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Volcanic Activity. Plumbing System of a Volcano. Fig. 5.1. Cross Section of the East Pacific Rise. Fig. 5.29. Volcanic Materials. Lavas – appearance depends upon viscosity Low viscosity – low SiO 2 lavas; high T; low volatile content - smooth lava

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volcanic materials
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
basaltic lavas
Basaltic Lavas
  • Pahoehoe – rope-like, glassy
  • Aa – fragmented, dull surfaces



basaltic lavas6
Basaltic Lavas
  • Pillow lavas – underwater “pillow” or “tube” shaped lava flow
pyroclastic materials
Pyroclastic Materials
  • Pyroclastic name based upon fragment size

ash – sand size

lapilli – walnut size

bombs (> 1 inch, cools in flight)

blocks (> 1 inch, solid before ejection)

volatile gases associated with volcanism
Volatile Gases Associated with Volcanism
  • Steam (H2O)
  • Carbon dioxide (CO2 )
  • Hydrogen sulfide (H2S)
  • Sulfur vapor
  • Many other constituents
sulfur encrusted fumerole galapagos islands

Sulfur-encrusted fumerole:

Galapagos Islands

Sulfur-encrusted fumerole:Galapagos Islands

Fig. 5.26

Christian Grzimek/Photo Researchers

volcanic landforms
Volcanic Landforms
  • Shield volcanoes
  • Cinder cones
  • Sratovolcanoes or composite volcanoes
  • Domes
  • Calderas
  • Volcanic Necks and Pipes
  • Fissure Eruptions
shield volcanoes
Shield Volcanoes
  • Very large
  • Composed of low viscosity basalt
  • Volcanoes have a gentle, shield shape
  • Example: Mauna Loa, Hawaii
cinder cone
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: Paŕicutin, Mexico

Cinder Cone

Fig. 5.12

stratovolcanoes or composite volcano
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
mount saint helens before may 1980
Mount Saint Helens – Before May 1980

Mount Saint Helens, Before May, 1980

Emil Muench/Photo Researchers

volcanic domes
Volcanic Domes
  • Small, dome or “inverted” cup-shaped landforms
  • Usually composed o rhyolie
  • Example: Lava Dome in the Mount Saint Helens crater
mount st helens lava dome
Mount St. Helens lava dome





Lyn Topinka/USGS

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

Fig. 5.17

Greg Vaughn/Tom Stack

volcanic necks and pipes
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.
fissure eruptions
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
columbia plateau flow basalts
Columbia Plateau Flow Basalts

Fig. 5.2

Martin G. Miller

relationship of volcanism and plate tectonics
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

types of volcanic hazards
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
volcanic hazards
Volcanic Hazards
  • Basaltic lavas (flows) may cover homes and roads, but flows move so slow that there is little loss of life
pyroclastic activity
Pyroclastic Activity
  • Usually rapid and explosive, accompanied by large volumes of poisonous gases. Can produce large losses of life and property.
vesuvian type pyroclastic eruption
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 >2000 people were buried intact by large ash falls.
Escaping a Pyroclastic Flow at Mount Unzen, Japan, 1991A type of Nuee Ardente (“glowing ash flow” eruption)

Fig. 5.9

AP/Wide World Photos

phreatic explosion
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) >100 megaton explosion; 36,000 people killed by tsunami or “tidal wave” produced by the explosion

Fig. 5.18

Maritime Safety Agency, Japan

volcanic mudflows lahars
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
lahar from nevado del ru z 1985
Lahar from Nevado del Ruíz (1985)

Barbara and Robert Decker