Volcanoes and Other
Igneous Activity
Chapter 5
NOT all Volcanic Eruptions are the Same
NOT all Volcanic Eruptions
are the Same
• Three factors determine the
“violence” or explosiveness of a
volcanic eruption:
...
Viscosity
• These three factors control the viscosity
of a given magma.
• Which in turn controls the nature of an
eruption...
Factors Affecting Viscosity
1. Temperature – Hotter magmas are less
viscous.
2. Composition – Silica (SiO2) content
–

Hig...
Factors Affecting Viscosity
3. Dissolved Gases
• The violence of an eruption is related to
how easily gases escape from ma...
Factors Affecting Viscosity
3. Dissolved Gases
–

–

Very fluid basaltic
magmas allow the
gases to migrate
upwards and esc...
Factors Affecting Viscosity

3. Dissolved Gases

– Highly siliceous magmas
undergo magmatic
differentiation leaving the
up...
The Nature of Volcanic
Eruptions

• In Summary:

– Fluid basaltic lavas generally produce quiet
eruptions.
• Basaltic flow...
Materials Extruded
from Volcanoes
1. Lava Flows
2. Volatiles
3. Pyroclastic Material
Lava Flows
• Types of Basaltic Flows:
• Pahoehoe lava
resembles a
twisted or ropey
texture.

Pahoehoe Lava Flow in
Hawaii ...
Pahoehoe
Lava Flow
in Hawaii
Volcanoes
National
Park
Pahoehoe lava flows can contain lava
tubes, cave-like tunnels that were
horizontal conduits for lava.

Lava Tube in Hawaii...
Lava Flows
• Types of Basaltic Flows:
• Aa lava has a rough,
jagged blocky texture.
– Cool and thick with gases
escaping f...
Lava Flows
• Types of Basaltic Flows:
– Pillow lavas – lava that formed
underwater.
• Occur along oceanic ridges.
• Lava c...
Dissolved Gases (Volatiles)
• Magmas contain varying amounts of
dissolved gases held in the molten rock
under confining pr...
Volcanoes and Climate
• Explosive eruptions emit huge quantities
of gases and fine-grained debris into the
atmosphere whic...
Pyroclastic Materials –
“Fire Fragments”
• Ash and Dust – Fine, glassy fragments
compose tuffs and welded tuffs.
• Pumice ...
Pyroclastic Materials –
“Fire Fragments”
• Lapilli – pyroclastic fragments 2-64 mm in size.
• Particles larger than lapill...
Anatomy of Volcanoes
Anatomy of Volcanoes
• General Features
– Magma chamber is connected to the surface by
a conduit or pipe that terminates a...
Anatomy of Volcanoes
• General Features
– Opening at the summit of a volcano:
• Crater – steep-walled, circular depression...
Anatomy of Volcanoes
• General Features
– Mature volcanoes develop fissures along the
flanks and base producing parasitic ...
Types of Volcanoes and
Their Characteristics
Plate Tectonics and Igneous Activity
• Global distribution of igneous activity is not random.
• Most volcanoes are located...
Plate Tectonics and
Igneous Activity
• Basaltic igneous activity is common in
both oceanic and continental settings.
• Gra...
Not all Volcanoes are the Same
• Factors determining the size
and shape of volcanoes:
1. Volume of lava erupted
2. Viscosi...
Shield Volcanoes
•
•
•
•

Broad, slightly domed-shaped.
Composed primarily of basaltic lava.
Generally cover large areas.
...
Shield Volcanoes
• Most grow up from the seafloor to form islands or sea
mounts.
• From ocean floor to summit, Mauna Loa i...
Cinder
Cones Haleakala
Maui

• During late stages, shield
volcanoes produce clusters of
cinder cones in summit area.
Shield Volcanoes
and Plate Tectonics
• Shield volcanoes are a product
of intra-plate volcanism in
oceanic crust.
– Activit...
Volcanism on a
Tectonic Plate
Moving over a
Hot Spot
Produces Shield
Volcanoes
(basaltic) and
Volcanic Island
and Seamount...
Global distribution of flood basalt provinces (black) and associated hotspots (red dots). Red dashed lines are hot spot tr...
Cinder Cone Volcanoes
Sunset Crater – a Cinder Cone
near Flagstaff, Arizona

