Hello, my name's Mrs. Niven and today, we're going to be talking about physical weathering and erosion as part of our unit on the carbon cycle and climate change.

What we do in today's lesson, you may have some experience of in your previous learning, but what we do today will help us to answer that big question of how can we explain changes that happen in the air, the oceans, and on land.

By the end of today's lesson, you should hopefully feel more confident being able to describe the differences between physical weathering and the erosion of rock and be able to provide examples of both.

Now, throughout the lesson I will refer to some keywords and these include weathering, expansion, freeze-thaw, and erosion.

Now the definitions for these keywords are provided here and you may wish to pause the video so that you can read through them or perhaps jot them down so you can refer to them later on in the lesson or later on in your learning.

So today's lesson is broken into three parts.

Firstly, we'll look at weathering in general before taking a closer look at physical weathering.

We'll then move on to look at erosion and how it's different to weathering.

So let's get started by looking at what we mean by the term weathering.

Now you may have noticed in some of your travels that rocks can be broken into smaller fragments and that process of breaking rocks into smaller pieces is known as weathering.

Now, weathering simply weakens and breaks apart a rock and it does this while the rock is in place.

So weathering does not move fragments from one location to another.

There are three types of weathering.

The first is called biological weathering and that occurs due to the action of plants and animals.

Now you'll be familiar with this, if you've ever seen a plant growing out of a crack in a rock, or if you've ever noticed perhaps weeds growing along the pavement.

You'll also be familiar with animals weathering rock if you've ever seen an animal burrow, for instance, for rabbits or a fox.

The second type is called chemical weathering, and this occurs due to the action of acid rain reacting with minerals in the rocks.

Now, it's important to recognise that rainwater is naturally acidic because of the reaction that occurs between carbon dioxide and water in the atmosphere.

Now that acidic nature of the rainwater can be altered due to polluting gases, also reacting with water in the atmosphere.

And you'll notice the action of chemical weathering when you look at statues most frequently because they tend to lose their features or become discoloured.

The last type of weathering is known as physical weathering, and that occurs due to the application of force.

And these come in the multiple different varieties.

For instance, an example might be wind that's blowing grains of sand across the rock, a bit like sandpaper be used or when water freezes, or when you have extreme temperature changes that occur for places like in the desert.

Now a key feature of weathering is that it occurs over a long period of time.

We have here two statues that are found on the western end of York Minster, so on the outside wall of York Minster.

Now the one on the left was installed in November 2022, and we can see all the features very clearly.

It's very clean stone, it hasn't discoloured in any way.

Whereas, if we look at the statue on the right, this was installed around about 550 to 600 years ago, and we can clearly see that pieces are missing, it's lost its definition and it doesn't have that same kind of colouring.

So what we can say then about weathering is that small forces can have a very large impact over time.

Okay, let's stop here for a quick check.

Which of these pictures shows physical weathering? Well done if you said A and D.

B is an example of biological weathering and C is not an example of weathering at all.

Well done if you got this correct guys, great start.

Okay, let's move on to our first task of today's lesson.

What I'd like you to do here is match the name of the type of weathering to its correct description and then to match each description to the most appropriate picture.

So you may wish to pause the video here so you can discuss your ideas with the people nearest you and then come back when you're ready to check your work.

Okay, let's see how you got on.

So biological weathering is caused by the action of plants and animals and the most appropriate picture then is the picture of the plant that is growing in the crack of the rock at the top.

Chemical weathering then is due to the reactions with minerals in the rock.

And the most appropriate picture was the bottom picture because it's lost that definition in the sculpture.

And then physical weathering then is due to the application of forces.

And the best one is the picture where it looks like wind has gone through this, almost looks like a cave of rock.

So very well done if you manage to get this correct.

For the next part of this task, I'd like you to look at this picture below and on it label two places where different examples of weathering are taking place.

And for each of the examples that you've chosen, I'd like you to describe what is happening.

So this I would definitely recommend you talk it over with the people nearest you and pause the video and come back when you're ready to check your answers.

Okay, let's see how you got on.

Well, one place that I found was actually the grass 'cause as the roots of the plants are growing, they can weaken rocks, which causes biological weathering.

Another location you might have found is where the snow is found.

So here we can see that the snow is caused by a change of temperature and that could actually cause physical weathering.

So very well done if you've got those correct.

Great job, guys.

Now that we're feeling more comfortable discussing what weathering actually is, let's take a closer look at physical weathering.

Now we'll all be familiar with the idea that water in its liquid state will flow and it will flow to fill the shape of where it's found.

So in the picture here we can see that water has filled an indentation in the earth forming a puddle.

You might be more familiar with water filling a glass or a mug.

