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Chapter 13 Notes
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J. Nguyen – Physical Science
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Chapter 13 Standard
3e. Students know there are two kinds of
volcanoes: one kind with violent eruptions
producing steep slopes and the other kind
with voluminous lava flows producing
gentle slopes.
J. Nguyen – Physical Science
Chapter 13 – Volcanoes
J. Nguyen – Physical Science
Review!!
1. Plate tectonics is the theory that explains why and
how continents move and is the study of the
formation of features in Earth’s crust.
2. The lithosphere is the thin, rigid, outer shell of
Earth that is the crust and part of the mantle.
a. Lithosphere is broken into several blocks called
tectonic plates.
3. Some volcanoes form when plate motions generate
magma that erupts on Earth’s surface.
I. 13.1 – VOLCANOES AND
PLATE TECTONICS
J. Nguyen – Physical Science
A. Formation of Magma
1. Magma is the liquid (melted) rock that
forms under Earth’s surface.
2. Magma is formed under three conditions:
a. Temperature increases above melting point
and the rock will melt.
b. With less pressure, the melting point
decreases and the rock will melt.
c. With the addition of fluids, the melting point
will decrease and the rock will melt.
B. Magma and Volcanism
1. Volcanism is any activity that includes
movement of magma onto Earth’s
surface.
2. Magma rises to Earth’s surface because
it is less dense (lighter) than the
surrounding rock.
3. Magma becomes larger at the surface in
two ways:
a. Magma can melt surrounding rock.
b. Magma is forced into cracks and crevices of
surrounding rock.
4. Lava is magma at the Earth’s surface.
5. Volcano is the vent in Earth’s surface
through which magma and gases are
expelled (escape).
Color and label
picture.
LAVA
MAGMA
GASES
C. Parts of a Volcano
1. Ash cloud – the cloud of ash and dust that form in the air
after some volcanic eruptions
2. Conduit – a passage through which magma (molten rock)
flows in a volcano
3. Crust – earth's outermost, rocky layer
4. Lava – Magma that reaches the earth’s surface
5. Magma chamber – contains magma (molten rock) deep
within the Earth's crust
6. Side Vent – a vent in the side of a volcano
7. Vent (central) – opening in the Earth's surface through
which volcanic materials erupt
Color and label
picture.
Vent
Conduit
Lava
Crust
Side Vent
D. There are three major volcanic zones
where most active volcanoes occur.
1. Subduction Zone – one tectonic plate goes
under another plate
a. Occurs along lithospheric plates
b. There are two types of subduction zones:
i. oceanic-continental – where oceanic
crust subducts under continental crust;
volcanoes form on the continental crust
next to the ocean and results in a
volcanic arc
Oceanic-Continental Subduction
Color and label
picture.
ii. oceanic-oceanic – where oceanic crust
subducts under oceanic crust; volcanoes form
on ocean crust and results in an island arc of
volcanoes
Oceanic-Oceanic Subduction
Color and label
picture.
c. Example of subduction zone: PACIFIC RING
OF FIRE
Color picture.
2. Mid-Ocean Ridges – tectonic plates are
moving away from each other
a. Occur along lithospheric plates.
b. Site of where there is the greatest amount of
magma that comes to the surface.
c. The interconnected mid-ocean ridges that
circle the earth form a major zone of
volcanic activity.
d. As plates pull apart, magma wells upward
along the rift zone and can form underwater
volcanoes.
3.
Hot Spots – area of volcanism within lithospheric
plates
a. Hot spots remain stationary, but plate above it
slowly drifts so that eventually a chain of volcanoes
getting younger in age form
b. Example of hot spots: Hawaiian Islands
Color picture.
Write 10 questions for this section.
Highlight key words and phrases.
Draw a picture.
J. Nguyen – Physical Science
Summary (one paragraph) – Page 3
The lithosphere is ______________. Magma
is _________________________. Volcanism
is _________________. Magma rises to the
surface because it is ____________________.
Lava is __________________________. The
three major volcanic zones are ____________,
______________, and ______________.
J. Nguyen – Physical Science
II. 13.2 – VOLCANIC ERUPTIONS
J. Nguyen – Physical Science
A. Viscosity can be used to
describe magma and lava.
