The Longest Cave System in the World
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Dr. Jesse Reimink: I hit record, Chris, i hit the button.
Chris Bolhuis: Well, hold on. I'm still, look, I'm still
Dr. Jesse Reimink: Still tapping, you're you're tippity tapping around moving all over your nasa panels there getting your stuff aligned. You just, you know what Chris, I [00:00:30] must say I'm gonna give you a compliment so get ready they don't come very
Chris Bolhuis: They don't come very often. I'm just your sidekick.
Dr. Jesse Reimink: Sidekicks don't deserve compliments. Um, you've been pretty techno savvy recently.
We haven't had many, uh, major hiccups out of you recently. I'm, I'm proud of you, man.
Chris Bolhuis: Uh, get this, so I got an email from our technology person at the high school today, and, or yesterday anyway, he said, I have three brand new computers to give away and I chose you because I know that you'll use the technology and blah, blah, blah, [00:01:00] blah, blah. And I'm like, Jesse would be so
Dr. Jesse Reimink: I would be, that does. That warms my heart. That warms me up. We've, we've, we've trained you up well over here at Plant and Geo, Chris, with all the technology.
Chris Bolhuis: know that all that comes with a new computer, it's been a time drain today.
If you know what I mean, like setting up a new machine getting logged into everything
Dr. Jesse Reimink: admin privileges and all this nonsense. I mean, yeah. Oh goodness.
Chris Bolhuis: yeah.
Dr. Jesse Reimink: well, you got your NASA set up now, so you're, uh, you're ready to rock with Planet Geo here. Pun intended.
Chris Bolhuis: Oh, it was. [00:01:30] Okay.
Dr. Jesse Reimink: It was, so Chris, this episode here, I'm excited about this. I know you are a cave guy.
you're a cave dweller. You like caves, right?
Chris Bolhuis: I do. I like caves, but I'm not a cave dweller. I don't know how to take that comment.
Dr. Jesse Reimink: I had
Chris Bolhuis: I'm not sure I like that. I'm a cave dweller. Um, you think Jenny would like it if I said, Hey, Jenny, Jesse just called you a cave dweller. You
Dr. Jesse Reimink: No, no, she's not. Jenny's a daughter of the light and the [00:02:00] rainbows and the butterflies. You, my friend, are a slug cave dweller, I think. You and your little recording booth downstairs and your little man cave recording booth you got. I mean, it's
Chris Bolhuis: I know. I like this place though. I've got it just how I want it. Yeah, I do like caves. You know what I do? I like though, Jesse is I like to learn the intricacies of how each cave works. They're so different. You know, you talk about like the formation of, we're going to mention today Jewel Cave and in the Black Hills and [00:02:30] Wind Cave.
I think Wind Cave has such a really cool
Dr. Jesse Reimink: Let me interrupt you real quick, Chris. Which one did we go on when I was a student on the summer science trip with you? Um. Because I know you've, switched these around, and I went, my dad led that trip, so like I went as a kid on that trip previously, and I think we might have gone to one or the other, I saw, which one did you, did I go on with you as a student?
Chris Bolhuis: I think wind cave, but I'm not sure we've also gone to Jewel. Uh, they have just really different [00:03:00] things to offer the cave when you get in it and you get into the nitty gritty of it, it's just really, really different they're very close together. I, it's just astounding that their stories are so different.
They're geologic stories. And so that's what I love about it. And, you know, everybody thinks that mammoth cave, which is. This is what we're doing. this is our first episode of a series on Mammoth Cave and the geologic story of it. people think it's simple and you and I know this is really not a simple story.
There's a lot going on [00:03:30] for Mammoth Cave.
Dr. Jesse Reimink: okay, a comment and then a question. Mammoth Cave is, well, here's what I like about caves, and I don't really like caves, I mean I don't hate being in them, But there's like bits of claustrophobia, or there's something about it that is, physically uncomfortable to me. The geology is amazing.
You get to see rocks in place. you get to see the inside of the earth in a cave, that's pretty cool. and what I like about caves is when you're standing in the rocks, basically like, geology is kind of fractal. you see it at all the [00:04:00] scales. You see a big tunnel, and then you see little, You see all the, the hydrothermal features and you see there's just so many scales of stuff happening from really minuscule tiny microbes to like huge tectonic reasons why the cave is there, so that's what I think is really interesting about caves,
So Chris, I, sorry, that was a long comment, but now to my, to my question here, um, because I went to Mammoth Cave on an undergrad field trip, actually, was one of the times I've been to Mammoth Cave. [00:04:30] What's your personal connection to Mammoth Cave?
