How Landslides Work

I sent this to you on Monday, and then I saw like a few hours later, Wow, and it was like, oh boy, I didn't you know. I was. I was on vacation, so I didn't hear about it. Um, but yeah, so it's super relevant. Well yeah it is, you know, apparently unintentionally relevant like our Black Boxes episode. Yeah, it's been happening weirdly. But yeah, if you have been uh not paying attention to the news at all lately, then

you may not know. But there was a massive landslide in Washington as of last count I think, um, the death tolls at like twenty four, which is an astoundingly high number for a landslide. Uh, at least in the United States because something like twenty five to thirty five people die in the US a year from landslides. This one was one single, enormous landslide, and if you haven't seen the pictures to get an idea of just how large it was, you should go online immediately, um and

check it out, because it's it was nuts what happened there. Yeah, it's about an hour north of Seattle, and I know we have a lot of fans in Seattle, so we're obviously thinking about everyone there. But um, it is you know, there's still you know, a hundred and seventy plus people missing, and it's it's it looks like it will be easily the deadliest landslide in US history by the time this is all said and done. It seems like it. But I'm clearly hoping there's more survivors. But it's just a

scary man. Oh Yeah, to think about like being trapped like that and possibly still alive. It's just like the whole thing is upsetting, Yeah, because I mean, if you were inside a structure it's now covered with mud, you might you know, there's a chance that you are you're not buried, the structure around you is buried. Um, So yeah, it's it's pretty awful stuff. Um, the to me, what's

even more awful? And I read an article where a resident, unnamed resident was saying like, yeah, we're not mad at the authorities, but yeah, apparently they didn't heat a lot of UM warnings. This area, the area that was covered in landslide was known since the sixties. In the area is Slide Hill that the area itself is called the Steelhead Landslide. So like, imagine if, um, the street you live on is is not an East Lake, but in Steelhead Landslide. Landslide is in the name of the area

that you live. So it wasn't like the biggest surprise. No, And there was a report by the U. S. Army Corps of Engineers that predicted a UM the potential for a large catastrophic failure right there where it happened. And that's exactly what happened. The landslide happened. It covered about a square mile and ums like fifteen feet deep. Right now, Well, you can't tell people where to live though, you know, no,

you definitely can't. I'm not saying they shouldn't have warned, but like, people still live in flood zones and people still build their houses on the sides of a hill in Malibu And yeah, and I guess if you're warned and like you were willing to take that risk and you wanted to, then yeah, I don't want to disagree with that, but I I don't know if um, I don't know if everybody was as aware of the potent tool. But apparently there was a landslide in the area as

recently as two thousands six. Yeah, so apparently this was the big one and it was coming a long time and that and set off by water in this case, right, Yeah, there was word that possibly it was an earthquake, but they think no, it was. Um, there was a lot of rain that that came before then. And so well, let's let's get down to explaining what happened exactly. The landslide there is actually technically a mud slide. Um, and mud slides, landslides, a bunch of other ones. They're all

they all fall under something called mass movements. Yeah, and that is the umbrella term, and that basically means gravity is at work moving something down a slope some kind of sediment. Um. It can be a landslide, which can is obviously devastating, or it can be super slow over centuries.

And we'll get into all that in a minute. But um, and well we'll get into all the triggers too, But I guess we should talk about their categorized depending on how fast it's moving, UM, what kind of materials are being moved. Um. In every case though, you're talking about soil moving off of bedrock, the friction being overcome by gravity. That's exactly what a landslide is. And it's like super fast erosion on any slope. You have soil over rock and it's being held in place by friction. It's kind

of scary to think about it really is. You know it's true, but then when you read it, it's like wow. Yeah. I mean like if you've ever like dug a hole in the ground, it's not easy. It's not like it's not like silt or something like that. It's it's like ground.

