Volcanoes, Earthquakes and Plate Tectonics

Volcanoes, Earthquakes and Plate Tectonics

1. WHY? Do earthquakes and volcanoes happen?

Because of……...

SO WHAT IS ‘TECTONICS AND HOW DOES IT CAUSE EARTHQUAKES AND VOLCANOES? WHY DO THEY HAPPEN………?

To understand plate tectonics first you need to know about…. The Structure of the Earth..... By understanding the structure of the earth and what goes under our feet we can begin to understand why we get earthquakes and volcanoes.

A cross-section through the earth 1000 C 4000 C 7000 C

Plate TectonicsScientific Definition The earth’s crust is divided into plates. There are seven large ones and many other smaller ones. They move around, floating on the mantle and it at the boundary where 2 of the giant plates meet that earthquakes and volcanoes occur and where mountains are built.

The Plates move because of convection currents:

CONVECTION CURRENTS………. …….work just the same as boiling up some pea soup!

Heat transfer from the core to the mantle produces slow convection of the mantle material (in the order of centimetres per year)

The huge plates move due to the convection currents bubbling away underneath them:

2. WHERE? Do they happen then?

Earthquakes and volcanoes happen along the boundaries of these plates… So where are the earth's major plate boundaries?

This map shows the distribution of earthquakes and volcanoes. As you can see they are concentrated along the plate boundaries.

But how do we know that these plates exist....... There is a theory called PLATE TECTONICS that explains the whole situation…

The breaking up of a supercontinent.... Wegener said that there at first the earth was a, gigantic supercontinent 200 million years ago, which he named Pangaea, meaning "All-earth". Pangaea was a supercontinent consisting of all of Earth's land masses. It began breaking up during the Jurassic period, forming 2 continents Gondwanaland and Laurasia, Pangaea started to break up into two smaller supercontinents, called Laurasia and Gondwanaland and eventually into land masses that look like our modern-day continents.

So it would have looked like this.......

And what does it look like today...... So was it just one supercontinent.....?

YES...and here's the evidence....

Anyway, back to those plates How do they cause volcanoes to happen…..There are three types of plate movement:

1. Constructive Plate Boundaries On a constructive plate boundary two plates move apart, allowing magma, or molten rock, to rise from the Earth's interior to fill in the gap. The two plates move away from each other like two conveyor belts moving in opposite directions

2. Destructive Plate Boundaries If 2 light continental plates collide they rise up forming mountains and volcanoes If a heavy oceanic plate and a light continental plate collide the heavy one sinks also causing volcanoes and mountains to form.

3. Conservative Boundaries A transform boundary occurs where two plates slide against each other. But rather than sliding smoothly, the plates build up tension, then release the tension with a spurt of movement. This movement is felt as an earthquake

So what do these volcanoes look like....

Volcanoes, Earthquakes and Plate Tectonics