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DATE: __________________
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Chapter # 8
Volcanoes
The Big Idea: Volcanoes form as a result of tectonic plate motions and
occur where magma reaches Earth’s surface.
Section 1:
Why Volcanoes Form
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 Where Volcanoes Form
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o Divergent Boundaries
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o Convergent Boundaries
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o Hot Spots
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 How Magma Forms
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o Increasing Temperature
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o Decreasing Pressure
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o Adding Fluids
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Section 2
Types of Volcanoes
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 Volcanoes at Divergent Boundaries
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o Lava at Divergent Boundaries
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o Mid-Ocean Ridges
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o Fissure Eruptions
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 Volcanoes at Hot Spots
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o Lava at Hot Spots
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o Shield Volcanoes
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o Parts of a Volcano
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 Volcanoes at Convergent Boundaries
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o Lava at Convergent Boundaries
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o Types of pyroclastic Material
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o Pyroclastic Flows
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o Cinder Cone Volcanoes
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o Composite Volcanoes
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Section 3
Effects of Volcanic Eruptions
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 Negative Effects of Volcanic Eruptions
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o Local Effects of Volcanic Eruptions
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o Global Effects of Volcanic Eruptions
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Benefits of Volcanic Eruptions
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o Volcanic Solids
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o Geothermal Energy
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o Other Benefits of Volcanic Eruptions
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Vocabulary
Volcano: a vent or fissure in Earth’s surface through which magma
and gases are expelled
Magma: liquid rock produced under Earth’s surface; igneous rock
form from magma
Lava: magma that flows onto Earth’s surface; the rock that forms
when lava cools and solidifies
Mafic: describes magma or igneous rock that is rich in magnesium and
iron and that is generally dark in color
Felsic: describes magma or igneous rock that is rich in feldspars and
silica and that is generally light in color
Lahar: a mudflow that forms when volcanic ash and debris mix with
water during a volcanic eruption
Aa: is lava that forms a thick, brittle crust. The crust is torn into
jagged pieces as molten lava continues to flow underneath.
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Pahoehoe: is lava that forms a thin crust. The crust wrinkles as it is
moved by molten lava that continues to flow underneath.
Pillow lava: forms when lava erupts underwater. This lava forms
rounded lumps that are the shape of pillows.
Blocky lava: is cool, stiff lava that does not travel far from the
eruption site. Blocky lava usually oozes from a volcano and forms
jumbled heaps of sharp-edged chucks.
California Standards
6.1a Students know evidence of plate tectonics is derived from the fit of
the continents; the location of earthquakes, volcanoes, and midocean
ridges; and the distribution of fossils, rock types, and ancient climatic
zones.
6.1d Students know that earthquakes are sudden motions along breaks in
the crust called faults and that volcanoes and fissures are locations
where magma reaches the surface.
6.1e Students know how major geologic events, such as earthquakes,
volcanic eruptions, and mountain building, results from plate motions.
6.2d Students know earthquakes, volcanic eruptions landslides, and
floods change human and wildlife habitats.
6.6a Students know the utility of energy resources is determined by
factors that are involved in converting these sources to useful forms and
the consequences of the conversion process.