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Lecture OutlinesLecture Outlines
Physical Geology, 14/ePhysical Geology, 14/e
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Plummer, Carlson & Plummer, Carlson & HammersleyHammersley
Volcanism and Extrusive RocksVolcanism and Extrusive RocksPhysical Geology 14/e, Chapter 4Physical Geology 14/e, Chapter 4
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Atmosphere – originally created from gases released from volcanic eruption
Hydrosphere – produced by condensation of volcanic water vapor
Biosphere both positively and negatively influenced by volcanism
• lava flows and ash weather to produce fertile soils
• violent eruptions can destroy nearly all life in their paths
• large amounts of ash and volcanic gases in atmosphere can trigger rapid climate changes and contribute to mass extinctions
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Volcanism & earth’s systemsVolcanism & earth’s systems
Lava – produced when magma reaches Earth’s surface
• explosive eruptions can produce rapidly cooled rock fragments called pyroclasts, size ranges from dust (ash) to boulders (blocks and volcanic bombs)
• calm oozing of magma out of the ground produces lava flows
• pyroclastics and lava flows form extrusive igneous rocks
• lava flows and pyroclasts pile up to form volcanoes
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Volcanic eruptionsVolcanic eruptions
Mythology, religion and volcanoes• Hawaii – Pele, Iceland – Loki
Growth of volcanic islands (Hawaii)Geothermal energy• natural steam harnessed as clean energy resource
Climatic effects• very large eruptions can result in measurable
global cooling resulting crop failures and famines
Volcanic catastrophes• Mt. St. Helens, Pompeii, Krakatoa, Tambora,
Crater Lake
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Living with volcanoesLiving with volcanoes
Violence of eruptions controlled by:• dissolved gases in the magma
• ease/difficulty of gases escaping to atmosphere
Viscosity- a fluid’s resistance to flow•higher silica contents produce higher viscosities•cooler lavas have higher viscosities•amount of dissolved gases, the more dissolved gases, the more fluid the lava
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Eruptive violence & physical Eruptive violence & physical characteristics of lavacharacteristics of lava
Scientific Investigation of Volcanism
• rocks, gases and events from observed eruptions compared to similar lavas elsewhere to infer the nature of past activity
Rock Composition• rhyolite - high silica; lightlight color
• basalt - low silica; darkdark color
• andesite - intermediate silica and color
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Extrusive rocks and gasesExtrusive rocks and gases
Vent - opening through which lava erupts
Crater - basin-like depression over the vent at the summit of the volcano
Caldera - volcanic depression much larger than the original crater, having a diameter of at least 1 km
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Volcanic landformsVolcanic landforms
Shield volcanoes• broad
• gently sloping
• composed of solidified lava flows
• flows often contain lava tubes
Cinder cones • small
• steeply sloping
• composed of a pile of loose cinders
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Types of volcanoesTypes of volcanoes
Composite volcanoes• aka stratovolcanoes• moderately to steeply sloping• constructed of alternating layers of
pyroclastic debris and solidified lava flows• composed primarily of intermediate
composition volcanic rocks (i.e., andesite)• most common type of volcano at
convergent plate boundaries
Volcanic domes• extremely high viscosity, degassed, felsic
lavas (often glassy, e.g., obsidian)
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Types of volcanoesTypes of volcanoes
Flood eruptions• very fluid (basalts)
• extremely large in volume
• create extensive lava plateaus
• eruption times correspond with largest mass extinction events
Submarine eruptions• nearly always basaltic
• mid-ocean ridge eruptions
• pillow basalts
Columbia river flood basalts
Pillow basalts
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Other eruption typesOther eruption types
Shield volcanoes• Venus, Mars, Io
Lava domes• Venus, Moon
Flood eruptions• very fluid (basalts)
• extremely large in volume
• extensive flat lava plains (Moon, Mars, Venus, Mercury?)
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Volcanism on other planetsVolcanism on other planets
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