this is a lecture on chapter 8 weathering soil mass movement so this lecture covers three main topics weathering mass wasting and erosion I know it's hard to see in this image here but weathering is the disintegration of rock and its decomposition at the Earth's surface so if we have exposed rock over here it's going to go through sleet rain snow all different types of weathering processes to break that rock up into smaller pieces mass wasting is the transfer of that rock material downslope unde
r the influence of gravity and then erosion occurs that incorporates an agent moving these really smaller much smaller sediment size and particles typically water but it can be wind or glaciers can move these smaller sediments to different areas on Earth's surface so let's talk about weathering first see this Boulder right here this erratic this was split open by a weathering process we call mechanical weathering that's the breaking of rock into smaller and smaller pieces this is pretty intense
I mean what happens here is when you have any really cold areas you have ice so it ever rains here water will infiltrate into these small little cracks and then when overnight temperatures drop below freezing water expands by volume so it'll actually force cracks open and rocks like this another type of weathering is chemical weathering and this is the transformation of minerals within the rock to new new and more stable minerals okay so these processes work simultaneously so let's pretend and t
hey actually help each other out they kind of accelerate the weathering process once you get some mechanical weathering in it but let's pretend we have this cube of granite and let's expose it to your surface and you can calculate the surface area that's exposed to the elements - rain - wind abrasion and all that all those weathering processes and when it's one big block like this it has 24 square units but if you have mechanical weathering starting to like break it apart into smaller pieces now
all of a sudden its surface area increases I almost by twice the amount and that's because see these interior surfaces are now exposed to a chemical attack so that's what happens with weathering mechanical weather and will break rock into smaller and smaller pieces and this exposes even more surface area for chemical weathering to take its role and so it accelerates the process so there's four important mechanical weathering processes one is frost wedging which I mentioned before and that's the
expansion of freezing water I know you've probably done this by accident like maybe you threw in a drink into the freezer you know being like all right I just wanted to get it cold real quick and then you forget about it and then you go back to check and the drink is exploded or expanded and broke the bottle and that's because water when it goes from its liquid to solid phase expands in volume by like nine percent so especially if you have a glass bottle that could be a big mess in your freezer
salt crystal growth is the same idea when you go to coastal areas let's pretend there's a coastal areas and there's waves crashing over here there's a lot of salt spray and that salt spray comes and coats coastal rocks and when that water evaporates away it leaves behind salt and that water can kind of infiltrate into the cracks of rocks and then as salt crystallizes it can expand those then there's cheating cheating is like layers of granite that kind of exfoliate outwards because of the lack
of pressure and it resembles a lot like an onion you know onions kind of come off in layers and the last example is biological activity here you have a tree growing directly on this rock and its roots are kind of forcing its way into the cracks and crevices of the rock and breaking it apart so those are all mechanical weathering processes here's just a visualization of frost wedging so in these cracks which would represent rocks kind of exposed of the Earth's surface over here it'll rain sleet s
now so water gets in these little crevices and pore spaces and cracks and then overnight it freezes it expands and then it forces rocks off that's where you have falling rocks pile up in this talus slopes at the bottom of Rock exposures and their mountains so that's frost wedging here's the visualization for sheeting okay here's the Half Dome Yosemite National Park and it's an intrusive igneous rock meaning that it crystallized deep underground kilometers underground and as it crystallized it wa
s under a lot of confining pressure but now over millions of years of erosion and uplift these intrusive igneous rocks that were once deep underground are exposed at the surface and because there's nothing on top of it there's no pressure confining pressure the rocks begin to expand and as they expand they can form these kind of sheets if you look at it close it's almost looks like peeling skin exfoliating skin joints can form this in this fashion as well all right chemical weathering this is wh
ere water plays a role in adding or removing elements and actually altering the minerals within the rocks water is the most important agent [Music] water has oxygen in it so dissolve the oxygen in water oxidizes a lot of the minerals and materials carbon dioxide also plays a role that dissolves in water and forms carbonic acid and that's slightly acidic and that can also alter a lot of rock material on the Earth's surface so let's take granite for example very common intrusive igneous rock and G
ranite's have a lot of potassium feldspar and potassium feldspar is susceptible to chemical weathering and so when it is exposed to precipitation it can slowly produce clay minerals and soluble salt or potassium bicarbonate and then silica in solution quartz in granite is very stable meaning that it's very weather resistant so it remains kind of unaltered and this is why quartz kind of breaks down perhaps into smaller pieces because of his mechanical weathering and eventually becomes sand and th
