Inside Earth: Chapter 3 Volcanoes

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Inside Earth Chapter 3- Volcanoes

• Section 2 Volcanic Activity

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Guide For Reading

• What happens when a volcano erupts?
• How do the two types of volcanic eruptions
  differ?
• What are some hazards of volcanoes?

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How Magma Reaches Earths Surface
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Why does magma rise?

• Magma rises because it is less dense that the
  surrounding solid material

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Guide For Reading What happens when a volcano
erupts?

• As the less dense magma rises, the pressure
  decreases
• The dissolved gas separates out and bubbles form
• A volcanic erupts when an opening develops in
  weak rock on the surface
• During a volcanic eruption, the gases dissolved
  in magma rush out, carrying the magma with them
• Once magma reaches the surface and becomes lava,
  the gases bubble out

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Inside a Volcano
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Magma Chamber

• The pocket beneath a volcano where magma collects

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Pipe

• A long tube through which magma moves from the
  magma chamber to Earths surface

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Vent

• The opening through which molten rock and gas
  leave a volcano

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Where are vents located?

• Usually there is one central vent at the top of
  the volcano
• Often times there are additional vents that open
  on the volcanoes sides

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Lava Flow

• The area covered by lava as it pours out of a
  volcanos vent

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Crater

• A bowl-shaped area that forms around a volcanos
  central opening
• Lava collects there

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Checkpoint (page 94) How does magma rise through
the lithosphere?

• Liquid magma in the asthenosphere is less dense
  than the rock in the lithosphere above it, so it
  flows upward through cracks in the rock
• The magma is stored in the magma chamber
• It continues upward (through the pipe) until it
  reaches the surface (exiting through a vent) or
  it is trapped beneath layers of rock.

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Characteristics of Magma
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Silica

• A material that is found in magma,formed from the
  elements oxygen and silicon
• The more silica the magma has the thicker it is

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What three factors contribute to how forceful a
volcanic eruption is? Explain how each
determines this.

• Amount of gas present
• How thick or thin the magma is (Temperature)
• Thinner (hotter) is more fluid
• The silica content
• If the silica content is high, magma is thick
• This causes the pressure to build

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Types of Volcanic Eruptions
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Quiet eruptions like the ones that take place on
_______ have built up the big island over _______
of _______ of years.

• Mount Kilauea
• Hundreds
• Thousands

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Pahoehoe

• A hot, fast-moving type of lava that hardens to
  form smooth, ropelike coils

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Aa

• A cooler, slow-moving type of lava that hardens
  to form rough chunks cooler than Pahoehoe

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What is the difference between the two types of
lava?

• Pahoehoe is a faster flowing lava that cools
  slowly resulting in a smooth texture
• Aa is a slower flowing cooler type of lava that
  hardens into rough chunks

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Figure 7 Inferring (page 97)What accounts for
the differences between these two types of lava?

• The temperature of the lava
• The speed at which the lava flows

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Checkpoint (page 97) What types of lava are
produced by quiet eruptions?

• Quiet eruptions produce two types of lava
  pahoehoe and aa
• Pahoehoe is a fast-moving, hot lava
• Aa is a cooler, slower-moving lava

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Pyroclastic flow

• The expulsion of ash, cinders, and bombs from a
  violent volcanic explosion

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Checkpoint (page 98) What causes an explosive
eruption?

• Magma that is thick and sticky causes a volcano
  to erupt explosively
• Magma can not flow freely causing pressure (gas)
  to build up until it explodes

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Guide For Reading How do the two types of
volcanic eruptions differ?

• Quiet eruptions occur when the lava flows more
  easily because gas dissolved in the magma bubbles
• When the lava is thick and sticky the gas
  continues to store increasing pressure
• When the pressure becomes so great an explosion
  takes place when the gas pushes the magma out
  with incredible force

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Stages of a Volcano
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What are the three stages of a volcano? Explain
each stage.

• Active
• A volcano that is erupting or has shown signs
  that it may erupt in the near future
• Dormant
• A volcano that is not currently active, but may
  become active in the future
• Extinct
• A volcano that is unlikely to erupt again

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Other Types of Volcanic Activity
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Hot Spring

• A pool formed by groundwater that has risen to
  the surface after being heated by a nearby body
  of magma

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Geyser

• A fountain of water and steam that builds up
  pressure underground and erupts at regular
  intervals

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Geothermal Energy

• Energy from water and steam that has been heated
  by magma
• Geothermal energy is produced by drilling a well
  into the ground where thermal activity is
  occuring.
• Once a well has been identified and a well head
  attached, the steam is separated from the water,
  the water is diverted through a turbine engine
  which turns a generator.
• Usually the water is injected back into the
  ground to resupply the geothermal source.

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Monitoring Volcanoes
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How do geologists monitor the activity of a
volcano?

• Measure tilt caused by magma movement underground
  using tiltmeters laser-ranging devices
• Monitor temperature underground
• Monitor small earthquakes that occur in the area
  around a volcano

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Volcano Hazards
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Guide For Reading What are some hazards of
volcanoes?

• Fire
• Bury entire towns
• Damage crops
• Landslides
• Avalanches of mud
• Damage car and jet engines