Lesson video

Hello and welcome.

My name is Ms. Harrison.

I'm really looking forward to learning with you today.

Today's lesson is called The Role of Geology in Coastal Erosion.

By the end of today's lesson, you'll be able to understand how geology can affect the development of coastal landforms. Before we can begin our learning, we need to define the keywords that we'll be using throughout this lesson.

Today's keywords are erosion, resistant, retreat, and geological structure.

Erosion.

This is the wearing away of rocks along the coastline.

Resistant.

This refers to rocks that are less likely to be eroded or weathered.

Retreat.

This is the process where cliffs move backward over time as erosion wears away the base of the cliff.

Geological structure.

This refers to the arrangement of rock structures.

Fantastic.

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

Our first learning outcome in today's lesson is, what are the different rock types? Different types of rock will be affected by erosion in different ways.

This is influenced by how resistant the rock type is.

Remember, resistant refers to rocks that are less likely to be eroded or weathered.

The rock's characteristics will determine how resistant they are.

Rocks are categorised as either usually hard or soft rocks.

Below is a scale where we have shown different types of rocks starting from most soft all the way to most hard.

In this diagram, the most soft type of rock is chalk, and the most hard type of rock is gneiss.

There are four main rock types, igneous, metamorphic, and sedimentary.

Igneous and metamorphic are usually hard rocks.

Sedimentary is usually a softer rock.

Glacial till is a form of unconsolidated material, which is formed from sedimentary rock deposits.

Igneous rocks are formed by the cooling and solidification of molten magma or lava that results from volcanic activity.

As the magma cools, it crystallises into solid rock, and therefore it has a dense mineral structure.

This makes rocks like granite, which is the example in the image, and basalt more resistant to erosion.

The Giant's Causeway is a great example of an igneous rock.

This is a type of basalt, which makes it more resistant to erosion and weathering.

Sedimentary rocks form from the buildup and compression of sediments, such as sand, silts, and clay, which are deposited in layers.

Over time, these sediments are cemented together through pressure.

Because of the way they're formed, sedimentary rocks are generally less dense than igneous rocks.

Examples of sedimentary rock are things like sandstone and shale.

And they're less resistant to erosion.

Let's test our knowledge.

True or false, sedimentary rocks are generally more resistant to coastal erosion than igneous rocks.

Pause the video here whilst you decide your answer, and press play to continue.

Fantastic.

The answer is false.

Are you able to explain why this answer is false? Pause the video here and press play to continue.

Great work.

Sedimentary rocks are usually softer than igneous rocks and so are less resistant to coastal erosion.

Igneous rocks are usually hard rocks, which are more resistant to coastal erosion.

Glacial till is a mixture of different-sized rocks, sand and soil that a glacier leaves behind as it retreats and melts.

Boulder clay, a type of glacial till, is made up of mostly clay.

Glacial till is made up of sedimentary deposits that can eventually form a sedimentary rock if the correct geological processes mean it gets compacted, cemented, and enough pressure placed on it over time.

Let's test our knowledge again.

True or false, boulder clay is an example of glacial till.

This is a sedimentary rock.

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

Excellent work.

The answer is false.

Are you able to explain why this statement is false? Pause the video here whilst you write your answer, and press play when you're ready to continue.

Fantastic.

The reason why boulder clay is not a sedimentary rock is because boulder clay is an example of glacial till, and glacial till is a sedimentary deposit, but it is not yet a sedimentary rock.

It'll only become a sedimentary rock once it has been compacted and cemented over a long period of time.

Metamorphic rocks are another type of rock.

They form from existing rocks that are exposed to high heat and pressure.

And because of this, it makes these rocks very dense.

Marble is an example of a metamorphic rock.

And this is formed when igneous activity heats and melts limestone, which is a sedimentary rock.

Metamorphic rocks are more resistant to erosion due to their crystallised minerals.

Let's test our knowledge.

What type of activity creates igneous rocks? Fantastic.

The answer is a.

Remember, igneous rocks are formed by the cooling and solidification of molten magma or lava that results from volcanic activity.

Well done.

What is the difference then between metamorphic and igneous rocks? Select your answer from the three options below and press play when you're ready to continue.

Excellent.