• Built from ejected lava
fragments – pyrocla...
Parasitic Cinder Cones, Mauna Kea, Hawaii
Late-Stage Cinder
Cones, Mauna Kea
Summit, Hawaii
Cinder Cone Volcanoes and
Plate Tectonics
• Cinder cone volcanoes are the product of latestage volcanism in various tecton...
Composite or Stratovolcanoes
• Large, classic-shaped volcano (1000’s of feet high &
several miles wide at base).
• Compose...
Composite or Stratovolcanoes
• Explosive eruptions that eject huge quantities of
pyroclastic material.
• Most are located ...
Mt. St.
Helens
1980
Eruption
Mt. St. Helens Following
the 1980 Eruption
Pyroclastic Flows
• Stratovolcanoes erupt
violently…
– Often produce a nueé
ardente (glowing
avalanche):
• Fiery pyroclast...
Pyroclastic Flows
• Nueé ardente (glowing
avalanche):
– Forms from the collapse
(overcome by gravity) of tall
eruption col...
Lahars
• Stratovolcanoes may produce lahars, or
volcanic mudflows:
– Mixture of volcanic debris and water.
– Moves rapidly...
Lahar from Mt. St. Helens -- On March 18, 1980, an explosive eruption on Mt. St.
Helens generated a 14-kilometer-high erup...
Lahars at
Mt. Rainer

The snow-covered peaks of the Cascade volcanoes in
Washington, Oregon, and northern California pose ...
Eruptive Frequency of
Cascade Range
Stratovolcanoes
Stratovolcanoes and
Plate Tectonics
• Stratovolcanoes are the product of subduction
zone igneous activity along oceanic-oc...
Igneous
Activity
Along
Subduction
Zones
Stratovolcanoes and
Plate Tectonics
• Associated with the Pacific Ocean
Basin margin is known as the “Ring
of Fire”.
• Mos...
Size Comparison of the
Three Types of Volcanoes
•
•
•
•
•
•

Calderas

Large collapse depressions with approximate circular diameter.
Steep-walled depressions at the summ...
Calderas

Form by one of the following processes:
1.

Collapse of the summit of a large composite volcano
following the er...
Calderas
2. Collapse of the top of a shield volcano caused
by subterranean drainage from the central
magma chamber to rift...
Calderas
3.

Image courtesy of the United States Geological Survey.

Collapse of large
area, independent
of any preexistin...
Calderas and Plate Tectonics
• Calderas are a product of intra-plate
volcanism in continental crust.
– Activity within a t...
Large Calderas in the U.S.
Yellowstone

Long Valley
Valles

• Long Valley, California
• Yellowstone, Wyoming
• Valles, New...
Long Valley Caldera
• Located in eastern
California.
• Caldera is elliptical in
shape.
• Approximately 10 X 20
miles acros...
Long Valley
Caldera,
Looking from
SW to NE

Inside the Long
Valley Caldera
Ash Deposits from Long
Valley Eruption, 730,000
years ago.

Potential Thickness of
Tephra from Eruption of less
than 1 km3...
Fissure Eruptions
and Lava Plateaus
• Huge volumes of volcanic
material are extruded from
fractures in the crust called
fi...
Flood Basalts and Plate Tectonics
• Flood basalts are a product of
intra-plate volcanism in
continental crust.
– Activity ...
Global distribution of flood basalt provinces (black) and associated hotspots (red dots). Red dashed lines are hot spot tr...
• Spreading Centers
– The greatest volume
of volcanic rock is
produced along the
oceanic ridge system.
– Continental or oc...
Lava Domes
Lava Dome on Mt. St. Helens

• Bulbous mass
of congealed
lava.
• Form in the
summit crater.

