Volcanoes

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Volcanoes

• Lab 5

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Concepts

• Location of active volcanoes
• Volcanism
• 3 categories
• Viscosity
• 5 types of extrusive volcanism
• Examples of each
• 3 types of lava flows
• Dangers of volcanic eruptions

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What do you notice about their locations?
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Volcanism

• Definition the origin and movement of magma
• Three categories
• Extrusive magma is expelled onto surface
• Intrusive magma solidifies in the shallow crust
  near the surface. Can be exposed after
  weathering.
• Plutonic magma solidifies deep inside the crust.
• Viscosity The ability for lava to flow.
  Reflective of the amount of silica present in the
  magma.
• LOW silica LOW viscosity nonexplosive
• HIGH silica HIGH viscosity explosive

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VolcanismExtrusive Examples
Mt. Shasta, CA
Mt. Fuji, Japan
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VolcanismIntrusive Examples
Right Stone Mountain, GA Below Devils Tower, WY
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VolcanismPlutonic Examples
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5 Types of Extrusive Volcanism1. Shield Volcano

• Central vent allows magma from chamber to spill
  out, slowly building the volcano in layers.
• Produces wide, gently sloping mountains
• Best example Hawaiian volcanoes (right Mauna
  Loa)

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5 Types of Extrusive Volcanism2. Composite
Volcano

• Stratovolcano
• Central vent allows magma to come up from chamber
  below
• Produces symmetrical, steep-sloped mountains
• Most explosive type of volcano
• Examples Mt Fuji,Mt Shasta, Mt St Helens

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5 Types of Extrusive Volcanism2. Composite
Volcano example Mt St Helens in 1980
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5 Types of Extrusive Volcanism3. Caldera Volcano

• Formed when the upper part of a volcano collapses
• The magma chamber below is (partially or
  completely) emptied after an eruption
• The emptied magma chamber can no longer support
  the weight of the overlying rock
• The overlying rock collapses into itself, forming
  a circular basin
• Volcanic activity can continue if there is still
  magma in the chamber below
• Example Crater Lake, OR

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5 Types of Extrusive Volcanism3. Caldera Volcano
example Crater Lake, OR
Crater Lake was formed after Mt Mazama (a
stratovolcano) erupted and collapsed back in on
itself.
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5 Types of Extrusive Volcanism4. Cinder Cones

• Smallest mountain formation of all volcanic
  landform types
• Cone-shaped peaks build up from small, solid
  particles, ejected into air by small volcanic
  vent
• Generally lt1,500 high
• Example Wizard Island

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5 Types of Extrusive Volcanism4. Cinder Cone
example Wizard Island in Crater Lake, OR
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5 Types of Extrusive Volcanism5. Lava Dome

• Plug Dome
• High-silica lava exits from a vent. Due to its
  high viscosity (doesnt flow very fast or far),
  it builds up into a dome.
• Effectively plugs the main vent. Can still emit
  ash, gases, and even lava.
• Example Lava Dome in Mt St Helens crater.

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3 Types of Lava Flows

• Aa
• Clinky
• Blocky, choppy lava flows that does not flow well
  over land
• Pahoehoe
• Smooth, unbroken lava
• Ropy surface
• Pillow Lava
• Lava emerges from underwater volcanic vents
• Lava cools crusts when it hits colder water
• When crust fractures, lava oozes out and creates
  billowing pillows

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Aa
Pahoehoe
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Pillow Lava
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Dangers of Volcanic Eruptions

• Burning Hot Lava
• Earthquakes, Landslides and Tsunamis
• These are often related an earthquake might jar
  some land loose, resulting in a landslide. The
  earthquake may set off the tsunami. Also, if the
  landslide falls into the ocean, can trigger a
  tsunami.
• Mudslides (Lahars)
• Ash Fallout
• Pyroclastic Flow (nuée ardente)

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Dangers of Volcanic EruptionsMudslide (Lahar)
examples
Mt. Pinatubo, Philippines 1991 eruption
Mt. St. Helens, WA 1980 eruption
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Dangers of Volcanic EruptionsAsh fallout
example Mt. Pinatubo, Philippines 1991 eruption
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Dangers of Volcanic EruptionsAsh fallout
example Mt. St. Helens 1980 eruption
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Dangers of Volcanic EruptionsPyroclastic flow
example Mt St Helens 1980 eruption

• Hot gases, ash, rock that become a fluid cloud
  that move down the side of the volcano. Can
  travel great distances.
• nuée ardente French for glowing cloud