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Volcanoes
Table of Contents
Volcanoes and Plate Tectonics
Properties of Magma
Volcanic Eruptions
Volcanic Landforms
Volcanoes - Volcanoes and Plate Tectonics
Volcanoes and Plate Boundaries
Volcanic belts form along the boundaries of Earth’s plates.
Volcanoes
Discussion Questions
•What is a volcano?
•A volcano is an opening, or rupture, in a planet's surface or
crust, which allows hot magma, volcanic ash and gases to
escape from below the surface.
•What is the difference between magma and lava?
•Magma (from Greek μάγμα "paste") is a mixture of molten
rock, volatiles and solids that is found beneath the surface of
the Earth, and is expected to exist on other terrestrial
planets.
•Lava refers both to molten rock expelled by a volcano
during an eruption and the resulting rock after solidification
and cooling.
Volcanoes - Volcanoes and Plate Tectonics
Volcanoes and Plate Boundaries
•Volcanoes often form where two oceanic plates collide or where an
oceanic plate collides with a continental plate.
•In both situations, an oceanic plate sinks through a trench.
Rock above the plate melts to form magma, which then erupts
to the surface as lava.
Volcanoes - Volcanoes and Plate Tectonics
Hot Spot Volcanoes
A volcano forms above a hot spot when magma erupts
through the crust and reaches the surface.
Volcanoes
Ring of Fire
•http://www.youtube.com/watch?v=gRlj5vjp3Ko
Volcanoes - Volcanoes and Plate Tectonics
Asking Questions
Before you read, preview the red headings. In a graphic
organizer like the one below, ask a where, what, or how
question for each heading. As you read, write the answers to
your questions.
Questions
Answers
Where are volcanoes
found?
Most volcanoes are found
along plate boundaries.
What are hot spots?
A hot spot is an area where
material from deep within the
mantle rises and then melts,
forming magma.
Volcanoes
End of Section:
Volcanoes and
Plate Tectonics
Volcanoes
Overview
•Viscosity refers to the resistance of a liquid to flowing
•Different liquids have different viscosities allowing some to flow
more easily compared to others
•This is due to the particles that make up the liquid and the
friction that exists when they are in motion
•Different types of magma have different viscosities which are a
result of temperature and silica content
•Silica (SiO2) is a compound consisting of Silicon and Oxygen
particles bonded together
•Silica content of magma varies between 50-70% on average
•Temperature of magma and lava varies between 750 – 1200 C
Volcanoes - Properties of Magma
Magma Composition
Magma varies in composition
and is classified according to the
amount of silica it contains. The
graphs show the average
composition of the two types of
magma. Use the graphs to
answer the questions.
Volcanoes - Properties of Magma
Magma Composition
Reading Graphs:
Study both graphs. What
materials make up both types
of magma?
Silica, other oxides, and other
solids.
Volcanoes - Properties of Magma
Magma Composition
Reading Graphs:
Which type of magma has
more silica? About how much
silica does this type of
magma contain?
Rhyolite-forming magma;
about 70 percent.
Volcanoes - Properties of Magma
Magma Composition
Estimating:
A third type of magma has a
silica content that is halfway
between that of the other two
types. About how much silica
does this type of magma
contain?
About 60 percent
Volcanoes - Properties of Magma
Magma Composition
Predicting:
What type of magma would
have a higher viscosity?
Explain.
Rhyolite-forming magma
would have higher viscosity
because it is higher in
silica.
Volcanoes
TYPES OF LAVA
There are three categories of lava, classified on the basis of
its silica (SiO2) content, which affects how readily it flows.
1. BASALTIC LAVA
a. Relatively low SiO2 content (less than 52%)
b. Relatively low viscosity (flows readily when hot)
2. ANDESITIC LAVA
a. Intermediate SiO2 content (between 52 and 63%)
b. Intermediate viscosity (does not flow readily)
3. RHYOLITIC LAVA
a. Relatively high SiO2 content (above 68%)
b. Relatively high viscosity (flows like wet concrete)
Volcanoes
Volcanoes
Pahoehoe lava is characterized by a smooth, billowy, or ropy
surface. Pahoehoe is hot, moves fast, and has lower viscosity.
Volcanoes
Aa is characterized by a rough or jagged surface. Aa lava
flows tend to be relatively thick compared to pahoehoe flows
meaning they have lower temperature and higher viscosity.
Volcanoes - Properties of Magma
Identifying Main Ideas
As you read the section “Types of Viscosity of Magma,” write
the main idea in a graphic organizer like the one below. Then
write three supporting details that further explain the main
idea.
Main Idea
Magma’s viscosity depends on its physical and chemical properties.
Detail
Detail
Detail
Magma is made of
elements and of
compounds, among
them silica.