• Most are associa...
Climbing Mount St. Helens
Climbing Mount St. Helens
Climbing Mount St. Helens
Volcanic Pipes
•
•
•
•

Most volcanic pipes are conduits that connect a magma chamber
to the surface.
Pipes may extend in ...
Volcanic Necks
• Erosion of the outer flanks of the
volcanic cone leave behind the moreresistant neck.

Shiprock, NM
– A V...
Columnar Joints
• Form as igneous rocks cool at or near the surface.
• Shrinkage fractures formed by tensional forces that...
Plutonic Igneous Activity
Plutonic Igneous Bodies
• Most magma is emplaced at depth in the
Earth.
• An underground igneous body, once
cooled and sol...
Classification of Plutons
•

Classification of Plutons:
1. Shape
•
•

Tabular (sheetlike)
Massive

3. Size
2. Orientation ...
Types of Intrusive Igneous Features
• Dike – a tabular, discordant pluton where
magma has injected into fractures.
– Pathw...
Vertical
Dike Near
Granby,
Colorado
Types of Intrusive Igneous Features
• Sill – a tabular, concordant pluton where magma
has injected along sedimentary beddi...
A Sill in the Salt River Canyon,
Arizona
Types of Intrusive Igneous Features
• Laccolith
– Similar to a sill (near-surface environment).
– Lens or mushroom-shaped ...
Types of Intrusive Igneous Features
• Two Types of Plutons (based on size)
– Batholiths
• Largest intrusive body.
• Surfac...
Types of Intrusive Igneous Features
• Two Types of Plutons (based on size)
– Stocks
• Smaller
• Surface exposure less than...
Batholiths of Western
North America

The Sierra Nevada Batholith exposed in
Yosemite Natl. Park
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  • We discussed the various types of igneous rocks last week and in general how they formed.
    Now we are going to look more deeply into their environment of formation.
    How does their chemistry affect the type of volcanic eruptions produced, rocks formed, and volcanic structures.
  • Show The Nature of Volcanic Eruptions Tutorial from Chapter 5 of the Geode Earth CDROM.
  • We discussed the various types of igneous rocks last week and in general how they formed.
    Now we are going to look more deeply into their environment of formation.
    How does their chemistry affect the type of volcanic eruptions produced, rocks formed, and volcanic structures.
  • The release of gases is like what happens when you pop the top off a soda bottle.
    There is a sudden release of pressure, but because the soda is very fluid, the gases escape easily and there is not explosion.
  • We discussed the various types of igneous rocks last week and in general how they formed.
    Now we are going to look more deeply into their environment of formation.
    How does their chemistry affect the type of volcanic eruptions produced, rocks formed, and volcanic structures.
  • Now I am going to discuss the various types of volcanoes and their eruptive styles.
    This will effect the types of rocks they produce and volcanic structures manifested.
  • Now I am going to discuss the various types of volcanoes and their eruptive styles.
    This will effect the types of rocks they produce and volcanic structures manifested.
  • Now I am going to discuss the various types of volcanoes and their eruptive styles.
    This will effect the types of rocks they produce and volcanic structures manifested.
  • We discussed the various types of igneous rocks last week and in general how they formed.
    Now we are going to look more deeply into their environment of formation.
    How does their chemistry affect the type of volcanic eruptions produced, rocks formed, and volcanic structures.
  • We discussed the various types of igneous rocks last week and in general how they formed.
    Now we are going to look more deeply into their environment of formation.
    How does their chemistry affect the type of volcanic eruptions produced, rocks formed, and volcanic structures.
  • محاضره جيو نضري الخامسه

