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Volcanoes
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Learning objectives
What is a volcano?
Why do volcanoes occur?
Where are volcanoes found?
What happened in the 1980 Mount St
Helens eruption?
Can volcanic eruptions be predicted?
Why do people live in volcanic areas?
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What is a volcano?
A volcano is an opening or vent in the earth’s surface
through which molten material erupts and solidifies as lava.
Volcanic vent
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Label this cross section of a volcano
Volcanic bombs,
ash, lava, gases
Magma chamber
Parasitic cone
Crater
Main vent
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Cross section of a volcano
Crater
Volcanic
bombs, ash
and gases
Parasitic
cone
Main vent
Magma
chamber
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Cross section of a volcano
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Volcanic emissions
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Volcanic emissions
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Do all volcanoes erupt?
Active volcano – liable to erupt e.g. Mt Etna.
Dormant (sleeping) volcano – a volcano which
has not erupted for many years. For example, Mt
Pinatubo erupted in 1991 after 500 years of
dormancy.
Extinct volcano – a volcano which has not
erupted for many thousands or millions of years
e.g. Edinburgh.
However, it is often very difficult to tell whether a volcano
will erupt again…El Chichon, Mexico erupted in 1982
after being dormant for approximately 1200 years!
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© Boardworks Ltd 2006
Learning objectives
What is a volcano?
Why do volcanoes occur?
Where are volcanoes found?
What happened in the 1980 Mount St
Helens eruption?
Can volcanic eruptions be predicted?
Why do people live in volcanic areas?
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Why do they happen?
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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Why do they happen?
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.
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Constructive plate boundary
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Volcano shapes
Why do volcanoes have different shapes?
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Volcano shapes
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Volcanic activity at plate margins
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© Boardworks Ltd 2006
Learning objectives
What is a volcano?
Why do volcanoes occur?
Where are volcanoes found?
What happened in the 1980 Mount St
Helens eruption?
Can volcanic eruptions be predicted?
Why do people live in volcanic areas?
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Where are volcanoes found?
Around which plate do we find most volcanoes?
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Hawaii
The Hawaiian islands are a chain
of volcanoes in the Pacific Ocean.
Look at their location on the map below.
Why is this an unusual place for them to
be located?
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Hot spot volcanoes
In the animation above, why are the volcanoes to the left of
the ‘hot spot’ extinct?
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© Boardworks Ltd 2006
Learning objectives
What is a volcano?
Why do volcanoes occur?
Where are volcanoes found?
What happened in the 1980 Mount St
Helens eruption?
Can volcanic eruptions be predicted?
Why do people live in volcanic areas?
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Mt St Helens eruption (May 1980)
Mt St Helens is located on the ‘Ring of Fire’.
Internet Links
http://volcano.und.nodak.edu/vwdocs/msh/msh.html
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Mt St Helens – causes of the eruption
Mt St Helens is located on a destructive plate boundary
where a continental plate (North American) meets an
oceanic plate (Juan de Fuca).
Juan de Fuca plate
North American plate
Which plate is denser?
Describe what happens when the oceanic plate
descends under the continental plate.
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Mt St Helens – the eruption
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Mt St Helens – consequences of the eruption
N
0
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10km
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Mt St Helens – consequences of the eruption
AFTER
BEFORE
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What damage did the eruption cause?
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Mt St Helens – consequences of the eruption
Why do you think animals such as
the vole and gopher survived the
blast?
How did their survival benefit the
area?
What benefits might the volcanic activity have brought to
Mt St Helens?
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Learning objectives
What is a volcano?
Why do volcanoes occur?
Where are volcanoes found?
What happened in the 1980 Mount St
Helens eruption?
Can volcanic eruptions be predicted?
Why do people live in volcanic areas?
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Predicting eruptions
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The problem of prediction
Volcanologists (people who study volcanoes)
are skilled at predicting the likelihood of an
eruption.
However, it's very difficult to pinpoint
exactly when an eruption will happen.
Often, moving magma doesn't result in an
eruption, but instead cools below the
surface.
Monitoring potential eruptions is expensive.
With many volcanoes erupting only every
few hundred years, it's not possible to
monitor every site.
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© Boardworks Ltd 2006
Learning objectives
What is a volcano?
Why do volcanoes occur?
Where are volcanoes found?
What happened in the 1980 Mount St
Helens eruption?
Can volcanic eruptions be predicted?
Why do people live in volcanic areas?
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Why do people live in volcanic areas?
This lava is weathered
(broken down) to form
a fertile soil.
Can you think of any other reasons?
Tourists are attracted to
areas of volcanic activity.
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Geothermal energy can be
produced in many volcanic areas.
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Internet links
Volcano World - a fun and informative web site
http://volcano.und.nodak.edu/
Virtual field visits
http://educeth.ethz.ch/stromboli/
The Michigan Technological University Volcanoes Page
http://www.geo.mtu.edu/volcanoes/
Global Volcanism Program
http://www.volcano.si.edu/gvp/
Fallout: Eye on the Volcano
http://www.nationalgeographic.com/features/98/volcanoes/
Savage earth
http://www.pbs.org/wnet/savageearth/
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