Chris Bolhuis: Same thing. almost exactly the same thing I just like I don't know, you know this about me You I love it when story comes together, when you learn about the formation of something. And so when you're walking around the area, when you're driving through this, and it's a huge area, right?
And then you get into the cave and And you know, something about it. I just, I love that aspect of it. And so that was [00:05:00] one of my like early field experiences actually, where, where that, yeah, where that clicked, you know, and I was like, Oh my gosh.
Dr. Jesse Reimink: So another. Quick question for you. In your experience or your opinion, is this a pretty common field trip for schools in the Midwest to do? To drive down and go to Mammoth Cave? Cause, you know, in Michigan there's not many outcrops, and uh, I don't know what the drive is, but I seem to remember like, you know, 6, 7, [00:05:30] 8 hours, something like that from Michigan.
I could be way off, but I feel like this might be a pretty common, weekend field trip for, let's say, geology majors, um, to go on. Do you think that's true, or no?
Chris Bolhuis: I would hope so. I mean, you went there with Hope. I went there with Grand Valley. I think they still do that. They do a trip down to Mammoth and, know, clubs do it too. Like geology clubs through the universities. Did you have one at Hope? Did you have a geology club at
Dr. Jesse Reimink: Yeah, I mean, but we didn't do too much separate stuff from classes, because [00:06:00] everybody's kind of taking the same classes at the same time through it, just the way the structure was set up, so,
Chris Bolhuis: I'll tell you, I could put together a trip a four or five day trip down to Kentucky seriously. And we would do Mammoth Cave as one part of that and spend then a couple, two, three days in Red River Gorge and just tear it up. It would be amazing.
Dr. Jesse Reimink: a great idea. Geology is so good. And it's, you know, it's close to a lot of stuff. So I feel like a lot of people have been to Mammoth Cave, even though it's not like one of the necessarily premier national parks, or most popular ones. A lot of people have been there because it [00:06:30] is kind of close to a lot of different stuff.
So let me Chris, let me just Set the stage here. So if you're listening to this in the podcast, this is part one of a probably end up three part series on Mammoth Cave National Park. if you're listening to this, the audio book version of this with images is probably live on the Camp Geo app.
So you can go there, you can listen to all three episodes, with the images that you need integrated with the audio book. You can download the first link in your show notes is the Camp Geo app. So head there, there's a bunch of free content and then some paid stuff as well, including the [00:07:00] Mammoth Cave National Park. this is part one, and we're gonna intro kind of the overview, this, episode chapter is gonna be the overview, geology, and then we're gonna get more specific in two and three,
Chris Bolhuis: that's right. We're going to get into, in part two, in chapter two, we're going to get into some of the specifics about Mammoth Cave Geology, and then we're going to tie up the loose ends in the
Dr. Jesse Reimink: I is
Chris Bolhuis: talking about the passage.
Dr. Jesse Reimink: yeah, This is the biggest cave, longest known cave system. And there's a reason for it. And we're going to talk about the reason. Like what is [00:07:30] the, again, back to scales. What is the tectonic reason, large scale reason why this is a huge cave compared to other ones all throughout the Appalachians and all over the place that are much smaller, right?
We're going to cover that if we're on Chris Bolhuis trip and we're on the bus driving down and, uh, Chris has got the, the microphone up front, what are you saying on the way down to Mammoth if Mammoth is our first stop? what's your pitch?
Chris Bolhuis: I don't know, we're going to go see the longest cave in the world, you know, that's, [00:08:00] that's kind of an impressive thing. Uh, let's put some numbers to it. Mammoth Cave is over 675 kilometers long or 420 miles. it is the longest cave in the world by far. It's not even a close call.
The second longest cave is somewhere in Mexico and it's 250 kilometers shorter, I take students to Jewel Cave and the Wind Cave in the Black Hills, those are five and six respectively in terms of their known [00:08:30] lengths. there are some things that we don't know about them yet in terms of, wind cave.