    1. 1. Volcanoes and Other Igneous Activity Chapter 5
    2. 2. NOT all Volcanic Eruptions are the Same
    3. 3. NOT all Volcanic Eruptions are the Same • Three factors determine the “violence” or explosiveness of a volcanic eruption: 1. Composition of the magma 2. Temperature of the magma 3. Dissolved gases in the magma
    4. 4. Viscosity • These three factors control the viscosity of a given magma. • Which in turn controls the nature of an eruption. • Viscosity is a measure of a material’s resistance to flow. – Higher viscosity materials flow with great difficulty.
    5. 5. Factors Affecting Viscosity 1. Temperature – Hotter magmas are less viscous. 2. Composition – Silica (SiO2) content – Higher silica content = more SiO4 chains/structures = higher viscosity • – felsic lava – rhyolite Lower silica content = fewer SiO4 chains/structures = lower viscosity or more fluid like behavior • mafic lava – basalt
    6. 6. Factors Affecting Viscosity 3. Dissolved Gases • The violence of an eruption is related to how easily gases escape from magma. – – Gas content affects magma mobility. Volatiles migrate upward and accumulate near the top of the magma chamber. enriching the upper portion of the magma chamber with dissolved gases. – Gases expand within a magma as it nears the Earth’s surface due to decreasing pressure. – Escaping gases provide the force to propel molten rock from the volcanic vent.
    7. 7. Factors Affecting Viscosity 3. Dissolved Gases – – Very fluid basaltic magmas allow the gases to migrate upwards and escape the vent with relative ease. Produces lava fountains extending hundreds of meters in height.
    8. 8. Factors Affecting Viscosity 3. Dissolved Gases – Highly siliceous magmas undergo magmatic differentiation leaving the upper portion of the magma chamber enriched in silica and dissolved gases. – The volcano summit begins to inflate and bulge months to years prior to eruption. – As the magma migrates up the vent, the gases collect into tiny bubbles. – The mixture is transformed into a gas jet containing tiny magma fragments that are explosively ejected. – Produces plumes of a hot ash-laden gases called eruption columns that extends thousands of meters into the atmosphere.
    9. 9. The Nature of Volcanic Eruptions • In Summary: – Fluid basaltic lavas generally produce quiet eruptions. • Basaltic flow rates between 30-1000 ft/hour. • Traveling up to 90 miles (150 km) from the vent. – Highly viscous lavas (rhyolite or andesite) produce more explosive eruptions. • Rhyolitic lava are much slower. • Seldom travel more than a few kilometers from their vents.
    10. 10. Materials Extruded from Volcanoes 1. Lava Flows 2. Volatiles 3. Pyroclastic Material
    11. 11. Lava Flows • Types of Basaltic Flows: • Pahoehoe lava resembles a twisted or ropey texture. Pahoehoe Lava Flow in Hawaii Volcanoes National Park
    12. 12. Pahoehoe Lava Flow in Hawaii Volcanoes National Park
    13. 13. Pahoehoe lava flows can contain lava tubes, cave-like tunnels that were horizontal conduits for lava. Lava Tube in Hawaii Volcanoes National Park
    14. 14. Lava Flows • Types of Basaltic Flows: • Aa lava has a rough, jagged blocky texture. – Cool and thick with gases escaping forming numerous voids and sharp spines. – Pahoehoe flows are hotter, richer in gases, and travel faster than aa flows. – Basaltic lavas can begin as pahoehoe flows and become aa flows.
    15. 15. Lava Flows • Types of Basaltic Flows: – Pillow lavas – lava that formed underwater. • Occur along oceanic ridges. • Lava cools quickly forming an outer skin. • Lava advances by breaking through the outer rind. • Forms elongated structures resembling pillows. Pillow Basalts, Olympic National Park, Washington
    16. 16. Dissolved Gases (Volatiles) • Magmas contain varying amounts of dissolved gases held in the molten rock under confining pressure. – Consists mainly of: • water vapor and carbon dioxide – Lesser amounts of: • nitrogen, sulfur dioxide, chlorine, hydrogen, argon – Contribute significantly the planet’s atmosphere (natural air pollution). – Rise into the atmosphere and may reside there for years potentially impacting climate.
