Glacier Lecture Part 1 of 2

本站添加: 2026-05-09

[00:00:00]welcome back it's time for our last lecture on glacial and cold climate landforms this is one of my favorites because I just love glaciers and what they can do and how they can change the landscape when we talk about glaciation we have to remember that our Earth's climate fluctuates we go through cooling periods and warming periods the cooling periods or glacial periods where we see an extent of glacial ice both in the polar regions and in the high altitude regions and then between as we go through the warmer periods for interglacial implying that we're going to at some point in the future go back to another racial period and just a quick note on climate change this is often used as an argument as to why it's okay that we're warming because we go through warm periods and cooling periods the warming that we've experienced the last hundred years or so has been unprecedented and how quickly it's taking place and so yes we were warming a little naturally but we shouldn't have warmed as much as we had so that's why that argument really doesn't have the full backing of science now the Pleistocene was the last period of time when we had glaciers and it was started about two million years ago and this is always strange to a lot of people that it ended quite recently in geologic time 10,000 years is a blink of an eye it's very very recent we've already seen humans populating most of all of the continents we were in South America of 10,000 years ago we're starting to see some of the cities in Central Asia starting to form so this is in human history relatively recent so we populated the earth during the last ice age during that period of time we had in addition to the expanse of ice covering South the South Pole we also had an expanse of ice over North America and Eurasia as well today man we've got some mountainous glaciers in the Rockies and Alps and scattered around in the Andes in different places but for the most part our clay shoe ice is held up in Antarctica and on Greenland that's where the bulk of ice remains today we would talk about glaciers there's two major types of glaciers and these two types of glaciers overlap in the terminology they over line up in a lot of the processes and sometimes within a glacial area you can have to the pull types of glaciers existing at the same time so we've got the continental glaciers but you consider the large ice sheets these are the EF climates large areas covered with ice um Antarctica and Greenland are are only two continental glaciers we have now photo you see in the background is Antarctica and when I say covered in ice there are still are mountains hooked up through the ice and there's coastal areas that are ice-free as well but they're covered in large part with a large sheet of ice now alpine or Valley glaciers these the ones that the ice flows through a valley and typically you're referring to alpine valley glaciers we're usually referring to those in the high altitudes where the altitude is what gives the colder temperatures and so as the ice forms in high valleys it flows down a valley and it creates its own features there is overlap you'll have continental glaciers that have valley glaciers that flow away from the edge of the main glacier or as you see here again in the picture there's an ice field in the foreground an ice field in the background and the ice is flowing from this higher altitude through a valley down into this lower altitude so if the ice were to magically disappear we'd see evidence of continental glaciation here Valley glaciation in through here and then again back to continental glaciation in this lower ice field down here an article the reason it has so much ice is that it's got all of your contributing factors to make the pulp it's the highest lighted you could you can beast ninety degrees south it's also a continent so you've got and the supple is pretty much near the center of the Antarctic continent so you've got Continental it's at high latitude and it's also a high altitude so the South Pole is roughly ten thousand feet in elevation and it's an extreme environment and a perfect place to collect ice pretty barren because of the cold temperatures there's no trees there's no megafauna there's no predators land predators there's the birds that are down here are flightless penguins because there's no need to flee from land predators because there are no land predators they need to port and but since there's little food to be found in this area and their food in the water so penguins basically have adapted to fly through the water and invade water predators and hunt for food in the water as opposed to on land note there are no polar bears at the South Pole there are no penguins at the North Pole so when Christmas rolls around and that damn coca-cola commercial comes on where they're drinking coke between the polar bears and the Penguins that's just wrong because we wouldn't find those two animals together the opposite ends of the earth Greenland ice sheet here with mountains poking up through it we'll talk about some of these landforms later I got really lucky flying home from Africa on a flight and we flew over which is perfect lighting I'm hitting Greenland and create a nice shadows we're running around the plane book I had a new available window