Volcanoes - Boardworks

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Volcanoes
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Boardworks Ltd 2005
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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 earths
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
Volcanic bombs, ash and gases
Crater
Parasitic cone
Main vent
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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 againEl Chichon,
Mexico erupted in 1982 after being dormant for
approximately 1200 years!
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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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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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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.
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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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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).
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
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
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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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Why do people live in volcanic areas?
Can you think of any other reasons?
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Internet links

• Volcano World - a fun and informative web
  sitehttp//volcano.und.nodak.edu/

• Virtual field visits
• http//educeth.ethz.ch/stromboli/
• The Michigan Technological University Volcanoes
  Pagehttp//www.geo.mtu.edu/volcanoes/
• Global Volcanism Programhttp//www.volcano.si.edu
  /gvp/
• Fallout Eye on the Volcanohttp//www.nationalgeo
  graphic.com/features/98/volcanoes/
• Savage earthhttp//www.pbs.org/wnet/savageearth/