    17. 17. Volcanoes and Climate • Explosive eruptions emit huge quantities of gases and fine-grained debris into the atmosphere which • Filter out and reflect a portion of the incoming solar radiation. • This can cause cooling on a global scale. • Examples of volcanism affecting climate: • Mount Tambora, Indonesia – 1815 • Krakatau, Indonesia – 1883 • Mount Pinatubo, Philippines – 1991
    18. 18. Pyroclastic Materials – “Fire Fragments” • Ash and Dust – Fine, glassy fragments compose tuffs and welded tuffs. • Pumice – Porous rock from “frothy” lava or rhyolitic composition. • Scoria – Vesicular rock of typically basaltic composition. • Cinders – Glassy vesicular fragments 4 32 mm.
    19. 19. Pyroclastic Materials – “Fire Fragments” • Lapilli – pyroclastic fragments 2-64 mm in size. • Particles larger than lapilli: • Blocks – pyroclasts more than 64 mm in diameter ejected in the solid state (rock torn from the vent wall). • Bombs – ejected blob of hot lava streamlined during flight (more than 64 mm in diameter). Bomb is approximately 10 cm long
    20. 20. Anatomy of Volcanoes
    21. 21. Anatomy of Volcanoes • General Features – Magma chamber is connected to the surface by a conduit or pipe that terminates at a surface vent.
    22. 22. Anatomy of Volcanoes • General Features – Opening at the summit of a volcano: • Crater – steep-walled, circular depression at the summit, generally less than 1 km diameter. – Produced by explosive excavation of rock during eruptions. • Caldera – a summit depression typically greater than 1 km diameter. – Produced by collapse following a massive eruption.
    23. 23. Anatomy of Volcanoes • General Features – Mature volcanoes develop fissures along the flanks and base producing parasitic cones and fumaroles (emit only gases and smoke).
    24. 24. Types of Volcanoes and Their Characteristics
    25. 25. Plate Tectonics and Igneous Activity • Global distribution of igneous activity is not random. • Most volcanoes are located within or near ocean basins or along continental margins. • Each type of plate tectonic boundary produces a specific type of igneous activity. Insert Plate Tectonic Boundary Features Animation #66
    26. 26. Plate Tectonics and Igneous Activity • Basaltic igneous activity is common in both oceanic and continental settings. • Granitic igneous activity is rarely found in the oceans.
    27. 27. Not all Volcanoes are the Same • Factors determining the size and shape of volcanoes: 1. Volume of lava erupted 2. Viscosity of lava: • Composition of the magma • Temperature of the magma • Dissolved gases in the magma
    28. 28. Shield Volcanoes • • • • Broad, slightly domed-shaped. Composed primarily of basaltic lava. Generally cover large areas. Produced by mild eruptions of large volumes of lava. Mauna Loa
    29. 29. Shield Volcanoes • Most grow up from the seafloor to form islands or sea mounts. • From ocean floor to summit, Mauna Loa is over 6 miles high (higher than Mt. Everest [~32,000 feet]). • Large steep-walled calderas occupy the summit. • Mature volcanoes erupt lava from the summit and rift zones that develop along the slopes (flank).
    30. 30. Cinder Cones Haleakala Maui • During late stages, shield volcanoes produce clusters of cinder cones in summit area.
    31. 31. Shield Volcanoes and Plate Tectonics • Shield volcanoes are a product of intra-plate volcanism in oceanic crust. – Activity within a tectonic plate. – Associated with plumes of heat upwelling in the mantle – mantle plume. – Form localized volcanic regions in the overriding plate called a hot spot. – Produces basaltic magmas creating: • Shield volcanoes • Volcanic chains and seamounts
    32. 32. Volcanism on a Tectonic Plate Moving over a Hot Spot Produces Shield Volcanoes (basaltic) and Volcanic Island and Seamount Chains
    33. 33. Global distribution of flood basalt provinces (black) and associated hotspots (red dots). Red dashed lines are hot spot tracks, which appear as lines of volcanic structures on the ocean floor. The Keweenawan and Siberian Traps formed in failed continental rifts where the crust had been greatly thinned. Whether there is a connection between the Columbia River basalts and the Yellowstone hot spot is still a matter of ongoing research.
