2004 Physical Geology Lecture 9 Eruptions
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Transcript of 2004 Physical Geology Lecture 9 Eruptions
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The Wrath of Vulcan:Volcanic EruptionsThe Wrath of Vulcan:Volcanic Eruptions
Geology 211, Physical Geology Copyright, 2004, Ron ParkerGeology 211, Physical Geology Copyright, 2004, Ron Parker
February 17, 2004February 17, 2004
RonParker,2003
RonParker,2003
Geo lo gy 2 11 , P hy si ca l Geo lo gy 2 00 3, R on P arke r
Volcanic Eruptions
Vulcan The Roman god of fire.
Volcano
An erupting vent through which moltenrock (magma) reaches the surface
A mountain built from magmatic eruptions
Volcanoes pose hazards to humans.
Many populated areas are located
near volcanic centers
Seattle Portland
Mexico City
Naples, Italy
Vulcan The Roman god of fire.
Volcano
An erupting vent through which moltenrock (magma) reaches the surface
A mountain built from magmatic eruptions
Volcanoes pose hazards to humans.
Many populated areas are located
near volcanic centers
Seattle Portland
Mexico City
Naples, Italy
Geo lo gy 2 11 , P hy si ca l Ge ol og y 2 00 3, Ro n P arke r
Vesuvio
79 A.D. Roman Empire
Mount Vesuvius erupted violently.
Pompeii and Herculaneum were
destroyed by pyroclastic flows.
20,000 + were incinerated
The ignimbrite preserved a complete
record of Roman daily life.
Jocelyn Karlans Vesuvius Webpage
W. W. Norton W. W. Norton
Leo C. CurranLeo C. Curran
W. W. Norton W. W. Norton
Mt. Vesuvius remains a threat to the 100s of thousands
of people living in and around modern Naples, Italy.
Expanding human populations put people at risk.
Volcanoes have killed 100,000 in the past 100 years
Mt. Vesuvius remains a threat to the 100s of thousands
of people living in and around modern Naples, Italy.
Expanding human populations put people at risk.
Volcanoes have killed 100,000 in the past 100 years
, 2002, DIGIT, Prentice-Hall
NASA NASA
Geo lo gy 2 11 , P hy si ca l Ge ol og y 2 00 3, Ro n P arke r
Volcanoes are unpredictable and dangerous
Volcanically active areas may erupt without warning
50 to 60 volcanoes erupt annually
Most in sparsely populated areas.
Rarely eruptions occur near cities.
Indonesia
Japan
Philippines
Mexico
Volcanoes are unpredictable and dangerous
Volcanically active areas may erupt without warning
50 to 60 volcanoes erupt annually
Most in sparsely populated areas.
Rarely eruptions occur near cities.
Indonesia
Japan
Philippines
Mexico
Volcanoes
Geo lo gy 2 11 , P hy si ca l Geo lo gy 2 00 3, R on P arke r
Paracutin (Central Mexico)
A man plowing his cornfield noticed strange smoke
1 week later cinders and
ash piled up 100m
Lava buried the
nearby village
Paracutin (Central Mexico)
A man plowing his cornfield noticed strange smoke
1 week later cinders and
ash piled up 100m
Lava buried the
nearby village
Volcanoes
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Geo lo gy 2 11 , P hy si ca l Ge ol og y 2 00 3, Ro n P arke r
Lava flows Sheets or mounds of lava
that flowed on the ground or sea floor
and then solidified.
Pyroclastic debris Fragmented
igneous material deposited on the
ground or the sea floor.
Volcanic gases Gases
and aerosols.
Volcanic Materials
Geo lo gy 2 11 , P hy si ca l Geo lo gy 2 00 3, R on P arke r
The type of lava flow depends on the magma composition
Magma compositions vary in silica (SiO2) content
Rhyolitic > 70% Explosive eruptions
Andesitic > 55% Intermediate
Basaltic < 50% Mellow eruptions
Lava Flows
The 3 Main Magma TypesBasaltic Andesitic Rhyolitic
Silica-poor Silica-rich Silica-rich
Geo lo gy 2 11 , P hy si ca l Geo lo gy 2 00 3, R on P arke r
Low viscosity basaltic magmas produce quiet eruptions.
