Hello, my name's Mrs. Harking.

Today's lesson is "Volcanic hazards," taken from the unit "Tectonic hazards: why is Earth restless?" Today's lesson does come with some guidance.

We will be looking at some potentially upsetting content.

So there will be one image which we show of plaster casts of Pompeii victims who died during the eruption of Mount Vesuvius in 79 AD.

So this was a long time ago, and I'd like to emphasise that these are not human remains.

These are casts taken from the voids that the ash has left behind.

They do capture the moment of death, so it could be upsetting for some people.

We'll also briefly discuss some more recent case studies, which do involve death as well.

So just a heads up that those themes will be coming up in today's lesson.

Saying that, I think the fact that we're having to do this guidance does show that this is such an important topic, as volcanic hazards really affect people's lives, and have a massive impact on those people who live near volcanoes.

And as we're going to look at today, actually, people who live quite far away from volcanoes as well.

I hope you find today's lesson really interesting.

Our outcome today is to explain what pyroclastic flows, ash, and lahars are and relate these to real life examples.

Before we start today's lesson, it's useful to have a look at some keywords that will come up.

We've got four keywords for today's lesson; pyroclastic flow, ash, lahar, and infrastructure.

If there's any of these that you're not familiar with, or you think would be useful to write down, please feel free to pause the video now and to take notes.

First of all, we have pyroclastic flow, a very hot mix of lava, ash, gases, and rock that flows rapidly down the side of a volcano.

Then we have ash, tiny fragments of volcanic rock ejected into the air.

Then we have lahars.

These are mud flows formed when volcanic ash mixes with water.

Now pyroclastic flow and lahars you probably won't have heard of before, so please don't worry.

They are coming up in today's lesson and you'll be learning a lot about them.

Infrastructure is our last key term.

You may have heard this one before.

All the basic systems in a country, such as transport and power supply.

Infrastructure is really important for a country to function.

Our lesson today comes in three parts.

First of all, we're going to be answering the question, why are pyroclastic flows deadly? Then we will look at why is ash a hazard? And finally, why are lahars so dangerous? First of all, why are pyroclastic flows deadly? Sam says, "As long as you avoid the lava flows, volcanoes are pretty safe, right?" Do you think Sam's correct? Interesting.

So there are actually many other dangerous hazards associated with volcanoes.

We're going to have a look at those today.

So volcanic eruptions can lead to a range of hazards, such as pyroclastic flows, ash, and also lahars.

So these images show each of these hazards, but we need to understand, actually, what is it we are looking at in a bit more detail.

So starting off with pyroclastic flows.

This is a fast-moving current of hot volcanic gases, ash, and rock.

Now when we think about volcanic hazards, we generally just think about the lava flowing down the volcano.

We don't think about all of the other elements that come with it.

So these flows are so, so dangerous because they're extremely hot.

They often reach temperatures of 300 to 1000 degrees C.

So if we think about boiling water, water boils at a hundred degrees Celsius.

So this is a minimum of three times hotter than the water that comes out of your kettle.

Extremely fast as well.

So these can reach speeds of 435 miles an hour.

Let's put that into context.

It is far faster than the 70 mile an hour limit on UK motorways.

So these are not something that you could outrun at all.

We couldn't, even if you had a road going in the perfect direction, you wouldn't be able to outrace this in a fast super car.

It wouldn't happen.

So true or false, pyroclastic flows can travel faster than a car? Nice easy one to start off.

True, well done.

So why is that true? Can you gimme any other detail here? Brilliant, they're extremely fast and can reach speeds of up to 435 miles per hour.

Did anybody get that? Remember that fact? It's a tricky one to remember.

Well done, everyone.

So why are they dangerous? Well, they can destroy nearly everything in their path, which is not surprising is it? We've heard how hot they are, and how fast they are, but if you think about the landscape they pass over: vegetation, buildings, infrastructure, all of this can be destroyed.

And obviously if that's all being destroyed, humans and animals are also at risk.

So it can burn people, or animals, it can block the lungs, poison, and cause oxygen deprivation.

So this can really harm people and animals, but also can kill people and animals.

Here's an example of a pyroclastic flow that's really famous.

So the city of Pompeii, in Italy, and its residents, were buried by several metres of volcanic material.

It was deposited by a pyroclastic flow from Mount Vesuvius in AD 79.

Now remember, right, we did a content guidance right at the start of the lesson.

This is where we're going to show that image I mentioned.

Bodies were sealed in by the volcanic material.

