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Volcanoes

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Title: Volcanoes


1
Volcanoes
Geology 12 Citadel High School
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Gas
What comes out of a volcano?
Most common H2O - water CO2 Carbon Dioxide SO2
Sulfur Dioxide HCl hydrochloric acid
4
What comes out of a volcano?
Lava
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A Pahoehoe lava flow
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A Typical aa flow
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Ash
What comes out of a volcano?
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A volcanic bomb
Bomb is approximately 10 cm long
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The Nature of Volcanic Eruptions
  • Factors determining the violence or
    explosiveness of a volcanic eruption
  • _______________ of the magma
  • _______________ of the magma
  • ________________ in the magma
  • The above three factors control the viscosity of
    the magma which in turn controls the nature of an
    eruption

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The Nature of Volcanic Eruptions
  • Viscosity is a measure of a materials resistance
    to flow
  • Example ____________is more viscous then
    ________ ? Most viscous to least viscous ?

11
The Nature of Volcanic Eruptions
  • Factors affecting viscosity
  • ___________________ - Hotter magmas are less
    viscous (more runny)
  • ___________________
  • Gas content affects magma mobility
  • Gases expand within a magma as it nears the
    Earths surface due to decreasing pressure
  • The violence of an eruption is related to how
    easily gases escape from magma
  • __________________(what its made of) - Silica
    (SiO2) content
  • Higher silica content higher viscosity like
    molasses (e.g., felsic lava such as rhyolite
    St. Helens)
  • Lower silica content lower viscosity or more
    fluid-like behavior (e.g., mafic lava such as
    basalt Hawaii)
  • -

12
Materials extruded from a volcano
  • Lava Flows
  • ___________________ are much more fluid
  • Types of basaltic flows
  • ________________ lava (resembles a twisted or
    ropey texture)
  • _______ lava (rough, jagged blocky texture)

13
Materials extruded from a volcano
  • Pyroclastic materials ____________________
  • Types of pyroclastic debris
  • ____________________ - fine, glassy fragments
  • ________________- porous rock from frothy lava
  • _______________ - walnut-sized material
  • _______________ - pea-sized material
  • Particles larger than lapilli
  • _____________ - hardened or cooled lava
  • _____________ - ejected as hot lava

14
Shield Volcanoes
  • Types of Volcanoes
  • _____________________
  • Broad, slightly domed-shaped
  • Composed primarily of basaltic lava
  • Generally cover large areas
  • Produced by mild eruptions of large volumes of
    lava
  • Mauna Loa on Hawaii is a good example

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____________Volcano
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____________ (Hawaii) A typical shield volcano
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____________ Volcanoes
  • Types of Volcanoes continued
  • Cinder cone
  • Built from ejected lava (mainly cinder-sized)
    fragments
  • Steep slope angle
  • Rather small volcanoes in size
  • Frequently occur in groups

18
______________ a cinder cone near Flagstaff,
Arizona
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___________________ also known as
_______________________
  • Types of volcanoes continued
  • Composite cone (Stratovolcano)
  • Most are located adjacent to the Pacific Ocean
    (e.g., Fujiyama, Mt. St. Helens)
  • Large, classic-shaped volcano (1000s of ft. high
    several miles wide at base)
  • Composed of embedded lava flows and layers of
    pyroclastic debris

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A composite volcano
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_______________ a typical composite
volcano
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Mt. St. Helens after its 1980 eruption
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Mt. St. Helens following the 1980
eruption
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Volcanic Hazards
Lava flows Ash fall Pyroclastic
flows Mudflows Volcanic Gases Tsunami
25
Other volcanic landforms include
  • ____________________
  • Steep-walled depressions at the summit
  • Size generally exceeds 1 km in diameter
  • ____________________
  • Consists of ash, pumice, and other fragmental
    debris

26
Caldera a hole that forms after a volcano has
collapsed
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Other volcanic landforms include
  • Pyroclastic flows continued
  • Material is propelled from the vent at a high
    speed
  • _______________ eruptions and lava plateaus
  • Fluid basaltic lava extruded from crustal
    fractures called fissures
  • e.g., Hawaii, Iceland

28
Other volcanic landforms
  • ___________________
  • Bulbous mass of congealed lava
  • Most are associated with explosive eruptions of
    gas-rich magma

29
A lava dome on Mt. St. Helens
30
Other volcanic landforms
  • Volcanic pipes and necks
  • Pipes are short conduits that connect a magma
    chamber to the surface
  • Volcanic necks (e.g., Ship Rock, New Mexico) are
    resistant vents left standing after erosion has
    removed the volcanic cone

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Formation of a volcanic neck
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1. At spreading centers (on the ocean floor),
low pressure triggers mantle meltingfluid
basaltic magma rises.
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2. Explosive volcanoes form at subduction
zones ?
35
3. Within plates, rising plumes of hotter mantle
feed hot spots multiple volcanoes result ? like
Hawaii.
36
Distribution of some of the worlds major
volcanoes
37
Distribution of magnitude 5 or greater
earthquakes, 1980 - 1990
38
Volcanoes and Climate
  • Explosive eruptions emit _________________________
    of gases and ______________________________ into
    the atmosphere which filter out and reflect a
    portion of the incoming solar radiation
  • Examples of volcanism affecting climate
  • Mount Tambora, Indonesia 1815
  • Krakatau, Indonesia 1883
  • Mount Pinatubo, Philippines - 1991

39
Connections
It is not by chance that earth quakes and
volcanoes are located in the same areas around
the earth! Plate tectonic _______________________
_____ are the location of most volcanoes and
most earthquakes.
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