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Volcanoes and
Volcanic Hazards
GEOL 101-002 / Physical Geology
Prof. Jules Goldspiel
George Mason University / Spring 2023
Feb 01, 2023
(USGS)
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Volcanoes and Volcanic Hazards
1.
2.
3.
4.
5.
6.
7.
8.
Volcanic Eruptions
Anatomy of a Volcano
Volcano Types
Other Volcanic Landforms
More on Calderas
Materials Extruded by Volcanoes
Volcanic Hazards
Volcanoes and Plate Tectonics
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Focus Questions
• How does magma composition affect the violence of
volcanic eruptions?
– What type of magmas erupt explosively?
– What type of magmas erupt effusively?
• How does magma temperature affect the violence of
volcanic eruptions?
• How are volcanic craters and calderas formed?
• What are the three main types of volcanoes?
– What are their general features?
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Focus Questions
• What is a Large Igneous Province?
– How did it form?
• What types of materials are extruded by volcanoes?
• What is a pyroclastic flow?
– What types of materials are in the flow?
• What is a lahar?
– Are lahars created on an active volcanoes, inactive volcanoes
or both?
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1. Volcanic Eruptions
• Nature of volcanic eruptions
– All eruptions involve magma
§ Magmas contain varying amounts of…
o Liquid
o Solids
o Dissolved gases
Eruption of Mt. Sakurajima, Japan,
Feb. 2016 (KYODO, Japan Times)
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1. Volcanic Eruptions
• Nature of volcanic eruptions
– Type of volcanic eruption is
determined by the properties
of the magma
§ Viscosity of the magma
§ Amount of dissolved gases in
the magma
Aa lava flow from Kilauea Volcano, Hawaii (USGS)
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1. Volcanic Eruptions
• Magma viscosity depends on temperature
– Hotter magmas are less viscous
– Cooler magmas are more viscous
Lava fountain from Kilauea Volcano, Hawaii (USGS)
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1. Volcanic Eruptions
• Magma viscosity depends on composition
– Most important is the amount of silica (SiO2)
§ Higher silica content à more viscous
§ Lower silica content à less viscous
Silica tetrahedrons linked to form a
chain (https://en.wikibooks.org/wiki/
Historical_Geology/Silicate_minerals)
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1. Volcanic Eruptions
• Magma viscosity depends on composition
– Recall also that magma composition evolves as it cools
Temperature
of cooling
magma
(Pl
a
Fe gioc
ld s las
pa e
r)
~1200 ⚬C
(Potassium
Feldspar)
~650 ⚬C
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Rock types
produced
Bowen’s Reaction Series
diagram for a mafic
magma (Colivine,
https://commons.
wikimedia.org/wiki/File:
Bowen%27s_Reaction_
Series.png). See also
Lutgens et al., 2018,
Fig. 4.20.
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1. Volcanic Eruptions
• Importance of dissolved gases in magma
– Gases expand when pressure decreases
§ Gases expand within a magma as it nears the surface
– Violence of an eruption is related to...
§ Amount of dissolved gas
§ How difficult it is for gas to escape
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1. Volcanic Eruptions
• Magma properties summary
Grain
Felsic
Intermediate
Mafic
Ultramafic
Coarse
Fine
75 %
Silica (SiO2) Content
40 %
Low
Magnesium and Iron Content
High
650℃
Temperature at Which Melting Begins
1250℃
High
Viscosity
5-8 %
Gas Content
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Low
0.5-2 % (by wt.)
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1. Volcanic Eruptions
• Volcanic eruption types
– Passive eruptions
§ Degassing of magma
Passive eruption at
Kilauea Volcano, Hawaii
(M. Poland, USGS)
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1. Volcanic Eruptions
• Volcanic eruption types
– Effusive eruptions
§ Quiescent Hawaiian-type eruptions
§ Associated with low viscosity magmas
Effusive eruption at
Kilauea Volcano, HI
(J. D. Griggs, USGS)
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1. Volcanic Eruptions
• Volcanic eruption types
– Explosive eruptions
§ Violent Mt. Saint Helens-type eruptions
§ Associated with high viscosity magmas
Explosive eruption of
Mt. St. Helens, WA,
on July 22, 1980
(M. Doukas, USGS)
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1. Volcanic Eruptions
• Volcanic Explosivity Index (VEI)
– Measure of the explosiveness of
volcanic eruptions
§ VEI 0: Effusive (Non-explosive)
§ VEI 1: Gentle (Small)
Mt. St. Helens
§ VEI 2: Explosive (Moderate) May 1980
§ VEI 3: Catastrophic (Large)
Hunga Tonga –
Hunga Ha'apai
§ VEI 4: Cataclysmic (Large)
Jan 2022
§ VEI 5-6: Colossal (Very large)
§ VEI 7: Super-colossal
§ VEI 8: Mega-colossal (Extremely large)
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(USGS)
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1. Volcanic Eruptions
• Hunga Tonga – Hunga Ha'apai eruption
– Major eruption Jan 15, 2022
– Submarine volcano (seamount)
– Intermediate composition magma
Smithsonian Global
Volcanism Program
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1. Volcanic Eruptions
• Hunga Tonga – Hunga Ha'apai eruption
– Easily seen by
weather
satellites...
