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Plate
Tectonics
and associated hazards
Plate movement
Earth structure, plate tectonics theory: convection currents and sea-floor spreading. Evidence: continental drift
and palaeomagnetism.
Destructive, constructive and conservative plate margins. Processes: seismicity and vulcanicity.
Associated landforms: young fold mountains, rift valleys, ocean ridges, deep sea trenches and island arcs.
Hot spots associated…

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Plate Movement
A Background to Plate Tectonics
Earth is 4.6 billion years old
o Started as a ball of molten materials
o Slowly cooled from surface inwards to form a crust of solidified rocks
o Gases escaping from volcanic activity formed an atmosphere
o Many asteroid impacts and wasn't yet…

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The Theory of Tectonics


The crust is fractured into huge
segments called tectonic plates
o These plates are moving
slowly by convection
currents within the mantle
Beneath the earth, temperatures
start to rise in the mantle (a zone
of molten silicates and other
minerals)
o The boundary is
transitional
o…

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The Crust
The crust is divided into chunks of solid rock called tectonic plates




The major plates:
o Pacific
o Eurasian
o African
o Antarctic
o North American
o South American
o Indo-Australian
o Other smaller plates
The plates are made of different materials:
o Continental
Thicker, older, lighter
Made…

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Vulcanicity
Volcano and Earthquake Location
This
map




shows how some of the world's volcanoes and earthquakes occur along tectonic plate boundaries.



Evidence for Plate Tectonics
Continental drift
o Francis Bacon
Noticed that continents either side seemed to fit together remarkably well
o Alfred Wegener
Had a theory that 300 million…

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the continents were joined at some point
Glacial evidence
o There is wide spread distribution of permocarboniferous glacial sediments in South
America, Africa, Madagascar, Arabia, India, Antarctica, and Australia
o The continuity of glaciers (striations and deposits) suggest the super continent
existed called Gondwanaland
o Striations indicated glacial flow towards…

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Plates are moving apart from each other
What happens at this Magma rises to the surface of the earth
boundary? When magma reaches the surface, it cools and solidifies to
form a new crust of igneous rock
Earthquakes often accompany magma rising
Volcanoes and
Volcanoes form when the magma builds…

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Conservative
Plates are sliding past each other, either in the same or the
What happens at this
opposite direction
boundary?
There is no destruction or creation of the crust
There is no volcanic activity
Volcanoes and Earthquakes are caused because friction is caused as the
earthquakes? plates rub against each…

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Destructive
(oceanic and
continental)
The oceanic crust moves towards (and disappears into the
mantle of) a continental plate
What happens at this This is because the denser oceanic plate is forced beneath
boundary? the continental plate into the subduction zone
As the oceanic plate is forced downwards, it melts due…

Page 10

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Destructive
(oceanic and
oceanic)
The plates are moving towards each other
What happens at this
When oceanic plates meet, one is forced under the other and
boundary?
the processes of subduction begin
Because the molten rock from the melting oceanic plate is
Volcanoes and
lighter, it rises to the surface…

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