Volcanoes

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Volcanoes

• Earth Science
• Chapter 8
• Scholz

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What is a Volcano
One dictionary meaning volcano is a vent in the
earth's crust through which rock or lava is
ejected.
Another, a volcano is a cone-shaped hill
or mountain built around a vent.
Most volcanologists disagree with both of these
dictionary definitions.
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Volcanic Eruptions

• Volcanic Eruptions come in two varieties.
• Non-explosive
• Explosive

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Non-Explosive Eruptions

• Non Explosive Eruptions are also called Lava
  Flows
• Lava can spray in the air
• Lava can also flow like a river

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Explosive Eruptions

• In an Explosive Eruption hot debris, gas,
  molten rock is blown into the air
• Solid rock is also thrown into the air
• Explosive Volcanoes actually shrink

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Parts of a Volcano
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What comes out?

• Lava
• Blocky
• Pahoehoe
• Aa
• Pillow
• Pyroclastic Material
• Blocks
• Bombs
• Lapilli
• Ash

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Lava Pahoehoe
Pahoehoe is a Hawaiian term for basaltic lava
that has a smooth, hummocky, or ropy surface. A
pahoehoe flow typically advances as a series of
small lobes and toes that continually break out
from a cooled crust. The surface texture of
pahoehoe flows varies widely, displaying all
kinds of bizarre shapes often referred to as lava
sculpture
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Lava Aa
Aa (pronounced "ah-ah") is a Hawaiian term for
lava flows that have a rough rubbly surface
composed of broken lava blocks called clinkers.
The incredibly spiny surface of a solidified aa
flow makes walking very difficult and slow.
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Lava Pillow
When basalts erupt underwater, they commonly form
pillow lavas, which are mounds of elongate lava
"pillows" formed by repeated oozing and quenching
of the hot basalt. First, a flexible glassy crust
forms around the newly extruded lava, forming an
expanded pillow. Next, pressure builds until the
crust breaks and new basalt extrudes like
toothpaste, forming another pillow.
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Pyroclastic MaterialBlocks

• A volcanic block is a solid rock fragment greater
  than 64 mm in diameter that was ejected from a
  volcano during an explosive eruption.

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Pyroclastic MaterialBombs

• Volcanic bombs are lava fragments that were
  ejected while viscous (partially molten) and
  larger than 64 mm in diameter. Many acquire
  rounded aerodynamic shapes during their travel
  through the air.

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Pyroclastic MaterialLapilli

• Rock fragments between 2 and 64 mm (0.08-2.5 in)
  in diameter that were ejected from a volcano
  during an explosive eruption are called Lapilli.

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Pyroclastic MaterialAsh

• Volcanic ash consists of rock, mineral, and
  volcanic glass fragments smaller than 2 mm (0.1
  inch) in diameter, which is slightly larger than
  the size of a pinhead.