Lesson video

Hi, geographers.

My name's Ms. Hoggett, and I'm really excited that you're here to learn some geography with me today.

I'm sure if you try your best, you're going to be absolutely fantastic.

Don't worry too much if you haven't studied this topic before.

I'm here to help you every step of the way.

Today's lesson is titled limestone landscapes, and this sits within the unit rocks, weathering, and soil: Why is geology important? Our learning outcome for today is that I can identify the key features of limestone and describe different limestone landscapes.

To help us through today's lesson, we have a number of key terms that are going to be really useful to us.

Limestone, limestone pavement, grykes, clints, and solution.

Limestone is a hard sedimentary rock.

Limestone pavement is a flat, exposed area of limestone.

Grykes are deep cracks on the surface of limestone pavements.

Clints are exposed blocks of limestone.

And solution is a form of chemical weathering where rock is slowly dissolved by acidic water.

So limestone, limestone pavement, grykes, clints and solution are going to be really useful to us in today's lesson.

Today's lesson is split into three learning cycles, the formation and erosion of limestone, surface features: limestone pavements, and underground features: limestone caves.

We're going to start with our first learning cycle now, the formation and erosion of limestone.

Limestone is a type of sedimentary rock that is made mainly from calcium carbonate.

It often forms from the remains of tiny sea creatures, such as coral and shellfish that lived millions of years ago.

When these organisms died, their shells and skeletons settled on the seabed where they were compressed over time.

to form a solid rock.

In the UK, one of the most important type of limestone is carboniferous limestone.

This rock mostly formed between 363 and 325 million years ago during a time in Earth's history called the Carboniferous period.

Back then, Britain was much closer to the equator and covered by warm, shallow tropical seas.

These seas were full of marine life, which contributed to the buildup of limestone over millions of years.

Limestone is widely used in construction for buildings and roads.

It's also important in industry as it can be heated to produce lime, a key ingredient in cement.

Additionally, limestone landscapes create dramatic natural features, such as caves, sink holes, and limestone pavements, which attract tourists and support local economies.

Let's check your understanding of what we've learned so far.

So what type of rock is limestone? Is it A, igneous, B, metamorphic, or C, sedimentary? Pause the video and have a go at completing this question.

If you said C, sedimentary, that's absolutely spot on.

Well done, geographers.

Now, limestone usually forms in warm, shallow seas.

Tiny sea creatures die and their shells, which are made of calcium carbonate, fall to the bottom of the ocean.

Over millions of years, these shells pile up and form thick layers of sediment on the sea floor.

Over time, pressure from the layers above and minerals in the water help compact and cement the broken shells and sediment together to form limestone.

So we can see there that limestone forms in the same way to all other sedimentary rocks and is compressed and compacted over time.

Now, limestone contains bedding planes and joints.

As limestone is a sedimentary rock, it forms in layers over time.

As new layers of sediment build up on top of each other, they create natural weaknesses in the rock.

These weaknesses take two main forms. The first is bedding planes, which are horizontal cracks that separate the different layers of sediment.

And we have joints which are vertical cracks that form when the rock is put under pressure and fractures.

Now, the joints and bedding planes make it easy for water to pass through the rocks, therefore making it permeable.

We're now going check what you've learned so far, and I'd like you to provide the keyword for the feature of limestone that's being described.

The first is the horizontal cracks between layers of sediment in limestone, and the second is the vertical cracks in limestone.

So pause the video and have a think about the key terms that describe those key features of limestone.

Well done for giving that are really good go, geographers.

Let's check your answers.

So the horizontal cracks between layers of sediment in limestone are called bedding planes, and the vertical cracks in limestone are called joints.

Fantastic effort, well done.

Now, limestone is affected by solution, which is a type of chemical weathering.

This happens when acid in rainwater react with the calcium carbonate in the limestone, slowly dissolving the rock over time.

Now, this happens because rainwater is slightly acidic because it absorbs carbon dioxide from the atmosphere as it falls.

This creates a weak acid called carbonic acid.

