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 the title of today's lesson is "Glacial Landforms." By the end of the lesson, you will be able to understand how glaciers shape the landscape through erosion, and you'll be able to identify and describe key glacial landforms. The are some key words that we'll come across in today's lesson.

They're corrie, truncated spur, arete, and U-shaped valley.

Now, a corrie is a steep-sided hollow at the head of the valley or on a mountainside.

A truncated spur is a ridge that ends in a steep cliff face where an interlocking spur formed by rivers has been cut off by a glacier.

And arete is a narrow ridge of rock between two valleys.

And a U-shaped valley is a valley with steep straight sides and a flat bottom, formed by the movement and scouring action of a glacier.

Today's lesson on glacial landforms is split into two learning cycles.

The first, what does a glacial valley look like? And the second, what other landforms does a glacial leave behind? So let's go on to look at our first learning cycle: what does a glacial valley look like? So glaciers are large, slow-moving rivers of ice, that form where snowfall exceeds melting over time.

So glaciers form when there's more snow falling than there is melting.

They move downhill and shape the land in two different ways through something called plucking.

Plucking happens when melt water freezes bedrock to the glacier.

When the glacier then moves forward, it pulls those loose rocks with it, leaves a jagged landscape behind.

Now, the other way that glaciers shaped the land is through abrasion.

Now, rocks that are stuck into the ice, they scrape and wear down the bedrock.

And that's also a way that the glaciers shape the land.

So they pull rocks out through plucking and they sandpaper the rocks down through abrasion.

So our first check of the lesson then.

Which of these processes.

Which of these are processes of glacial erosion? Is it A, attrition, B, plucking, C, abrasion, or D, weathering? Which of these are processes of glacial erosion? 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? Which of these are processes of glacial erosion? Attrition, plucking, abrasion, or weathering? And the answer is plucking and abrasion.

Did you get that? Well done.

So, glaciers transform V-shaped river valleys into U-shaped valleys.

Can you see this image here? This is surely U-shaped valley.

It's a U-shaped valley in North Wales.

It creates the steep-sided valleys that are created by erosion.

And the valley floor is flat, formed when the glacier smooths the landscape.

So those V-shaped valleys that we have from rivers, the glaciers come and bulldoze through that and create a U-shaped valley with steep valley sides and a flat valley floor.

So another check then.

Which of these are characteristics of a U-shaped valley? Is it A, steep sides, B, gentle sides, C, flat floor, or D, bumpy floor? What do you think? So pause the video, write down your answer, and then let's come back and let's see how you got on.

Okay, how did you get on? Which of these are characteristics of a U-shaped valley? And the answer is A and C, steep sides and a flat floor.

Well done.

Okay, so Lucas asks, "Why are glacial valleys U-shaped?" That's a really, really good question.

The immense weight and movement of the glacier erode the sides and bottom of the valley evenly creating the U-shape.

So because it's so, so big and so, so heavy and the movement erodes the sides and the bottom evenly, creating that U shape.

Another check then.

True or false, glaciers erode valleys evenly? Is that true or false? So pause the video for a moment, 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 erode valleys evenly? That is true.

Why is it true? The immense weight and movement of a glacier erodes the valleys sides and floor evenly, resulting in the characteristic U-shape.

Did you get that? Well done.

Okay, so interlocking spurs, they are ridges of land that jut into the V-shape of a river valley.

So can you see them on that image there? They're jut into the land, a little bit, of the V-shaped river valley.

Now, when a glacier cuts through that V-shaped valley, cuts through those interlocking spurs, it creates a U-shaped valley and the interlocking spurs become truncated spurs.

As it erodes all the way through, it gets rid of that V-shape and turns it into a U-shape.

Those interlocking spurs become truncated.

Now, the valley is straighter, deeper, and wider.

Those truncated spurs sit high above the valley floor.

And you can see here that this is the cliff-like face of a truncated spur in Glen Lochy, which is in Scotland.

Now, this diagram here is a diagram of a U-shaped valley and it's got some features on it there.

These hanging valleys, they sit high above the main trough, the main glacial trough.

They are small valleys which are created by tributary glaciers.

Now, often, waterfalls flow out of these high valleys between two truncated spurs, so it makes them quite easy to spot.

So hanging valleys, they sit high above the main trough.

They are small valleys created by tributary glaciers.

Often, you get waterfalls pushing out of the high valleys between the two truncated spurs, so they're really easy to spot, which you can see on this diagram, this image here, this photograph here.

You can see the truncated spurs and the waterfall is coming out of that hanging valley high above.

Another check then.

True or false, glaciers create landforms called interlocking spurs? 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 create landforms called interlocking spurs? That's false.

Why is it false? Interlocking spurs are ridges of land that jut into a winding river valley.

When a glacier cuts through these interlocking spurs, the cliff face of truncated spurs form the sides of a U-shaped trough.

Right, so first task of the lesson then.

So the first thing you need to do is label the key features of this U-shaped valley.

So you can see a picture there of the U-shaped valley, and you need to label the key features that we've just talked about.

The second task, describe and explain the differences between interlocking spurs and truncated spurs.

