Lesson video

Hi, there.

Welcome to today's geography lesson with me, Ms. Roberts.

This lesson is from our unit all about coasts where we are investigating what happens at the coast, where the land meets the sea.

Today's lesson focuses on how the coast is constantly changing and we will be investigating the processes that make those changes happen.

By the end of the lesson today, you are going to be able to use some geographical vocabulary to describe those coastal processes.

First, let's look at some keywords that are going to be very useful for you to use and understand during the lesson today.

The first key word is sediment.

You may have heard sediment before.

Sand that we find on our beaches or shingle that we can find on other types of beaches are both types of sediment.

Sediment is natural materials that have been moved by water or by air and end up in a new place.

The next two keywords for today are processes.

You may have heard of these processes before.

The first process is erosion, and the second process is deposition.

Erosion is the process that happens when the Earth's surface, whatever surface we are talking about, whether that is rock or soil.

When that surface is worn away, it is eroded.

And that eroded material can then be transported to a new place.

Deposition is when that transported material that has been eroded is taken to a new place and it is dropped.

When the sea or the river or the winds that is moving that material loses its energy and drops that material, it deposits it.

That's deposition.

There are two parts to this lesson.

First, we are going to think some more about sediment and how it is transported.

Then we are going to think about deposition and how that process changes our coastlines.

So let's make a start with the first part of our lesson about transportation of sediment.

Take a look at the picture here, which shows a very dynamic coastal environment.

You can see some cliffs there, and the water that is constantly moving around this coastline.

Coasts are always changing.

Some changes can happen very, very slowly over many thousands of years, but other changes can happen very quickly and very dramatically.

There are three main processes that happen at the coast.

Those processes are erosion, transportation, and deposition.

Take a closer look at what is happening to the coastline in the photograph by clicking on the watch button.

This will take you to a video where you can see all of these processes in action.

Let's look in some more detail at each of the processes now, beginning with erosion.

Erosion happens when powerful waves interact with the coastline.

Powerful waves erode the coastline.

They are the cause of erosion.

Erosion creates coastal features such as cliffs, caves, and arches.

When erosion happens at the coastline, it causes lots of sediment to be present in the sea.

The sediment comes from those services that have been eroded by the waves.

There are lots of different types of sediment that we can find at the coast, and those types of sediment all vary as well in size, shape, and weight.

Here are three pictures of different types of sediment that we can find.

The stones are the largest and heaviest type of sediment here.

Sand and mud are both made of much smaller particles, which are individually very tiny, so that makes them much lighter.

Sediment at the coast is transported by the sea.

Transportation occurs when material is moved from one place to another by the water, by the waves.

The sea and the waves transport that sediment, which includes mud, sand, and stones.

It will then be deposited somewhere later on.

Let's pause here for a quick check for our understanding about what we know so far on sediments.

We'll stick with the same three pictures that we have been looking at.

Of these three types of sediments, which sediment is the largest in size? Have you decided? The largest sediment size here is, of course, stones.

Stones are much larger than tiny particles of sand or mud.

We've spoken about how the sediment is transported by water, by the sea.

The amount of sediment that can be carried at any time, depends on the power or the energy of the wave.

Calm seas that have very, very small waves have very little power.

They don't have much energy.

This means that calm waters can only transport very small sediments such as mud or sand.

Where does the energy come from then to enable the sea to carry bigger sediments? Bigger sediments can be carried when seas are stormy, when there is a wind that can provide more energy and create bigger waves.

Thanks to the increased energy in stormy seas, a much wider range of heavier and larger sediments can be transported.

Let's have another check of our understanding about that concept.

Here are the three types of sediment that we have been looking at, mud, sand, and stones.

And there are some incomplete sentences below.

I would like you to pause the video briefly whilst you complete the sentences.

Don't forget, you can always work with a geography buddy for some extra support.

All done? Good job.

I'm going to share some example answers with you.

I wonder if you had some of the same ideas.