It's hard ground. But you know that stuff is it's not fused to the bedrock beneath it's it's there's there's a kind of um, there's a friction that's holding it in place, and that can that can fail, and that's that's what a landslide is exactly like you said, gravity overcomes friction. Yeah, and it hand on some very large scales, it can on small scales. Um. And then like you said, depending on the type of movement, how it moves, what's moved,

you have different categories of mass movements. Land slides are just one of them, or a slide is one category. The slides, creeps, slumps, and flows. Yeah, creeps are obviously super slow. It can be uh months, years, it can be centuries of creep. And that is when the sediment, uh, when the friction is is not working, but it's not completely destroyed, so there's still some friction. It's just moving

super slow. And that's usually as a result of a lot of freezing and thawing going on to change the composition of the soil. Yeah. When the when a freeze comes through, the sediment in the soil um is pushed upward as it freezes, and when it falls, it falls back downward. So what you have, if you look at it on a geological time scale, is basically an undulation up and down of the soil that is moving downward

on a slope like millimeters at a time. Right, and then uh, the telltale signs though, you can see that creep is happening because telephone poles will be kind of a skewed trees or something like that. Yeah. You that means that you're standing on or looking at a slumping slope and you won't see it happening. No, but I can see a pretty awesome gift. I can't remember where was it time lapse. Yeah, it's the time lapse gift.

And it wasn't over the course of the year. Is over the course of I think several days in San Bernardino or whatever. But it's just like whoa there goes. It makes you feel unstable. Yeah, like the earth beneath your feet. Yeah, well, I mean the the earth is a constantly evolving mass, you know, soil is being moved from here to there, and there's all sorts of different agents of change. But and it moves in different ways. It can creep. Um. I think I said a slumping slope.

That's not true. That was a creeping slope. A slump is when you have a big chunk that breaks off as a single whole chunk and moves. That's a slump. Yeah, and that can be the the actual thing can be called a slump too. It can have a couple of meanings there for that word, like the big piece can be called a slump, or if the movement is the slump, if they're not sliding like they used top uh, and that is when um basically the base can't support this

big chunk on top of it. And again it's usually due to UH moisture and water is the general cause for slumps as well. Yeah, waters, like the primary all time leading winning is cause of mass movements because either like um in a slump. A good analogy or a good example is if you're at the beach and you just see like a whole um, whole hunk of wet sand cheer off of another hunk of wet sand. Did

you just witnessed the slump? And actually water can create stability for sandy, loamy or clay soil, Like you build a sand castle, you want the sand wet exactly up to a point when you had too much water becomes saturated and then you have a slump or you have a slider a flow um and then with other types of mass movement, that water can get underneath and interrupt the friction between the soil and the bedrock, and that's when you have some sort of movement as well. So

that's creep, and that's slump. And then finally we have flow, which is uh just basically a soupy mix of water and rock and uh soil and other materials, and it's just those are usually the deadliest because they spread further. That's like a mud flower and avalanche. They get everywhere, they'll like enter into everything. That's not just it's just like a bunch of dirt. It's it's like a river, a moving a fast moving river of mud and debris. And I misspoke earlier. That's um in oh So, Washington,

that's what that's what that was. That was the mud flow that started it, that came down and covered everything, which actually hampered rescue UM operations because apparently it's just like quicksand right now, Yeah, so in the case of well, in the case of anything other than a creep or slump, if you're talking about a quick landslide, it happens just like in a snap. It's it's going and picking up speed, but it is the result of years and years of

of like slow steady erosion. Classically, it's not something that just happens out or it can be triggered. We'll talk about like earthquakes and stuff like that, but in general, it's the weathering down of objects. And I guess the difference we should describe between weathering and erosion is erosion is transporting the weather material and weathering is is the

actual wearing down of that material. So they're different. So if you have a rock that's a nice, big solid piece, millions of years later, it's been weathered into a bunch of soil, and then as as as it's lost its composition, it can move more easily, and when it moves, it's being eroded. So erosion is the is the process of movement. The weathering is everything that leads up to that ability

for it to be moved. Yeah, and weathering is important because it's your weathered landscape is going to be much more likely the landslide um. That's why you'll see them in more extreme environments where you get like tons of rain or like a lot of snow maybe uh, heat, cold water, and oxygen. Those are all things that impact weathering cause weathering. And there's there's two types of weathering.

