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Exam questions on tectonic hazards
i) Describe the distribution of
earthquakes and volcanoes
• ii) Explain why earthquakes and
volcanoes are often found together
[6]
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….
By understanding the structure of the earth and what goes under our feet
we can begin to understand why we get earthquakes and volcanoes.
1000 C
earth spinning.gif
4000 C
7000 C
Plate Tectonics
Scientific 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:
Do they happen then?
Earthquakes and volcanoes happen along the boundaries
of these plates…
This map shows the distribution of earthquakes and volcanoes.
As you can see they are concentrated along the plate
boundaries.
There is a theory called PLATE
TECTONICS that explains the
whole situation…
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.
How do they cause volcanoes to happen…..There are three
types of plate movement:
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
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.
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
Geography
Volcanoes
Not just one type
 Tom Abbott, Biddulph High School and made available through
www.sln.org.uk/geography and only for non commercial use in schools
Ash and Cinder Cone
Geography
Paracutin - Mexico
The volcano is built
up of layers of ASH.
When it erupts it is
normally with great
explosive force.
Volcanic Bombs
3,000m
Pipe
Layers of Ash
and Cinder
 Tom Abbott, Biddulph High School and made available through
www.sln.org.uk/geography and only for non commercial use in schools