Lesson video

Hello, my name is Mrs. Grey and I'm so excited that you've decided to join me for today's geography lesson.

Today's lesson is in our unit of ice and glaciers: how are cold places affected by a warming planet? And today's lesson is on glacial processes.

By the end of the lesson today, you will be able to describe the glacial processes of erosion, transportation and deposition.

There are some keywords that we'll come across in today's lesson.

They are plucking, abrasion, and moraine.

Plucking is a process where meltwater at a glacier's base refreezes on the bedrock.

Then as the glacier moves forward, loosened rocks are pulled from the ground.

Abrasion is where rocks that are carried beneath the ice scratch and sandpaper the bedrock.

And moraine is a ridge or mound of debris that has been deposited by a glacier.

Today's lesson is split into two learning cycles.

The first, how do glaciers erode the land? And the second, how do glaciers transport and deposit material? So first, let's look at how do glaciers erode the land? So glaciers erode the land as they move through the processes of plucking and abrasion.

Do you remember that plucking and abrasion, they are two of our keywords for today's lesson? So plucking is where rocks that are frozen onto the underside or the sides of the glacier are pulled out as the glacier moves.

And then abrasion is where rocks that are being carried in the glacier sandpaper the side and underneath the glacier.

And we're gonna look at both of those in a little bit more detail now.

So plucking occurs where rocks and stones that are frozen to the sides and base of the glacier.

So some rocks and stones get frozen underneath the glacier at the base and around the sides of the glacier as well.

Now, as the ice moves, those rocks that are frozen to the glacier remain trapped to it and are torn out of the ground.

So because those rocks are frozen into the glacier, when that glacier then moves, they are ripped out of the ground, and pulled out of the ground and stay in the glacier.

And this then leaves behind a jagged-looking landscape.

So can you imagine some rocks? If they've had bits of it pulled out or ripped out, that's gonna make it look quite jagged, and that's what's left behind after plucking occurs.

So we can see where glaciation once has been and where plucking has occurred by looking at whether or not the landscape is jagged.

So this is the Lake District in the UK.

Can you see that image there of that U-shaped valley where the glacier has been and where it's eroded the land? And there's an arrow pointing to where the Lake District is there in the North West of England.

Now, you can actually see on that image that the landscape is quite jagged.

Can you see that? The landscape, the rock there is jagged, and that's evidence of glacial plucking.

That's where some parts of those rocks have been frozen to the underside or the sides of the glacier.

And then as it's moved, it's pulled them out, and that jagged landscape has been left behind.

So we're onto our first check of the lesson now then.

The question is what is plucking? Is it A, where rocks carried beneath the ice scratch and sandpaper the bedrock? Is it B, an accumulation of rocks and sediment deposited where glacial ice melts? Or is it C, when meltwater at a glacier's base refreezes to bedrock, loosened rocks will be torn away as the glacier moves forward.

Here rocks freeze to a glacier and they're pulled from the ground as it moves.

Let's have a look at those answers.

Pause the video and then come back and let's see how you got on.

How did you get on then? What is plucking? And the answer is C.

When meltwater at a glacier's base refreezes to bedrock, loosened rocks will be torn away as the glacier moves forward.

Here rocks freeze to the glacier and are pulled from the ground as it moves.

Did you get that? Well done.

So let's move on to looking at what abrasion is then.

We've looked at what plucking is.

Now let's look at what abrasion is.

So abrasion occurs where rocks carried beneath the ice scratch and sandpaper the bedrock.

So we've got rocks that are carried underneath the ice.

They scratch and sandpaper against the bedrock that's underneath.

And this is like a sandpaper effect.

It rubs it away, just like sandpaper would.

This creates a smooth surface with striations where large rocks embedded into the ice scratch grooves into the rock.

So it's relatively smooth with some scratches that we call striations where the large rocks that are embedded into the ice scratch into the bedrock and scratch those grooves.

Now, this is Eryri National Park in Wales, which is in the UK.

