Lesson video

Hello and welcome.

My name is Ms. Harrison.

I'm so excited to be learning with you today.

Today's lesson is called Coastal Erosion Landforms. Grab everything that you might need for today's lesson and let's begin our learning.

By the end of today's lesson, you'll be able to describe the characteristics and explain the formation of landforms resulting from coastal erosion.

Before we can begin this, we'll need to define the keywords that we'll be using throughout today's lesson.

The keywords in today's lesson are hydraulic power, erosion, and retreat.

Hydraulic power, this is when waves compress air into cracks in the rock.

They put pressure on them and they cause them to break over time.

Erosion.

This is the wearing away of rock along the coastline.

Retreat.

This is the process by which a coastline, a cliff, or other landforms move inland due to erosion.

Fantastic.

Now that we've defined these keywords, we can begin our learning.

The first question we are going to explore in today's lesson is how are caves, arches, and stacks formed.

Cliffs at the coast are exposed to weathering and erosion.

The image on your screen shows several features of a headland including cliffs, caves, arches, and stacks.

Headlands are areas of more resistant rock that stick out into the sea.

They're constantly exposed to the forces of erosion which shape them into the dramatic landforms that we associate with coastal landscapes.

Before we dive into landforms, we need to make sure we understand our erosional processes.

Erosion is the process where rocks and sediment are worn away by natural forces.

At the coast, erosion is driven by the power of waves.

Unlike weathering, which breaks down the rocks in place, erosion involves the movement of material.

This means that erosion doesn't just wear away the coastline, but it also transports the broken material elsewhere, reshaping the land as it goes.

There are three main types of erosional processes that we need to be clear on.

The first one is hydraulic power, and this is when waves compress air inside cracks in the rock face and they weaken it.

Attrition.

This is when rocks hit each other in the waves and are broken into smaller pieces.

Abrasion.

This is when rocks carried by the waves scrape against the rock face.

Fantastic.

Now we understand this, we can continue our learning.

This headland is in Portugal and has been eroded by wave action.

I would like you to identify two landforms of coastal erosion that you can see in this photo.

Pause the video here whilst you try and identify at least two landforms and press play when you're ready to continue.

Fantastic.

The erosional landforms that you might have spotted are stack, arches, cliff, bay, and a headland.

Well done if you managed to spot these.

Juan has said that he describes a headland as being like a finger of high land that sticks out into the sea.

And this is a really good way of remembering it as we're able to identify something that sticks out into the sea clearly on image, but also on a map if we know it's by the coast.

Headlands are continuously exposed to weathering and erosional processes.

Let's start with how caves are formed.

A cave begins as a small crack or joint in the rock, often at the base of a headland.

Waves use hydraulic power to compress the air into the crack.

They force it to widen.

Abrasion helps it to erode the rock further.

And over time, the crack becomes a hollowed out cave.

If the erosion of a cave continues, it may eventually break through the headland, creating an arch.

This process involves the same erosional forces, hydraulic power and abrasion.

They wear away the rock on either side of the headland.

This results in a natural, bridge-like structure with an open space underneath, and this is known as an arch.

The image on your screen is of Durdle Door, and Durdle Door is located in Dorset, England.

The base of the arch will continuously be eroded by the waves, and the roof of the arch will be weakened by weathering.

Eventually, the arch will collapse, leaving a stack, which is an isolated column.

Over time, the base of the stack is eroded by waves, causing it to collapse as well.

What's left is a shorter stump, which is often visible at low tide.

This sequence from crack to stump shows the long-term impact of erosion on headlands.

Let's test our knowledge.

What is the correct order in which a stump is formed? Is it, A, cave, crack, arch, stump, stack? B, crack, cave, arch, stack, stump? C, cave, arch, stack, crack, stump? Or D, crack, arch, cave, stack, stump? Pause the video here whilst you decide and press play when you're ready to continue.

Excellent.

The answer is B.

The correct order in which your stump is formed is crack, cave, arch, stack, stump.

Well done.

True or false? Caves, arches, stacks are only formed through weathering.

Pause the video here whilst you decide and press play when you're ready to continue.

