Volcanoes

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Volcanoes
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7.1 Volcanoes and Plate Tectonics

• Magma hot liquid rock
• Volcanism movement of magma toward suface
• Lava magma on the surface
• Vent structure which magma flows to surface
• Volcano material built up around the vent
• Fissures cracks, Iceland
• Hot spots volcanism in plate

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http//www.nationalgeographic.com/forcesofnature/i
nteractive/index.html?sectionv
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Where are Volcanoes? P.11

• Subduction zones
• Mid-ocean ridges
• Hot spots
• - found within a plate not at a plate
  boundary

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Magma p.12

• Magma is a complex high-temperature fluid
  substance. Temperatures of most magmas are in the
  range 700C to 1300C
• May reach as hot as 1600C.
• Called magma when in the earth and lava when it
  is on the surface of the earth.

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Felsic Magma p.13

• SiO2 gt70
• Fe-Mg 2
• Temp lt 900C
• Viscosity High
• Eruptive behavior explosive
• Distribution hot spots in continental crust
  (Yellowstone National Park), continental rifts,
  island arcs

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Yellowstone

• The Yellowstone Caldera is the largest volcanic
  system in North America. It has been termed a
  "supervolcano" because the caldera was formed by
  exceptionally large explosive eruptions.
• The amount of ash and gases released into the
  atmosphere probably caused significant impacts to
  world weather patterns and led to the extinction
  of many species, primarily in North America.

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Gases from Volcanoes p.14

• Water vapor is typically the most abundant
  volcanic gas, followed by carbon dioxide and
  sulfur dioxide.
• Sulfur dioxide kills vegetation and can cause
  acid rain.

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Homework

• After viewing the video, write a paragraph that
  states what fact you found the most interesting
  (disturbing) and why?

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Eruptions
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7.2 Volcanic Eruptions

• A. Kinds of Eruptions
• B. Volcanic Rock Fragments
• C. Volcanic Features
• 1. Types of volcanoes
• 2. Craters and Calderas
• D. Predicting Volcanic Eruptions

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Volcanic Eruptions

• 2 types of lava chemically, effects eruptions
  intensity
• 1. mafic lava dark, rich in Mg and Fe
• From ocean crust
• Less explosive, quiet
• 2. felsic lava lighter color, lots of silica,
  much less Mg and Fe
• Found in continental crust
• More explosive, contains dissolved gases
• Other types are in between
• Pahoehoe mafic lava cooling rapidly will
  wrinkle
• Aa when the lava breaks into chunks
• Pillow lava midocean ridge cools so rapidly
  forms round blobs

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Pahoehoe

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Aa
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A. Kinds of Eruptions

• If magma has a lot of gases more explosive
• Ocean islands usually quiet
• Continental volcanoes with felsic lava have
  cooler and thicker lava so traps gases (H2O and
  CO2) big explosions

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B. Volcanic Rock Fragments

• Felsic lava explodes so throws materials
• Pyroclastic material rock fragments (some still
  molten, others cooled)
• Volcanic ash - lt2 mm
• Volcanic dust - lt.25 mm
• Lapilli - lt .64 mm
• Volcanic bombs red-hot lava cools in the air in
  shape of spiral or round bomb
• Volcanic blocks big solid rocks as big as a
  house

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bombs
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Volcanoes Can Cause Climate Change!

• Ash from a large volcano can shut out the
  sunlight for hundreds of miles.

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C. Volcanic Features

• What it looks like
• 1. Types of volcanoes
• 2. Craters and Calderas

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1. Types of volcanoes

• 1. Shield volcanoes cones with broad base and
  gentle slope, made up of lava layers
• Hawaii
• 2. Cinder cones cone is made up of fragments
  ejected
• 3. Composite volcanoes (stratovolcanoes)
• Combination of layers of lava and fragments from
  some quiet and expolsive eruptions
• Ex. Mt. Fuji, Rainier, Hood, Shasta
• St. Helens

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Types
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2. Craters and Calderas

• Crater funnel-shaped on the top vent
• Explosion forms
• Caldera depression from collapsed crater
• Crater Lake National Park

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Caldera
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Crater Lake - Oregon
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D. Predicting Volcanic Eruptions

• Not where we need to be yet
• Saves lives
• Seismographs
• Temp
• Pressure
• Bulging surface
• Gases given off
• History/past
• Dormant for long periods can be active

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7.3 Extraterrestrial volcanism

• Moon
• Mars
• Lo

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Moon

• Surface covered with craters meteorites
• Lava flow evidence does show volcanic activity
  long ago
• Nothing active
• No plates for movement or convection current
  evidence
• ? Not sure how

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Mars

• See pictures of
• None prove active
• They are much larger than earths because no
  continental drift

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Lo

• Moon of Jupiter
• Pictures of active volcanoe
• Think the material is sulfur and sulfur dioxide
  from color
• Constantly erupting

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