Lesson video

Hello and welcome.

My name is Ms. Harrison.

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

Today's lesson's called The Role of Geology at the Coast.

Grab everything you might need for today's lesson and let's begin our learning.

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

The keywords in today's lesson are rock type, geological structure, discordant coastline and concordant coastline.

Rock type.

This is the physical and chemical characteristics of rocks.

Geological structure.

This is the arrangement of rock layers and rock features.

Discordant coastline.

This is where rock layers, hard and soft, run perpendicular to the coastline.

Concordant coastline.

This is where rock layers, hard and soft, run parallel to the coastline.

Brilliant.

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

The first question we're going to explore in today's lesson is what are different rock types? Let's take a closer look at how different rock types are affected by erosion.

Erosion is the process where natural forces like waves wear down rock surfaces over time.

However, not all rocks erode at the same rate.

This is because each rock type has unique characteristics that make it more or less resistant to these erosional forces.

The key factor here is resistance, how strong a rock is when faced with continuous wave action through abrasion or even weathering.

Resistance depends on several characteristics such as hardness.

Some rocks like granite are extremely hard and can withstand intense wave action.

Density.

Rocks with dense structure like basalt are less likely to be worn away over time quickly.

Mineral composition.

Rocks containing tough minerals like quartz are more durable although rocks that are made up of softer materials like clay erode more easily.

Layering.

Sedimentary rocks often have lots of layers and they can be broken apart by wave action much easier.

This makes them more vulnerable.

On the screen, we've created a scale so you can see rock types that are less resistant going all the way to rock types that are more resistant.

Now, let's examine how different rock types are affected by coastal erosion.

Igneous rocks are formed from cool magma or larva and these are very resistant to erosion due to their dense mineral structure.

Metamorphic rocks.

These are created from existing rocks which are exposed to extreme heat and pressure and these rocks are highly resistant.

Sedimentary rocks.

These are formed from compressed sediments and are generally less resistant to erosion though some like limestone can be quite durable.

Glacial till is a type of unconsolidated sediment which is made up of various particle sizes deposited directly by glaciers.

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

As magma cools, it crystallises into solid rock with a dense mineral structure.

This makes rocks like granite and basalt more resistant to erosion.

On the screen is an example of what granite looks like.

The Giant's Causeway in Ireland is made up of basalt and it showcases how volcanic activity shapes coastlines.

This resistance helps maintain steep cliffs and rugged coastlines.

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

Over time, these sediments are cemented together.

Sedimentary rocks are generally less dense than igneous rocks.

Sedimentary rocks like shale are less resistant to erosion.

Let's now 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 this statement is true or false and press play when you're ready to continue.

Excellent.

This statement is false.

I would now like you to explain why this statement is false.

Pause the video here and press play when you're ready to check your answers.

Fantastic.

The reason why this statement is false is because 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.

Well done if you managed to explain that correctly.

Let's now talk about glacial till.

It's also known as boulder clay.

Glacial till is a unique type of sediment that is left behind by glaciers as they retreat to melt.

It's made up of a mixture of different size materials like large boulders, pebbles and rocks and sand and clay particles.

This mixture is called unconsolidated sediment meaning that it hasn't been compacted into solid rock.

Because it's loosely packed and not cemented together, glacial till is extremely weak and vulnerable to erosion.

When it's exposed to the coast, the sea can easily erode it often much faster than other types of rock.

Imagine waves crushing against a cliff made up of solid granite compared to one made up of glacial till.

The granite will barely be affected while the glacial till will rapidly break down causing the cliff to collapse more frequently.

This makes areas with glacial till especially prone to coastal erosion often leading to landslides and retreating coastlines.

Eventually, if it's buried and cemented over time, it will form sedimentary rock.

Let's test our knowledge.

True or false, boulder clay is a sedimentary rock.

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

Excellent.

This statement is false.

I would now like you to explain why this statement is false.

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

Fantastic.

The reason why this statement is false is because boulder clay is not a sedimentary rock.

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

Well done.

