UNIVERSITY OF SOUTH ALABAMA
GY 111: Physical Geology
The eruption of Mount Tavurvur volcano
August 29th, 2014. Captured by Phil
McNamara.
http://www.youtube.com/watch?v=BUR
EX8aFbMs
By Taro Taylor (originally posted to Flickr as Tarvurvur)
UNIVERSITY OF SOUTH ALABAMA
GY 111: Physical Geology
Lecture 7: Volcanic Landforms, Features
and Case Studies
Instructor: Dr. Douglas W. Haywick
Last Time
1. Review of where volcanoes occur
2. Properties of magma/lava (viscosity)
3. Basic types of volcanoes
Where Volcanoes Occur
2) Convergent P. B.
3) Hot Spots.
1) Divergent P. B.
Divergent Plate
Boundaries
Rapid rise of
magma to surface
because of multiple
fractures and faults
(low resistance)
Magma (molten rock inside
the Earth) rises upwards
along fractures and fault as
plutons (inverted tear dropshaped blebs 100’s to
1000’s of m in diameter).
Why?.... Buoyancy. Hot
magma is less dense than
cool country rock
Convergent Plate
Boundaries
Subduction
35
km
Plutons rise at convergent plate
boundaries too….
… but they have to burn their way up.
This is not an easy trip to the surface.
Hot Spots
Properties of Magma/Lava
1.
2.
3.
Magma derived from just below the lithosphere (e.g., 100
km down) is hot (2000 °C) and very fluid (low viscosity)
Lava erupted at divergent plate boundaries and oceanic
hotspots has made it to the surface of the Earth quickly and
is still hot (up to 1800 °C) and fluid (low viscosity).
Lava erupted at convergent plate boundaries and
continental hotspots has made it to the surface of the Earth
very slowly. It is cooler (as low as 800 °C) and very
contaminated by country rock and water (high viscosity)
Types of Volcanoes
http://volcanoes.usgs.gov/Imgs/Jpg/Photoglossary/30424305-084_large.JPG
Cinder cone in Hawaii
http://www.discoverourearth.org/student/volcanoes/images/shield_volcanoes_big.jpg
Shield Volcanoes (Mauna Loa, Mauna Kea, HI)
Composite Volcanoes
in Japan (Mt. Fuji)
Pyroclastic flows
Shield volcanoes
produce annoying
eruptions (but
generally not
disastrous)
Today’s Agenda
1. Volcanic Landforms
2. Volcanic eruptions (case studies)
3. Measurements of activity
Web notes 7
Cross-section of an
Active Composite
Volcano
Chalk board time
Landforms of Extinct
Volcanoes
http://www.uwgb.edu/dutchs/GRAPHIC0/ROCKMIN/Ig-Rocks/CALDERA.GIF
Calderas: Can form via
collapse (boring) or
explosion (exciting).
When filled with water they
are called crater lakes.
Volcanic Islands
(Island Arcs)
Island Arcs: chains of composite volcanic islands that pop up on
the overriding plate along an oceanic-oceanic plate boundary
Volcanic Islands
(Island Arcs)
Island Arcs: chains of composite volcanic islands that pop up on
the overriding plate along an oceanic-oceanic plate boundary
Volcanic Eruptions (Rocks)
Shield Volcanoes, fissure eruptions, oceanic hot spots: all
produce low viscosity lava flows that when cooled, form rocks
like basalt
Volcanic Eruptions (Rocks)
Shield Volcanoes, fissure eruptions, oceanic hot spots: The lava
flows come in two main “flavors”
Pahoehoe (AKA ropey)
Aa (AKA jagged)
Volcanic Eruptions (Rocks)
Composite Volcanoes and continental hot spots: produce high
viscosity lava flows that might flow and form rocks like
rhyolite…
Volcanic Eruptions (Rocks)
Composite Volcanoes and continental hot spots: produce high
viscosity lava flows that might flow and form rocks like
rhyolite… or blow-up and form pyroclastic deposits like
volcanic ash
Volcanic Eruptions (Rocks)
Composite Volcanoes and continental hot spots: are dangerous
Mt. Pinatubo
David H. Harlow/U.S.Geological Survey
Volcanic Eruptions (Case Studies)
1) Kilauea, Hawaii
Volcanic Eruptions (Case Studies)
2) Mt Nyiragongo, Africa
http://www.gomafilmproject.org/images/nyiragongopretty.gif
Volcanic Eruptions (Case Studies)
2) Lake Nyos, Africa
Volcanic Eruptions (Case Studies)
2) Lake Nyos, Africa
Volcanic Eruptions (Case Studies)
2) Lake Nyos, Africa
Volcanic Eruptions (Case Studies)
2) Lake Nyos, Africa
Volcanic Eruptions (Case Studies)
3) Mt Pelée, Martinique
Volcanic Eruptions (Case Studies)
3) Mt Pelée, Martinique
Nueé Ardent
Volcanic Eruptions (Case Studies)
3) Mt Pelée, Martinique
Volcanic Eruptions (Case Studies)
4) Mt Unzen Japan
Volcanic Eruptions (Case Studies)
4) Mt Unzen Japan
Lahar
Volcanic Eruptions (Case Studies)
4) Mt Krakatoa
today
Lahar
Volcanic Eruptions (Case Studies)
4) Mt Krakatoa
http://www.drgeorgepc.com/Tsu1883Krakatau15daysBefore.jpg
1883
Volcanic Eruptions (Case Studies)
4) Mt Krakatoa
1883 (7 weeks later)
Volcanic Eruptions (Case Studies)
4) Mt Krakatoa
Tsunami
15 meter (45 feet!)
Travel Times (minutes)
Tsunami height (metres)
http://www.drgeorgepc.com/Tsunami1883Krakatau.html
Volcanic Eruptions (Case Studies)
4) Mt Krakatoa
Anak Krakatoa
Today (kind of)
Volcanic Activity
Three states of activity are recognized:
Volcanic Activity
Three states of activity are recognized:
1) Active - the volcano is either erupting now, or there is a
historical record of it erupting in the past (e.g., Mt. Vesuvius
in Italy)
Volcanic Activity
Three states of activity are recognized:
2) Dormant - no record of recent activity (i.e., no historical
observations), but the volcano looks “fresh” and may show
some signs of thermal activity (e.g., Mt. Shasta, California)
Volcanic Activity
Three states of activity are recognized:
3) Extinct: it may be a volcano, but it is badly eroded, tree
encrusted and shows no signs of thermal activity (e.g.,
Diamondhead, Oahu, Hawaii).
http://www.sternwarte.uni-erlangen.de/~ai32/hawaii/diamondhead.jpg
Volcanic Activity (recap)
Three states of activity are recognized:
1) Active - the volcano is either erupting now, or there is a
historical record of it erupting in the past
2) Dormant - no record of recent activity (i.e., no historical
observations), but the volcano looks “fresh” and may
show some signs of thermal activity
3) Extinct - it may be a volcano, but it is badly eroded, tree
encrusted and shows no signs of thermal activity
Today’s Homework
1. Come up with a plan for world peace
2. Minerals exam in Haywick’s labs this week
Next Time
1. Quiz 4: definitions
2. Bowen’s Reaction series and the
crystallization of magma
GY 111: Physical Geology
Lecture 7: Volcanic Landforms, Features and
Case Studies
Instructor: Dr. Doug Haywick
dhaywick@southalabama.edu
This is a free open access lecture, but not for commercial purposes.
For personal use only.