There's, there's a lot of it that hasn't been mapped yet, but, but, That's where we're at right now. and so it's just, I don't know, the biggest on the planet. Um, you're a big deal then just by
Dr. Jesse Reimink: yeah, yeah, no, that's right, you're the biggest and the, maybe, arguably, the best because of that, and if you go into Mammoth, Mammoth Cave is called Mammoth Cave for a reason, it feels huge, there are rooms in there, there are passageways that [00:09:00] are Unbelievably big.
really can't imagine, at least I found it hard to comprehend how this could exist with stuff above us. this is so big, right? The scale inside is amazing. The details are not important. Find a map when you go to the National Park Store that's detailed and shows you all the stuff.
We just put this here because this is a huge cave network, importantly.
Chris Bolhuis: That's that's right. And that's no, no, no. That's my next point. That's you get the segue word because you don't mammoth cave is [00:09:30] this, this network of caves and there are over 400 of them in this. mapped area that we're pointing out in image number one here. So, it's aptly named, let's just say that. Ma calling this thing Mammoth Cave. Is It is. It lives up to its name for sure.
Dr. Jesse Reimink: I mean, Chris, you're exactly right. This is a huge cave system. Let's talk briefly about the type of cave, because there are different types of caves, and really the types, what we mean is, how did it form?
How did we get a cavern forming? This one was [00:10:00] formed by water dissolving rocks, And the rocks themselves are what we call Mississippian aged, which Mississippian is a time period. It's 355 to 300 million years ago. These are carbonate rocks, and we exist in what's called karst topography. And those two are intimately linked, and we'll talk about those in more detail later on.
But, this is a solution cave. And Chris, question. Do you cover cave types in your research? College level geology classes you teach students? And if so, [00:10:30] how do you lead it in? Or maybe you don't?
Chris Bolhuis: I do, but I don't parse them out this way and say, these are subcategories of caves. I talk about lava tubes. I think they're really important, you know, in terms of how lava can spread laterally for these vast distances because it stays, well, it's like in a thermos, you know, when
Dr. Jesse Reimink: Yeah
me say something real quick, Chris. was going to be impressed if you taught your students the different cave types. Because this is, you know, this is deeper level stuff. This is like, getting [00:11:00] into upper level geology classes in college if you're covering kind of the cave types. But Let me just give an overview of what this cave type thing means.
It just means, what's the physical process by which you formed this, this underground hole, really, that is a cave? And you said lava tubes, that's a great one. Lava with, uh, that's flowing underground, has crystalline rock above it, and it creates this tube. You can get ice caves as well. You can get aeolian caves, which are caves, formed in sand dune type areas, and, sort of windblown things, [00:11:30] and sea caves.
I think sea caves are probably one of the, uh, Most common are the ones that people would think of, you know, there's Solution Caves, which we're going to talk about, and Sea Caves, you just imagine the wave action is cutting a cave into a cliff. That's really what's going on.
Chris Bolhuis: Right. these are, fairly common, with the river systems in Kentucky where you can go kayaking and you can go into these, they're not really sea caves, but they're caves in limestone right along running water. You know, they're pretty spectacular. That's a really fun thing to do [00:12:00] actually.
So yeah, I don't get into though all of that, you know, in terms of caves. So sorry, I'm, I'm not all that impressive. just,
Dr. Jesse Reimink: you're,
Chris Bolhuis: moderately
Dr. Jesse Reimink: you're
Chris Bolhuis: impressive.
Dr. Jesse Reimink: just mostly very impressive. Just not, you know, fantastically
Chris Bolhuis: right. That's right. Well, okay. So Jesse, let's transition into because this episode is all about general. Really limestone cave formation, right? Because that's the most common type, right? Any student or anybody that's ever taken an [00:12:30] intro level geology class has had to identify the rock limestone or they had to identify the mineral calcite.
And I don't know, I'd be hard pressed to imagine going through a class without having the opportunity to drop some weak hydrochloric acid on a limestone or a calcite crystal it effervesce and watch it fizz. It just shows the reactivity. Of limestone, which is calcium carbonate.
You mentioned that earlier in weak acid [00:13:00] solutions. caves, vast majority of caves in the world involve the rock
Dr. Jesse Reimink: And Chris,
Chris Bolhuis: down.
Dr. Jesse Reimink: this is a great place to start. If we were to list, and we have this on image number two in our stack, the ingredients, the recipe for a solution cave, if you're going to form a solution cave, which is formed by the dissolution, dissolving of rock, this is what you need. The four things.