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

This makes the rocks very dense.

Marble is a metamorphic rock that is formed when igneous activity heats and melts limestone which is a sedimentary rock.

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

On the screen is a closeup of what marble looks like.

Let's test our knowledge.

What type of activity creates igneous rocks? Pause the video here whilst you decide and press play when you're ready to continue.

Excellent.

The answer is A.

Igneous rocks are made up from volcanic activity.

What is the difference between metamorphic and igneous rocks? Is it A, metamorphic rocks form from cooling magma while igneous rocks form from heat and pressure? Is it B, metamorphic rocks form from heat and pressure while igneous rocks form from cooling magma or lava or is it C, metamorphic rocks form underwater while igneous rocks form on land? Pause the video here whilst you decide and press play when you're ready to continue.

Well done.

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

Well done on this task.

I would now like you to complete the grid about the characteristics of different rock types.

We're focusing on igneous, metamorphic and sedimentary.

I would like you to explain how they form, how dense they are and provide an example of each of them.

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

Excellent, well done.

Let's check our answers.

Your answers should read like this.

Igneous rocks, how they formed, they are formed through volcanic activity when magma cools and solidifies.

They're extremely dense.

An example of this is granite and basalt.

Metamorphic rocks.

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

They have a really high density.

An example of this is marble.

Sedimentary rocks.

They are made up of buildup of compressing of layers of sediment.

They have a low density.

An example of this is shale.

Well done on this task.

You've done brilliantly.

Let's now investigate our final question of today's lesson.

How can geological structure influence coastlines? Geological structure refers to the arrangement of rock layers along a coastline which can influence its shape.

Coastal features are heavily influenced by the geological structure of the coastline.

Let's break down the two main ways.

Concordant coastlines.

Concordant coastlines have rock layers that run parallel to the coastline.

This often results in fewer dramatic landforms initially as the outer harder rock layer protects the softer rock behind it.

Discordant coastlines.

In this case, the rock layers run perpendicular to the coast leading to alternating bands of hard and soft rock.

This creates more varied landforms such as headlands and bays.

We'll soon see how these structures create distinctive landforms. A discordant coastline occurs when different layers of rock, hard and soft, run perpendicular to the coastline like you can see on the screen.

There are differing layers which are both exposed to the sea.

The softer rocks erode faster as they are less resistant to coastal erosion from waves.

This will create features such as bays like you can see in the screen.

The harder rock will erode much slower as it's more resistant to coastal erosion and this will form features like headlands.

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

I'm going to pause the video here whilst you try and identify where there's a hard rock, where there's a headland and with a softer rock where there's a bay.

Press play when you're ready to check your answer.

Excellent.

Let's see if you managed to label them correctly.

A headland is out in the corner where it juts out into sea and this is because it's made of harder rock so it's less likely to erode and the bay is made up of softer rock.

Well done if you managed to identify these.

Let's now 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 this statement is true or false and press play when you're ready to continue.

Excellent.

The answer is false.

I would now like you to explain why this statement is false.

Pause the video here and press play when you're ready to check your answer.

The reason why this is false is because discordant coastlines have layers of hard and soft rock running perpendicular to the coastline.

Well done.

What coastal erosion landforms will form along a discordant coastline? Is it A, just bays, B, just headlands or C, bays and headlands? Pause the video here whilst you attempt this task and press play when you're ready to check your answer.

Excellent.

The coastal erosional landforms that will form along discordant coastlines are C, bays and headlands.

Well done.

Concordant coastlines are where rock layers, hard and soft, run parallel to the coastline.

The outer hard rock layer protects softer rock layers behind it.

This leads to fewer erosional landforms because the harder rock is more resistant.

However, if there is a weakness in the outer layer of hard rock, erosion of this point will eventually cause the soft rock to become exposed.

The waves can then erode the soft rock behind the hard rock and a cove may be formed like you can see on the image on your screen.

Swanage Bay in Devon is a discordant coastline.

We can see that Swanage Bay has formed because there are less resistant rocks.