The hardest sediment for a wave to move is the stones.

This is because stones are the heaviest sediment, so waves need lots of energy to transport and carry them.

Your sentences may not have been exactly the same as mine, but did you have the same idea about sediment size and energy of the wave? Let's move along now and think some more about how sediment is transported at the coast.

This photograph shows a wave breaking on the shore.

When we say that a wave breaks onto the shore, we're talking about the point at which the water meets the shoreline where it begins to wash up the beach.

Breaking waves bring water onto the beach.

When a wave breaks and washes up the beach, we call this the swash.

When the water then rushes back out to sea, we call this the backwash.

So we have swash and we have backwash.

You can see swash and backwash taking place at the shoreline in this photograph by clicking on the Watch button now.

Did you see the swash and backwash there? So when a wave breaks onto the shore and the swash moves up the beach, it's not just water that is in that swash.

Within the sea water, within the wave is any sediment that was being transported.

So any sediment that was in that water is dragged up the beach by the swash and possibly dragged back down the beach also by the back wash.

This is a coastal process, and we call this process longshore drift.

I'm going to take a few moments now to explain the process of longshore drift to you in a little more detail.

Waves approach the coast at an angle.

They don't approach the coast head on.

They're always at an angle, because of the winds found at the coast.

The waves hit the coast in the same direction as the prevailing winds.

The white arrow in this diagram shows the direction that the wave is approaching the coastline.

It is approaching the coastline at an angle.

The red arrows on the beach show you the direction of the swash.

The swash moves at the same angle as the wave breaks on the shore.

The swash moves in the same direction as the prevailing wind.

Sediment is caught up in that swash.

So the sediment is also transported along the beach.

The blue arrows represent the backwash.

Notice how the backwash goes straight out to sea.

The backwash is not at an angle like the swashes.

That's purely because of gravity.

The water washes straight back out to sea.

There is no prevailing wind having any effect on it.

The prevailing wind, which we have labelled here on the white arrows affects the swash, because the swash moves in the same direction as the wave and the prevailing wind.

Let's look at this process step by step and make sure that we really understand what's happening.

The swash, which is shown by the red arrows in this diagram, carries sediment up the beach at an angle due to the prevailing wind.

That's the first step in this process.

Now we're going to look at the blue arrows, which represent the backwash.

We've just seen how the swash and the prevailing wind affect the transportation of sediment.

The next step is for the backwash to carry any sediment back down towards the sea, and that happens because of gravity.

Now, this process will repeat and repeat itself along the coastline and it actually forms a zigzag movement.

Can you imagine joining up the red and the blue arrows on this diagram? You would have swash and backwash, swash and backwash, swash and backwash.

You would have a zigzag movement happening in the direction of that grey arrow on the diagram.

That process, that zigzag movement is what we call long longshore drift.

You're doing very well to take on board all of this new learning today.

Let's put our new knowledge to use by trying some more activities about longshore drift.

Starting with this check for understanding, which is a diagram of longshore drift just like the one that you've already been looking at today.

You can see here that the prevailing winds, the squash, and the backwash are labelled for you.

I would like you to add one more arrow to this diagram.

The arrow needs to show me the direction of longshore drift.

In other words, show me which direction the sediment is moving in.

Pause the video now whilst you decide the direction of longshore drift.

Ready? What you need to identify first of all is the direction of the prevailing wind because that's the direction that the swash moves in.

This then shows you the direction that long shore drift will be moving in.

And in this case, we can see how long shore drift is affected by the prevailing wind.

Well done.

Let's move to our next activity, which is another diagram about long shore drift.

There are less parts of this diagram that have been labelled for you, and that's because it's up to you to complete the diagram.

I would like to add the rest of the arrows for the swash and the backwash, and there's a label missing for those white arrows there.

I'd like you to complete that label as well.

When you've done that part of task A, come back, and I'll share the answers with you before we move on to the second part of the activity.

Pause the video now.

Ready? Let's have a look now at the answers together.