Fantastic.

This statement is false.

I would now like you to explain why the statement is false.

Pause the video here and press play when you're ready to continue.

Excellent.

The reason why the statement is false is because caves, arches, and stacks form mainly through erosion.

Waves erode rock through hydraulic power and abrasion.

These processes create caves, which can become arches.

And when an arch collapses, it leaves a stack.

Weathering weakens the rock, but erosion is the main process.

Well done if you managed to explain that correctly.

I would now like you to sort these statements into the correct order to show the stages leading to the formation of a stump.

Pause the video here whilst you attempt this task and press play when you're ready to continue.

Excellent.

Let's now check our answers.

Your answers should read in this sequence.

Wave action and erosion widen a crack, forming a cave.

The cave deepens due to erosional processes, forming an arch.

The arch weakens as erosion continues, eventually causing it to collapse.

The collapse of the arch leaves a tall, isolated stack.

The stack is eroded at its base, weakening it until it collapses, leaving a stump, which is usually exposed at low tide.

Well done if you managed to sequence that correctly.

I would now like you to correctly label the landforms indicated in the diagram below.

Pause the video here whilst you attempt this task, and press play when you're ready to continue.

Fantastic.

You should have been able to label the features on this landform.

Let's go through them.

You should have a crack, cave, arch, stack, and stump.

But let's just summarise how caves, arches, and stacks are formed along the coastline.

The process begins with waves targeting weaknesses in the headland, such as a crack or joints in the rock.

Waves use hydraulic power, the force of water compressing air into the cracks, which weakens and breaks the rock.

Over time, the crack grows larger and becomes a cave.

As the waves continue to erode the cave often through abrasion, where sediment carried by the waves scrapes against the rock, the cave deepens and may eventually break through the headland, forming an arch.

However, arches are not permanent.

The base of the arch is eroded by waves, while weathering weakens the roof.

Eventually, the arch collapses, leaving behind a tall, isolated column called a stack.

Even stacks don't last forever.

The waves continue to erode the bases, making them unstable, which is shorter and often visible only at low tide.

This sequence from cracks to cave, arches, stacks, and stumps shows how powerful forces of erosion gradually transform headlands over time, creating some of the most dramatic coastal features.

Well done on this task.

We're now going to explore our final learning question in this lesson.

How are cliffs and wave cut platforms formed? Different factors are going to affect how cliffs are formed and their characteristics.

For example, stronger, more resistant rocks are associated steeper cliffs.

This is because erosion takes a lot longer to take place.

A steeper cliff looks like the image on the top.

Weaker, less resistant rocks are associated with lower cliffs that have a shallower slope, and this is because processes like erosion, weathering, a mass movement can take place here.

And shallower slopes look a bit like the image on the bottom.

Weathering, mass movement, and geological structure and erosional processes are important factors in creating these landforms. Erosion doesn't just create dramatic landforms, it also causes the cliff itself to retreat.

What does this mean? Coastal retreat is the process where the land is worn away, causing cliffs, headlands, or other features to move inland over time.

This happens because the waves attack the base of the cliff through processes like hydraulic action and abrasion.

Over time, the base becomes so eroded that the cliff above collapses.

This repeated process causes the coastline to retreat backwards, which is what we call retreat.

Coastal retreat is especially common in areas where there are powerful waves.

I'm going to show you what it would look like on the screen.

This is where the cliff would've first been many, many, many years ago.

Through erosion, the cliff was retreated back to this position now.

And eventually, it's now formed its current position.

As a result, a wave cut platform is sometimes formed.

It is a flat feature that extends from the base of the cliff into the sea.

A wave cut notch is an indentation at the base of the cliff created through hydraulic power.

As you can see at the base of the cliff, there is the wave cut notch.

And the wave action has repeatedly eroded the bottom of the cliff through hydraulic power.

Over time, the repeated hydraulic power at abrasion erodes a notch into the cliff, which becomes deeper and wider, like you can see on the screen right now.

As the wave cut notch becomes deeper, the rock above it is left unsupported and it can't hold its own weight, and eventually it'll begin to collapse.

