Igneous Activity and Volcanoes

							    Igneous Activity and Volcanoes




What is the relationship between plate tectonics and volcanoes?
Plate Boundary Features
The pattern of igneous activity is not
               random




  What patterns can you observe?
 What is the Relationship between Plate
   Tectonics and Igneous Activity?
• Most volcanic activity is associated with plate
  boundaries.
• Plate motions provide the mechanism by which
  mantle rocks melt to form magma
   • Convergent plate boundaries
      • Descending plate partially melts, magma rises
         • Volcanic island arcs in an ocean (Aleutians)
         • Continental volcanic arcs (Andes Mountains)
 What is the Relationship between Plate
   Tectonics and Igneous Activity?
   Divergent plate boundaries
      • The greatest volume of volcanic rock is produced
        along the oceanic ridge system




Mid-Ocean Ridges
 What is the Relationship between Plate
   Tectonics and Igneous Activity?
• What about continent-continent convergence?




• What about transform faults?
• No Volcanic activity
Types of Igneous Activity
• Extrusive
• Intrusive
Intrusive Igneous Features
     Intrusive Igneous Activity
      Magma moves into the crust but
          not onto the surface

• Granitic Batholiths
Formation of the Sierra Nevada
           Granitic Batholiths
  Batholiths form above ocean-continent
  convergent subduction zones
• Magma intrudes, melts and incorporates pre-
  existing rock
           Granitic Batholiths
• Magma cools to form a granitic batholith
• Uplift and subsequent erosion exposes the granite
  batholith
Sierra Nevada Batholith
 Extrusive Volcanic Activity and
        Plate Boundaries
• Rift volcanoes - divergent - e.g. Iceland where the
  sea floor spreads
        Pacific Ring of Fire




• Convergent plate boundaries – Subduction
  Hot spot volcanoes - mid-plate
above a hot spot buried in the mantle
Hawaiian Hot Spot
      What are the products of
       Volcanic Activity?
• Gases - water vapor, hydrogen sulphide,
  carbon monoxide, nitrogen
• Pyroclastics - dust, ash, lapilli, volcanic
  bombs
• Lava
  – basaltic
  – andesitic
  – rhyolitic
A volcanic bomb




Bomb is approximately 10 cm long
         Figure 9.6
Volcanoes and Magma Composition
 • Magma composition determines:
   – the shape of a volcano
   – the nature of its eruption.
              Basaltic Lava
• Basaltic lava is fluid and free-flowing like
  molasses
• Basaltic lava erupts relatively quietly
  through fissures in the earth’s crust
  – forms plateaus of flood basalts such as the
    Columbia Plateau
  – forms shield volcanoes such as those in Hawaii
  – forms cinder cone volcanoes if it is gassy
Flood Basalts

        • Basaltic lava floods
          from fissures drowning
          the pre-existing
          landscape
        • Lava flows form a
          plateau like the
          Columbia Plateau
                 Columbia Plateau


• The Columbia river
  cuts through the
  plateau on its way to
  the ocean
            Shield Volcanoes




• Lava flowing from fissures forms low angle slopes
• Basaltic lava erupts quietly
Shield Volcanoes


          • Sometime the lava
            forms fountains like
            these on Kilaueu
Cinder Cones
       • At night, glowing
         fragments create a
         fireworks display
       • Cinder cones are short
         and short-lived volcanoes
       • Cinder cones rarely rise
         more than 1000 feet
What type of volcano?
    What Kind of Volcanoes Form the
          Hawaiian Islands?




•   Shield Volcanoes
•   Lava flowing from fissures forms low angle slopes
•   Basaltic lava erupts quietly
•   What is the cause of Hawaiian volcanism?
•   A hot spot in the mantle
     Shield Volcanoes and Hot Spots
• Shield volcanoes form
  above hot spots buried in
  the mantle
• The Hawaiian Islands
  formed above a hot spot as
  the Pacific Plate moved
• Shield volcanoes may also
  form above rift zones such
  such as Iceland
   Andesitic Lava Forms Composite or
             Stratovolcanoes
• Composite or strato-
  volcanoes form above
  subduction zones
• What two plates converge
  to form the Cascade
  Ranges?
• Juan de Fuca and North
  America plates
            Pacific Rim of Fire




• Convergent plate boundaries – subduction
Cascade Volcanoes
         Composite Volcanoes or
            Stratovolcanoes
• Composite volcanoes
  are explosive
• They are composed of
  layers of andesitic lava   Mount Shasta, California
  and pyroclastics
• The Cascade
  volcanoes are
  dangerous!
Mount Pinatubo




                 December 2000

   1991
    Mount Pinatubo Sulfur Dioxide




• Sulfuric acid aerosols made 1992 Coolest year since 1986
• Contributed to reduced ozone levels in Southern
  hemisphere
Mount St Helens
• Mount St. Helens is
  part of the Cascade
  Mountains
• An explosive eruption
  in 1980 caused:
   – suffocating clouds of
     ash
   – mudflows
   – debris avalanches
   – blast and blowdown
Debris Avalanche and Eruption of Mount St. Helens,
                  Washington
   Mount St. Helens- after May 18, 1980




• Lost 1300 feet off its top
• Left a crater a mile and a half wide
Ash and Dust are a major hazard


                   • Suffocation from
                     ash was a major
                     hazard in 1980
Glowing Clouds (Nuee Ardente)

                 • Glowing clouds of ash
                   and gases may
                   descend the slopes at
                   over a 100 mph
Mudflows


    • Many composite eruptions
      throw massive quantities of
      water and ash downslope
Composite Volcanoes May Blow
        Their Top Off
Formation of Crater Lake
Crater Lake, Oregon
• The biggest cause of loss of life from
  Mount Pinatubo was from:
  – A. Lava flows
  – B. Mud flows
Question
• What is the most abundant volcanic gas?
  –   A. Chlorine
  –   B. Carbon dioxide
  –   C. Sulphur oxide
  –   D. Water vapor
  –   E. Nitrogen
What kind of Volcano?
• A – Klamath Mountains
    – Complex Mountains
• B – Coast Ranges
    – Complex Mountains
• C – Cascade Ranges
    – Composite Volcanoes
• D – Modoc Plateau
    – Flood Basalts
• E – Sierra Nevada
    – Granitic Batholith
• F – Central Valley
    – Sediment filled basin
• G – H Great Basin
    – Fault Block Mountains
• I - Transverse Range
    – Complex Mountains
• J – Peninsula Ranges
    – Granitic batholiths
• K – Salton Trough
    – Graben
     Where would you go to find
      Volcanoes in California?
•   Cascade Ranges - Mt.Lassen and Mt.Shasta
•   Mt. Konocti, Clear Lake
•   Long Valley Caldera, Mammoth Lakes
•   Sutter Buttes, Marysville
•   Mammoth Mountain
•   Glass Mountain
•   Mono Craters
•   Lava Beds National Monument