here. We're having fun. We're doing the podcast. It's great, man. I love it. We're talking about the Grand Canyon. It's super fun stuff.
SPEAKER_00It is, it is. So you should not be contemplating whether or not you're having a good day.
SPEAKER_02Okay. That's true. That's true. Good job. Just to be clear. Uh, before we get into the Grand Canyon, let's do some introductions real quick. You, okay, my friend, are Chris Bullheis, my former high school teacher. And you're a high school teacher from the great state of Michigan. You're award-winning, nationally recognized for your vigor in front of the high school students. Let's say it that way.
SPEAKER_00Yeah. Yep. And you're Dr. Jesse Rymanck. And I don't like to call you doctor very often because, you know, I told you I'd only say that once. I'm saying that a whole lot more than once these days. I know. I don't know.
SPEAKER_02I don't like it. This is my grand ploy to do a podcast with you, is to get you to say it more and get you more comfortable.
SPEAKER_00But you are Dr. Jesse Rymanck, uh, one of my former students. Extraordinaire, also. And um, yeah, this is Planet Geo, and this is where we talk about our amazing planet, how it all works, and why it matters to you.
SPEAKER_02That's right. So this week we're doing a little something a little special. Before we get into the Grand Canyon, we're covering the Grand Canyon this week. Really awesome episode, amazing topic. Like, you can't go wrong with it. Great geology. Great geology. But before we get into that, we're gonna do a little like promotion thing here. So we had some we had some stickers made, some Planet Geo stickers, Chris. And you got one. I know you got one. Where is yours?
SPEAKER_00Mine is on the front of my desk at school. And so my kids are always they're always asking about it. Mr. Boys, what's the name of your podcast? And I just point to it. It's right there.
SPEAKER_02That's the logo, that's the name. It's got it all. So, I mean, I think it's a pretty cool logo, right? We designed it, it's pretty cool. Uh, the stickers, they're really high quality. I mean, I got one in my water bottle. You know what? We'll throw it on the Instagram. We'll throw a picture of our of our sticker on the Instagram at Planet GeoCask. So, what are we doing? We're gonna send out stickers to listeners. We're gonna send it to the first 50 people who send us an email with their name and their address, and we'll ship it to you.
SPEAKER_00What do they gotta do though? What do they have to do?
SPEAKER_02Something it's not a you know, there's no free lunch in this world, right? So you gotta do something for us to do this. And I think, I don't know, Chris, maybe we have two options of what people could do. One, I'm thinking go to your listening platform, give us a five-star rating, and leave us a review, write that review, take a screenshot of that, and send that to us in your email. And I think that's deserving of a sticker. What do you think?
SPEAKER_00I I agree, but the one I prefer is just give us the name, just the first name of somebody that you shared the podcast with.
SPEAKER_02So here's my thought, Chris. I mean, these are pretty good stickers. This is no sweatshirt, but they're pretty good stickers. I think they're worth more than one person that you share it with. I think that's a good point. Two, three, four. I don't know. What do you think?
SPEAKER_00How tell me this though? You know, how does our planet and the importance of our planet, how can you not have two or three people that you can share this with? Let's go three. I think three is sticker worthy.
SPEAKER_02Yeah, they are pretty good stickers. That's true. Yeah, right, right. Okay, so here's the deal. To summarize, if you want a sticker, you send us an email. Our email is planetgeocast at gmail.com, and you send us an email with your name and your address in there, but you got to do something for us. You have to either give us a five-star rating and leave a review on whatever your podcast platform is, take a screenshot of that, throw it in your email, we'll send you a sticker, or you got to share Planet Geo with three of your friends. What do you think about that, Chris?
SPEAKER_00I do. I like it a lot, but you know what? I have a preference. I prefer the share rather than the rating. Okay, that's fair. You know, like the rating is what it is, but you know, I prefer the share because we want to share this with a lot of people. Yeah, word of mouth matters, right?
SPEAKER_02Yeah. Yep.
SPEAKER_00Um, don't forget to include your address.
SPEAKER_02That's right. Include your address, the first 50 people to send us an email. Done. Stickers on the way.
