Volcanoes

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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
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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 ?

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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)
• -

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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)

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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

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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

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______________ 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
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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

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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

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Other volcanic landforms

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

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A lava dome on Mt. St. Helens
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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 ?
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3. Within plates, rising plumes of hotter mantle
feed hot spots multiple volcanoes result ? like
Hawaii.
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Distribution of some of the worlds major
volcanoes
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Distribution of magnitude 5 or greater
earthquakes, 1980 - 1990
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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

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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.