at's why a lot of our beaches in the state of Florida are mainly composed of quartz and then all the other silica minerals we've talked about they'll produce insoluble iron oxides and other clay minerals so here's the breakdown courts really residual just becomes the quartz grains a little bit of silica solution I felt sparse break down into clay minerals plus this material goes into the groundwater system and then amiable and olivine so you're more Ferro magnesium minerals will break down into
clay and iron oxides so a lot of oxidation occurring another type of chemical weathering is called spheroidal weathering this generates rounded rocks and you see this in Joshua Tree Park California really hot dry desert area and this happens over time you have exposed bedrock in this case it's sandstone and water penetrates the joint it of rock right so mostly initially kind of like a physical or mechanical weathering process and then chemical weathering does its bidding and then starts to round
the edges of the exposures until they become completely around here right don't believe the History Channel no it's a geologic process ok so when you have a lot of mechanical weathering that aids chemical weathering like we talked about before breaking it down to smaller pieces and because of that increasing surface area but there are a lot of important factors that affect how fast things whether one is the mineral composition okay some minerals are more susceptible to weathering than others ca
lcite in limestone is very susceptible to weathering it's very sauce so like so you had marble that would weather very easily potassium feldspar whether these with easily other minerals like quartz don't whether as much and then also the rock itself if it has a lot of physical features like joints or expansion cracks that will accelerate the process of weathering so if you guys thought about your tombstones I know maybe maybe you're not thinking about that or haven't planned for it but everyone
you know goes to the grave right and that's what's the guarantees in life you're gonna die and you have to pay taxes well when you we know at some point in your life you may I don't know maybe you want to get cremated I don't know maybe you want to be buried in a cemetery but if yeah so if you want to if you're gonna get buried in a cemetery choose your headstones wisely okay this is a granite with not too with a limited amount of feldspar in it and this was erected in 1868 and we can still read
who this person was 1801 to 1868 Peter sweat I'm guessing is that that's how you pronounce his name anyways someone went all fancy and chose marble for their headstone and they they died after Peters sweat for years afterwards but can you even read this who was I don't even know was that say Ted I don't know Roosevelt I don't know so this marble headstone has weathered away because it's made of marble and it's made of calcite a mineral called calcite which is very susceptible to weathering so y
eah choose your headstones wisely guys alright so the rates of weathering really are dependent on a few factors the most important is climate if you have a moist and warm environment Florida those are crucial chemical weathering is the most effective in those types of types of environments and so differential weathering occurs when you have rocks exposed at the surface that may be composed of different minerals and some of those minerals will rock units will weather out faster than others and so
we call that differential weathering meaning like different Rock units will weather at different rates some faster some slower and what ends up happening is it causes pretty unusual and spectacular rock formations and landforms kind of like oh the old cover of the book had the arches from arches nat'l park or you know you maybe you've seen this Red Dead Redemption kind of base their landscape on real locations out west also you could see these almost these mushroom shaped don't push them over t
hey take thousands of years to form you get arrested for it too but yeah so the this process and this unusual alien landscape is produced by differential weathering alright let's jump to soil soil is interesting because it's kind of like an interface between different earth systems so so we have the geosphere and rocks right those are inanimate like nonliving things and then we have on the other end organisms and rocks break down slowly into regolith that eventually becomes soil and then organis
ms grow out of the soil and then we either you know things that grow from the soil or the organisms that eat the things that grow from the soil Wow long story short soil is can connects the kind of geosphere to the biosphere okay and what soil is is a combination of mineral matter water air and humus which is right to put that in there that's organic material okay and so when rocks break down into smaller smaller pieces that becomes regolith those are rock and mineral fragments and that supports
the growth of plants that's the only gif I could find of soil that's a very multi soil so a great example but here you go this is much better it's mostly mineral matter okay we've got some organic matter which is good that's called the humus water and air subsoil so soil has texture I don't know if you noticed this but it's made up the texture refers to the proportions of the particle sizes so sand is the largest this is kind of review from sedimentary rocks then silt is smaller than that and t
hen clay is the smallest so all soil is made up of these three our proportions of these three particle sizes and most soils are considered a Lome which is a mix of all three so it'd have like maybe ten percent clay 20 percent silt and 70 percent sand would be alone it would be a sandy loam and this texture diagram helps describe all the different soils so if you had 100 percent clay you'd plot right here if your soil had 100 percent silt you'd plot over here and if you're at the beach this is wh
