Volcanic Activity

							        How Magma Reaches the
               Surface
   Magma forms in the (asthenosphere) mantle.

   Magma is less dense than solid material so it
    rises toward the surface.

   When a volcano erupts, dissolved gases form
    bubbles that rush out, taking the magma with
    them (like opening a can of soda pop)

   the magma with them. Like When a volcano
    Reaches Earths Surface
                 Inside a Volcano
   Pipe: a long tube in the
    ground that connects the
    chamber to the Earth’s
    surface.
   Vent: where magma, and gas
    leave the volcano.
   Lava flow: the river of lava
    that comes out and over the
    land.
   Lava: Magma that reaches
    the surface is called lava.
   Crater: a bowl-shaped area
    that forms around the vent.
   Magma chamber: collects in
    pockets beneath the
    volcano.
Characteristics of Magma



   The force of an eruption depends on four things……
        Amount of gas in magma
        How thick or thin the magma is
        Its temperature
        Silica content
   Silica also determines how easily the magma flows.
   More silica = thicker and lighter colored lava = sticky
        Makes obsidian and Rhyolite and pumice

   Less Silica = darker colored lava + flows easily
        Makes basalt
        Types of Volcanic Eruptions
 Quiet Eruptions
 Magma is thin and flows easily
    Pahoehoe: is a fast-moving
     hot lava, mass of wrinkles,
     billows and ropelike coils
     when it hardens.
    AA: is a slow moving cool
     lava, rough and jagged when it
     hardens
   Explosive Eruptions- thick
    magma, pipe gets plugged and
    explodes when pressure builds
    up.
       Causes pyroclastic flow
        explosive eruption hurls out
        gas, ash (sand-like), cinders
        (pebble sized), and bombs
        (larger pieces, ranging from
        baseball to car sized).
           Stages of a Volcano

1.   Active or live volcano that is erupting or
     shows signs that it erupt in the near
     future.
2.   Dormant or sleeping – scientists expect
     the volcano to erupt in the future and
     become active.
3.   Extinct or dead is unlikely to erupt again.
Volcanic Landforms
Landforms from Lava & Ash
A. Shield Volcanoes
B. Cinder Cone Volcanoes
C. Composite Volcanoes
D. Lava Plateaus
E. Calderas
             Shield Volcanoes
 Thin layers of lava
  pour out of a vent and
  harden on top of
  previous layers.
 Build a wide, gently
  sloping mountain.
 Hawaiian Islands are
  shield volcanoes over
  a hot spot.
Mauna Loa, Hawaii
Cinder Cone Volcanoes
            A steep, cone-shaped
             hill or mountain.
            Ash, cinders, and
             bombs pile up around
             the vent.
            Cinders erupt
             explosively.
            Sunset crater is an
             example.
Composite Volcanoes
             A steep, cone-shaped
              volcano built up of
              layers and of rock
              fragments.
             Steep at the top,
              flatens at the bottom
             Magma- high in silica,
              making it pasty.
             Erupt explosively.
             Mount St. Helens and
              Mount Rainier are
              examples.
 St.   Augustine volcano, Alaska.
                  Lava Plateaus
   Continued eruptions
    form high, level
    areas.
   Lava flows out of
    several long cracks,
    and after millions of
    years, these layers
    form high plateaus.
   Example: Columbia
    Plateau
Columbia Plateau
            Calderas
A  huge eruption may empty the
  main vent and the magma chamber
  beneath the volcano.
 Mountain becomes a hollow shell
  and the top collapses in.
 Huge hole left is called a caldera.
 Example: Crater Lake, Oregon
   Poas Volcano,
    Costa Rica




   Crater Lake,
    Oregon
           Volcano Hazards
 Mount St. Helens erupted in 1980 after 123
  years of being dormant. Before that people
  viewed it as a peaceful mountain.
 Quiet eruption hazards- lava flows from vents,
  burning everything in their path.
 Explosive eruption hazards- volcano will send
  out burning clouds of volcanic gases, cinders
  and bombs.
 Volcanic ash can bury entire towns, damage
  crops and clog car engines. Wet ash can cause
  roofs to collapse and plane engines to stall.