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Tectonic plates
The Earth consists of four concentric layers: inner core, outer core, mantle and crust. The crust is made up of tectonic
plates, which are in constant motion. Earthquakes and volcanoes are most likely to occur at plate boundaries.

The structure of the Earth
The Earth is made up…

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Distribution
The Earth's crust is broken up into pieces called plates. Heat rising and falling inside the mantle creates convection
currents generated by radioactive decay in the core. The convection currents move the plates. Where convection
currents diverge near the Earth's crust, plates move apart. Where convection currents converge, plates…

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Different plate boundaries


At a constructive boundary the plates move apart.

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At constructive boundary the plates are moving apart. The plates
move apart due to convection currents inside the Earth.
The Helgafjell volcano on Westman Island, Iceland
As the plates move apart (very slowly), magma rises from the mantle.
The magma erupts to the surface of the Earth. This is also…

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They are moving in a similar (though not the same) direction, at
slightly different angles and speeds.
As one plate is moving faster than the other and in a slightly different direction, they tend to get stuck.
Eventually, the build-up of pressure causes them to be released.
This sudden release…

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On a collision margin as the plates crash together the sediment goes up with them, becoming part of the
mountains.




The rock layers get twisted together as they collide together.
An example of the fold mountains is the Alps.

Characteristics of the Alps
High mountain ranges, eg Mont Blanc, which…

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Volcanoes
Volcanoes form when magma reaches the Earth's surface, causing eruptions of lava and ash. They occur at destructive
(compressional) and constructive (tensional) plate boundaries.
The immediate effects of volcanic eruptions can be devastating, but they may be beneficial in the long term.
Key facts
A volcano is formed by…

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The magma chamber is a collection of magma inside the Earth, below the volcano.
The main vent is the main outlet for the magma to escape.
Secondary vents are smaller outlets through which magma escapes.
The crater is created after an eruption blows the top off the volcano.
An eruption…

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There is little ash because it doesn't erupt as frequent because of less pressure building up.

Supervolcanoes.
A supervolcano is a volcano on a massive scale. It is different from a volcano because:
it erupts at least 1,000 km3 of material (a large volcano erupts around 1 km3)
it forms…

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Earthquake energy is released in seismic waves. These waves spread out from the focus. The waves are felt most
strongly at the epicentre, becoming less strong as they travel further away. The most severe damage caused by an
earthquake will happen close to the epicentre.




Main Features of an Earthquake…

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