When they decomposed, broke down, voids, or holes, remained in the hardened ash layers.

Archaeologists poured plaster into these voids to create detailed casts of the victims. So they poured in the plaster cast, waited for it to dry, and then they removed the ash from around the plaster cast.

So what remained was the positions, even the expressions on the faces were seen as well, that people died in.

It is possible to visit Pompeii, in Italy, and you can go up Mount Vesuvius, you can go visit the the remains of buildings, and also have a look at these casts as well.

So it's a big tourist attraction now.

You would've thought that actually the area wouldn't be somewhere that people would visit, maybe, or wouldn't be somewhere that people would live because such a huge disaster has happened and is really, really famous.

However, we have these tourists coming to the area, and in addition, there are huge settlements around the area.

So people still live in these areas, which is really interesting.

Right, time for a quick check.

Which of the following pyroclastic flows destroy? Is it A, vegetation, B, buildings, C, infrastructure, or D, people? You can pick more than one.

Well done.

So if you picked vegetation, buildings, infrastructure or people, you were correct, but really what I was looking for was all of the above.

So all of these can be destroyed by pyroclastic flows.

They can take out their landscape, and they can really harm people and even kill people.

More recently, in December, 2021, Mount Semeru erupted violently, dramatically affecting the surrounding communities on Java island in Indonesia.

At least 62 people killed and thousands had to flee their homes due to the destruction caused by the pyroclastic flows, and the ash that buried homes, and infrastructure.

So you can see it on the map on the left hand side where Mount Semeru is located in Indonesia, and you can see on the right hand side here images of the homes that have been destroyed by pyroclastic flows and the ash that has actually affected the area.

GIS, or geographical information systems, is a really useful tool that we can use when we're looking at volcanoes, and we can use it to interpret pyroclastic flows, for example.

Can you have a look at this map here, and can you see where Mount Semeru is, and where the pyroclastic flow travelled? You might want to take a look at the key, and the key's found in the centre of the page, so we can see the symbol for the volcano.

And another useful thing to have a look at there at the bottom of the key is the red diagonal shading, which shows us where pyroclastic flows are.

Have a look on the map, make sure you can identify where that is.

Good.

So you've got Mount Semeru here and the pyroclastic flows, we can see three of them on this image, and they are flowing to the south and to the southeast.

Now GIS can actually be used to measure the distance that these flows have travelled and this is a really useful tool.

You can see it being used here measuring how far this particular flow has travelled.

And this one is 33 kilometres from the crater.

That's really quite far.

It might be worth taking a moment just to think about how far 33 kilometres is thinking about where you are locally, what's 33 kilometres from you? To give you some ideas about a half hour drive or six hours of walking.

Quick check time now.

GIS can also be used to map impact.

So how many structures were affected to the south of the main road in the satellite image here? Was it two, five or six? Remember we've practised using the key and that is a good thing to look back to.

Well done, yes, it's B, five.

We can see them represented as red squares to the south of the main road, which is the white line labelled "main road" on the satellite image we have.

Right, our practise task time now.

So, for task A, I would like you to do two things.

First of all, complete the gap fill.

So pyroclastic flows are flows of hot volcanic gases and they destroy nearly everything in their path, including vegetation.

And what else? They are deadly as they can burn, block, something, poison and cause deprivation.

What are those words that need to fill in the gaps? Task two here is to use arrows to match the four facts to the correct case studies.

So on the left we have Mount Vesuvius and Pompeii, in Italy, and on the right we have Mount Semeru.

So let's just practise this now so you understand what I'm asking.

Our first fact was that victims' last moments were preserved.

Was this for Mount Vesuvius or Mount Semeru? It was Mount Vesuvius.

So we just put an arrow to our Mount Vesuvius case study.

Please pause the video now to give yourself time to do the task.

Well done.

Let's have a look at some answers.

Your answers should look like this.

So, completing the gap fills should look like: "Pyroclastic flows are flows of hot volcanic gases, ash, and rock.

They destroy nearly everything in their path, including vegetation, buildings, and infrastructure.

They are deadly as they can burn, block lungs, poison and cause oxygen deprivation." So did you get those? It was ash, rock, buildings, infrastructure, lungs, and oxygen.

If there was any missed, make sure you tweak that now and add that in.

Our next question was to use the areas to match the four facts to the correct case studies.

So our first fact was for Mount Vesuvius, as we've mentioned, then we've had they suffered from a pyroclastic flow.

