Hello, my name's Mrs. Harking.

Today's lesson is the 2018 Sunda Strait Tsunami taken from the unit "Tectonic Hazards: Why is Earth restless?" Today, we'll be exploring what a tsunami is, how it happens, and what happened in the Sunda Strait.

There are going to be some tricky themes today as we'll be talking about the consequences of the tsunami including deaths.

So just to make you aware before we start the lesson, but I'll be with you the whole way through to explain everything.

The outcome of today's lesson is to explain how a tsunami occurs and what happened in the Sunda Strait in 2018.

Here are some keywords that are useful to know before we get into the lesson.

First of all, we have tsunami.

This is a series of large, powerful ocean waves caused by a sudden disturbance.

We'll explain in a lot more detail what that word means, where it comes from, in depth in the lesson, but it's a good idea to have an idea of roughly what a tsunami is before we begin.

Displace, so this is to move something from its original position.

For example, ocean water.

And lastly, infrastructure.

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

Today's lesson comes in two parts.

Firstly, what causes a tsunami.

And secondly, why was the Sunda Strait tsunami so devastating? Let's start with what causes a tsunami.

A tsunami is a series of large, powerful ocean waves caused by sudden disturbance.

You can see an example of tsunami happening in the image here to give you an idea of what it might look like.

"Tsunamis are one of the most deadly hazards," Alex tells us, and he's right.

The word tsunami comes from Japanese.

Notice when we say tsunami, we don't say the T, but when we're spelling it, we must remember to include that T.

So the word tsunami has two parts to it.

We've got the tsu and the nami.

So tsu means harbour or port, and nami means wave.

So this word actually makes a lot of sense because it literally means harbour wave.

This is because the waves often cause the most damage when they reach harbours or coastal areas.

So we can understand where that words come from.

It can help us to understand what a tsunami is and remember the word as well.

Tsunamis are created when a physical event displaces ocean water.

They involve the whole column of water from the seabed to the ocean surface.

By contrast, waves that are driven by the wind only affects the near-surface layer of water.

So the waves that you would normally see if you've been to a beach or any coastal area, those would be created by the wind blowing over the water and they're very different to a tsunami.

The tsunami is the whole column of water and it's caused by something far more significant displacing a lot of water.

Do you remember that displace means to move something from its original position? So in this case, the ocean water is moved or shoved out of its place.

Let's do a quick check for understanding now.

True or false? Tsunami waves are like wind-driven waves, just bigger.

Well done.

That is false.

Can you tell me why? Good, so tsunami waves involve the movement of the whole column of ocean water, all the way from the seabed to the ocean surface, whereas wind-driven waves only involve the surface layer, the water right at the top.

Tsunami waves also move much faster than wind-driven waves, so they can actually move 800 kilometres an hour.

There are three tectonic triggers which can displace ocean water to cause a tsunami.

There are some non-tectonic ones as well, but we're going to focus on tectonics today.

So first of all, we've got undersea earthquakes.

This can displace water and cause this ripple of waves or tsunami to form.

The volcanic eruptions can all cause tsunamis.

They can be under the sea or into the sea.

Now we have our third one.

Now, this is landslides and they can be caused by a number of different reasons, but earthquakes can trigger landslides into the sea, which could cause a tsunami, and also volcanic eruptions can cause landslides into the sea, which can cause tsunamis as well.

Time for a check for understanding now.

Which of the following cannot trigger a tsunami? Is it A, wind? B, earthquake? C, volcanic eruption? Or D, landslide? Well done, it's the wind.

Wind cannot trigger a tsunami.

The wind is what causes our normal ocean waves to happen, and that's what you will have seen if you've ever visited the coast.

The displaced water causes waves in the ocean, which spread out from the source, travelling at high speed.

You can see this in the animation on the right-hand side.

They almost look like ripples in the water, don't they? So if you think about dropping a pebble into a puddle, the pebble would displace the water and ripples would emanate from where that pebble has dropped in.

And that's really similar to a tsunami, but on a far larger scale.

And in this case, it's probably going to be a tectonic trigger that's actually triggering this rippling effect.

These small waves grow dramatically in height when the tsunami approaches land.

You can see that happening in the animation on the right-hand side.

So actually, tsunami waves don't always look very big at all out at sea.

It's only when they get towards land that their significance in their height really shows.

