Lesson video

Hello, geographers.

My name's Mrs. Hormigo.

I'm really looking forward to teaching you today.

I hope you're going to enjoy the lesson and learn lots.

Let's get started.

Today's lesson is about ice-shaping processes.

By the end of the lesson, you'll be able to understand the processes by which ice shapes the landscape.

There are four key words for today's lesson.

Ice sheet, glacier, freeze-thaw weathering, and glacial till.

An ice sheet is a vast, continuous expanse of ice covering a very large area of land.

A glacier is a large mass of ice that forms on land and moves slowly due to gravity.

Freeze-thaw weathering is the breakup of rocks caused by water regularly freezing and thawing.

And glacial till is a mixture of unsorted debris.

There are three parts to today's lesson.

Let's get started now on the first part, what was the extent of ice coverage across the UK? This map shows ice sheets found in Antarctica and Greenland.

Ice sheets are vast masses of ice that cover large areas of land, over 50,000 square kilometres, and they're only found in these two locations today.

Glaciers are rivers of ice that flow downhill from high altitude areas like mountains.

They form in areas where more snow accumulates in winter than melts in summer.

So ice sheets and glaciers are products of long-term snow accumulation and compression, and this is shaped over decades to millennia, so a very, very long time.

Their growth reflects the balance between snow accumulation and melting, and this is affected by climate change.

The last Ice Age, known as the Pleistocene epoch, peaked around 20,000 years ago during the last glacial maximum.

This map uses GIS and there's a layer showing us where we could find ice sheets.

You'll see that there are ice sheets covering large parts of North America and Europe, as well as Antarctica.

Let's have a quick check now.

True or false, during the last glacial maximum, 20,000 years ago, ice sheets covered all continents.

Pause the video and make your decision.

Hopefully you thought back to that map and said false, but why did you say false? Pause the video and think about what your reasons would be.

You may have said something like this.

While ice sheets did cover large areas of the Northern Hemisphere, including large areas of North America and northern Europe and a small part of Asia, they did not cover all continents.

Well done.

In Europe, ice sheets originating from Scandinavia spread across Northern Europe.

The British and Irish Ice Sheet extended over Scotland, northern England, including the Lake District, and large areas of Wales and Ireland, and that's shown with that blue area on the map.

Southern England remained largely ice-free, but periglacial conditions dominated.

That meant that it had frozen ground and a very harsh, tundra-like climate.

Very different to what we see there today.

Another check for you.

Which areas in the UK were most affected by ice coverage during the last Ice Age? Is it A, eastern and southern regions, B, northern and western regions, or C, Southern and central regions? Pause the video and come back when you've decided.

Looking at the map, I hope you said northern and western regions.

Well done.

First task for today's lesson.

Question number one, describe the difference between an ice sheet and a glacier.

Question number two, using this map, identify regions in the UK that were covered by ice during the last Ice Age.

Pause the video when you've had a go and come back when you've had a go at these two questions.

For question number one, describe the difference between an ice sheet and a glacier, your answer might have included this.

Ice sheets are vast masses of ice that cover large areas of land, over 50,000 square kilometres, whereas glaciers are rivers of ice that flow downhill from high-altitude areas like mountains.

They form in areas where more snow accumulates in winter than melts in summer.

And for question number two, your answer may have included, Scotland, northern England, including the Lake District, Wales and Northern Ireland were covered by ice sheets during the last glaciation.

Well done.

Let's move now to the second learning cycle for today's lesson.

How do glaciers erode the landscape? Glaciers shape the land through processes of erosion and deposition, and this creates very distinct landforms. You can see in this photo that we can identify a few of these.

We have a peak, an arete, a valley, a U-shaped valley, and these have all been shaped by glaciers in the past.

Freeze-thaw weathering is the main weathering process in cold environments.

It breaks rocks apart, making them easier for glaciers to erode.

And this process also produces piles of angular rocks, known as scree, which collect at the bottom of slopes.

