Lesson video

Hello, I'm Ms. Roberts and welcome to today's geography lesson, which is a lesson from our unit all about what shapes life at the coast.

In today's lesson, we are going to be investigating specific types of land forms that we can see at the coast, and these are land forms that are all formed by deposition, depositional coastal land forms. By the end of the lesson today, you will be able to explain processes that are involved in deposition and describe the types of coastal land forms that these processes create.

Let's begin by looking at some key words for this lesson.

These words you will hear a lot today, and I would like you to be able to use these words confidently when you are describing depositional land forms. The first of our keywords has to be deposition.

Deposition happens when material such as sand, mud, rocks, or any other material that's being carried by water, in this case by waves, is dropped.

So when the load that is being carried is dropped, it is deposited, that's deposition.

The second key word for today is another process, and that's transportation.

Transportation is the process of that material being moved by a wave or by water at the coast.

The next key word is swash.

Swash is when a wave breaks on the shore and the water rushes up the beach.

That water that we see rushing up the beach when a wave breaks is called the swash.

After a wave has rushed up the beach in the swash, it then retreats straight back to the water and that is the backwash.

So we have swash, which is a wave rushing up the beach, and backwash, which is the water going back down to the sea.

Our final key word for today is sediment.

Now sediment is material, it's natural material that's been moved by water or by air, and it's settled in another place, that is the sediment that's there.

Okay, so during this lesson we're gonna have two parts.

The first part is about how deposition shapes our coastline, and then the second part is about depositional land forms. So what types of coastal land forms are created by deposition? Let's get started now and think in some more detail about deposition itself.

Deposition is something at the coast that happens when waves lose energy.

So the waves have been moving and they have been transporting material that is held within them and that's the load.

If the wave loses its energy, it can't carry the load anymore.

It needs a lot of energy to keep carrying its load.

So this can happen when a wave reaches a very sheltered area, for example, like in a bay, and when that energy is lost, the material that was being carried is dropped 'cause the wave can't carry it anymore, so it's dropped there at that location.

That could mean that sand or mud or rocks or anything else is dropped at the coast.

So this includes other types of debris that are not natural.

We know that there is a major problem of plastics, microplastics, and litter in our season oceans, and quite often we see this washed up on our shorelines and beaches.

You can actually see a little of this material.

It looks like some netting is caught up there in the material that's being deposited on the seashore.

When sediment, like sand or shingle, is deposited at the coast, it can create land forms like beaches.

Yes, a beach in itself is a land form.

One of the main ways that material is transported and then deposit it along our coastlines is through a process that we call longshore drift.

Now I'm going to explain some more about longshore drift in a moment, but before I do that, let's just pause for a very quick check and see if you can answer this question.

I would like you to identify which two sentences here about deposition are true.

A, deposition only happens in bays, B, waves can deposit sediment and other debris at the coast, C, deposition happens when waves have lots of energy, D, deposition happens when waves lose energy.

Pause the video if you want to and choose which two sentences are true.

Okay, have you decided? Great, the first true sentence is B, waves can deposit sediment and other debris at the coast, and the next true full sentence is D, deposition happens when waves lose energy.

It's not when waves have lots of energy, 'cause when they have lots of energy, they can carry all that heavy load and keep hold of that sediment that they have.

When they lose energy, that's when deposition happens.

Okay, so I mentioned something just before called longshore drift.

Let's discover some more about that process now.

Longshore drift happens when the waves have approached the coast at an angle, and that's because of the prevailing wind.

Prevailing wind is the wind that a location experiences most often, what direction is that wind coming from? Yes, wind can come from many different directions, especially if it's a stormy wintry day, but any location usually has a prevailing wind which comes from one direction and that's the one that happens most.

If you look at this diagram here of a beach, you can see the white arrows at the bottom and they indicate the direction of the prevailing wind in this location.

You can see that the arrows are not heading directly to the beach, they are at an angle to the beach.

That angle is created by the direction of the prevailing wind.

Sediment that is brought up the beach by the wave is then transported along the coastline.

Let's see how that happens.

It happens when the swash, so that's the waves moving up the beach, moves the sediment along at the same angle of the prevailing wind.

There's the swash indicated by the red arrows, the swash is the wave moving up the beach, and we have that happening in the same direction at the same angle as the prevailing wind.

Look at the red and white arrows on the diagram.

Notice how they are in the same direction.

Swash and the prevailing wind are at the same angle.

Before we move on to the next stage of this, let's just check where we are right now with our knowledge about swash.

Can you tell me if this is true or false? Swash carries sediment up the beach.

What do you think? That is, of course, true.

The swash is when a wave breaks onto the shore, when it meets the shore, and washes up the beach.

It happens at the same angle as the prevailing wind.

Well done, let's see what happens next.

After the swash has moved the sediment up the beach, backwash then moves water back down the beach towards the sea.

As it does so, that water continues to take the sediment with it.

This is indicated by the arrows in the diagram.

You can see we have the prevailing wind, we have the swash coming in at the same angle as the prevailing wind, and then gravity takes the swash straight back out to sea, and that is the back wash.

Sediment moves with the swash and the backwash along the beach, following the pattern of the arrows in this diagram.

This process keeps on happening, it repeats itself, and if you look closely now, you you should be able to see that this creates a zigzag pattern along the coast, with swash and backwash, swash and backwash, swash and backwash.

And whilst the swash and backwash is moving in and out along the shore, the sediment is moving with it.

That is longshore drift, and the direction in which the swash and backwash are moving is the direction that longshore drift is happening in.

This process is happening along much of the UK coastline.

Before we move on to an activity about these processes, let's quickly check our knowledge there about backwash.

Is this statement true or false? Backwash carries sediment up the beach.

