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A Level Geography - Tectonics Summary revision notes
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Summary revision notes for Geography - Superpowers - Pearson Edexcel specification
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A hazard is a potential threat to human life and property caused by tectonic events.These occur around plate boundaries.
Earthquakes
- Distributed around the ring of fire in pacific oceans or around tectonic plate
boundaries.
- These are caused by plates moving past each other, where they can subduct or
collide causing huge amounts of pressure to build up. When this pressure
exceeds the strength of faults, the rock fractures causing a sudden release of
pressure.
Volcanoes
- Distributed around tectonic plate boundaries. These occur in destructive or
convergent plate boundaries, where one plate subducts another causing the
build up of pressure
Tsunami
- Occur in the pacific basin associated with activity at the plate margins. Most
are generated with convergent boundaries where tectonic plates meet each
other. Eg: Japan.
- Sub-marine earthquakes displace sea bed as a result of tectonic movement in
subduction zones. This displaces a large amount of water causing water
column displacement.
Convergent (Destructive) plate boundaries: This occurs when the denser
oceanic plate subducts the continental plate. This leaves behind an ocean trench.
- This subduction leads to the formation of fold mountains
- Friction created between colliding plates causes earthquakes.
- Magma created by the melting oceanic crust causes pressure to build up and
pushes up through faults to reach the surface where it causes volcanic
eruptions.
When oceanic plates meet together, built up pressure causes underwater volcanoes.
It creates new land.
,Divergent (Constructive) plate boundaries: This occurs when two plates are
moving apart which leads to magma rising between these gaps which leads to the
formation of new crust. In oceans, this forms mid-ocean ridges. In land, it forms rift
valleys.
Conservative plate boundaries: Two plates slide past each other. This leads to
friction to be built up causing pressure. This can be released in the form of
earthquakes.
Processes affecting tectonic movements:
1) Mantle convection = Heat produced by decay of radioactive elements in
Earth’s core heats the mantle creating convection currents. These move in
circles in the asthenosphere (mantle) causing plates to move.
2) Slab pull = Newly formed oceanic crust at mid-ocean ridges becomes less
dense as it cools causing it to sink into the mantle under its own weight which
pulls the rest of the plate further down with it.
3) Subduction = plates collide with another causing subduction.
4) Seafloor spreading = Mid ocean ridges are formed when hot magma is forced
up when oceanic plates divert from one another. This magma cools and
hardens, forming new oceanic crust. This new crust pushes tectonic plates
apart in seafloor spreading.
- Matching Coal (found in tropical conditions has been found in temperate
conditions) and fossils and rocks are found in different continents showing that
earth was once connected.
- Paleomagnetism = study of ancient magnetism preserved in rocks.
, Earthquakes:
Type of waves:
1) Primary waves (P waves)
- They are the fastest waves so the first ones to reach the surface
- Causes the least amount of damage (low amplitude and energy force).
- Waves push and pull in compressing motions in the direction of travel
meaning that they wouldn’t deal as much damage towards buildings as
there is less energy to shake the buildings horizontally.
2) Secondary waves (S waves)
- Larger waves, amplitude and energy force
- They shake in up and down motion at right angles to direction of travel,
so they cause considerable damage.
- They do more damage than p waves
3) Love wages
- Have the highest amplitude and energy force so it’s more destructive.
- They move in a horizontal motion from side to side so building
foundations could be shaken horizontally so buildings collapse.
- It focuses all its energy of earth’s surface so causes most damage.
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