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   Vulcanicity


                 Intro vid
What is a volcano?
   A volcano is an opening in the Earth’s
    crust from which materials such as magma
    and gases are ejected.
   Volcanoes may be described as:
       Active
       Dormant
       Extinct
Active Volcano
   An active volcano is one which erupts and
    has a high level of vulcanicity.
   These volcanoes are ones that are currently
    erupting or noticeably building pressure in
    preparation of an eruption.
   Eg Lassen Peak (California) and Mt St
    Helen’s
BEFORE
AFTER
Dormant Volcano
   Dormant Volcanoes are volcanoes which has
    been inactive for a long period of time eg. 100
    years
   One that has been known to have erupted in
    modern history but is now inactive or "sleeping"
   Eg. Mount Rainier (Washington State), Mount
    Hood (Oregon) and Mount Shasta (California)
Mt Reinier
Mt Hood
Extinct Volcano
   An extinct volcano is one that scientist
    believe will not erupt again because it
    shows no volcanic activity.
   However, we cannot be absolutely certain.
    Eg. Mt St Helens (Extinct        Active)
Types of volcanoes
   Broadly, volcanoes can be classified into 3
    types:
       Basic lava volcano (shield)

       Acid lava volcano

       Composite volcano
Basic Lava Volcano
   This type of volcano is formed from lava which
    flows quite rapidly spreading over a large area
    before it solidifies.
   This category of volcano is made from quiet,
    rapid lava flows spread over a large area. After
    several eruptions, a gentle dome mountain is
    formed (e.g.. Mauna Loa in Hawaii)
   Eruption in this case is gentle.
Acid Lava Volcano
   The acid lava which forms this volcano is
    thick or viscous.
   It is slow flowing and solidifies quickly
    near the vent
   This produces a cone with steep slope.
   Eruptions in this case is usually violent.
   Eg. Mt Stromboli in italy
Mt Stromboli
Composite Volcano
   A composite volcano consists of alternate
    layers of viscous lava, ash and cinder.
   Slopes of the volcano are usually steep near
    the summit and gentler near the base
   Lava often escapes through the sides of the
    cone and builds up to form secondary
    cones.
   Eg Mt Mayon in the philippines
Mt Mayon
Distribution of volcanoes
3 major zones
   1. Ring of Fire: This goes all around the
    edge of the Pacific Ocean

   2. Mediterranean Zone: the extends across
    Asia and into India including Italy, Greece
    and Turkey

   3. Mid-Atlantic Ridge: Passes through
    Iceland and down the middle of the Atlantic
    Ocean.

				
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posted:8/8/2012
language:English
pages:22