Volcanoes
October 6, 2010
Warm up 10/6
1. What are the three types of plate
boundaries?
2. At which type(s) of boundar(ies)
would volcanoes be created?
3. How are volcanoes and mountains
related?
Objectives
• I will be able to identify what makes a volcanic
eruption explosive.
• I will be able to compare materials that come
out of a volcano.
• I will be able to compare the different types of
volcanoes.
Key Points
• A magma’s viscosity is directly related to its silica content.
• A lava flow with a surface of rough, jagged blocks and sharp,
angular projections is called aa flow.
• As the temperature of lava increases, the viscocity decreases.
• Highly explosive volcanoes tend to have magma with high silica,
high viscosity, and higher gas content.
• The particles produced in volcanic eruptions are called
pyroclastic material.
• Pyroclastic materials include ash, cinders and lapili.
• The most abundant gas associated with volcanic activity is
water vapor.
• A cinder cone is a type of volcano that is built almost entirely
from ejected lava fragments.
• The pipe is the hollow center of the volcano.
Factors Affecting Eruption
• Volcanoes can erupt explosively or mildly.
They can erupt with lots of lava spewing out
or slowly oozing out of the mouth. Some
volcanoes erupt ash and dust with no lava at
all. So what makes all of them so unique?
• Let's watch!
• Let’s take a look at the factors that affect the
eruption of a volcano.
Factors Affecting Eruption
Viscocity - a substance’s resistance to flow.
– This means that something that has a high
viscosity does not flow easily. A substance with a
high viscosity would be honey. A substance with
a low viscosity would be water.
– If the lava of a volcano has high viscocity, the
eruption of a volcano will be highly explosive.
– There are three factors that affect the viscocity of
lava: silica content, gas content, and
temperature.
Factors Affecting Eruption
1. Silica – the more silica in lava, the more viscocity it
has. A magma’s viscosity is directly related to its
silica content.
2. Gas content - the more gases in lava, the more
viscocity it has.
3. Temperature – as temperature in lava increases,
the viscocity decreases.
• Example: heating up syrup.
***Bottom line: Highly explosive volcanoes tend to
have magma with high silica, high viscosity, and
higher gas content.
Volcanic Material
There are three main types of materials that come out of
volcanoes: Lava flows, gases, and pyroclastic material.
Lava flows:
1.aa flow (AH ah): A lava flow with a surface of rough,
jagged blocks and sharp, angular projections.
view here! Think “ow!” it hurts to step on!
1.pahoehoe flow: lava flows that flow slowly forming flows
that look like twisted braids in ropes.
view here!
Gases:
The most abundant gas associated with volcanic activity is
water vapor.
Volcanic Material
Pyroclastic Material – the particles produced in
volcanic eruptions.
• Pyroclastic materials include ash, cinders and
lapili.
• These particles can range in size from fine dust
to pieces that weigh several tons!
Types of Volcanoes
Anatomy of a volcano
• While there are several different types of
volcanoes, each have a “typical” anatomy with
the following parts:
A. Pipe
B. Vent
C. Lava
D.Crater
Types of Volcanoes
• The three main types of volcanoes are cinder
cones, shield volcanoes and composite cones.
• Magma composition plays a major part in
determining the form of a volcano.
Types of Volcanoes
• When you think about a typical volcano, what
do you see?
• Usually a cinder cone – highly explosive lava.
1.A cinder cone is a type of volcano that is built
almost entirely from ejected lava fragments.
– This give it a cone shape over time.
– Learn more here!
Cinder Cone Volcano
Cinder Cone from Pu'u'O'o eruption of Mount Kilauea
Types of Volcanoes
2. Composite Cones – a large, symmetrical
volcano composed of both lava and
pyroclastic deposits.
About Composite Cone Volcanoes
Composite Volcano
Mt. Shasta
Types of Volcanoes
3. Shield Volcano – have the shape of a broad,
slightly domed structure.
• Most shield volcanoes grow up from the
ocean floor – like the islands of Hawaii or
Iceland.
More about shield volcanoes
Shield Volcano
Iceland
CHECK-IN
• Answer the check-in questions in COMPLETE
SENTENCES on a separate sheet of paper.
• Your check-in questions for this whole unit will
be collected and taken as a quiz grade.
• These will also be THE BEST thing for you to
study before your next quizzes/tests.
VOCABULARY
• Your vocabulary is due on Friday
• Use this time wisely to work
• REMEMBER you need
–The definition
–The source for the definition (where
you got it)
–The definition in your own words
Brownie Ticket 10/6
1. A magma’s viscosity is directly related to its:
A. depth B. color C. age D. silica content
2. The particles produced in volcanic eruptions
are called ____.
A. laccoliths B. volcanic stocks C. pyroclastic material
D. calderas
3. What type of volcano is built almost entirely
from ejected lava fragments?
A. Shield B. Composite Cone C. Cinder Cone
Warm up 10/7
1. Name the three types of volcanoes.
2. A magma’s _______________is directly related to
its silica content.
3. A lava flow with a surface of rough, jagged blocks
and sharp, angular projections what type of flow?
4. As the temperature of lava increases, the viscocity
_______________________.
5. Highly explosive volcanoes tend to have magma
with what three things?
6. The particles produced in volcanic eruptions are
called ________________________.
Announcements
• We will have a QUIZ tomorrow on Volcanoes!