Number one, by far, is suitable rocks. that's first and foremost. And if I gave I think any first [00:13:30] week of class, you know, my big lecture hall, 250 students in it, within the first week, if I said, gave them five rocks, picked a granite and a basalt and a metamorphic rock and a, calcite crystal, you know, and a quartz crystal and said, which one is the easiest to break apart?
They're probably going to pick the calcite crystal, right? It just, you could pick it up and you can look at limestone and you can kind of just feel that this rock. is going to be kind of easy to break down and dissolve, I think.
Chris Bolhuis: Jesse, I love what you just said [00:14:00] because I've started doing this with my classes is rock identification. Limestone can be a hard rock because as we've said before many, many times, it's the Katy Perry of rocks. It has so many different
Dr. Jesse Reimink: You've said, Chris, I've never been quoted saying that, but you have.
Chris Bolhuis: All the time. My kids know it like by heart now, but, but I say this, like, just shut your eyes, hold the rock in your hand. Don't you feel that it's soft? It just,
Dr. Jesse Reimink: It's
soft It's light
It can, you know, [00:14:30] it's, it's just, There's something about it that you can feel. And, you don't have to handle too many rocks to kind of realize this is not granite. Granite will be hard to dissolve. This rock limestone will be easier to dissolve.
So number one, suitable rocks in
Chris Bolhuis: As an example, just to contrast that the reactivity of a suitable rock, another rock, sedimentary rock, that's closely related to limestone is dolostone, but it's far less reactive in order to get this to effervesce, to fizz and acid, you have to like [00:15:00] take a scissors create a powder on top of the rock, create a lot of, a lot more surface area, and then drop acid on it, and it'll fizz like a flat pop, you know, so it's much less reactive.
So, Caves, most often, here's the suitable rock. It's limestone, which is calcium
Dr. Jesse Reimink: And it can be dolostone, it can be marble. Marble is just metamorphosed limestone, so it's the same chemical constituents. Gypsum and halite, those are minerals also that are quite easy to dissolve. If you have in the recipe, [00:15:30] which is a solvent. Chris, what do we mean by solvent here?
Chris Bolhuis: Something to dissolve something else. That's what I think of when I think of a solvent. We're talking about slightly acidic groundwater is the solvent that's involved in this kind of cave formation.
Dr. Jesse Reimink: It's the Chris Bolhuis family chili recipe compared to your stomach lining. Right? the award, the award winning, multiple award winning Bolhuis family chili recipe that [00:16:00] fights you when you eat it.
Chris Bolhuis: and we're going to come back and talk more about each of these in a little bit, but we're just kind of running down the four necessary ingredients. So we need a solvent. And then Jesse, third one maybe is not as easy to imagine. And this is hydraulic gradient. So can you go ahead?
Dr. Jesse Reimink: got an image for that. save that for a minute. the last piece we need, which is intimately related to hydraulic gradient and really all chemical reactions is time we need time for these [00:16:30] chemical reactions to kind of drive themselves forward.
So we kind of already talked about in detail, number one, the suitable rock types, limestone, dolostone, marble, gypsum, Why do we focus on limestone though? Chris,
Chris Bolhuis: well, because it is very reactive, but like you said, it's not the most reactive. gypsum and halite are more soluble than limestone for sure, but Limestone is the most common sedimentary rock that exists at the surface of the earth.
And so, by default, then [00:17:00] it's going to be the most important in terms of cave formation.
Dr. Jesse Reimink: right, that's right, marble, there are places, Sequoia, Kings Canyon, Yosemite, that have marble around, and Marble's not, you don't form this big extensive network of marble, or big extensive layer of marble like you do in sedimentary sequences with a big package of limestone, so it's hard to make a big continuous network of caves in a rock type that's not a big continuous package of rocks.
Chris Bolhuis: And that's one of the shocking things when you [00:17:30] go to Mammoth is the vertical extent, this vertical stack of, rock, limestone. It's, immense. It's impressive. You don't get that with rocks like marble or gypsum or halite. It's far less common, I should say. So Jesse, let's get into. Why is groundwater acidic?