Viscosity is a
property of magma.
Viscosity depends
on silica content and
temperature.
Volcanoes
End of Section:
Properties of
Magma
Volcanoes - Volcanic Eruptions
Anatomy of a Volcano
When a volcano erupts, the force of the expanding gases pushes magma from
the magma chamber through the pipe until it flows or explodes out of the vent.
Volcanoes
Key Terms
•Magma chamber is the area beneath the volcano where magma
collects
•The pipe is the vertical tube connecting the magma chamber to the
vent (or outside world)
•The vent is the opening near the top of the volcano where gas and
magma flow out towards the surface
•Side vents refer to pipe like projections that run on the sides of the
volcanoes mountainous structure
•A crater is the bowl-shaped area that can form around the top of the
volcano or vent
Volcanoes
Volcanic Eruptions
Basically there are two types of volcanic eruptions: Quiet & Explosive
Quiet eruptions are what you have on the island of Hawaii
*Quiet eruptions occur when the magma has:
1. Lower silica content
2. Higher temperature
3. Lower viscosity
Explosive eruptions are what you typically have along subduction zones
*Explosive eruptions occur when the magma has:
1. Higher silica content
2. Lower temperature
3. Higher viscosity
Volcanoes
•Ash
•Gas
•Lahars
•Tephra
•Landslides
•Lava Flows
•Pyroclastic Flows
Volcanic Hazards
Volcanoes
Volcanic Activity Classification
•Volcanologists use the terms active, dormant, or extinct
to describe a volcano’s stage of activity
•An active volcano refers to a current eruption taking
place or a possibility of it erupting in the near future
•A dormant volcano refers to a volcano that has not
erupted for an extended period of time, but still can erupt
at any given time
•An extinct volcano also has not erupted for a very long
time and poses little to no threat of erupting again
*The prediction of a volcano eruption is more accurate
than earthquake prediction, but still not perfected!
Volcanoes - Volcanic Eruptions
Kinds of Volcanic Eruptions
Within the last 150 years, major volcanic eruptions have
greatly affected the land and people around them.
Volcanoes - Volcanic Eruptions
Using Prior Knowledge
Before you read, look at the section headings and visuals to
see what this section is about. Then write what you know
about volcanic eruptions in a graphic organizer like the one
below. As you read, write what you learn.
What You Know
1.
2.
3.
Lava flows out of a volcano.
Eruptions are not all the same.
Some volcanoes are dormant.
What You Learned
1.
2.
3.
Magma rises toward Earth’s surface through a pipe that leads to a
vent.
Differences in gas and silica content cause some eruptions to be
explosive and others to be quiet.
Dormant volcanoes can become active at any time.
Volcanoes
End of Section:
Volcanic
Eruptions
Volcanoes - Volcanic Landforms
Landforms From Lava and Ash
Volcanic eruptions create landforms made of lava, ash, and
other materials. These landforms include composite
volcanoes, shield volcanoes, cinder cone volcanoes, and
lava plateaus.
Volcanoes - Volcanic Landforms
Landforms From Lava and Ash
A caldera forms when an
volcano’s magma chamber
empties and the roof of the
chamber collapses. The
result is a large, bowlshaped caldera.
Volcanoes - Volcanic Landforms
Landforms From Magma
Features formed by magma include volcanic necks, dikes,
and sills, as well as batholiths and dome mountains.
Volcanoes - Volcanic Landforms
Batholiths
A batholith is a mass of rock formed
when a large body of magma cools
inside the crust. Several large batholiths
form the core of mountain ranges in
western North America. Half Dome in
Yosemite National Park, California, is
part of the Sierra Nevada batholith.
Volcanoes - Volcanic Landforms
Outlining
As you read, make an outline
about volcanic landforms that
you can use for review. Use
the red headings for the main
topics and the blue headings
for the subtopics.
Volcanic Landforms
I. Landforms From Lava and Ash
A. Shield Volcanoes
B. Cinder Cone Volcanoes
C. Composite Volcanoes
D. Lava Plateaus
E. Calderas
F. Soils From Lava and Ash
II. Landforms From Magma
A. Volcanic Necks, Dikes and
Sills
B. Dikes and Sills
C. Batholiths
D. Dome Mountains
III. Geothermal Activity
A. Hot Springs
B. Geysers
C. Geothermic Energy
Volcanoes
End of Section:
Volcanic
Landforms
Volcanoes
Graphic Organizer
V olcani c
mountains
include
Shield
volcanoes
produce
Lava
Composite
volcanoes
produce
Lava and
ash
Cinder
cones
produce
Ash, cinders,
and bombs
Volcanoes
End of Section:
Graphic Organizer