SPEAKER_00Stick around, Grand Canyon coming up.
SPEAKER_02All right, here we go. Let's get into it.
SPEAKER_00So, on that note, what are we talking about today? Today, we are going to talk about the Grand Canyon.
SPEAKER_02Oh man, the Grand Canyon. I love the Grand Canyon. It is such a cool place.
SPEAKER_00It is. You know, we've done a lot of stuff in the the Rocky Mountains in the West and so on. And why not go with the Grand Canyon, right? That's right.
SPEAKER_02And as the great Ron Swanson says, crying is acceptable at funerals in the Grand Canyon. That is so that is so true and so good. It is totally true. It is one of like the all-time views that you can have, as far as I'm concerned, that I've seen in my life is standing there looking at the Grand Canyon. It's an unbelievable thing.
SPEAKER_00Yeah, you know, today when I'm just getting ready to talk to you, I found myself in in a place that I'm not really I'm not there very often. I was very nostalgic, you know, about like the I was. I was uh thinking about the last time I was there with with my family. We spent about a week there and we spent four days down in the bottom of the Grand Canyon and just had the best time. I have a lot of stories about our experiences down there, and just ha it it it grabbed me. I I'm emotional when I think about the Grand Canyon.
SPEAKER_02Yeah, that's I mean it pulled on some heartstrings. It's a it's a very cool place, and it's a very uh it's a kind of a basic place for geology or for geoscience, and it's uh also a historical place, meaning it's been thought about with the geologist or geoscience lens for you know since the 1860s, really. It's just one of these classic places that the first time I went there was during an undergrad geology field trip class, right? And and because it's a place that you can go and teach the basics fairly obviously. It is for sure.
SPEAKER_00I mean, this is this is one of the best examples on the planet of stratigraphy and relative dating. I mean, we just taught we did an previous episode on geochronology, and this is just textbook that you don't get often.
SPEAKER_02I was just in the Grand Canyon relatively recently with some friends um who are nowhere near being geoscientists at all. And so we went on a hike, you know. I mean, it was a day, half-day hike, but you walk down, right? And it's just so bloody obvious that these are sedimentary layers that are layered down horizontally. So, you know, I was obviously interested in talking about the geology or the geoscience, but they were just as happy to listen and learn. And I think they came away with a really deep appreciation. So it's a really like intuitive place to start to understand the earth if you don't have any experience exposure to geoscience at all.
SPEAKER_00I agree. It's the best place, I think, to do this, to get your first exposure to geology or the geosciences and these basic principles. Because in geology, it's very difficult to take what you learn in a book, which is on a page in front of you or on a computer screen in front of you, and then you see it in the field, and it is so much bigger, right? And and in geology, that's the difficulty is trying to take the big and make it small, make it so we can comprehend them. And that's what the Grand Canyon kind of does. You can see it all from certain viewpoints laid out in front of you, almost as if it's on a computer screen right in front of you, and uh, you know, something that anyone can understand.
SPEAKER_02Yeah, it is amazing. Absolutely, absolutely. So we're gonna kind of take this geoscience tour of the Grand Canyon, and we're gonna start by talking about the oldest features and the oldest rocks in the Grand Canyon, and then working to younger features as we go through this podcast.
SPEAKER_00Which means we have to start at the bottom of the canyon and work our way up.
SPEAKER_02All right, Chris, yeah, so we're working from the bottom to the top of the Grand Canyon, and we're working from oldest to youngest. So we're gonna start with the oldest rocks. And I've actually never been down to the Colorado River in the deepest part of the canyon. You have, I think, been down there, right? So why don't you take this away? Tell what what do they look like?
SPEAKER_00So, yeah, before we talk about down at the bottom of the canyon, I want to talk about getting down there. This was something that I did with my wife and two kids. We spent four days down at the bottom of the Grand Canyon, and this was a part of one of our like three to four week long expeditions that we do every summer just as a unit of four people, my my three favorite people on the planet.
SPEAKER_02Oh, I'm a I'm deeply offended to not be in the category of your family, Chris. You're close to the cross. I mean, come on, come on.
