Revision Notes A2 AQA Geography Tectonics

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  • Created on: 04-06-12 10:43
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Plate Tectonics and Associated
Hazards- Revision Notes
Plate Movement
Earth Structure
The Earth is comprised is of three layers
The core comprises of dense rocks, (density 12) especially of iron and nickel alloys. The inner core
is solid and the outer core is liquid. The outer core is where the Earth's magnetic fields originate,
due to electrical currents flowing in the metallic core. Fluid moves due to convection currents. It is
thought there is a radioactive decay happening in the core which powers the convection currents.
The inner core is 1100km deep. The outer core is 2400km deep
The mantle is less dense than the core as the rocks are comprised of lighter elements such as
silicon and oxygen with varying densities depending on the proximity to the core. Close to the
core rocks have a density of 5.7 and 3.0 near to the crust. The junction between Core and Mantel
is known as the Gutenberg Discontinuity or Moho discontinuity the junction between the Mantle
and Crust.
Continental Oceanic
Age 3800 million 200 million
Thickness 30-70km 5-9km
Density 2.7g/cm 3.0g/cm3
Main rock type Granite Basalt
Materials SIAL SIMA
The density of the crustal rocks is lower than the core and mantle because of lighter elements
such as oxygen, silicon, aluminium, potassium and sodium. There is a large difference in the
thickness of the crust depending on what is on the surface. It can range from only 5km thick below
the oceans to up to 65km think below mountain ranges.
The theory of plate tectonics suggest of three more layers incorporating different parts of the Crust
Mantle and Core.

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The Lithosphere is the crust and the rigid upper part of the mantle forming a layer which is 80km
thick; this is divided in to 12 larger plates and numerous smaller ones
The asthenosphere is semi-molten material below the lithosphere on which the plates of the
lithosphere `float'.…read more

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Alongside each other: TRANSFORM or transcurrent.
Constructive Margins
Plates move away from each other, for example, N. American and Eurasian plates, cresting
mid-ocean ridges such as the Mid Atlantic Ridge. New material appears at the ocean ridge.
Features of Constructive margins
Mid-Ocean Ridges- long high and often complex structures of rifts and scarps
Volcanoes- occur along mid-Atlantic ridges, sometimes rising above the sea to form islands
such as Surtsey, Iceland.…read more

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Volcanoes- heat generated by friction, cause the plate to melt in an area known as the
Benioff zone. This is lighter than the surrounding asthenosphere and rises towards the
surface as magma. This is viscous and forms composite and explosive volcanoes.
Island arcs- magma comes to the surface under water to form a line of volcanoes
e.g. the Mariana Islands formed in association with the Mariana trench.
Conservative margins
Plates slide past each other and there is no creation or destruction of crust.…read more

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Pahoehoe: rope like surface due to partial cooling
Aa: block, rough lava flow
Major forms of extrusive activity- Volcanoes
Fissure Eruptions
o Occur where an elongated crack in the crust allows lava to spill out over a large area.
o Location: Constructive margins
o Made of: Basaltic rocks
o Eruption: Gentle, persistent
o Example: Antrim lava Plateau, Northern Ireland, Giant's causeway
Shield Volcanoes
o Form gently sloping cones from layers of less viscous lava.…read more

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Minor forms of extrusive activity
As well as volcanoes there are other features on the surface due to volcanicity
o Water heated by volcanic activity is intermittently discharged of water
o Ejected as a turbulent eruption of water and vapour
o Water is above boiling point
o Examples: Old Faithful, Yellowstone National Park and Geysir, Iceland
Hot Springs
o The emergence of geothermally heated groundwater from the earth's crust
o Can be found all over the world
o Occur where water temperature is below…read more

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Volcanic landsides
Climate change- brought about by the injection of vast amounts of debris into the
atmosphere, which can reduce global temperatures
Intrusive activity
With all volcanic regions, the majority of magma never reaches the surface but cools to form coarser
grained igneous rocks beneath the ground. To form intrusive activity magma cools slowly under the
surface and changes the local rock and metamorphic rocks are formed, harder rocks and a
metamorphic aureole surrounds this with precious metals such as gold zinc, tin and lead.…read more

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Case Study
Volcanic eruption- Eyjafjallajokull, Iceland, 2010
Eyjafjallajokull is a volcano 1660m high in the south of Iceland 200km
from the capital of Reykjavik.
Situated on top of the Mid-Atlantic ridge and a constructive margin and a
hot spot which makes eruptions more common.…read more

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If there was another ash cloud more research has been done in to the effect of ash on
airplane engines it has been discovered that all flights don't need to be grounded plane are
just required to flu at a lower height
Case Study
Volcanic Eruption-Nyiragongo, Democratic Republic of Congo, 2002
Mount Nyiragongo is about 20 km north of the town of Goma and Lake
Kivu and just west of the border with Rwanda
Located in the African Rift Valley, where the crust is…read more

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Long term effects
Those who did flee to Rwanda found that there was a problem with
food and shelter provision in the small country there was also the
worry of cholera and diarrhoea due to cramped conditions
There was also limited drinking water; this meant that many people
suffered from dysentery,
Medical supplies where limited because of the effects of smoke and
fumes from the lava which caused eye irritation and respiration
problems as well as burn treatment for those who had crossed the
lava.…read more


Finn McGowan

nas 1 sonny

Connor McDonagh

Awesome, covers everything

Idrees Ahmed

I dont normally type here, but when I do, its only to say that this is the best resource I have found for tectonics for which I am doing the 40 mark essay on. Looking to add more case studies but it has everything on there. Beautiful


amazing, you absolute life saver


thanks so much!!



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