Mass Wasting - Part 3 of 3

Added: 2026-05-15

[00:00:00]welcome to the last installment for this module mass wasting the term mass wasting is also referred to as mass movement and it's the mass part is is the earth itself so it's in reference to movement of large amounts of surface material so you know we can't often just would have called this a landslide but there's different specific types of mass wasting and when we're dealing with - wasting remember this is the movement of material downslope so in order to have mass wasting you've got to have a slope it's gotta be on an angle fortunately there's very few perfectly flat surfaces on earth so just about every surface of the earth is affected to some extent by the influences of mass wasting the really when we talk about mass wasting we they're usually referred to as mass wasting events now with the exception of creep which is one type and I'll get to it later most of these mass wasting events is a sudden movement or a movement over a period of weeks you usually don't have something that's in constant flow down a hill it usually moves because something has caused it to move and if if it was in constant movement it would have reached an equilibrium point at some point where the slope angle wasn't enough to overcome the force of friction so when we talk about mass wasting there's something that caused it to happen those are the triggers what are the triggers for mass wasting events so for example gravity we can't change the force of gravity but we can change its influence if the material gets heavier so for example when it rains that water soaks into the Granada mix that around heavier when we put structures on top of a hill that makes it heavier when you do landscaping with large trees and that makes it heavier so all of that can increase the downward force and thus increasing the likelihood that that slope could fail now friction just if you have a pile of dirt it's the friction between the material that holds it in place now if you were to lubricate that slope in some ways by adding water to it when it rains I could reduce the friction and increase the likelihood that that slope could feel water is kind of funny is a little bit of rain is actually really good is the surface tension of water how water molecules like each other that will hold the soil in place too much of it reduces the friction and actually causes the material in the soil to kind of push away from each other and it lubricates the soil and then we can also if you had a leaky swimming pool that would soak into the soil make it heavier and reduce the friction we think well how can you make a slope steeper well this could be through NASA through documents through uplift more than likely what happens is that somehow or another you've changed the slope angle by the base of the slope so a cutaway from a stream or roading at the base of a hill or a road cut eating away at the base of the hill but nothing's holding the slope in place and it becomes too steep this stuff will just fall down the hill now vegetation works two ways we've got deep rooted plants they'll hold the soil in place and keep it from falling if you have shallow roots they may be easily slough off the side of the hill and exposed the dirt to the water from the rain and the nakid lead to a mass wasting event the grasses for example in California historically prior to the Spanish arriving had really really deep roots the new grasses that have kind of replaced them have shallow roots and we're seeing that typically more mass wasting events in California than we did historically in a large part is to the changing grasses that we have on our hillsides now ice plant is a favorite of landscapers the plant to keep the soil in place it grows from cuttings it grows really quickly it doesn't take much care to it but it's all horrible horrible plant for keeping a slope in place it evolved as a sand dune plant and great if you've got a stand you want to keep in place that's good but other than that it's terrible and you'll see the picture below what happens is this ice pipe is so heavy there's so much moisture in these leaves they're so heavy that it's constantly inflow down the side of a hill and it grows so fast you don't realize that this particular plant here in a year or two will be down here and then in a year or two will be down here see all this dead pile of ice plant that's the stuff that's slowly been sloughing off the hill because it's so heavy and such shallow roots well this one rainfall the surface ice plant washed down exposed the soil and then the water was able to just wash it away and I have a personal dislike of ice plant running levy so when we look at different types of mass wasting events different types of varying depending on how fast they are and how much moisture is involved I'll take extremes for example the really fast wet event would be a mud flow which makes sense you fell on rainfall collects the loose material it flows almost like a thick River downhill which moves very very quickly another quick event but is completely drying would gear up fall where rocks fall off the side of a cliff the slow events such as creep this is it's complicated and we'll get to it but it's that slow downward movement from the expansion and contraction of the soil that takes place over decades or longer and this is something that's almost imperceptible where you