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Class Announcements
Term Break extra credit
option due by end of period
today.
Sign up to attend a Papago
Park extra credit field trip
(worth 20 points).
Options:
Wed., April 16: 10-11AM or 4-5 PM
Thurs., April 17: 10-11AM or 2-3 PM
Today’s Lecture: Chap. 9 Volcanoes
Class presentations:
Cancer-causing gas in Beverly Hills CA - Michael Zara
Mt. Rainier - Nathan Policar
Intermediate volcanoes (cont.)
Calderas
Volcanic hazards
Case Study: Mt. Saint Helens
Economic aspects:
Hydrothermal activity
Mineral deposits
Volcanic Activity on Other Planets
Some Other Important Volcanic Features
a. Calderas
 summit crater greater than 1 km wide
 from collapse of summit
b. Lava domes
 viscous felsic magma
 usually form after explosive eruption of gas-rich magma
Fig. 09.11ab
W. W. Norton
Volcano starts
to erupt.
Full magma
chamber
Ash and
debris
Main explosive
eruption
Magma chamber
empties.
Newly formed
caldera
Collapsed
blocks
Empty magma
chamber
New volcanic
cone grows.
Lake fills
caldera.
Fig. 09.29b
© 1997 Birke Schreiber
Mount St. Helen’s
Lava dome
Case study: Mt. St. Helens
Case study:
Mt. St. Helens
•Located in the
Cascade volcanic
range, NW US.
•Result of
past/present
subduction of
oceanic crust in
the Cascadia
Trench
•Many volcanoes
there are still
active
Case study:
Mt. St. Helens
9500’
 Ejected nearly a
cubic kilometer of ash
& rock debris
 59 deaths
8150’
 Ash blown over 11
miles high!
(1350’ shorter!)
Fig. 09.15
W. W. Norton
Fig. 09.16abc
W. W. Norton
Fig. 09.22e
Photo by J. Marso, U.S. Geological
Survey
Volcanic mudflows
Mount Saint
Helens
A lava dome
formed
in crater
after major
eruption.
GENERAL FEATURES
OF HYDROTHERMAL
SYSTEMS
 Hydrothermal
Systems:
 Develop
anywhere that
fluids coexist
with a heat
source.
 Typical heat
source a magma
intrusion.
 Effects:
Alteration of
adjacent rocks
and deposition
of mineral
deposits, often
of economic
importance.
 Also a source of
geothermal
energy.
Grand Prismatic Spring
Videos: Types of Volcanic Eruptions
1: Lava flows
2: Ash falls
3: Ash flows
4: Mud flows
VENUS
Volcanoes Elsewhere in Solar System
MARS
Fig. 09.30a
JPL / NASA
Olympus Mons: Largest Volcano in the Solar System
Olympus Mons, Mars
Jupiter’s moon “Io”
From Scientific American, Feb 2000
 Jupiter’s moon “Io”
Volcanic Eruptions in Progress on Io
Fig. 09.30b
JPL / NASA