Transcript File - Units 1 & 2 Geography

Plate Tectonics
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Constructive plate boundary
At a constructive plate boundary, two plates move apart.
As the two plates move apart, magma rises up to fill the
gap. This causes volcanoes. However, since the magma
can escape easily at the surface the volcano does not
erupt with much force.
Earthquakes are also found at constructive boundaries.
An example of a constructive boundary is the Mid-Atlantic
Ridge.
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Constructive plate boundary
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How fast do plates move?
Tectonic plates move at different rates.
The Nazca and Pacific plates are moving apart at a rate of
18cm per year while the Eurasian and North American
plates are moving apart at a rate of 3cm per year.
To the nearest metre, how far will the Nazca and Pacific
plates have moved over the next 200 years?
6 metres
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36 metres
200 metres
928 metres
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Constructive plate boundaries
mid-ocean ridge
B
A
ocean
mantle
Where would you find older rocks – at A or at B?
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Destructive plate boundary
A destructive plate boundary is found where a
continental plate meets an oceanic plate.
The oceanic plate descends under the continental plate
because it is denser. As the plate descends it starts to
melt due to the friction caused by the movement between
the plates. This melted plate is now hot, liquid rock
(magma). The magma rises through the gaps in the
continental plate. If it reaches the surface, the liquid rock
forms a volcano.
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Destructive plate boundary
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Destructive plate boundary
Match the labels to the letters.
F
E
A
B
D
1.oceanic plate
2. The oceanic crust sinks under
the less dense continental crust.
4. continental crust
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C
5. explosive volcanoes
3. The oceanic crust
melts and rises.
6. mantle
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