can't stand outside and see creep happening where this is something it can move faster than you can run Sala flexion is weird this is the freeze-thaw cycle of sort of slopes I'm not going to worry about that because we don't get that around here these middle ones they're really closely related it's slight differences in moisture content will make a slump we're kind of or it's also called a rotational slide where the slope fails and it kind of pivots in place and then kind of boulders out as a bulb if this was a little bit wetter it probably would be more fluid and like an earth flow if it was a little bit drier and failed it might behave like the landslide everything kind of tumbles down the hill as opposed to moving in a cohesive block so these are all very similar and usually you you'll have kind of an overlap where some of it will move in cohesive pieces you'll get some of this rotational movement within it and then at the nose of it the wetter stuff will flow a little bit farther so they they're these three typically have an overlap to some extent it's rare that you get a nice perfect slump or a nice perfect earth globe I'll show you some pictures in a little bit that demonstrate those different ones they do have in common this a semicircular scar on the side of the hill and that's usually how do you identify them vegetation will grow over this and really all you'll see is kind of this semicircular scar and then I'll pile in a degree at the base and you'll see for every single one in order to determine what it was you'd have to remove all the vegetation or these things through the vegetation to see what the surface looks like to determine if it was a slump in her flow or a landslide but again they're close enough we're not too stressed about that here we've got a rockfall a very steep slope moisture was not involved it's usually from freeze-thaw rocks expand from heating whatever and then they just tumble down and create a pile of rocks at the base so you've got your scar up here and your pile of rocks that fell down from the rock fall at the base so that the talus is the pile of rocks at the base here you can see the scar it was recent enough the vegetation hasn't had a chance to grow over this and the talus here what your scar from a here notice how steep this slope is this is a vertical slope another one in Yosemite vertical slope this one's a little bit older but this is by the awanee lodge or whatever we're calling it now and these are huge boulders I mean I'm 6 feet tall here I like this one cause it just kind of appeared overnight P you can see this crack right here this is a joint in the rock we talked about joints already it's a crack in the rock so up at the surface I'm scrolling off the screen sorry up at the surface there's probably the trap extends all the way if they're so water's been able to creep in through this crack you can see that a little bit of water so this crack gierek's goes blind this rock then comes back out over here this is the same joint here that you're seeing right here and so you can see this dark spot where the water has made it down in well there's kind of the more that water got in there the more it was kind of releasing any attachment that this Rock had to here maybe there was a freeze thaw maybe there were some plants that got in there and then at one point it just failed and noticed there's no water involved in here this is a dry event a rock fall you can see some of these on everybody's a different road name for this PCH bits that stretch of post highway between Tina Point and San Clemente the technical name for it is Beach Road but the your there's a series of rock falls in through there some of overgrown with vegetation some are more recent if you are going I'm here and looking at these you're really careful because people try both idiots on this stretch of road and the last thing you want to be doing is looking at the cool rock fall and then get crashed into or crash into somebody else also if you're closer to the southern end of this down near San Clemente some of those walls have cement some of these cliff faces excuse me have cement on them to covering them up slump known as rotational slides they're actually pretty common in an around our area our hills have the right consistency the right slope angle and so you'll see a lot of these and hopefully there's not one by your house then when you're driving around you'll you'll notice these weird semicircular scars on the hill this one down here is probably more of an earth flow but you can still see this as my circulars are this one kind of moved to the cohesive block and you and here's the scar at the top what probably happened is this road cut remove remove the pace of the hill nothing supporting it here and so it just failed so these rotational slides can happen one of two ways you either maybe remove something at the base or you have additional water or lubrication up here that causes either more weight here or something not holding the base down here at this side of the hill is kind of falling off into where the stream cut is coming through this one it says slump but it's more of a North flow where you can kind of see it's bulbous like really thick mud kind of moving down the side of the hill now these are more local rotational you can see the debris kind of pushed up here this kind of moved in this manner and when it did so you can see