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Today – 4/13
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More volcanoes!
First Mars shot - hill
Matian basalt
Martian dune field
Frozen Martian Sea
Last Time
Hotspots – mantle plumes reach the surface;
decompression melting to form basaltic
magma; Hawaii, Mars, Venus; independent
of plate boundaries
Intrusive v. extrusive: coarse v. fine texture
depends on cooling rate
Three kinds of volcano: shield,
stratovolcano, caldera – depends on magma
type
Last Time – Shield Volcano
Built up from repeated basalt flows
Basalt has high Fe / Mg, high temperature,
low Si, low gas content, low viscosity
(stickiness)
MOR’s, hotspots, areas of continental
extension
Stratovolcano
Built from alternating
layers of pyroclastic &
andesite lava flows
 Magma – intermediate
temperature, gas
content, composition,
viscosity
 St. Helens, Monserrat,
Pinatubo, Tambora
 Form above subduction
zones
 Wet melting of the
mantle
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Wet Melting of the Mantle
Mount Ngauruhoe, New Zealand
Classic Stratovolcano
--- 1000s of feet high.
Pyroclastic
Flows
- - - - Mayon
Philippines
1968
- - - - o
Hot: 600 C
Fast:
60 to 100
mph
Mt. Vesuvius & Pompeii, Italy AD 79
Cascade
Volcanic
Arc
----Lassen Peak
Crater Lake
Mt.St.Helens
Mt. Rainier
- - - Part of Pacific
Ring of Fire.
Mt. Saint Helens, May, 1980 Eruption
After
Before
Mount St. Helens Volcanocam
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http://www.fs.fed.us/gpnf/volcanocams/msh/
Space Needle view
Seattle, WA and
Mount Rainier:
Most dangerous
volcano in North
America?
Mount Rainier, Most dangerous volcano in
North America?
Mount Pinatubo Tectonic Setting
Volcanoes – Agents of Climate Change
Mount Pinatubo, Philippines 1991
Mt. Pinatubo Ash Circles the Earth
Earth’s surface cooled 1 °F for two years.
Climatic Effects of Volcanism
Volcanic particles in stratosphere interact with
man-made CFC’s to destroy ozone. Particles
settle out in 2-3 years, ozone layer recovers.
Volcanoes add CO2 to the atmosphere (10% of
anthropogenic emissions), contributing to longterm global warming
SO2 in the stratosphere reacts with water to form
sulfuric acid, which absorbs solar energy and reradiates it into space, creating short term cooling.
Sulfuric acid droplets settle out after several years
Edvard Munch’s “The Scream”
Indonesia Tectonic Setting
Indonesia Volcanoes – 130 Active!
Tambora, April 1815
Largest stratovolcano eruption in recorded
history
1816 – year without a summer. June snow
in New England, frost in July and August.
Crop failure – oats from 12 cents to 92
cents. Settlers move to midwest, Mary
Shelley writes Frankenstein. Famine in
Europe.
Stratovolcano v. Caldera Explosions
5000
4500
4000
3500
3000
2500
2000
1500
1000
500
0
St Helens Tambora
1815
Ystone
1.2 Ma
Ystone
0.6 Ma
Ystone La Garita
2.2 Ma
28 Ma
St. Helens v. Caldera Explosions
Caldera Explosions
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Caldera – LARGE volcanic crater caused
by the collapse of a magma chamber
after a big eruption
Convergent margins, hotspots under
continents
Wet melting of the continental crust
Inconceivably cataclysmic
Often called “supervolcanoes”
Magma – low temperature, high gas
content, high viscosity, high silica
content = HIGHLY explosive
“Nice” Caldera – Kilauea
Wet Melting of the Continental Crust
Calderas
Often formed
by explosive
eruption.
Crater Lake fills
caldera formed
by collapse during
massive eruption
of Mt. Mazama
6600 years ago.
Caldera Formation
Eruption  Collapse
Figure 7.12: Sequence of events in the formation of Crater Lake.
Last Big One – 74 Ka, Toba, Sumatra
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2,800 cubic kilometers of material ejected
Cause of the human genetic bottleneck?
Long Valley Caldera, California
- A very dangerous volcano
http://quake.wr.usgs.gov/recenteqs/Maps/Long_Valley.html
Left:
Cross section of
Long Valley
Caldera.
Right: Lasers monitor ground
swelling at Long Valley Caldera
Hot Spot Volcanism
Yellowstone
Hot Spot
Yellowstone Hotspot
Volcanoes
Go to the Movie
Internal Heat Generation
Earth
Remnant heat from formation, much of
which is stored in the liquid core
Decay of radioactive elements
Satellites of large planets
Gravitational energy turned into heat –
“tidal friction”
Io – Most Volcanically
Active Spot in the
Solar System
Io v. Titan
Io – moon of Jupiter
Sulfur / silicate magma
Titan – moon of Saturn
Ammonia-water solution magma
Igneous Rock Bodies
Small ones
Sill – horizontal tabular body
Dike – vertical tabular body
Volcanic neck – pipelike remains of a vent
Big ones
Pluton – large igneous intrusion
Batholith – really large igneous intrusion
Igneous Rock
Bodies
Figure 7.15 on page 148 of The Blue Planet
Igneous intrusive landforms
Plutons and Batholiths: Large igneous intrusive rock bodies.
Crystallized deep within crust. Exposed by uplift and erosion.
Igneous intrusive
rocks formed close
to surface: Dikes,
Sills, Volcanic Necks
Sills
Volcanic Necks
Dikes
QuickTime™ and a
Photo - JPEG decompressor
are needed to see this picture.
Beneficial Aspects of Volcanoes
Outgassing formed oceans, atmosphere
Ash produces rich, fertile soil
Mineral deposits
Geothermal energy
Beautiful sunsets!
Geyser, New Zealand
Water circulates through cooling magma
bodies.
Hot brines
deposit
minerals
with copper,
lead, zinc,
gold, silver.
Gold & Quartz Veins
gold
quartz
Deposited in fractures by hot water
(50 to 200 oC).
Volcanic Hazards
Ash falls – choke people, animals, kill animals that eat it,
collapse roofs – worsened by rain
Pyroclastic flows – suffocation and burning, knock over
anything in their way
Mudflows (lahars) – ice and snow melt, rain on ash flow
Volcanic landslide
Lava flow
Poisonous gas emission – Lake Nyos in Cameroon, 1700
CO2 suffocation deaths
http://perso.wanadoo.fr/mhalb/nyos/webcam.htm
Igneous Rocks Tell Their Story
Just as sedimentary strata record the
environments of their deposition, igneous
rock bodies and layers record the history of
magmatism and volcanism in and on the
Earth. Rock types and rock distribution tell
what kind of activity occurred and
radioisotopic dating tells when