Video: Mass movement

﻿Good day, geographers and welcome to this coast lesson today about mass movement. Over winter, we had lots of large storms and I saw many news articles about cliffs collapsing in different locations. We're going to have a look today at why. So, for today's lesson, all you need is a pen and paper. In a second. I'm going to ask you to pause and take a moment to get those things and clear away all those distractions around you. Alternatively, you might choose to move to a quieter place, where you won't be disturbed during this lesson. Pause now and I'll see you again in a second. Now, you're ready, we can start. So, at the top of your page, please write down the title, mass movement and underline it beautifully. Can you make sure you pause, if you need a moment to do that and we'll start to have a look at mass movement. So, our cliffs are changing all the time. We've got photos on the screen of two different cliffs and they have both suffered from material falling off them but it's happened in different ways. And we're going to be looking at three different types of mass movement today. Our cliffs are affected from erosion by the waves at the bottom and weathering at the top, and combined that leads to material falling off them. We've used this term, mass movement and it's our title today, so we need to know what it means. Mass movement is the downward movement of material under the force of gravity. It's really important you can be word perfect for that, so jot down that definition and make sure you've got it correct. The downward movement of material under the force of gravity. Anything we had in our hand, if we dropped it, gravity would pull it straight back down. We're going to be learning three different types of mass movement and we've got pictures of them all there. So, the first one is sliding. Sliding is where large sections of rock rapidly shift down slope but along a straight slip plane. You can see in that picture, it's sliding down in a straight line and you can remember it really easily because when you sit on a slide in a playground, you slide straight down. Slumping is different, slumping is where material shifts downwards but rotate it along a curved slip plane. And it's usually because the material becomes saturated, so if there's been lots of heavy rain, then the soil will become wet, the soil and the rock will become heavier and the weight will pull that down, so gravity will pull that material but it comes down in a rotational way. I think easiest way to remember that is when you get home from the end of the school day, you kind of slump down in your chair. Okay, so you're slumping down on your chair, on the sofa and cliffs when they slump, go down in that curved way. The final one is rockfall. Rockfall is when fragments of rock break away from the cliff and they fall. Quite often, they've been weathered by freeze thaw weathering. So, three types of mass movement, sliding down a straight slip plane, slumping on a curved slip plane and rockfall where bits of rock are going to fall off. Okay, so time to test you're learning. Which word is not included in the definition of mass movement, you've only got five seconds. Write it down. Okay, so which word is not included? It is waves. So, mass movement is the downward movement of material under the force of gravity. Waves is an interesting one though because waves eroding the base of the cliff, through abrasion, can make mass movement worse because it undercuts the bottom. So, the material above is unsupported and more likely to move through mass movement. Which process is the odd one out? You've got four to choose from, five seconds, get thinking. And we're going for? Freeze thaw, tell me why now, why is freeze thaw the odd one out? Yes, so you've got sliding, slumping and rockfall are the three types of mass movement, freeze thaw is a type of weathering. Okay, can you remember now, which type of mass movement is this, sliding, slumping or rockfall? Tell me out loud, in three, two, one. Yes, well done. Okay, so that type of mass movement is slumping, you slump down on your sofa. It's along a curved slip plane. Right, let's have a little bit more information about mass movement. So, mass movement is more likely after heavy rain, water will, number one, act as a lubricant, so along those slip planes, okay, there's then the liquid there to make them move more easily. And also the rock can become saturated, so water can trickle into all the spaces in the rock and it can make it heavier. Mass movement causes cliffs to retreat and by retreat we mean for the cliffs to move backwards. So, mass movement will cause the cliffs to retreat. And finally, it provides an input to the coastal system. If you look at that photo, all of that loose material will eventually get to the bottom of the cliff and when it's at the bottom of the cliff, we can see the waves in the sea, the waves are going to erode those, they're going to break down the material and they're going to transport it away. So, it's really important we do have mass movement because we need those particles and sediments further along the coast. Right, so time for a task now, we've learnt the three processes of mass movement, I would like you now to pause the video and match the key terms with their correct definition. Good luck. Right, okay, let's see how you've got on. Did you get, sliding is when large sections of rock rapidly shift down slope along a straight slip plane? Did you get, that