this car now some of these are easier to see in person than they are in photographs I don't know if you can see that this part here is bulged upward a little bit the base of this hill was undercut by a stream here this was just loosely compacted soil that was packed up too steeply they should have had a more gentle angle for this along the side of the road like this one this one's bright off the lure take a highway what are the side canyons and notice how steep this slope is and this would have been the original position of this little block material and it just kind of slumped into that position that you're seeing there that means over time more and more of this little cliff face here is gonna be stuffing off and falling down into the canyon below this one I'm not gonna test you on translational slide is just another type of slide where it's usually you've got sedimentary rock that are in layers and there's some type of weakness between one layer of rock and another layer of rock like a shale or something so when it gets wet it gets slippery so this whole block moves as a cohesive group so you see how these kind of blocks are sloughing off down here it's gonna also happen when you've got exfoliation domes where the the rounding of it creates these type of joints and then the rocks just kind of slough off and so for here for example this fence is still in its original angle and it just kind of went from this position down to this position because I'm getting to Bluebird Canyon slide that happened in Laguna Beach and that was had a translational element to it so in 2005 a section of Bluebird Canyon failed overnight remember the state was the day we were leaving for Ireland and I was kind of disappointed that we were gonna be gone for a month and I wasn't gonna get back this get a good view of it until after they'd already cleaned some stuff up so these are downloaded photos unfortunately this was a big event and you can see that some of these units have moved in pennant this house used to be up here and so it moved down more like a translational slide where other portions of it you can kind of see that these homes are leaning backwards for this piece kind of rotated the winter of 2004 2005 was exceptionally wet we had 30 plus inches of rain and it took literally months for that water to percolate down in the soil to hit a layer of shale that kind of lubricated it that combined with this construction down here which weakened the toe of the slope this is a new building this week in the toe of the slope so between the lubrication and weakening the toe this whole thing failed it happened over a period of hours nobody died in this people they think here the cracking they'd make them to hear the loud noises they'd feel the movement of the house they can get out and so everybody was able to get out when this occurred a bluebird canyon was the site of another landslide so nobody should have been surprised about instability to give you an idea of how close these two locations are this is where the 78 slide was this is where the 2005 slide was so they're literally next to each other so the it's not like there was a big distance between the two locations when the event occurred the Brule estate is actually slightly less expensive if you look at the average cost per square foot in Laguna Beach Bluebird canyons a little bit cheaper and there's a reason it's a little bit cheaper looting Laguna Niguel had it in 98 now this was more modern construction I mean these homes should have never been built on these slopes but the property ownership goes back decades prior to a lot of rules this one this was a big development the good in account they actually tried to mitigate the the chances of a slope failure so this is a more gentle slope they have good brain itch in it they did some cuts where they were looking for any weaknesses in the rocks they did one here did one here and did one here they didn't do one here you know you can't do it every square inch well this had an ancient failure in it and then that combined with they needed more parking spaces for these condos so they've made the parking lot a little bit bigger and undercut the toe of the hill whoops and so this failed as well again this took place over a period of hours I've had students who lived in this house and one of these houses over here um this one has been subsequently torn down but this was the people that appear heard the sirens and then they came out to watch what was going on the person that lived here could hear the cracks and the Pops and the noise that was making as the hill started failing now it's just a cleared spot there's no homes there so there's one that's easy to see near Oso and Antonio and it's on the side of the hill here so that the Taco Bell is over here by the carwash it Oh San Antonio and if you went this way I know so you're heading towards the five freeway so this view is kind of looking towards the west and you can see this car here the pile of debris here the scar the pile of debris this one depends on the vegetation how easy it is to see in the spring it's usually a little bit more more overgrown and harder to see but the developers here didn't even put homes on this side they backed him away now they would have been way more valuable because they would have been nice hillside with a nice view but instead they put him on the other side of the street to create less