How is carbonic acid created? First of all, what is carbonic acid? Well, we don't have long. We're keeping this, you know, this is, [00:18:00] this is for everybody. This is for the families walking around, going to get into Mammoth Cave. And so they know what they're looking at and how it all happened. So doctor, let's keep this, uh,
Dr. Jesse Reimink: let's keep it out of the weeds. Okay. Well, you and I have talked a lot about this, including in our Earth's Climate book, which is basically all about the carbon cycle for all intents and purposes. and groundwater acidity is intimately related to CO2 in the atmosphere.
When you have CO2 in the atmosphere and you have water, exposed to that [00:18:30] rainwater, groundwater, surface water, the CO2, some amount of CO2 is going to dissolve in the water as carbonic acid or bicarbonate ions. And so, That creates acidity. Now, there's a bunch of different ways to create acidity in water, but that's one of the big ones.
That's one of the most important ones, and it's intimately related to how carbon cycles throughout our Earth. And there's a couple different rates of cycling. There's a fast carbon cycle, slow carbon cycle, etc. All sorts of complicated and very important geochemistry [00:19:00] is related to this. But, I don't know, Chris, is that how you people as well?
Chris Bolhuis: absolutely. I mean, everybody knows that carbon dioxide is a really important gas. talked about all the time because of effect on the greenhouse effect and climate change. Carbon dioxide is in our atmosphere. It's in pretty small amounts, but it's there and it's important. But the way that I talk about this in terms of something that maybe I think everybody can relate to is a carbonated beverage.
Let's say, Okay. bottle of Mountain Dew or, or [00:19:30] a diet Coke that you buy at the store. It's mostly water it's got some other stuff in it. And then they, they carbonate it and that carbon dioxide dissolves in the water. and so your pop is going to be acidic. Also, it's going to have carbonic acid.
So that's how I kind of, you know, relate this in terms of, if you put carbon dioxide and water together, some of that carbon dioxide is going to dissolve in it and it's going to create a weak acid, a weak carbonic
Dr. Jesse Reimink: And it's important, [00:20:00] Chris, cause that's all you need is a weak acid. if you took a geology class at some point, you're listening to this and you remember dropping a little bit of HCl hydrochloric acid onto calcite or limestone or dolostone, that's not strong stuff, right? Like I'm sure you got that out of your fingers and it wasn't very strong.
now that dissolved it really quick because it's much stronger, much more acidic than the groundwater we're talking about, but all you need is a little bit of acidity, and then you need our fourth recipe ingredient is thyme. You have more thyme even if it's weakly [00:20:30] acidic groundwater, we have many hundreds of thousands or millions of years to do this. This reaction can progress forward over time, so you don't need, Really acidic stuff.
That's, that's kind of the only point, Chris. Okay. We covered recipe ingredient number two. Number three is hydraulic gradient.
Chris Bolhuis: can I have a crack at this one? I want to crack at this one. Because one of the things that I do, I like to take a little. I knock a little chunk of limestone off one of my rocks and I put it in a little Dixie cup, little clear cup and I [00:21:00] pour Mountain Dew in it and I just let it set, right?
first and foremost, we weigh the limestone on a scale so it's dry and we weigh it and then I just drop it in the cup and put some Mountain Dew on it. Is usually what I use. And the thing is, is that Mountain Dew quickly becomes saturated with calcium It can't hold a ton of it.
So nothing really happens. I can let that sit for a couple of weeks and it'll turn to this nasty gel or whatever. But what I need to do [00:21:30] is I need to dump out the Mountain Dew every couple of days and put new stuff in that way I can keep the reaction going. And this is how I think of hydraulic
Dr. Jesse Reimink: Ooh, Chris, this is a great analogy for, I think, explaining why you need a hydraulic gradient to do this cave formation thing. So this is great. sorry, interrupt. I just want to say that
Chris Bolhuis: me to
Dr. Jesse Reimink: of you know
Chris Bolhuis: me.
Dr. Jesse Reimink: to sort Exceptional specimen, uh, category here.
Chris Bolhuis: so
Dr. Jesse Reimink: very, extremely impressive.
