Download Volcano Notes

Magma
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Magma is a mixture of molten rock, suspended
mineral grains, and dissolved gases deep
beneath Earth’s surface.
Pressure and water are two factors that
determine whether rock will melt to form
magma.
A liquid’s resistance to flowing is called its
viscosity.
Substances such as honey, liquid soap, and
motor oil have a higher viscosity than water,
vinegar, and gasoline.
Rhyolitic magma has the greatest viscosity.
Types of Magma
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Basaltic magma has low silica content
and the least explosive eruption.
Andesitic magma has intermediate silica
content and an intermediate eruption.
Rhyolitic magma has high silica content
and an explosive eruption; greatest
viscosity.
Anatomy of a Volcano
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An opening in the Earth’s surface
where magma escapes is called a
vent.
A bowl-shaped depression around the
vent of a volcano is called a crater.
If a volcano collapses, the very large
crater that is left is called a calderas.
Types of Volcanoes
Shield Volcano:
Mountain with broad, gently sloping
sides and a nearly circular base.
Shield volcanoes form when layer
upon layer of basaltic lava
accumulates during non-explosive
eruptions.
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Cinder-cone Volcano
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Forms when material ejected high into
the air falls back to Earth and piles up
around the vent. Cinder-cone
volcanoes have steep sides and are
generally small. Cinder-cone
volcanoes are more explosive in
nature than shield volcanoes.
Composite Volcanoes
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Forms when layers of volcanic fragments
alternate with lava. The magma that forms
composite volcanoes commonly contains
large amounts of silica, water, and gases.
They are larger than cinder-cone volcanoes,
and, because of their violently explosive
nature, they are potentially dangerous to
humans and the environment.
Hot Spots
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Hot spots are unusually hot areas in
Earth’s mantle that are stationary for
long periods of time, where high
temperature plumes of magma
material rise toward the surface.
Some volcanoes are located far from
plate boundaries and these form as a
result of hot spots.
Where Do Volcanoes
Occur?
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Most volcanoes form at plate
boundaries.
80% of all volcanoes are found along
convergent boundaries.
15% are found on divergent
boundaries.
Only 5% occurs far from plate
boundaries.