Download Chapter 12 Section 4

Chapter 12 Section 4
Volcanoes
Chapter 12 Section 4 – What You’ll Learn - page 373
Before you read - write the reading’s objectives in this space:
1 – _____________________________________________
________________________________________________
________________________________________________
2 – _____________________________________________
________________________________________________
________________________________________________
________________________________________________
Chapter 12 Section 4 – What You’ll Learn - page 373
Before you read - write the reading’s objectives in this space:
1 – Describe the types and causes of different types of
volcanic eruptions
2 – Explain the patterns of occurrence of volcanoes and its
link to plate tectonics.
What are faults?
_________________
_________________
_________________
_________________
What is decompression?
_________________
____________________________________________
____________________________________________
Why is decompression important to volcanism?
____________________________________________
____________________________________________
1
What are faults?
Weaknesses along Earth’s
crust where movement
takes place.
What is decompression?
The release of pressure due
To movement of fault lines.
Why is decompression important to volcanism?
Decompression changes (lowers) the melting point of rock.
The rock can become liquid at the same temperature.
Convection keeps our mantel flowing:
As fluids heat they
Expand becoming less
dense
And more buoyant.
Due to lower density
fluids will rise
Once fluids rise away from
the heat source they cool
and sink.
As long as there is a heat
source the cycle begins
again.
Cools, Spreads, and Sinks
Heat Rises
Cycle
Begins
Again
2
Why does magma rise?_________________________
_________________________________________
_________________________________________
Where does most surface
lava occur?
_________________________________________
_________________________________________
_________________________________________
_________________________________________
________________________________________
3
Why does magma rise?
Heated rock is less dense causing it to rise. It will surface
as long as it has a path to follow (cracks or fissures).
Where does most surface
lava occur?
On or near boundaries of
plates and above hot spots
What solids erupt from volcanoes?
What are Pyroclasts? ___________
___________________________
___________________________
Globule or volcanic bomb–________
___________________________
___________________________
___________________________
Ash ________________________
___________________________
___________________________
Blocks ____________________
_________________________
Volcanic Bomb –
notice rain drop type shape
Volcanic Ash
Volcanic
Block
4
What solids erupt from volcanoes?
What are Pyroclasts? All solid materials
expelled by a volcano.
Globule or volcanic bomb– cooled globs
of lava (solid material)
Volcanic Bomb –
notice rain drop type shape
Ash - dust (smallest particles) falls
furthest from source.
Volcanic Ash
Blocks – chunks of solid material
ripped from the volcano during
eruption. Falls closest to source.
Volcanic
Block
What is the most common
volcanic gas? __________
What other gases can be
expected? ____________
___________________
All of gasses that are
expelled are super heated!!
Evidence has shown that
volcanoes contribute
enough greenhouse gas to
affect climate long after the
eruption has ended!
5
What is the most common
volcanic gas? Water vapor
What other gases can be
expected? Carbon dioxide
and sulfur compounds
All of gasses that are
expelled are super heated!!
Evidence has shown that
volcanoes contribute
enough greenhouse gas to
affect climate long after the
eruption has ended!
Pyroclastic flow –
the most dangerous part of a volcano
The flow looks like
ground-hugging
grey smoke, but
consists of a
mixture of
poisonous gas, ash,
globules, and dense
hot lava blocks.
Pyroclastic flow is what covered Pompeii
The Tambora volcano in
Indonesia erupted in April
1815, but North America
and Europe did not notice its
effects until months later. In
1816, known as "the year
without a summer", gases,
ashes and dust arrived over
the Iberian Peninsular and
reached the stratosphere,
where they remained long
enough to create "an
enormous sun filter".
Krakatau: The Last Days
Pyroclastic Flow Clip
Anak (Child of) Krakatau has grown at an average rate of
five inches (13 cm) per week
Today
What is viscosity? ____________________________
_________________________________________
What is more viscous, water or syrup? ______________
_________________________________________
What affects viscosity? ________________________
_________________________________________
Which tube has the most
viscous material?
____________________
6
What is viscosity? A measure of the resistance of a fluid to
flow.
What is more viscous, water or syrup? Syrup – more
resistant to flow.
What affects viscosity? Heat, composition, and gas
content.
Which tube has the most
viscous material?
Far right
Volcanoes erupt in different ways. Viscosity will affect the
kind of eruption. Eruptive style is strongly linked to
temperature and composition and can be linked to the type
of plate boundary associated with it.
How will thick magma
erupt? _________________
______________________
How does runny, low
silica, high temperature
magma erupt?
_____________________
7
Volcanoes erupt in different ways. Viscosity will affect the
kind of eruption. Eruptive style is strongly linked to
temperature and composition and can be linked to the type
of plate boundary associated with it.
How will thick magma
erupt? Cause pressure
to build and will explode.
How does runny, low
silica, high temperature
magma erupt?
Quiet, free flowing
eruptions.
Click me
Click me
Plate Boundary Setting
Most of Earth’s volcanoes lie in subduction zones
where continental and oceanic materials are being
mixed and partially melted.
8
What are hot spots? ___________________________
__________________________________________
__________________________________________
Examples include: Hawaii and Yellow Stone National Park
Where do scientists think they come from? ____________
__________________________________________
9
What are hot spots? Volcanically active sites that arise in
places where large quantities of magma move to the surface
in large, column-like plumes.
Examples include: Hawaii and Yellow Stone National Park
Where do scientists think they come from? Extra heat in the
Earth’s mantle.
Volcanoes are classified according to their size, shape, and the
materials that compose them.
Cinder cone volcanoes form ________________________
___________________________________________
These volcanoes are small.
10
Volcanoes are classified according to their size, shape, and the
materials that compose them.
Cinder cone volcanoes form when the primary eruptive
products are large fragments of solid material.
These volcanoes are small.
Shield volcanoes are _______ and _______ made from
______________of Basaltic lava.
11
Shield volcanoes are broad and flat made from
many layers of Basaltic lava.
Composite volcanoes form from _____________________
____________________________________________
____________________________________________
12
Composite volcanoes form from alternating explosive events
that produce pyroclastic materials, and lava flows
The figure below compares actual size of average volcanoes
Can you match the volcano to it’s type?
Section Check
Question 1
Where do most volcanoes occur?
13
Section Check
Question 1
Where do most volcanoes occur?
Answer
Most volcanoes occur at plate boundaries where
huge pieces of the crust pull apart or push
together. As a result, the crust often fractures,
allowing magma to reach the surface.
Question 2
Section Check
What type of volcano is formed by an explosive
eruption followed by a quiet eruption?
A. cinder cone volcano
B. composite volcano
C. fissure eruption
D. shield volcano
14
Question 2
Section Check
What type of volcano is formed by an explosive
eruption followed by a quiet eruption?
A. cinder cone volcano
B. composite volcano
C. fissure eruption
D. shield volcano
Answer
The correct answer is B. Composite volcanoes
erupt explosively releasing large quantities of gas
and ash. They are followed by quieter eruptions
that form a lava layer over the ash.
Section Check
Question 3
How does a hot spot volcano form?
15
Section Check
4
Question 3
How does a hot spot volcano form?
Answer
A volcano forms above a hot spot when magma
erupts through the crust and reaches the surface.
Hot spot volcanoes may lie in the middle of
plates far from any plate boundaries or near or
on plate boundaries.