of a likelihood of anything happening to the homes las Flores has las Flores and some of the other new construction like post 1995 and post 2000 they've really gone and done a lot of work to to avoid landslides in those areas this is near Antonio and Ortega a little southeast of the college this is Mission Viejo company land Rancho Mission Viejo and you can see the scars on the hills and through here Ladera trenches up above it up there and so this is Antonio down here this all down here is now Sendero that's the new mission viejo company development which backs right up against this slope there's some bigger ones make permanent possibilities his whole neighborhood had to be evacuated because it was slowly sliding down the hill calls for a spoon insulin big chunks of it that are not a good location for home now this one a few years ago this one it was another one that should have been avoided this one they had a loss of life there were homes that were down in this area down here and the it was a rainy winter the stream here was kind of the outer edge of the stream and I weakened the slope a little bit and then this whole thing just kind of slumped down but once it hit the water the water lubricated the sliding it's lit across the valley floor and so this is for the homes were that were damaged now from your limited experience in looking for clues that mass wasting events have taken place like these curvilinear scars half-circle scar is there anything you notice in the valley that might be hints that this area might be prone to mass wasting events yeah Arsenal all sorts of clues so the state geologist decades ago and said nope don't build here pile got shoved away somewhere and people ignored it they built here and people died same thing here with the earth though in 2005 in la Conchita Allah Conchita is the last little development along the coast highway before you get to Santa Barbara area and its really a big little neighborhood and that hillside collapsed on January 10th with but that part about this one was as people were down here looking up noticing there were cracks in it there was some movement in the wall down here and the people who were in these homes one of the guys came down and got a cup of coffee and went back home and then those hillsides fell on him and he died this one again shouldn't have been a surprise because it was nearly adjacent to a slide that had failed just ten year the side of the hill that had failed just ten years before even the it's hard to if you look at topographic maps from the past they all show a different contour for this area because it just seems to be constantly being destroyed from mass wasting events this is farmland up here and this land was owned by the railroad and when they sold it off they refused to sell the coastal land this land down here they refused to sell for residential development because the dangers involved they even built their railroad tracks right along the edge of the ocean because it was easier to protect the railroad against crashing waves and wave erosion than it was from this hillside collapsing it on top of it at least hold it for farmland and then the farmer resold it for residential use so it happened in 88 five I mean this is all recent history and nowadays you can't get a mortgage on a home in here so these are all cash only homes their value is obviously slightly less but again you're living with a little a chance that the hillside to fall down on you and kill you but at least you get a nice oceanfront property there's another area that's continually moving Mount Soledad this one is that last Hill as you're heading south into San Diego the last Hill before you get to Mission Bay then everything happens up and what makes me laugh about this one is been offensive where I've thought about buying a home up in here in the 1960s and they didn't and they've always been commenting how lucky they were that they've been this is another area that's that seems to be in constant movement and constant problems what is the best part of our best part about Muscle a minute this is one of the model homes so they and even and the development going and one of the model homes them down the hill so that should have been a giant clue two people had not build here now the most common type of mass wasting is soil creep soil creep happens on any slope and if there's hardly any flat surfaces on the Earth's surface everywhere has a slight slope what is the time on how common creep is happens virtually everywhere this is the reason your house has cracks in it this is the reason that your try way doesn't quite look as nice as it did 20 30 years ago it's the slow downward movement of the slope happens in a couple of ways in cold environments that freezing of the soil and the surface when the moisture in it it expands and so it causes material that expand at a right angle from the surface and then when it thaws gravity acts upon it and it comes back down this way so it expands outward at a right angle and then contracts straight downhill due to gravity well locally we get the wetting and drying so when everything was wet it acts like a sponge it kind of expands outward and then when it contracts it contracts downward the watering of your lawn the watering of a hillside for landscaping all of that is contributing to that slow downward movement of the surface now these two drawings unfortunate make