mass movement is the downward movement of weathered material under the force of gravity? We then moved onto rockfall, which is when fragments of rock break away from the cliff face and fall, and that's often due to freeze thaw weathering. And our last one is slumping, when material shifts downwards, rotating along that curved slip plane, usually as a result of becoming saturated. Well done. So, now we know what mass movement is, let's move on to have a look at what the impacts of this could be. We've got a photo, I would not like to live in that house. Okay, we've got a cliff collapsing, we've got mass movement happening and we've got several houses very near to that cliff. So, an impact of mass movement is that cliffs are retreating. Property, if it's on the clifftop, may be damaged. Tourism can suffer as a result of mass movement. I live near Bournemouth and Bournemouth suffered from a large area of mass movement and it meant that the beach huts below and a cable car and toilet blocks were all blocked off, so people didn't get hurt, so it can impact tourism. And finally, any infrastructure, so roads, et cetera, that are on the top, can be lost. If this was an exam question, it might be phrased like, explain the possible impacts of mass movement so let's have a look what we can do. The photo shows a house on the edge of the cliff that has experienced mass movement. This means that the residents will have had to evacuate their house and possibly leave the area. Resulting in them feeling isolated away from friends and family. So, we've taken one impact, okay, a house on the edge of the cliff, it means that residents would have to evacuate, so therefore, they feel isolated. What would improve this answer would be to categorise this impact at the start, okay, so a social impact of mass movement is. Okay, so we've seen a model, it's now your turn to get stuck in. You've got two questions to do. Number one, using the photo, explain how mass movement can affect the shape of the coastline. And to do that, I would like you, for the first mark, to name the type of mass movement you can see, so really look carefully at the photo to see if you think it's rockfall, whether you think it's sliding or whether you think it's slumping. And for the second mark, I would like you to tell me how the coastline has been affected. For question two, I would like you to use the photo again and I would like you to suggest the possible impact of mass movement and for this, I'm looking for two different explained impacts. And ideally, see if you can challenge yourself to come up with one social impact and one economic impact. But if you're explaining them, I'm looking to see connectives in your writing, this means that, therefore. So, pause the video, best of luck and resume once finished, so we can check your answers. Okay, let's see how you got on. Question number one was explaining how mass movement can affect the shape of the coastline. Your first mark came from saying, that the photo shows the cliff is experiencing slumping. How do we know that? Well, if you look by the white house, just in front of it, you can see that the land has dropped away. You can see the brown soil where parts of the cliff have slumped. If it was sliding, it would have been whole chunks of cliff happening rapidly, so we know that this, therefore, is slumping. The second mark comes from saying, this will affect the coastline because the cliff will eventually retreat. Two marks, give yourself a tick where you've earned them. For the second question, we were asked to suggest the possible impacts of mass movement. The photo shows mass movement, and in brackets I've put slumping, may have had an economic impact as hard engineering defences will have had to be installed at the base of cliff. One mark. This will be expensive, reducing the money the council could invest elsewhere, like on infrastructure. So, we've got one developed point there and it was an economic impact. Possible social impacts of the slumping are that several houses are located near the cliff edge. One mark. This means that people may need to leave their homes and communities leaving them feeling isolated. Second mark. So, these are only possible suggestions, you may have had something different but I would like you to check you've categorised your impact and you've got a connective to explain your answer, so, this means that, consequently. Pause the video, if you need to make any improvements, well done for tackling that question. So, that brings us to the end of today's lesson. Thank you very much for your hard work. We've learnt about the three different forms of mass movement, slumping, sliding and rockfall. Next time, we're going to have a look at how coasts can transport sediment and why de-position occurs but don't think you get to slump on your sofa and turn on the TV yet, before you disappear, I need you to click on the next page and spend a few minutes completing your quiz, so you can show me how much you've learnt. I look forward to seeing how you get on. Thanks very much for your time today, take care and I look forward to you joining me soon as we move through transportation together. Have a great day.

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Completed: Mass movement

In this lesson we will look at the different types of mass movement that occur along our coastline.

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Mass movement

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