Lesson video

Hello and welcome to another geography lesson with me, Ms. Roberts.

This lesson is from our unit all about what shapes life at the coast, and in this lesson, we are going to be looking at some of the most beautiful and unique landforms that we can find in coastal locations.

The one thing that the landforms we will see today all have in common is that they were created by the processes of erosion.

By the end of the lesson today, you are going to be able to explain those erosional processes that are taking place, and you'll be able to describe the coastal landforms that those processes create.

I'd like you to be able to use some really good geographical terminology in your descriptions and explanations, so let's have a look at some key words for this lesson.

You've heard me use the first keyword already, and that word is landform.

Landform are natural features, and they're created by the processes such as erosion or deposition.

The landforms we'll see today are landform we find at the coast, but we can find landforms in many other places.

Erosion is a process.

It's the process whereby the Earth's surface, whether that is made of rock or soil or any other natural material, is worn away and then transported somewhere else.

Our next key word is geology.

The geology of any area or location is its physical structure.

We are talking about the rocks and the minerals that exist in that location.

What rock is that area made from? And our final keyword is rate.

A rate is a measure of the quantity or the frequency or the speed at which something happens or occurs.

When we talk about rates today, we are thinking about speed.

We're thinking about how quickly something like erosion takes place.

I'll be taking you through two parts to this lesson.

First, we're gonna think about erosion and how it shapes our coastlines.

Later, we'll be looking at the landforms that result from that process.

So let's begin now and think more about what's happening at our coasts.

Erosion is the process where rock at the coast is worn away and broken down.

Erosion helps to change the shape and the look of the coastline in many different ways, and there are four main types of erosion that we are mostly concerned with at the coast.

Those four types of erosion are abrasion, hydraulic action, solution, and attrition.

It is through those natural processes that erosion takes place.

Those processes of abrasion, hydraulic action, solution, and attrition wear away the coastline.

When cliffs and rocks are worn away, their shape changes, and as a result of that, erosional landforms are created.

For example, the arch that you can see in this photograph.

It almost looks like someone could have stuck that arch onto the front of that cliff, doesn't it? But that's not the case.

What's happened here is parts of rock around that archway have been eroded, and the landform before us, the arch, has been created.

We'll find out some more detail about that in a little while.

At this point, have a go at this question.

Which of these coastal processes is a type of erosion? The options are A, saltation, B, suspension, C, solution.

Hmm, have a think.

Which of those is a type of erosion? Have you decided? It's solution.

That's correct.

Solution is one type of erosion.

It's where rocks are dissolved by seawater.

Suspension and saltation are actually types of transportation.

So let's find out some more about those four processes of erosion.

We begin with abrasion.

Abrasion is a process where the pieces of rock and stone that are being carried within a wave, they're being held there in the wave, as the wave crashes into a cliff face, those rocks that are in the wave, they crash into the cliff face and bang into it, all this constant knocking against the cliff face.

As that happens, the cliff face is worn away because of the constant knocking into it of those particles that are being carried by the wave.

This wears the cliff face down, it weakens it, and eventually, pieces of rock will start to break off from the cliff.

Next, we have the process of hydraulic action.

You can see there, we are highlighting a crack in the cliff face.

This is, again, related to what happens when waves knock into the cliff face.

As the wave knocks into the cliff face, any air that was there is forced into those cracks.

This puts pressure on the cracks, and those cracks start to widen and expand.

You'll be able to see there's some other small cracks starting to appear around the larger cracks in the diagram.

This weakens the rock, and eventually more parts of the cliff will start to break away.

That is hydraulic action.

The other two processes of erosion are solution, which I mentioned before.

That is when rocks are dissolved into the water.

You might think that the line there is actually just pointing to nothing, just to the water.

That's because with solution, sometimes the particles of rock are dissolved so finely that they become so small, we cannot see them with the naked eye.

So that is solution.

Some types of rock, such as limestone and chalk, for example, are more vulnerable to this type of erosion than other types of rock are.

And finally, we have the fourth process of erosion, which is attrition.

This is, again, to do with the rocks that are being carried by the wave, but instead of the rocks hitting the cliff face, this time they are hitting each other, and as they hit each other and they knock and they bounce away from each other, they can break and become smaller.

That's what attrition is, is when rocks within a wave hit each other and reduce in size.

All right then.

So were you listening carefully to that information about the processes of erosion? I would like you to read these statements and decide if they are true or false.

If they are false, can you correct them for me? Pause the video now whilst you do this quick activity.

Okay, let's have a look at the answers together.

The first statement says that attrition is waves forcing air into cracks in cliffs.

Air is forced into cracks in cliffs, but not by attrition, so that's false.

The process that should be named here is hydraulic action.

The next statement says that hydraulic action is rocks in waves knocking against cliffs, but we've just established that hydraulic action is forcing air into cracks.