SPEAKER_00You're close, you're there. So we started hiking on our first day in. So we took the we took the kaibab trail down. We started at like 4 a.m. You know, so we hiked down. You know, that's the easy part, right? You go through some tunnels down near the bottom, you go across this really cool bridge uh where you cross the Colorado River down near the bottom. You then when you get down into the bottom and you walk to this place and it's called the inner gorge of the Grand Canyon, that's where you see the oldest rocks. And these rocks, they're we're gonna call them, Jesse, the metamorphic basement rocks. Yeah. Okay. Why do we call them the basement? Like, what does that whole term mean?
SPEAKER_02Yeah, it's basically it means that they're the roots of the continents. So they're they're often sediments are deposited on top of these old things. They're the basement. Think of the basement to your house, it's at the bottom. I mean, it's the basement to the continents for all intents and purposes. They're the kind of metamorphosed deep roots.
SPEAKER_00And they're almost always pre-Cambrian, correct?
SPEAKER_02Yep, they're often very, very old.
SPEAKER_00Yes, which means what? What does that mean?
SPEAKER_02That means older than about 600 million years ago. And pre-Cambrian, Cambrian is basically the era of multicellular life on Earth. And so Pre-Cambrian is before multicellular life on Earth. Um, and so that means it's just a time older than about 600 million years old.
SPEAKER_00Good deal. So you get down into this inner gorge, and what you see is a very dark colored rock. It's called the Vishnu schist. And the Vishnu part of that is not important, but the schist part is. This is a moderate to high grade, like regionally metamorphosed rock that's at the bottom of the Grand Canyon.
SPEAKER_02So metamorphosed, it just means it's been really altered, deformed, and it's just been cooked.
SPEAKER_00Right. It means intense heat and intense pressure. So these rocks were formed very deep and under a lot of heat, too. So very dark colored rocks, and then they're intruded with a bunch of like lighter colored igneous veins. We call those veins where they you have these cracks and the schist and lava or magma squirts into these cracks, and so they form these veins. So let's talk about this then, because these are the oldest rocks that exist in Grand Canyon. In fact, they believe that these rocks formed 12 miles beneath the surface. They were covered by 12 miles of rock. So I want to pause a second, Jesse, and can you address that a second? How do they have any idea how these rocks formed that deep? Because that's a lot to comprehend.
SPEAKER_02Yeah, it's it's tough. The way that we know this is by looking at the composition of the rock itself and the minerals that are stable in it. So if you take a rock, if you heat it up to high pressure, high temperature, the minerals that form will change depending on the pressure and temperature that you're at. So some minerals like a lot of pressure. Diamond, for instance, we had an episode on diamonds. Diamonds like really high pressure. Some minerals don't like high pressure, some minerals like high temperature, some like high pressure and high temperature. So we can look at this rock, which is now exposed at the surface, we can look at the minerals in it, we can look at the composition of the rock, the chemical makeup of it, and we can figure out where in the earth, in pressure and temperature space, that rock was happy when it was last quote unquote stable.
SPEAKER_00So there's a recipe then for temperature and pressure conditions to form the minerals that exist in the schist. Is that what you're doing?
SPEAKER_02Exactly. So this schist has a lot of garnets in it, and those garnets are only stable, fairly deep, and so and also at some temperature range. So we can kind of put some upper and lower bounds on pressure, temperature, uh, and and kind of map this out in space.
SPEAKER_00So here we are now. These rocks are exposed at the surface. So, like, that's incredible to me. These rocks were formed 12 miles beneath the surface. There were probably uh, you know, miles and miles and miles of sedimentary rocks on top of them. Now, here they are exposed at the surface. How did they get there?
SPEAKER_02So these rocks really formed during the initial stages of this part of North America being formed. So these are, as you said, 1.7 billion years old. And these are the subduction of oceanic crust kind of smooshed things together, thickened the crust up. These rocks were buried deep in the continent crust, they were heated up, high pressure, high temperature, new minerals formed. And then at some point, that was the middle of the continental crust that had to get to the surface, right? And so we lost that mountain belt. In our plate tectonics episode, you alluded to the competing forces of uplift and erosion. And uplift is driven by plate tectonics, and erosion is driven by rivers and rain and weathering and erosion going on and wiping down the mountain ranges. In the end, the erosion won, and this crust was brought to the surface because all the stuff on top of it, that 12 miles of stuff on top of it, was eroded away.