ere sand would be 100 percent sand so in reality clays just plot anywhere this would be a clay with a lotta this would be a soil plot of clay this would be a soil plot of sand and this would be one plot of silt a perfect mixture would be kind of like in this area okay so this basically describes all the different types of soil Florida soils would be in this aegeon okay so what controls soil formation well the parent material the residual soil in the area that's the bedrock that's breaking down t
o create the regolith that's really important we call soil that forms in situ in the area called residual soil so it just remains there and slowly hundreds of years and then there are areas on earth that receive a lot of transported soil and so soil may be forming in upland areas and then is eroded away and carried by water and then deposited in like a river valley a low-lying area and so in those low-lying areas you get a lot of transported soils time is really important in terms of the soil fo
rmation it's the amount of time that the soil has to evolve okay and become like a good enough soil to support plant life and soil does take a long time because you need the kind of slow weathering processes to kind of break up the regolith and the mineral matter and deliver kind of minerals to the soil itself so that it can support the plant growth so it's in the order of hundreds of years per soil formation climate is very important although it's a little deceiving a lot of people kind of wron
gly think or their intuition tells them that a man rain forests and tropical areas must have the best soil because the rain forests are just exploding with all kinds of life in green in fact soil in the tropics is actually poor and a lot of the nutrients are found in the plants themselves because the tropics rain so much it's an overload of chemical weathering and that leeches a lot of the soil of important minerals so you need a good balance of chemical and physical weathering and that typicall
y is in latitudes where you have like overnight freezing so you can have some of that freezin thaw mechanical during breakup some of the bedrock in the residual soil okay and then plants and animals influence the soil itself here in Florida we have a lot of areas where there are like pine trees for example and Palmetto or that will grow underneath them and the pine needles once they fall off the tree they become part of the soil that's some of the organic matter being added to it but that raises
the acidity of the soil because the pine needles are acid like so depending on where you are on the earth and what plants are covering that landscape they're gonna have an influence on the soil because that's the organic matter that's going to make up a portion of the soil okay another important factor is your slope steep slopes have very poorly developed soils because they erode very quickly the best-case scenario is flat land or undulating land okay so that's just really slow gradual Hills wo
uld be great places for soil to form and then at high elevations I'm sorry not high elevations high latitudes when you're closer to the poles orientation becomes important because if your land is facing one of the poles for example it's going to receive less Sun and so that's not as good for soil formation so here are your examples you don't get so much soil development in dry areas because of lack of water and steep kind of steep slopes you get no erosion because of erosion because no soil form
ation because of erosion here in low-lying valleys and rivers you get a lot of transported soils so we do a lot of agricultural farming in these areas and then here in fact these are the best areas for soil formation our areas where it's kind of Haley slightly undulated land surface or or flat okay or really gradual hills think of Kansas okay that's really flat lying area where you have soils developed in app in siege ok the soil profile refers to the different levels and different layers of the
soil beneath the surface under ideal conditions the it's it's like you know if you were if you had a cake and you cut out a piece of the cake you can see the different layers of icing and you know whatever is in the cake the soil itself this is an ideal soil profile ok the topsoil is the over aizen and the a horizon together ok the top layer is the over isin because this is the area with a lot of partly decayed organic matter that's how I remember it Oh for organic and then a is the layer with
some organic matter a lot of mineral matter and this is what supports plant growth ok this top soil area now below the oh and a horizon is the e horizon and in the eager isin this is the area of the Louvre iation and leaching so water moving through this will leach out a lot of materials and clays downward to the B horizon and this is where the accumulation of clay is transported downwards ok so that's that B horizon then the C horizon is partially altered parent material this is the parent mate
rial is the bedrock okay this is what's breaking down slowly into smaller and smaller pieces the regolith and then becoming part of the C horizon ok so here's just kind of a repeat of what I just talked about so let's let's compare different soil profiles this is in Puerto Rico ok and here this is in South Dakota so in Puerto Rico very hot very beautiful great music ok not great soil because it rained so much the climate has a lot of that there's a lot precipitation so that water kind of leeches
a lot of the important minerals in developing soils and so it makes for an immature soil and so a lot of times especially rain forests as well when they cut down the rainforests to you know have grassland or agriculture or farms it's good for about two years and then you basically removed all the minerals and important features of the soil for agriculture and it's essentially useless like your crop fuels will go down in South Dakota there's a good mix of physical or mechanical and chemical weat
hering and so you have a very well-developed soil profile you got the Oh a C and B okay so how do we classify soils well there's a lot of scientists that study soils and they developed a whole soil taxonomy there's almost like eleven thousand different soils so here's the major ones and here's our global soils see the ones where topics are called oxisols because they're heavy heavily oxidized ok the the good latitudes for agriculture would be in this green area the mazels ok and in here all righ