So this is also false, and the correct process here is abrasion.

That is when waves that have rocks in them knock into the cliffs.

Our next statement is solution is rocks dissolved by seawater.

That one is true.

And finally, abrasion is rocks in waves knocking against each other.

Earlier, we noted that abrasion is rocks in waves knocking against cliffs.

So this is false as well, and the correct process here should be attrition.

Well done.

Did you get those correct? Good job.

Erosion isn't something that happens very quickly or overnight.

Erosion takes millions of years.

The landforms that we are looking at today have been on planet Earth for millions of years.

The geology of any coastline will determine the rate of erosion in that area.

So in other words, the type of rock that's there will determine how quickly or slowly erosion takes place.

The geology, remember, refers to the types of rock that the coastline is made from.

So these cliffs that you can see here, the type of rock that that cliff is made from, and these rocks here that you can see in the foreground of the photo, what rock are they made from? That's the geology.

When we talk about types of rock, we are not just talking about types of rock that we can name.

We're talking about categories of rock, and in particular, we are thinking about soft rock and hard rock.

Many coastlines have areas of soft rocks and areas of hard rocks, often right next to each other.

Areas of soft rock will erode at a faster rate than areas of harder rock.

So the rate of erosion differs between different types of rock.

The softer a rock is, the quicker it will erode.

The harder a rock is, the longer it will take to erode.

So there is a scale there of erosion.

The differences in those rates of erosion are what causes particular landforms to be created.

So as an example, let me tell you about the formation of a bay, which is what you can see in this diagram.

I'll take you through this diagram here now.

When an area of soft rock sits in between two areas of hard rock, okay, that's what's happening here, the soft rock in the middle is going to erode at a faster rate than those two areas of hard rock either side of it.

This means that the soft rock in the middle will wear away faster.

It will start to wear away whilst those areas of harder rock remain pretty much as they are.

As the soft rock is worn away, it retreats, it moves backwards, and that is what forms a bay.

That's where that beach is that you can see there, in the bay.

Those two areas of hard rock that remain sticking out, we call those headlands.

So headlands and bays are landform that are created as a direct result of areas of harder and softer rock at a coastline.

Okay, so think about that situation now.

Think about the geology of coastlines and what effect that has whilst you look at this statement.

Can you tell me if this is true or false? To say that all coastlines erode at the same rate, is that true or is that false? It's false.

Well done.

Now, can we say why? What explanation could you provide here? It's false because it all depends on the geology of the area.

If it's got areas of softer rock, then they're going to erode at a quicker rate than areas of hard rock will.

Okay, well done.

You've been listening really well today.

So let's now put our new knowledge about the processes of erosion to use by doing this activity together.

Here you can see waves crashing onto a rocky coastline.

I want you to explain what is taking place there while that is happening.

What happens when that wave there crashes into that rocky coastline? I would like you to use the words in the table below in your explanation.

Those words are erosion, abrasion, attrition, hydraulic action, and solution.

Pause the video now to give yourself time to complete this activity, and when you're ready, I'll share an example answer with you.

Good luck.

Ready? Well done.

Let's have a look together at an example from one of the Oak Academy children.

When waves break on a coastline, the processes of erosion occur.

There are four kinds of erosion that affect coasts.

When the wave crashes into the cliff, hydraulic action forces air into cracks, and rocks carried in the water crash against the cliff, causing abrasion.

These processes cause the cliff to wear away, and pieces of rock can break off.

Solution and attrition are happening in the seawater.

When pieces of broken rock get carried by the waves, they bang into each other and break up.

This is called attrition.

Solution is when seawater dissolves the rock.

I think that's a very thorough explanation.

It's well-written and has used a lot of geographical terminology.

So now we know what is happening.

We know about the processes of erosion, so let's look now at what happens as a result of those processes.

Let's look at the coastal landforms that erosion creates.

Look at that beautiful picture there.

Coastlines are permanently exposed to the power of the waves and the weather.

It's the action of those waves, as we have just described, that contributes to the processes of erosion taking place.

When that erosion continues and continues and continues to happen over very, very long periods of time, its effects on the landscape become more and more visible.

Eventually, different coastal landforms are created, just like the one here in the picture.

This picture shows us an arch.

An arch is an erosional coastal landform made from hard rock.

This picture, in particular, is probably the most recognisable arch in the UK.

It's called Durdle Door, and it is found in Dorset in the south of England.

This arch was created around 140 million years ago, and it's made from a very hard rock called limestone.

Durdle Door is an incredible 61 metres tall, so if you ever get a chance to go and visit it, it's very impressive to stand underneath and look up at this huge towering arch above you.

Thinking then about Durdle Door and everything you have just heard about it, can you tell me which of these statements about Durdle Door are true? A, Durdle Door was created millions of years ago by erosion, B, Durdle Door was created by the erosion of soft rock, C, Durdle Door is a famous cliff found in Dorset, and D, Durdle Door is made of a hard rock called limestone.