    34. 34. Cinder Cone Volcanoes Sunset Crater – a Cinder Cone near Flagstaff, Arizona • Built from ejected lava fragments – pyroclastic cinders or clinkers (glassy vesicular fragments). • Fragments range in size from ash to bombs, primarily lapilli. • Product of gas-rich basaltic magma (scoria). • Steep slope angle. • Rather small size. • Frequently occur in groups.
    35. 35. Parasitic Cinder Cones, Mauna Kea, Hawaii
    36. 36. Late-Stage Cinder Cones, Mauna Kea Summit, Hawaii
    37. 37. Cinder Cone Volcanoes and Plate Tectonics • Cinder cone volcanoes are the product of latestage volcanism in various tectonic environments. – Basaltic magmas: • Associated with hot spot volcanism in oceanic crust: – Shield Volcano Flanks and Calderas • Associated with hot spot volcanism in continental crust: – Flanks of Calderas • Associated with subduction zones between oceanic-oceanic crust and oceanic-continental crust: – Stratovolcano Flanks and Calderas
    38. 38. Composite or Stratovolcanoes • Large, classic-shaped volcano (1000’s of feet high & several miles wide at base). • Composed of interbedded lava flows and layers of pyroclastic debris. • Primarily andesitic in composition with lesser basaltic and rhyolitic lavas.
    39. 39. Composite or Stratovolcanoes • Explosive eruptions that eject huge quantities of pyroclastic material. • Most are located adjacent to the Pacific Ocean (e.g., Fujiyama, Mt. St. Helens). Mt. St. Helens
    40. 40. Mt. St. Helens 1980 Eruption
    41. 41. Mt. St. Helens Following the 1980 Eruption
    42. 42. Pyroclastic Flows • Stratovolcanoes erupt violently… – Often produce a nueé ardente (glowing avalanche): • Fiery pyroclastic flow made of hot gases infused with ash, pumice, and other debris. • Felsic and intermediate magmas. • Material ejected at high velocities. Nueé Ardente on Mt. St. Helens
    43. 43. Pyroclastic Flows • Nueé ardente (glowing avalanche): – Forms from the collapse (overcome by gravity) of tall eruption columns. – Moves down the slopes of a volcano at speeds up to 200 km (125 miles) per hour. – Traveling up to more than 60 miles from the vent. – Ground-hugging portion is rich in particular matter suspended by jets of buoyant gases (nearly frictionless).
    44. 44. Lahars • Stratovolcanoes may produce lahars, or volcanic mudflows: – Mixture of volcanic debris and water. – Moves rapidly down slope (30 kph or more) following stream valleys. – Triggered when large volumes of ice and snow melt during an eruption. – Also generated when heavy rainfall saturates weathered volcanic deposits. – Highly destructive.
    45. 45. Lahar from Mt. St. Helens -- On March 18, 1980, an explosive eruption on Mt. St. Helens generated a 14-kilometer-high eruption plume. Melted snow from the eruption produced the dark-colored lahar seen in this photo. Part of the lahar flowed into Spirit Lake (lower left). However, most of the lahar flowed into the North Fork of the Toutle River valley (right), eventually reaching the Cowlitz River, 80 kilometers downstream. Courtesy of Thomas J. Casadevall, USGS.
    46. 46. Lahars at Mt. Rainer The snow-covered peaks of the Cascade volcanoes in Washington, Oregon, and northern California pose a clear threat to surrounding towns and villages. Past events suggest that a catastrophic lahar could lie in the future of Mt. Rainier, the largest of the Cascade volcanoes. The 4,000 m high summit of Mt. Rainier contains the largest system of alpine glaciers in the Cascade Range. The periodic melting of glacier ice from Mt. Rainier has generated at least 50 major lahars over the past 10,000 years. The largest of these mudflow deposits, one of the world's largest, is the ~5700-year-old Osceola lahar, shown in the adjacent map (green) (courtesy of USGS). The Osceola lahar traveled down the White River, over 112 km from its source. It then spread out at its mouth to cover an area of over 300 square kilometers along the shoreline of Puget