Instead of breaking and then retreating at the coast, like a normal wave would, so if you've ever been to the coast, you'll have seen the waves coming in, breaking, where you end up with the white bubbles forming on the waves, and then retreating or going back into the sea again, and you get that routine happening over and over.

That is not what happens with tsunamis.

With tsunamis, the waves can travel kilometres in land.

They just keep going and going and going, and that can be devastating.

Earthquakes are the most common cause of tsunamis, and we're going to watch an animation which shows us all the way from the triggering earthquake through to how the coastline experiences the tsunami.

Before the tsunami hits the land, the water is drawn back from the coast, like a fast-retreating tide.

There can even be fish left stranded on the beach.

And I would like you to look out for that in this video and it's something to note because if you ever experienced this, if you ever travelled and found yourself in a situation where actually this was happening, you would know that a tsunami was on its way and you'd know you needed to act fast.

So really good video to pay close attention to.

This is our earthquake happening under the ocean.

The seabed has shifted, displacing the water, and we can see the ripples forming or our tsunami wave and that is spreading out from the source from where this earthquake has happened.

These ripples are going to gain in height as they get towards land.

Ooh, look, this is what we wanted to watch out for.

So the the sea is retreating back significantly and this is fast.

Okay, so if you ever saw this happening, you would know, I really need to take action straight away.

This is potentially really dangerous.

Right, watch for the tsunami coming.

And watch how this wave acts.

It gets higher as it comes to land and then it doesn't retreat back again.

It just keeps going and it's flooding all those coastal areas.

Absolutely devastating.

Now here's a second wave, and this is something that people often don't know, that actually it's not just one wave.

There's a series of waves that hit the coastline.

Time for a check for understanding now.

Put the following statements in order to show how an earthquake can cause a tsunami.

I'm going to show my answer as the four letters in the correct order.

I'll obviously show that at the end.

Not here.

Let's run through the different sentences first.

So A, instead of breaking and retreating at the coast, like wind-driven waves, tsunamis can travel kilometres inland.

B, these waves grow dramatically in height as the tsunami approaches land.

C, before the tsunami hits the land, the water is drawn back from the coast like a fast-retreating tide.

And D, an earthquake disrupts the ocean floor and ocean above it, creating fast-moving ripples that spread out from the source.

I'll give you five seconds to put these in the correct order.

Well done, everyone.

So hopefully, you've got something similar to mine.

So D is our first one for sure.

An earthquake disrupts the ocean floor and ocean above it, creating fast-moving ripples that spread out from the source.

Then we have B.

These waves grow dramatically in height as the tsunami approaches land.

Then C, before the tsunami hits the land, the water is drawn back from the coast like a fast-retreating tide.

Finally, A, instead of breaking and retreating at the coast, like wind-driven waves, tsunamis can travel kilometres inland.

And A definitely has to be last.

B and C may have the other way around, and that's fine, but we should definitely have D first and A last.

Well done, everyone.

Great effort.

Let's have a look at our case study now.

A tsunami occurred in the Sunda Strait due to the eruption and partial collapse of the volcano, Anak Krakatau.

You can see the location here on the map and we've got a satellite image to show us actually what the volcano looks like in terms of its island formation.

We can see where the volcano is located on our map here.

Anak Krakatau means child of Krakatoa.

The volcano emerged in 1927 from the collapsed volcanic remains left by the 1883, you can see it happening now, Krakatoa eruption, one of the most violent volcanic events in recorded history.

So Krakatoa is a significant volcano.

Many people have heard of it because it was so, so violent.

And actually, this Anak Krakatau formed, as you can see in the animation on the left-hand side, from the remains of that really, really destructive volcano.

We can use the Geography Visualizer to zoom in and locate the volcano.

Geography Visualizer is just one example of a geographical information system where we have layers of information on maps.

Indonesia is a country in Southeast Asia, and the Sunda Strait is a body of water connecting two seas.

Sumatra and Java are the two islands either side of the Sunda Strait.

Anak Krakatau is located in the Sunda Strait between the islands of Java and Sumatra.

Here, we could see a zoomed in satellite image of our volcano, Anak Krakatau.

In 2018, the southwest side of Anak Krakatau collapsed into the sea during an eruption.

We can see that on a really zoomed in satellite image here.

This displaced water, causing waves in the ocean, which spread out from the source.

We know that is called a tsunami.

Quick check for understanding now.

