Lecture 1 INTRODUCTION by dffhrtcv3

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									                Summer
                  2008

EARTH’S CRUST
     and
  INTERIOR
    Volcanic Hazards
Housekeeping: the MIDTERM

• VOLCANIC HAZARDS
      explosive eruptions present the greatest hazard

• VOLCANO TYPES
      depend on proportions of lava and explosion debris

•   PLATE TECONIC SETTING
      different causes of melting in different settings
Headlines

• Lava viscosity and gas pressure are the keys to
understanding volcanic hazards

• They explain the likelihood of explosive eruptions,
which in turn determine the hazard and the volcano
shape.

• They relate to the melting process which varies with
plate tectonic setting
Volcanic hazards

  •   Lava flow           -   slow, downhill
  •   Ash fall            -   slow, downwind
  •   Pyroclastic flow    -    very rapid, downhill
  •   Dome collapse       -   rapid, downhill
  •   Mudflows (Lahars)   -   rapid, downstream
  •   Gas exhalation      -    downhill / downwind
  •   Sector collapse     -    downhill
  Earth’s crust and interior




Volcano types – the big ones
• SHIELD VOLCANO
          – huge, flat, nearly all lava, not explosive
                        – Oceanic hotspots     e.g. Hawaii

• STRATOVOLCANO
          – large, steep, lava and pyroclastics; highly explosive
                       – Convergent arcs     e.g. Japan, Philippines, Cascades

• COLLAPSE CALDERA
          – large collapse depression
                        – Convergent arcs    e.g. Crater Lake;
                        – Continental hotspots e.g. Long Valley, Yellowstone
 CONICAL COMPOSITE
 (Stratovolcano)
                     SHIELDS and CONES



                        SHIELD VOLCANO

Mt Hood




                                         Mauna Loa
                                                          Cinder Cone

    VOLCANO
SIZE COMPARISON                                           Stratovolcano




    Old Extinct Shield Volcano                            Stratovolcano




          Young Extinct Shield Volcano




                         Active Hawaiian Shield Volcano
 Earth’s Crust and Interior


Volcano types – the small ones
• (RESURGENT) DOME
           - small, nearly all lava, viscous silica-rich lavas
           - Convergent arcs - aftermath of explosive eruption
• SPATTER CONE
           - very small, nearly all lava, fluid basaltic lavas
           - Hot spots - lava fountains
• CINDER CONE
           - small, nearly all pyroclastics
           - All volcanic terrains
• EXPLOSION CRATER
           - small blow-hole
           - All volcanic terrains
• FUMAROLE
           - tiny gas vent
           - All volcanic terrains
JAPAN




           Martinique



        Resurgent domes
JAPAN
              and spines
 SHIELD VOLCANO                                     Idaho




                                     SPATTER CONE

      CONICAL
      COMPOSITE
      VOLCANO



CINDER CONE       Reunion

                            CINDER
                            CONE




                                     Cones
A cinder cone
  Lava spilling from summit !
GEO 1 Earth’s Crust and Interior


                               High Lava Viscosity       Low Lava Viscosity

                    2 bad factors                    1 bad factor

                                                         Cinder Cones
High                    Stratovolcanoes
Gas Pressure                                            Spatter Cones
                       Collapse Calderas               Explosion Craters

                    1 bad factor                     0 bad factors

                       Resurgent Domes                   Shield Volcanoes
Low                                                      Fissure Eruptions
Gas Pressure             Lava Domes
                                                      Small Summit Calderas


                                                            Volcano types
                                                      in risk factor matrix
How do we rate
dormant volcanoes?
• Volcano shape
      - related to risk factors
• Volcano composition
      - lava to ash ratios
• Lava composition
      - more silica in more viscous lavas
• Volcano location
      - tend to behave like their neighbors
GEO 1 Earth’s Crust and Interior




     Check out the neighbors!
        • Amboy, Sunset Crater, Ubehebe
                    - part of a scattering of small extinct cinder cones
                    - probably already extinct
        • Kilauea (Hawaiian island chain)
                    - youngest in a line that ages progressively to NW
                    - will become extinct and drown
        • Mt St Helens (Cascade mountain range)
                    - one in a North-South line with random eruption ages
                    - much more to come, potentially much more violent
                            (e.g. Mt Shasta, Mt Hood, Mt Ranier)
                    - compare with Mt Mazama; now Crater Lake!
Short-term precursors
• Earthquake swarms and harmonic tremors

• Bulging of the volcano outline

• Changing temperature and fluid levels in lava lake

• Steam and gas eruptions
Headlines

• Lava viscosity and gas pressure are the keys to
understanding volcanic hazards

• They explain the likelihood of explosive eruptions,
which in turn determine the hazard and the volcano
shape.

• They relate to the melting process which varies with
plate tectonic setting

								
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