Now if we were to zoom in on that water, we can see the individual water molecules in their liquid form that are randomly arranged and rather close together.

What's interesting though is that when liquid water freezes, so it changes from the liquid state to the solid state, the molecules have less kinetic energy and because of that, an attractive force can form very specifically, between these molecules and it holds those water molecules in a particular fixed position and that fixed position is actually further apart than how those molecules were arranged in their liquid state.

What this means then is that when water freezes expansion occurs, the attractive forces that form cause its volume to increase.

So the same amount of water molecules in its liquid form would actually take up a larger volume when it froze and changed into a solid form of ice.

Now, if liquid water is in an enclosed space when it freezes, its increasing volume could actually cause damage.

It's one of the reasons why if we have a bottle of water, you are highly recommended to not put that in the freezer because of the damage that could cause when that water then freezes and its volume increases, causing expansion.

Let's stop here for a quick check.

True or false, the volume of water decreases when it freezes.

Well done if you said false, but which of these statements best justifies your answer? Well done if you chose B, at lower temperatures forces between those water molecules, hold them in a particular position that's further apart.

Now, A is also a correct answer.

Water molecules will have less kinetic energy at lower temperatures, but that doesn't explain the volume of water difference that occurs when water freezes.

So B is the better answer.

Very well done if you manage to get those correct, guys, great job.

So if you're like me, you might be wondering, why do I care about water freezing and what's happening to those water molecules? Well, crucially, if you remember, it rains and liquid water can collect in a rock via its pores or the spaces between the grains or any cracks in that rock.

And if the temperature drops below zero degrees centigrade, the freezing point for water, that water will freeze.

And as the water changes then from liquid water into that solid ice, the volume that it occupies is going to increase, it's expanding.

Now that expansion then puts pressure on the rock and it weakens the rock around where that ice has formed.

Now, once that ice melts because the temperature then rises above zero degrees centigrade, that water can now sink deeper into the crack.

And if the temperature drops below that freezing point of zero degrees Celsius, again, that process is repeated.

Now, that repeated process of water filling in a crack, freezing and expanding, melting, filling in further in the crack, freezing, expanding that entire process is known as freeze-thaw.

Now, freeze-thaw, physical weathering occurs on an incredibly large scale, and that's because all it needs is three main things, rocks that have pores or cracks in them, water and a temperature change both below and above zero degrees Celsius for that water to freeze, melt and freeze, and melt again, that repeated process of melting and freezing is necessary.

Let's have a go now at the second task of today's lesson.

Firstly, I'd like you to match each keyword to the best description.

So pause the video and come back when you're ready to check your answers.

Okay, let's see how you got on.

So weathering is the weakening and breaking apart of rock in place.

And freeze-thaw is a process by which water seeps into the cracks, freezes and then expands.

But expansion then, is when the volume of a substance is increasing.

And the melting point then, is the temperature at which there's a change of state between a liquid and a solid.

So very well done if you manage to match those correctly.

Great job guys.

For the next part of this task, I'd like you to consider a syringe that's been filled with some water and we've popped a rubber cap on the end of that syringe to block it and then the syringe has been put into a freezer.

At room temperature, there's round about 7.

5 centimetres cubed of water in this syringe, but what will happen to its volume when it freezes? And what I'd like you to do with this is explain why you think this will happen.

So I'm looking for you to include a because clause in your answers.

Now, you may wish to discuss your ideas with the people around you, so please do pause this video, and come back when you're ready to check your work.

Okay, let's see how you got on.

So what do we think might happen to the volume of this water when we put the syringe into the freezer? Well, you should hopefully have said that the volume of water will increase when it freezes.

And this happens because when water freezes, the water molecules will slow down, but more importantly, a strong attractive force forms between those water molecules.

Now that's important because those attractive forces hold the water molecules in fixed particular positions which are further apart, making that solid water take up more space than that liquid water.

So well done if you manage to say that the volume of water will increase, but incredibly well done if you were able to explain why as well.

Great job, guys, that's a tricky one to answer.

Now for the last part of today's task, I want you to consider this rock.

Now, many rocks that we look at look like they have cracks, but this one has actually been split all the way through and some students are discussing how that rock actually split.

So what I'd like you to do is to read their statements on the next slide and then answer the questions.

Okay, I will go through the statements that these students have made in a moment, but what I want you to consider as we read them out is who do you think is correct about how that rock split and can you explain your answer? So again, we're looking for that because clause.

Now I should think that there must have been an earthquake to break the rock that much, whereas Jacob reckons that water in the rock expands when it freezes and pushes out the rock.

Sophia thinks that it must have been a very cold to freeze enough water to break that rock.

Whereas Sam reckons, water in the rock must have frozen many times to break it up the way it has been broken.

