AQA Geography A2 Plate Tectonics listening notes

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Preview of AQA Geography A2 Plate Tectonics listening notes

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Plate Tectonics
The structure of the earth
The earth structure is split up into four layers, these are the crust , mantle, outer core and
inner core.
The crust: The crust covers the mantle and is the earth's hard outer shell, the surface on
which we are living. Compared to the other layers the crust is much thinner. It floats upon
the softer, denser mantle. The crust is made up of solid material but this material is not the
same everywhere, this layer has the least dense and coolest. There are two types of crust,
the oceanic and continental, these have a range of thickness with up to 70 kilometres on
the continental crust and only 10 kilometres on the oceanic crust. It is separated from the
Mantle by the Mohorovijic (Moho) boundary.
The mantle: The layer above the core is the mantle. It begins about 6 miles (10 kilometres)
below the oceanic crust and roughly 19 miles (30 km) below the continental crust. The
function of the mantle is to separate the inner mantle and the outer mantle. It is about
1,800 miles (2,900 kilometres) thick and makes up nearly 80 percent of the Earth's total
volume. It is a semi-molten layer at about 5000°c, at these high temperature there are
convection currents in the mantle.
The outer core: The outer core is about 1,800 miles below the earth's surface and is roughly
the size of Mars. The core is a dense ball of the elements iron and nickel which are liquid at
about 6000°c.
The inner core: This is also at 6000°c but due to the high pressure the nickel and iron which it
is made up of remains solid it is at the centre of the earth.
This is the layer of the earth which consists the ridged top part of the Mantle and the crust
The asthenosphere is the ductile part of the earth just below the lithosphere, including the
lower mantle. The asthenosphere is about 180 km thick.

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Both parts are in a series of interlocked pieces called plates
The point between 2 plates is called a plate boundary
The plates are constantly moving (very slowly). In parts of the world where the plates are
moving apart, a constructive (or divergentl) plate boundary is formed. New oceanic crust
is formed as the magma rises and solidifies e.g. Eurasian and North American Plates.
In other parts of the world the plates are moving together e.g.…read more

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Evidence to support this includes:
Fossil evidence - same species of land animals found on opposite sides of the Atlantic Ocean
Climate evidence - coal deposits and fern fossils in Antarctica (showing it used to be more
equatorial). Also glacial deposits in India, South America, Africa and Australia which are too
hot for glaciers today.…read more

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Typical slopes of 15°
Lava flows down slope, away from the central vent
Many shield volcanoes have a central caldera
Examples: Hekla and Katla
Ocean Ridge Volcanoes
Volcanic activity under water, for example at the Mid Atlantic Ridge
Submarine oceanic ridge volcanoes e.g. Surtsey 1964, form new islands
Passive volcanic activity, low magnitude and not dangerous
Volcanic activity at conservative plate margins is often associated with fissure type eruptions.…read more

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Destructive Plate Boundaries
These types of boundaries are:
Continental-Continental Boundaries
Oceanic-Oceanic Boundaries
Oceanic-Continental Boundaries
Continental-continental Boundaries
When two continents meet in a collision
zone, there is very little/no subduction (no
volcanic activity as neither are absorbed into
the mantle) as both are relatively light and
buoyant, resisting downward movement. The
outcome is that two continental masses
become crumpled and compressed together
to form Fold Mountains e.g. The Himalayas.…read more

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Waves travel at 800kilometres an hour , but due to enormous wavelength the wave
oscillation can take 20-30mins to complete a cycle and has amplitude of 1metre.
Very difficult to detect over deep water meaning they go unnoticed by ships
Management of Tsunamis
Pacific Ocean Tsunami Warning System - gives an early warning - however there is no such
thing in the Indian ocean (poor suffer more)
Communication in MEDCs e.g.…read more

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The magma is very gaseous, particularly when enriched with water vapour - high explosive
Stratovolcanoes are constructed from feeder conduits extending to the surface
Granitic (rhyolitic) intrusions are also formed, becoming trapped within the volcanic pile
overlying the region of subduction giving potential for very explosive eruptions
Stratovolcano/ composite volcanoes
These are volcanoes which alternate between periods of lava flows (constructive phase) and periods
of explosive eruptions (destructive phase).…read more

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The rising mantle material is called a mantle plume.
Very passive eruptions from shield volcanoes due to the magma's composition
Case Study: Hawaii
Long chain of 129 volcanoes, of which 123 are now extinct as the plate moves north-west
As the plate continues to move there will be a new Hawaii and islands further up the chain will die to
form submarine seamounts.
Extrusive volcanic Features
Geysers: water is heated at depth in the crust by magma changes.…read more

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Most damage will occur at the epicentre, the point on the earth's surface immediately above
the focus.
P and S Waves
P waves: primary waves: these are longitudinal waves which push and pull the earth.
They are the fastest body wave with speeds of 6 kilometres a second meaning they
arrive first
S waves: secondary waves: these are transverse waves which shake the earth from side
to side. They arrive second at speeds of 4 kilometres a second.…read more

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Risk Assessment involves not only hazards from a scientific point of view but also the socio-economic
impacts. Risk is a statement of probability that an event will cause a certain amount of damage or a
statement of economic damage of an event.…read more


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