95% ofbasaltic magmas reach the surface.
High viscosity rhyolitic magmas produce violent eruptions.
Most of these magmas do not reach the surface, cooling at depth
Those that do reach the surface explode to form calderas.
Intermediate andesitic magmas are in between
Composition and Extrusive Style
DIGIT, 2002DIGIT, 2002
PahoehoePahoehoe
Hot, fluid basalt flows rapidly
Creates a ropy texture
Develops a glassy surface
Hot, fluid basalt flows rapidly
Creates a ropy texture
Develops a glassy surface
Geo lo gy 2 11 , P hy si ca l Geo lo gy 2 00 3, R on P arke r
Aa Far from the vent,
basaltic lava cools, loses
gases and thickens.
This type of lava:
Flows slowly for
short distances
Is rough and jagged
Is known as Aa (ahh
ahh) because thats
what you say if you
walk on it with bare
feet!
Far from the vent,
basaltic lava cools, loses
gases and thickens.
This type of lava:
Flows slowly for
short distances
Is rough and jagged
Is known as Aa (ahh
ahh) because thats
what you say if you
walk on it with bare
feet!
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Pahoehoe can form lava tubes preventing cooling
Lava can flow for many miles underground in tubes.
Lava tubes act to expand the size of the island
Pahoehoe can form lava tubes preventing cooling
Lava can flow for many miles underground in tubes.
Lava tubes act to expand the size of the island
Lava TubesLava Tubes
Geo lo gy 2 11 , P hy si ca l Geo lo gy 2 00 3, R on P arke r
Columnar JointingColumnar Jointing When lava flows cool uniformly, they sometimes
form vertical fractures called columnar jointing.
Columns have a hexagonal cross-section.
When lava flows cool uniformly, they sometimes
form vertical fractures called columnar jointing.
Columns have a hexagonal cross-section.
http://www.ivanweb.net/Nelmondo/Irlanda/irlanda.htmhttp://www.ivanweb.net/Nelmondo/Irlanda/irlanda.htm
Geo lo gy 2 11 , P hy si ca l Ge ol og y 2 00 3, Ro n P arke r
Pyroclastic Fire fragments
Types of pyroclastic debris
Ash and dust - fine, powdery, glassy fragments
Cinders - pea-sized material
Lapilli - walnut-sized material
Pumice - porous rock from frothy lava
Particles larger than lapilli
Blocks - hardened or cooled lava basketball to TV sized Bombs - streamlined blocks ejected as hot lava
Pyroclastic Fire fragments
Types of pyroclastic debris
Ash and dust - fine, powdery, glassy fragments
Cinders - pea-sized material
Lapilli - walnut-sized material
Pumice - porous rock from frothy lava
Particles larger than lapilli
Blocks - hardened or cooled lava basketball to TV sized Bombs - streamlined blocks ejected as hot lava
Pyroclastic DebrisPyroclastic Debris
TephraTephra
Tephra is particulate material ejected by volcanoes.
Tephra ranges in size from car size blocks to fine
clay sized ash.
Bombs ejected by volcanoes can kill.
Tephra is particulate material ejected by volcanoes.
Tephra ranges in size from car size blocks to fine
clay sized ash.
Bombs ejected by volcanoes can kill.
Airfall Volcanic AshAirfall Volcanic Ash
Volcanic Ash FragmentVolcanic Ash Fragment
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Pyroclastic Flow (Nue Ardente)Pyroclastic Flow (Nue Ardente)
Pyroclastic flows:
Are 100s of degrees
Race downslope at 30 kph
Incinerate everything
Famous examples:
Pompeii (Italy) 79 A.D.
St. Pierre (Martinique) - 1902
Pyroclastic flows:
Are 100s of degrees
Race downslope at 30 kph
Incinerate everything
Famous examples:
Pompeii (Italy) 79 A.D.