And Lucas thinks that all the rocks at the South Pole will be broken up because it's always very cold there.

So again, who do you think is correct about a rock that has split in multiple places all the way through and why? So you may wish to pause the video here so you can discuss your ideas with people nearest you and then come back to check your answer.

Okay, let's see how you got on.

So if you chose Sam or Jacob, you were absolutely correct about how this rock has split.

And the reason is because water can seep into those pores and small cracks within the rock, and as it freezes, the water expands pushing the rock from the inside weakening it.

So that's what Jacob was getting onto.

Sam meant about this taking place multiple times.

And that's really important because over many freeze-thaw cycles, that's how the rock is further weakened until it eventually becomes fully crumbly and cracks all the way through.

So very well done if you chose Sam or Jacob and incredibly well done if you manage to include that because clause.

Great work.

For this next part, I'd like you to consider what you might say to those people who were incorrect about why this rock has broken all the way through to help them understand the reasons why.

So pause the video and come back when you're ready to check your answers.

Okay, let's see how you got on.

Now, Aisha said that there must have been an earthquake to occur in order to break the rock as much as this one has been, but what you could say to her is that an earthquake is not the only process that can break apart a rock.

Rocks can be cracked without there being a major event.

And a really good example of that is the freeze-thaw weathering and a reminder that small forces over a long period of time can have a very large impact.

Now, Sophia had mentioned that it needed to be very cold for it to freeze enough water to break that rock, and this is a very subtle indication that she thinks the water's only frozen once.

And we need to remind Sophia that actually repeated cycles of freeze-thaw are needed in order to break a rock a little bit.

More water has to enter those pores and cracks during each thaw, and then each freeze causes a little bit larger expansion until that rock is cracked completely through.

So the key here about freeze thaw is that it isn't just one cycle, but multiple cycles.

So again, those small changes over a long period of time having a large impact.

Now Lucas then suggested that all the rocks in the South Pole would be broken up because it's always very cold there.

Well, what we could say to him is that actually rock in the Antarctic is permanently frozen.

So because the temperature isn't rising above zero degrees Celsius, in order for that water to melt, it wouldn't be able to undergo freeze-thaw damage.

It's very well done if you managed to get any of those correct or on the same ideas.

Great job, guys, that was a really tricky question.

Now that we're feeling more comfortable talking about what weathering is and specifically physical weathering, let's look at how it's different to this idea of erosion.

Fragments of rock can be moved naturally and this process is called erosion.

Now because erosion can sometimes cause rock fragments to break apart further, erosion and weathering are often mistaken for each other.

Now, weathering, if you remember, is the breakdown of rock into fragments, but in place they're not moving.

Erosion is the movement of fragments of rocks by moving processes.

Now there are six main erosion processes, and you'll be familiar with these as I go through them.

The first one I wanna look at is gravity.

Essentially rock fragments are transported from higher ground to lower ground purely by falling, okay? So a landslide is a really good example of this.

Rain is another example.

When it splashes down on land, specifically land that's on an incline, it can dislodge some of those rock fragments and then carry them away.

Another example is wind.

When wind is blowing, it can carry some of that freed material, usually quite small material things like sand and dust from one location to another.

Another erosion process involves rivers and streams. Flowing water can carry fragments various distances from the source of where that rock fragment was formed in the first place due to weathering.

Another example is oceans.

Whenever those waves or the tides are moving onto the coastlines, they can loosen material and move them from different levels along that coastline.

And finally, glaciers.

We may have less experience of glaciers in this country, however, we can still see the effects of them because the enormous size of these ice sheets and the weight of them can erode larger pieces of rock fragments, say boulder size rather than those fine pieces like the sand and dust that wind can erode.

Now during these erosion processes, rock fragments could sometimes be broken down even further than the size they were when they were originally weathered into that fragment.

And that's because when they're being moved from one location to the other, they don't stay in a line or arrange in a particular way.

They'll be moving along and hitting each other.

And when that happens, those rock fragments can break off those sharp edges, creating more rounded and smoother fragments.

Let's stop here for a quick check.

Which of these pictures show an example of erosion? Well done if you chose A, B, C and E.

Pictures, D and F are not showing erosion, they are showing examples of weathering.

Very well done if you manage to get those correct guys, fantastic work.

Now, a feature of erosion is that it can result in changing land forms and that can happen in mere seconds because of landslides or over millions of years.

Now when glaciers melt or retreat, the changes that occur because of that erosion are more easily seen.

For instance, you could get depressions or the formations of valleys.

Now remember that rivers and streams can transport rock fragments and material different distances, but that's gonna depend on multiple factors.

The thing is though, erosion by moving water can actually lead to the deposition or the dropping of those materials in various locations, and that can change the landscape.