The difference between metamorphic and igneous rocks is b, metamorphic rocks form from heat and pressure while igneous rocks form from calling magma or lava.

I would now like you to complete this grid about the characteristics of the different rock types, igneous, metamorphic, and sedimentary.

I would like you to research how each of them form, what their densities are, and some examples of them.

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

Excellent.

Hopefully you've been able to complete the grid about the characteristics of different rock types.

Your answers could include some of the points below.

For igneous rock, we can say that it's formed through volcanic activity when magma cools and solidifies.

And it has a high density.

And some examples are granite and basalt.

Metamorphic rocks are formed when existing rocks are exposed to heat and pressure.

And they also have a high density.

An example of metamorphic rocks is marble.

Sedimentary rocks are formed by a buildup of compressing of layers of sediment.

They, on the other hand, have a low density.

Examples of sedimentary rock include sandstone and shale.

Well done.

Excellent work.

The next learning outcome that we're going to be learning about is how geological structures influence coastlines.

Geological structure refers to the arrangement of rock layers along a coastline, and this can influence its shape.

The type of geological structure will influence the type of erosional landforms found along the coastline.

There are two types of geological structures found along coastlines.

There are discordant coastlines and concordant coastlines.

A discordant coastline occurs when different layers of rocks, hard and soft rocks, run perpendicular to the coastline, as you can see in the image on the screen.

The softer rock is going to erode much faster as they're less resistant to erosion from waves.

This creates features such as bays, labelled in the diagram.

The harder rocks will erode much slower as they're more resistant to coastal erosion.

This forms features such as headlands, which jut out into the sea.

Swanage Bay in Dorset is an example of a discordant coastline.

I wonder, are you able to spot where the bay and the headlands are? Pause the video here whilst you try and find them, and press play when you're ready to continue.

Fantastic.

The headlands are easily spotted as this is the hard rock which has undergone less erosion.

And the bay is where the softer rock is because this has undergone a lot more erosion.

Let's test our knowledge.

True or false, discordant coastlines only have layers of hard rock running perpendicular to the coastline.

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

Fantastic.

The answer is false.

Are you able to explain why? Pause the video here and press play when you're ready to continue.

Fantastic.

Discordant coastlines have layers of hard and soft rock running perpendicular to the coastline.

What erosional landforms will form along a discordant coastline? Is it a, bays and headstones, b, beaches and headlands, or c, bays and headlands? Pause the video here whilst you decide, and press play when you're ready to continue.

Excellent.

The answer is bays and headlands are the erosional landforms found along discordant coastlines.

Concordant coastlines are another type of geological structure.

And they're where rock layers, both hard and soft, run parallel to the coastline, as you can see in the image on the screen.

The outer hard rock layer protects the soft rock layers behind.

This means that there are going to be fewer erosional landforms found along concordant coastlines.

If there is a weakness in the outer layer of harder rock, erosion of this point will eventually cause the softer rock to become exposed.

Over time, the waves will erode more and more of the soft rock behind the hard rock, making a circular shape.

This then creates a cove, which is a small sheltered bay surrounded by cliffs of the harder rock that didn't erode as quickly, as you can see in the image on the screen.

The image on the screen is a map of the geology of Dorset.

Dorset has two different types of coastlines.

It has the Jurassic Coast, which is found along a concordant coastline.

And it also has a discordant coastline, where Swanage Bay is found.

I wonder, are you able to identify where these coastlines are? Pause the video here and press play to continue.

Excellent work.

I've clearly labelled where the discordant coastline is and the concordant coastline is.

We should have been able to spot where the discordant coastline is because we should see the headlands that are jutting out into the sea.

And the headlands have been formed by more resistant chalk rock.

We're also able to spot where Swanage Bay is because there's been a lot of erosion formed.

And that is because it is made up of sandstone.

We're also able to identify where the concordant coastline is because there are far less erosional features there, but we are able to spot a cove which has been formed from hard Portland stone.

Excellent work.

Now, I would like you to find out which image below shows a cove on a concordant coastline.

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

Fantastic.

The answer to this question is b.

B is the image that shows a cove on a concordant coastline.

What erosional landform will form along a concordant coastline? Is it a, headlands, b, coves, or c, bays? Pause the video here and press play when you're ready to continue.

Fantastic.

The coastal erosional landforms that will be found along a concordant coastline are b, coves.

