火山与岩浆活动

Felsic andesitic lava → high silica → high viscosity (stiffer) → cooler→ more gases → more explosive → steeper cones Example: Mt St. Helen (cascade volcanoes), subduction zone volcanoes
• Type of magma: Andesitic/felsic • Example Island arcs; Andes Mountains
Plate Tectonics and Igneous Activity
Intraplate Volcanism (Hot Spot) not a plate margin
What’s in a Volcano’s arsenal?
• Pyroclastic flow (very hot ash) • Lahar (deadly mud flow) • Crater Lake’s deadly gases
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Mt. St. Helens – a typical composite volcano
Shield volcano
• • • • • Broad, slightly domed Primarily made of basaltic (fluid) lava Generally large size Associated with ocean floor magmatism e.g., Mauna Loa in Hawaii
• dikes
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Plutons
Type – II: Massive irregular bodies:
Batholiths Stocks
A sill in the Salt River Canyon, Arizona
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A batholith exposed by erosion
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End of Chapter 7
a. b. c. d. Mafic/Ultramafic Felsic/Andesitic None of these I am not sure
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3-Which Magma is Hotter?
a. b. c. d. Mafic/Ultramafic Felsic /Andesitic None of these I am not sure
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9-Which volcano type produces lava + pyroclastic flows
a. b. c. d. e. Mt St Helens (Washington State) Kula (Hawaii) Mauna Loa (Hawaii) All of these a and c only
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10-Volcanoes with steep cones have
a. b. c. d. Fluid lava Viscous lava No relation whatsoever I am not sure
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11-Volcanoes at divergent boundary erupt mainly…lava
Mt. Hood, Oregon
Mt. St. Helens Pyroclastic flow
A lahar along the Toutle River near Mt. St. Helens
Formation of a caldera
Crater Lake in Oregon
Formation of a volcanic neck
A Pahoehoe lava flow
A typical aa flow
A size comparison of the three types of volcanoes
A volcanic bomb
Bomb is approximately 10 cm long
Types of Volcanoes
Locations of some of Earth’s major volcanoes
Igneous Bodies
Are bodies formed by the solidification of magma or lava
Intrusive igneous structures exposed by erosion
Controls of Volcanic eruptions
Mafic lava → low silica →low viscosity (more fluid) → hotter → less gases → less explosive → flatter cones
Example: Hawaiian volcanoes, ocean floor volcanoes
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Plutons
Type – I: tabular sheet like bodies
Concordant bodies (parallel):
• Sills (tabular) • Laccoliths (irregular)
Discordant bodies (cut through):
a. b. c. d. Felsic to Andesitic Mafic None of these I am not sure
Baidu Nhomakorabea33
Clicker test, do not talk, please.
1-Which Magma is more viscous?
a. b. c. d. Basaltic Felsic/Andesitic Ultramafic None of these
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2-which magma traps more gases?
A composite volcano (stratovolcano)
Features of Volcanoes
General features
• • • • • • • Conduit, or pipe Crater Vent Crater Fumaroles Caldera Crater Lake
Types of Hawaiian lava flows
Types of lava
• Pahoehoe lava (gas filled, resembles braids in ropes)
• Aa lava (gas free, rough, jagged blocks)
Go to Youtube to watch videos
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4-Which magma produces more violent eruptions?
a. b. c. d. Mafic/Ultramafic Felsic/Andesitic None of these I am not sure
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5-Magma viscosity is a function of…
• Form over a stationary pocket of magma; type of lava: Basaltic • Form a chain of volcanoes Example: Hawaiian volcanic chain • The only active volcano is over the hot spot
Sunset Crater – a cinder cone near Flagstaff, Arizona
Types of Volcanoes
Composite cone (or stratovolcano)
• • • • • • Large size Steep slope Interbedded lava flows and pyroclastic material Most violent type of eruptions Associated with subduction zones Most are adjacent to the Pacific Ocean (e.g., Cascade, Andes volcanoes)
Plate Tectonics and Igneous Activity
Volcanism at Divergent plate margins:
• Type of magma: Basaltic • Example: Mid Ocean ridge
Volcanism at Convergent plate margins
Volcanic eruptions
Factors affecting magma viscosity
• Temperature (hotter magmas are less viscous) • Chemical 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 → explosiveness
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8-Which one is a Composite cone?
a. b. c. d. e. Mt St Helens (Washington State) Sunset Crater (Arizona) Mauna Loa (Hawaii) All of these a and c only
Volcanoes and Other Igneous Activity Chapter 7 (page 207)
Volcanic eruptions
Factors that determine the violence of an eruption
• • • • Composition of the magma (silica content) Temperature of the magma (hot or cool) Dissolved gases in the magma (volatiles) Viscosity of magma (Viscosity is a measure of a material's resistance to flow; it is determined by the amount of silica content in the magma)
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7-Which one is a Shield Volcano?
a. b. c. d. e. Mt St Helens (Washington State) Mt Rainier (Washington State) Mauna Loa (Hawaii) All of these a and c only
a. b. c. d. e. Temperature Silica content Gases content All of these b only
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6-Which volcano is over a hot spot?
a. b. c. d. e. Mt St Helens (Washington State) Mt Rainier (Washington State) Mauna Loa (Hawaii) All of these a and c only
Types of Volcanoes
Cinder cone
• • • • • Built from ejected lava fragments (cinder) Steep slope angle Rather small size Frequently occur in groups Associated with subduction zones