Eruption Jan 15,
2022 (NOAA)
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1. Volcanic Eruptions
• Hunga Tonga – Hunga Ha'apai eruption
– Easily seen by
weather
satellites...
Eruption Jan 15,
2022 (NOAA)
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1. Volcanic Eruptions
• Hunga Tonga – Hunga Ha'apai eruption
– Generated shock waves
in the atmosphere
Eruption Jan 15, 2022,
atmospheric shock
wave seen in infrared
(NOAA)
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1. Volcanic Eruptions
• Hunga Tonga – Hunga Ha'apai eruption
– Generated tsunami
Tsunamic travel times
for eruption on Jan 15,
2022 (Gusman and
Roger, GNS Science)
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2. Anatomy of a Volcano
• Volcano general features
– Conduit
Vent
§ Fissure through which
magma moves
– Vent
§ Surface opening of a conduit
– Volcanic cone/shield
§ Overall construct created by
successive eruptions
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Conduit
Volcano cut-away
figure (USGS). See
also Lutgens et al.,
2018, Fig. 5.11, and
associated tutorial
(https://goo.gl/
nbwG5k).
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2. Anatomy of a Volcano
• Volcano general features
– Parasitic cone
§ Cone built from lava and
pyroclastic material erupted
from flank vent
Parasitic cone on Réunion Island (Indian
Ocean east of Madagascar) (B.Navez,
https://commons.wikimedia.org/wiki/File:
FormicaLeo_%26_PitonDeLaFournaise_2.jpg)
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2. Anatomy of a Volcano
• Volcano general features
– Crater
§ Relatively small depression
o < 1 km (0.6 mi) in diameter
Hi`iaka pit crater on
Kilauea Volcano, HI.
Crater about 600 m
across. (J.D. Griggs,
USGS)
– Caldera
§ Relatively large depression
o > 2 km (1.2 mi) in diameter
La Cumbre Volcano on
the Galapagos Islands.
Caldera is 5-6 km
across. (NASA/JSC)
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3. Volcano Types
• Three common types of volcanoes
– Shield volcanoes
– Composite volcanoes
– Cinder cone volcanoes
Sketches of the three
common volcano types.
Sketches are not to scale.
(Utah Geological Survey)
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3. Volcano Types
• Shield volcanoes
– General features
§ Broad, slightly dome-shaped
(like a shield)
§ Produced by effusive eruptions
of large volumes of basaltic lavas
§ Largest volcanoes are this type
Flank vent
Crust
Ma
Caldera
ntle
Magma
chamber
Conduit
(https://en.wikipedia.org/wiki/Shield_volcano)
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3. Volcano Types
• Shield volcanoes
– Mauna Loa is largest shield on Earth
Mauna Loa Volcano, Hawaii, a shield volcano (J. D.
Griggs, USGS) (see also Lutgens et al., 2018, Fig. 5.12)
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Five overlapping shield
volcanoes make up the big
island of Hawaii (USGS)
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3. Volcano Types
• Shield volcanoes
– Olympus Mons on Mars is
largest shield volcano in
the Solar System
Olympus Mons shield volcano on
Mars compared to Hawaii shield
volcanoes (NASA/JPL, USGS)
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3. Volcano Types
• Composite volcanoes
– Also called stratovolcanoes
– General features
Sketch of the
interior of a
composite
volcano (USGS)
§ Classic cone-shape
§ Composed of interbedded lava flows
and layers of pyroclastic debris
§ Large, but smaller than shields
2006 eruption
of Augustine
Volcano, Alaska,
a composite
volcano (C. Read,
AVO/USGS)
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3. Volcano Types
• Cinder cone volcanoes
– Also called scoria cone volcanoes
– General features
§ Built from ejected lava fragments that
begin to crystallize in flight
§ Relatively small
Sketch of the
interior of a
cinder cone
(USGS)
Cinder cone figure (USGS). See also
Lutgens et al., 2018, Fig. 5.15 and
associated video (https://goo.gl/X9JvXE).
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4. Other Volcanic Landforms
• Large igneous provinces
– Also called basalt plateaus
– Large areas of basaltic lava flows
Kilauea Volcano, Hawaii, fissure
complex with small basalt lava
flows (HVO/USGS). See also
Lutgens et al., 2018, Fig. 5.25.