A good example of this is a straight river, over time due to this erosion could turn into a meandering river that snakes its way through where that straight river was before.

Let's stop here for another quick check.

Mount Roraima is the highest tabletop mountain in the world.

Now it can be found in South America and is 2,810 metres high.

But how much do you think Mount Roraima has eroded in height over the last 1 million years? Well done if you said D.

Now that was a tricky question to answer, but for a bit of context, if we think that a loss of just one millimetre of height over 100 years, that's actually the loss of 10 metres in height over 1 million years.

So really tiny changes, but an incredibly long time can impact to large changes overall.

So that occurs with both weathering and erosion.

Okay, let's move on to the last task of today's lesson.

For this first part, I'd like you to imagine what it might be like to walk at the bottom of a cliff.

It can be quite dangerous because sometimes loose rocks can fall down and these could be quite large.

What I'd like you to do is to use the words either weathering or erosion to fill in the gaps below to explain how both of those processes make it dangerous to walk at the bottom of a cliff.

So pause the video and come back when you're ready to check your answers.

Okay, let's see how you did.

As I go through the answers, please do tick the words if you got them in the correct place, fix them if you got it wrong and definitely fill in any blanks you may have left because this task is a really good example of how to use these two words that are easily confused in the correct way.

So rock on a cliff face is worn away by erosion.

Roots of plants can grow into the rock and they cause weathering and weaken the rock.

Water can soak into pours and cracks in the rock, and if this water freezes and thaws many times, it can weaken the rock and make it crack more.

This is an example of weathering.

Sometimes big pieces of rock fall off a cliff.

In a storm, wind and rain can dislodge rock that is loose, this is erosion.

At other times, wind can cause erosion by blowing tiny particles of sand and grit at the surface of the rock.

So very well done if you manage to get all the words in the correct places because as I said, these two words are very easy to confuse and I'm incredibly impressed if you've managed to use them correctly here.

Great, great job guys.

For this next part, I'd like you to consider this picture of Robin Hood's Bay in North Yorkshire, and I'd like you to label two different examples of erosion that are taking place here.

For each example, please do describe what is happening now.

You may wish to discuss your ideas with the people nearest you.

So pause the video here and come back when you're ready to check your answers.

Okay, let's see how you got on.

Now one example you may have noticed is that waves could crash into the rock moving those rock fragments from the cliff along the beach.

You may have also said about tides.

Now they wouldn't crash into the rock, but they would be able to pick up rock from the beach and move it to another location along the beach.

Wind might have been another example where it blows sand and grit.

So those smaller pieces from the rock face and gravity could also have been another example of erosion because we can see that land has slipped from a higher location to a lower location onto the beach.

So very well done if you managed to get at least two of those and incredibly well done if you were describing what happened as well.

Good, good job, guys.

Okay, moving on to the last part of this task, but staying at the beach.

Pebbles are formed by both weathering and erosion.

What I'd like you to do is to put the statements provided into an order that will describe how pebbles are formed on a beach at the bottom of a cliff.

Now the first statement has been provided for you and beware, some of the statements are not needed.

I highly recommend you discuss your ideas with some other people.

So definitely pause the video and come back when you're ready to check your answers.

Okay, let's see how you got on.

Now, I gave you the first statement, which was water soaked into the pores and cracks in the rock.

The second statement then should be the one directly below the water froze and thawed many times, and the rock then becomes crumbly.

Now, waves then can crash into the bottom of the cliff and pieces of the rock then would break off.

Waves, also crash onto the beach then and move those rocks over the beach.

That movement then causes the pieces of rocks to knock into each other and sharp corners are knocked off it.

So that's the creation of pebbles along a beach at the bottom of a cliff.

Then the other three statements are the ones that you didn't need.

Now that was a particularly difficult task to do, so incredibly well done if one, you managed to choose the correct statements to use, and two, if you managed to put them into the correct order.

I am mightily impressed, guys, fantastic work.

Wow, we have gone through a lot of information in today's lesson, so let's take a moment to summarise what we've done.

Well, we've learned that weathering is the slow breakdown of rocks on earth's surface, and it happens when rocks are in place so there's stationary and not moving.

Now, rocks can be weathered then biologically by plants and animals chemically by rainwater or physically by forces applied to those rocks.

Erosion then is the process that removes material from where bedrock has been broken down or weathered and moves it to another location.

Rock then can be eroded by many different processes.

Wind, rain, flowing streams and rivers.

The oceans, ice flows like glaciers and gravity.

But ultimately, both of these processes, weathering and erosion, can cause very small changes that over time can leave a very large impact on Earth's surface.

I've had a great time learning with you today.

I hope you had a good time learning with me, and I hope to see you again soon.

Bye for now.