t so one of the big issues is that it can erode and it moves into different areas especially if a land area is kind of exposed or laid what kind of barren for you know you start planting crops so the the natural rates of solar erosion this occurs naturally humans have kind of exacerbated the problem with our agricultural practices but it depends on [Music] the slope of the land and the type of vegetation that exists the process that erodes soil water plays a big role brain droplets dislodge soil
particles and then the flowing water carries it away two-thirds of all US soil undergoes erosion and the wind does play a role itself in erosion but usually during droughts that's when wind plays a bigger role so the problem with this is that a lot of soil erosion can cause reservoirs to fill up with sediment that's you know we don't out west they this is a bigger problem because they don't have as much readily available groundwater they use a lot of surface water so they dam up a lot of the ri
vers that create reservoirs so if you have a 'grill area surrounding it a lot of that soil can seep into those reservoirs which can be bad because a lot of times farmers will use pesticides and fertilizers and that can run through those areas as well here you can see in Iowa there's some reels forming after a heavy rain when their farmlands kind of bare okay and then here's a gully cutting through some farmland and creating you can see kind of soil washing away here so how do we control soil ero
sion well don't farm on steep slopes but if you do you could do terrace crop planting in between your crops put in grass waterways I'll show you a picture and then tree windbreak barriers are good to prevent wind erosion so I'm sure you've seen this if you flown around in an airplane okay right and you look down and then you can see different farmlands and you see trees that outlines different properties that's to slow down the wind and prevent wind erosion here are those grassed waterways in be
tween in between kind of cornfields and you can see that this farmer has got it going on he or she planted corn kind of to follow the the ridges and the elevation of of their land which is a good idea and so this these grass waterways help catch the soil that may erode from these corn not rose okay here's a close-up view of those grass waterways all right so it's a good way of conserving the soil and it's in the farmers best interest I mean if they can serve this little land and they're gonna ha
ve you know great crop crop yields in the future okay mass wasting is our last topic this is the downslope movement of rock regolith and soil under the influence of gravity gravity is essentially the controlling force that will pull this stuff downwards please click on that video it's an amazing mass wasting event I'll just say it's a lot like where's the final destination type stuff enjoy it that's pretty cool anyways one is if you saturate this material with water that can trigger an event fro
m occurring like a little landslide or a soil flow or a slump or something and so the reason why this happens is because water is heavy ever try to like Phillipa like a home depot orange bucket filled with water and then try carrying it I can get pretty heavy fast so imagine an area that has been just drenched with water that water will percolate through all the pore spaces in that soil and regolith and just make it super heavy so if that's like on an over steep and slope the chances of a mass w
asting event are increased exponentially and I'm sure you've noticed this if you go to the beach you ever try to build a castle with dry sand you can't do it right it just kind of piles up like this but if you add a little bit of water initially water acts as like a cohesive material and then it kind of sticks the sand grains together so you can build a nice Sandcastle but if you over saturate your sand in water it's just going to become a sloppy mess over here and that's the problem so if you h
ave a lot of water falling down torrential rains it gets pretty sloppy and heavy and that can cause another trigger to mass wasting events are over steepening slopes what that essentially means is is that like say you have a mountain or a hill or something and typically we're like oh we want to build a road around this or through it or something so we start blasting the side of a mountain and then we create like an artificial wall that's an over Steven slope okay and that can trigger a mass wast
ing event because gravity wants to pull that material down into an angle of repose an angle of repose is like the kind of a stable slope right so here you have a bunch of piled up sand this is the angle of repose this is the angle at which sand is kind of stable if you were to add any more sand it would just kind of roll down the sail and then to the bottom but what we do is we'll just cut this off and then this would be an over steep in slope and eventually gravity wants to pull this stuff down
so this could collapse okay another trigger to mass wasting events are the removal of vegetation through a forest fire or you know perhaps we do it on purpose doing like control blaze or something but this is especially true like out in California I recommend going on and just putting up like highway hill fire California and it's unbelievable they have brush fires that will just roll across mountains and then just burn all the vegetation on it and when that happens like plants their roots ancho
r the material the soil the regolith in place so if you burn all the vegetation away all of a sudden mass wasting can occur at a much higher risk because those things are no longer in place and to top it all off California has earthquakes and if you have any kind of seismic waves moving through the ground that can also kind of trigger a landslide or a mass wasting event from occurring okay so mass wasting processes are defined by the material that's moving whether it's debris whether it's mud sa
