Volcanic Activity

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Volcanic Activity
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Plumbing System of a Volcano
Fig. 5.1
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Cross Section of the East Pacific Rise
Fig. 5.29
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Volcanic Materials

• Lavas appearance depends upon viscosity
• Low viscosity low SiO2 lavas high T low
  volatile content - smooth lava
• High viscosity high SiO2 lavas low T high
  volatile content rough lava
• Pyroclastic material fragmented material due to
  explosive volcanic activity
• Associated with magmas with high volatile gas
  content
• Volcanic gases water, carbon dioxide, sulfur,
  sulfur dioxide, hydrogen sulfide

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Basaltic Lavas

• Pahoehoe rope-like, glassy
• Aa fragmented, dull surfaces

Aa
Pahoehoe
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Basaltic Lavas

• Pillow lavas underwater pillow or tube
  shaped lava flow

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Pyroclastic Materials

• Pyroclastic name based upon fragment size
• ash sand size
• lapilli walnut size
• bombs (gt 1 inch, cools in flight)
• blocks (gt 1 inch, solid before ejection)

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Volcanic Bombs
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Volcanic Blocks
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Volcanic Tuff
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Volatile Gases Associated with Volcanism

• Steam (H2O)
• Carbon dioxide (CO2 )
• Hydrogen sulfide (H2S)
• Sulfur vapor
• Many other constituents

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Sulfur-encrusted fumeroleGalapagos Islands
Sulfur-encrusted fumerole Galapagos Islands
Fig. 5.26
Christian Grzimek/Photo Researchers
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Volcanic Landforms

• Shield volcanoes
• Cinder cones
• Sratovolcanoes or composite volcanoes
• Domes
• Calderas
• Volcanic Necks and Pipes
• Fissure Eruptions

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Shield Volcanoes

• Very large
• Composed of low viscosity basalt
• Volcanoes have a gentle, shield shape
• Example Mauna Loa, Hawaii

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Mauna Loa, Hawaii
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Shield Volcano
Fig. 5.10
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Cinder Cone

• A relatively small volcanic cone composed of
  unconsolidated pyroclastic material
• Cinder cones may be composed of basalt,
  andesite, or rhyolite fragments
• Usually active for a short period of time
• Example Paricutin, Mexico

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Cinder Cone
Fig. 5.12
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Paricutin, Mexico
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Paricutin, Mexico
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Cerro Negro Cinder Cone, near Managua, Nicaragua
in 1968
Fig. 5.13
Mark Hurd Aerial Surveys
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Stratovolcanoes or Composite Volcano

• Steep, symmetrical volcanic cones
• Composed of alternating layers of lava and
  volcanic ash
• Usually composed of andesitic material
• Examples Fujiyama, Japan Mt. Saint Helens, Wa

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Stratavolcano
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Fujiyama, Japan
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Mount Saint Helens Before May 1980
Mount Saint Helens, Before May, 1980
Emil Muench/Photo Researchers
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Mount Saint Helens After May, 1980
After May, 1980
David Weintraub/Photo Researchers
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Volcanic Domes

• Small, dome or inverted cup-shaped landforms
• Usually composed o rhyolie
• Example Lava Dome in the Mount Saint Helens
  crater

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Fig. 5.11
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Mount St. Helens lava dome
Lava Dome
Fig. 5.11
Lyn Topinka/USGS
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Inyo Obsidian Domes-California
P. L. Kresan
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Caldera

• A large, circular depression produced by the
  collapse of a volcano following the emptying of a
  subterranean magma chamber
• Example Crater lake, Oregon

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Formation of a Caldera
Fig. 5.16
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Crater Lake, Oregon
Fig. 5.17
Greg Vaughn/Tom Stack
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Volcanic Necks and Pipes

• Remnants of volcanic vents and conduit systems
• Exposed after erosion has removed the
  surrounding, soft volcanic rubble and country
  rock
• Examples Shiprock, N.M.

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Shiprock, N.M.
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Fissure Eruptions

• Very extensive, sheet-like lava flows that
  originate from long cracks (fissures) rather than
  central vents or volcanoes.
• Flood lavas or basalts are associated with this
  type of activity
• Example Columbia river basalts, Washington and
  Oregon

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1971 Fissure Eruption, Kilauea, Hawaii
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Fissure Eruptions Form Lava Plateaus
Fig. 5.20
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Extent of Columbia River Basalts
Fig. 5.22
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Columbia Plateau Flow Basalts
Fig. 5.2
Martin G. Miller
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Relationship of Volcanism and Plate Tectonics

• Volcanoes of the Earth are associated with
• Plate Boundary Volcanism
• Divergent Plates
• Convergent Plate
• Interplate Volcanism
• Hot spot or plume volcanoes

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The Worlds Active Volcanoes
Fig. 5.28
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Volcanism Associated with Plate Tectonics
Fig. 5.30
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Types of Volcanic Hazards

• Lava Flows e.g. Hawaii, 1998
• Gas e.g. Lake Nyos (Cameroon), 1984
• 1700 people killed
• Ash fall e.g. Mt. Pinatubo, 1991
• Pyroclastic flows e.g. Mt. Pelee, 1902
• 28,000 killed
• Lahars (mudflows) e.g. Nevado del Ruiz, 1985
• 23,000 killed
• Tsunami e.g. Krakatoa, 1883
• 36,417 killed

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Volcanic Hazards

• Basaltic lavas (flows) may cover homes and roads,
  but flows move so slow that there is little loss
  of life

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May 1990 Eruption of Kilauea, Hawaii
James Cachero/Sygma
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January 17, 2002 Nyiragongo Volcano D.R. Congo
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January 17, 2002 Nyiragongo Volcano D.R. Congo
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January 17, 2002 Nyiragongo Volcano D.R. Congo
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January 17, 2002 Nyiragongo Volcano D.R. Congo
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January 17, 2002 Nyiragongo Volcano D.R. Congo
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Pyroclastic Activity

• Usually rapid and explosive, accompanied by large
  volumes of poisonous gases. Can produce large
  losses of life and property.

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Vesuvian Type Pyroclastic Eruption

• Mount Vesuvius, Italy (79 A.D.)
• Three day rain of volcanic ash buried the cites
  of Pompeii and Herculaneum
• The cities along with gt2000 people were buried
  intact by large ash falls.

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Escaping a Pyroclastic Flow at Mount Unzen,
Japan, 1991A type of Nuee Ardente (glowing
ash flow eruption)
Fig. 5.9
AP/Wide World Photos
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Mt. Pelee, 1902
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Pyroclastic Flow from the 1998 Eruption on
Montserrat
R.S.J. Sparks
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Phreatic explosion

• Produced by groundwater seepage into the interior
  of a volcano
• Water is converted into superheated steam with
  subsequent explosive release (flash vaporization)
• Example Krakatoa, Indonesia (1883) gt100 megaton
  explosion 36,000 people killed by tsunami or
  tidal wave produced by the explosion

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Fig. 5.18
Maritime Safety Agency, Japan
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Volcanic Mudflows - Lahars

• Hot volcanic gases and phyroclastic eruptions can
  melt glacial ice on the flanks of volcanoes,
  producing a fast moving wall of mud that can
  travel tens of miles
• Example Nevado del Ruíz, Colombian Andes (1985)
  20,000 deaths

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Lahar from Nevado del Ruíz (1985)
Barbara and Robert Decker
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U.S. Active Volcanoes