Lesson video

Hi there, I'm Ms. Roberts and I'm here for the third lesson in this unit of work, which is all about coasts, we are investigating what happens at the coast where the land and the sea meet.

This lesson is all about a very important process called coastal erosion.

Don't worry if you're not too sure what erosion is now, I'm here to help you, and by the end of the lesson today, you will be able to explain why the sea erodes the land.

We're going to begin as ever with some important words that are going to be really helpful to you in this lesson, these are our keywords for today.

So let's begin with our first word, which is waves.

Then we have erosion, which you've already heard, and our third word is geology, not geography, geology.

So let's just look at the meanings of those keywords.

Waves, waves is movement of sea water, or water in the oceans.

It's the movement of energy across a body of water.

Erosion is a process.

It's a process where the Earth surface, whatever type of surface that may be, rock or soil, et cetera, it's when that surface is worn away by something, and then it can be transported from its original site to another place.

Geology, the third keyword there, geology, is all to do with the physical structure of a place.

What type of rock is an area made from? What rocks and minerals exist there? So as we move through this lesson about coastal erosion, there'll be three sections today.

First, we are going to think about where waves come from.

Then we are going to think about the coastal features that are caused by erosion, and then we'll be thinking about the affect that geology has on erosion.

So let's begin now with the first part of this lesson, all about waves and where they come from.

So we know what waves are, we've just said that waves are the movement of energy across a body of water.

Those waves are formed by the wind blowing over the surface of the sea or the ocean, it's the wind that's providing this energy that moves across the water creating the waves.

Waves always travel in the same direction as the winds that is blowing them, they don't go against the wind.

You can see here the waves in this photograph are moving in the same direction as the arrow, which shows the winds direction.

So were you listening to that explanation? Let's find out with this quick check for understanding.

Listen to this sentence.

Waves are formed by the gravitational pull of the Moon.

Is that sentence true or is that false? Have a think now and choose your answer.

Ready? This sentence is in fact false, I'm glad you were listening well, so can you justify why this is false? That means can you give a reason? Here's a couple of options, which of these do you think is the best reason here? Waves are created by the spin of the Earth, or waves are created by wind blowing over the sea.

You got it, waves are created by wind blowing over the sea.

And remember, the waves travel in the same direction as the wind that is blowing them, well done! Now, there are lots of different factors that can affect waves, and we're going to investigate some of those now.

You're going to hear a lot of new terminology, but don't worry, I'm going to explain everything step by step.

So waves can vary in size.

We can get small waves and we can get huge waves, okay? Now what causes waves to be those different sizes? There's a few things that we need to consider.

Firstly, the size of a wave really depends on the strength of the wind that is blowing it, and also the length of time that the wind has been blowing.

The depth of the water is also a factor.

There are some places around the world that have very, very, very big waves, and these kind of places are very popular with people who like to take part in sports, such as surfing.

Take a look more closely at the diagram on the screen.

Can you see how the size of the wave increases the further away from the shore? Notice that the wind is blowing in that direction, it is blowing away from the shore.

Now, the distance that a wave has travelled, that's the same as the distance that the wind has blown that wave for, that distance is called the fetch, okay? So if we have a very strong blowing wind that has a lot of energy, then that wind can continue to blow waves for a very long time.

That means they can blow further, which means they will have a greater fetch.

Winds that have very little energy, very light breezes, they can't blow waves very far, so they will have a very small fetch.

You can see from the diagram that the size of the wave increases, starting with micro ripples close to the shore, where the winds are gentle, these ripples become larger as the fetch increases, and the wind is stronger, and then further out to sea, we have waves that are called chop.

Have you ever heard the expression, "Oh, that sea's choppy?" What that means is the sea is bobbing up and down a lot because the wind is increasing and the waves are starting to grow.

As a wave grows, eventually, it will become a large, fully developed wave.

I mentioned earlier that people who take part in sports, like surfing, like places with very large waves.

Can you think of any of those places? One place is called Hawaii.

Have you heard of Hawaii before? Hawaii is an island in the Pacific Ocean, it's actually part of the USA.

The Pacific Ocean is the world's largest ocean and it completely surrounds Hawaii.

This means that winds can travel from all directions for a very long time, and across a very vast distance to reach Hawaii.

By the time the waves reach Hawaii, they have grown into some of the biggest waves that we have seen.

People really do enjoy jumping on surfboards and riding the waves in places like Hawaii.

Now remember, that the distance of wind travels over an ocean and blows the waves is called the fetch.

Here's a map showing us where Hawaii is.

It's right here in the middle of the Pacific Ocean.

So you can see that huge fetch, the huge distance there that is travelled by the waves coming towards Hawaii, okay? Let's have a little check for understanding now, before we move on, this is a multiple-choice question.

I'd like you to decide which two of these factors help to create large waves.

Pause the video and make your choices.

