Geology Study Guide: Volcanoes

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Geology Study Guide: Volcanoes
2013-10-09 11:39:46
Geology Volcanoes

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  1. How is the location of volcanoes related to plate tectonics? (In general, where do we expect to find volcanoes?)
    Divergent Plate Boundaries

    • Convergent Plate
    • Boundaries (o/c, o/o)

    Hot Spots
  2. Give specific examples of volcanoes at each tectonic setting.
    O/C Convergent Boundaries: Mt. St. Helens

    Hot Spots: Mauna Loa
  3. Shield Volcanoes
    • Massive
    • Broad, gentle sloping shape         

    Fluid basaltic lava    

    • Made of layers of basalt
    • Very little pyroclastics or pyroclastic flow     

    E.g.  Mauna Loa, Kilauea, Iceland 

    Tectonic Setting: Hot Spots
  4. Composite Cones
    Large, conical shape

    Interbedded lavas and pyroclastics

    Silica rich magma (doesn’t flow far), often of andesitic composition

    Violent eruptions

    Tectonic Setting: O/C Convergent Boundaries

    E.g. Mt. St. Helens, Mt. Rainier
  5. Cinder Cones
    Generally a single event (thus small size)

    Steep slope angle (30-40 degrees)

    Built from pyroclastics (ejected lava fragments)

    Occasionally may eject lava, usually from base

    Gas-rich basaltic magma

    Tectonic Setting: Anywhere there is a pocket, or chamber, of basaltic magma

    Sunset Crater
  6. Discuss why some volcanoes are explosive and some have relatively mild eruptions.  Give specific examples.
    • Volcanoes that have explosive eruptions contain more viscous magma. High pressure caused by the viscosity of the magma cause it to burst out explosively. Volcanoes with
    • mild eruptions contain magma that is more fluid, thus it has less pressure.

    Mt. St. Helens: Explosive

    Mauna Loa: Mild
  7. Discuss viscosity, silica content, volatiles, and
    temperature as each relates to magma composition.
    Increase Silica, more viscous
  8. Identify and briefly describe the hazards associated with explosive volcanic eruptions.
    Lava Flows

    • Pyroclastics – Fragments
    • of rock in the air from a volcanic eruption

    Hot Gases

    Pyroclastic Flows – Mix of ash and hot gases flowing down the volcano

    Lahars – Volcanic mudflows, ash mixed with water
  9. List the various materials that erupt from volcanoes.
    Volcanic Neck – forms when magma hardens within a vent. Shiprock

    Calderas – Collapsed magma chamber (e.g. magma chamber) Crater Lake

    Lava Domes – Old composite cone volcanoes. Mt. St. Helens

    Basalt Plateaus – Form from successive flows of lava. Cascade Mountains
  10. List and briefly describe benefits of volcanoes.
    Rich agricultural soil: rich soil in Idaho (potatoes)

    Mineral resources: from igneous rocks

    • Geothermal resources: heat and
    • electricity: Iceland

    water and atmosphere

    rock resources (e.g. pumice)

  11. List the various types of plutonic igneous bodies (including whether each is massive or tabular and concordant or discordant).
    Batholith – massive, discordant: irregular mass of intrusive igneous rock

    Laccolith – massive, concordant

    Dike – tabular, discordant: A sheetlike discordant igneous intrusion that cuts across layers of bedded country rock.

    Sill – tabular, concordant: sheetlike body formed by the injection of magma between parallel layers of preexisting bedded rock.
  12. Discuss the origin, composition, and location of
    batholiths and give a California example.
    • Batholiths form when magma pushes aside the surrounding rock and solidifies before it rises to
    • the surface.

    They are felsic.

    Sierra Nevada
  13. What is the ophiolite complex?
    The structure of the ocean crust