Intro Quiz: What are the processes operating across meanders?

Video: What are the processes operating across meanders?

﻿Hello, welcome to this next lesson in the rivers unit. Today, we are going to be looking at landforms that occur in the middle and the lower course. We are going to be looking at meanders and the processes which are operating across them. What you need to do is get all the normal equipment that you need. So something to write with, an exercise book or a piece of paper, and you need to be somewhere quiet where you can focus. I also suggest that you turn your phone off. So when you have done those things, and you're ready, hit Play and we will start properly. Hello, my name is Mr Burton, welcome to this next lesson in the rivers unit of work. In today's lesson we will be learning about meanders, which are an example of a landform which exist in the middle and lower course of a river, and we're going to be looking at the processes which operate across them. So for today's lesson, you need, as ever, a pen, a pencil and either an exercise book or a piece of paper to write on. Pause the video here to go and get those things and hit Play when you're ready so we can properly start. A meander is a bend in the river. And you can see one in the photograph there on the right hand side. These are found in the middle and lower courses of rivers. They form due to a combination of lateral, sideways erosion, and deposition. So in contrast to waterfalls, which occur in the upper course due to vertical erosion, meanders are different because they're found lower down in the river in the middle and lower courses, and they form due to a combination of deposition and lateral erosion. So there are two key bits of key terminology I would like you to write down. So river velocity is the speed at which water moves within the river channel. And deposition is when a river loses energy, it drops or deposits its load. And if you remember, a river's load is the sediment and rocks that are carried or transported within it. So please pause here to note down those two bits of key terminology. Okay, I'm going to give you five stages by which meanders form. I'd like you each time to listen to my explanation before drawing your own mini-sketch diagram with a pencil that's neatly labelled and annotated. Okay. Here is step one. In a river there is a line of fast flowing water known as the thalweg, and on the diagram that's the red arrow. Water flows fastest on the outside of the bend, causing erosion, and if you follow that red arrow, it goes from outside of the bend, to the outside of the bend, to the outside, to the outside. And each time, it's causing erosion here, and you can see the outside of the bend is marked by A on that diagram. Step two, on the inside of the bend, velocity and force of the water is less, therefore, deposition takes place. And you can see that marked as B on your diagram. So please draw your second diagram to represent this second step, please. Thirdly, over time, the thalweg swings from outside bend to outside bend, causing lateral or sideways erosion. This means the meander migrates across the valley floor and the horseshoe becomes tighter. Fourthly, on the outside of the bend, the force of the water erodes and undercuts the river bank. This forms a river cliff and is what is taking place at A. Lastly, number five, on the inside of the bend, the river flow is slower, therefore, deposition takes place which forms a gently-sloping bank known as a slip-off slope and this is what's taking place at B. Last thing to note, please have a look at that pink line which I've drawn on between B and A across that bend in the river. We're going to look at a cross section next along that line. And here is that cross section of the river, of a meander, and you'll see that I've drawn on B and A. You've got to imagine this time that you've taken a slice through the meander and that the river is flowing out towards you from the screen. So the river's flowing out towards you. So you can see the steep river class at A, which is being formed by erosion from the fast current, or the thalweg. At B, the gently sloping slip-off slope has been formed by deposition from the slower current. So please draw this cross section next to your other stage diagrams please. Now here is a mini-task for you to do as a quick check. So pause the video here to complete it. For each of the following statements, write down whether they are true or false. If they are false, say why they are false. So note down one, two, three, four, five, say whether they are true or false. Let's read them now. So number one, river velocity is high on the outside of the bend. Number two, deposition takes place on the outside of the bend. Number three, meanders form from a combination of vertical erosion and deposition. Number four, a slip-off slope forms on the inside bend. And number five, a river cliff forms on the outside bend. Pause here, note down whether they are true or false, and if they're false, say why they're false. Okay, here are the answers, let's have a look. So river velocity is high on the outside of a bend. That's true, this is what leads to erosion. Secondly, deposition takes place on the outside of the bend. That is false. Deposition takes place on the inside of the bend where the current is slower. Erosion is what's taking place on the outside of the bend 'cause it's here where you've got the line of fastest flow or the thalweg. Number three, meanders form from a combination of vertical erosion and deposition, that's false. The deposition bit is true, but meanders do not form from vertical erosion, they form from lateral, sideways erosion. Number four, a slip-off slope forms on the inside bend. True. Number five, a river cliff forms on the outside of the bend. True. So as another quick and another quick task, pause the video here to complete it. You've got a photograph of a meander, which I've added in labels A and B. Can you add in the correct words from the box that would fit those labels A and B? Pause the video here to do that please. Here are the answers. So at A we've got a slip-off slope and deposition taking place 'cause it's the inside of the bend. At B we've got erosion taking place and we would have a river cliff 'cause it's the outside of the bend. So pause here, mark your work please. Okay, here is your final extended written task today. So pause the video here to complete it. You need to explain the processes which operate across a meander and you've got two success criteria. Firstly, include all the key terms from that box. Secondly, ensure the answer is in the correct sequence or order. So let's read the key terms box together. So we've got thalweg, outside bend, inside bend, lateral, erosion, deposition, slowest, fastest, river cliff, slip-off slope. So this is a model answer that I've written, let's read it together. So firstly the slowest current is on the inside of the bend, this creates deposition on the inside bend. On the outside bend, the velocity is fast and the force of the water is high. This causes erosion such as hydraulic action, and lateral erosion to take place. So feedback that we'd give this student for this answer. The sequence and order is correct so that's good. However, not all of the words from the box are included, therefore, it doesn't fully meet the success criteria. So what I'd like you to do, pause here, have a go at this task, it should take you eight minutes and you need to have a mini-paragraph written in your notes. So pause here, so eight minutes, off you go. That's brings us to the end of today's lesson, well done for all the the fantastic learning you have achieved. In the lesson today, we have looked at the landform of meanders, where they form and how they form. Your job now is to complete the quiz to consolidate your learning from today. In the next lesson, we are going to be looking at another feature which occurs along a river's long profile. Hopefully I see you then.

Exit Quiz: What are the processes operating across meanders?

Completed: What are the processes operating across meanders?

In this lesson we will be learning how meanders form within the middle and lower courses of a river. We will examine the processes operating across them.

Geography

What are the processes operating across meanders?

Introductory Quiz

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Final Quiz

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