How did you get on? Let's see, did you say that A and D are factors that create large waves? The strength of the wind, and the length of time.

The stronger the wind, the bigger the wave, the longer the wind has been blowing, the bigger the wave will be.

Now, try this activity, this is Task A.

You have a map of the United Kingdom here, and I have labelled a place called Newquay, which is in Cornwall.

And here we have Dover, which is where there is a large port, and we can catch ferries across to France in Dover.

I would like you to explain, which of these two locations you think will usually receive the largest waves and which will have the smallest waves.

Hmm, pause the video now and share your ideas.

Ready, what did you think? I think that Newquay in Cornwall has the largest waves.

That's because winds have to travel across the Atlantic Ocean to reach Newquay, that's a very long way.

Dover, on the other hand, will have the smallest waves because the English Channel separates England from France at Dover, and that's quite a short distance, so the fetch is smaller, which means the waves will be smaller.

Did you have those ideas as well? Good job.

Now we're going to explore coastal erosion and how it creates coastal features that we are familiar with.

The waves that we've just been looking at, reach the land at the coast.

When powerful waves hit the shore, they cause erosion.

Erosion can cause rocks to break apart and it can even cause cliffs to collapse.

We can see that's what's been happening in this photograph.

You can see how the rocks strewn around the shore are all broken up.

There are lots of rocks piled up here at the base of this cliff, and although erosion itself actually takes place over very long periods of time, something like a cliff collapse can happen very suddenly, and this is why cliff sides are very dangerous places to be.

Waves have helped to create some of the most beautiful features that we can see on our coastal landscapes.

Whenever the sea meets the land, it changes it, it erodes it.

Erosion can create features like these, such as caves, and arches along the coastline.

The photo on the left, can you see the big hole? That's a cave, that happens because waves are constantly eroding as they hit the cliff when the tide comes in, and in that one particular location, a cave eventually forms. Here is an arch.

This arch is in a place called Lulworth in Dorset.

An arch is a giant piece of rock with a hole in the middle.

When a cave continues to erode and erode and erode, eventually, it becomes an arch.

So the process of erosion creates a cave and then it creates an arch.

Erosion can also create features like these, which are called stacks.

If an arch becomes weaker and weaker and weaker over time, as the waves continue to erode it, eventually, the top portion of the arch will collapse.

It will fall down into the sea below, and the two sides of the arch will be left sticking out on their own like a pillar.

You can see two stacks here that were once part of an arch.

So were you listening then? Let's check, look at these three photographs.

Which of these photographs shows an arch, A, B, or C? Ready? It's photograph A, that's that beautiful arch in Lulworth in Dorset there.

And sticking with the same three photographs, which of those three photographs is a cave? Have you decided? It's option B, well done, okay? And option C there is a shoreline and we can see some rocks and some cliffs, and a lighthouse in the distance.

Let's move now on to Task B for this lesson.

There's a couple of things I want you to do here.

First, I want you to label this diagram.

You need to identify the stacks, the arch, and the cave.

When you've labelled the diagram, I would like you to explain what could happen to the arch in the future.

Pause the video here while you complete the activity, and then when you come back, I'll be going through some example answers with you.

Ready? Good job, let's have a look together, first at the labelling, we have a cave, we have a sea stack, or just a stack, and we have an arch.

Well done if you got all three of those labels correct.

Now, what might happen to that arch in the future? So as the arch will continue to be eroded by the waves hitting the rock over and over and over again, eventually, the top half of that arch will collapse, it will fall into the sea, and that will leave another sea stack.

Well done.

Now I wonder, do all rocks erode in the same way? Hmm, let's find out by looking at the final part of today's lesson, and consider how geology can affect erosion.

Geology determines how quickly a coastline will erode.

Now remember from our keywords earlier, geology is thinking about what type of rock an area is made from because not all cliffs and not all coasts are made of the same type of rock, there are many, many different kinds of rock.

There are very, very, very hard rocks.

This is an example of a hard rock, granite, rocks like this erode very slowly, they are difficult to erode.

It would be absolutely impossible for you to try and break a rock like granite with your own hands.

Some rocks, however, are very, very soft.

For example, a rock called boulder clay.

If you squeeze rocks like this very, very hard, it will just break apart in your hand.

These soft rocks erode very, very quickly, they are very easy for the waves to erode.

Were you listening carefully to that explanation? Let's check our understanding with this quick question.

Listen to this statement and decide if it is true or false.

Harder rocks erode more quickly than softer rocks, is that true or false? Pause the activity and make your choice.

Ready? This statement is definitely false, but we can't just say something is false without backing ourselves up with a reason why.

So let's justify our answer here.

Which of these is the best reason why, is it that harder rocks are easier for waves to break apart? Or is it that softer rocks are easier for waves to break apart? Make your choice now.

Ready? Of course, it's option B.

