Lesson video

Hello, my name is Mr. March, and I'm here today to teach you all about the global distribution of earthquakes and volcanoes.

So grab everything that you need for today's lesson, and let's get going.

So by the end of today's lesson, you will be able to explain how most earthquakes and volcanoes are located at plate margins.

Now, there are four keywords for today's lesson, and those are epicentre, magnitude, margin, and hotspot.

Epicentre refers to the point on Earth's surface that is directly above where an earthquake happens underground.

Magnitude refers to a measure of the energy released by an earthquake.

Margin refers to the boundary where tectonic plates meet.

And finally, hotspot refers to an area in Earth's mantle where unusually hot magma rises towards the surface, creating volcanic activity.

Now, there are three learning cycles for today's lesson, and we're gonna begin with learning cycle one, which is looking at what is the global distribution of earthquakes? Now, how do we actually know where earthquakes occur? We know that most earthquakes occur because of movements within the Earth's crust.

And an earthquake releases seismic waves, which then travel through the Earth's crust.

These seismic waves can be measured using a seismometer, as seen on the screen in front of you.

And a network of these seismometers can be used to pinpoint the exact location of any earthquake's epicentre.

Now, the locations of all of these earthquakes are regularly updated, and these can be viewed using a GIS layer, such as Recent Earthquakes, as seen on the screen in front of you.

The location of these recent earthquakes on this GIS layer includes information about their magnitude, their intensity, the strength of those seismic waves, the depth of the epicentre, and the date on which they occurred.

Earthquakes under the sea are recorded as well as the earthquakes which happen on land.

Now time for a quick learning check.

True or false? It isn't possible to know exactly where every earthquake occurs as some occur underwater.

So what I'd like you to do right now is pause the video whilst you consider and then make your answer.

And the correct answer was false.

Now, once again, I'd like you to pause the video whilst you consider as to why this statement is false.

And the reason it's false is because earthquakes release seismic waves which are recorded by seismographs.

A global network of these seismographs is used to monitor all earthquakes and record their location.

And this works just as well for those earthquakes that happen on land as it does for those under the sea.

So really, really well done if you were able to get those two answers correct.

Now, there are nearly 150 years of seismograph readings, so we have a long history of recorded earthquakes.

Combining records of earthquake locations over decades and then mapping them shows us the global distribution of those earthquakes, as can be seen in this map on the screen in front of you, which is showing the location of all earthquakes between 1963 and 1998.

We can see that there were a phenomenal 358,000 different events.

And as we know, the Earth's crust is broken up into tectonic plates, as outlined in this map that you can see in front of you.

The global distribution of earthquakes closely matches the edges or margins of those tectonic plates, as shown via the thicker black line on the map in front of you.

Now then, if we overlay that map with this map, which is showing the location of earthquakes of magnitude 6 or above between 1900 and 2017, we see a clear correlation between where earthquakes are happening and those plate margins.

We can see that generally, most earthquakes seem to be happening along those fault lines.

So, a quick learning check.

True or false? There is a close relationship between the global distribution of earthquakes and the location of tectonic plate margins.

So please pause the video here whilst you consider and then make your answer.

And the correct answer was true.

Now, once again, I'd like you to pause the video whilst you consider as to why this statement is in fact true.

And the reason it is true is because plotting the location of these earthquake epicentres over time on a world map and comparing the distribution with a real world map of tectonic plates shows that most earthquakes are occurring at or near plate margins.

So once again, really, really well done if you were able to get those two answers correct.

Now, while most earthquakes and especially almost all higher-magnitude earthquakes occur near plate margins, some actually do not.

If we turn our attention to this map of the UK that you can see in front of you and begin looking at those orange dots on this map, these are the locations of recent earthquakes of magnitude 4 and above.

Now, the UK is actually located very far from any plate margins, but around 250 earthquakes occur in the UK every single year.

Most are very small, under magnitude 4, so these really are too small for people to even sense.

So once again, a learning check.

True or false? All earthquakes occur at plate margins or near to them.

So, pause the video here whilst you consider and then make your answer.

And the correct answer was false.

Now, once again, I'd like you to pause the video whilst you consider why this statement is false.

And the reason it's false is because although most earthquakes do indeed occur at plate margins or near them, some earthquakes do occur a long way away from the margin, as shown in the previous slide with a map of the UK, which is a long, long way away from any plate margin.

The thing is that these earthquakes are usually very low-magnitude earthquakes.

So, really, really well done if you were able to get those two answers correct.

So onto our practise task now.

And I would like you to use the Map And the key to describe the global distribution of earthquakes shown in the map.

You may wish to use an atlas to help you.

Now, what I'd like you to really focus on in this answer is the legend, which is showing you the intensity or the magnitude of those earthquakes.