And when this acidic water comes into contact with limestone, a chemical reaction occurs.

This reaction slowly dissolves the limestone and carries it away in solution, leading to changes in the landscape.

Let's check what you've learned so far.

So what type of weathering impacts limestone most commonly? Is it A, physical, B, chemical or C, biological? Pause the video and have a go at answering this question.

So let's check what you've got.

So the answer is chemical.

We know that chemical weathering highly impacts limestone, particularly solution.

Well done, team.

So we're now going have a go at practising everything we've learned in learning cycle one.

And I'd like you to summarise three key features of limestone for part one of this practise task.

And for part two, I'd like you to explain how and when the UK's carboniferous limestone was created.

You may use diagrams to help you if that's useful to you.

Pause the video and have a go at this practise task.

Well done for having a go at that geographers.

Let's check your answers and see what you've got.

So for part one, we needed to summarise three key features of limestone.

So firstly, it is made from calcium carbonate, or you could have said it was formed during the carboniferous period, or it contains horizontal blocks called bedding planes, or it has vertical cracks called joints.

Or lastly, you could have said limestone is susceptible to solution, a form of chemical weathering from acid rain.

So any of those would've been fine and you just needed three to successfully answer that question.

Well done.

For part two, we needed to explain how and when the UK's carboniferous limestone was created.

You could have included those diagrams if that was helpful to you.

But we could have said, "Limestone usually forms in warm, shallow seas.

Tiny sea creatures die and their shells, made of calcium carbonate, fall to the bottom of the ocean.

Over millions of years, the shells pile up and form thick layers of sediment on the sea floor.

And over time, pressure from the layers above and minerals in the water help compact and cement the broken shells and sediment together to form limestone.

Well done for giving that a really good go.

We're now ready to move on to learning cycle number two, surface features: limestone pavements.

Limestone pavements are large, flat expanses of exposed limestone rock.

They were formed during colder periods of the last Ice Age when massive glaciers moved across the landscape, scraping away the soil and loose rock that once covered the limestone beneath.

As a result, the solid limestone was left exposed to the elements.

Now, there are different processes that cause limestone payments to form.

The first is glacial erosion.

So during the last Ice Age, thick glaciers moved across limestone landscapes, stripping away the overlying soil and weaker rock layers.

This left behind a bare, flat surface of limestone.

Chemical weathering also played a really important part because after the ice melted, rainwater, which is slightly acidic, began seeping into natural cracks in the limestone, gradually dissolving the rock through a process called solution.

And then the widening of the cracks occurred because over thousands of years, the cracks, which we know to be called joints and bedding planes, became wider and deeper, creating distinctive patterns of what we call clints and grykes.

Now, clints and grykes are some of the main features of limestone pavements.

Grykes are deep cracks on the surface of limestone pavements and clints are exposed blocks of limestone.

True or false? Clints are deep cracks on the surface of limestone.

Pause the video and have a go at answering this question.

We know that grykes are deep cracks on the surface of limestone pavements, whereas clints are exposed blocks of limestone.

Good work, geographers.

Now, grykes and clints were formed due to chemical weathering of limestone.

Being a permeable rock, water was able to seep into the cracks of limestone once the top soil had been worn away.

The rainwater reacted with the limestone, dissolving the stone and enlarging the joints and bedding planes.

This separated the surface into raised blocks with deep cracks.

As the water runs over the surface of the clints, it makes them uneven, so they're continuing to evolve and reshape over time.

An example of a limestone pavement in the UK is the top of Malham Cove found in the Yorkshire Dales.

Sofia says, "Did you know that Harry and Hermione's camp site in "Harry Potter and the Deathly Hallows Part 1" was filmed at Malham Cove?" I didn't know that, Sofia.

Thank you.

Now, this isn't the only example of a limestone pavement in the UK.

There are many others as well.

They include Ingleborough in the Yorkshire Dales, another famous limestone pavement found near caves and sinkholes, and The Burren in Ireland, a vast limestone landscape with pavements stretching for miles.