Harder rocks do not erode more quickly than soft rocks, they erode a lot more slowly, and the reason for that is that soft rocks are much easier for the waves to break apart.

Remember, if you have something like boulder clay and you squeeze it, it will just fall to pieces in your hand.

So now, look at these two coastlines.

Given what you know about hard rock and soft rock, and how quickly they erode, which of those two coastlines do you think is made of hard rock? Have you chosen? It's the first one.

This photograph definitely shows a coastline that's made of hard rock because it has so many cliffs and headlands, and the headlands are sticking out into the sea because they are taking such a long time for the waves to erode.

In the second picture, we see a sandy beach, which means that the waves have been able to erode the sea, and the coastline is retreating.

So let's have a look now at a map of a coastal area.

Looking at maps and identifying headlands and bays like the places we've just seen in those two photographs, can help us to decide whether coastlines are made of hard or soft rocks.

On this map, we can see parts of the coastline that have been eroded back and some other parts that stick out into the sea, this is a place called Swanage.

So headlands are made of hard rock.

They stick out into the sea, and waves take a very long time to erode headlands.

Soft rock is found in places that have bays.

The soft rock erodes more quickly and the bay is created.

Remember, bays are often curved, and if you look further down again, we can see Peveril Point, places with point in the name are usually headlands, and this means that we have more hard rock in this area because the headland is sticking out.

Look down again, and we see another bay, this is Durlston Bay, and as we have just said, bays are created where there is soft rock.

So as you can see, just by looking at this map, we've identified that we have an area of hard rock, followed by an area of soft rock, followed by another area of hard rock, followed by another area of soft rock, the layers are alternating along this coastline.

Here's a map of the UK.

I'm going to zoom in on one specific place called Flamborough Head.

Flamborough Head is on the North Yorkshire Coast, and it's a very good example of a headland.

This headland is made of a rock called chalk.

Chalk is a very hard rock, it's much, much harder than the boulder clay, which is what the areas to the north and south of Flamborough head are made of.

You can see two bays here, one to the north and one to the south, and that shows us that those areas must be made of soft rock, which has eroded more quickly than the chalk of the headland.

So the map tells us everything we need to know about the geology of the coastline in this area, from Flamborough head, with its hard rock there in the middle, and then the two bays, which show us areas of soft rock.

And again, here we can clearly see that we have an area of soft rock, followed by an area of hard rock, and then another area of soft rock.

So we have these alternating layers of hard and soft rock along this coastline as well.

Now at Flamborough Head, there are lots of beautiful coastal features that we can see.

Flamborough Head also has some other coastal features that are very pretty to look at, including some stacks and an arch as well, just like the ones in the picture.

So let's put what we know to use now in this check.

Here we can see three maps.

Each map shows a different coastal area in different parts of the UK.

I want you to study the maps carefully, and use them to help you to decide, which of these map extracts show an area that has both hard rock and soft rock? Pause the video now whilst you make your choice, and remember, you can work with a geography buddy for extra support.

Have you decided? Excellent.

The correct choice here is map extract B.

Think about the layering that we were talking about before, that's what you were looking for here, layers of hard and soft rock that alternate along the coastline.

B has alternating layers of hard and soft rock because we can see both a headland and a bay.

The other two map extracts show us just a nice straight piece of shore, which must all be the same type of rock.

Time for your third task for this lesson, Task C.

This is an opportunity for you to get creative, as I would like you to create your own informative leaflet about coastal erosion, like the sort that takes place at Flamborough Head.

I have given you some sentence starters and I have given you some words that you can use to complete the sentences.

I would also like this leaflet to include a labelled diagram of an arch.

So pause the video now, get creative by completing your own informative and beautiful geography leaflets.

When you're ready, come back and I'll share an example with you.

Ready? I hope you enjoyed creating your leaflets.

This is an example of how I have completed the sentences.

The rock at Flamborough Head is hard, which means that it forms a headland and it sticks out into the sea.

Erosion happens along the coastline because waves that are created by the wind crash into the cliffs.

The coastline has a range of features, including an arch and a stack.

The C stack was formed when an arch collapsed.

Here is my drawing of an arch, I have labelled the arch, and I have labelled the roof, which is about to collapse, and will leave a stack.

I bet you have produced some brilliantly leaflets, great work.

So at the end of this lesson now, let's review all of our new learning.

We know that waves are created by the wind, and lots of things can affect the size of waves, such as the strength of the wind, and the length of time it's been blowing, and the distance that the wind blows across the water for.

Waves cause coastal erosion, and coastal erosion creates features like arches, caves, and sea stacks.

We can find lots of these in different places around the UK.

Areas that are made of hard rock will result in a headland, headlands are areas that stick out into the sea.

Maps can be used to identify headlands and bays that are formed due to having different geology, hard rock or soft rock.

Well done, for listening really well today, and taking in some very technical information.

I can't wait to see you again for another exciting lesson about coasts, bye, for now!.