The white arrows are, of course, the prevailing wind.

Did you complete that label correctly? Well done.

And the arrows, we have arrows in the same direction as the prevailing wind for the swash, and we have straight arrows for the backwash.

Well done.

I did say there were two parts to this activity, so time for part two.

Here are four steps that are all involved in the process of longshore drift.

I would like you to put these four steps in the right order.

Pause the video now whilst you complete the activity, and remember, you can always work with a geography buddy for some extra support.

Finished? Great job.

Let's have a look at the correct order together now.

Okay, so the first step in long shore drift is the waves approaching the coast at an angle according to the prevailing wind.

After that, the swash will carry the sediment towards the beach at that same angle.

Then the backwash carries the sediment back down towards the sea because of gravity, and this process continues repeatedly along the coast in a zigzag movement.

That is longshore drift.

Well done.

You're doing really well so far today.

So let's keep going and move into the second part of our lesson now about processes of deposition and how they can change our coastlines.

At the coast, deposition happens when water or the waves, the sea loses energy.

When they lose their energy, it's harder to transport sediment, and instead of carrying the sediment, it is deposited.

Sediment that is deposited can then build up, and that buildup of sediment is what creates different land forms that we see at our coasts.

Some coastal landforms that are formed by deposition include beaches, bars, tombolo, and spits.

We're going to look at those features in some more detail.

The first one we are going to look at is beaches.

I'm sure you all have an idea of what a beach looks like, but have you ever wondered how that beach got there? How was it even formed in the first place? Beaches are formed by material that has been eroded at the coastline and then transported by the sea.

When waves have very little energy, they can no longer carry that sediment and they drop it.

They deposit the sediment.

This happens often when waves enter a sheltered bay or a cove.

That's because there is less wind in those areas.

This causes the energy to be lost and any sediment to be deposited, which creates a beach, just like this beach here at Lulworth Cove in Dorset.

This beach at Lulworth is a sandy beach.

Sandy beaches are usually found in bays or coves where there is shallow water and the waves have less energy.

But not all beaches are sandy.

Some beaches are made of shingle, which is a combination of small pebbles and stones.

Pebble beaches like this often form where there are lots of cliffs that are being eroded and they form because there is higher energy waves that are constantly attacking the cliffs and breaking up the sediment.

So based on what you've just discovered about depositional land forms, listen to this statement.

Sandy beaches will often form where there are cliffs being eroded.

Would you agree that that statement is true or false? Have a think and make your choice.

What do you think? This statement is, of course, false.

But how do we know it is false? What can we say to prove that we know it is false? I'm going to give you two possible sentences.

I'd like you to choose which one is the best reason why this is false.

A, because the water in bays is shallow and the waves have less energy, or B, because there are higher energy waves near cliffs.

Have a think and make your choice now.

Ready? The best explanation here is that water in bays is shallow and the waves have less energy.

That's where sandy beaches are formed.

Sandy beaches not formed where cliffs are being eroded.

Well done.

Good work.

Let's look at some of those other depositional land forms that we mentioned earlier.

I'm going to show you several here on a diagram.

The sediment patterns that are created when sediment is transported and deposited at the coast reflects the wave energy and the wind direction.

Landform that are created by deposition include tombolos, bars, and spits.

You can see those in the diagram, and I'm going to tell you more about them now.

Beginning with spits.

Spits are a deposition or landform.

Spits are created when sediment is carried by longshore drift, and then when the coastline changes direction, it causes the waves to lose energy, and that's what makes them deposit the sediments.

This continues over and over and over again, and the amount of deposited sediment gets larger and larger and larger, or longer and longer and longer, and this creates a spit.

This is a closeup of the spit that you can see in the diagram.

Behind this spit is something called a salt marsh.

This is because the area behind the spit is very, very sheltered.

In sheltered areas, there is very little energy and very little water movement.

This means that marshes and mud can build up in these areas.

Have you been listening carefully? Let's check with a quick question.