St. Pierre (Martinique) - 1902
Mount PeleeNue Ardente destroyed the city of St. Pierre, Martinique in 1902
Mount PeleeNue Ardente destroyed the city of St. Pierre, Martinique in 1902
Pyroclastic HazardsPyroclastic Hazards
Ash fall Buries landscapes
Lateral blasts Destroy large land areas
Pyroclastic flows Incinerate and bury land
Ash fall Buries landscapes
Lateral blasts Destroy large land areas
Pyroclastic flows Incinerate and bury land
Geo lo gy 2 11 , P hy si ca l Geo lo gy 2 00 3, R on P arke r
One to six percent of a magma by weight
Mainly water vapor and carbon dioxide
Gas content affects magma mobility.
Gases expand within a magma as it nears the Earths surface due to
decreasing pressure.
The violence of an eruption is related to how easily gases escape
from magma. Low viscosity (basalt) easy escape, mellow eruption
High viscosity (rhyolite) difficult escape, violent eruption
Volatiles (Dissolved Gases)
Geo lo gy 2 11 , P hy si ca l Ge ol og y 2 00 3, Ro n P arke r
Magma composition controls most volcanic features.
Magma chamber
Vent
Crater
Caldera
Size and shape
Volcanic Architecture
Geo lo gy 2 11 , P hy si ca l Geo lo gy 2 00 3, R on P arke r
Volcanic ventsVolcanic vents
Flank of Mauna Kea shield volcanoFlank of Mauna Kea shield volcano
Volcanic vents are smaller scale openingsVolcanic vents are smaller scale openings
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Crater Conical depression at the top of a volcano.
Craters are several km across.
Crater Conical depression at the top of a volcano.
Craters are several km across.
Geo lo gy 2 11 , P hy si ca l Geo lo gy 2 00 3, R on P arke r
CalderaCaldera A giant depression formed by collapse of a volcano
into emptied magma chamber.
Much larger than a crater (10s of km across).
Crater Lake is a Caldera formed by the collapse of
Mount Mazama ~8000 years ago.
A giant depression formed by collapse of a volcano
into emptied magma chamber.
Much larger than a crater (10s of km across).
Crater Lake is a Caldera formed by the collapse of
Mount Mazama ~8000 years ago.
USGS Fact Sheet FS092-02USGS Fact Sheet FS092-02
Geo lo gy 2 11 , P hy si ca l Ge ol og y 2 00 3, Ro n P arke r
Volcano Types Shield volcano
Broad, slightly domed-shaped
Composed primarily of basaltic lava
Generally cover large areas
Produced by mild eruptions of large volumes of lava
Mauna Loa on Hawaii is a good example
Geo lo gy 2 11 , P hy si ca l Geo lo gy 2 00 3, R on P arke r
Cinder cone
Built from ejected lava (mainly cinder-sized) fragments
Steep slope angle
Rather small size
Occur in groups
Volcano Types
Geo lo gy 2 11 , P hy si ca l Ge ol og y 2 00 3, Ro n P arke r
Composite cone (Stratovolcano)
Most are located adjacent to the Pacific Ocean (e.g., Fujiyama, Mt.
St. Helens)
Large, classic-shaped volcano (1000s of ft. high & several miles wide
at base)
Composed of interbedded lava
flows and layers of pyroclastic debris
Volcano Types
Geo lo gy 2 11 , P hy si ca l Geo lo gy 2 00 3, R on P arke r
A Composite Volcano
DIGIT, 2002DIGIT, 2002
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W. W. Norton W. W. NortonGeo lo gy 2 11 , P hy si ca l Geo lo gy 2 00 3, R on P arke r
Composite Volcanoes Most violent type of activity (Mt. Vesuvius)
Often produce a nue ardente
Fiery pyroclastic flow made of hot gases, ash and other debris
Move down the slopes of a volcano at speeds up to 300 km per hour
May produce a lahar (a volcanic mudflow)
Lahars common if volcano was glaciated
Lahars magnify the damage and destruction
Most violent type of activity (Mt. Vesuvius)
Often produce a nue ardente
Fiery pyroclastic flow made of hot gases, ash and other debris
Move down the slopes of a volcano at speeds up to 300 km per hour
May produce a lahar (a volcanic mudflow)
Lahars common if volcano was glaciated
Lahars magnify the damage and destruction
Geo lo gy 2 11 , P hy si ca l Ge ol og y 2 00 3, Ro n P arke r
Case History Mount St. Helens
May 18th, 1980, 8:32 A.M.