1. Viscosity – the internal resistance to flow
a. Example: honey is more viscous than water
and moves slower than water
2. The higher the temperature of the magma
or lava, the lower the viscosity (fast
moving).
3. The higher the silica content (crystalline
molecule), the higher the viscosity (slow
moving).
B. There are three types of magma.
1. basaltic magma
2. andesitic magma
3. rhyolitic magma
Copy table.
Magma
Type
Types of Magma
Source of
Magma
Viscosity Amount
Silica
Type of
Eruption
Basaltic
Magma
Upper
Mantle
Low
viscosity
50%
silica
Quiet
Andesitic
Magma
Oceanic
Crust and
Oceanic
Sediments
Intermediate
Viscosity
60%
Silica
Moderate
Rhyolitic
Magma
Continental High
Crust
Viscosity
70%
Silica
Explosive
C. There are two types of lava.
1. mafic lava – dark colored when
hardened and is rich in magnesium
and iron
2. felsic lava – lighter colored when
hardened and has little amounts of
magnesium and iron, is rich in silica
D. There are three types of lava flows.
1. Pahoehoe – Solidified mafic lava with a
wrinkled surface
2. Aa lava – jagged chunks of lava formed
by rapid cooling on the surface of a lava
flow
3. Blocky lava – forms chunky volcanic rock
when it cools.
E. There are volcanic rock
fragments that are released.
1. Felsic lava explodes, throwing pyroclastic
material into the air
2. Pyroclastic material – rock fragments
ejected from a volcano
a. pyroclastic material is sometimes called
TEPHRA
Pyroclastic Material
Type of Material
Size
Volcanic Dust
Less than 0.25 mm
Volcanic Ash
Between 0.25 mm and 2 mm
Lapilli
Between 2mm and 64 mm
Volcanic Bombs
As big as cars
Volcanic Blocks
As big as buildings
F. There are three types of volcanoes.
1. Shield Volcanoes – broad at the base and have
gently sloping sides
a. Covers a wide area and generally results from
nonexplosive lava eruptions
b. Layers of hot mafic lava flow out of vent,
harden, and slowly build up to form the cone
2. Cinder Cone Volcanoes – very steep
slopes and are not very tall
a. Result from explosive pyroclastic eruptions
b. Made of solid fragments ejected from the
volcano
3. Composite Volcanoes / Stratovolcanoes –
alternating layers of lava and pyroclastic material
a. Has both quiet eruptions and explosive eruptions
b. THEY NEVER BOTH erupt at the same time, the lava
layer will erupt, then the pyroclastic layer and so on.
c. Examples: Mt Fuji (Japan) and Mt St Helens
(Washington)
Lava
Pyroclastic
Material
Lava
Pyroclastic
Material
G. Craters and Calderas
1. Crater – the funnel shaped pit at the top of a
volcanic vent
2. Craters are formed when material is blown out of
the volcano by explosions
3. When the magma chamber below a volcano is
emptied, the volcanic cone may collapse, leaving
a large, basin-shaped depression called a
caldera.
H. Scientists use clues to help predict
volcanic eruptions.
1. Use seismographs to detect small
earthquakes that may be triggered by
magma moving upward.
2. Watch for slight bulging of surface of a
volcano.
3. Indications of dangerous amounts of gases
in air by volcanoes.
Write 10 questions for this section.
You should have a total of 20 questions.
Highlight key words and phrases.
Draw a picture.
J. Nguyen – Physical Science
Summary (one paragraph) – Page 4
Viscosity is ___________________. The two
types of lava are _________ and __________.
The three types of lava flow are __________,
__________, and ____________. Pyroclastic
material is _______________________. The
three types of volcanoes are __________ which
has ___________________, ___________
which has ____________________, and
_____________ which has ________________.
J. Nguyen – Physical Science
Notes Points
Name __________________________________ Period _______
Chapter 13 Notes
Points
Earned
Points
Possible
Highlight Key Words/Phrases
2
Copy Notes: pictures + color + label
28
Questions: 20 questions + arrows
10
Summary: 2 paragraph(s)
10
Drawings: 2 drawing(s)
4
TOTAL
J. Nguyen – Physical Science
54