So that was both Mount Vesuvius and Mount Semeru.

It happens in AD 79.

That was Mount Vesuvius and Pompeii's destruction.

And then at least 62 people died and thousands fled.

And that was in Java.

So that was for Mount Semeru in Indonesia.

Well done, everyone.

We are now on our second part to the lesson today: "Why is ash a hazard?" When a volcano erupts violently, volcanic rock may be shattered and ejected.

Volcanic rock fragments, less than two millimetres in diameter, are called ash.

So if you look at a ruler and just think about what two millimetres looks like.

So really quite small, it has to be smaller than that for it to count as ash.

You can see an image at the bottom right of a sample of ash.

So it looks like dust really doesn't it? Ash is shot up into the air to form an ash cloud above the volcano.

The size of the area affected by the ash clouds depends on the wind speed and direction.

So if there is a strong wind, it can carry the ash quite far away from the volcano.

The direction the wind is blowing will determine where that ash is distributed.

Ash eventually falls to earth and can blanket the ground in a layer metres thick.

As the ash travels away, the layer of ash that is deposited tends to be thinner.

People can experience breathing problems if ash enters their lungs.

Buildings are buried and roofs can collapse under the weight of the ash layer, as we've seen in the photo, and ash smothers crops affecting the harvest.

So the immediate impacts of ash on crops in farms is that it will destroy them.

We've also got the problem that machines may stop working.

So for example, aircraft engines, if ash got into plane engine, then the plane might stop functioning, and that could obviously lead to serious accidents if the plane is flying at the time.

In 2010, Eyjafjallajokull erupted an Iceland, this grounded flights across Northwest Europe for days.

Winds had spread the ash cloud so far that it affected the travel plans of millions of people across 20 countries.

Quick check now, true or false? Ash is only a problem for areas local to the volcano.

Of course, it's false, well done.

Why is that? Well done.

Winds can carry ash far away from a volcano, and can ground aeroplanes , meaning the travel plans of people for a much wider area can be disrupted.

The area surrounding Mount Semuru, in Indonesia, was significantly affected by ashfall after the December 2021 eruption.

Closer to the volcano the ash layer was thicker, as we've mentioned before.

These houses were almost entirely buried by volcanic ash.

So this photo that we saw before is taken from Mount Semeru, and it's a really clear example of what a massive impact ash can have.

Which volcano almost buried these homes with ash? Was it Mount Vesuvius, in Italy, Eyjafjallajokull, in Iceland, or Mount Semeru, in Indonesia? Well done.

Yes, it was Mount Semeru in Indonesia.

Time for our task now.

So for task B, I would like to answer these three questions.

Firstly, what is ash? Can you use the following words to help you: rock, cloud, and ash? Second question is to give two reasons why ash is dangerous.

And the third question is the name and area affected by ash.

Feel free to pause the video now to give yourself time to do the task.

Well done, everyone.

Your answer may look like this.

So what is ash? Volcanic rock fragments, less than two millimetres in diameter, are called ash.

Did you remember the two millimetres in diameter part? That's a nice detail to add in.

They are created when rock is shattered during a volcanic eruption.

Ash is shot up into the air to form an ash cloud above the volcano.

Ash eventually falls to earth and can blanket the ground in a layer metres thick.

So I've identified the words that I asked you to use by colouring them turquoise.

So you can have a look at how I've used those there.

Nice and clearly.

Feel free to edit your answer now.

Your answers for question two and three might look like this.

So for question two, give two reasons why ash is dangerous.

People can experience breathing problems if ash enters their lungs.

Buildings are buried and roofs can collapse under the weights of the ash layer.

Ash smothers crops affecting harvest.

Question three, name an area affected by ash.

So the area surrounding Mount Semeru, in Indonesia, after the eruption in 2021 was affected.

So houses were almost entirely buried by volcanic ashfall.

Feel free to edit your answers now.

Right, onto the third parts of our lesson today.

Why lahars so dangerous? So first of all, what lahars? So this is Mount St.

Helens, in the USA, and you can see an example of a lahar here.

Lahars are mud flows.

They form when volcanic material like ash, which we've just covered, mixes with water such, as heavy rain, and melting snow, or even lake water.

So it's ash plus water.

So they're mixed in together.

The lahar flows downhill following the valleys.

Lahars can happen during or a long time after a volcanic eruption.

So, for example, a volcanic eruption can happen.

Our ash cloud forms, it's ejected out of the volcano.

Then the ash cloud falls and creates a layer of ash.