And it's not just the fact that it featured in "Harry Potter and the Deathly Hallows Part 1" that makes them important.

Actually, limestone pavements help geologists understand past glacial activity and how landscapes evolve over time.

The deep grykes provide a unique micro habitat for plants that may not survive in open landscapes.

And they're also really important for tourism because many limestone pavements, such as Malham Cove, attract visitors who enjoy walking, photography and studying various different geographical landscapes.

So we're going check what you've learned in learning cycle two, and you're gonna to complete these two tasks for this practise task.

Number one, I'd like you to annotate the image of the limestone pavement at Malham Cove where the clints and grykes are.

And for part two, I would like you to explain how limestone pavements are formed.

Pause the video and have a go at completing this task.

Let's check your answers.

So for part one, we needed to annotate the image of the limestone pavement at Malham Cove with where the clints and grykes are.

So we could have annotated some of the ones I have on the screen, but there are plenty more you could have added on.

Well done.

And for part two, we had to explain how limestone pavements are formed.

So limestone pavements are formed through a combination of processes over thousands of years.

To start, thick layers of limestone were deposited in ancient marine environments.

These were then covered by soil, which was worn away by glaciers through erosion.

Once exposed, rainwater, which is slightly acidic due to dissolved carbon dioxide, began to chemically weather the limestone.

The weathering dissolved the limestone along its bedding planes and joints, deepening the cracks into grykes.

The remaining solid blocks of limestone left behind are called clints.

This whole process creates distinctive limestone pavements, such as Malham Cove in the UK.

Good work, geographers.

We're now ready to move on to our final learning cycle, underground features: limestone caves.

Now, limestone is a permeable rock, meaning that water can pass through it.

This is because limestone contains natural cracks called joints and bedding planes, which allow water to seep deep underground.

Over thousands of years, this process plays a crucial role in shaping limestone landscapes, creating unique features, both above and below the ground.

Over thousands or even millions of years, solution weathering and erosion create dramatic underground land forms, including swallow holes, which form when rainwater finds weaknesses in the rock and enlarges it.

Over time, the surface may collapse, creating a hole where the water disappears underground, but also caves and caverns.

As water continues to dissolve the limestone, small cracks expand into tunnels, which can grow into large caverns.

There are many famous limestone caves, such as the Cheddar Gorge in Somerset and the Gaping Gill in Yorkshire.

Now, as water drips from the top of the cavern, it evaporates and solid calcium carbonate is deposited.

Over time, the deposits grow into long, thin mineral formations called stalactites.

And as you can see, we've got stalactites at St Michael's Cave in Gibraltar in the image on the screen.

Now, some drops of water fall to the floor, splash and then evaporate.

This creates a more spread out deposit of calcium carbonate, which are stumpier than before.

And these are what we call stalagmites, so similar but slightly different.

Sometimes the stalagmites and stalactites grow together to form a pillar.

Let's check your understanding.

So as water drips from the top of the cavern, it evaporates and solid calcium carbonate is deposited.

What are these deposits called? Is it A, stalagmites, B, stalactites or C, swallow holes? Pause the video and have a go at answering that question.

Well done if you said B, stalactites.

That's absolutely spot on.

The Mendip Hills are a range of limestone hills located south of Bristol and Bath in Somerset in England.

They're an important upland limestone area known for their dramatic scenery, underground caves and rich history.

The Mendips are made primarily of carboniferous limestone, which formed around 350 million years ago when Britain was covered by warm, shallow tropical seas.

Over time, the remains of marine organisms settled on the seabed, compacting into solid rock.

The limestone was later uplifted by tectonic activity, forming the hills that we see today.

Like other limestone landscapes, the Mendip Hills are shaped by chemical weathering.

Rainwater, which is slightly acidic, dissolved the limestone, creating caves, sinkholes and dry valleys.

The area is also well known for its caste landscape where water drains underground rather than forming surface rivers.

Now, there are famous features on the Mendip Hills.