SPEAKER_00So I'm gonna give a crude analogy, and I don't know what you want to do with this. Let's just see if it works, right? But imagine a big container ship loaded with layer upon layer upon layer of these containers, right? Sitting in water. So this is a good one. I like this one. Layered with these containers, right? And so you have the the bottommost container, that's our Vishnu schist, right? The bottom layer sitting in contact with the bed of the ship. Okay. And so as you remove these containers, then as it gets to port and you start to unload it, you remove the containers. What happens? Well, you remove containers, and then the ship then uplifts a little bit higher, sits a little bit taller in the water, right? And you remove more containers and it sits a little bit higher in the water until you removed all of those containers, and now you have the bottom layer of containers exposed at that level, right? And that's what the earth does. Does that make sense, Jesse? What I'm totally.
SPEAKER_02Absolutely. Let's push that point now and and move on to the next sequence of rocks. Chris, how do we know that this formerly 12 miles deep Vishnu schist was exposed at the surface at some point in time? How do we know that?
SPEAKER_00Yeah, this is the thing. This is the like this is the thing that gets us as geologists excited as hell. When you have sedimentary rock, unaltered sedimentary rock, like sandstones and limestones and shale sitting right on top of Vishnu schist, and it's like a razor edge. This is what we call in geology a knife-like contact. There's no transition between that schist and the sandstone sitting right on top of it.
SPEAKER_02So we have this boundary here between this rock, the Vishnu schist that was happy at 12 miles deep beneath the crust. And then we have sediment that's laid down on top of it. And that's a really sharp contact, is what you're saying right there. That boundary is really sharp.
SPEAKER_00It is sharp as can be. There's no transition between them. It's this and then it's this. And see, the thing is, is that those could the sedimentary rocks could not have been there when the schist formed, right? So we're talking about a massive amount of missing time between the time that the schist formed and was very slowly and gradually brought to the surface, eroded relatively flat, like a beveled surface, and then sea level returned and deposited new sedimentary rocks on top of this now cold schist. That's the only way that happens. That boundary right there is called the Great Unconformity. And you can see it in the Grand Canyon.
SPEAKER_02And unconformity is you know the opposite of conformable. So there's missing time. The inference here is that there's missing time in this unconformity. There's actually over a billion years of missing time on the Great Unconformity in some parts of the Grand Canyon, right there, between the Vishnu Schist and the other sedimentary rocks that are deposited right on top of it, right? And there's missing time, but there's also missing events. There's a whole missing mountain range of in there and a whole and the erosion of that mountain range. There's a huge amount of missing events. Yeah, you're missing 12 miles of rock.
SPEAKER_00Yeah, and a lot of time. And then we're talking about relative data. We're thinking we're putting things in order, which includes events.
SPEAKER_02Okay, so let's move to the younger rock sequence here. Because if you're coming to the Grand Canyon, if you don't hike down into the bottom gorge, you might never actually see the Vishnu Schist from the top rim. It's hard to see the Vishnu Schist. There's a lot of rock on layered on top of the Vishnu Schist in a lot of geologic time. So let's move into those ones.
SPEAKER_00Younger than the Vishnu Schist, we have the pre-Camb, what we call the Pre-Cambrian supergroup. This is just a host of sedimentary rocks that are laid down on top of the Vishnu Schist.
SPEAKER_02So they're sedimentary rocks, they were deposited in an ocean somewhere. Is that right? An ancient ocean? Okay.
SPEAKER_00These are very specific environments of deposition. You have limestones and you have you have sandstones and shales and some conglomerates too, which are really cool actually. And so they indicate then like shifting shorelines. We have this sea that invaded the area, and the sea would transgress, which means it would advance, and then it would regress, which falling sea levels and so on. And it would just kind of wag back and forth over time. No, you've got some famous ones that are deposited in here. You have the bright red-orange uh Hakatai shale. You know, that's a famous like shale layer down there in the inner gorge and down there at the bottom.
