Download Volcanoes

Volcanoes – Part 1: Introduction
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Learning objectives
What is a volcano?
Why do volcanoes occur?
What happens when a volcano erupts?
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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
Secondary cone
Crater
Main vent
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Cross section of a volcano
Crater
Volcanic
bombs, ash
and gases
Secondary
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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Learning objectives
What is a volcano?
Why do volcanoes occur?
What happens when a volcano erupts?
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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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Destructive plate boundary
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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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Constructive plate boundary
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Constructive plate boundary
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Types of Volcanoes
Volcanoes are divided into three main types
depending upon the material thrown out
in an eruption
1. Composite Cone Volcano (ex. Mount St.
Helens, Mount Etna)
2. Acid Lava Volcano (ex. Mount Pelee)
3. Shield Volcano (ex. Mauna Loa)
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Volcano shapes
Why do volcanoes have different shapes?
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Volcano shapes
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Volcano shapes
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Volcanic activity at plate margins
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Volcanic activity at plate margins
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Learning objectives
What is a volcano?
Why do volcanoes occur?
What happens when a volcano erupts?
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Task 1
• Read Interactions pgs. 34-35 (see next slide).
• Do “Activities” nos. 2, 3 and 4 in your
exercise book.
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Task 2
• Download and print out a copy of the
following worksheet “Cross section of a
volcano outline.doc”
• Using Interactions pgs. 32-33 (see next
slide)copy and complete the following
worksheet the same way as Diagram A on pg.
32.
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