The Sunda Strait tsunami was caused by? Was it A, a dramatic earthquake under the seabed? B, the collapse of one side of an erupting volcano? Or C, a tropical storm that brought torrential rain? Yes, well done.

It was the collapse of one side of an erupting volcano, so B was the correct answer.

Now it's time for Task A.

I would like you to complete the flow chart to explain the formation of a tsunami.

Firstly, there are three main tectonic triggers that displace ocean water to cause a tsunami.

Can you list those three? Then this event causes waves in the ocean that.

Can you finish the sentence? These waves grow in height as.

Again, can you finish the sentence? Before a tsunami reaches the coast, the water.

Instead of breaking and retreating like wind-driven waves, tsunamis.

So a little tip before we start.

I would recommend if you are doing this from scratch without a sheet to make sure that you don't draw the boxes first, do the writing and then you can draw the boxes around the writing.

That way it doesn't limit how much you write because you run out of space.

Right.

Well done, everyone.

I will give you five seconds now just to pause the video because you'll need a chunk of time for this to make sure you do it really well.

Good luck, Right.

Well done, everyone.

Let's take a look at the answers.

So your answer may look like this.

There are three main tectonic triggers that displace ocean water to cause a tsunami.

Firstly, we have earthquakes under the seabed, explosive volcanic eruptions, or landslides caused by earthquakes or eruptions.

I'm expecting you'll have earthquakes, volcanoes, and landslides.

Can you check that you've got the rest of the detail there as well, please.

Next, this event causes waves in the ocean that spread out from the source.

Thinking about rippling effects, aren't we here? Just like if you dropped a pebble in a puddle.

These waves grow in height as the tsunami approaches land.

Before a tsunami reaches the coast, the water is drawn back from the coast like a fast-retreating tide.

Instead of breaking and retreating like wind-driven waves, tsunamis can travel kilometres in land, causing widespread flooding and carrying debris out to sea.

Well done, everyone.

If you need to pause the video now so that you can add anything that you missed, feel free to do that.

We're now into the second part of our lesson.

Why was the Sunda Strait tsunami so devastating? The tsunami waves reached nearby coastlines within 30 to 45 minutes.

We can see on the map here the time of arrival and height of waves shown by the red text.

The hardest hit areas included Banten Province in Java and Lampung Province in Sumatra.

The affected areas are shown by the cyan colour.

That's that bright blue.

And you can see they also labelled affected areas in the same colour.

Just so you can identify where it was that people were affected.

Cyan zones indicate areas affected by the tsunami.

The tsunami affected.

Was it A, some coastlines 100 kilometres from the volcano? B, some coastlines over 50 kilometres from the volcano? Or C, only coastlines within 50 kilometres of the volcano? Take a look at the dashed lines that show distance from the source, from Anak Krakatau, and use those to help you answer the question here.

Well done, really good.

So it's B, isn't it? Some coastlines over 50 kilometres from the volcano were affected by the tsunami.

That's pretty far.

If you look at the map, you can see the dashed line showing the areas 50 kilometres away from the volcano, and it's really clear that there are some cyan areas that are affected further out than that 50 kilometre line.

Another check for understanding.

The highest tsunami waves were recorded at: Is it A, Rakata? B, Marina Jambu? Or C, Bengkunat? Well done.

Yes, so it's Rakata, isn't it? We can see that at Rakata, the height of the waves was up to 25 metres, which is extremely high.

The Sunda Strait tsunami destroyed homes, hotels, and infrastructure along the coastline.

Unfortunately, over 430 people died and thousands of people were hurt as well.

So this was a devastating tsunami.

One of the reasons why the tsunami was so bad was because this strait, the Sunda Strait, is a relatively narrow body of water.

And when tsunami waves are funnelled through a narrow space like this, the result is high wave heights and more flooding.

If you think about all of that water being funnelled into quite a narrow space, it's almost like it's getting squeezed and that means that the wave height increases.

Check for understanding time.

True or false? The physical location of this tectonic event made its impacts worse.

Remember physical and natural features.

Well done.

It's true, isn't it? So can you tell me why? Good, well done.

So when waves are funnelled through a narrow space like the Sunda Strait, higher waves and more flooding result.

There were also some human reasons that influenced the fact that this tsunami was so devastating.

Indonesia had a network of buoys and tidal gauges to detect unusual sea level changes, but many were broken or had been vandalised.