A few weeks later, maybe, it rains.

And that rain water gets mixed in with the ash.

That gets mixed into such an extent that the ash becomes a muddy flow, and that muddy flow flowing down slopes of the volcano is called a lahar.

Time for a quick check, now.

Lahars are, is it A, a flow of hot volcanic gases, ash, and rock, B, mud flows, or C, a flow of meltwater.

Correct, it's B, mud flows.

Lahars are extremely disruptive as they can cause deaths due to their speed, their force, and the heat of them.

They can wipe out infrastructure, bury settlements, alter landscapes, block rivers, and destroy farmland.

Right, we're going to think about this now in a slightly different way.

We're going to think about how these impacts could have knock on consequences for food supplies.

So in our quick check now, how could lahars affect food supply in an area? Can you think of any answers? Yes, well done.

There's more than one potential answer you could have included.

Here I've got: lahars wipe out infrastructure preventing access for aid or to shops.

They block rivers that might have been used for fishing and they destroy farmland, preventing food production.

So I suspect many people went for the third bullet point there, which is destroying farmland, and that's brilliant, well done.

We also need to think about the fact that the question asked about food supply.

So not just the production of food initially, but also the transport of foods.

And by affecting the infrastructure, lahars can have a really broad effect, not only on the production in the area, but also on bringing food in from elsewhere.

In early 2022, after the Mount Semeru eruption, the area experienced heavy rainfall.

Rainwater mixed with a thick layer of ash and moved downhill as lahars.

So this is a really clear example of where that volcanic deposit plus the water, in this case from rainfall, has led to an even more dangerous hazards.

Deforestation in the area, that means the felling trees or the cutting down trees, reduce the natural protection that the forest offers to slow down the lahars and absorb them as well.

So this meant that homes, and infrastructure, were damaged further, and the recovery from the eruption was delayed.

And this is a theme we will see throughout different topics in geography that actually where humans have interfered with the landscape often through deforestation, that has meant that that area, and the people in that area, are then more vulnerable to natural disasters.

Quick check time now.

The 2021 to 2022 Mount Semeru disaster is an example of how: A, rainfall can be helpful after a volcanic eruption.

B, deforestation can make a community more vulnerable.

Or C, rainfall can worsen a volcanic hazard.

You can pick more than one answer if you'd like.

Well done, it should be B, deforestation can make a community more vulnerable, and C, which is rainfall can worsen a volcanic hazard.

Time for our last task now.

I'd like you to complete the equation to explain how lahars form using the options below.

So what is the first ingredient for a lahar? What is the second ingredient? And then what does this lead to? I've given you lahars, or mud flows, water, or heavy rain, for example, and volcanic material like ash.

Next we've got name three reasons lahars are dangerous.

And lastly, why was the area surrounding Mount Semeru more vulnerable to lahars? Please pause the video now to give yourself time to do this.

Well done, everyone.

Your answer may look like this.

For the order the explanation to explain how lahars form.

I would expect you to have volcanic material like ash plus water, for example from heavy rain, melting snow, or lakes, equals lahars or mud flows.

Did you get that right? For question two, I asked you to name three reasons lahars are dangerous.

So clearly this list lists a lot more than three reasons.

I think it's a great idea to add a few more to your list, even if you've got three really good ones, doesn't hurt to add some more on as well.

If you've got more than three originally, well done.

So first of all, cause deaths, and that's due to the speed, force, and heat.

Secondly, it's wipe out infrastructure.

Thirdly, bury settlements.

Alter landscapes, block rivers, and destroy farmland.

Did you get three of those? Well done.

So question three, why was the area surrounding Mount Semeru more vulnerable to lahars? So deforestation reduced the natural protection trees offer to slow and absorb lahars.

Did you say deforestation? Did you use that key term? Brilliant, if you haven't, do make sure you use that because it's a really good one to be utilising when you're writing about geography.

Well done, brilliant work, everyone.

So we're onto our summary.

Volcanic eruptions can lead to a range of hazards.

Pyroclastic flows are flows of hot volcanic gases, ash, and rock.

Ash is made out of tiny pieces of volcanic rock.

This can damage lungs, machines, crops, and buildings.

And lahars and mud flows caused by volcanic material mixed with water.

Mount Semeru in Java, Indonesia, erupted in 2021, triggering damaging pyroclastic flows, ashfall, and lahars.

I hope you found today's lesson interesting.

I certainly enjoyed learning with you.

I hope to see you next time.

Bye.