Chris Bolhuis: really what we're [00:22:00] talking about with hydraulic gradient is a steeply inclined water table where water's going to flow through the rocks. And what happens when you get this is. The same thing with my Mountain Dew effect. If I just have water standing there, not circulating through and moving and then getting replaced by fresh water behind it, the water gets saturated with calcium carbonate.
it can't soak up any more limestone. So if you have this [00:22:30] gradient, gradient is just the geology fancy word for slope. Rise over run, If we have this steeper gradient, then we're constantly getting fresher, cleaner water in that can soak up like a sponge, more of the limestone. It can dissolve more of
Dr. Jesse Reimink: That's exactly right, Kristen. The way, let me just build on that. Just two additional points that we should probably make here is Why do you need more fresh water? Or more, not fresh water, but more New acidic water. Let's put it that way. [00:23:00] Well, the reason is because when it dissolves ions, when it dissolves the rock, that neutralizes the acid.
You said that earlier. So you need to bring in fresh stuff because you want to keep the reaction going forward. it's like the old, you know, high school chemistry class. Products and reactants. You know, you drive the reaction this way or that way depending on you have more of, right? And so we want more of the reactants.
We want more acidic groundwater flowing through there. Which will drive this reaction faster and faster. The second [00:23:30] point is where do we get these hydraulic gradients or why do they ever exist? I mean, I think this is a not necessarily an intuitive thing because people often think of lakes. When you think of groundwater, you kind of envision this lake where the surface is flat in a lake.
It's not that way in the groundwater system. And the reason is because groundwater, percolates through, it takes the groundwater time to percolate from the surface down. So when rain hits the surface, it percolates down in, there is slope to the groundwater table, [00:24:00] it kind of follows Yeah, it kind of follows topography, right?
So if you're up on a mountain and you drill down beneath your feet, you might have to go down, you know, a hundred feet to get to a groundwater table, uh, to hit groundwater, but if you're down by the river bottom and the river bottom, that's a key to this puzzle. If you go down to the river bottom and you're near the river, might have to drill down two feet to hit groundwater, right?
Why is that? Well, it's because the groundwater is flowing down to the [00:24:30] river the river place is usually where the groundwater level hits the surface, intersects the surface. And so basically the groundwater follows topography a bit. It's close to topography at least,
Chris Bolhuis: That's right. And then also just to reiterate that what you're saying is that rivers, especially in this case, in the formation of Mammoth Cave, rivers are fed by groundwater. So the groundwater is percolating through this, calcium carbonate, this limestone rock, and it's making its way [00:25:00] down slope, downhill.
to the river. And so because that river has incised so deeply, we have a fairly steep slope. And so we have water that's moving through and then getting replaced by fresh water, which keeps it able to dissolve these
Dr. Jesse Reimink: That's exactly right. And image number three, Chris, shows a hydraulic gradient, what's called a hydraulic gradient. It just shows, you can see there, there's some topography to this, there's a, you know, a hill there, there's wells [00:25:30] drilled into this, and, and you can see up high, The height of the water in the well is going to come close to the surface, maybe just above it, whereas when you're down further, the water is going to come up a lot higher because there's more sort of hydraulic pressure there, but that groundwater is following, that groundwater table there kind of broadly follows the topography.
It's a little bit more subdued version of the topography. shape of the land surface, but it broadly follows that so water is going to be flowing downhill in the ground there and you're going to be [00:26:00] bringing fresh water or, new acidic water from up high through the rocks down as it goes out down to the right is where a river would be in this image here.
Chris Bolhuis: And then, The last ingredient, Jesse, we talked about at time, and there's not really a lot that we need to say about time to add to what we've already said, the bottom line is these rocks are old. We hit it right at the outset. These are Mississippian age rocks. These are rocks that were deposited 350 to roughly 300 million years ago.
the rocks are [00:26:30] old. The caves are relatively. just to put a number on this, the cave formation began about 10 million years ago, but I think three and four hydraulic gradient and time, they go hand in hand. you have to have water circulating through the rock, but we also do need geologic time because limestone is, it is soluble, but it's not that
Dr. Jesse Reimink: yeah. And Chris, let me just say we need time, we need to have a [00:27:00] long time that all three previous ingredients are together there, because there's a lot of different ways to change the ingredient structure. You can remove the solvent if the land surface raises up and the groundwater table drops and then there's no more solvent in contact with your rocks.
If you deposit some new rocks or change the tectonics, you kind of remove those rocks or metamorphose those rocks. You're going to destroy the cave and remove one part of the recipe for cave formation. So you got to have kind of a long, stable [00:27:30] paleoenvironmental condition here that allows water to circulate for, like you said, 10 million years in this instance to form something massive, like Mammoth Cave Formation.