Refer to continents.

Refer to compass directions.

So what I'd like you to do is pause the video at this point whilst you attempt this practise question.

Good luck.

And now some feedback.

So, this is an answer that you could have included in your own.

It says: Most earthquakes have occurred along the west coasts of North and South America and along the east coast of East Asia, Southeast Asia, and north and east of Australia.

This is also the location of the highest-magnitude earthquakes, 8 and above.

There are also chains of lower-magnitude, 6 to 7, earthquakes in the Atlantic Ocean and Indian Ocean.

There are generally very few earthquakes inside the continents themselves, though exceptions to this include Southeast Europe and South Asia.

Really, really well done if you were able to include any of that answer in your own.

We're on now to our second learning cycle, where we're now gonna turn our attention to what is the global distribution of volcanoes? So this map in front of you shows us the global distribution of volcanoes.

Those red triangles you can see in front of you show the position of both active and inactive volcanoes.

And once again, we can see a few clear things, the first of which is that most volcanoes are occurring at plate margins.

If we follow those lines, we can see that most of those red triangles seem to be occurring at or near those plate margins.

However, it is also true that some are occurring far away from plate margins, under the sea.

These are known as submarine volcanoes.

So while some are occurring on land, and while some are occurring along those plate margins, some are also occurring undersea, these submarine volcanoes, far, far away from plate margins.

So, a learning check.

This map shows the global distribution of volcanoes, but from a very unusual perspective.

I'd like you to consider which continent has been marked as X.

So read through your options, pause the video here whilst you consider, and make your answer.

And the correct answer was Antarctica.

Really, really well done if you were able to identify that.

Now again, it maybe come as some sort of surprise that Antarctica, looking at this map, does indeed have some active volcanoes and some active volcanic activity on that continent.

Now 75%, though, of the world's active volcanoes occur in something called the Pacific Ring of Fire.

Now, this includes volcanoes which are on land but also includes volcanoes which are submarine, under the sea.

And if we look closely at this map, the Ring of Fire is absolutely enormous.

It is around 40,000 kilometres long and contains 452 volcanoes.

Some of these are active, and some of these are dormant, by which I mean sleeping volcanoes, in Antarctica, which is also not shown, which actually closes this ring that you can see on the map in front of you.

So again, a learning check.

Which of the following maps shows the location of the Pacific Ring of Fire? A, B, or C? So I'd like you to look at the three maps, pause the video here whilst you consider, and then make your answer.

And the correct answer is C.

Really, really well done if you were able to identify that as the map of the Pacific Ring of Fire.

Now some practise tasks.

And this practise task asks you to look at these two maps which are both showing the global distribution of volcanoes, albeit from a slightly different perspective.

What I'd like you to do is look at Map A and Map B and describe one difference between them.

I'd also like you to try and give one advantage and one disadvantage of each map.

So, study Map A, study Map B, pause the video here whilst you consider, and then make your answer.

Best of luck with these tasks.

Okay, so the first question asks you to describe one difference between Map A and Map B.

You may have said some of the following, the fact that Map A has the Pacific at its centre, while Map B is centred on the Prime Meridian and has the Atlantic at its centre.

Map A also includes more detail about the plate movements, the names of places, and features, while Map B has less detail but does show more volcanoes.

Map A shows the continent outlines accurately, while Map B shows a more blurry view, including both continents and the continental shelf.

Map A is more colourful with bright colours for the oceans and continents, while on Map B, colour is actually only used for the volcanoes.

Map A shows the location of the Ring of Fire, while Map B does not pick out any particular groups or patterns of volcanoes.

In terms of advantages and disadvantages, you may have included some of these.

An advantage of Map A is that because it is actually centred on the Pacific, you're able to see the Pacific Ring of Fire much more clearly.

A disadvantage, though, of Map B is that it splits the Ring of Fire, so it looks like two different distributions of volcanoes instead of one continual feature, one continual ring.

An advantage of Map B, though, is that the global locations of volcanoes is clear to see because the red triangles really stand out against that grey background.

A disadvantage, though, of Map A is that other information on the map makes the volcano details much harder to see.

For example, in Africa.

There were other answers available, but once again, really, really well done if you were able to include any of those in your own answer.

We're on now to our final learning cycle, which is what are hotspot volcanoes? Now, Hawaii is a fantastic example of an area of volcanic activity, but it is also an exception to the Ring of Fire pattern.

Hawaii is made up of 137 volcanic islands.

But as shown on this map, circling it there in the centre, it is actually 3,200 kilometres away from the nearest plate margin.

Yet, it still has a tremendous amount of volcanic activity.

I wonder why that is.

Time now for a quick learning check.

And in this learning check, I would like you to try to identify and locate the Hawaiian Islands.