Why don't you pause the video, read through those statements again, and when you've made your choices, I will share the answers with you.

Ready? Okay, so the first statement that is definitely true is that Durdle Door was created millions of years ago by erosion.

Which other statement do you think is true? Is it B? Something's not quite right about B.

Or C? Something's not quite right there either.

The next true statement is actually D, Durdle Door is made of limestone, which is a very hard rock.

So B is not true because it's not soft rock, and C is not true because Durdle Door is an arch, not a cliff.

Arches are not the only landforms created by erosion of the coast.

Let's have a look at some others together.

Erosional landforms include caves, stacks, stumps, and headlands and bays, which we mentioned earlier in the lesson.

On this extract from an OS map here, you can see an area of coast that has a headland.

The headland is that area of land that is sticking out into the sea.

Being in that location, in that position sticking out into the sea makes headlands very vulnerable to erosion.

Over time, over many millions of years in most cases, new landforms will be created out of that headland, and those landforms follow a particular sequence, which we are now going to see.

There is a headland.

You can see the green area is where people would walk if you were going for a walk at the coast.

So that's the top of the cliff there.

The sequence goes from left to right on this diagram.

We start with the headland.

As you have just seen in the OS map, the headland is sticking out into the sea.

Over time, caves will appear.

Notice the little crack there to the left of the caves.

A crack will eventually become a cave.

Those caves will grow and grow over time, and eventually we will see an arch, like the arch we saw at Durdle Door.

More time will pass, and erosion will continue, and eventually the top of that arch will collapse into the sea.

What is left behind is called a stack, and again, more erosion will happen, and many years will pass, and eventually that stack will be eroded into a smaller outcrop called a stump.

None of this happens quickly.

We're talking about millions of years for these processes to happen, but they always happen in the same order, from headlands to caves, to arches, stacks, and stumps, and there are examples of all of these landforms all around the coastline of the UK.

So let's try a quick activity together.

Here are those coastal landforms that have been created by erosion.

I want you to number them from one to five in the sequence that they are created.

Ready, steady, go.

All done? Good job.

Let's have a look at the answers.

We start with the headland.

That's where we begin.

From a headland, we see some caves start to develop.

Caves grow and grow into arches.

The top of an arch collapses leaving a stack, and then over time, the stack is further eroded into a stump.

Did you get those in the correct sequence? Well done.

Time for an activity now about erosional coastal landforms. Here, you can see the diagram of coastal landforms again.

I have labelled the landforms A to E, and I would like you to put the correct names on the diagram, please.

When you have done that, I would like you to move to part two of this activity, which is about Durdle Door.

We looked at Durdle Door earlier.

It's a very famous arch in Dorset, and it's made of limestone, which is a hard rock.

I would like you to explain in your own words how the geology of the coastline has contributed to the creation of that erosional landform.

You can pause the video while you complete these tasks, and when you are ready, come back and I will share the answers with you.

Ready? Excellent.

Let's have a look first at naming the landforms. Let's check that we can remember them all correctly.

So we start there with a headland.

Then, we have the appearance of some caves.

Caves become an arch.

The arch becomes a stack, and a stack becomes a stump.

Did you get all five correct? Well done.

Then, you were asked to talk about the geology of Durdle Door, and how the geology has contributed to that arch forming.

Here is an example now from one of the Oak Academy students.

Geology tells us about the type of rock at a coastline.

That's good, that's a great way to start because they're setting out what geology is.

Geology tells us about the type of rock at a coastline.

There are hard rocks and there are soft rocks, and they all erode at different rates.

Soft rocks erode at a quicker rate than hard rocks.

This leaves the harder rock sticking out to form headlands.

Headlands are vulnerable to erosion because they stick out from the coast.

Over time, erosion creates other coastal landforms, such as caves, arches, stacks, and stumps.

Durdle Door is an arch.

It was formed about 140 million years ago, and has eroded slowly over time because it's made of limestone, which is a hard rock.

That's a very well-written answer.

It explains the processes of how landforms are created, and then gives some specific information about Durdle Door.

Did you have similar ideas in your response? Good job.

You have seen and heard a lot of new information in this lesson, so let's review everything now as we bring this lesson to a close.

We know that there are four types of erosion, and they are abrasion, hydraulic action, attrition, and solution.

We know that the geology of a coastline has an impact on the rate of erosion.

That's the type of rock that exists in an area.

Coastal landforms, such as arches, are formed through erosional processes over millions of years.

The sequence of landforms from a headland to a stump is headlands, then caves, caves become arches, arches become stacks, and stacks become stumps.

Well done for listening so well to all of that new information and all of that new terminology.

I'm looking forward to seeing you again for our next lesson to find out more about what shapes life at the coast.

Bye for now.