it sound like individual parts of the soil gets lifted up and floating in space and then come back contract back down this whole layer would expand outward and then contract downward and so what happens is that outer surface it goes up and then down out and then down out and didn't know and so you see everything on the surface from a leaning down hill that's slowly moving downhill the I mean nobody puts in our lines and fences at an angle trees they're trying to correct myself those trees want to grow up towards the sky so as they start leaning downhill as the hill isn't leaning downhill the trees try to correct themselves this is a larger area of movement this slopes moving downhill this one's moving a little quicker visits kind of a really rocky soil and at a high altitudes the freeze-thaw really works on this nobody puts a fence in at this angle a retaining walls really early career solutions even with these four by fours they're not enough to hold back the weight of the entire slope more like a temporary retreat a temporary wall to kind of slow the process down but again it's this constant pushing downhill of the slope is gonna cause that lean alright so you may notice some creep around your neighborhood so make sure as you're driving home and around the hair look for those trees that are all leaning those are evidence of soil creep and then they become more common once you start looking for them and didn't realize just how much of this surface was moving what I'm gonna show you is an area that's moving a little bit quicker when we were looking for a home dozen or so years ago one of the areas we were looking was Shore cliffs in San Clemente the average price was slightly lower we liked San Clemente so this is Shore cliffs on the right up on the hill and this is the view from the parking lot of the DMV in San Clemente the area we're talking about is just an over from the outlets and by the shore cliffs golf course and the DMV is over in here so this was the neighborhood we were looking and as soon as we were driving through the neighborhood there was just weird signs of something as unusual going on like who doesn't but they're siding all the way down and why is this cracked in through here and why are so many homes doing stucco repair my home mantle has stucco spams most of you guys have stucco fighting stucco repair is really really rare and we were seeing half a dozen homes in that neighborhood who were doing stucco repair well what was happening the whole hill was creeping a little bit and when the home moved that stucco you guys know what stucco is it's that some basically cement siding on your house it doesn't flex and so when the hole moves it causes the crack and it has to be repaired then there were other clues like this had been recently resurfaced but nobody would pour cement with an one-inch gap in it so this home is pulling away from the curb this is new cement so that doesn't count but right in through here that one inch gap is this is moving in that direction and this angle doesn't show very much you'll see in a second but this home is leaning it's leaning backwards so this is downhill to the left I'll go run to the other side look at the garage and that you can notice the leaning a little bit more so this garage door is still square the whole house is leaning over that's why it's tight up there at the bottom this is downhill the direct wall is pointing towards the downhill so it's actually been moving enough to pull apart these solid bricks and if we move down this fence towards the left and downhill so at one point this brick was touching this brick it pulled apart they filled it with cement and then it pulled apart anymore and they just gave up you can see all this how its stretched and have a pulled towards the left so if I turn and look left this is the area so it was along that fence over there they've actually had to tear it on the house so of course ignore the police line and walk over to here and you can see how it still kind of Leaning here this is not an optical illusion this guy's backyard is actually dipped down in this corner so much that it would almost render this backyard pata ball patio unusable and if you turn around this is the view to the other direction and this guy's this is Sue's picket fence in this grass this was up here and then one night in July it just went shoe didn't filled it up so I'm standing here taking the picture and a guy sticks his head out the sliding glass window starts screaming at me to get away and stop taking pictures and I think hey I'm what psychologists I'm gonna use this for my students he starts talking to me and he said they were in the house heard a big crashing noise he went over to the back window to see what was going on and he was standing at the sliding glass window he didn't go outside fortunately but he was standing there and it took him a while to realize that his backyard was gone so since the house is going to was going to be torn down after this event it wasn't damaged so much that they couldn't get their stuff out so they were able to get their stuff out and then the house was torn down and the other side of that fence is the five freeway and then it's still happening there was this place a few years later and then there was another one recently as well so we decided not to buy in that area all right thank you everybody and we'll see you in the next module