Sound. The recent geologic history of Mt. Rainier demonstrates that a major mudflow descends down the White River once every 600 years. The younger 500-yearold Electron lahar (see map – yellow) was also generated from Mt. Rainier. It flowed 56 kilometers down the Puyallup River to within 15 kilometers of Tacoma, Washington. More than 300,000 people now live in the area covered by these extensive lahars! Unlike floods, such catastrophic mudflows can occur with little or no warning. Some volcanologists have predicted that Mt. Rainier will be the site of the next Cascade eruption. Therefore, the volcano is monitored closely, with the hope that we can warn the local population before the next lahar strikes.
    47. 47. Eruptive Frequency of Cascade Range Stratovolcanoes
    48. 48. Stratovolcanoes and Plate Tectonics • Stratovolcanoes are the product of subduction zone igneous activity along oceanic-oceanic and oceanic-continental convergent plate boundaries. – Occur in conjunction with deep oceanic trenches. – Descending plate causes partial melting (wet melting) of the mantle. • A volcanic island arc if in the ocean – evolves from early-stage mantle-derived basalts to mature andesites and rhyolites. • A continental volcanic arc if along a continental margin – primarily andesites and rhyolites lesser basalts.
    49. 49. Igneous Activity Along Subduction Zones
    50. 50. Stratovolcanoes and Plate Tectonics • Associated with the Pacific Ocean Basin margin is known as the “Ring of Fire”. • Most of the world’s explosive volcanoes are found here.
    51. 51. Size Comparison of the Three Types of Volcanoes
    52. 52. • • • • • • Calderas Large collapse depressions with approximate circular diameter. Steep-walled depressions at the summit. Size generally exceeds 1 km in diameter. Formed by the eruption of large volumes of magma from a shallow underground magma reservoir. Results in loss of structural support for the overlying rock. Leading to collapse of the ground and formation of a large depression.
    53. 53. Calderas Form by one of the following processes: 1. Collapse of the summit of a large composite volcano following the eruption of silica-rich pryroclastic eruption (Crater Lake). Crater Lake Caldera, Oregon (6 miles diameter)
    54. 54. Calderas 2. Collapse of the top of a shield volcano caused by subterranean drainage from the central magma chamber to rift zone – flank eruptions (Mauna Loa).
    55. 55. Calderas 3. Image courtesy of the United States Geological Survey. Collapse of large area, independent of any preexisting volcanic structures, caused by discharge of colossal volumes of silica-rich pyroclastics along ring fractures (Yellowstone). Yellowstone Caldera
    56. 56. Calderas and Plate Tectonics • Calderas are a product of intra-plate volcanism in continental crust. – Activity within a tectonic plate. – Associated with plumes of heat upwelling in the mantle – mantle plume. – Form localized volcanic regions in the overriding plate called a hot spot. – Produces granitic magmas creating: • Calderas
    57. 57. Large Calderas in the U.S. Yellowstone Long Valley Valles • Long Valley, California • Yellowstone, Wyoming • Valles, New Mexico
    58. 58. Long Valley Caldera • Located in eastern California. • Caldera is elliptical in shape. • Approximately 10 X 20 miles across. • Last volcanic activity ~550-600 years ago at Inyo Craters. • Huge eruption 730,000 years ago ejected about 600 km3 of material.
    59. 59. Long Valley Caldera, Looking from SW to NE Inside the Long Valley Caldera
    60. 60. Ash Deposits from Long Valley Eruption, 730,000 years ago. Potential Thickness of Tephra from Eruption of less than 1 km3 of Magma.
    61. 61. Fissure Eruptions and Lava Plateaus • Huge volumes of volcanic material are extruded from fractures in the crust called fissures. • Fluid basaltic lava extrude via fissure eruptions (flood basalts) building up a thick lava plateau. • e.g., Columbia River Plateau (nearly 1 mile thick of flood basalts).
