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Section 2 Volcanic Activity

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					              Section 2: Volcanic Activity

                               Friday, March 12, 2010
                                  Pages 183 -- 192



Arenal Volcano -- Costa Rica
              Objectives
• Describe what happens when a volcano
  erupts.
• Explain how the two types of volcanic
  eruptions differ depending on the
  characteristics of magma.
• Identify some hazards of volcanoes
• Identify types of volcanic activity other
  than eruptions.
         Vocabulary Words
•   Magma chamber   •   Aa
•   Pipe            •   Pyroclastic flow
•   Vent            •   Active
•   Lava flow       •   Dormant
•   Crater          •   Extinct
•   Silica          •   Hot spring
•   Pahoehoe        •   Geyser
                    •   Geothermal energy
         Origin of Magma
• Lava begins as magma in the mantle.
• The magma is under great pressure
• Magma flows upward because it’s less
  dense than surrounding materials.
• Magma will continue to rise until it
  reaches the surface or until it becomes
  trapped beneath rock.
         Volcanic Eruptions
• The trapped gases found in magma are
  under great pressure.
  – Ex: soda bottle
• As the magma reaches the surface, the
  pressure decreases.
• The gases begin to separate out, forming
  bubbles.
• During volcanic eruption, the gases dissolved
  in the magma rushes out, carrying the
  magma with them.
                            Stromboli -- off the North coast of Sicily.
Exploring a Volcano
                                             Dust Cloud



       Vent                         Crater
               QuickTime™ and a

Pipe
                 decompressor
         are neede d to see this picture.     Side Vent
                                                 Lava Flow
                                                  Lava

                   Magma
                                            Magma Chamber
   Characteristics of Magma
• There are many types of magma.
  – Some are thick and flows slowly.
  – Some are fluid and flow very easily.
  – The temperature of the magma will
    determine how it flows.
         The Role of Silica
• The amount of silica in magma also
  helps to determine how easily the
  magma flows.
• What is silica?
  – It’s a material formed from 2 different
    elements -- oxygen and silicon.
  – There are lots of silica found on the Earth’s
    crust and mantle.
   The Role of Silica -- Cont’d
• The more silica
  magma contains,
  the thicker it is.
• Magma with a lot of
  silica produces light-         QuickTime™ and a
                                    decompressor
                           are need ed to see this picture.

  colored lava.
• Rhyolite is an
  example of a rock
  formed from magma
  with lots of silica.                                        Rhyolite
       Role of Silica -- Cont’d
• Magma that is low in
  silica flows easily
  and produces dark-
  colored lava.
• Basalt is an
                                   QuickTime™ an d a
                                      decompressor
                             are need ed to see this p icture .




  example of a rock
  with very little silica.
 Types of Volcanic Eruptions
• The type of magma that flows from a
  volcano will determine whether the
  eruption is quiet or explosive.
            Quiet Eruptions
• If the magma flows easily, the eruption will be
  quiet.
• This is because the gases in the magma
  bubble out slowly.
• The lava is usually thin and runny.
• There are 2 types of lava produced this way.
  – Pahoehoe
  – aa
                                     Pahoehoe
                                         • Fast moving
                                         • Looks wrinkled,
                                           rope-like
      QuickTime™ an d a
         decompressor
are need ed to see this p icture .
                                   aa
                                    • This type of lava is
                                      cooler.
                                    • It is slower-moving.
      QuickTime™ and a
                                    • When cooled, the
                                      surface is jagged
        decompressor
are neede d to see this picture.




                                      and chunky.
       Explosive Eruptions
• Eruptions are explosive if the magma is
  thick and sticky.
• The thick magma prevents the lava from
  flowing freely.
• Instead, the magma builds up slowly in
  the pipe and acts as a plug.
• The trapped gases build up until it
  explodes.
 Explosive Eruptions -- Cont’d
• The lava is pushed out violently.
• The lava is broken into fragments that
  cool quickly.
  – Can be as small and fine as volcanic ash
  – Can be as large as a car
• This type of flow is called pyroclastic
  flow.
           Mount St. Helen
• This is an example
  of pyroclastic flow.


                               QuickTime™ and a
                                 decompressor
                         are neede d to se e this picture.
       Stages of a Volcano
• Active
  – The volcano is alive.
• Dormant
  – The volcano is asleep.
• Extinct
  – The volcano is unlikely to erupt again.
          Other Types of Volcanos
                                                    • Hot Springs
                                                       – Formed from the heating
                                                         of underground water by
                                                         a nearby body of magma
                                                       – This water may contain
                       QuickTime™ and a
                         decompressor
                 are neede d to see this picture.
                                                         dissolved gases and
                                                         other substances found
                                                         deep within the Earth.



Mt. Princeton Hot Springs, CO
          Other Types of Volcanos
                                                    • Hot Springs
                                                       – Formed from the heating
                                                         of underground water by
                                                         a nearby body of magma
                                                       – This water may contain
                       QuickTime™ and a
                         decompressor
                 are neede d to see this picture.
                                                         dissolved gases and
                                                         other substances found
                                                         deep within the Earth.



Mt. Princeton Hot Springs, CO
       Other Types of Volcanoes
                                               • Geyser is a fountaiin
                                                 of water and steam
                                                 that erupts from the
                                                 ground.
                  QuickTime™ an d a
                    decompressor
           are need ed to see this p icture.   • This is a result of
                                                 water and steam
                                                 that is trapped
                                                 underground.
Old Faithful -- Yellowstone
       Geothermal Energy
• This is a form of alternative energy.
• This form of energy is clean and
  reliable.
• Is energy source is used in Iceland,
  northern California and New Zealand.
             Homework
• Workbook 6.2 (3/15)
• Vocabulary quiz 6.2 (3/17)
• Workpacket 6.2 (3/17)

				
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