we could find to take pictures the flight attendants were doing it too and they obviously have seen this kind of stuff before so if they were excited about I knew it was unusual now again with climate change we're starting to see more melting during this summer and so these for some of the surface ponds that appear on the surface of Greenland remember water has a lower albedo and ice and so this water is absorbing some heat which kind of amplifies the warming and melting that's taking place on the surface of Greenland we will talk about accumulation and inflation later but with your continental glaciers Greenland and Antarctica the center of the island of Greenland the center of Antarctica is the area where you're accumulating some snow and ice and it flows outward under its own weight from the center of it and then around the edges is where it melts so with your alpine glaciers we still have an area we're accumulating it and it's at the higher altitudes higher altitudes humid collects us so it's no it stays year after year and then the weight of the ice it flows downhill and of course in the mountains downhill is gonna be the valley and the valley bottom so here's the area were collecting the snow and then it flows down to the lowest point which would be the valley bottom electing a higher elevation flowing down the valley one of my favorite things to do on vacation if I've got an opportunity is to go to either volcano or a glacier and someone we went to Chile we got lucky because we got to see both and so we went to the serrano glacier in the southern end of Chile how excited am I'm at a glacier it's awesome now where do we get glacial ice from well it's that snow that doesn't melt from year to year so you've gotta have average temperatures below 32 degrees which you're gonna find in the interior of Greenland which you're gonna find in the interior of Antarctica which you're gonna find at the high altitudes so you've gotta have that snow stay not melt and accumulate over time maybe in the summertime it melts a little bit it's softer it's compressed and the weight of the next year's snow on top of it compresses it some more it creates this kind of granular gravel like material called fern and then eventually that gets pushed together to become your dog of the background she's Tate chasing her own tail she's that excited about glacial ice so this was in this actually was in Norway and this is fern that had fallen off one of the upper levels of a glacier that we were visiting here you can see like the density increasing with the late and so here this crystal blue ice is not blue in color it's just the way light passes through it as it's been compressed together and all the air bubbles and gaps have been pushed away so when we were at serrano glacier yeah Brett's Toronto glacier they were chipping away at one of the little icebergs that was floating in the water and I was all excited because a guy doing it was working the food services on our ship so we got back to the ship and so they served us pisco / glacial ice and like an idiot the big bite of the ice cube forgetting that that ice was formed under pressure so it's very very dense it's not like ice cube ice from your freezer this is much denser because the ice ma the water molecules are compressed closer together but it was tasty but I've almost broke a tooth and this is what I read when I'm on vacation look at my lap is over the edge of the world which is a book about Magellan's voyage around the world and since I was going near the Strait of Magellan I thought it was an appropriate book to read and then the one I'm about to start his collapse by Jared Diamond how collapse the climate change has led to some civilizations over time - and basically mystify their own little civilization so some like vacation reading for me I keep talking about glacial ice moving it behaves like a fluid a very thick viscous fluid moving very slow when you talk about things moving at a glacial pace that's the inference that glaciers aren't flying down the hill they're slowly creeping a few inches or a few feet depending on the glacier every year so when a weight of the ice pushes down on the ice and Neph it causes it to deform and it causes it to move push towards the lowest point and so if you're on the side of a hill and you're pushing towards the lowest point it's gonna push it down to the valley bottom and it's gonna push it downhill if you're on a continent and you're accumulating a big pile of ice at the center of the continent the weight of it is gonna push it out to the sides and it's gonna push it out to the sides of the continent during the summer you may get a little bit of warming a little bit of melt and so this there may be a thin layer of water underneath the ice and through here but throughout the year this top layer since there's not a lot of weight on it it's gonna be brittle it's gonna break because if you try and twist an ice cube it's gonna break but if you slow steady pressure to an ice cube over say a few months you can get that ice cube to deform but the top layer not enough pressure on it as the ice twists and turns as it goes down valleys it will become brittle and break and you'll see crevasses in the top of the ice though that this the bottom part of the ice is solid and so here you've got the weight at the