Well done.

I would now like you to use the words below to complete the text correctly to explain the formation of discordant coastlines.

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

Excellent work.

You should have been able to use the words to complete the text correctly.

Your text should read, a discordant coastline is created when layers of different rocks are placed perpendicular to the coast.

These layers include both hard and soft rocks.

The waves hit the coastline, causing the softer rock to wear away faster than the harder rock.

The softer rocks wear away faster and create bays.

This leaves the harder rocks sticking out in the sea to form headlands.

An example of a discordant coastline is found at Swanage Bay, Dorset, England.

Well done.

Our final learning outcome for today's lesson is how a distinctive land form is created.

At discordant coastlines, hardened soft rocks run perpendicular to the coastline, and we have features like bays and headlands.

The headlands at discordant coastlines are continuously exposed to weathering and erosional processes.

Wave action will attack a weakness in the headland such as a fault and will begin to create a crack.

Over time, erosional processes will continue to widen this crack and create a cave.

Over time, the erosional process will continue to erode the cave.

And eventually, it will cause a breakthrough in the headland, and this will create an arch.

An example of an arch is Durdle Door in Dorset, which we can see on the screen.

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

Eventually, the arch will no longer be able to hold itself and will collapse.

This will leave a stack, an isolated column of rock.

Over time, the stack will be continuously eroded at its base by wave action, making it unstable.

Eventually, the stack collapses, and it leaves a shorter and often submerged feature called a stump.

Let's test our knowledge.

What is the correct order in which a stump is formed? Pause the video here and press play when you're ready to continue.

Fantastic.

The correct answer is b.

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

True or false, stumps are formed along concordant coastlines.

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

Excellent.

The correct answer is false.

Are you able to explain why? Pause the video here and press play when you're ready to continue.

Excellent.

Stumps are formed along discordant coastlines where headlands and bays are formed.

They're a result of erosion of a headland over a long period of time.

Another erosional landform is a wave-cut notch.

A wave-cut notch is an indentation at the base of a cliff created by waves and erosional processes.

Over time, the repeated wave action erodes a notch into the cliff.

And over time, this becomes deeper and wider.

As the wave-cut notch becomes deeper, the rock above it is left unsupported, and it's unable to hold its own weight.

So eventually the rock will collapse into the sea.

This process is repeated over time.

It causes the cliff to retreat inland.

This then leaves an extensive wave-cut platform behind.

What causes a wave-cut notch to form at the base of a cliff? Is it a, the sun heating the rock, b, waves eroding the base of the cliff, or c, plants growing on the cliff? Pause the video here and press play when you're ready to continue.

Fantastic.

The correct answer is b, waves eroding the base of the cliff.

True or false, a wave-cut platform results from cliff retreat.

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

Excellent.

The answer is true.

Are you able to explain why? Pause the video here and press play when you're ready to continue.

Brilliant.

As a wave-cut notch grows larger, the cliff above eventually collapses as it can't hold its own weight.

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

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

Pause the video here whilst you sort these statements, and press play when you're ready to continue.

Excellent work.

You should have been able to sort these statements into the correct formation just like below.

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

Pause the video here whilst you identify them, and press play to continue.

Excellent work.

You should have been able to correctly identify the crack, the cave, the arch, the stack, and the stump.

Well done.

Well done.

We've come to the end of our learning today, and you've done brilliantly in learning about the role of geology in coastal erosion.

But before we end this lesson, let's summarise everything that we've learned today.

We know that there are different types of rocks.

We have igneous, metamorphic, sedimentary, and glacial till.

And each of these rocks will be affected by erosion in different ways.

This is dependent on their rock type.

Rocks will either be more or less resistant to erosion.

Geological structure will vary along coastlines.

We have discordant coastlines, which have bands of more and less resistant rocks that run perpendicular to the coastline, and they create landforms like bays and headlands.

We also have concordant coastlines, which have bands of more and less resistant rocks, but these run parallel to the coastline.

There are a few erosional landforms found here apart from coves.

Different erosion land forms found along discordant coastlines are things like caves, arches, stacks, stumps, wave-cut notches, and platforms. Well done.

You've done brilliantly in today's lesson.

Thank you for learning with me, and I look forward to learning with you again soon.