Lesson video

Hi, everyone.

I'm Miss Reid and welcome to another lesson on mountains, volcanoes and earthquakes.

Let's have a look at today's lesson question.

So today's lesson question is, how does an earthquake occur? Well, in this lesson, we're going to be learning about why tectonic plates move, what an earthquake is and why they occur.

So for today's lesson, all you'll need is an exercise book or a piece of paper, a pencil, and your brain.

Please take a moment now to clear away any distractions, including turning off any notifications or apps that you have running in the background, if you know how to.

Finally, if you can try to find a quiet place where you won't be disturbed during the lesson.

Pause the video now so you can get what you need and find a quiet place to work.

Great, now you have everything you need, let's move on.

So we are geographers and geographers are types of scientists who study the earth, and this includes the land, the physical features, and it includes the people who live within the land, and that's the human features.

So today we'll be questioning, why are tectonic plates moving? What is an earthquake? And what causes an earthquake? Now, as you already know, the earth's inner and outer core are extremely hot.

And this means that a lot of heat energy is constantly being created.

This heat energy, heats the mantle and causes the molten or liquid rock to move.

This movement happens in a cycle and it's called a convection current, what's it called? Convection current, that's absolutely right.

Now, we're going to look at the convection current in four steps or stages.

So the first thing that happens is that hot molten rock rises because it is lighter, and as it rises close to the crust, it cools, that's the second stage.

The cooler molten rock then sinks back down towards the core.

Once it's there, it is heated again, and is begins to rise.

So there's four stages.

Hot molten rock rises.

The molten rock cools.

The cooler molten rock sinks.

And the molten rock is heated again and rises, those four stages of the convection current.

Now the tectonic plates lie on top of the mantle.

So these constant movement in the mantle is what causes the tectonic plates to move.

So here we have a question, convection currents happen when.

Let's take a closer look.

A, warm material rises while cool material sinks in a circular pattern.

B, convection currents happen when cool material rises while warm material sinks in a circular pattern.

C, convection currents happen when warm material sinks while cool material rises in a circular pattern, or D, convection currents happen when warm material rises while cool material sinks in a vertical pattern.

Pause the video now and choose the answer that you think is correct.

Let's check the answer.

So the answer is A, convection currents happen when warm material rises while cool material sinks in a circular pattern.

Pause the video now so you can tick or fix your answer.

Excellent, let's move on.

We've got another question.

Tectonic plates move because.

Let's take a closer look.

A, tectonic plates move because they are moved by the convection currents in the inner core.

B, the tectonic plates move because they're moved by the convection currents in the mantle.

C, tectonic plates move because they are moved by the convection currents in the atmosphere.

Or D, tectonic plates move because they are moved by the convection currents in the outer core.

Pause the video now and choose the answer that you think is correct.

Let's see if you got the right answer.

So the answer is B, tectonic plates move because they are moved by the convection currents in the mantle.

Pause the video now so you can tick or fix your answer.

Great work, everyone.

Give yourself a pat on the back, if you got that, alright? And give yourself a pat on the back, if you corrected your answer and now know the correct answer, great work.

So what is an earthquake? Well, sometimes when tectonic plates move pressure that has built up over time is released and this causes the ground to shake.

This is called an earthquake.

An earthquake is measured using the Richter scale.

My turn, your turn, Richter scale.

What's an earthquake measured using? That's right, the Richter scale.

Now the size of an earthquake is measured using the Richter scale, as you know.

The Richter scale measures earthquakes from zero, that's the least severe, to nine, that's the most severe.

Earthquakes that measure over 6.

0 on the Richter scale can cause lots of damage.

Now let's take a closer look at this graph.

This graph shows that the higher, the earthquake measures on the Richter scale, the more people are due to die and the more money it will cost to repair the damage.

So for example, an earthquake that measures between six and eight on the Richter scale is likely to kill between 10 and 1000 people and could cost anywhere from thousands to millions of dollars to repair.

So now, you know why it's important that we have a scale to measure earthquakes because scientists and geologists need to be able to know how many people are going to be at risk and how much money it could cost to repair the damage.

So here's the question, what does scientists use to measure the strength of an earthquake? Shout out your answer, the, scale.

What is it, the? Did you get that right, the Richter scale.

Give yourself a pat on the back if you did.

So what causes an earthquake? Well, earthquakes happen when two plates rub against each other, along a fault line.

A fault line is the place where two plates meet and move past each other.

When the plates move past each other, they sometimes get stuck and pressure starts to build up because the mantle underneath the plates is still moving.

The plates continue to push against each other until small bits of rock break off.

The point where the rocks break is called the focus.

What's the point why the rock breaks called? That's right, focus.

Eventually, the rocks breaking causes the plates to release and jolt forwards, which results in an earthquake.

Now, the epicentre of an earthquake is the place on the earth's surface above where the rocks broke off.

It's above the focus.

Here's a question for you, let's take a closer look.

The epicentre of an earthquake is.

A, the centre of an earthquake.

B, the epicentre of an earthquake is the place where the rock broke off.

C, the epicentre of an earthquake is the place on the earth's surface above where the rock broke.

Or D, the epicentre of an earthquake is the crack in the earth's surface left behind after an earthquake.

Pause the video now and choose the answer that you think is correct.

Well done, let's see if you got the right answer.

So the answer was C, the epicentre of an earthquake is the place on the earth surface above where the rock broke.

Pause the video now, so you can tick or fix your answer.

Great, let's move on.

So what causes an earthquake? We're still thinking about that question.

Now, an example of a fault line, we've just learned about fault lines, is the San Andreas fault in California, which was formed by the North American plate and the Pacific plate moving past each other.

It's is a crack in the Earth's crust, that is about 1,200 kilometres long, and the plates are moving between three and five centimetres every year.

Here's a question for you.

Earthquakes happen when.

Let's take a look.

A, earthquakes happen when two plates move toward each other.

B, earthquakes happen when two plates rub against each other.

C, earthquakes happen when two plates move away from each other.

Or D, earthquakes happen when one plate breaks in two.

Pause the video now, and choose the answer that you think is correct.

Did you get the right answer? Let's check.

So earthquakes happen when two plates rub against each other.

Pause the video now, so you can tick or fix your answer.

Great work, let's move on.

So earthquakes happen very often, because plates are moving past each other all the time.

In fact, about 50,000 earthquakes happen every year.

However, some of these are really small and therefore not noticed by humans.

Bigger earthquakes, however, can be very dangerous.

But scientists have not yet found a way of accurately predicting when an earthquake will happen or how large it will be.

So people who live in these places need to be prepared, and we'll learn out a little bit more about how people prepare for earthquakes in another lesson.

So here's a task.

What or, sorry, why are earthquakes often a surprise? Here's a sentence starter and you need to complete the sentence.

Earthquakes are often a surprise because.

Pause the video now, so you can complete that sentence.

Well done for having a go, let's compare your answer with my answer.

So I said earthquakes are often a surprise because scientists have not found a way to predict when an earthquake will happen.

Pause the video now, so you can tick or fix your answer.

Great work, everyone.

Well, that brings us to the end of today's lesson.

A really big well done on all of the fantastic learning you've achieved today.

If you're able to, please take a picture of your work and ask a parents or carer to share it with your teacher so they can see all of the fantastic things that you've learned today.

And if you'd like, you can ask your parent or carer to send a picture of your work to @OakNational on Twitter, so I can see your lovely work too.

Don't forget to complete your end of lesson quiz.

Enjoy the rest of your learning today.

Bye.