When these rocks are picked up by glaciers, the fragments of angular rock help glaciers to erode the land.

Now, let's think exactly what happens during freeze-thaw weathering.

During the day, higher temperatures will cause the snow to melt.

The water will seep into cracks in the rock as we can see in this little image.

At night, as the temperatures get colder and drop below zero degrees Celsius, the water will freeze and as it does so it expands.

As it expands, the ice pushes against the rock, which makes the crack larger.

This process repeats as freezing and thawing occur over time, and eventually the crack grows and eventually the rock will weaken and pieces will break off.

Check for you now, can you put these images in the correct order for freeze-thaw weathering? Pause the video and come back when you've decided.

As you do this, you may want to discuss what is happening in each image with your partner.

This will help you to put them in the correct order.

Hopefully you said A was number two, B was number three, and it started with number C, one.

So you can see in the image and C, the water is seeping into the cracks during the daytime as the snow melts.

In A, during overnight as the temperatures drop below zero degrees Celsius, the water freezes and expands, and over time that constant freezing and thawing cycle causes the rocks to weaken, push apart, and eventually break.

Well done.

There are two main types of glacial erosion caused as a glacier moves, plucking and abrasion.

We're gonna think now about each of those.

For the process of plucking, it occurs when meltwater beneath a glacier goes into the cracks in the bedrock.

When the meltwater freezes, it becomes attached to the bottom of the glacier.

And then as the glacier moves, it pulls chunks of rock away creating a jagged surface.

Abrasion happens when rocks and rock flour, which are tiny particles of rock that are embedded in the base of the glacier, grind against the bedrock, a little bit like sandpaper, and that erodes the bedrock as the glacier moves downhill.

It leaves behind scratches in the rock, which we call striations, and the rocks are also smoothed and polished by the process of abrasion, as well.

And we can see there evidence of striations in those rocks in the photograph.

Another check for you now.

Can you match the process to its correct definition? Read them carefully and make your decisions.

Come back when you're ready.

Hopefully your answers matched up like this.

Abrasion is the process where rocks and debris carried by a glacier scrape and wear away the surface beneath it.

Plucking is when a glacier pulls chunks of rocks from the bedrock as it moves over it.

And freeze-thaw weathering, a weathering process where water enters cracks in rocks, freezes, expands, and eventually over time breaks the rock apart.

Well done.

As glaciers advance, flowing downslope due to the force of gravity, they erode the landscape by plucking and abrasion.

Glacial erosion is very powerful and has a range of effects including the deepening of existing valleys, widening existing V-shaped river valleys into U-shaped valleys with wide bases and steep sides, and they create deep hollows in the ground that later fill with water to form lakes.

Check for you.

Ice only changes a landscape when it's melting.

Is that true or false? And can you think of a reason why? Pause the video and come back when you're ready.

Hopefully you said false and your reason for that may have been it is true that when a glacier melts it deposits material creating moraines, but ice changes landscapes the most when glaciers erode the land, deepening and creating valleys.

Well done.

Let's move now to task B.

Can you annotate this diagram to explain the processes of plucking and abrasion? Pause the video and come back when you think you've had a go.

Your answer may have looked something like this, plucking occurs when meltwater beneath the glacier freezes into the cracks.

Then as the glacier moves, it pulls chunks of rocks away creating a jagged surface.

, Abrasion happens when rocks embedded in the base of a glacier grind against the bedrock, acting like sandpaper as the glacier moves, eroding the rock away.

Well done.

Let's move now to the learning cycle three.

How do glaciers transport and deposit material? So, glaciers move through three processes, basal sliding, internal deformation, and rotational slip.

Let's have a look at each of these in a little bit more detail.

Basal sliding happens when meltwater at the base of the glacier acts like a lubricant, which allows the glacier to slide over the ground beneath it.

And you can see in that image there zoomed in, you've got a layer of meltwater which allows that glacier to move more easily downhill.