center of Antarctica the ice accumulating and it's pushing me out the ice out towards the sides of the continent if we could remove this top layer of brittle ice underneath it would be a solid block of blue probably not blue because there's a lot of debris that's falling on top of it but there'd be a solid block of ice that's moving in an S pattern down through this and Valley same thing here solid block underneath this is just that top layer as you try and bend and twist it going around a curve it causes it to crack and crevices to form here we're going from an ice sheet at higher elevation to an ice sheet of lower elevation so as the sheet moves to the top of the photo it goes over the slight little rise causing it to crack and creak crevasses one of the things we'll see with the photographs of God of the glaciers there's usually nothing for a reference for size on here and so anarchic especially I'm dependent on somebody else to tell me what the size of these crevasses are this particular one these are about 20 to 30 feet across a little melt on top of a glacier so the area where the ice is accumulating or the snow is accumulating from year over year that's the area where the snow isn't melting that name makes perfect sense the zone of accumulation and so the ice is flowing out from the zone of accumulation it's constantly flowing downhill due to its own weight well if you're moving downhill you're moving into an area of warmer temperatures and you're probably not gonna be accumulating snow in fact you're gonna see the opposite you're gonna see that snow melting and evaporating actually ice doesn't evaporate it sublimates but we'll just call it operation for right now so we have an area where we're losing Silla snow so an area where we're collecting snow area the zone of accumulation and then the area where we're losing snow the zone of ablation and unfortunately ablation is not one of those terms you use in day to day life and so I'm just hoping you can remember ablation is where you're losing snow accumulation is where you're gaining snow and so the glacial ice flows from the zone of accumulation down into the zone of ablation at some point what we'll see is that the rate that the ice is coming down the hill is going to be equal to the rate at which we're losing ice at the bottom of the hill and so we would say that it's reached equilibrium we're losing it as fast as we're gaining it and then the ice will reach a constant position at the end even though it looks like it's not moving the reality is is that even though that edge is relatively in the same spot that ice is still moving it's just as but this comes down the hill we're losing it as fast as we're replacing it now the the the crappy little sorry the poor quality image you're seeing here the snout is actually retreating just a little bit because what's happening it's losing the ice faster than it can be replaced and that's what we're seeing with climate change and global warming is that we're losing the ice faster than it can be replaced this ice is still flowing down the hill is just that it's melting faster that it can be replaced and so where it was in 1978 its up the hill a little bit they love you that was a bad expression ice doesn't literally backed up the hill where the position of the end of the glacier it changes in migrates uphill the ice is still moving downhill it's just melting faster than it can be replaced and you're repeating this all around the world of every glacial area has a net ice loss and we're seeing over and over again places where the ice just in the past few decades has retreated miles in some cases Antarctica especially it's kind of been accelerated in the past 20 years in Antarctica there's been a few models that have sheesh but initial predictions of ice loss its far outstrip those just this last February we had the warmest temperature recorded in Antarctica 65 degrees Fahrenheit and so this is the beginning of February and then just nine days later you'll see all of the ice and that little Inlet is gone the some of these coastal areas have retreated there's actually some melting on top of this island here in the ice that's here and this was just in a period of nine days to see a pretty dramatic change in the amount of ice because of that warming to here in 2000 and 2002 lost kilometer lumpy glacier we could repeat this over and over again as far as it's not just that where the end of the glacier is no longer down here its way appear its thickness has changed so not only has it retreated it's actually thinner back here than it was 60 years before I've already mentioned that we're melting ahead of some of the predictions and its continuing about where we're losing it I know housing it now this video that I'm not going to show you here because it doesn't translate well to be the software I'm using for our presentations I'm going to put on canvas it's just a fascinating image to see so much I swear basically you're going to see ice that's gonna heave hundreds of feet into the air ice blocks taller than the tallest buildings in New York collapsing and rolling through the water it's it's it's dramatic and somewhat scary as well but again it's chasing ice and it will be in the canvas shell for this module and having said all that about losing ice there are some places of relational ice