There's mechanical weathering and there's chemical weathering and mechanical weathering is basically, um, the material is broken down, but it retains its same chemical composition. Right it was, It's still the rock, but it was broken down into smaller pieces of itself, um, say by wind or something like that,

or water lapping against it. Now, if you had that pieces of those pieces of rock that were in water that ultimately, over the course of years dissolved it, it would be in solution and it would no longer chemically resemble itself. That's chemical weathering. So like if you pour acid on your hand, Uh, it's gonna reconstitute into something else. On the other end, the whole that burns through it, the stuff that ends up on the table is not really the same thing as your hand. You just chemically

weathered your hand. That's a pretty extreme example. Um. And then you talked about the constant state of movement on the Earth that's going on at all times, and that's basically if you're gonna have erosion, you're gonna have a deposit somewhere, and it's just a constant cycle on the earth of weathering carried away by erosion and being put

somewhere else. In in cases of landslides the bottom of hills. Yeah, when we toward Guatemala, you Jerry and I and um or I should say me, Um, we we're at the site of a landslide that had happened. Um, I will

never forget. Yeah, and they you know, you could still see in the sort of jungle like forest the swath that had been cut through years earlier, because all the stuff on either side was old growth and then the stuff through the landslide slow was Yeah, it was like it was much younger, Yeah, shorter, like a different kind of green as well. And they pointed out that we were like twelve feet higher than uh basically standing on uh yeah, the old village they were unable to recover

about two deep people. It was really upsetting. Yeah, and I remember their children were running around, all these orphan children, Um, like they are just kind of they belong to the remaining village. Now. It was really something else. Well. Yeah, and just when they said, like, you're like twelve feet higher than just the whole land raised up because of

this month's line. It was one of those ones that like you just kind of chewed on for a little while before you finally understood, like the full gravity of it, even though like while while I was standing there, I was like, oh this is nuts. Yea. Then the more I thought about it, think none of your got uh So the sediment, Um, we we talked about the deposition at the bottom of the hill. The sediment is known as talus, right, let's the official word for it when

when it's from a landslide. Yeah, yeah, that's what's being carried down. And um, with erosion, there are five different things that can act on it, which are water, which we've covered in wind and then gravity of course which we mentioned, and then waves and glaciers too. And technically gravity is a part of all of them, right, Yeah, that's true, a part of all mass movement. But um, those five agents of erosion, there are different things that

can trigger a landslide or a mass movement. Um. And and and really, if you think about it, all a mass movement is like a landslide, it's just erosion in at high speed. Sudden and high speed erosion is is basically what that is. Rather than taking millions of years to move from here to there through wind or waves or whatever, it's just happens in a moment, and it happens on mass all right, So you mentioned the triggers. We will cover those right after this message break. All right, So

we mentioned triggers. Uh, the landslide always has to have a trigger, that has to be something to actually set it off. Even though it maybe years and years in the making, something finally pushes that button to make it happen. Um. It forces gravity to overcome friction. That's right. One of the things that we mentioned already in the case of Washington was water, and that is probably the most common

heavy rainfall I know in California and Los Angeles. When you see houses slipping off the hill in Malibu just because they don't get a lot of rain, and when they do, things like that happen. Yeah, And it's either water saturating the ground and just making it so heavy that it flows downward, or it gets down in between the soil and the bedrock and just causes the whole thing to undermines everything. Either way, water equals a lot