SPEAKER_02Famous amongst geologists, let's say it's varying levels of fame.
SPEAKER_00But then, Jesse, we have these lava flows that are interbedded with the sedimentary rocks. So can you talk about that? Because Jesse, these are not intrusions, they're flows. Uh how do we know their flows? And then what about the dating of them? Why are they important?
SPEAKER_02Yeah. So how do we know their flows? First of all, is that usually a lava flow, when it flows out on the surface, it flows flat. It's very much like a sediment in that it's deposited, for the most part, flat on the surface. So they're kind of interbedded with the sediments in that sense. We also know their lava flows because we can look at they often have gas vesicles in them. Um, they they have physical features that tell us that they were erupted onto the surface, not intruded in the body of the earth. And why they're important when we're thinking of understanding the geologic history of the Grand Canyon is that we can date lava flows pretty easily. So go back a couple weeks ago when we talked about how we date rocks, and radiometric dating is very good in lava flows and very precise and accurate in lava flows. It's not always the case with sediments, with sandstones or limestones. Those can be kind of difficult to date. So if we have a sequence of sandstone, limestone, sandstone, limestone, lava flow, and sandstone, limestone, sandstone, limestone, lava flow, that lava flow gives us a point in time that we can basically associate with the rest of the sequence of rocks that are deposited there.
SPEAKER_00So if I could interject real quick, then like we can't date the sediment within a sedimentary rock.
SPEAKER_02Sedimentary rocks are extremely difficult to date, particularly in the Precambrian, because there's no multicellular life forms. In the Cambrian, post-Cambrian, after about 600 million years, we can use the fossil record to kind of get a rough age for sediments. It's not so back in the Precambrian, it's much more difficult.
SPEAKER_00Which is interesting. I want to just interrupt you a second. So these rocks they don't have those kinds of fossils in them, they have stratoolites in them, these cyanobacteria, these like algal mats that precipitated limestones, but no life more complicated than that.
SPEAKER_02That's right. No, no eukaryotes, no multicellular life. So we've got this entire sequence of flat-lying sediments, flat-lying sandstones, but they're no longer flat-lying, they're tilted now. So, what that means is that all these rocks were deposited, they were laid down in this shallow sea, this ocean that was kind of transgressing and regressing, going back and forth, laying down different rock types, some lava flows came in there. They were deposited horizontally and then they were tilted. And that tilting had to occur after they were deposited, after they formed rocks. And actually, we know that there's another missing piece of time in the Grand Canyon, because on top of those tilted rocks now is a flat erosional surface, and then we have a new sequence of sedimentary rocks that are flaid down flat on top of that. So we have Vishnu Schist, really high grade metamorphism, 12 miles deep, major gap in time, major gap in time. On top of that is this Precambrian supergroup with lava flows. That whole sequence is tilted, eroded flat again, and now we have the new rocks on top of that that are flat line.
SPEAKER_00And for those of you that are more geologically inclined, that is called an angular unconformity. We're not concerned with that. It is a gap in time, and it's a major gap in time. So it's called an angular unconformity, unimportant in terms of that. You don't have to like understand the terminology to get the gist of what's going on. That leads us then, Jesse, to the next sequence of rocks, the Paleozoic strata.
SPEAKER_02Yeah, the ones that are most probably most striking when you're sitting on the Grand Canyon Visitor Center looking at the Grand Canyon.
SPEAKER_00So we're talking really about a host of rocks that spans about 300 million years. It's an incredible incredible.
SPEAKER_02It really is. It's so cool.
SPEAKER_00And again, it turns back to what I took what I said before is we had shifting shorelines, we had trans. Transgressing, rising seas, falling seas, and so on. And so that's how you get this vertical accumulation of rocks stacked up on top of each other. And that's what this host of rocks is characterized by.
