Creepy Soil
Dr. Jesse Reimink: [00:00:00] Welcome to Planet Geo, the podcast where we talk about our amazing planet, how it works, and why it matters to you.
Chris Bolhuis: Dr. Reimink, how you doing?
Dr. Jesse Reimink: you again, huh?
Chris Bolhuis: How often do you get called Reimink.
Dr. Jesse Reimink: Uh, not very much, but my wife does in the hospital. She gets called all sorts of things in the hospital.
Chris Bolhuis: [00:00:30] I don't know if I wanna know the backstory to that,
Dr. Jesse Reimink: No, no, just like rink, Reimink, Reimink.
Chris Bolhuis: Reimink. All right. That's a good
Dr. Jesse Reimink: uh, yeah, she gets, there's all sorts of different pronunciations for my name, but yours too, probably.
Chris Bolhuis: Oh yeah. In fact, I was just talking to our little friend, handy Andy, just a couple hours ago and he called me and I didn't pick up 'cause I was in a meeting and then I called him right back after the meeting and he, he's like, he, he's laughing right when he picks up and I'm like, what, what is, is going on?
What are you laughing [00:01:00] at? He said, every time I have my headset on and you call, I always get this call from. And he just thinks that's funny every single
Dr. Jesse Reimink: I think it's funny too, whenever I use Siri, I have to say I've said this before, I'll say it again. Every time I use Siri, I have to say Chris Paulis, because Siri, that's how Siri knows your name. If I say Chris Bullis, then I sometimes get different Chrises that are in my phone book, but
Chris Bolhuis: Come on, you don't have any other [00:01:30] Chrises in your phone book?
Dr. Jesse Reimink: I do, I, I, shockingly I know more Chris' than just the one, but not as many that I like, as much as you, Chris, or not as many that I spend as much time with either. So,
Chris Bolhuis: That that is true. We do spend a lot of time together.
Dr. Jesse Reimink: it's true. And I ain't sick here yet.
Chris Bolhuis: I'm not gonna say the same 'cause I am actually quite sick of you.
I'm
Dr. Jesse Reimink: just keep me around, huh?
Chris Bolhuis: I do. I don't know why I, sometimes I wake up at night and I wonder, what am I doing? Why am I [00:02:00] doing this?
Dr. Jesse Reimink: You turn to Jenny and say, why do I keep talking to this guy all the
Chris Bolhuis: She said, what are you dreaming about? I said, I'm dreaming about Jesse. It's like, it's, uh, it's really frustrating
that's, that's right.
Dr. Jesse Reimink: Well, Chris, What do we got today?
Chris Bolhuis: We are gonna talk about soil creep today. And you know, to be fair, we've talked a a little bit about this, I think, uh uh, quite a while ago. But we're gonna devote an entire episode to this kind of mass wasting movement and we'll talk about what that is. 'cause that's kind of a [00:02:30] funny term in and of itself.
Yeah,
Dr. Jesse Reimink: I have a question for you, Chris. Is mask wasting your favorite section to teach in your class?
Chris Bolhuis: that's really interesting that you asked that. Why do you ask that?
Dr. Jesse Reimink: I ask it because okay, it's, it's a, it's cool. Like all Geology is cool or all geoscience is cool. It's not my favorite topic. And I find, I kind of think you're weirdly, you are above average interested in mass wasting. I think,
Chris Bolhuis: Why do you think this
Dr. Jesse Reimink: I don't know. I don't know. I, but 'cause you, you, I think [00:03:00] maybe, is it just you like the term mass wasting?
Is that what's Uh,
Chris Bolhuis: but, I do like the term because it adds confusion, like the, the kids are like, you know, I assign, actually, I do this section a little differently than. Most of the other sections I teach, I actually assign a chapter reading for them to, so they read it and they take notes on it, and then I give 'em a test on it.
Okay. And, and when they, after they take the test, then I spend, you know, whether it's a day or [00:03:30] two days, I need to talk about mass wasting with them. And the reason I do it that way is because I just have to, I have so much material that I have to get through to get 'em ready for the exam at the end of the year from Dr.
