1 Earth Science, 10e Edward J. Tarbuck & Frederick K. Lutgens.
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Transcript of 1 Earth Science, 10e Edward J. Tarbuck & Frederick K. Lutgens.
1
Earth Science, 10e
Edward J. Tarbuck & Frederick K. Lutgens
2
Volcanoes and Other Igneous Activity
Chapter 8
Earth Science, 10e Stan Hatfield and Ken Pinzke
Southwestern Illinois College
3
Volcanic eruptions
Factors that determine the violence of an eruption • Composition of the magma (% silica content)• Temperature of the magma (Very hot and cool)• Dissolved gases in the magma (Water vapor
etc…)
Viscosity of magma (function of silica content)
• Viscosity is a measure of a material's resistance to flow
4
Let’s Review
• What types of Magma are there?...
• How does temperature relate to a type of magma?
• How Does viscosity relate to a type of Magma?
5
Volcanic eruptions
Viscosity of magma • Factors affecting viscosity
• Temperature (hotter magmas are less viscous)
• Composition (silica content)
• High silica – high viscosity (e.g., rhyolitic lava)
• Low silica – more fluid (e.g., basaltic lava)
• Dissolved gases (volatiles)
• Mainly water vapor and carbon dioxide
• Gases expand near the surface
• Hotter magmas have less gases
• Cooler magmas trap more gases
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Volcanic eruptions
Viscosity of magma (continued…)• Factors affecting viscosity
• Dissolved gases (volatiles) thicken the magma
• Provide the force to extrude lava
• Violence of an eruption is related to how easily gases escape from magma
• Easy escape from fluid magma
• Viscous magma produces a more violent eruption
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Fluid Lava: The Columbia River basalts
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Let’s summarize
• Viscous magma: Felsic/Andesitic or Mafic?
• Cooler magma Felsic/Andesitic or Mafic?
• Violent eruptions: Felsic/Andesitic or Mafic?
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Materials associated with volcanic eruptions
Types of Basaltic Lava flows • Basaltic lavas are more fluid• Types of basaltic lava
• Pahoehoe lava (resembles braids in ropes)
• Aa lava (rough, jagged blocks)
Gases • Represent one to 5 percent of magma by weight• Mainly water vapor and carbon dioxide
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A Pahoehoe lava flow
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A typical aa flow
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What is a Hot Spot?
• An intermittent stationary source of magma that originates deep inside the core or the mantle
• Plates riding over a hot spot form a chain of volcanoes. i.e. Hawaiian chain
• The chain changes direction as the plate changes its direction over the hot spot
• Only the volcano over the hot spot is active
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A size comparison of the three types of volcanoes
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Types of Volcanoes
There are three types of volcanoes defined according to their shape and size:
1. Shield volcano• Broad, slightly domed
• Primarily made of basaltic (fluid) lava
• Generally large size
• e.g., Mauna Loa in Hawaii
• Mostly found on the Ocean floor and/or over
hot spots
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A shield volcano
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Types of Volcanoes
Types of volcanoes (continued…) 2. Cinder cone
• Built from ejected lava fragments
• Steep slope angle
• Rather small size
• Frequently occur in groups
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Sunset Crater – a cinder cone near Flagstaff, Arizona
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Types of Volcanoes
Types of volcanoes (continued…)• Composite cone (or stratovolcano)
• Are made of Interbedded lavas and pyroclastics
• Most are adjacent to the Pacific Ocean also called Ring of Fire (e.g., Mt. St. Helens, Mt. Pinatubo,…)
• They are of large size
• They produce the most violent eruptions (i.e. Mt. St Helens May 18, 1980 eruption)
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Volcanoes
Types of volcanoes (continued…) • Composite cone (or stratovolcano)
• Often produce nuée ardente (Pyroclastic flow)
• Fiery pyroclastic flow made of hot gases infused with ash
• Flows down sides of a volcano at speeds up to 200 km (125 miles) per hour
• May produce a Lahar – deadly volcanic mudflow
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A composite volcano (stratovolcano)
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Mt. St. Helens – a typical composite volcano
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Pyroclastic flow on Mt. St. Helens
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What’s on a Volcano’s arsenal?
