Why do earthquakes and volcanoes happen?. In this presentation, I will learn; How to explain where earthquakes and volcanoes gghappen Why earthquakes.

Why do earthquakes and volcanoes happen?

In this presentation, I will learn;

How to explain where earthquakes and volcanoes gghappen

Why earthquakes and volcanoes happen

How many earthquakes?

Think back over the last week. How many earthquakes do you think will have happened around the world?

There are around 200 earthquakes a week, some will happen and people will feel them, some will go unnoticed.

Some will have devastating effects and kill hundreds of people, others may cause a roof tile or two to fall of the roof.

What is the earth like?

If you imagined the earth to be like a piece of fruit, what would it be like?

A peach

Crust

Mantle

Inner Core

Outer core

What is the earth like?

The structure of the earth helps us explain why earthquakes and volcanoes occur

The crust is the earth's surface and ranges from 3 - 44 miles deep

But it is not one solid piece, it is made up of plates of various sizes

There are 2 types of crust

Oceanic (under the sea) Continental (land we can see)

The plates

What is special about the plates?

These plates do not stay still, they move. It is this movement which causes earthquakes and volcanoes

The plates are constantly moving but you would not feel this movement as it is similar to the speed which your nails grow. However, as the plates do not move smoothly and friction can build up. It is the release of this friction which causes an earthquake

So why do they move?

As you move towards the inner core the temperature increases, this turns solid rock into molten rock. The hotter molten rock rises and takes the place of cooler rock. This a convection cell and there are many of these below the crust. It is these convection currents which move the plates.

What's the proof?

How do we know the plates move?

If we look at the continents we can seehow they used to fit together.

This theory was put forward by a German scientist called Wegnerin the early 1900’s.

Ring of fire

Most activity takes places at the edges of the plates (plate boundary) so this is where the effects of tectonic activity are mostly felt. The plate boundary of the Pacific plate is called the ring of fire as this is a location of great tectonic activity

Conservative

This is were 2 plates slide past each other. It is this type of movement which most commonly results in an earthquake as lots of pressure can build up and then the plates slip and the pressure is released

Volcanoes do not occur with this type of movement.

Destructive

This is when plates move towards each other. If the 2 plates are of the same type then the land will be pushed upwards and fold mountains occur. If the two plates are different then they will have different weights, oceanic crust is denser than continental is. When these two plates move together, the oceanic plate is pushed (sub ducted) underneath the continental plate.

This will not be a smooth movement and pressure can build up and will be released as an earthquake.

Destructive

In addition to earthquakes occurring, volcanoes can also occur at these plate boundaries

We have already seen that there is molten rock beneath the crust. This is called magma. There are gaps in the earth’s crust and the magma can seep through these gaps. Pressure can build up beneath the crust and when this pressure is released the lava is forced through the gaps in an explosion. This is a volcano. When the magma reaches the surface, it is now known as lava. The lava cools and forms rock

Constructive

This type of movement does not result in earthquakes. This is because as the plates move apart, molten rock rises between the gap made and solidifies to form new crust. This is a volcano. This can occur at the surface or under ground.