Volcanoes

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Volcanoes
Volcanology The study of volcanoes Vulcanologists
scientists who study volcanoes
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Anatomy of a Volcano

• Central vent where major eruption occurs
• Flank vent secondary vent
• Magma chamber where magma stays until pressure
  forces it up the vent
• Fumarole flank vent that releases gas only

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A. Magma and Lava

• Volcanism any activity that includes the
  movement of magma towards or on the Earth's
  surface

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Magma

• Magma liquid rock - volcanic rock found below
  the Earth's surface solid rock can become magma
  when liquid (water) is added (subduction zones)

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Lava magma that erupts onto the Earth's
surface Magma can flow onto Earth's surface
through an opening - vent - or crack - fissure A
volcano is any structure formed on Earth's
surface by the vent and volcanic material that
builds up around it
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B. Major Volcano Zones

• 1. Subduction zones
• a. oceanic lithosphere melts as it plunges
  beneath the continental plate, water added to
  mantle material creates magma ex. Ring of Fire
• b. ocean trenches where oceanic subducts under
  oceanic creates volcanic islands arcs
• ex. Aleutian Islands, AK, Japan

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• 2. Mid-ocean ridges
• magma flows up through rift zone, can form
  underwater volcanoes
• ex. Iceland - MOR above sea-level contains many
  fissures

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• 3. Hot spots - in the middle of a plate is a spot
  where magma flows upward plate moves over the
  hot spot and form a volcano volcano is carried
  away by plate and become extinct
• ex. Hawaiian Islands
• A new Hawaiian island forming underwater - Loihi

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C. Types of Lava

• The violence of an eruption depends on
• type of magma (minerals)
• temperature of the magma
• The amount of dissolved gases

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Viscosity

• viscosity - resistance to flow
• More viscous - flows slowly
• Less viscous - flows quickly

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Mafic Lava

• Dark colored
• Contains magnesium and iron
• Makes up oceanic crust
• Is hot and thin, less viscous - flows quickly -
  gases escape easily - "quiet flow"
• ex. Hawaiian volcanoes

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Pahoehoe

• If mafic lava cools slowly forms wrinkly crust -
  pahoehoe - Hawaiian for "ropy"

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Aa

• if it cools quickly it forms rough, jagged
  chunks - aa

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Lava Tubes

• If outer edges cool quickly and inner lava still
  flows creates tunnel called lava tubes

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Pillow Lava

• Lava flowing out of fissures on ocean floor
  cools quickly forms rounded pillow lava

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Felsic Lava

• Is light colored
• Contains silica
• Makes up continental crust
• Is cool and thick, more viscous - lots of trapped
  gases - explosive!
• ex. continental volcanoes - Mt. St. Helens

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D. Pyroclastic material

• These are rock fragments sent into the air from
  explosive felsic lava eruptions
• They are described by size

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Volcanic Dust and Ash

• Volcanic dust lt 0.25 mm in diameter
• Volcanic ash gt 0.25 - 2 mm
• These may travel far from the eruption!!

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Lapilli, Bombs and Blocks

• Lapilli "little stones
• 2 - 64 mm they fall near the vent
• Volcanic bombs -clumps of lava sent spinning thru
  the air
• Volcanic blocks - large rocks blasted from
  fissure can be house-size

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Pyroclastic flow

• The most deadly aspect to volcanic eruptions
• Combination of hot, toxic gases coming from
  vents, up to 1000 C, and 750 km/hr
• More dense than air, so rolls into villages
  killing victims quickly (e.g. Pompeii)
• Video http//videos.howstuffworks.com/discovery/
  7153-volcanoes-pyroclastic-flow-video.htm

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E. Volcano Typeshow do volcanoes form?
http//videos.howstuffworks.com/discovery/27683-as
signment-discovery-formation-of-volcanoes-video.ht
m
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1. Shield Volcanoes

• Form when hot, mafic lava builds up around the
  vent - form cones
• Have wide, broad bases and gently sloping sides,
  medium height
• ex. Hawaiian Islands

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2. Cinder Cone Volcanoes

• Very steep sloped sides, short (few hundred
  meters)
• Formed from layers of ash and other explosive
  pyroclastic materials
• ex. Sunset Crater, AZ

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3. Composite Volcanoes, or Stratovoclanoes

• Composite means a mix of unlike things, strato-
  means layer
• Formed from alternating layers of lava and ash
• ex. Mt. Fuji, Mount Hood, Mt. St. Helens

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Crater

• A pit at top of volcano, formed when material is
  blown out
• Usually widens due to weathering and erosion
• Often a smaller cone may form inside crater
• When filled with water a crater lake - Crater
  Lake National Park, Oregon

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Caldera

• A large, basin shaped depression formed from a
  crater
• If magma chamber is empty, the crater collapses -
  forms caldera
• Also formed from huge eruptions
• ex. Krakatau

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F. Predicting Volcanic Eruptions
Scientists use the following to predict EQs 1.
seismographs monitor for small EQs from growing
pressure, that often precede eruptions 2. slight
bulging of surface from magma pushing out 3.
change in ground tilt
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• 4. gases
• 5. history of previous eruptions
• Very few volcanoes have a lengthy history to
  study constant monitoring is required

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G. Extraterrestrial Volcanoes

• Moon - was once volcanically active - evidence of
  lava flows
• Craters - a result of bombardment by meteorites)

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• Mars - many volcanoes and volcanic features
• Olympic Mons - shield volcano - 28 km above
  surface, base 600 km probably stayed on lava
  source for millions years (no plate tectonics)
• Still active volcanoes on Mars?? Not sure, but it
  is seismically active

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Io

• Moon of Jupiter
• Many active volcanoes - more eruptions more
  material ejected than on Earth each month
  probably sulfuric lava
• Spectacular eruptions - umbrella-shaped plumes
  hundreds km high
• Vulcanism probably caused by friction

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Importance of Volcanoes

• all original rocks on Earth's crust were formed
  from cooled magma and/or lava
• water vapor from volcanoes early in Earth's
  history may have formed oceans
• gases from early eruptions formed the atmosphere
• volcanism adds new crust and reshapes planet each
  year

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Supervolcanoes

• What are they?
• http//6.cn/watch/3812360.html
• Several on youtube.com
• ex under Yellowstone National Park
• http//dsc.discovery.com/convergence/supervolcano/
  supervolcano.html

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Tsunami and landslides

• Alaska http//geology.com/records/biggest-tsunami
  .shtml
• Volcano driven East coast US (when ?)
  http//www.history.com/videos/mega-disasters-east-
  coast-tsunamimega-disasters-east-coast-tsunami
• 10 ways the Earth will end