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4. Other Volcanic Landforms
• Large igneous provinces
– Columbia Plateau is an example
§ Formed by Columbia River Basalts
Columbia River Basalts Province
(Camp et al., 2017, USGS). See
also Lutgens et al., 2018, Fig. 5.26.
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4. Other Volcanic Landforms
• Large igneous provinces
– There are several more around the globe
Columbia
Plateau
(20 Ma)
Global distribution of large igneous
provinces (LIPs) formed over the
last 500 million years. Numbers
shown are ages in billions of years
(Large Igneous Provinces
Commission). See also Lutgens et
al., 2018, Fig. 5.32 and associated
tutorial (https://goo.gl/O2Z6Sl).
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4. Other Volcanic Landforms
• Lava domes
– Small dome-shaped masses
– Built from rhyolitic or
intermediate lava
Lava dome in crater of Mt. St. Helens formed
after major eruption in 1980 (L. Topinka, USGS).
See also Lutgens et al., 2018, Fig. 5.27.
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4. Other Volcanic Landforms
• Volcanic necks
– Also called volcanic pipes
– Remnants of magma that solidified in a
volcanic conduit
Conduit
Volcanic neck in Shiprock, New
Mexico (B. Snodgrass,
https://commons.wikimedia.org/
wiki/File:Shiprock.snodgrass3.jpg).
See also Lutgens et al., 2018, Fig.
5.28 and associated tutorial
(https://goo.gl/TjW5uh).
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Volcano cut-away
sketch (USGS)
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5. More on Calderas
• Caldera
– Result of surface collapse after
an eruption
§ Different styles and circumstances
of collapse
La Cumbre Volcano on the Galapagos Islands.
Caldera is 5-6 km across. (NASA/JSC)
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5. More on Calderas
• Crater Lake-type caldera
– Collapse of the summit of a large composite volcano
– Summit loses support suddenly as magma chamber
drains quickly
Left: Crater Lake caldera,
Oregon, with bathymetric
image of caldera floor (USGS).
Right: Sketch of caldera
formation process (USGS). See
also Lutgens et al., 2018, Fig.
5.23, and associated animation
(https://goo.gl/kUCPNB).
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5. More on Calderas
• Hawaiian-type caldera
– Collapse of the summit of a
shield volcano
– Summit loses support
gradually as magma chamber
drains slowly
Halema’uma’u Crater withing Summit caldera of
Kilauea Volcano, Hawaii, also showing the USGS
Hawaiian Volcano Observatory (M. Poland, USGS)
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5. More on Calderas
• Yellowstone-type caldera
– Collapse of a large area after an
enormous eruption
Volcano and Earthquake Monitoring
Plan for the Yellowstone Volcano
Observatory, 2006-2015
– Large region loses support and
collapses after colossal volumes
of magma are erupted
§ Collapsed area is vast and poorly
defined
Yellowstone caldera outlined in black (USGS).
See also Lutgens et al., 2018, Fig. 5.24, and
associated tutorial (https://goo.gl/y44zXb).
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50 km
Scientific Investigation Report 2006-5276
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U.S. Department of the Interior
U.S. Geological Survey
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6. Materials Extruded by Volcanoes
• Lava
– Lava flow composition statistics
~1%
Grain
Felsic
~90%
Intermediate
Mafic
Ultramafic
Coarse
Fine
75 %
Low
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< 10%
Silica (SiO2) Content
40 %
Magnesium and Iron Content
High
High
Viscosity
5-8 %
Gas Content
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Low
0.5-2 % (by wt.)
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6. Materials Extruded by Volcanoes
• Lava
– Aa and Pahoehoe flows
§ Basaltic (mafic) lavas
§ Aa
o Flows have surfaces of rough
jagged blocks
§ Pahoehoe
o Flows have smooth surfaces
Aa lava flowing over pahoehoe lava (Smithsonian).
See also Lutgens et al., 2018, Fig. 5.6.
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6. Materials Extruded by Volcanoes
• Lava
– Pillow lavas
§ Basaltic (mafic) lavas
extruded under water
§ Pillow- or tube-like structures
stacked on top of each other
Pillow lava off Hawaii coast (NOAA). See also
Lutgens et al., 2018, Fig. 5.8.