is advancing but one of which is related to climate change and the other one is kind of its unique local situation so the one that's related to climate change is a part of bricks puddle green in western Norway and why that ice is advancing is because it's accumulating in that part of the ice sheet faster than they're losing it and the reason it's accumulating faster is because of the warmer water in the North Atlantic there's more evaporation or evaporation means that there's more moisture in the air and when that moisture the precipitation Falls in the winter time in Norway there's more snow in that western part of Norway but it's because there's more moisture in the air so then there's more snow the bricks Donnell brain breaks off from a larger ice sheet I believe it's called yo Stata brain and joke Stata brains total ice volume has been reducing so there's just this one little finger of it that's got unusual characteristics but it's because of more evaporation not because of cooler temperatures and then Hubbard glacier in Alaska it's a weird glacier because the bays disenchantment in Russell fjord that it goes down in a relatively shallow and so the ice sits on the valley floor and it's kind of muddy so every now and then it'll surge forward as it slides on the mud at the bottom of the fjord but it's it's not a function of greater accumulation it's just kind of overcoming the friction on the floor of the of the underneath the glacier and it allows it to move forward in a big surge so it's there it's different processes so I have relatives who deny climate change and every now and then they'll some of the articles about like either Brooks Todd will bring or Hubbard glacier and they're sending it at all their friends saying look see climate changes and real these glaciers are moving so then I have to go through the science behind both of them I do a reply hall and my relative stop setting me this kind of stuff and I'm not quite sure why I thought they'd appreciate being educated so the physics of how the ice moves is fascinating but what really amazes me is how glaciers can dramatically change the landscape in a very short amount of time they can do much more damage sorry not damage but changing of valleys in a million years that a river ever could do in that amount of time just because of their mass and their contact with the surface is much greater than what a stream would be and since it's a solid not a fluid moving through an area it has the ability to scour scrape and move more material than a stream could we didn't recognize this kind of until a little bit later after some of the Glacial processes have been named so the terms like abrasion plucking they're so weak compared with what they should be called as like scouring and plucking just as picking up rocks but again it doesn't do it justice for the amount of material that's removed by a glacier and then we'll talk about the mass wasting as well so what happens is the ice as it moves over material it's scouring the bed it's moving across and as it scours across it it picks up rocks debris sand gravel and that's used to grind into the surface even more which scours more materials which is kind of it's it's a giant erosive sand paper moving across the surface sometimes rock will freeze into the ice that's blocked rocks and then at the end it's melting and it's reached that equilibrium point where the ice is still flowing the meltwater can't move that material so we end up seeing a buildup of material as it moves out and we'll come back to a radix later just remember this image of a boulder on top of the ice so abrasion this little striations you see on the rock that's why I thought it was like oh it's just you know polishing the surface it's actually called glacial polish and the reality is this rock was probably a hundred feet thicker before the last ice age and then it scoured it all the way back to this point you'll see different shapes within ice the rock surface from whatever moved across it and so you may get these weird cupping shapes you'll get the striations and polish or more common then every now and then you'll get these striation rocks where they just whatever the rock is gets pushed so hard into the bedrock that it scours a little tunnel through the bedrock and that's what you see here at Kelly's island and notice how this one has a v-shape it's kind of informed with the v-shape here had a student once who was from Ohio needs to go play here during the summertime and they never knew what these were for and I was always disappointed that they didn't have signage explaining it was from the last ice age that created these unusual little tubes Devil's Postpile and behind mammoth the top of it is flat and that flatness has from the glacial ice moving across it you can see the direction that the ice moved by the striations and that's what smooths out the top of it all of that grinding and pulverizing of rock as well is gonna create a really fine grain material Pohl glacial flour and this is a lake the velocity of a lake is zero we should not see sediments in it because if there's a velocity of zero that stuff should settle to the bottom the slightest movement allows thank Rachel flower to remain in suspension and so areas that are fed by glaciers have to have this characteristic blue water look to them and