A little tip is that the Hawaiian Islands are a state of the United States, yet they are many thousands of kilometres away from the United States mainland and in fact are thousands of kilometres away from any plate margin.

So, please pause your video here whilst you do your best to locate the Hawaiian Islands.

And the answer is right here, located more or less in the centre of the Pacific Ocean, located almost 3,000 kilometres away from the United States mainland and indeed roughly the similar distance from any plate margin.

So really, really well done if you were able to identify and locate the islands of Hawaii.

Now, why is it that some volcanoes occur far away from plate margins, such as those found in the chain of Hawaiian Islands? We know, for sure, that the vast majority of tectonic activity, including volcanic activity and earthquake activity, occurs along plate margins, particularly at destructive plate boundaries.

And yet, why is it that some areas seem to be tectonically active yet far away from any of these plate margins? What I'd like you to do right now is pause the video whilst you consider your own answer to that question that you can see on the screen.

Best of luck.

So, what did you come up with? Well, we have a few suggestions here.

Sam says that maybe the answer is that volcanoes occur if there is a weak point in the crust.

This is a very valid suggestion and indeed does go some way to explain why there are certain volcanic activity far, far away from plate margins.

Jacob, though, meanwhile says, "Maybe we don't know where all the plate margins are?" Again, a reasonable suggestion, but in this case, completely wrong.

We do know where the plate margins are.

We are able to identify those plate margins by looking at tectonic activity using seismographs to understand exactly where that tectonic activity is taking place.

For that reason, we know the location of plate margins, and in this instance, unfortunately, Jacob is incorrect.

So, how did you get on? Did you have anything similar to what Sam suggested? Volcanoes away from the plate margins can also form along faults or at hotspots.

A hotspot is thought to be where a plume or an upwelling from deep within the mantle.

When this hot material reaches the base of the lithosphere, it causes the partial melting, creating this magma.

The magma then rises and bursts through the crust to form that volcano.

And as a tectonic plate slowly moves over that hotspot, a chain of volcanoes, just like in Hawaii with those 137 volcanoes we mentioned just before, this is how that chain of volcanic islands or volcanoes forms over time.

This process created those Hawaiian Islands.

We can think about the creation of hotspot volcanoes through a series of stages.

The first is that there is a hotspot in the mantle, this plume, this upwelling, of significantly hot magma rising up through the lithosphere.

This partial melting of the lithosphere creates magma.

The magma rises and bursts through the crust, which then leads to the creation of a volcano.

So, learning check.

Which feature on this diagram represents a volcano formed by a hotspot? I would like you to consider whether it's A, B, or C.

So, pause the video here whilst you identify the correct answer.

And the correct answer was A.

Really, really well done if you were able to identify that volcanic landform that you can see right there.

So, a practise task.

How is the distribution of earthquakes and volcanoes related to plate margins? Now, at this time, I'd like you to write three or more quiz questions that would help a teacher assess whether students actually know the answer to this question.

I'd also like you to provide the correct answers for those questions.

So, pause the video here whilst you attempt this practise question.

Best of luck.

And now some feedback.

So here are a sample of the different questions and answers you may have come up with.

The first one is, 75% of all active volcanoes occur in a region known as the Ring of.

Now, there were three options, weren't there? Asia, Fire, or Magnitude.

Now, the correct answer is Fire.

The second question you may have created is, how is the distribution of earthquakes and volcanoes related to margins? The answer, most earthquakes and volcanic eruptions occur at or near to plate margins.

Another question you may have come up with is, true or false, all volcanoes and earthquakes occur at or near to plate margins? And then explain your answer.

Well, the answer is false because a few earthquakes and a few volcanoes occur very far away from plate margins.

For example, hotspot volcanoes.

The fourth question you may have had is, which of the following has volcanoes caused by a hotspot? Is it Iceland, Hawaii, or the Ring of Fire? And the answer was Hawaii.

And the fifth and final question is, earthquakes and volcanoes do not occur under the sea.

Is that statement true, partially true, or completely false? The answer is, completely false.

Earthquakes and volcanoes both do occur under the sea as well as on land.

And remember, a volcano which occurs under the sea is known as a submarine volcano.

So, those were my five sample questions, which you may have come up with yourself.

If you did, really, really well done.

Onto the summary.

So, what we need to know from this lesson is that most earthquakes and volcanoes are located at or near plate margins.

75% of active volcanoes and 90% of earthquakes occur in the Pacific Ring of Fire.

Some earthquakes and volcanoes occur away from plate margins.

And hotspots explain the location of chains of volcanoes away from plate margins.

So really, really well done during today's lesson.

It was a pleasure to have you with me, and I'll see you on the next lesson, goodbye.