• Pyroclastic flow (very hot ash)
• Lahar (deadly mud flow)
• Crater Lake’s deadly gases
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A lahar along the Toutle River near Mt. St. Helens
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Other volcanic landforms
Calderas • Steep walled depression at the summit • Formed by collapse of the crater• Nearly circular • Size exceeds one kilometer in diameter• When filled with water calderas form
crater lakes
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Crater Lake, Oregon is a good example of a caldera
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Crater Lake in Oregon
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Materials associated with volcanic eruptions
Pyroclastic materials • "Fire fragments" • Types of pyroclastic material
• Ash and dust – fine, glassy fragments • Pumice – from "frothy" lava • Lapilli – "walnut" size • Cinders – "pea-sized" • Particles larger than lapilli
• Blocks – hardened lava • Bombs – ejected as hot lava
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A volcanic bomb
Bomb is approximately 10 cm long
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Volcanoes
General features • Conduit, or pipe caries gas-rich magma to the
surface • Vent, the surface opening (connected to the
magma chamber via a pipe) • Crater
• Steep-walled depression at the summit
• Caldera (a summit depression greater than 1 km diameter)
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Mt. St. Helens following the 1980 eruption
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Other volcanic landforms
Volcanic pipes and necks • Pipes are short conduits that connect a magma
chamber to the surface • Volcanic necks (e.g., Ship Rock, New Mexico)
are resistant vents left standing after erosion has removed the volcanic cone
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Origin of magma
Magma originates when essentially solid rock, located in the crust and upper mantle, melts
Factors that influence the generation of magma from solid rock • Role of heat
• Earth’s natural temperature increases with depth (geothermal gradient) is not sufficient to melt rock at the lower crust and upper mantle
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Origin of magma
Factors that influence the generation of magma from solid rock • Role of heat
• Additional heat is generated by
• Friction in subduction zones
• Crustal rocks heated during subduction • Rising, hot mantle rocks
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Origin of magma
Factors that influence the generation of magma from solid rock • Role of pressure
• Increase in confining pressure causes an increase in melting temperature
• Drop in confining pressure can cause decompression melting
• Lowers the melting temperature
• Occurs when rock ascends
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Origin of magma
Factors that influence the generation of magma from solid rock • Role of volatiles
• Primarily water
• Cause rock to melt at a lower temperature
• Play an important role in subducting ocean plates
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Plate tectonics and igneous activity
Global distribution of igneous activity is not random • Most volcanoes are located on the margins of
the ocean basins (intermediate, andesitic composition) called subduction zone
• Second group is confined to the deep ocean basins (basaltic lavas) called Mid Ocean ridges
• Third group includes those found in the interiors of continents at Continental rift valley
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Locations of some of Earth’s major volcanoes
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Plate tectonics and igneous activity
Plate motions provide the mechanism by which mantle rocks melt to form magma • Convergent plate boundaries
• Deep-ocean trenches are generated • Descending plate partially melts • Magma slowly rises upward • Rising felsic to andesitic magma can form
• Volcanic island arcs in an ocean (Aleutian Islands)
• Continental volcanic arcs (Andes Mountains)
40
Plate tectonics and igneous activity
Plate motions provide the mechanism by which mantle rocks melt to form magma • Divergent plate boundaries
• The greatest volume of volcanic rock is produced along the oceanic ridge system
• Lithosphere pulls apart
• Less pressure on underlying rocks
• Partial melting occurs
• Large quantities of fluid basaltic magma are produced
41
Plate tectonics and igneous activity
Plate motions provide the mechanism by which mantle rocks melt to form magma • Intraplate igneous activity
• Activity within a rigid plate
• Plumes of hot basaltic magma rise
• Form localized volcanic regions called hot spots
• Examples include the Hawaiian Islands and the Columbia River Plateau in the northwestern United States
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Tectonic Settings and volcanic activity
• Divergent margin: Has volcanic activity
• Convergent margin: Has volcanic activity
• Transform fault: Is a margin but has no volcanic activity
• Hot spot: Not a margin but has volcanic activity
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Formation of a volcanic neck
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Intrusive igneous activity
Two types of igneous intrusive features • Sills, Laccoliths, and dikes
• Lens shaped masses
• Batholiths and Stocks• Largest intrusive bodies
• Often occur in groups Surface exposure 100+ square kilometers (smaller bodies are termed stocks)
• Frequently form the cores of mountains
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Intrusive igneous structures exposed by erosion
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A batholith exposed by erosion
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Intrusive igneous activity
Most magma is emplaced at depthAn underground igneous body is called a
plutonPlutons are classified according to
• Shape• Tabular (sheetlike)
• Massive
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Intrusive igneous activity
Plutons are classified according to • Orientation with respect to the host
(surrounding) rock • Discordant – cuts across existing structures
• Concordant – parallel to features such as sedimentary strata
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Intrusive igneous activity
Types of igneous intrusive features • Dike, a tabular, discordant pluton • Sill, a tabular, concordant pluton
• e.g., Palisades Sill, NY
• Resemble buried lava flows
• May exhibit columnar joints
• Laccolith • Similar to a sill
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A sill in the Salt River Canyon, Arizona
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End of Chapter 8
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1-Which Magma is more viscous?