SPEAKER_02And so in this sequence, there are several kind of famous rock layers. But really, what's going on here is that we have this ocean, this ancient ocean, between 570 million years ago and 270 million years ago, that's again going back and forth, coming in and out. It's depositing different types of rocks on top of it. And we have totally cool stuff here. Like we have big limestones, like the kibab limestone that forms the cliffs. So anytime you see a cliff, if you're hiking the Grand Canyon, that's either a limestone or a sandstone because these are rocks that are hard to weather and they form cliffs. So we have the Tapete sandstone with the Hermit Shale, which forms a slope, and then the Kaibab limestone that forms another cliff on top of it.
SPEAKER_00So this is what I like I call roadside geology, right? This is geology at 70 miles an hour. Okay, you can spot shale a mile away because shale forms slopes. Sandstones and limestones form cliffs, and that's what characterizes the Grand Canyon. You have this cliff slope, cliff slope, cliff slope kind of thing going on that is really evident in this Paleozoic strata group that we're talking about right now.
SPEAKER_01That's right. That's right.
SPEAKER_00This group also has a lot of fossils in it. That's really interesting. They're very neatly organized from bottom to top, they progress through in a very organized fashion. I'm talking just about fossils like brachiopods and mollusks and corals, which everybody knows what a coral is, and then the trilobites, which anyone that has had any kind of geology training knows what a trilobite looks like. I'm a huge fan of trilobites. So these rocks are very diverse in terms of the fossils that they contain, also.
SPEAKER_02Yeah, and there was just a lot going on during this time. So the ocean was going back and forth and back and forth. Sometimes it was moving out so much that erosion took over, and the rocks that were deposited started to be eroded back again. And this creates things called disconformities, but they're again little gaps in time. It's not a billion years here, it would be on the order of millions of years or tens of millions of years, but there are.
SPEAKER_00And you said that's called a disconformity, which is unimportant. But for those of you that are well versed in geology, you'll know what those are.
SPEAKER_02That's right. And then high up in the canyon has what is one of my favorite rock types that's exposed throughout the southwestern United States is the is the Coconino sandstone, which has these huge crossbeds in it, which are these big kind of shallow scoop-shaped features, which indicate that it was windblown or sometimes water blow, water move sand. These are huge dune deposits, which I love crossbeds.
SPEAKER_00I mean, well, you and I are a fan of sandstone, period. Yeah. I mean, think about the amount of miles that we have traveled together just to get us some ripple mark sandstones. Think of the rattlesnakes that we've had a battle to get some ripple mark sandstone.
SPEAKER_02Yeah, yeah. Real and real and in imagined rattlesnakes. We've battled both of them to the death.
SPEAKER_00But but the real ones are the important ones. Okay. That's right. That's right. For me to battle rattlesnakes, and I have a very unhealthy fear of snakes. Um, there must be some impressive sandstones. So, yeah, sandstones are really important.
SPEAKER_02Yeah, we love sandstones. And if you want some hiking recommendations for the Grand Canyon, tune in in a couple weeks. We have a Geo short coming out about that.
SPEAKER_00Yep. And the other interesting thing is too, is at various points, whether you're hiking down or you're hiking up and you stop and you turn around, that you can see. I don't know how to say this best, but when you have these canyons that cut like perpendicular to the Colorado River, to the Grand Canyon, right? Things like the Bright Angel Canyon, for instance, it is so straight and it has this creek that runs through it that's so straight. Those are faults that are cutting across that plateau where the Grand Canyon is. When you see linearity in geology, quite often that signifies, oh, that's seismicity, that's earthquakes and faults that are cutting across that.
SPEAKER_02Yeah, these are rocks breaking, seismic disaster, and then the river is just exploiting that weakness in the rocks, and the river is creating this really straight canyon where it normally wouldn't.
SPEAKER_00And so because the faults are straight, so are the rivers. And Bright Angel Creek, which is right at the bottom of the Grand Canyon, there where most of the hiking is is kind of concentrated, is a great example of that that you can see as you walk out of the canyon or down the canyon. Bottom line, Jesse, old rocks, young canyon.
SPEAKER_02That's right.
