Volcanoes:
http://www.snagfilms.com/films/t
itle/volcano_natures_inferno
• Watch this national Geografic
documentary on volcanos.
A. What is A Volcano ?
1. An opening in Earth’s
crust through which
molten rock, ash and
gases erupt.
2.Volcano: The
landform that
develops around the
opening.
3. A way for Earth to
release heat energy
from the interior due
to radioactive decay.
D. Peebles
B. Types of Volcanoes?
1. Composite
2. Shield
G. Vaughn
USGS
Mt. St. Helens, WA
Mauna Loa, HW
3. Cinder
A. Heisey
Sunset Crater, AZ
C. How Do Volcanoes Differ?
1. Size
2. Shape
3. Composition
4. Location
Tarbuck & Lutgens
Questions
• Which type of volcano is the widest?
A. Cinder B. Composite C. Shield
• What type of volcano typically produces
the largest explosions?
A. Cinder
B. Composite C. Shield
D. Composition
1. Magma viscosity
– Silica content: more = thicker
(most explosive)
– Temperature: higher= thinner
– High Viscosity = thick, pasty
– Low viscosity= Thin and runny
Kilauea, HW
2. Mafic
–
–
–
–
Little silica
low viscosity (runny)
Produces Dark color rocks
Ex.Basalt
3. Felsic
- Silica rich
- High viscosity
- Light color rocks
- Granite
- Explosive, high gas content
4. Pyroclastic- Fire Rock. What
comes out of the volcano
Explosive volcanic events.
D. Peebles, USGS
Mt. St. Helens,
WA
D. Weintraub
Questions 3
•
Which variable determines how
explosive a volcanic eruption will be?
A. Gases
B. Silica
C. Temperature
E. Types of Lava Flow
1. Flow types: depend
on temperature and
comp.
– Pahoehoe: fast
moving, hot lava, low
viscosity
– Aa Aa: slower moving,
cooler, higher viscosity
Aa Flow
J.D. Griggs, USGS
Pahoehoe Flow
J.D. Griggs, USGS
http://www.youtube.c
om/watch?v=Z9iW_o
XMBB8
http://www.youtube.
com/watch?v=iyIV5f
d1Aww
D. Peebles, USGS
J. Judd, USGS
F. Shield Volcanoes
1. Mafic lava (fluid)
– nonexplosive eruptions, slow
build up
– Hot spots and ridges (mantle
material)
2. Structure
– Low angle slope Why ?
Because the lava can travel
long distances due to its
fluidity. Low gas content!!
Tarbuck & Lutgens
Questions
•
Shield volcanoes are composed of what
type of lavas?
A. Mafic
•
B. Felsic
C. Andesitic
The shape of a shield volcano is due to
A. fluid, low viscosity lavas B. high viscosity lavas
C. pyroclastics
D. gases
•
Shield volcanoes are usually associated
with what landform feature/s or processes?
A. pyroclastic flows
C. steep sided cones
B. explosive eruptions
D. Gentle sloped cones
G. Cinder Cones
1. Mafic lavas (can be felsic)
– Large amt. pyroclastics
– Gentle & explosive
– High viscosity
2. Structure
– High slope
A. Heisey
3. Deep crater
Tarbuck & Lutgens
Example: Paricutin
• West of Mexico City
• 1943 eruption began
• Cornfield of Dionisio
Pulido
• Earthquakes
• 1st day 130 feet
• 5th day +330 feet
• Lava flows from base
• Nine years of eruption
T. Nichols
Cinder Cones
Pelee’s Cinder Cone, HW
Fire Fountain=Pyroclastics
USGS G. Lewis
USGS G. Lewis
USGS G. Lewis
Parasitic Cone
Question
•
Cinder cones are mainly composed of -?lavas
A. Mafic
B. Felsic
C. Andesitic
I. Composite Volcanoes
• Felsic lavas
– Large amt. pyroclastics
– Viscous lavas
– Explosive / catastrophic
eruptions
– Subduction boundaries
• Structure
– Symmetrical cone
– Medium to high slope
• Ring of Fire
M. Giannechini
Pomerape & Parinacota, Chile
Cascade Range
• 50+ eruptions in U.S.
in past 200 years
(mainly in Alaska)
• Pyroclastic Flows
• Lahars
USGS
USGS
Pre 1980 Eruption
Post 1980 Eruption
Questions
•
Composite volcanoes are composed of -?lavas
A. Mafic
•
B. Felsic
The volcano with the steepest slope is a
A. Shield cone
•
C. Andesitic
B. Cinder cone
C. Composite cone
Volcanoes of the Cascade Range are
mainly
A. Shield
B. Cinder
C. Composite
K. Volcanoes Locations
1. Located along plate boundaries
2. “Ring of Fire”- major volcanic belt, formed
around the Pacific Ocean.
3. Hot spots-stationary plume of magma continually rising through the
crust from the athenosphere. Can occur in the middle of a plate.
Check it out!
Looking at the current
location of the
Yellowstone hot spot
1. If hot spots never
move in which
direction is the north
American continent
moving?
West, south west!
Bell Ringer.
• In your comp book draw
a data table using a
ruler, showing the
following, Size, shape,
composition, and
Eruption type. Do this
for the 3 types of
volcanoes.
Other Volcanic Features
Rift Eruption
G. Vaughn
Lava Plateaus
G.
J. Vaughn
Shelton
D. Falconer
T. Bean
Lava Dome
Volcanic Neck
K. Other Volcanic Structures
1. Plateaus- flat area
caused by lava flow.
2. Volcanic necksmagma left in vent,
extinct volcano
3. Dikes- molten
material that vertically
cut across rock layers
4. Sill- molten material
that horizontally cut
across rock layers
Tarbuck & Luntgens
4. Laccoliths- domelike
magma bulge under the
surface.
5. Batholiths- large rock
structure, magma cools
inside crust
6. Active- erupting or will
erupt soon.
7. Dormant- erupt in the
future.
8. extinct- unlikely to erupt
again
Check Your Volcano Knowledge
• What purpose do volcanoes
serve on Earth?
• What is magma?
• List three factors that
determine the nature of a
volcanic eruption.
• What are the major gases
released in volcanic eruptions?
• What does Pahoehoe and Aa
refer to?
• What are the three types of
volcanoes? Describe each
one.
• What type of materials make
up pyroclastic flows?
• Generally, where are
volcanoes located on Earth?
• How does a caldera form?
• What are Lahars and what
type of volcano are they
usually associated with?
• Which type of volcano is the
most explosive?
• Name and describe three other
igneous features.
J. Calderas
Long Valley, CA
1. Huge hole left by the
collapse of a whole
mountain.
Crater Lake, OR
USGS G. Lewis
USGS G. Lewis
Mauna Loa, HW