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6. Materials Extruded by Volcanoes
• Lava
– Block lavas
§ Andesitic (intermediate) and
rhyolitic (felsic) lava
§ Upper surface consists of large,
detached blocks
Block lava in Nea Kameni, Santorini, Greece
(https://www.sandatlas.org)
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6. Materials Extruded by Volcanoes
• Pyroclastic materials
– Airborne solid and
semi-molten materials
– Also called tephra
– Wide size range
Ash from pyroclastic flow at
Mt. St. Helens, Washington
state (D. Weiprecht, USGS)
§ Volcanic ash (< 2 mm, < 0.08 inch)
§ Cinders (2-64 mm, 0.08-2.5 inch)
§ Blocks and bombs (> 64 mm, > 2.5 inch)
Pyroclastic cinders (http://academic.
brooklyn.cuny.edu/geology/leveson/core/
linksa/ROCK%20CYCLE/craters_moon_8.jpg)
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6. Materials Extruded by Volcanoes
• Pyroclastic materials
– Blocks vs. bombs
§ Blocks are ejected as hardened
(cooled) lava
§ Bombs are ejected as semi-molten
(hot) lava
Geologist inspecting pumice blocks at edge
of pyroclastic flow at Mt. St. Helens, WA
(D. A. Swanson, USGS)
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6. Materials Extruded by Volcanoes
• Gases
– Volatile component of magmas
– Common gases
§ Water vapor (H2O)
§ Carbon dioxide (CO2)
§ Sulfur dioxide (SO2)
Augustine Volcano, Alaska, a composite volcano
erupting in Jan. 2006 (C. Read, AVO/USGS)
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7. Volcanic Hazards
• Volcanoes present several types of
immediate hazards to life and property
– Pyroclastic flows
– Lahars
– Volcanic ash
– Volcanic gases
– Tsunamis
• Volcanoes can also have
longer term effects
– Climate
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Volcano cut-away
figure showing
hazards created
at the surface
during and after
eruptions (USGS)
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7. Volcanic Hazards
• Pyroclastic flows
– Mixture of ejected materials that flows
down the slope of a volcano
§ Hot gases
§ Solid particles (ash, cinders, blocks)
§ Semi-molten lava (bombs)
– Most frequently generated by collapse of
tall eruption columns
Volcano cut-away
figure with
pyroclastic flows
marked (USGS)
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7. Volcanic Hazards
• Pyroclastic flows
– Can devastate area near volcano
§ Saint-Pierre, Martinique (1902)
o Mt. Pelée
o 28,000 killed
Sanint-Pierre after 1902
eruption of Mt. Pelée
(see also Lutgens et al.,
2018, Fig. 5.19)
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7. Volcanic Hazards
• Pyroclastic flows
– Can devastate area near volcano
§ Pompeii, Italy (C.E. 97)
o Mt. Vesuvius
o Estimated 13,000 killed in
Pompeii and other towns
Casts of victims in Pompeii of
Mt. Vesuvius eruption in C.E. 97
(Lancevortex, https://commons.
wikimedia.org/wiki/File:Pompeii_
Garden_of_the_Fugitives_02.jpg
Feb 01, 2023
Region of ash and cinder
falls from Mt. Vesuvius
eruption in C.E. 97
(MapMaster, https://
commons.wikimedia.org/
wiki/File:Mt_Vesuvius_
79_AD_eruption.svg)
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7. Volcanic Hazards
• Lahars
– Mudflow on an active or inactive volcano
§ Volcanic debris become saturated with water
and move quickly down slope
– Can be triggered by…
§ Magma nearing the surface of ice and snow
covered volcano
§ Heavy rains saturating weathered volcanic
deposits
Volcano cut-away figure
with lahars marked (USGS)
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7. Volcanic Hazards
• Lahars
– Can devastate area near volcano
§ Nevado del Ruiz, Colombia (1985)
o More than 23,000 killed
Nevado del Ruiz
lahar path from
1985 eruption
(USGS). Town of
Armero marked.
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Armero after Nevado del Ruiz lahar
from 1985 eruption (USGS)
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7. Volcanic Hazards
• Volcanic ash
– Can accumulate on and damage structures
– Can damage jet engines
• Volcanic gases
– Gases can be fatal to humans and animals
• Volcano-related tsunamis
– Collapse of a oceanic volcano flank
– Eruption underwater
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7. Volcanic Hazards
• Volcano effects on climate
– Can be complicated because of the different feedbacks...
§ Ash particles from volcanoes can block sunlight
o Can result in temporary cooling of climate
§ Volcanic gases can cause greenhouse effect
o Can result in temporary warming of climate
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8. Volcanoes and Plate Tectonics
• Volcanism has a strong (but not exclusive) association with
lithospheric plate boundaries
– Volcanism at convergent
plate boundaries
§ Ring of Fire
– Volcanism at divergent
plate boundaries
§ Ocean ridges
Ring of Fire figure (USGS). See also Lutgens
et al., 2018, Fig. 5.29.
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References for Further Reading
• Lutgens, F. K., et al., 2018, Essentials of Geology, 13th Edition.
[Chapter 5]
• Johnson, C., et al., 2017, An Introduction to Geology (online).
[Chapter 4]
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