You can see the image there and the arrow pointing to where that is in the UK.

You can see the surface is smooth, but that it's also got big scratches in it.

So this is evidence of glacial abrasion.

It's being smoothed like a sandpaper effect, but we've got those striations in the rock where the big bits of rock have have scratched and made grooves, and this is evidence of glacial abrasion.

So another check then.

True or false? Abrasion has a similar effect to the use of sandpaper.

Is that true or false? So pause the video, write down your answer, and then come back and let's see how you got on.

Okay, how did you get on? True or false? Abrasion has a similar effect to the use of sandpaper.

That's true.

Why is it true? So abrasion occurs when rocks and stones carried in the ice rub against the land at the base and the sides of the glacier.

This can have a similar effect to the use of sandpaper for large stones embedded into the ice might scratch grooves in the rock as well.

Do you get that? Well done.

Okay, so we're onto our first task of the lesson.

Your task is to match these statements with the erosional process they refer to.

So we've got six different statements here, and you have to decide whether they are referring to glacial abrasion or glacial plucking.

So let's have a look at what the different statements are.

A, this occurs when rocks and stones are frozen to the sides and base of the glacier.

B, this has the same effect as using sandpaper.

C, this occurs when rocks and stones carried in the ice rub against the land at the base and sides of the glacier.

D, as the ice moves, the rocks are torn out of the ground.

E, a jagged landscape is left behind.

And F, this creates a smooth surface with scratches.

So have a look at those six statements and decide which of them refer to abrasion and which of them refer to plucking.

So pause your video, write down your answer, and then come back and let's see how you go on.

Okay, how did you get on? So you're gonna match those statements with the erosional processes.

So for abrasion, the answers were C.

This occurs when rocks and stones carried in the ice rub against the land at the base and sides of the glacier.

Then B, this has the same effect as using sandpaper.

And then F, this creates a smooth surface with scratches.

And then plucking, we had A, this occurs when rocks and stones are frozen to the sides and base of the glacier.

Then D, as the ice moves, the rocks are torn out of the ground.

And then E, a jagged landscape is left behind.

Did you get all that right? Well done.

Okay, so we've looked at how do glaciers erode the land, and we've looked at some of those erosional processes.

Now we're gonna move on to the second learning cycle, which is how do glaciers transport and deposit material.

So glaciers pick up rock and debris as they move, yeah? So they pick up that rock as they move.

Now, the sources of sediment or debris include rockfaces above as well as beneath the ice.

Loose rock fragments can fall onto the ice from above.

Now, this image here is the Mer de Glace glacier in France, and you can see the arrow pointing to whereabouts that is in France.

There is evidence of rock material being carried in the ice because it looks dirty.

Can you see the picture of that glacier there? That looks quite dirty.

And that's because there's material, rock material being carried in the ice, what makes the ice look dirty.

Rocks and other material are also being carried on top of the glacier, which you can see in the image there.

Okay, so true or false? Glaciers are white.

Is that true or false? So pause the video, write down your answer and then come back and let's see how you got on.

Okay, how did you get on? True or false? Glaciers are white.

That is false.

But why is it false? Glaciers can appear dirty because they carry material.

Did you get that right? Well done.

So this GIF shows the Baltoro Glacier in Pakistan flowing from 1991 to 2002.

Can you see it flowing? Now, you can actually see rock debris on the surface of the glacier.

It's highlighted there, the little circle.

Can you see it moving, actually moving along with the ice? Now, glaciers transport rock material downslope.

Can you see that little image there at the end of a glacier? Now, at lower altitudes, so lower down, the temperatures are warmer.

It's much, much colder at the higher altitude at the top of mountains.

But as we get down to lower altitudes, those temperatures are much warmer.

And eventually where significant melting occurs, the rock debris that the glacier is carrying is deposited.

So because when we get lower down, the temperatures are warmer, the glacier, which is made of ice, is going to start to melt.