it's actually the Glacial flower isn't blue it's just the light reflect reflect Rula the light refraction makes it look blue but it's super fine grain material pulverized by glacial Arushi a Wilton a my French is horrible as the heist moves over if you're not going to get nice perfectly smooth surface and what will happen is it'll braid one side of whatever it's moving over and then as it moves down the other side rock will freeze into it and be pulled off the side these can vary in size from a few feet to 50 feet high I'll show a picture later from one in Norway that's pretty massive when you're in a valley glacier typically the Russia Bhutanese are always gonna point down valley which makes perfect sense because you've got this smooth side and then the steep side but if you're in an area that has continental glaciation where there's no penalties how do you know which direction the ice was moving and this one in Canada is an indicator that guys was moving from right to left across the photograph smoothed out one side and plucked rocks from this side and for scale those are somebody's legs and boots right they're the ones we saw in Finland were roughly double this length but about the same height and I cannot find those pictures anywhere and it's frustrating here the glacial ice has it moved across western Norway and into the North Sea removed all of the topsoil it all froze into the glacial ice if we look at mountainous area before it's glaciated to your primary factor in the erosion is gonna be stream erosion and as the streams are cutting down to their base level all of the erosion that's picking places in this stream channel so that's where you get this v-shape to a stream cut channel in the higher altitudes we mentioned this before when we talked about youthful streams the this stream is going to cut to its base level which is this stream and it's just simply a function of its gradient and the discharge is gonna allow it to cut down notice that there's no waterfalls we kind of see a smoothing of the inter flus the any rough surface would be eroded away and so you have kind of like rounded hillsides this would be a stream formed landscape when the glacial ice is here all things change now instead of just having a row shown in the bottom of a stream that is hilarious now instead of just having erosion down in where the stream channel is we're getting erosion across the entire valley itself and the sides and the greater the ice mass the greater it's going to push down and remove material and so before these side streams feeding in we're feeding down to their base level now the streams are cutting based on their mass and so this smaller stream sorry this big the ice is cutting downward based on its mass so the smaller ice flow isn't cutting down as fast as this big ice flow and there's also notice there side to side erosion instead of being this v-shape with a gentle slope you've got these steeper slopes so that side-to-side erosion is point to as it comes in on these ridge lines it's going to sharp from the ridge lines because the sides of these hills are being undercut from both sides so we go from a rounded landscape to these sharp edges and then when we remove the ice the entire landscape has changed so now you have these u-shaped valleys these sharp ridges and you have valleys where the stream isn't cutting down through its base level anymore because what happened when this was glaciated this ice was cutting down faster then this this ice could and it kind of leaves this u-shaped valley hanging into the side of the main valley as far as terminology in general I'd be happy if you would recognize that these sharper Ridge lines are indicative of glacial erosion four terms just this u-shaped valley hanging valley and horn i'll come back to Hany Valley in the u-shaped valley in just a second but the horns would be these sharp Peaks that you find in a glaciated area and this was that smaller one that we saw on the side showing the ice kind of eating out sideways creating the u-shaped valley and the retreating leaving the u-shaped valley the sharp edges the arete s-- these ridge lines the horns the horns and you can't see because this is still a shooter right now there are you see valleys and through here and of course there are horns wait a minute this is a glacier called peak but it's an Anaheim well this one's modeled after this one a real Matterhorn in Switzerland which is a glacier carved mountain peak and know for your photo project you can't use this picture of a Matterhorn for glaciation unless you talk about how it's related to this one we've got a UC Valley in Yosemite Valley and that's our third reasons and why would Half Dome is half a dome with the earth when I say the reason Britain I would talk about you Africa first time because it was granted second time because it was an exfoliation dome and now the third time is the half part of it is that has the glacier cut sideways it encountered a joint a vertical joint in the rock and that rock I left off and it kind of amplified the vertical side of this particular valley so you can see most of the u-shape or use somebody' valley there's also a hanging valley over here the side glacier couldn't enter into the main glacier is fast this is Bridal Veil Falls but notice the valley floor is flat what happened was after