AQA GCSE Geography A the restless earth revision notes

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Why is the earth's crust unstable?
The structure of the earth

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Types of plate margin
Destructive plate margin
Convection currents in the mantle cause plates to move together. If one plate is made from oceanic
crust and the other from continental crust, the denser oceanic curst sinks under the lighter continental
crust in a process known as subduction. Great pressure is exerted and the oceanic crust is
destroyed as it melts to form magma.
If two continental plates meet each other, they collide rather than one sinking beneath the other.…read more

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Constructive plate margin
When plates move apart, a constructive plate
boundary results. This usually happens under the
ocean. As the plates pull away from each other,
cracks and fractures form between the plates
where there is no solid crust. Magma forces its
way up into the cracks and makes it way to the
surface to form volcanoes. In this way ne land is
Conservative plate margin
At conservative plate margins, the plates are
sliding past each other.…read more

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Both fold mountains are ocean trenches result from the plates moving together. If both landforms
occur in the same area, they are found in association with subduction. In fold mountains occur by
themselves they are in areas where collision is taking place. Either way, the sequence relation to the
formation is similar.…read more

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Case study: The Alps
The Alps are a mountain range in Europe. They were formed about 35 million years ago by the
African plate pushing north against the Eurasian plate.
Most farms are located on the sunny south facing slopes. The traditional farming method was using a
system called transhumance (the seasonal movement of animals).…read more

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RELIEF: mainly high and steep, rock outcrops are frequent and many mountain valleys are
rocky and narrow. This means there is little flat land for settlements or farming.
CLIMATE: increasing height brings colder, windier, wetter weather. The growing season is
short and cannot take place at high levels.
SOILS: mountain soils are typically stony, thin and infertile. The good soil is in valleys.
ACCESSIBILITY: roads and railways are expensive and difficult to build and travel on.…read more

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Roads and bridges became unusable After effects killed 700 people.
hindering any help.
6 people died directly.
Immediate responses
Long term
Monitoring and predicting volcanoes
Tilt meters can measure small changes in the landscape.
Changes in temperature can be detected on satellite images.
Robots called `spiders' measure changes in gas.…read more

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Time lapse cameras allows geologists to look at craters and make safe observations
What is a supervolcano?
A supervolcano is a mega colossal volcano that erupts at least 1,000km³ of material.
Characteristics of a supervolcano
Case Study: Yellowstone
The likely effects of an eruption
INITIAL EFFECTS: the clearing of any tourists in the national park and any one in a 100 mile
radius. The park would be closed. The volcano would erupt fine materials, shooting them up
80,000 feet into the air.…read more

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Worldwide travel would cease and day would be turned to night. It would alter the climate
and make everywhere much colder. The ash would stay in the atmosphere for up to 6 years
and worldwide trade would be affected too.
What are earthquakes and where do they
Characteristics of earthquakes
The place where earthquakes begin, deep within the earth's crust is called the focus; deep-focus
earthquakes cause less damage and are felt less than shallower ones.…read more

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How do the effects of earthquakes differ in
countries at different stages of development?
KOBE (Japan) EARTHQUAKE ­ January 7th 1995, 5.46am ­ 7.2 Richter scale ­ 20 seconds long MEDC
SIHUAN (China) EARTHQUAKE ­ May 12th 2008, 2.28pm ­ 7.9 Richter scale ­ 2 minutes long LEDC
· Kobe lies on the Nojima fault above a destructive plate margin. Here, the heavier, oceanic
plate (the Philippine plate) is forced under the lighter, continental Eurasian plate. Sudden
movement of the fault caused this earthquake.…read more



thank you

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