We could also see that headland is being formed because it's got more resistant rocks.

The Jurassic Coast is a concordant coastline.

We can identify that there's a cove that's being formed in hard Portland stone.

Let's now test our knowledge.

Which image shows a headland on a discordant coastline? Pause the video here and press play when you're ready to check your answer.

Excellent.

The image that shows a headland on a discordant coastline is A.

Well done.

Which of these coastal erosional landforms is most characteristic of a concordant coastline? Is it A, a headland, B, a cove or C, a bay? Pause the video here whilst you attempt this task and press play when you're ready to continue.

Fantastic.

The coastal erosion landform that is most characteristic of a concordant coastline is B, a cove.

I would now like you to complete this task.

I would like you to identify the landform in grid square 0582.

Remember, when we're looking at grid references, we go along the bottom of the grid reference to read the first number and then we go up the grid to read the second number.

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

Fantastic.

Before we check our answer, I want us to complete one more task.

I would like you to explain how headlands and bays are formed.

I've provided an image on the screen for you to help remind you of how headlands and bays are formed.

Sam has made a great point and said that bays and headlands are formed along discordant coastlines.

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

Excellent, let's check our answers.

For the first question, I asked you to identify the landform in grid square 0582.

The landform in that grid square is a headland.

Well done.

I then asked you to explain how headlands and bays are formed.

Your answer might include some of the following points.

Bays and the headlands are formed on discordant coastlines where layers of rock run at an angle at the shore.

The process starts when the sea begins to erode the coastline.

Softer rocks like clay or limestone erode more easily.

Harder rocks like granite are more resistant to erosion so they don't wear away as quickly.

Over time, the waves erode the softer rocks more creating a curved shape of the coastline called a bay.

The layers of hard rock on either side of the rock are not eroded as easily as they remain sticking out into the sea as headlands.

So bays and headlands result from the geological structure of discordant coastlines.

Well done, I hope you managed to include some of the following points.

The answer on the screen is great because it clearly explains in detail what happens on a discordant coastline and what a discordant coastline is.

It also uses geographical terms like geological structure, bays, headlands and discordant coastlines.

Well done on this task.

We've now come to the end of our lesson on The Role of Geology at the Coast and you've done brilliantly throughout this lesson but let's summarise what we learned in today's lesson.

Coastlines are constantly changing but the way they develop over time depends heavily on two key geological factors, the rock type, the kind of rock that makes up the coastline and geological structure, how these rocks are arranged in relation to the shoreline.

Let's start with rock type.

There are three main categories of rocks.

Igneous rocks.

These are formed from cooled magma or lava making them very hard and resistant to erosion.

An example of this is granite and basalts.

Sedimentary rocks.

These are formed from compressed layers of sediment.

These rocks can vary in hardness.

Shale and sandstone are common examples.

Metamorphic rocks.

These are rocks that have been transformed by heat and pressure making them dense and resistant.

Marble and slate are good examples of this.

Now, let's move on to geological structure.

This refers to how rock layers are positioned relative to the coastline.

There are two main types of geological structure that significantly influence the formation of coastal landforms, the first being concordant coastlines.

Here, rock layers run parallel to the shore.

The arrangement often results in fewer initial features but erosion of weak points can lead to the formation of coast.

Discordant coastline.

In contrast, rock layers run perpendicular to the coastline.

This leads to alternating bands of hard and soft rock being exposed to wave action forming headlands where the harder rock resists erosion and bays where the softer rock is worn away.

For example, Swanage Bay in Dorset is a perfect case study of a discordant coastline with alternating layers of hard and soft rock forming distinct headlands and bays.

Meanwhile, the Jurassic Coast demonstrates concordant structures with fewer prominent features until erosion breaches the harder outer layer rocks.

So by understanding both rock types and geological structure, we can explain why some coastlines have dramatic cliffs and headlands and while some others have more sheltered base and coves.

Well done for your learning in today's lesson.

You've done brilliantly.

I look forward to learning with you again very soon.