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Volcanic Activity

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Volcanic Activity Plumbing System of a Volcano Cross Section of the East Pacific Rise Volcanic Materials Lavas appearance depends upon viscosity Low viscosity ... – PowerPoint PPT presentation

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Title: Volcanic Activity


1
Volcanic Activity
2
Plumbing System of a Volcano
Fig. 5.1
3
Cross Section of the East Pacific Rise
Fig. 5.29
4
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

5
Basaltic Lavas
  • Pahoehoe rope-like, glassy
  • Aa fragmented, dull surfaces

Aa
Pahoehoe
6
Basaltic Lavas
  • Pillow lavas underwater pillow or tube
    shaped lava flow

7
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)

8
Volcanic Bombs
9
Volcanic Blocks
10
Volcanic Tuff
11
Volatile Gases Associated with Volcanism
  • Steam (H2O)
  • Carbon dioxide (CO2 )
  • Hydrogen sulfide (H2S)
  • Sulfur vapor
  • Many other constituents

12
Sulfur-encrusted fumeroleGalapagos Islands
Sulfur-encrusted fumerole Galapagos Islands
Fig. 5.26
Christian Grzimek/Photo Researchers
13
Volcanic Landforms
  • Shield volcanoes
  • Cinder cones
  • Sratovolcanoes or composite volcanoes
  • Domes
  • Calderas
  • Volcanic Necks and Pipes
  • Fissure Eruptions

14
Shield Volcanoes
  • Very large
  • Composed of low viscosity basalt
  • Volcanoes have a gentle, shield shape
  • Example Mauna Loa, Hawaii

15
Mauna Loa, Hawaii
16
Shield Volcano
Fig. 5.10
17
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

18
Cinder Cone
Fig. 5.12
19
Paricutin, Mexico
20
Paricutin, Mexico
21
Cerro Negro Cinder Cone, near Managua, Nicaragua
in 1968
Fig. 5.13
Mark Hurd Aerial Surveys
22
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23
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

24
Stratavolcano
25
Fujiyama, Japan
26
Mount Saint Helens Before May 1980
Mount Saint Helens, Before May, 1980
Emil Muench/Photo Researchers
27
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Mount Saint Helens After May, 1980
After May, 1980
David Weintraub/Photo Researchers
30
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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

32
Fig. 5.11
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Mount St. Helens lava dome
Lava Dome
Fig. 5.11
Lyn Topinka/USGS
34
Inyo Obsidian Domes-California
P. L. Kresan
35
Caldera
  • A large, circular depression produced by the
    collapse of a volcano following the emptying of a
    subterranean magma chamber
  • Example Crater lake, Oregon

36
Formation of a Caldera
Fig. 5.16
37
Crater Lake, Oregon
Fig. 5.17
Greg Vaughn/Tom Stack
38
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.

39
Shiprock, N.M.
40
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

41
1971 Fissure Eruption, Kilauea, Hawaii
42
Fissure Eruptions Form Lava Plateaus
Fig. 5.20
43
Extent of Columbia River Basalts
Fig. 5.22
44
Columbia Plateau Flow Basalts
Fig. 5.2
Martin G. Miller
45
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

46
The Worlds Active Volcanoes
Fig. 5.28
47
Volcanism Associated with Plate Tectonics
Fig. 5.30
48
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

49
Volcanic Hazards
  • Basaltic lavas (flows) may cover homes and roads,
    but flows move so slow that there is little loss
    of life

50
May 1990 Eruption of Kilauea, Hawaii
James Cachero/Sygma
51
January 17, 2002 Nyiragongo Volcano D.R. Congo
52
January 17, 2002 Nyiragongo Volcano D.R. Congo
53
January 17, 2002 Nyiragongo Volcano D.R. Congo
54
January 17, 2002 Nyiragongo Volcano D.R. Congo
55
January 17, 2002 Nyiragongo Volcano D.R. Congo
56
Pyroclastic Activity
  • Usually rapid and explosive, accompanied by large
    volumes of poisonous gases. Can produce large
    losses of life and property.

57
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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60
Escaping a Pyroclastic Flow at Mount Unzen,
Japan, 1991A type of Nuee Ardente (glowing
ash flow eruption)
Fig. 5.9
AP/Wide World Photos
61
Mt. Pelee, 1902
62
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63
Pyroclastic Flow from the 1998 Eruption on
Montserrat
R.S.J. Sparks
64
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

65
Fig. 5.18
Maritime Safety Agency, Japan
66
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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70
Lahar from Nevado del Ruíz (1985)
Barbara and Robert Decker
71
U.S. Active Volcanoes
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