Okay, so that's the four pieces for this type of cave to form. Chris, the last thing we should cover here in this sort of really high level intro into Mammoth Cave is karst, what's called karst topography, or karst regions. So, man, [00:28:00] karst is such a cool thing. It's just, it makes this crazy beautiful landscape.
You're you?
Chris Bolhuis: I'm feeling karst y. Absolutely. Absolutely. We, we did a, we did a whole episode. I think we might've done one or two episodes on just karst in and of itself. I mean, it's, it's worthy of that. So the bottom line is we need to talk about sinkholes before we can talk about karst, and
Dr. Jesse Reimink: Well, hold on, let me just say, Mammoth Cave is located, this whole region is a big Karst [00:28:30] region, around Mammoth Cave. if you are driving, if you're close to Mammoth, you're driving through Karst topography. Just, let's leave it at that. You look around you, you're in Karst terrain. we'll explain that.
So, sinkholes.
Chris Bolhuis: so we need to define what that is. So sinkholes are when you have caves near the surface, and then those caves, you have these, big openings just below the surface, well, collapse happens. And so the, the roof of the cave just collapses down in on itself, and it creates this
Dr. Jesse Reimink: so Chris, quick story real quick. We had, uh, last [00:29:00] year, At Penn State, where we live in Karst topography up here in State College, we had, a sinkhole open up right near a parking deck right underneath one of the main parking decks on campus and had to close down the parking deck, so, they managed to repair it.
It wasn't a massive one, but this happens, you you know, there's a grocery store that almost got swallowed. I mean, this was a decade ago, but big sinkhole opened up in the parking lot and all of a sudden you're like, wait, we didn't know there's a sinkhole here. We don't know how big it is.
You got to survey it. Like, you know, these things are not infrequent in Karst topography.
Chris Bolhuis: Yeah, there was a massive one [00:29:30] that opened up, within the last three years in the Black Hills, uh, right in a developed area. Um, it was a big, big deal out there, uh, just outside of Rapid City. So for sure, if you have caves, near the surface, then you're going to have sinkholes that are a potential hazard.
And they are actually is a natural geologic hazard. So. That's what a sinkhole is, is when the roof of a cave collapses down and it kind of leaves this big dimple on the surface and then it can lead to things like disappearing streams, which are just awesome [00:30:00] geologic features where you have this river that is flowing and then it, dumps into the sinkhole and just disappears.
Dr. Jesse Reimink: yeah. Disappears into the groundwater, right? So you can kind of, in cars, regions, you get the groundwaters coming in and out of the ground a lot faster than other, or a lot more frequently than in other parts, other types of topography because there's sinkholes and there's stream channels that, dump out onto the surface really quickly.
Um, so yeah, it's a very interesting landscape.
Chris Bolhuis: So if you have [00:30:30] this potential for sinkholes, karst is when you have a whole region that is just full of sinkholes. So you have, water flowing through the ground, creating caves. The roof collapses down in, and you get these sinkholes. When you have this whole myriad of sinkholes at the surface, we call that karst. And this then also shows how it progresses with depth. As water continues to percolate down through the limestone, it'll open then different caves [00:31:00] at different levels, especially if the river continues to downcut and incise, which keeps that hydraulic gradient steep and allows for the dissolution of the limestone.
Dr. Jesse Reimink: exactly right, Chris. And so, this is going to become very important when we talk about the specifics of Mammoth Cave here, that last point that you made, the last frame in this GIF kind of shows you, I don't know, this resonates with me, like driving around karst topography, this makes sense.
You're driving around hills, there's rivers. There's caves, there's [00:31:30] sinkholes, and the rocks beneath your feet are easily dissolved. And that's a really important constraint, or that's a really important, recipe there. And so, um, Here in Pennsylvania, in state college area, we have limestone in the valleys and the valleys are fundamentally there because the limestone's there and the limestone in these humid regions in eastern North America where we get a lot of rain, they're easy to dissolve and so they get dissolved in the valleys form.
The hills are more resistant rocks, it [00:32:00] all comes back to the same thing. Limestone's easily dissolved. You can make this car's topography out of it.
Chris Bolhuis: for you then about your Pennsylvania area. Do you have a lot of disappearing streams there?
Dr. Jesse Reimink: There are some. They're not as common as, I think, down in Kentucky and Tennessee area. we have caves, certainly. They're not as big, but there are certainly caves here, yeah. I rocks are, I can't think of an example. I mean, you do see some that are smaller, know, unnamed streams that, you know, These are smaller little tributary [00:32:30] streams.
