Tectonic Settings of Igneous Activity

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Tectonic Settings of Igneous Activity
Fig. 4.8
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Volcanic Island Arc, Indonesia
Fig. 4.8
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Oceanic Hot Spot
Hawaii
Fig. 4.8
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Oceanic hot spots
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Lava flow at Volcanoes National Park,
Hawaii
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Continental Volcanic ArcN. Cascades
Fig. 4.8
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Volcanic Island Arc Java, Indonesia
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The Worlds Active Volcanoes
Fig. 5.28
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Plumbing System of a Volcano
Fig. 5.1
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Volcanism Associated with Plate Tectonics
Fig. 5.30
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Material ejected from volcanoes

• Nonvolatile material

• Lava magma that has flowed on the surface of the
  Earth.
• Tephra fragments that solidified in the air
  during eruption.

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Eruptive styles and landforms

• Fissure eruptions (flood basalts)
• Shield volcanoes
• Domes and cones
• Stratovolcanoes (composite)
• Submarine eruptions

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Fissure eruptions

• When low-viscosity lava erupts from cracks in the
  Earth tens of kilometers long.

Laki fissure (Iceland) erupted in 1783 extruding
the largest lava flow in human history.
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Lava floods

• Mafic lava solidifies to basalt
• Fissure flows
• Plateau basalts
• Columnar structure or jointing

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Flood basalts
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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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Shield volcanoes

• Low-viscosity lava flows
• Low-silica magma mafic
• Basalt
• Pahoehoe
• Aa
• Gently sloping flanks between 2 and 10 degrees
• Tend to be very large
• Spatter cone minor feature

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Shield Volcano
Fig. 5.10
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Mauna Loaworlds largest structure- 10km above
ocean base
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Hawaii, Kilauea- September 9th 2002
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Aa Lava
Pahoehoe Lava
Kim Heacox/DRX
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Pillow Lava
Fig. 5.4
Woods Hole Oceanographic Institute
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Cinder Cone
Cinder Cone

• Formed of pyroclastics only
• Steep sides 30 degrees
• Relatively small
• Short duration of activity

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Cerro Negro Cinder Cone, near Managua, Nicaragua
in 1968
Fig. 5.13
Mark Hurd Aerial Surveys
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Pyroclasic Eruption at Arenal Volcano, Costa Rica
Fig. 5.6
Gregory G. Dimijian/Photo Researchers
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Pumice
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Volcanic Bomb
Fig. 5.7
Science Source/Photo Researchers
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Breccia
Volcanic Breccia
Fig. 5.8
Doug Sokell/Visuals Unlimited
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Welded Tuff California
Fig. 5.23
1 foot
Gerals and Buff Corsi/Visuals Unlimited
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Ash-flow Sheets Draping Topography, Japan
Fig. 5.24
S. Aramaki
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Volcanic domes

• Forms above a volcanic vent
• Viscous lava usually silica-rich (or cooler
  magma)
• Associated with violent eruptions

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Mt. St. Helens
Lava Dome
Lyn Topinka/USGS
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Composite volcano

• Alternating pyroclastic layers and lava flows
• Slopes intermediate in steepness
• Intermittent eruptions over long time span
• Mostly andesite
• Distribution
• Circum-Pacific
• Belt (Ring of Fire)
• Mediterranean Belt

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Mt Fujiyama, Japan
Fig. 5.15
Raga/The Stock Market
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Caldera formation
Caldera
Fig. 5.16
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Santorini I
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Santorini II
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Santorini III
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Santorini IV
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Crater Lake, Oregon
Fig. 5.17
Greg Vaughn/Tom Stack
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Eruption
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What To Do When a Volcano Erupts
If Volcanic Ash begins to fall Stay
indoors. If you are outside, seek shelter
such as a car or building. If you cannot
find shelter, breathe through a cloth, such as a
handkerchief, preferably a damp cloth to filter
out the ash. When the air is full of ash,
keep your eyes closed as much as possible.
Heavy falls of ash seldom last more than a few
hours -- only rarely do they last a day or more.
Heavy fall of ash may cause darkness during
daylight hours and may temporarily interfere with
telephone, radio, and television
communications. Do not try to drive a car
during a heavy fall of ash -- the chance of
accident will be increased by poor visibility.
The thick accumulation of ash could increase
the load on roofs, and saturation of ash by rain
could be an additional load. Ash should be
removed from flat or low-pitched roofs to prevent
a thick accumulation. Volcanic Mudflows
(Lahars) Valleys that head on the volcano may be
the routes of mudflows which carry boulders and
resemble wet flowing concrete. Mudflows can move
faster than you can walk or run, but you can
drive a car down a valley faster than a mudflow
will travel. When driving along a valley that
heads on a volcano, watch up the river channel
and parts of the valley floor for the occurrence
of mudflows. Before crossing a highway
bridge, look upstream. Do not cross a
bridge while a mudflow is moving beneath it.
The danger from a mudflow increases as you
approach a river channel and decreases as you
move to higher ground. Risk of mudflows
also decreases with increasing distance from a
volcano. If you become isolated, do not
stay near a river channel, move upslope.
During an Eruption - Move Away From A Volcano
- Not Toward It Most Important -- Don't Panic -
Keep Calm
USGS Earthquake Information Bulletin
46
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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May 1990 Eruption of Kilauea, Hawaii
James Cachero/Sygma
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San Juan, Mexico, Buried by Paricutin Lava Flows
E. Tad Nichols
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U.S. Active Volcanoes
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Mt. St. Helens I
Before May, 1980
Emil Muench/Photo Researchers
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Mt. St. Helens II
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Mt. St. Helens III
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Mt. St. Helens IV
After May, 1980
David Weintraub/Photo Researchers
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Japan
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Mt. Pinatubo
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Mudflow or Lahar

• A mixture of water and pyroclastic material and
  sand, gravel, and boulders, in a concrete-like
  slurry capable of moving up to 100 km/hour
• Flow is supported by collisions between clasts

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Mudflow
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23,000 killed in 1985 by volcanic mudflows,
Nevada del Ruiz
Barbara and Robert Decker
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Columbia
The only remaining buildings in Armero, Colombia,
72 km dowstream from Nevado del Ruiz volcano,
destroyed and partially buried by lahars on
November 13, 1985. Lahars reached Armero about
2.5 hours after an explosive eruption sent hot
pyroclastic flows across the volcano's broad ice-
and snow-covered summit area. Although flow
depths in Armero ranged only from 2 to 5 m, three
quarters of its 28,700 inhabitants perished.
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Mt. Rainier
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Mt. Rainier I
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Escaping a Pyroclastic Flow at Mount Unzen,
Japan, 1991
Pyroclastic flow (nueé ardente)

• Mixture of hot gases, ash, and rocks forming a
  super heated and dense current capable of moving
  150 km/hr.
• Buoyancy due to heated gas, density due to ash-
  turbulence keeps particles suspended in flow

AP/Wide World Photos
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Montserrat
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Pyroclastic flows erupted by Mount Pinatubo on
June 15, 1991, buried the Marella River valley
(SW of Pinatubo) with pumice, ash, and other
volcanic rocks to depths of between 50 and 200 m.
This eruption was one of the largest in the 20th
century, depositing about 5.5 km3 of rock debris
over nearly 400 km2.