the glacier retreated this became a lake in Yosemite floor it was called you somebody lake it's not a very creative name or thank you somebody's sorry and a lot of siva like a zero so it filled up with sediments and kind of flattened out the valley floor it's roughly where El Capitan is is where the end of the lake was so as you're coming in to use semi give alley if you come in directly from the West most of us come in slightly from the South if you're coming directly from the West you can see the v-shape of the canyon about a mile or actually four miles later when you're in Yosemite Valley itself it's this nice flow broad area so it's the difference between being over here versus over here in Yosemite Valley for how dramatic the difference is in the landscape be shaped now glacially are you shape from English like art I mentioned they've got a u-shaped valley with nice vertical sides you shade with the melting of the glaciers after the Pleistocene obviously sea level rises and some of those coastal valleys that have been glaciated that have that use shape become flooded and so a flooded coastal glacial part of the valley is referred to as a fjord it's a norwegian term so if yours in british columbia jordan's and alaska lords and she laying a horse what you see here is a fjord in Norway now when you have a ice sheet some of that downward pressure is amplified to the lowest point and so these fjords can be very very deep deeper than you would expect hundreds of feet deep because the weight of all of this mass the lowest point would have been this valley floor and so these can be very very deep and then when they get in the open ocean there's talking a little bit of a lip before they get out there so this is Greg if yard in here and it's this area right here which I'm going to zoom into here and there's a little village right on the side of the hill this dates back to the feudal period and this is somebody's farm that's why they trees are cleared now nobody lives there now these are just simply tourist attractions you can hike too and I'm completely serious that when the farmer worked his fields he was tied off so he didn't case he tripped you wouldn't fall into the water down below there's a little bit higher up the side of the valley no it's also where you can find freakish Poland it's the highest vertical drops out kind of dips in a little bit so in other words if you were to jump off of here you'd freefall longer here than you would in any other place so if he jumped off the edge of Half Dome it actually slopes outward ever so slightly it's not completely vertical so you can bounce all the way on half dome here you would freefall quite a fall long distance neither of which I recommend these crazy Norwegians they'll sit on the edge they'll bang out the feet over the other side got picnic lunches up here no I haven't been up here yet this is my picture from the valley floor below in a boat looking up at breakfast alone and mentioned this before with hanging melyandd you cemani finale and the bridal veil falls in that side glacier that's cutting in that can't cut downward as quickly as the main glacier and so it leaves these beautiful waterfalls and in this case a nice fall where this cyclist can't feed as fast as the main glacier which is retreated way back to here the main glacier would have been through here before and as we've gone through this warming period the glacial ice has retreated leaving behind this tributary glaciers feeding into it here's bright Lille falls again this beautiful u-shape it's a classic hanging valley of course collation minister national park what would you expect to find there glaciers so I was so excited when I saw this image because it had everything I've been talking about it's got the Hanging Valley with a little diagram down here with the tributary Glacier and then the u-shaped valley even like how they curve the you I need to start putting that into my lecture to where I start curving some of the words in it and this is all of that together there's the hanging valley there's the u-shaped valley here's an arete at sharp edge now jackson glacier this the only place you can see from the road in leycester National Park it's obviously only a shadow of what it once was the estimates that there will be no active glaciers in Glacier National Park in 20 years sorry in 2030 so in less than ten years I wondered if they're gonna rename the glacier to use to a place yours National Park so some of the this is coming in from the eastern side of the Rockies you can see a nice beautiful u-shaped isis's multiple glaciers came into this single point in fat down Valley climates mountain this is a horn this is near Logan Pass burp up tree line up into the tundra behind my little junior geographer here you can see the erect in the background and then this is actually the Continental Divide and so here's our u-shape Valley and that clay shal ice would have fed into the Atlantic drainage system and then this glacial ice would have fed into the Pacific drainage system this is also where we got to see the grizzly bear that's it down there after the grizzly bear whoops went too fast fortunately there was a crevasse of little Canyon between us and him because those things are really really scary and in part two we'll talk about icebergs and glacial deposition