The problem is that we're in the Ridge and Valley Province, so all the limestones are tilted on their side in the Ridge and Valley Province, so you don't get this long, flat lying structure that you get out to the west, um, the west of us
Chris Bolhuis: Okay. That makes sense. That makes sense. Cause those are just disappearing streams. And then when they rise back up as just a,
Dr. Jesse Reimink: we do get Chris a lot of groundwater seeps that feed the streams though so you can go, you can see often, especially in the winter if you go in the stream can be you know sometimes ice cover just a slight layer of ice and you'll go [00:33:00] see the little bubbling areas where the sand is kind of looks like the sand is boiling up, and it's just groundwater feeding into a little pocket feeding into the stream so we do get those, features, for sure it's just, just a really beautiful landscape.
Chris Bolhuis: Well, Jesse, and then one, final thing as we wrap this episode up on just general cave formation involving limestone is that these karstie areas where this karstie is a word that Jesse and I use, it's not really something you'd see in
Dr. Jesse Reimink: It's made up. It's
Chris Bolhuis: we like word karstie.
Dr. Jesse Reimink: and Chris is feeling [00:33:30] karstie when he's talking about caves.
Chris Bolhuis: That's right. And why not? But they do make fantastic aquifers too. So, residential wells and things like this because you have this really, if you tap into the right place, then you can get free flowing water beneath the
surface. And so they,
Dr. Jesse Reimink: point
Chris Bolhuis: important aquifer.
Dr. Jesse Reimink: a very important aquifer and it's also, it's a very rapid aquifer because, in Michigan where we talk about, when you talk about the aquifer, you're talking about kind of a sandy layer [00:34:00] down in the ground. So, the water is flowing through sand or sand and mud.
So, it kind of takes a while It's better at filtering out stuff. in state college, Pennsylvania, actually this happened a couple years ago. Karst groundwater is very It's quick flowing and therefore kind of easy to pollute there's this example.
They put a highway in and they didn't deal with the pyrite that was in one of the shale layers. And so you generated sulfuric acid, and that ended up. dumping in it didn't end up contaminating [00:34:30] anybody's wells, but there was a big concern because that groundwater goes really rapidly, gets dispersed throughout the groundwater system.
So it's actually kind of easier to contaminate in some ways because it's, it's a stream flowing underground rather than water percolating through rock or densely packed soil. which is, I think an easy visual to kind of wrap your head around, right?
Chris Bolhuis: Especially when you look at it in the context of image number four, I think that's pretty easy to, to visualize, what you said, it's easy to contaminate, but it's, it's probably also [00:35:00] easier to mitigate a pollution problem. If you can isolate the source of the pollution, then you can shut that off and it's going to clean itself out because it's going to make its way out of there relatively fast, as opposed to something like mine, my water may just move, you know, a few centimeters per
Dr. Jesse Reimink: exactly right. So quicker to pollute, quicker to clean up or easier to clean up perhaps too. So, and again, because the water's moving much faster, and that goes back gradient thing where we need to have a constant [00:35:30] supply of water here to create this cave system.
So, all right, Chris, I think, Is that a pretty good wrap for the uh, the intro here to Mammoth Cave? Like I mean we've covered a lot here. Cave formation, the recipes for solution caves, karst topography, which we've talked about before on the podcast, but you know we have to reintroduce with this cool image, for the, for the book here and for Mammoth Cave in particular.
Chris Bolhuis: I think we can wrap it up just by summing it up again for this kind of cave formation, we need to have a suitable rock, we need limestone, [00:36:00] we need to have a good solvent, carbonic acid, and groundwater is acidic, slightly acidic because of the carbon dioxide, we need good hydraulic gradient to enable us to keep on dissolving the limestone, and we need time, we need geologic time.
Dr. Jesse Reimink: long time for the reaction to progress and build these massive, beautiful caverns in Mammoth Cave. Okay, hey, well, that's a wrap. This, again, is part one. If you're listening on the podcast, you can go to the Camp Geo app. You can get full access to all the, um, [00:36:30] Mammoth Cave episodes. There's going to be about three of them.
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Chris Bolhuis: Cheers.
Dr. Jesse Reimink: Peace. [00:37:00]