• Vocabulary for Chapters 8 and 10 are due
TOMORROW!
• Remember, this is the time to make a NEW start
and get a good grade for this new report card!
• Final laptop deployment TONIGHT at 6:00 pm.
Objectives
• I will be able to relate plate tectonics to
volcanoes by describing where magma comes
from, the types of boundaries that produce
volcanoes.
• I will be able to graph the locations of
volcanoes on a map and compare patterns of
volcanoes to plate tectonics.
Key Points
• Magma composition plays a major part in
determining the form of a volcano.
• Magma forms when solid rock in the crust and
upper mantle melts.
• The composition of the material, water content
and confining pressure are factors that affect the
melting point of rock.
• Magma tends to rise towards Earth’s surface
primarily because rocks become less dense when
they melt.
• Most of the active volcanoes on Earth are located
in a belt known as the ring of fire.
• Identify an O-C plate boundary creating a volcano.
How Volcanoes Form
• How Volcanoes Form Video
Magma
• As we know, magma composition plays a
major part in determining the form of a
volcano.
• But where does magma come from?
• Magma forms when solid rock in the crust and
upper mantle melts.
Magma
• How does rock melt?
– There are three factors that contribute to rocks
melting, or the formation of magma.
1. Heat
– As you go deeper in the earth, the temperature rises.
– Subduction creates friction and causing heat
– As magma rises, it heats rocks closer to the earth’s
surface.
•
But this alone is not enough to create all of the
magma that we know exists below the earth’s
crust…
Magma
2. Confining Pressure
– As confining pressure is decreased, the melting
temperature of rocks is lowered.
– This means that as rocks can melt easier as they
are released from the confining pressure deep
within the earth.
– This process is called decompression melting.
Magma
3. Water Content
– Water in rocks can cause a rock to melt at lower
temperatures.
– Rocks with more water in them melt easier than
rocks that are “dry”.
•
BOTTOM LINE: The composition of the
material, water content and confining pressure
are factors that affect the melting point of rock.
Magma
• Now that we know how magma forms, why
does it come to the surface of the planet?
• Let’s discuss.
• Write down what you think:
__________________________________
__________________________________
Magma
• Magma tends to rise towards Earth’s surface
primarily because rocks become less dense
when they melt.
• What does that mean? When rocks change
from a solid state to a liquid state, they become
lighter!
• What is lighter will rise, just like heavy things
sink!
Plate Tectonics and Volcanoes
• Most of the active volcanoes on Earth are
located in a belt known as “The Ring of Fire”.
• Others are located seemingly sporadically
around the globe.
• Scientists could not explain the worldwide
distribution of volcanoes until the
introduction of the theory of Plate Tectonics.
The Ring of Fire
• Watch a slideshow of the Volcanoes on the
Ring of Fire HERE!
Plate Tectonics and Volcanoes
• Plate movement forms volcanoes in three zones:
1. Convergent Plates
– Ocean – Ocean
•
Rising magma can form volcanic island arcs in an
ocean (Aleutian Islands).
– Ocean – Continent
•
Rising magma can form continental volcanic arcs
(Andes Mountains).
Convergent Boundary Volcano
Was type of
convergent
boundary
caused Mt. St.
Helens?
How do you
know?
Mount St. Helens emitting volcanic ash 2
months after it’s May eruption in 1980.
Plate Tectonics and Volcanoes
2. Divergent Plate Boundaries
– When plates pull apart, there is less pressure on
the rocks below.
– Because of the decrease in pressure, rocks melt
and magma is formed.
Plate Tectonics and Volcanoes
3. Intraplate Igneous Activity
–
Intraplate means activity inside a tectonic plate away
from plate boundaries.
– This is caused by Hot spots.
– Examples of this are the Hawaiian Islands
Kilauea, an Intraplate Volcano
Mapping Volcanoes Lab
Follow the directions on the handout to map
volcanoes around the world.
After you finish plotting the volcanoes, answer
the questions in complete sentences.
Brownie Ticket 10/7
1. Magma tends to rise towards Earth’s surface
primarily because:
A.
B.
C.
D.
water is abundant in magma
silica is abundant in magma
rocks become more dense when they melt
rocks become less dense when they melt
2. Most of the active volcanoes on Earth are located
in a belt known as the:
A.
B.
C.
D.
circum-Atlantic belt
Ring of Lava
East African Rift Valley
Ring of Fire
3. Name at least one of the factors affects the
melting point of rock.
Warm Up 10/8
1. Most of the active volcanoes on Earth are
located where?
2. Explain how magma forms.
3. What three things affect the melting point of
a rock?
4. Why does magma rise to earth’s surface?
Announcements
• Turn in Vocabulary!
• Agenda Today:
– Online Lab
– Quiz
– National Parks Project Introduction
• TEST next Friday (a week from today!)
Viscocity Lab
Quiz - #14
14. RANK the following samples of magma from
LOWEST to HIGHEST viscocity using the chart
below: (write the red and fill in the blanks)
Magma
Sample:
GAS
SILICA
TEMPERATURE
#1
HIGH
HIGH
LOW
#2
HIGH
LOW
LOW
#3
LOW
LOW
HIGH
Lowest Viscocity: sample _______
Middle Viscocity: sample _______
Highest Viscocity: sample _______
National Parks Project