Maddox, you know, So I just, I do it this way. It allows me to cover mass wasting because they're already familiar with it. But every time I assign it, they look at me and they, they're questioning and I'm like, what? What's going on? And I always forget. And they're like, what is this mass wasting thing that you speak of?
Dr. Jesse Reimink: Yeah,
Chris Bolhuis: this?[00:04:00]
Dr. Jesse Reimink: what the heck does that term mean?
Chris Bolhuis: it is one of my favorite things to teach though, and I didn't know that you knew that about me.
Dr. Jesse Reimink: Okay. No, I, I didn't know that. I just have kind of, it was a guess. It was a random guess. But I have two questions for you and I want you to answer them in order. First of all, define mass wasting. Can you do that for us? And then second of all, tell me why it's your favorite. why do you like teaching it so much?
First, define it because I think, you know, the listener, our listener is thinking, what the heck are we talking about this episode? So [00:04:30] let's get that out front.
Chris Bolhuis: Mass wasting is the movement of material down slope, and it's always governed by gravity of course. So weathering happens first. Then mass wasting happens, and then erosion happens, right? It, it'll be removed in a, in a different sort of way.
Dr. Jesse Reimink: so mass wasting can be, you know, rock falls soil creep, which we're gonna talk about today. You know, landslides, uh, what other ones we can have? solar flexion. We talked about solar flexion earlier, um, [00:05:00] when we kind of briefly touched on soil creep.
So there's a whole bunch of stuff that could be kind of mass wasting movement of mass down slope, usually at a, a decent clip, except for soil creep. So why are you, why so excited to teach it, Chris?
Chris Bolhuis: Because mass wasting and humanity. Have a really interesting intersection, where we put roads. I think about this when I drive through the Smoky Mountains. You have these, road cuts that, really go in kind of [00:05:30] precarious places. That it makes me a little bit nervous actually.
When you see this like metamorphic fill light and schist rock, that's foliated in the direction of the slope. and you have these signs then that say, watch for Falling Rock. And then you look up at the cliff, you know, you look at the edge and you see this net kind of holding everything back.
And I'm like, oh good. I was worried until I saw net.
Dr. Jesse Reimink: Yeah, right. This mountain might
Chris Bolhuis: is,
Dr. Jesse Reimink: and the net is gonna catch it. Sure.
Chris Bolhuis: yeah, pure [00:06:00] sarcasm. But, yeah, it's this interesting intersection between like, retaining walls, for instance, what happens with retaining walls and the way that they, kind of move and lean over time. it has a lot of practical application.
So
Dr. Jesse Reimink: that's a great reason to do it, Chris. I, I think that's a, that's a great. Answer to the question of, you know, why are you more interested in this than other chapters maybe or above average, interested in teaching mass wasting?
Chris Bolhuis: Yeah, but I can't really say, I can't really say that. [00:06:30] It's above. I don't know if that's the right way to put it, because everything that I teach, I, I do get excited about. I, I
Dr. Jesse Reimink: Well, that's true, but I mean, what I mean by above average, you're, you're more excited than the average teacher of earth science classes. You're, you get more excited about math wasting than the average person. So that's a, that's a great reason. And Let's maybe move into, the narrower version. So mass wasting is this big, catchall term for a bunch of different processes. One of the processes, the one we're gonna talk about today is soil creep. I think, [00:07:00] Chris, the best way to visualize this is if you've ever walked, I have this vision of walking through the streets of Washington DC where the house is built up a little bit above the sidewalk on a hill, and there's a retaining wall, an old retaining wall, like a stone retaining wall from.
Many, many, many decades, if not a century ago, and that's retaining wall. The top of it is tilted in, so you kind of have to walk with your shoulders sort of to one side. If you're, and if you're passing somebody on the sidewalk and they're on the outside and you're on the inside, [00:07:30] it gets a little uncomfortably close because you kind of are being pushed away because the wall is tilted, the top of the wall is tilted out into the sidewalk.