    62. 62. Flood Basalts and Plate Tectonics • Flood basalts are a product of intra-plate volcanism in continental crust. – Activity within a tectonic plate. – Associated with plumes of heat upwelling in the mantle – mantle plume. – Form localized volcanic regions in the overriding plate called a hot spot. – Produces basaltic magmas creating: • Flood basalts in continental environments (Columbia Plateau).
    63. 63. Global distribution of flood basalt provinces (black) and associated hotspots (red dots). Red dashed lines are hot spot tracks, which appear as lines of volcanic structures on the ocean floor. The Keweenawan and Siberian Traps formed in failed continental rifts where the crust had been greatly thinned. Whether there is a connection between the Columbia River basalts and the Yellowstone hot spot is still a matter of ongoing research.
    64. 64. • Spreading Centers – The greatest volume of volcanic rock is produced along the oceanic ridge system. – Continental or oceanic rifting. – Results in partial melting of mantle (decompression melting). – Large quantities of basaltic magma are produced.
    65. 65. Lava Domes Lava Dome on Mt. St. Helens • Bulbous mass of congealed lava. • Form in the summit crater. • Most are associated with composite cones that produce explosive eruptions of silica- and gas-rich lavas. • Typify late stages if mature, chiefly andesitic cones.
    66. 66. Climbing Mount St. Helens
    67. 67. Climbing Mount St. Helens
    68. 68. Climbing Mount St. Helens
    69. 69. Volcanic Pipes • • • • Most volcanic pipes are conduits that connect a magma chamber to the surface. Pipes may extend in a tube-like manner to depth exceeding 200 km (rare). Enables ultramafic rocks from the mantle to reach the surface that have undergone very little alteration. Diamond-bearing kimberlite dikes.
    70. 70. Volcanic Necks • Erosion of the outer flanks of the volcanic cone leave behind the moreresistant neck. Shiprock, NM – A Volcanic Neck
    71. 71. Columnar Joints • Form as igneous rocks cool at or near the surface. • Shrinkage fractures formed by tensional forces that cracks the rock as it contracts during cooling. • Produces elongated, pillar-like columns. • Common is lava flows and sills.
    72. 72. Plutonic Igneous Activity
    73. 73. Plutonic Igneous Bodies • Most magma is emplaced at depth in the Earth. • An underground igneous body, once cooled and solidified, is called a pluton.
    74. 74. Classification of Plutons • Classification of Plutons: 1. Shape • • Tabular (sheetlike) Massive 3. Size 2. Orientation with respect to the host (surrounding) rock: – Discordant – cuts across existing structures or rock units. – Concordant – parallel to existing structures of rock units.
    75. 75. Types of Intrusive Igneous Features • Dike – a tabular, discordant pluton where magma has injected into fractures. – Pathways that fed ancient lava flows. – Occur in clusters – radiating around neck.
    76. 76. Vertical Dike Near Granby, Colorado
    77. 77. Types of Intrusive Igneous Features • Sill – a tabular, concordant pluton where magma has injected along sedimentary bedding surfaces. – Occur in shallow environments less force required to move overlying rock layers. – Frequently cut across layers and resume concordant nature at a higher level.
    78. 78. A Sill in the Salt River Canyon, Arizona
    79. 79. Types of Intrusive Igneous Features • Laccolith – Similar to a sill (near-surface environment). – Lens or mushroom-shaped mass. – Generated by accumulation of more viscous magma. – Arches overlying strata upward.
    80. 80. Types of Intrusive Igneous Features • Two Types of Plutons (based on size) – Batholiths • Largest intrusive body. • Surface exposure of 100+ square kilometers. • Frequently form the cores of mountains.
    81. 81. Types of Intrusive Igneous Features • Two Types of Plutons (based on size) – Stocks • Smaller • Surface exposure less than 100 square kilometers. • Batholiths consist of large numbers of distinct plutons (including stocks) that were intruded over millions of years.
    82. 82. Batholiths of Western North America The Sierra Nevada Batholith exposed in Yosemite Natl. Park
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