This process is going to repeat over time.

It'll cause a cliff to retreat inland, leaving extensive wave cut platform behind.

Wave cut platforms are visible at low tide and provide clear evidence of coastal erosion.

I now would like us to test our knowledge.

Which of these is the OS map symbol for flat rock? This is used to show wave cut platform at the coast.

Pause the video here whilst you attempt this task, and press play when you're ready to continue.

Excellent.

The answer is B.

Well done.

True or false? A wave cut platform results from cliff retreat.

Pause the video here whilst you decide if this statement is either true or false, and press play when you're ready to continue.

Excellent.

This statement is true.

I would now like you to explain why this statement is true.

Pause the video here once you complete this task and press play to continue.

Fantastic.

The reason why this statement is true is because as a wave cut notch grows larger, the cliff above eventually collapses.

This process repeats, and the cliff retreats inland, leaving a flat, rocky area at the base called a wave cut platform.

As we know, we can see wave cut platforms during low tide.

Well done on this task.

I would now like you to name the feature shown at A.

Pause the video here whilst you take a closer look at the map, and press play when you're ready to check your answer.

Excellent.

Before we check our answer, we're going to look at one more question.

I would like you to explain how a wave cut platform is formed.

There's image on the screen to help you with this, but Alex has also made a valid point here, that he knows that a wave cut notch forms at the base of the cliff due to erosion caused by waves.

The erosion that's caused by waves is through hydraulic power, abrasion, and attrition.

Pause the video here whilst you attempt this task and press play when you're ready to continue.

Fantastic.

Let's now check our answers.

For the first question, I asked you to name the feature shown at A.

The feature shown at A is a wave cut platform, and its symbol is a flat rock.

Well done if you managed to get that correct.

I then asked you to explain how a wave cut platform is formed.

Your answer may include some of the following points.

Hydraulic power and abrasion erode the base of the cliff.

Over time, this erosion creates a wave cut notch, which is a small indent at the base of the cliff.

The wave continues to erode the notch.

And as it gets deeper, the weight of the cliff above becomes very unstable.

Eventually, the overhanging rock becomes too heavy and collapses, which causes the cliff to retreat.

As the cliff retreats, the area at the bottom where the rock has been eroded forms a wave cut platform.

This is a flat, rocky surface at the base of the cliff, usually exposed at low tide.

The process continues over time, so the cliff retreats further, and the wave cut platform gets wider.

Well done if you managed to include some of the following points in your answer.

This answer is good because it has given a step-by-step process of how a wave cut platform is formed.

It's also used geographical terminology like hydraulic power, erosion, and retreat.

Well done on this task.

Fantastic.

We've now come to end of our lesson on coastal erosion landforms. Let's summarise what we've learned in today's lesson.

Caves, arches, and stacks are landforms that we can find along the coast.

The process starts with waves targeting weaknesses in the headland, such as cracks or joints.

Waves use hydraulic power where water compresses air into the cracks, weakening the rock.

Over time, the crack widens into a cave.

As the erosion continues often through abrasion where sediment scrapes the rock, the cave grows deeper.

If it breaks through the headland, it forms an arch, which is a natural, bridge-like structure.

However, arches are temporary.

Continued erosion at the base and weathering at the top cause the arch to collapse, leaving behind a stack, an isolated column of rock.

Even stacks don't last forever.

Waves erode their bases until they collapse, forming stumps, which are shorter and often visible only at low tide.

Cliffs and wave cut platforms are caused when waves erode the base of the rock, creating a wave cut notch.

As the notch grows, the overhanging rock becomes unstable and collapses.

This repeated process causes the cliff to retreat in land.

What's left behind is a wave cut platform, which is a flat, rocky area at the base of the cliff, and it's exposed at low tide.

This platform shows where the cliff once stood and demonstrates the power of constant wave erosion.

Both caves, arches, and stacks, as well as cliffs and wave cut platforms highlight the relentless force of waves.

Coastal erosion is a continuous process, constantly shaping the coastline and creating these fascinating landforms over time.

Well done.

You've done brilliantly in today's lesson.

I look forward to learning with you again very soon.