I would like you to put these three sentences in order to describe how a spit is formed.

Pause the video now and decide the order that you think is correct.

Ready? Okay, so first of all, the sediment is carried by long shore drift along a coastline, but when that coastline starts to change direction, it causes the wave to lose energy, and this means that it can't carry all that sediment anymore, so the transported material is deposited.

This will continue over a long period of time and then a spit will develop.

Okay, so let's look at another land form now.

This time we can see a bar in this diagram.

A bar is a type of spit, but what's happened here is a spit has grown from one piece of land to another.

So essentially, what we've got is two headlands that have been joined by the bar between them.

This cuts off some water behind the bar and that area of water that has been cut off is called a lagoon.

And the next landform we are looking at is a tombolo.

Like a bar, a tombolo is another type of spit, and it joins two pieces of land, but in this case, it connects the mainland to a smaller island.

Rather than joining two pieces of the mainland together, it connects an island to a mainland.

So now you've heard all about those depositional land forms. Let's try some activities about them.

First of all, let's have a quick question to check our understanding at this point.

Which of these forms behind a bar? Is it a salt marsh, a spit, or a lagoon? Make your choice now.

Ready? It's a lagoon.

Salt marshes are found behind spits.

A lagoon is an area of water that is cut off behind a bar.

Here is task B for this lesson.

This is the same diagram that you saw earlier, but the labels are all missing.

You know what I would like you to do? I would like you to put the labels onto this diagram.

Use the word bank at the bottom of the screen to help you.

You can pause the video now while you complete the task, and then when you come back, I'll show you all of the answers so you can check your work.

Ready? Well done.

Let's go through the answers to this together now.

So first of all, we have a spit.

Then we have a salt marsh behind that spit.

We have a tombolo.

We have a bar.

And behind the bar, we have a lagoon.

Did you get all of those correct? Good job.

So let's complete task B now.

Part two of this task is about writing a geographical glossary.

A glossary is a bit like a dictionary, but it's where you can write a bit more detail about what something is.

I would like you to write a glossary definition for these land forms, a bar, a spit, a salt marsh, a beach, a tombolo, and a lagoon.

Something else you should remember though is that a glossary is always written in alphabetical order.

So make sure that you get those terms in the correct order.

Pause the video now whilst you write your glossary definitions.

All done? Good job.

I'm going to share my definitions with you now.

Your definitions may be similar to these.

So in alphabetical order.

The first feature is a bar.

A bar is formed when a spit grows across a bay joining two headlands.

Then beach, a beach is created when waves enter a sheltered bay or a cove, they lose their energy and they deposit their sediment.

Then we have lagoon.

When a bar cuts off the water behind from the open sea, it creates a lagoon.

Moving on now.

The next word will be salt marsh.

A salt marsh is that zone behind a spit where it's very, very sheltered.

The water movement there slows down enough so that even the finest materials like mud can be deposited, which creates the salt marshes.

Then we have a spit.

Spit is sediment that's been transported by longshore drift, when the waves meet a change in direction of the coastline, then they lose their energy and the material is deposited.

Our last word is tombolo, and this is formed when a spit connects the mainland to an island.

Did you put them all in the correct alphabetical order? Well done.

There was a lot of new learning in today's lesson and you have done so well to take it all on board.

This is a quick summary of what we now know about our changing coastline.

We know that the sea transports sediments like mud, sand, and stones, and that this sediment can create patterns of landform at the coast caused by erosion and deposition.

We know that calm seas can only transport the smallest particles of sediments, but stormy seas with stronger winds have a lot more energy, and that means that they can transport a very wide range of sediments.

Sediment patterns of depositional land forms at the coast reflects the wave energy and the wind direction.

We have learned how the process of longshore drift can cause deposition or features like beaches, spits, tombolos, and bars.

Thanks for listening today.

Thank you for working so well on those activities.

I can't wait to see you again for our next exciting geography lesson about our coastlines.

Bye for now.