Volcanoes - PowerPoint PPT Presentation

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Volcanoes

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Volcanoes Magma Reaches the Earth s Surface KEY CONCEPT:When a Volcano erupts, the force of the expanding gases pushes magma from the magma chamber through the pipe ... – PowerPoint PPT presentation

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Title: Volcanoes


1
Volcanoes
2
Magma Reaches the Earths Surface
  • KEY CONCEPTWhen a Volcano erupts, the force of
    the expanding gases pushes magma from the magma
    chamber through the pipe until it flows or
    explodes out of the vent.
  • The volcano has a pocket of magma below the
    surface called a magma chamber. A long tube,
    called a pipe, connects the magma chamber to the
    surface.
  • The opening at the top of the pipe is called the
    vent.
  • When it leaves the volcano magma becomes lava.

3
Kinds of Eruptions
  • KEY CONCEPTGeologists classify volcanic
    eruptions as quiet or explosive.
  • How a volcano erupts depends on the magma.
  • A quiet eruption moves slowly because it is low
    in silica and flows very easily.
  • An explosive eruption has magma that is high in
    silica and does not flow easily. Magma builds up
    until it explodes out of the vent.

4
Stages of Volcanic Activity
  • KEY CONCEPT Geologists often use the term
    active, dormant, or, extinct to describe a
    volcanos stage of activity.
  • Active volcanoes are erupting or showing signs
    that it will erupt soon.
  • Dormant volcanoes are no longer erupting, but can
    again in the future.
  • Extinct volcanoes are not likely to erupt any
    longer.

5
Where Volcanoes Form
  • KEY CONCEPT Volcanoes form along the boundaries
    of the Earths plates.
  • A Volcano is a weak spot in the crust where
    melted material comes to the surface.
  • Most Volcanoes happen at plate boundaries.
  • Lava can build up to form islands and mountains.
  • Some Volcanoes form above a hot spot when magma
    erupts through the crust and reaches the surface.
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