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Plate tectonics

Earth structure:
The core: Roughly the size of
Mars. Made of rocks rich in iron
and nickel so is the densest part
of the Earth, roughly 6000C.
Inner Core: Solid
Outer Core: Semi-molten
Mantle: composed of molten and
semi-molten rocks containing
lighter elements such as silicon
and oxygen.…

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asthenosphere that causes crustal plates to move." Hot mantle rises up as it is less dense from the
core that has been heated by radioactive decay in the core and transfers its heat the base of the
lithosphere. The mantle that has lost heat in this way becomes slightly denser…

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Formation: Where convection currents rise and diverge they create high temperatures that cause
up doming of the crust and tensional forces that pull it apart when the plate pull apart the magma
from the core (1200C) rises up to fill the gap forming new land.

Volcanic Structure and Characteristics:

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Formation: When convection currents converge they pull plates towards each other they meet. If
the plates are oceanic and continental as the oceanic plate is denser than the continental plate the
oceanic plate is sub-ducted underneath into the upper mantle. As the oceanic crust descends there is
friction between the…

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Associated Landforms:
Island arcs: The volcanoes that form are usually over laid with ocean so therefore the will eventually
form islands. They have been formed by magma from the Benioff zone. They usually form in curving
lines of new volcanic land.
Ocean trenches: The oceanic plate pulled down being sub-ducted…

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Hot spots: "A site of enhanced long-term volcanic activity, typically where a rising plume within the
mantle gives rise to large volumes of basaltic magma." Result of plumes of magma that originate
deep within the mantle. Hawaii is 3,200km from the nearest plate boundary so geologists think that
the formation…

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Major extrusive:

Plate Margin Constructive Destructive
Type of Magma Basaltic Rhyolite
Lava Low Viscosity High Viscosity
Characteristics Low Silica High Silica
From Core (1200C) From melted plate (600C)
Type of eruption Little violence: gases escape easily as Potentially explosive: lava shatters
the more fluid magma allows for gas into pieces.…

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2. Shield volcanoes
Shape: Gently sloping cones built up from
numerous less viscous lava flows
Location: Hot spots and where oceanic crust
meets oceanic crust. Mauna Loa, Hawaii.
Rock type: Basaltic
Eruptions: Gentle and predictable

3. Composite volcanoes
Shape: Layers of ash from initial explosive
phases and subsequent layers of…

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Lahars: Volcanic mud flows when the volcanic ash mixes with rain water. Pinatubo eruption
Flooding: Melting of glaciers of ice caps. Grimsvotn glacial burst on Iceland (November 1996)
Tsunamis: Giant sea waves generated after violent caldera forming eruptions. Krakatoa
(1883) drowned 36,000 people
Climatic change: Ejection of volcanic…

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Collapsing buildings
Destruction of road surfaces and other forms of communication.
Water and electricity supplies disrupted.
Fires from ruptured gas pipes.
Food shortages
Impact on economy.
Tsunamis: giant sea waves generated by shallow-focus underwater earthquakes or
landslides from volcanic eruptions.

Causes of earthquakes away from plate boundaries:


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