Internal deformation.

So, under the pressure, sorry, under pressure from the weight of the glacier, ice crystals will slide past each other and this is known as internal deformation and it allows glacier to flow downhill even in very, very cold environments where the base of the glacier is frozen to the bedrock.

And then rotational slip.

It's a circular movement of the glacier in hollows high in the valley.

Check for you now.

What are the three ways a glacier moves? Is it A, basal sliding, B, internal sliding, C, rotational slip, or D, internal deformation? Pause the video and decide which ones you think are correct.

You should have chosen A, basal sliding.

That's where the meltwater acts like a lubricant and allows the glacier to slide downwards, rotational slip, which is a circular movement up in hollows high up in the mountains, and internal deformation, that's where the ice crystals can move past each other, allowing the glacier to move even in very cold environments.

As glaciers move, they will carry material, and this material is known as glacial till.

You can see in that image there that the glacier looks quite dirty, and that's because there's a lot of material around the edges and on top of the glacier.

This material comes from falling onto the glacier via rockfalls and glacial erosion itself.

It may be that freeze-thaw weathering on the valley sides contributes material to the top of the glacier.

So, glaciers transport material in different ways depending on its position within the ice.

it may be carried on the surface, supraglacial.

Englacial is when material is buried within the glacier.

And subglacial is when it is moved along at the base of the glacier.

And we can see on that image there, we've got material on the surface within the glacier and at the base.

Bulldozing occurs when the glacier's force pushes rocks and debris in front of it downhill.

A different way of transporting material.

Deposition occurs when a glacier melts.

The material that was carried by the glacier is then laid down.

We can see here that glacial till is deposited at the front of the glacier, known as the snout, on the valley floor or the valley sides.

And this glacial till is a mixture of unsorted debris, which includes clay, rock fragments, pebbles, and boulders of varying sizes and shapes, and it's often very angular.

The meltwater flows out of the glacier's snout, and that creates meltwater rivers.

And these rivers will then transport large amounts of the till, which continues to be broken down by the process of attrition to form outwash.

Water deposits its load differently from ice.

It drops the heaviest sediments first, so the outwash deposits are sorted, whereas the glacial till is not.

Here's a check for you now.

When a glacier melts, what happens? Can you complete the labels to explain what's going on in this image? You should have included meltwater flows out of the glacier's snout, creating meltwater rivers, and glacial till is deposited at the front of the glacier, or the snout, on the valley floor or the valley sides.

Well done.

Final task then for today's lesson, explain how glacier's transport material.

You may want to include an annotated diagram.

Key words that you should try to include is glacial till, bulldozing, supraglacial, englacial, and subglacial.

Think carefully over what we've learned in this learning cycle and pause the video.

Come back when you're ready.

Your diagram may have included answers like this.

Glaciers move slowly, transporting material called glacial till in different ways depending on its position within the ice.

Material may be carried on the surface of the glacier, known as supraglacial.

It may be buried within the glacier, known as englacial.

Or material may be transported at the base of the glacier, subglacial.

The glacier's force pushes rocks and debris in front of it downhill as well, and this is known as bulldozing.

That's fantastic if you've managed to include all of those keywords and explain them in a similar way to this answer.

Let's look now at a summary of today's lesson.

We've included a lot of keywords and processes.

During the last Ice Age, ice sheets extended across large areas of the Northern hemisphere.

The British and Irish Ice Sheet extended over Scotland, northern England and large areas of Wales and Ireland.

Freeze-thaw weathering is an important weathering process in cold environments.

Glaciers erode the landscape by the processes of abrasion and plucking.

Glaciers transport till in, on, and under the glacier.

Glaciers deposit material when they melt.

And glacial erosion and deposition create distinct landscapes.

It's really important that you understand these key processes are erosion, transportation, and deposition as we move further into the glacial landscapes topic.

Well done today.

I hope you've enjoyed it and I look forward to seeing you again soon.