What do you think? It's false, isn't it? And why is it false? It's false because the swash is when waves break onto the shore and wash up beach, the backwash is the flow of water due to gravity back toward the sea, well spotted.

So let's complete an activity together now about these processes.

I would like you to label A, B, C, and D in the diagram with the labels that are provided.

One of them is the direction of the prevailing wind, another is the direction of longshore drift, and then there is the swash and the back wash.

Add those labels to the correct place in the diagram.

Pause the video now whilst you complete the activity.

Okay, right, let's have a look at the correct places for these labels together, here is the diagram, and our first label, A, is the white arrows and they represent the incoming direction of the prevailing wind.

Then we have the swash, those red arrows there, which are the same angle, the same direction as the prevailing wind.

The black arrow at the top is showing us the direction in which longshore drift is happening, and that leaves us with the last set of arrows pointing straight back to the sea and they represent the backwash.

So this process of longshore drift is continuously happening and sediment is being transported along our coast and deposited through longshore drift.

So if longshore drift is continuously happening, what are the effects of that? What coastal land forms does deposition create? Let's find out in the second part of the lesson.

Take a look at this diagram of a coastline here.

This coastline shows us some common positional land forms. They are spits, bars and tombolos.

We're going to find out some more about these landform now.

First of all, let's look at spits.

Spits are very common land forms in the UK, and a spit happens as a result of longshore drift.

Longshore drift takes place and that's where sediment is carried along our coastline, we've just been learning about this.

When the waves meet something like a change in direction of the coastline, you can see here the coastline sort of turns a corner.

You can think of that as a change in direction of a coastline, but the longshore drift doesn't turn the corner with the coast.

The longshore drift carries on in the same direction.

So the transportation and the deposition of the sediment continues in the same direction, it doesn't change.

This means that the sediment starts to build up in that direction in the sea instead of along the coast.

Eventually, this will form a very long, narrow ridge made off the sand or shingle or whatever the sediment type is that was being transported and that long narrow ridge of land, it's called a spit.

You can see here that this spit is curved on the end, it looks a bit like a hook shape.

That hook has happened because when the spit has reached this far out to sea, there is a change in the direction of the prevailing wind and that's what causes the spit to then begin to curve because as we know, longshore drift happens in the same direction as the prevailing wind.

So if that changes, then the longshore drift changes too.

I've got a short activity for you now to check on your understanding of how spits are formed.

We have five stages of the formation of a spit listed here.

All I would like you to do is add the numbers one to five, starting with the first stage and five being the last stage.

Put the numbers in to show the formation of a spit.

Pause the video now whilst you complete this activity.

Ready? Let's see.

Did you get all of these in the correct place? We have longshore drift to begin with, which is sediment transported the longer beach.

This continues until there is a change in direction of the coastline, but then longshore drift will continue in the same direction.

Eventually, this leads to the buildup of sediment which forms a spit, and over time the spit can change into a hook shape, well done.

Now, you may have noticed that behind the spit in the diagram is an area of land that is labelled as a salt marsh.

Salt marshes often form behind spits.

That's because this is a sheltered area since the waves can't get past the spit.

So there's a huge loss of energy in this area.

It's so great that even the finest, lightest particles, like mud, can be deposited in these areas, and it's all salt water, so only salt tolerant plants can grow in salt marshes.

Now, you might remember earlier I mentioned two other depositional land forms called bars and tombolos.

I'm going to just show you what those are now before we reach another activity.

This diagram shows a bar.

A bar is a special type of spit that joins two headlands.

It forms by longshore drift just as a spit does, but in this case, the spit joins one headland to another.

The area of water behind a bar, which has been cut off from the sea, is called a lagoon.

This diagram is a tombolo.

It's another type of spit, but in this case, instead of two headlands being joined together, it's when the mainland is connected to an island, okay? So were you listening? Where do salt marshes often form? Are you shouting B, behind a spit? Well done, salt marshes form behind a spit because they're so sheltered that waves can't get past the spit and this lack of energy allows salty marshes to build up.

Here's your activity to bring this half of the lesson to a conclusion.

I would like you to label this diagram of deposition land forms. After you have labelled the diagram, I would then like you to complete boxes one to five with short sentences to describe how the spit and the salt marsh in this diagram were formed.

If you would like to draw small sketches, you could do that as well.

Pause the video now whilst you complete this activity.

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

Here are the labels for the deposition land forms. We have our spit and salt marsh on the left, and then I have added the labels for the tombolo, which connects the island, and the bar, which connects the two headlands.

The lagoon is that area of water behind the bar.

One of the Oak Academy children have shared their answers as an example for part two, and they have written the following.

"One, waves deposit sediment at the coast and longshore drift transports it.

Two, when the coast changes direction, transportation and deposition continues happening in the original direction.

Three, sediment, like sand or stones, builds up over time, creating a long, narrow ridge called a spit.

Four, the spit curves around into a hook shape when there's a change in the wind direction.

And five, salt marshes form behind spits.

That's where waves have low energy and only salt tolerant plants can grow there." What a great, thorough response.

I hope you manage to use lots of our key keywords in your responses as well.

Let's end by looking back at our new knowledge from today.

We now know that longshore drift is the movement of sediment across the beach, and that happens because of the swash and the backwash.

We know that longshore drift creates depositional land forms, such as spits, bars and tombolos.

We know that spits are long, narrow ridges and they're made from sand or shingle, which project from a coastline into the sea.

We know also that salt marshes can form behind spits because they are low energy zones, and we know that spits can curve into a hook shape if the prevailing wind direction changes.

I hope you have enjoyed finding out about these unique coastal land forms today, and join me again for the next lesson in this unit to find out more about our coasts.

Bye for now.