And when enough melting occurs, the rock that the glacier is carrying, that is then dropped, that is deposited onto the land.

And that creates a new feature in the landscape, which is called moraine.

So once the glacier ice is melted and all of that rock debris that it was carrying is now dropped onto the landscape, what's left behind, those mounds of rock, that is called moraine.

So moraine is debris, such as rocks and sediment that has been deposited as glacial ice melts.

So when we get down to lower altitudes and it's warmer, the ice is gonna start to melt.

And so all of the rock and the debris that the glacier is carrying, that is then going to be deposited and put down onto the land.

So we look around at old glacier landscapes where glaciers once were, we see mounds of rock.

Those mounds, those are called moraine.

Now, we also get something specific called a terminal moraine.

And a terminal moraine is found at the end of a glacier.

So right at the very end of a glacier or the glacier snout, that's what we call the end of the glacier, which you can see on that image there.

That's the very edge, the end of the glacier called its snout.

The rock that is deposited there, that is called terminal moraine.

And so actually, over time, as the glacier retreats, retreats back up the valley because of melting, we're going to have lots and lots of old terminal moraines being created.

And that's how we can look at where the glacier came to, the extent of the glacier because we can see when it started to melt, that moraine that's been left behind.

Okay, so we're onto another check then.

True or false? Rock debris that has been transported by a glacier always comes from bedrock beneath the ice.

So the debris that the glacier is carrying, does that always come from bedrock beneath the ice? So is this true or false? What do you think? So pause the video, write down your answer and then come back and let's see how you got on.

Okay, how did you get on? True or false? Rock debris transported by a glacier always comes from bedrock beneath the ice.

That is false.

And why is it false? It's false because some of the debris carried by a glacier may have fallen onto the ice, onto the glacier from above.

So not all of it comes from beneath.

Some of it comes from above.

Okay, so we're on to our final task of the lesson now and we've got some questions for you to answer.

So question one, explain how rock faces above a glacier are a source of rock debris found on a glacier.

So you need to explain how rock faces that are above a glacier, how are they're a source of rock debris found on a glacier? And then question two, 2a, what happens to the rock debris carried by a glacier at lower altitudes? So when we get to those lower altitudes, what happens to that rock debris that the glacier is carrying? And then 2b, what is moraine? Okay? So you've got some questions to answer there.

So have a little think, pause the video, write down your answers to those three questions and then come back and let's see how you got on.

Okay, how did you get on with those questions? Let's have a look then.

So question one, explain how rock faces above a glacier are a source of rock debris found on a glacier.

So you could have written sources of sediment or debris include rock faces above as well as beneath the ice.

So the debris doesn't just come from beneath the ice, it can also come from rock faces above.

Now, on those rock faces, loose fragments of rock can fall onto the ice from above and then be transported by that glacier.

Did you get that one? Well done.

Let's have a look at those two questions for question two then.

So 2a, what happens to the rock debris carried by a glacier at lower altitudes? So when that glacier reaches those lower altitudes, what happens to the rock debris that's being carried? So at lower altitudes, temperatures are warmer.

So eventually, when lots and lots of melting has occurred, and when that glacier is melted, the rock debris that the glacier is carrying is then deposited and that creates new features in the landscape, mounds of material in the landscape.

And those land forms are called moraine.

And then 2b, what is moraine? So moraine is the rocks in sediment that are deposited as the glacial ice melts.

And we have something called a terminal moraine, and that's found where the glacier ends right at the very end of the glacier or at that glacier snout.

Did you get those ones? Well done.

Okay, so now we're at the end of our lesson on glacial processes, let's have a little look at what we've learned today.

So glaciers erode the landscape by plucking and abrasion.

Eroded and weathered rock material is transported by the glacier as it moves down the valley.

And where the glacier melts, it drops or deposits debris as moraine.

The snout or downslope end of a glacier is where the terminal moraine is found.

Thank you for joining me for today's geography lesson.

I hope you've really enjoyed it.

See you next time.