That's what I have in my head. Tilted trees also represent mass wasting, like when the, when the stump of the tree is kind of tilted down slope, even though the trunk is very straight. Right. That's another example of this. What do you picture, when you're teaching this very passionately, what, what do you, what slide do you show of soil creep?
Chris Bolhuis: I always show a slide of the dunes along [00:08:00] Lake Michigan where these trees are coming out on this really steep slope and one of the dead giveaways to soil creep and this movement of soil, really slowly, almost imperceptibly down slope. You can see the bend along the base of the trunk, almost like right above the root system.
It's bending down slope, but then, like you just said the trees straighten back out. So I start with that and then you know, and that's a picture that I took. And then I also show a picture of, um, a, a [00:08:30] few years ago I was walking through Harper's Ferry, the cemetery there in, um, right along the, triple junction, the states, the three states there, and.
These old headstones in this cemetery, it's on a hillside, and the headstones are tilted like at a 45 degree angle, you
Dr. Jesse Reimink: a great one. Yeah, yeah, yeah. The headstone tilting, that's a great one to show for sure. So soil creep is the slowest of the mass wasting processes, but it does take place on human time skills, as you said, on tree growing time. Skills [00:09:00] like this happens over, uh, maybe not in a year, but in decades for sure.
You can see this with older buildings. You can see this with older sidewalks. You can see this with older retaining walls or headstones, et cetera, or trees that are, you know, more than a decade old.
Chris Bolhuis: Even in cracks in a road or a driveway, for instance, you can see this, this kind of uneven movement of the surface, and it causes cracks in concrete and asphalt too. So that's a Another one too. That is a nuisance to a lot of people actually.[00:09:30]
Dr. Jesse Reimink: So how, um, How do you explain this? do you have a great analogy for soil creep or the process of it? I guess? How, how do we get into it? We've kind of described what it is, so everybody's got the visual in their head. What is it? What's going on? What's the amazing geologic process that's that's sort of driving this?
Chris Bolhuis: Well, like I said before, it's driven by gravity, but there are three things that really play in. To making soil creep a, a big deal, and those things are, first of [00:10:00] all, water, water plays a, a big role in this whole thing because, it makes the soil less cohesive and it just kind of aids, it lubricates the movement down slope, if you will.
And so the steeper the slope, obviously, and the wetter the soil is. The faster the soil's gonna creep down slope. So that's one thing. Right. But the other thing, and I'm gonna throw this back to you because when we talked about this before, you explained it quite well actually, was the, the role of ice [00:10:30] wedging on little tiny particles right at the surface.
So what happens with that?
Dr. Jesse Reimink: Yeah, so the way I think about this is when I'm kind of thinking of it like the hillside breathing in and out, and if the hillside breathes in, meaning it gets saturated with water, it's going to expand. And how does it expand? Like think of one particle right on the edge of the hill. Let's say it's this big.
Hill, that we can kind of envision the particle right at the peak of the [00:11:00] hill. It's gonna go straight up when the whole hill expands, that particle's gonna go straight up. But a particle on the side of the hill is not going to expand straight up. It's gonna expand outwards at like a 45 degree angle,
Chris Bolhuis: And it's expanding because of freezing, right?
Dr. Jesse Reimink: Or, you know, water, if it gets saturated with water, that water can kind of push the whole hill out just a little bit. Um, so many factors. Temperature can do this. It can kind of breathe in and out slightly because of temperature fluctuations, but ice wedging is a big one So when the hill like [00:11:30] breathes in, expands, the particles are going to move outwards at like a 90 degree angle to the slope. So if we're looking at this hill, the top one moves straight up, but on the sides, they're moving out to the side. Those particles are moving out to the side.
Now when it relaxes, when it breathes out and the hill relaxes back down, where do those grains go? Well, gravity pulls them straight down. So Chris, we had this great analogy. I think it's kind of similar to Longshore current in this way When a wave [00:12:00] hits the shore at an angle, it moves the grain up at an angle.
