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Inside Earth: Volcanoes
Section 2: Volcanic Activity
Major Volcanoes Around the World
What you need to know…
• What happens when a volcano erupts?
• How do the two types of volcanic
eruptions differ?
• What are some hazards of volcanoes?
How Magma Reaches Earth’s Surface
Why does magma rise?
• Magma rises because it is less dense
that the surrounding solid material
What happens when a volcano
erupts?
• As the less dense magma rises, the
pressure decreases
• The dissolved gas separates out and
bubbles form
• A volcano erupts when an opening develops
in weak rock on the surface
• During a volcanic eruption, the gases
dissolved in magma rush out, carrying the
magma with them
• Once magma reaches the surface and
becomes lava, the gases bubble out
Inside a Volcano
Magma Chamber
• The pocket
beneath a volcano
where magma
collects
Pipe
• A long tube
through which
magma moves from
the magma
chamber to Earth’s
surface
Vent
• The opening
through which
molten rock and
gas leave a volcano
Where are vents located?
• Usually there is one central vent at
the top of the volcano
• Often times there are additional
vents that open on the volcanoes
sides
Lava Flow
• The area covered
by lava as it pours
out of a volcano’s
vent
Label a Volcano
Using the labels given
find the correct part.
Crater
• A bowl-shaped area
that forms around
a volcano’s central
opening
• Lava collects there
There are three types of
volcanic cones:
• ______
Cinder – explosive eruptions, small
but steep slopes, pyroclastics
• _______
– nonexplosive eruptions,
Shield
fluid basaltic lava, gentle broad
slopes
Composite – alternating between
• _________
lava and pyroclastics, explosive and
nonexplosive eruptions, steep and tall
Classify Volcanoes
• Composite
• Active
• Cinder
• Intermittent
• Shield
• Dormant
• Extinct
Question 1: How does magma rise
through the lithosphere?
• Liquid magma in the asthenosphere is less
dense than the rock in the lithosphere
above it, so it flows upward through cracks
in the rock
– The magma is stored in the magma chamber
• It continues upward (through the pipe)
until it reaches the surface (exiting
through a vent) or it is trapped beneath
layers of rock.
Characteristics of Magma
Silica
• A material that is found in
magma,formed from the elements
oxygen and silicon
• The more silica the magma has the
thicker it is
What three factors contribute to
how forceful a volcanic eruption is?
Explain how each determines this.
• Amount of gas present
• How thick or thin the magma is
(Temperature)
– Thinner (hotter) is more fluid
• The silica content
– If the silica content is high, magma is
thick
– This causes the pressure to build
Types of Volcanic Eruptions
Quiet eruptions like the ones that
take place on _______ have built
up the big island over _______ of
_______ of years.
• Mount Kilauea
• Hundreds
• Thousands
Pahoehoe
• A hot, fast-moving
type of lava that
hardens to form
smooth, ropelike
coils
Aa
• A cooler, slowmoving type of lava
that hardens to
form rough chunks;
cooler than
Pahoehoe
What is the difference between
the two types of lava?
• Pahoehoe is a faster flowing lava that
cools slowly resulting in a smooth
texture
• Aa is a slower flowing cooler type of
lava that hardens into rough chunks
Inferring
What accounts for the differences
between these two types of lava?
• The temperature of the lava
• The speed at which the lava flows
Question 2: What types of lava are
produced by quiet eruptions?
• Quiet eruptions produce two types of
lava: pahoehoe and aa
– Pahoehoe is a fast-moving, hot lava
– Aa is a cooler, slower-moving lava
Pyroclastic flow
• The expulsion of
ash, cinders, and
bombs from a
violent volcanic
explosion
Question 3: What causes an
explosive eruption?
• Magma that is thick and sticky causes
a volcano to erupt explosively
• Magma can not flow freely causing
pressure (gas) to build up until it
explodes
How do the two types of volcanic
eruptions differ?
• Quiet eruptions occur when the lava flows
more easily because gas dissolved in the
magma bubbles
• When the lava is thick and sticky the gas
continues to store increasing pressure
– When the pressure becomes so great an
explosion takes place when the gas pushes the
magma out with incredible force
Stages of a Volcano
What are the three stages of a
volcano? Explain each stage.
• Active
– A volcano that is erupting or has shown signs
that it may erupt in the near future
• Dormant
– A volcano that is not currently active, but may
become active in the future
• Extinct
– A volcano that is unlikely to erupt again
Other Types of Volcanic Activity
Hot Spring
• A pool formed by
groundwater that
has risen to the
surface after being
heated by a nearby
body of magma
Geyser
• A fountain of water
and steam that
builds up pressure
underground and
erupts at regular
intervals
Geothermal Energy
• Energy from water and steam that has been heated by magma
• Geothermal energy is produced by drilling a well into the ground
where thermal activity is occuring.
• Once a well has been identified and a well head attached, the
steam is separated from the water, the water is diverted
through a turbine engine which turns a generator.
• Usually the water is injected back into the ground to resupply
the geothermal source.
Monitoring Volcanoes
How do geologists monitor the
activity of a volcano?
• Measure tilt caused by magma
movement underground using
tiltmeters & laser-ranging devices
• Monitor temperature underground
• Monitor small earthquakes that occur
in the area around a volcano
Volcano Hazards
What are some hazards of
volcanoes?
•
•
•
•
•
•
Fire
Bury entire towns
Damage crops
Landslides
Avalanches of mud
Damage car and jet engines
The _________
Galapagos Islands are a volcanic
group of islands 600 miles off the
coast of Ecuador on the equator.
Lava flowing underground created
lava _____,
tube large enough to
this _____
walk through.
Kilauea on Hawaii is a good example of
shield
a _______
cone, with less explosive
eruptions and less viscous lava.
Mt Rainier and Mt St Helens are good
examples of __________
composite cones, with
explosive eruptions and erupted materials
such as ash, bombs, and blocks.
Mt St Helens
Mt Rainier
Crater Lake in Oregon is a __________formed
caldera
from the collapse of the gigantic volcano Mount
Wizard Island
Mazama. ________________in
the center of
the lake is a small cinder cone.
Igneous Rocks
Igneous rocks comes from a
volcano.
These rocks can form from
cooled lava outside the volcano.
These rocks can also form from
hardened magma inside the
volcano.