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Powerpoint Presentation Physical Geology, 10e


e.g., Basalt. Porphyritic - larger crystals in a matrix of much finer crystals or glass ... Vesicular basalt. Pumice. Fragmental - particles blasted apart by ... – PowerPoint PPT presentation

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Title: Powerpoint Presentation Physical Geology, 10e

Volcanism and Extrusive RocksChapter 4
4.1 Volcanism and Earths Systems
  • Atmosphere originally created from gases released
    by magmas
  • Hydrosphere produced by condensation of volcanic
    water vapor
  • Biosphere both positively and negatively
    influenced by volcanism
  • Lava flows and ash weather to produce fertile
  • 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

Volcanic Eruptions
  • Lava is produced when magma reaches Earths
  • Explosive eruptions can produce rapidly cooled
    rock fragments called pyroclasts
  • Size range from dust (ash) to boulders (blocks
    and volcanic bombs)
  • Calm oozing of magma out of the ground produces
    lava flows
  • Lava flows and pyroclasts pile up to form

Living with Volcanoes
  • Mythology, religion and volcanoes
  • Hawaii - Pele
  • Iceland - Loki
  • Growth of volcanic islands (Hawaii)
  • Geothermal energy
  • Natural steam harnessed as clean
  • energy resource
  • Climatic effects
  • Global cooling
  • Resulting crop failures and famines
  • Volcanic catastrophes
  • Mt. St. Helens, Pompeii, Krakatoa,
  • Tambora, Crater Lake

4.2 Eruptive Violence and Physical
Characteristics of Lava
  • Violence of eruptions controlled by
  • Dissolved gases in magma
  • Water vapor, carbon dioxide, sulfur dioxide, etc.
  • Ease/difficulty of gases escaping to atmosphere
  • Viscosity- a fluids resistance to flow
  • Silica content
  • Higher silica contents produce higher viscosities
  • Lava temperature
  • Cooler lavas have higher viscosities
  • Amount of dissolved gases
  • The more dissolved gases, the more fluid the lava

Extrusive Rocks and Gases
  • Scientific Investigation of Volcanism
  • Rocks, gases and events from observed eruptions
    compared to similar lavas elsewhere to infer
    past activity
  • Rock Composition
  • Rhyolite - high silica light color
  • Basalt - low silica dark color
  • Andesite - intermediate silica and color

Extrusive Textures
  • Texture - appearance of a rock with respect to
    size, shape and arrangement of its grains
  • Glassy - glass without mineral crystals
  • Obsidian
  • Fine-grained - most crystals lt 1 mm
  • e.g., Basalt
  • Porphyritic - larger crystals in a matrix of much
    finer crystals or glass
  • e.g., Andesite

Extrusive Textures
  • Vesicular/Frothy - trapped gas bubbles
  • Vesicular basalt
  • Pumice
  • Fragmental - particles blasted apart by explosive
  • Dust and ash (lt2 mm)
  • Cinders (2-64 mm)
  • Blocks and bombs (gt64 mm)

4.3 Volcanic Landforms
  • 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

Types of Volcanoes
  • Shield volcanoes
  • Broad
  • Gently sloping
  • Composed of solidified lava flows
  • Cinder cones
  • Small
  • Steep-sided
  • Composed of a pile of loose cinders

Other Eruption Types
  • 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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