Then gravity pulls that grain straight down the beach front, And so over time the grains are moving to the left or the right, depending upon which way the waves are hitting. The, the shore. The same thing is happening here with the hill when ice wedging kind of makes the hill breathe in and expand, the grains are moving out at an angle, and then when the thaw happens and the hill relaxes, they're moving straight down.
So they go out then down out,
then down. Yeah. The zigzag, it's[00:12:30]
Chris Bolhuis: So,
Dr. Jesse Reimink: zigzag. I.
Chris Bolhuis: I have a picture of this that I show. I was in the Smoky Mountains in February, Jenny and I like to take a midwinter break and go out in the mountains for like three or four days.
Dr. Jesse Reimink: you get into big hiking competitions with high schoolers on the trail down there in the wintertime, if I remember correctly.
Chris Bolhuis: That is true. That is true. Um, anyway, If the conditions are just right, you get these ice formations, I think they're called ice curls, actually. It's really long, skinny ice [00:13:00] crystals that grow out from the ground. And I got, yeah, they're really cool. And I saw at the, tip of one of these ice crystals, Soil particles, they had been heaved out.
So I got down with my phone and I took a really good picture of it. All right. It's, it is really a cool thing, and you can see exactly what's happening. It's exactly what you described. These ice curls shove that those little soil particles perpendicular away from the slope. And then during the [00:13:30] day, they'll melt and they'll drop it straight down. And so that little particle just moved, you know, just a couple millimeters down slope. Right. And it's like you, you throw that picture up there and it's like, oh my gosh. You can actually see soil creep in actions
Dr. Jesse Reimink: That's such a great one. And I think Chris one, one last point is that, this doesn't happen in flat areas, right? Flat areas. The soil is just breathing up and then down, up and then down up and then down on a hill slope it goes out and then down out and then down. That's the important point here.
And [00:14:00] so what's so, okay, water was the first one. This sort of ice wedging phenomenon was the second one. What's the third one, Chris?
Chris Bolhuis: It's just simply rain splash, which makes sense. Rain hits a slope and it's gonna splash the particles down slope. So those are the three things that really contribute to Soil Creek. But look, we're talking about just a few centimeters a year. Usually. Now it can be faster than that, but this, we're talking an inch, two inches, just a few centimeters on a like a year to year basis.
So this is [00:14:30] not fast movement, but it's unrelenting. it's a real force to be reckoned with actually.
Dr. Jesse Reimink: Totally, totally. And, and I think one important thing here, Chris, is that the edges or the tops of the soil move a lot faster than the interior of it. So that's why we get this sort of tilting. And if you imagine that headstone that you were talking about, that's a great example. You know, maybe two thirds of the headstone is above ground and one third is down in, the ground.
And. The surface of the soil is moving down slope faster than the interior. So [00:15:00] right at the surface is moving downhill faster than an inch down into the soil. And so that's why this thing tilts. It kind of tilts down because you're getting this more rapid movement right near the surface, and as you go into the soil, there's less rapid movement.
That's a, I think, an important kind of, uh, point to make here as we're thinking about this.
Chris Bolhuis: That's right. And I, I actually, uh, you know, I'm, I'm ashamed to say this, but I have a retaining wall, but I didn't do this, uh, okay. I, I bought the house that I live in, but I do have a retaining wall. It's a concrete [00:15:30] wall and it has a gigantic crack running right through the middle of it.
It's not, structural or anything like that, but it's a result of. know, soil creep 100%. you know, so it does that, it, it can damage the foundations of buildings. can damage roads and sidewalks and, and obviously retaining walls. And so it, it's a, it's a thing to be dealt with. It's a, it's a force to be reckoned with.
So how can we slow it down? You know, how can we kind of mitigate or, or deal with this [00:16:00] phenomenon?