SPEAKER_00I like to when I think about geology in the field, what I emphasize to my kids, and I'm sure you do too, is that you need to envision each stage where we are. Okay, where we left this story does not give us the canyon. Where we are right now is this shallow sea that's coming and going. We're at sea level, we're below sea level, we're right at sea level.
SPEAKER_02Yeah.
SPEAKER_00So how do we get to the Grand Canyon?
SPEAKER_02That's right. I mean, we're talking about rocks that are formed in an ocean or maybe in a dune environment, but now they're exposed pretty high up, right? The Grand Canyon is on a plateau and it's pretty high up. So old rocks, young canyon. How old is the Grand Canyon, Chris? When did the Grand Canyon form?
SPEAKER_00Most believe the Grand Canyon is younger than five million years old.
SPEAKER_02The canyon itself. It's a pretty young feature on the landscape. You know, so we kind of have to end this discussion with how did the Grand Canyon get to be so grand? We talk about the rocks that are exposed there, but how did it get to be so grand? How did it get to be so deep? How so wide? Such a shocking feature on the landscape. And most people think it's about five million years old. There's some disagreement about that. Some people would say the canyon is actually much older. But basically, you need a river that is cutting down into the earth. And in order to give a river the energy it needs to cut down into rock, that takes quite a bit of energy to cut down through these rock layers. You have to push the rocks up. And so the rocks have to be lifted up in some way so that the river can cut down through them, if that makes sense.
SPEAKER_00Yes. But, and this is hard to paint a picture in a podcast, though. And I don't know how to do this justice. That the river as it exists today didn't exist when this uplift happened. You know, the river eroded its way into this uplift, much in the same way that say, oh, okay, everybody can envision a waterfall, right? Okay, uh just uh for to the listener, just envision the last time you saw a waterfall and behind the waterfall you noticed that there was this kind of dugout part where you could almost like a lot of waterfalls, you can walk behind them, right? Yeah, that's just a natural part of the process of erosion. It's called headward erosion in geology. But when it erodes that part out behind the waterfall, the rock above it is left unsupported. And so eventually then that will collapse and then it will scour out again behind the waterfall and so on, leaving the rock unsupported. And and this is how then waterfalls migrate upstream the older they get. And this is what happened to this river that as the uplift was happening, rivers that were running away from this uplift, think of like uh it wasn't exactly like this, but you can think of spokes on a wheel, you know, where the rivers were kind of running away from the central uplift. They were eroding in this kind of headward way and incising and carving their way down then through this uplift and then connecting courses with other rivers.
SPEAKER_02So let me interrupt you there. So they're basically they're cutting this sort of migration of the waterfall upstream means that the river is cutting straight down, basically. You know, a waterfall is a pretty steep drop-off and it's cutting straight down. So the river will cut down very rapidly, and then it will cut out. Once it's down, once it reaches a level where it's fairly happy, then it winds back and forth side to side. And you can really just imagine this. Think of hiking along a mountain stream. That stream is pretty straight, right? It's flowing pretty much straight downhill for the most part. There's some side bends and stuff in little pools, but it's pretty much going straight downhill. That's a river that's cutting straight down because it has a lot of potential energy to it that's cutting downward. And then think of a river in the valley, right? Think of a river that's kind of meandering through this valley. We call it a meandering stream because it's wandering side to side, and it's actually doing most of its erosion on the sides, so it's actually cutting out at that stage. So a river cuts down and then it cuts out. And so when this uplift occurred, the Colorado River cut down deep, and then since that time, it started to cut outward and made the canyon really, really wide. And you can also think of this in the differences in the rock layers. So the river will cut down through really weak rock until it hits a hard rock layer, and then it'll start to cut out a little bit, and then it'll cut down through that rock, that hard rock layer again, and then it'll cut out again. And so that's where we get this cliff slope, cliff slope, cliff slope as we go as we look at the Grand Canyon, which gives it this really spectacular structure to it.
SPEAKER_00Yeah, which is interestingly enough, roughly 18 miles from rim to rim.
SPEAKER_02It's just amazing.