of movement. Earthquakes that can definitely trigger a landslide. Um. We've covered earthquakes. You should go listen to that show if you have, and it's a good one. But you've got the vibrating of the Earth's crust, and that UM is going to disrupt that friction pretty easily. Another big one is wildfires, which you would think, well, how would

a wildfire trigger that. I'll tell you how UM. Vegetation, the roots of vegetation can lock soil into basically a totally solid, cemented state, and as long as you have thick vegetation on a slope, it's gonna be fairly stable. When a fire comes through burns out all the vegetation, it often burns the roots as well, leaving not only less stable soil, but actual pockets in that soil too. So now it's kind of pebbled, which makes it a

lot more vulnerable to landslides after a wildfire. Yeah, I would I'm just guessing here, but I would guess a landslide could happen like even long after wildfire, Like if those roots die away, it would just become even less stable. Uh. And then volcanoes. Uh. Volcanic action is a big cause. And there are a couple of um different kinds of flows that can contribute to a landslide from a volcano.

When it's called a pyroclastic flow, and that is after your dome has collapsed or during interruption, and these are super high speed. They've clocked him at four hundred and fifty degrees fahrenheit Alva flowing at you at four. I can't even imagine that, Like, can you imagine seven twenty four kilometers per hour? That's easier. Well, there you go. Then you just imagine four. Yeah, but I mean I don't even know what that looks like, you know, or

de yeah, exactly. Uh. And then they are something called a lahar, which is an Indonesian word. And this isn't uh doesn't have to be during interruption, but it can be. And it is set off by water as well. Um, it's almost always near something called a stratovolcano, which are like super steep cones, and a lot of times there's either a crater lake or it's snow capped up top, and so that's the water agent. A lot of times it's the snow and it it sort of looks like

wet concrete flowing downhill. Yeah. And it may or may not be set off during an actual volcanic eruption. It can happen anytime. Yeah, and it's it's much slower, you know, an hour, but still if you're in a golf cart, you're dead. Yeah, that's a good point. Uh. And while it's not fast, it has um a lot more rock, So it is one of the deadliest lahar is, I think because of just the sheer like you can carry like a big boulder. Yes, in the middle of that

wet concrete, plus of volcano also. Um, it's just it's not very stable because the composition of it is usually pretty loose rocky soil. So yeah, if you had water, it immediately turns the slurry um. And when they erupt, they tend to shake the ground a little bit, which is what happened in the largest recorded landslide in Mount St. Helen's. Everybody knows the eruption, but there was actually an attendant

landslide that's on YouTube you can check out. As a matter of fact, Um, we're putting a post up of just amazing landslide footage that you can check out on our website. Um, just go to stuff you Should Know dot com and check out that post. There's just a just some crazy stuff that people just happened to be filming and all of a sudden, the earth changes right before your eyes. And one of them is this Mount St. Helen's eruption where just the whole mountain is basically just

melting in front of you. I remember that one, do you? Oh? Yeah, that was only four Yeah, I was nine, So it was on my radar that one traveled at speeds of a hundred and fifty miles and again Washington State, not getting a break, destroyed twenty seven bridges, about two hundred homes, miles and miles of road, and covered three square miles with debris. Yeah, that was a Mount St. Helens. Well,

you know it was the landslide. Another another frequent hazard associated with landslides is you think about it, Um, when all of this earth is coming down, it's coming downward into a lower space, which is very frequently a valley, which is very frequently a river valley, which means that

the river's damn now, so it's flooding behind it. Yeah. Right, so you have a flood, a flood hazard immediately, and then if that river or if that damn breaks, then you have another flood hazard down river all of a sudden two, which is something that's going on in Washington right now. Yeah, the same thing happened, and um, I think it's the most expensive landslide in US history in Thistle Utah uh in night, the same thing happened there. It damned up the Spanish Fork River and caused like

much more problems just because of the flooding. And that was two hundred million dollar fix in ninety four dollars. And that was even when Reagan was in office. So it's not too much different from the two thousand uh. The submarine landslide we should probably talk about that is in the ocean, and that is you can you can have an earthquake under the ocean triggering a landslide underwater

which will trigger a tsunami. Yeah, I can a one to three punch basically of natural disasters happening all in concert. Um that and then actually I don't know if this really technically counts, but it's seeing that um little bit triggered a memory of the Lake Pinier disaster in Louisiana.