You can see on the photograph here an example of a tsunami detection buoy, and these float in the sea and they use a lot of measurements to calculate anything unusual and they can then send a message to land to warn people that a tsunami might be coming.

Because there wasn't any working, this left the country relying on earthquake-triggered alerts, which failed, because the tsunami was not caused by an earthquake.

It was caused by the collapse of the side of Anak Krakatau.

Not an earthquake.

It was a volcanic trigger.

Why did the tsunami detection buoys not detect the tsunami early? Can you remember? Yes.

Well done.

Many buoys were broken or vandalised.

The response to this event was further slowed by the time of day that it happened, so it happens at night where many people were sleeping or relaxing on the beach.

They didn't have time to get to high ground or get to inland areas.

Also, debris and flooding caused problems, so a lack of safe access routes left survivors stranded without aid.

Here's an account of a tourist who survived the tsunami.

"It was dark, and we were enjoying music near the beach outside our hotel.

The sea looked strange and started to retreat, then I knew something was wrong.

We ran to a high floor in the hotel.

The roar! I still can't believe I survived.

I'm so grateful, the hotel was built so well and did not collapse.

I know many buildings did." This is a fisherman's experience of the tsunami.

"I was in bed when I heard shouting and a strange, loud roar.

I leapt out of bed and dashed outside.

Water was already rushing into the village.

Luckily our house was on higher land and the tsunami didn't reach us.

Unfortunately, not everyone was that lucky." Time for a check for understanding now.

What should you do if you see the sea retreat very suddenly? Yes, well done.

So run to high ground, inland, you'd have to get there very fast, or a high floor of a strong building if not.

So these are good things to do if you were ever found in that situation and could well save your life.

Time for our Task B now.

First of all, I'd like you to describe the area affected by the Sunda Strait tsunami.

Then I would like you to tell me why was the Sunda Strait tsunami so devastating? I've put this map here so that you can use that to help you describe the area.

What I would say is it's a really good idea to actually use all of the information on the map.

So thinking about those cyan areas, thinking about the kilometres from Anak Krakatau that are shown by those dashed lines.

We've got the names of locations, the height of waves, and the timing.

There is also latitude and longitude located on the outside of this map, which is another really useful tool to use.

Pause the video now to give yourself time to do this task.

Well done, everyone.

Let's take a look at some answers.

For the first question, describe the area affected by the Sunda Strait tsunami, your answer may look like this.

The Sunda Strait tsunami affected coastal regions in the Sunda Strait, including Banten Province, Java, and Lampung Province in Sumatra.

Now, one thing to note that this sentence says that it says coastal regions.

Have you remembered to include that? I know we discussed including information from the map, but also saying whether the regions were coastal or inland that were affected is quite important, especially for tsunamis.

So it's coastal regions.

Between 5.

5 to 7 degrees South and 104.

9 to 106 degrees East were affected badly.

And coastlines over 50 kilometres from Anak Krakatau were affected.

For example, a 0.

35 metre wave, which reached Ciwandan in Java.

You're free to edit your answer now.

For our second question, why was the Sunda Strait tsunami so devastating, your answer may look like this.

The Sunda Strait tsunami was very destructive because the narrow strait funnelled the waves, meaning they were higher and more flooding occurred.

It damaged homes, hotels, and the roads along the coast of Java and Sumatra.

More than 400 people were killed and thousands were injured.

The warning system didn't work well because many sensors were broken, and the tsunami was caused by a volcanic collapse, not an earthquake, so earthquake alerts failed.

There were no sirens or text warnings to alert people, and the tsunami happened at night when many people were asleep and they could not escape.

Flooding and debris also made rescue efforts difficult, increasing the disaster's impact.

Well done, everyone.

Really great effort.

If you'd like to pause the video now to edit your own answer, feel free.

Well done, everyone.

We've reached the summary.

A tsunami is a series of large, powerful ocean waves caused by sudden disturbance.

Undersea earthquakes, volcanic eruptions, and landslides can displace sufficient water to trigger a tsunami.

In 2018, a tsunami was caused by the collapse of the Anak Krakatau volcano in the Sunda Strait in Indonesia.

Tragically, the tsunami led to the deaths of over 430 people.

The impact was devastating due to the insufficient warning systems, the shape of the Sunda Strait, which funnelled the waves, and because it occurred at night where many people were in bed.

I hope you found today's lesson really interesting.

I hope to see you next time.

Goodbye.