Dr. Jesse Reimink: Yeah, well unfortunately biology comes into play here, but biology vegetation is the great, like soil immobilizer. Anytime. We don't want soil to move. You can put vegetation on it, Especially trees with deeper roots. Those are great at sort of locking soil into place. so that's one kind of relatively simple one.
That's not always feasible though, especially when you're like making a retaining wall around a house. You don't wanna plant a tree that's gonna dig its roots into your foundation right next door. Right. So what are some other [00:16:30] ways, there's some cool engineering things I think that people have figured out.
Chris Bolhuis: there's a thing called Tough cells, and there are different brands of this, but it, it's basically this honeycomb network that it can be made up of many different materials, but think of like this honeycomb plastic thing that you set on the slope and then put sediment in the honeycomb spaces.
Alright. Does that make
Dr. Jesse Reimink: And these honeycombs. Yeah, these honeycombs are like a couple inches wide. So you think of like a, beehive honeycomb except the cells are a couple inches [00:17:00] wide or so that's kind of the scale of what we're thinking of. Roundabout, maybe a foot or something like that, but
Chris Bolhuis: basically then what it does is it just arrests the downhill movement of, of material because it's all connected to each other because it's in these spaces, it has nowhere to go. and so like, I guess that's one way to, you know, maybe even stop soil creep from happening altogether if you're on a steep slope.
Dr. Jesse Reimink: Yeah, that's right. That's a, that's a good one, Chris. And there's, there's a few, that some people would put. [00:17:30] Reinforcements into a concrete wall like you have like retaining walls with big rebar running in and put an anchor way back in the hill that is kind of anchoring the wall in place.
Those are like structural things that are just trying to make the wall more forceful, but it's not actually stopping that pressure movement, whereas these tough cells are kind of distributing that. Down slope movement pressure a bit more and, and kind of changing the physics of the hill slope as opposed to just trying to make your wall stronger.
Right? There's a kind of two different approaches to the, the [00:18:00] problem here. So, but it's a difficult one and it's, and it happens over a long timeframe, so, we might not be thinking, you know, 40 years ahead of when we're building, but we should be many times. So.
Chris Bolhuis: hard to stop Geology, Jesse.
Dr. Jesse Reimink: It's very hard to stop Geology. Oh, that you, you need a shirt with that?
It's hard to stop Geology.
Chris Bolhuis: I, I, I don't know. That's a really good idea actually.
Dr. Jesse Reimink: a good one. What was the other shirt we were gonna have? We're gonna have erosion happens, right? Was that the one? Erosion happens and it's hard to [00:18:30] stop. Geology Crisp Heis.
Chris Bolhuis: I'm not gonna claim the erosion happens one. I think that one is, I think the Grand Canyon came up with that. They have it on a bunch of those shirts. Erosion happens and it doesn't get any more appropriate than
Dr. Jesse Reimink: No, totally not.
Chris Bolhuis: Canyon. So,
Dr. Jesse Reimink: It's hard to stop Geology. That's a good Chris Bullism right there. I love it. Love
Chris Bolhuis: to me just like that, that
Dr. Jesse Reimink: Nicely done.
Chris Bolhuis: Yeah. Thank you. Appreciate that.
Dr. Jesse Reimink: Hey Chris, I think that's a wrap. If you wanna send us an email, we love getting emails, [00:19:00] we love getting questions, listener questions.
We're always putting together office hours episodes. Send us an email, planet Geo cast@gmail.com. You can also visit our website, planet geo cast.com. There you can subscribe, you can support us. A bunch of people have done that recently. We really appreciate that actually.
If you wanna learn about all the basics of geoscience, you can head over to camp courses. That's geo.camp courses.com. You can learn all about the basics with visuals. I think we've done a, a pretty good job of that. And the interface is newly revised and I think looks a lot better than it did initially, Chris.
[00:19:30] So head over there, let us know what you think. And as always, leave us a review and a rating. We always appreciate it.
Chris Bolhuis: Cheers.
Dr. Jesse Reimink: You can't stop Geology.
Chris Bolhuis: True
