Download Chapter 18- Volcanic Activity

Chapter 18- Volcanic Activity
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I. Magma
A. How magma forms
1. All volcanoes are fueled by magma
deep beneath Earth’s surface.
2. Magma forms when temperatures
are high enough to melt the rocks
involved.
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3. Pressure is one factor that
determines whether rocks will melt to
form magma.
4. The presence of water also
influences whether a rock will melt
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B. Types of magma
1. There are three major igneous rock typesbasalt, andesite and granite. These rocks
form three types of magma.
2. Basaltic magma, andestic magma and
rhyolitic magma.
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Basalt
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Andesite
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Granite
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C. Viscosity
1. The viscosity of magma and of its
counterpart, lava depends on both
temperature and composition.
2. The hotter the magma or lava, the
lower the viscosity.
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II. Intrusive Activity
A. Plutons
1. Intrusive igneous rock bodies are
called plutons, can be exposed at
Earth’s surface as a result of uplift and
erosion are classified based on their
size, shape and relationship to
surrounding rocks.
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2. The largest plutons are called batholiths.
3. Laccolith is a mushroom- shaped pluton
with a round top and flat bottom.
4. A sill is a pluton that forms when magma
intrudes parallel to layers of rock.
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Batholiths
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Laccolith
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Sill
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5. A dike is a pluton that cuts across
preexisting rocks.
6. Many plutons are formed as the
result of mountain-building processes.
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B.
Tectonics
1. The Earth’s crust and rigid upper mantle
are broken into enormous slabs called plates.
2. Tectonic plates move in different directions
and at different rates over Earth’s surface.
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THE BAD LANDS
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More Bad Lands…..
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Needles Point
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Old Faithful
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Morning Glory
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Unique Land forms
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More Unique Land forms
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Acid Boiling lakes
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Yellowstone
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More Yellowstone….
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Continental Divide
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Continental Divide
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Grand Teton Mountains
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III. Volcanoes
A. Anatomy of a volcano
1. At the top of the volcano, around the vent
is a bowl shaped depression called a crater.
2. Larger depression called caldera can form
when the side of the volcano collapses into
the magma chamber.
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Crater
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Caldera
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B. Types of volcanoes
1. A shield volcano is a mountain with
broad, gently sloping sides and a nearly
circular base.
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2. Cinder – Cone volcanoes forms when
material ejected high into the air falls
back to Earth and piles up around the
vent.
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3. Composite Volcano- forms when
layers of volcanic fragments alternate
with lava.
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C. Volcanic material
1. Rock fragments thrown into the air
during a volcanic eruption are called
tephra.
2. Some tephra cause tremendous
damage and can kill thousands of people.
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D. Where volcanoes occur?
1. The distribution of volcanoes on
Earth’s surface is not random. Most
volcanoes form at plate boundaries.
2. Most volcanoes form at plate
boundaries.
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3. About 80% of all volcanoes are found
along convergent boundaries and 15%
are found along divergent boundaries.
4. Only about 5% of volcanoes occur
far from plate boundaries.
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5. The volcanoes associated with
convergent plate boundaries form two
major belts- the Circum- Pacific belt
(Pacific ring of fire)
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6. Mediterranean belt.
7. Some volcanoes are located far from plate
boundaries, these volcanoes form as the
result of hot spots, which are unusually hot
regions of earth’s mantle where hightemperature plumes of mantle material rise
toward the surface.
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THE END
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