Okay? So pause the video, answer those two questions, and then come back and let's see how you got on.

Okay, how did you get on? So your first task was to label the key features of this U-shaped valley.

And hopefully, you'd labelled the steep valley sites, include cliff-like truncated spurs, and a wide, flat valley floor.

The second question was describe and explain the differences between interlocking spurs and truncated spurs.

Your answer may include: "Interlocking spurs are ridges of land that project into a river valley.

Truncated spurs are the steep, cliff-like edges left behind when a glacier erodes through interlocking spurs.

Interlocking spurs are shaped by rivers while truncated spurs are formed by glaciers.

Interlocking spurs are found in V-shaped river valleys, whereas truncated spurs are found in U-shaped valleys.

In interlocking spurs, erosion follows the winding path of the river, creating a zig-zag pattern.

In truncated spurs, glacial erosion straightens the valley, cutting off the spurs.

How did you get on with those questions? Well done.

Okay, so we finished our first learning cycle and we've looked at what a glacial valley looks like.

Now, let's move on to our second learning cycle.

What other landforms does a glacier leave behind? So, corries are bowl-shaped hollows formed by glacial erosion at the head of the valley.

How many of them can you spot in this diagram? Have a look at this diagram.

How many corries, bowl-shaped hollows can you spot? There are five.

Now, often a small lake within that hollow makes most corries quite easy to spot.

Corrie lakes are also known as tarns.

Can you spot them now in that diagram? So how is a corrie formed? Snow accumulates in a north-facing hollow and it compacts into ice over time.

The glacier erodes the hollow through plucking and abrasion.

So the back wall becomes steep and the hollow deepens.

After the glacier melts, a small lake may form in that hollow known as a tarn.

Now, this is a corrie in the Lake District.

Can you see that steep back wall? There's a hollow there and a small lake, the tarn, is filled in that hollow.

So another check then.

What is the small lake found in a corrie called? Is it A, spur, B, tarn, or, C, arete? 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? What is the small lake found in a corrie called? And the answer is B, it's a tarn.

Well done.

Another check.

Which of the following are characteristics of a corrie? Is it A, gently-sloping back wall, B, steeply-sloping back wall, C, a flat shape, or D, a bowl shape? What do you think? Pause the video again, write down your answer, and then come back and let's see how you got on.

Okay, how did you get on? Which of the following are characteristics of a corrie? The answer is B, steeply-sloping back wall and D, bowl shape.

Did you get both of those? Well done.

Okay, now we're gonna move on to aretes.

So aretes are sharp ridges to formed when two corries form side to side.

And this is an arete in the Lake District called Striding Edge, a really famous arete.

Can you see that sharp ridge when two corries are formed side to side? So two glaciers erode opposite sides of a mountain, creating those really steep slopes.

That remaining ridge is known as an arete.

It becomes narrow and jagged as plucking erodes and steepens the slope on either side.

Okay, so another check then.

What is an arete? Is it A, a sharp ridge between two corries, is it B, bowl-shaped hollows, or is it C, a small lake? What do you think? 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? What is an arete? The answer is A, a sharp ridge between two corries.

Did you get that? Well done.

Okay, so we're onto our final task of the lesson now then.

The first part, label the key features of a corrie.

So you can see this image here.

You need to label the key features of that corrie.

The second part, describe how an arete is formed.

Oh, Alex has given us a reminder.

This is an arete in the Lake District called Striding Edge.

So you can see the image there of Striding Edge in the Lake District.

You need to describe how an arete is formed.

Okay? So pause the video, write down your answer to these two questions, and then come back and let's see how you got on.

Okay, how did you get on? So the first thing was to label the key features of the corrie.

So you see this image here of the corrie? Label there the steep back wall.

You were also to label the hollow, and then in that hollow is a tarn, which is the lake.

Did you get that? The next part of the question was describe how an arete is formed.

Okay, remember that arete that.

You saw that image of Striding Edge in the Lake District.

Describe how the arete is formed.

So your answer may include, you may have written: Aretes are sharp, narrow ridges formed between two neighbouring corries.

So we've got two corries forming side by side.

Aretes are the sharp, narrow ridges that form between those two corries.

They develop when glaciers erode opposite sides of a mountain.

So we've got a mountain and we've got two glaciers eroding opposite sides of that mountain.

They carve out steep slopes.

And the remaining ridge is left, is jagged and slender.

So it's a thin ridge that's left behind.

And a well-known example is Striding Edge in the Lake District.

Did you get all of that? Well done.

So we're at the end of our lesson today on glacier landforms. Let's have a little look at what we've learned today.

Glaciers erode wide and deep U-shaped valleys.

Truncated spurs are formed when a glacier cuts off interlocking spurs, which are landforms created by the work of a river.

Corries, they are bowl-shaped hollows found at the head of glacial valleys.

It's easy to spot a corrie on a map or photograph as they often feature a small lake.

That lake is called a tarn.

And then aretes are sharp ridges formed where two corries erode side-by-side, and they leave that sharp ridge at the end.

I've really enjoyed today's geography lesson on glacial landforms, and I hope you have too.

I look forward to seeing you next time.