volcanoes how and where do they form? analyze how magma forms as a result of plate motion and...
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VolcanoesVolcanoes• How and Where do they Form?
• Analyze how Magma forms as a result of plate motion and interaction
• Magma and Erupted Materials• What different materials erupt from a volcano?
• Volcanic Landforms• What sort of landforms result from volcanic activity
• How and Where do they Form?• Analyze how Magma forms as a result of plate motion and interaction
• Magma and Erupted Materials• What different materials erupt from a volcano?
• Volcanic Landforms• What sort of landforms result from volcanic activity
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Violent VolcanoesViolent Volcanoes
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Top 5 Volcano Webcams
Top 5 Volcano Webcams
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10 Most Active Volcanoes
10 Most Active Volcanoes
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Mt. Etna, ItalyMt. Etna, Italy
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Origin of magma Origin of magma Magma originates when essentially solid rock, located in the crust and upper mantle- melts
3 Factors that influence the generation of magma from solid rock:• 1) Heat• 2) Pressure• 3) Volatiles (Fluids/ Gasses)
Magma originates when essentially solid rock, located in the crust and upper mantle- melts
3 Factors that influence the generation of magma from solid rock:• 1) Heat• 2) Pressure• 3) Volatiles (Fluids/ Gasses)
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Role of HeatRole of Heat
• Earth’s natural temperature increases with depth (geothermal gradient) is not sufficient to melt rock at the lower crust and upper mantle
• Does not melt rock completely
• Earth’s natural temperature increases with depth (geothermal gradient) is not sufficient to melt rock at the lower crust and upper mantle
• Does not melt rock completely
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Role of Pressure(In magma formation)
Role of Pressure(In magma formation)
Pressure:
•Increase in confining pressure causes an increase in melting temperature
•So…. More pressure = ???????•Drop in confining pressure can cause decompression melting •So drop in pressure = ??????? •Occurs when rock ascends
Pressure:•Increase in confining pressure causes an increase in melting temperature
•So…. More pressure = ???????•Drop in confining pressure can cause decompression melting •So drop in pressure = ??????? •Occurs when rock ascends
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Role of Volatiles Role of Volatiles Volatiles:
•Primarily water•Cause rock to melt at a lower temperature
•Play an important role in subducting ocean plates • Seafloor being pulled under continent is easier to melt
Volatiles:•Primarily water•Cause rock to melt at a lower temperature
•Play an important role in subducting ocean plates • Seafloor being pulled under continent is easier to melt
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Distribution of Volcanos
Distribution of Volcanos
• Ring of Fire- Most volcanoes are located on the margins of the ocean basins
• Mid Ocean Ridges- Second group is confined to the deep ocean basins (basaltic lavas)
• Hot Spots- Third group includes those found in the interiors of continents(Hawaii)
• Ring of Fire- Most volcanoes are located on the margins of the ocean basins
• Mid Ocean Ridges- Second group is confined to the deep ocean basins (basaltic lavas)
• Hot Spots- Third group includes those found in the interiors of continents(Hawaii)
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Locations of some of Earth’s major volcanoes Locations of some of Earth’s major volcanoes
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Plate Motions and Volcanoes
Plate Motions and VolcanoesPlate 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 magma can form
•Volcanic island arcs in an ocean (Aleutian Islands)
•Continental volcanic arcs (Andes Mountains)
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 magma can form
•Volcanic island arcs in an ocean (Aleutian Islands)
•Continental volcanic arcs (Andes Mountains)
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Subduction Zone MeltingSubduction Zone Melting
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Magma Formationm @ Divergent Boundaries Magma Formationm @
Divergent Boundaries Decompression Melting:
• Plates are spreading apart, releasing pressure from rock, and allowing magma to rise to surface.
• The greatest volume of volcanic rock is produced along the oceanic ridge system
Decompression Melting:• Plates are spreading apart, releasing pressure from rock, and allowing magma to rise to surface.
• The greatest volume of volcanic rock is produced along the oceanic ridge system
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Hot Spots Hot Spots
• Hotspots•Activity within a rigid plate •Plumes of hot mantle material rise•Form localized volcanic regions called hot spots
•Examples: Hawaiian Islands, Yellowstone
• Hotspots•Activity within a rigid plate •Plumes of hot mantle material rise•Form localized volcanic regions called hot spots
•Examples: Hawaiian Islands, Yellowstone
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Hawaiin Hot SpotHawaiin Hot Spot
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Why do volcanoes erupt?
Why do volcanoes erupt?