They include Cheddar Gorge, one of Britain's most famous limestone gorges with steep cliffs, underground caves, and the famous Cheddar Caves where Britain's oldest complete human skeleton, the Cheddar Man, was found.

There's also the Wookey Hole Caves, a large cave system formed by the underground River Axe, known for its spectacular rock formations.

There are also limestone pavements there, which are areas where glacial erosion has exposed the limestone, creating characteristic clints and grykes.

And there are finally, swallow holes and underground rivers where rainwater disappears into the limestone through cracks, reemerging at springs and further down the landscape.

The Mendip Hills is really important because it's home to a variety of rare plants and animals.

The deep grykes on limestone pavements provide sheltered habitats for ferns and mosses while the open grasslands support wild flowers and butterflies.

Parts of the Mendip Hills are also protected as an area of outstanding natural beauty, ensuring conservation efforts to protect that landscape.

In the Mendip Hills, limestone caves can be found such as Gough's Cave.

This formed over thousands of years as rainwater, made slightly acidic by absorbing carbon dioxide, seeped into the joints in the limestone.

Now, in the photo, you can see Aladdin's cave, a chamber inside Gough's Cave.

Now, chemical weathering dissolved the limestone here, creating large underground chambers and caves.

Over time, stalagmites and stalactites developed as dissolved minerals were deposited.

Gough's Cave is one of the most famous limestone caves in the UK.

The first 820 metres of the cave is open for public viewing, so you could go and visit it if you wanted to.

True or false? Limestone caves are carved out by rainwater falling from the sky.

Pause the video and have a go at answering this question.

Well done if you said false.

We know that limestone caves are formed when acidic water seeps into limestone joints and dissolves the rock over thousands of years.

If we're inside a cave, we can't have water falling from the sky above us.

So absolutely the water has to seep through the limestone.

So we're now going to practise what we've learned so far, and I'd like you to help me correct Alex's statement.

Now, Alex has made five mistakes when describing Gough's Cave and explaining how it formed.

Can you find them and correct them? So Alex originally says, "Gough's Cave in the Yorkshire Dales formed quickly as rainwater made, slightly acidic by absorbing oxygen, seeped into joints in the limestone.

This acidic water slowly dissolved the rock through a process called abrasion, enlarging the cracks to form underground passages and chambers.

Over time, the cave developed stunning features like stalactites and stalagfites, which formed as dissolved minerals in the water were deposited.

Today, Gough's Cave is one of the most famous limestone caves in the UK." I'd like you to now pause the video, have a go at finding where those five mistakes are, and then have a go at correcting them.

Good luck.

Let's check how you got on, geographers.

So we've identified the five mistakes.

We know that he said Yorkshire Dales is the location.

He's also said they formed quickly and that the water was made slightly acidic by absorbing oxygen.

He said that the water was dissolved through a process called abrasion, and he's also recognised that there were stalactites, but also said there were stalagfites.

So we now need to correct those.

And what Alex should have said was, "Gough's Cave in the Mendip Hills formed over thousands of years as rainwater, made slightly acidic by absorbing carbon dioxide, seeped into the joints in limestone.

This acidic water slowly dissolved the rock through a process called solution, enlarging the cracks to form underground passages and chambers.

Over time, the cave developed stunning features like stalactites and stalagmites, which formed as dissolved minerals in the water were deposited.

Today, Gough's Cave is one of the most famous limestone caves in the UK." Thank you for correcting Alex's answer.

You've done a fantastic job.

Now that brings us to the end of today's lesson looking at limestone landscapes.

So in summary, we know that limestone is a sedimentary rock made of calcium carbonate.

Grykes are deep cracks on the surface of limestone pavements formed by chemical weathering.

Clints are exposed blocks of limestone separated by grykes.

Limestone landscapes include limestone pavements, such as Malham Cove and limestone caves such as Gough's Cave and Cheddar Gorge.

You've been absolutely fantastic today, geographers, and you've done an excellent job.

I look forward to seeing you in our next lesson.