In Texico, was drilling in Lake Pinier and apparently they didn't consult the map closely enough, and they were using a fourteen inch diameter drill, and they drilled into the lake bottom, which was on top of a salt mine, and they drilled into an operational salt mine, and the lake got sucked into the hole in the giant whirlpool. Um that took about like thirty to fifty of the surrounding acreage around the lake in into the lake with it. Eleven barges were sucked in the um flow of water reverse,

so it went from freshwater to saltwater. It sucked the gulf into it for a second, and then a couple of days later after they were like four hundred foot geysers as like these shafts were filling with water and the air was being displaced, and um, a couple of days later, after the water pressure stabilized, like nine of the bar just popped back up and like went back to floating after being sucked down into this diamond mine. It's crazy and then nuts and apparently there's footage of it.

It's it's awesome. It's like just the most amazing thing. I guess more amazing than that is no one died. Yeah, there was one guy on the lake who was operating the drill. He got all and then there was a guy fishing on the lake and he zoomed his boat to shore and made it like win far enough that he made it, but I think three dogs died Lake Pen your p e I G N e U R disaster check it out. I was all excited and then

the yea, um, man, that's crazy. But there had to be some of erosion going on there, and technically it was submarine erosion. Um. The most deadly UH landslide in the history of the world is was a nineteen twenty in China, December of nineteen twenty. It was triggered by an earthquake and as many as two hundred thousand people died in that holy and some of that was from the earthquake, but they said the landslide was responsible for most of the deaths. Yeah. Like I said, in the US,

it's like twenty five to thirty five deaths a year. Worldwide, it's more like four thousand, and then on on years where there's terrible earthquakes, it will go up into the tens of thousands um. And then there was there was a munths like for there was a mud slide in nine in Vargus, state of Venezuela that killed like thirty thousand people. It just covered a bunch of towns like all at once. It was a mud slide or mud flow.

I guess. Well. One thing I thought was interesting was that um and I think Jennifer points us out early in the article that while in the state so we don't see a lot of uh deaths from landslides each year, they're the most expensive natural disaster over I think tornadoes, earthquakes combined in this country. And if you will consult your homeowners insurance, you will almost definitely find that the

landslides are not covered. Yeah. Noope, Well, I guess we should get to the point then that or is it us? Is it humans that are causing these things? Yes? Always, not always. No. Animals can cause it, like a goat can cause a landslide if it really is unsure footed. But goats don't blast mountain tops with dynamite, that's one. Yeah. They don't DeForest. Yeah, deforestation is a big problem road

building and through the mountains. Yeah, because think about it, when you have a mountain and you cut a road through it, all of a sudden, what was once a relatively gentle slope are now too steep slopes on either side just aiming right at the road. Well, yeah, and I think everyone's probably driven on mountain roads where they either have uh, chain link fencing on the side of it, which is scary enough, or I guess it's even scarier when they don't have fencing, but they have signs that say,

you know, watch out for falling rocks. Are good luck pal? Yeah. Um, there are things that people are doing though. When they do build roads, they sometimes we'll put in drainage pipes to carry away water, which helps h in permeable membranes like plastic cheating. Yeah, so it can't trickle down. Yeah, retaining walls and reforestation. So if you're gonna clear cut an area, if you're gonna harvest timber, maybe go back in there and try and reforest plant something. Yeah, you