Factors that determine the violence of an eruption • Composition of the magma • Temperature of the magma• Dissolved gases in the magma
Viscosity of magma • Viscosity is a measure of a material's resistance to flow
Factors that determine the violence of an eruption • Composition of the magma • Temperature of the magma• Dissolved gases in the magma
Viscosity of magma • Viscosity is a measure of a material's resistance to flow
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Volcano LavaVolcano Lava
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Volcanic eruptions 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
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
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Lava ViscosityLava Viscosity
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Volcanic eruptions Volcanic eruptions Viscosity of magma
• Factors affecting viscosity•Dissolved gases (volatiles)
•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
Viscosity of magma • Factors affecting viscosity
•Dissolved gases (volatiles) •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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Materials associated with volcanic eruptions
Materials associated with volcanic eruptions Lava flows
• Basaltic lavas are more fluid• Types of lava
•Pahoehoe lava (resembles braids in ropes)
•Aa lava (rough, jagged blocks)
Gases • One to 5 percent of magma by weight• Mainly water vapor and carbon dioxide
Lava flows • Basaltic lavas are more fluid• Types of lava
•Pahoehoe lava (resembles braids in ropes)
•Aa lava (rough, jagged blocks)
Gases • One to 5 percent of magma by weight• Mainly water vapor and carbon dioxide
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A Pahoehoe lava flow
A Pahoehoe lava flow
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A typical aa flowA typical aa flow
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A typical Aa flowA typical Aa flow
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Materials associated with volcanic eruptions
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
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 A volcanic bomb
Bomb is approximately 10 cm long
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Pyroclastic Flows: The Real Threat
Pyroclastic Flows: The Real Threat
Bomb is approximately 10 cm long
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Lahars: “Cold Lava”Lahars: “Cold Lava”
Bomb is approximately 10 cm long
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Volcanoes – 3 MAIN TYPES
Volcanoes – 3 MAIN TYPES
Types of volcanoes • Shield volcano
•Broad, slightly domed •Primarily made of basaltic (fluid) lava
•Generally large size •e.g., Mauna Loa in Hawaii
Types of volcanoes • Shield volcano
•Broad, slightly domed •Primarily made of basaltic (fluid) lava
•Generally large size •e.g., Mauna Loa in Hawaii
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A shield volcano A shield volcano
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Volcanoes Volcanoes Types of volcanoes
• Cinder cone •Built from ejected lava fragments •Steep slope angle •Rather small size •Frequently occur in groups
Types of volcanoes • 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
Sunset Crater – a cinder cone near Flagstaff,
Arizona
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Volcanoes Volcanoes Types of volcanoes
• Composite cone (or stratovolcano) •Most are adjacent to the Pacific Ocean (e.g., Mt. Rainier)
•Large size •Interbedded lavas and pyroclastics
•Most violent type of activity
Types of volcanoes • Composite cone (or stratovolcano) •Most are adjacent to the Pacific Ocean (e.g., Mt. Rainier)
•Large size •Interbedded lavas and pyroclastics
•Most violent type of activity
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A composite volcano
(stratovolcano)
A composite volcano
(stratovolcano)
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A size comparison of the three
types of volcanoes
A size comparison of the three
types of volcanoes
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Volcanoes 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)
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 – a typical composite volcano Mt. St. Helens – a typical composite volcano
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Mt. St. Helens following the
1980 eruption
Mt. St. Helens following the
1980 eruption
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Volcanoes Volcanoes Types of volcanoes
• Composite cone (or stratovolcano)•Often produce nuée ardente
•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 - volcanic mudflow
Types of volcanoes • Composite cone (or stratovolcano)•Often produce nuée ardente
•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 - volcanic mudflow
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A nueé ardente on Mt. St. Helens
A nueé ardente on Mt. St. Helens
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A lahar along the Toutle River near Mt.
St. Helens
A lahar along the Toutle River near Mt.
St. Helens
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Mt. St. Helens Eruptions. OMGMt. St. Helens Eruptions. OMG
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Yellowstone SupervolcanoYellowstone Supervolcano
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Other volcanic landforms
Other volcanic landforms Calderas
• Steep walled depression at the summit • Formed by collapse • Nearly circular • Size exceeds one kilometer in diameter
Fissure eruptions and lava plateaus • Fluid basaltic lava extruded from crustal fractures called fissures
• e.g., Columbia Plateau
Calderas • Steep walled depression at the summit • Formed by collapse • Nearly circular • Size exceeds one kilometer in diameter
Fissure eruptions and lava plateaus • Fluid basaltic lava extruded from crustal fractures called fissures
• e.g., Columbia Plateau
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Crater Lake, Oregon is a good example of a calderaCrater Lake, Oregon is a good example of a caldera
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Crater Lake in OregonCrater Lake in Oregon
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The Columbia River basalts
The Columbia River basalts
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Other volcanic landforms
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
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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Formation of a volcanic neckFormation of a volcanic neck
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Intrusive igneous activity
Intrusive igneous activity Most magma is emplaced at
depthAn underground igneous body is called a pluton
Plutons are classified according to • Shape
•Tabular (sheetlike)•Massive
Most magma is emplaced at depth
An underground igneous body is called a pluton
Plutons are classified according to • Shape
•Tabular (sheetlike)•Massive
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Intrusive igneous activity
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
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
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
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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Intrusive igneous structures
exposed by erosion
Intrusive igneous structures
exposed by erosion
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A sill in the Salt River
Canyon, Arizona
A sill in the Salt River
Canyon, Arizona
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Intrusive igneous activity
Intrusive igneous activity Types of igneous intrusive
features • Laccolith
•Lens shaped mass •Arches overlying strata upward
• Batholith•Largest intrusive body •Often occur in groups Surface exposure 100+ square kilometers (smaller bodies are termed stocks)
•Frequently form the cores of mountains
Types of igneous intrusive features • Laccolith
•Lens shaped mass •Arches overlying strata upward
• Batholith•Largest intrusive body •Often occur in groups Surface exposure 100+ square kilometers (smaller bodies are termed stocks)
•Frequently form the cores of mountains
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A batholith exposed by erosion
A batholith exposed by erosion
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End of Chapter 8End of Chapter 8