turated in water if it's earth or rock and also how the material moves if it's a freefall of just rock pieces down a slope is it a slide like a whole bunch of material slides along a curved surface or or a kind of straight surface or if it's a flow meaning that it's is it a viscous fluid like saturated in all this material so here this would be a freefall of material this would be a rock slide here okay so these rocks just kind of came tumbling down and this building heavily damaged as a result
we also define mass wasting processes by the rate at which they move there's fast and they're slow here are the two examples on the left that's a fast landslide and that blocks the road and that's a big problem that sucks right and then on the right that is a slow mass wasting process those really really nice homes close to the looks like there's either a coastline this looks like a road over here you see this is an over steep and slope and this material wants to move down because of the force o
f gravity and it eventually will and then these peoples those homes are definitely condemned there's no way that people are allowed to live here anymore their yards are just kind of when the foundations are probably all messed up it's a shame those look like really nice out anyways here's a slump this is the rapid movement of Earth material on a curved surface so here's that curved surface right there and this typically occurs over a long over steep and slopes like if example I was showing you a
nd so what's left behind is you have a scarf and then also this would this whole movement here would be called the sum thump blah slump block okay and then the material that was on top we call that earth flow which is soil regolith kind of moving downward here's another example this is close to the coastline another Road this is in California Point fermium but scarps start the form here and this material kind of just falls downward which is pretty dangerous these are nice homes again their yards
just go right into the ocean alright this is a rock slide rock slides are very fast they're very dangerous they can damage cars it can you can get buried in them and it's heavy rock material with a lot of mass moving down very fast speed so very dangerous so you can have a surface here rupture and all this material will move downwards really high velocities okay debris flows include a lot of water so this could be a major like low-pressure system or hurricane dumping or storm just dumping a lot
of water in an area and then all this saturated material will come kind of careening down the kind of low-lying valleys and tributaries along elevated areas this has happened in California as well after major brush fires if there's any rains the rain will carry that material and be saturated and sometimes you know like if you live in areas with a change in slope this this muddy material can kind of rush into your house and then you've got all this mess inside your house possible to clean okay i
n some areas we have volcanoes these debris flows can come from volcanoes and we call those lahars earth flow this is also very rapid this happens on hillsides in very in regions this is when water kind of saturates the soil and then you get a small little scarp and then some movement here okay liquefaction also can occur with earth flows sometimes they're associated with earthquakes but it really requires the saturation of water beneath the surface and then you get some movement here creep is t
he very slow movement of soil and regolith down a steep hill this has a lot of profound effects on stuff that are around it it can cause utility poles the tilt trees the tilt and fences the kind of kind of spillover and then one of the last types of mass movement is called solu flexion and that is the movement of material above permafrost in soil okay and they're only active in the summertime and this this typically occurs at really high latitudes I'll show you a picture but here's creep so cree
p forms in areas where there's a freezing daily freeze and thaw and so when you have a freeze you get material expanding and when you have a thaw it contracts and this kind of occurs over and over and over again and then this material slowly moves downhill that's why it's called creeping slow and so that can cause the bedrock to actually bend as a result of this movement okay here's the actual example here are the bent rock layers next cool picture of it here's a sketch of it if you have a cemet
ery those tombstones will be falling over trees their trunks will start to grow curved as a result of that movement maybe you received one of those emails or like oh the Bulgarian forest is haunted and all the trees are are misshapen like this that's not has nothing to do with ghosts or haunted forests or anything like that that's just a geologic process called creep okay retaining walls look at this jerry-rigged retaining wall they're trying to hold on to dear life before it falls over but yeah
this stuff is really slowly millimeters at a time moving and it starts breaking painting walls you get tilted fences all kinds of problems and then here's all you flexion notice there are no trees this is an area really high latitude you can get very cold in the winter times in fact these areas are so cold that they have a permanently frozen part of the ground it's called permafrost wait and then only in the summertime does the kind of outer few centimeters thaw right and so this area thaws and
it'll move downslope under the influence of gravity on top of the solid section and what that does you can see here it's kind of you can kind of see these like almost like as if the landscapes melting downwards and it kind of is because the the the soil and regolith here is is mobile because it's warm enough and thaws and a Musel along a solid surface over here
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