know ructure. I can't believe that that's not a law that if you take X number of trees down, you have to plant X number of trees and the number you plant should be more than the number you Is that not a law? I'm I'm quite sure it's not. We can't even get black box recorders ejected for an extra like fifty bucks a plane, remember I remember, there's no law for that. Hey. But here in Georgia we just passed the law where you can bring guns into churches and uh, bars, oh, I thought you were gonna

say that. I'm actually rejoicing for another law. I don't know if it was signed in the law or if the House passed it and it's on its way. It is now a crime to drive slow in the fast lane, or it will soon be when they passed this law. Give me some parameters, you know, called the slow poke bill. Okay, And if you are impeding the flow of traffic, not even if you're going under fifty five or under forty five.

They're so aware that Georgia drives fast that they say, if you're impeding the flow of traffic, even if other people are breaking the law and you're going the speed limit, you are breaking the law by being a slow poke in the fast lane, which is the most glorious law any any city or state has ever come up with. Well, if he states, right, if you go to Europe, the left lane is just for passing, Like, you shouldn't even

be traveling in the left lane. Right, it's supposed to be you go around someone and then you stay out of it. It's supposed to be that way here too. Boy, it ain't no. But if you got the chops, you can travel in the fast lane, as long as you're not holding people up, the ones that are really like you need to go to jail, or ones that are just knowingly or like I'm driving the speed limit so right,

you don't own the road. It's like, well, there's ten people behind you that you're holding up, So you're the one who goes to jail. Now, in Georgia, that's gonna be tough to enforce. It's totally subjective to I mean, it's like a cop can It's totally up to the cop to enforce or not. But yeah, it's still I just think it's a it's a grand gesture, agreed. Okay, So, if you want to learn more about landslides, you can type that into the search bar at how stuff works

dot com. You should also check out geology dot com. They have a really great UM page with lots of different sub pages on land slides. Yeah, and if you're in the area and have been impacted, we would love to hear from you, for sure. We're thinking about you guys. Obviously. Um, I think did we say search bar at any point? Yes, Well, then that means it's time for listener mail. All right, I'm gonna call this Um, possibly the Union bomber is writing us. Hey, guys, I want to send out a

note from the Great North. I've been listening since my buddy Adam played me the Lego podcast a few years ago, and since then I've been a fairly regular listener, but never more so than over the past few months, because last spring I moved from Minneapolis to Juneau, Alaska for job gardening at a public uh arboretum. It sounds like a lovely job, by the way. I live in a little shack in the woods near my work, about twenty five miles out of town, about a half a mile

from my nearest neighbor, almost free of rent. Close b send me to work, and uniqueness of the situation is what drew me to it. I have no internet, I have no cell phone service, so UM, every time I head into town, I stopped by the library or coffee shop and download more of your podcasts. UH new stuff and oldies, but goodies that are still new to me. I have gotten into the habit of listening to you

guys most evenings while making or eating dinner. I know some people in our town, but in the interest of using less gasoline and sparing my more or less meager bank account. I spend the majority of my nights out here alone. Whenever I do go into town um or one of my friends make their way out here, I tell them about whatever I've learned from you guys. Listening to you banter and learning a lot of interesting new things has definitely helped me keep my firm grip on

my sanity. Uh. Winter is basically wrapping up here. It was long and harsh. We had ninety six inches of snow in December alone. I'm really looking forward to springing summer when Alaska, to life with tourist seasonal workers in long sunny days. But I'll still find time to listen to your good stuff, so keep it rolling. I am happy I decided to live out here this past winter. It's a beautiful spot and a good adventure, but would have been a lot more difficult without the company of

you guys. You rule And that is from Will and Will that sounds like my kind of life, buddy, I'd love to do that. That is your Union bomb or esque. I could sands the bombing. I could be the UNI bomber. Well, I'm glad you're enjoying yourself. Will thank you for letting us know that we're helping you out out there. Um, if you want to let us know that we're helping you out, whether you live alone or are part of a Brady Bunch or something like that, you can get

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