a. Basaltic
b. Felsic/Andesitic
c. Ultramafic
d. None of these
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2-which magma traps more gases?
a. Mafic/Ultramafic
b. Felsic/Andesitic
c. None of these
d. I am not sure
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3-Which Magma is Hotter?
a. Mafic/Ultramafic
b. Felsic /Andesitic
c. None of these
d. I am not sure
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4-Which magma produces more violent eruptions?
a. Mafic/Ultramafic
b. Felsic/Andesitic
c. None of these
d. I am not sure
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5-Magma viscosity is a function of…
a. Temperature
b. Silica content
c. Gases content
d. All of these
e. b only
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6-Which volcano is over a hot spot?
a. Mt St Helens (Washington State)
b. Mt Rainier (Washington State)
c. Mauna Loa (Hawaii)
d. All of these
e. a and c only
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7-Which one is a Shield Volcano?
a. Mt St Helens (Washington State)
b. Mt Rainier (Washington State)
c. Mauna Loa (Hawaii)
d. All of these
e. a and c only
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8-Which one is a Composite cone?
a. Mt St Helens (Washington State)
b. Sunset Crater (Arizona)
c. Mauna Loa (Hawaii)
d. All of these
e. a and c only
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9-Which volcano type produces lava + pyroclastic flows
a. Mt St Helens (Washington State)
b. Kula (Hawaii)
c. Mauna Loa (Hawaii)
d. All of these
e. a and c only
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10-Volcanoes with steep cones have
a. Fluid lava
b. Viscous lava
c. No relation whatsoever
d. I am not sure
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11-Volcanoes at divergent boundary erupt mainly…lava
a. Felsic to Andesitic
b. Mafic
c. None of these
d. I am not sure
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12-Volcanoes at convergent margins produce mainly…lava
a. Felsic to Andesitic
b. Mafic
c. None of these
d. No relation whatsoever
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13-Which volcanoes are more explosive?
a. Shield volcanoes
b. Composite cones
c. Cinder cones
d. None of these
e. I am not sure
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14-Volcano explosiveness is influenced by …
a. Viscosity
b. Temperature
c. Amount of gases
d. All of the above
e. A and c only
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15-A Pahoehoe lava is
a. Gases-free with jagged surface lava
b. Wrinkled, ropy, and gaseous lava
c. Explosive ash and fragments flow
d. None of these
e. I am not sure
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16 - Quartzite is what type of metamorphic rock?
a. Regional metamorphism
b. Contact metamorphism
c. Not a metamorphic rock
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17 – In what type of metamorphism do pressure and temperature work
together?
a. Contact metamorphism
b. Regional metamorphism
c. All of the above
d. None of the above
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18 - What is the parent rock of limestone?
a. Quartzite
b. Granite
c. Marble
d. Basalt
e. This does not make sense
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19 – Which one of these is a foliated metamorphic rock?
a. Marble
b. Granite
c. Mica-schist
d. Basalt
e. Shale
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20 - Which one is the metamorphic rock?
Do not take
a. SANDSTONE for
b. GRANITE (granted)!
Have a
c. GNEISS (nice) day!
72
THE END
THAT’S ALL FOLKS!
THANK YOU!!!