SPEAKER_00Okay, that is amazing. But the thing is, is that you can see the lateral continuity of the rock layers, right? That's what it's a principle in geology called the principle of lateral continuity, which means that sedimentary rocks are laid down laterally continuous, like a big blanket, okay, because they're deposited in such specific environments, and you can see that better in the Grand Canyon than anywhere else on the planet.
SPEAKER_02The one the uh the first time I went to the Grand Canyon was, as I said, during this uh undergrad geology trip, and we were walking down the Bright Angel Trail, and we took uh out onto the plateau. At the base, you kind of walk out onto this plateau to look down at the Grand Canyon, and that plateau is you're kind of you walk down really steep down into the canyon, and then you start to walk horizontally out. And that horizontally out is when the river was cutting outwards because it had already cut down to this through the shale or through the limestone, I mean, yeah. Yeah, to this really hard rock layer. And so the reason that the Grand Canyon is grand is because the river has been doing this erosion for about five million years, and that can't that works out to be about one inch every century of the amount of erosion that's going on.
SPEAKER_00Which of course it didn't do it like that. It was punctuated, you know, by by floods and and so on. But that's a really interesting stat.
SPEAKER_02It's a g it's a good thing to kind of keep in your head when you're thinking about the Grand Canyon, is one inch every century. It's kind of crazy.
SPEAKER_00Uh but that's what I love about geology, is the the craziness that you have to comprehend sometimes.
SPEAKER_02Yeah, exactly. And then the last, you know, sort of point of interest when we're talking about the Grand Canyon, we'll kind of wrap up the podcast here on this point, is these small lava flows that occur kind of everywhere in this region. And I we stayed when I was there uh recently this past year, we stayed at an Airbnb towards Williams to the south of the Grand Canyon, and we were kind of staying amongst these little hills, which are actually little cinder cones or little former volcanic eruptions.
SPEAKER_00They're former hills formed by ancient volcanic eruption, and they're so cool because man, they look like cinder cones geologically. You're like, wow, that is a volcano right there.
SPEAKER_02Yeah, that's just a little tiny volcano right there. It's really they're so cool. They're so cool. And they they're young. The oldest ones are a few million years old, and the youngest ones are a hundred thousand, or some of people think even a thousand years old, or some of the youngest ones. And this to me is uh Chris, I want to put this on the bucket list for you and me to go to. There's a spot in the western Grand Canyon, I think I've never been there, but uh maybe you have. Have you been to Torweat Point or not?
SPEAKER_00No, I have not. I have not.
SPEAKER_02Nope, nope. Okay, but there's a spot where one of these ancient lava flows flows down into the canyon, and you can kind of see where the ancient lava flow flowed into the canyon and it dammed up the Colorado River at that point.
SPEAKER_00Sounds like I'm all in. Okay, I'm all in. I can't stand the phrase bucket list, but uh, you can put me on it. Okay, all right. All right. I'm I'm I'm there with you. Yeah, well, one of my favorite there's a place right near the Grand Canyon called Sunset Crater, and this is like a thousand-foot-tall cinder cone. It is so impressive. Just a again, very cool place uh that's associated with the same kind of lava and igneous uh activity that you're talking about here.
SPEAKER_02So yeah, all right. So that's a wrap on the Grand Canyon. I mean, I I freaking love the Grand Canyon, it's such a it's a hell of a cool place, and I would go back and spend a lot of time there.
SPEAKER_00The thing is, and you know, Jesse, we're gonna have to put together maybe I think a series of geo short shorts on this because um I have a lot of things that I want to share that have nothing really to do with the geology of it, but just kind of experiencing it. It's such a special place. Absolutely, and that doesn't do it justice, those words are inadequate. Man, I'll tell you, some of the best family time that I've ever had, we invested in each other in the Grand Canyon.
SPEAKER_02That's very cool. So cool to have that personal connection to a place. That's awesome. All right, with that, you know, that's a wrap on the Grand Canyon episode. And uh, you know, check it out. And if you're going there, if you're planning a summer trip at some point or a spring trip, check out the hiking recommendations and the GeoShore.
SPEAKER_00Yeah. Have a good week. Alright. Cheers.