Initial debris avalanche and lateral blast removed the upper
396 meters of the volcano
This killed 57 people
USGSUSGSGeo lo gy 2 11 , P hy si ca l Geo lo gy 2 00 3, R on P arke r
Eye Witnesses Mount St. Helens Geologists Keith and Dorothy Stoffel, were in a small plane 1000
feet over Mount Saint Helens when i t erupted.
"noticed landsliding of rock and ice debris in-ward into thecrater. Within a matter of seconds, the whole north side ofthe summit crater began to move. The nature of movementwas eerie.... The entire mass began to ripple and churn up,without moving laterally. Then the entire north side of thesummit began sliding to the north along a deep-seated slide
plane. We took pictures of this slide sequence occurring, butbefore we could snap off more than a few pictures, a hugeexplosion blasted out. We neither felt nor heard a thing.
W. W. Norton W. W. Norton DIGIT, 2002DIGIT, 2002
Mount St. Helensbefore May 18th, 1980 8:32 a.m.
Mount St. Helensbefore May 18th, 1980 8:32 a.m.
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DIGIT, 2002DIGIT, 2002
Mount St. Helensafter May 18th, 1980 8:32 a.m.
Mount St. Helensafter May 18th, 1980 8:32 a.m.
Melted glaciers triggered debris flows (lahars) that
clotted the Toutle River
Temporarily stopped shipping on the Columbia River
Melted glaciers triggered debris flows (lahars) that
clotted the Toutle River
Temporarily stopped shipping on the Columbia River
Case History Mount St. HelensCase History Mount St. Helens
Geo lo gy 2 11 , P hy si ca l Ge ol og y 2 00 3, Ro n P arke r
Case History Mount St. HelensCase History Mount St. Helens
Disrupted highways and rail lines.
The blast devastated 596 square kilometers,
Destroyed timber valued at several 100 million dollars.
Ash fell as far east as North Dakota.
Disrupted highways and rail lines.
The blast devastated 596 square kilometers,
Destroyed timber valued at several 100 million dollars.
Ash fell as far east as North Dakota.
USGSUSGS
Geo lo gy 2 11 , P hy si ca l Ge ol og y 2 00 3, Ro n P arke r
Plate Tectonics & Igneous Activity Global distribution of igneous activity is not random
Most volcanoes are located within or near ocean basins
Basaltic rocks are common in both oceanic and
continental settings, whereas granitic rocks are rarely
found in the oceans
DIGIT, 2002DIGIT, 2002
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Geo lo gy 2 11 , P hy si ca l Ge ol og y 2 00 3, Ro n P arke r
Intraplate volcanism
Associated with plumes of heat in the mantle
Form localized volcanic regions in the overriding plate
called a hot spot
Produces basaltic magma sources in oceanic crust (e.g., Hawaii
and Iceland)
Produces granitic magma sources in continental crust (e.g.,
Yellowstone Park)
Plate Tectonics & Igneous Activity
Geo lo gy 2 11 , P hy si ca l Geo lo gy 2 00 3, R on P arke r
Volcanoes and Climate
Explosive eruptions emit huge quantities of gases and fine-
debris into the atmosphere. These filter and reflect incoming
solar radiation. Examples of volcanism affecting climate
Mount Tambora, Indonesia 1815
Krakatau, Indonesia 1883
Mount Pinatubo, Philippines 1991
El Chicon, Mexico 1982 Sulfur dioxide
Geo lo gy 2 11 , P hy si ca l Ge ol og y 2 00 3, Ro n P arke r
Predicting Eruptions
Usually, signals that precede an eruption permit
advanced warning.
Seismic activity Earthquakes accompany magma movement
Heat Volcanoes heat-up before eruptions, sometimes visible
on Infrared satellites.
Topographic inflation Volcanoes expand when magma
chambers inflate.
Lasers
Tiltmeters
Volcanic gas emanation
Geologic history