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Classroom presentations to accompany Understanding Earth, 3rd edition prepared by Peter Copeland and William Dupré University of Houston Chapter 5 Volcanism
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Fig. 5.1 Plumbing System of a Volcano
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May 1990 Eruption of Kilauea, Hawaii James Cachero/Sygma
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Volcanic rocks Major difference between plutonic and volcanic rocks is texture, a reflection of cooling rate.
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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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Types of Lava aapahoehoe
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Kim Heacox/DRX Fig. 5.3 PahoehoeLava Aa Lava
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Martin G. Miller Fig. 5.2 Columbia Plateau Flow Basalts
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Tephra Pyroclastic flow Air-fall Mudflow (lahar)
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Pyroclastic flow (nueé ardente) Mixture of hot gases, ash, and rocks forming a super-heated and dense current capable of moving 150 km/hr.
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R.S.J. Sparks Pyroclastic Flow from the 1998 Eruption on Montserrat
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AP/Wide World Photos Fig. 5.9 Escaping a Pyroclastic Flow at Mount Unzen, Japan, 1991
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Science Source/Photo Researchers Fig. 5.7 Volcanic Bomb
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Doug Sokell/Visuals Unlimited Fig. 5.8 Volcanic Breccia
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Submarine eruptions Pillow basalt Phreatic explosions
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Woods Hole Oceanographic Institute Fig. 5.4 Pillow Lava
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Maritime Safety Agency, Japan Fig. 5.18 Phreatic Explosion in the Pacific
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Glen Oliver/Visuals Unlimited Fig. 5.5 Vesicular Basalt
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Gregory G. Dimijian/Photo Researchers Fig. 5.6 Pyroclasic Eruption at Arenal Volcano, Costa Rica
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Eruptive styles and landforms Shield volcanoes Stratovolcanoes (composite) Domes and cones Fissure eruptions (flood basalts) Submarine eruptions
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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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NASA, Viking Orbiter 1 Olympus Mons Shield Volcano
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Cinder cones Formed of pyroclastics only Steep sides — ~30 degrees Relatively small Short duration of activity
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Fig. 5.12 Cinder Cone
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Mark Hurd Aerial Surveys Fig. 5.13 Cerro Negro Cinder Cone, near Managua, Nicaragua in 1968
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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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Fig. 5.11
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P. L. Kresan Inyo Obsidian Domes-California
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Lyn Topinka/USGS Fig. 5.11 Lava Dome
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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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Fig. 5.14 Composite Volcano
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Raga/The Stock Market Fig. 5.15 Mt Fujiyama, Japan
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Emil Muench/Photo Researchers Before May, 1980
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David Weintraub/Photo Researchers After May, 1980
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Caldera Depression at top of volcano produced during an eruption May have younger domes within it
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Fig. 5.16
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Greg Vaughn/Tom Stack Fig. 5.17 Crater Lake, Oregon
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Fred Padula Fig. 5.19 Shiprock, New Mexico an exposed volcanic pipe (diatreme )
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Fissure eruptions When low-viscosity lava is issued from cracks in the Earth tens of kilometers long.
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1971 Fissure Eruption, Kilauea, Hawaii
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Fig. 5.20 Fissure Eruptions Form Lava Plateaus
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Tony Waltham Fig. 5.21 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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Fig. 5.22
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Martin G. Miller Fig. 5.2 Columbia Plateau Flow Basalts
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Welded Tuff: California Gerals and Buff Corsi/Visuals Unlimited Fig. 5.23 1 foot
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S. Aramaki Fig. 5.24 Ash-flow Sheets Draping Topography, Japan
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Caution: Volcanologist at Work Maurice Krafft/Photo Researchers Fig. 5.25
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Volcanic Mudflow (lahar): A mixture of water and pyroclastic material in a concrete-like slurry capable of moving up to 100 km/hour!
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Barbara and Robert Decker 23,000 killed in 1985 by volcanic mudflows, Nevada del Ruiz
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Other material ejected from volcanoes Volatile material Steam (H 2 O) Carbon dioxide (CO 2 ) Hydrogen sulfide (H 2 S) Many other constituents
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Christian Grzimek/Photo Researchers Fig. 5.26 Sulfur-encrusted fumerole: Galapagos Islands
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Simon Fraser/Photo Researchers Fig. 5.27 Stokkur geyser in Iceland
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Tectonic setting of volcanoes Convergent plate boundaries Divergent plate boundaries Within plate “hotspots”
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The World’s Active Volcanoes Fig. 5.28
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Fig. 5.29 Cross Section of the East Pacific Rise
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Volcanism Associated with Plate Tectonics Fig. 5.30
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Effects of volcanoes on humans Growth of Hawaii Geothermal energy Effect on climate Volcanic catastrophes »Mt. St. Helens »Vesuvius »Krakatoa »Mt. Pelée »Montserrat
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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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E. Tad Nichols San Juan, Mexico, Buried by Paricutin Lava Flows
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Roger Ressmeyer/Corbis Fig. 5.31 Scientists Investigate Mt. Pinatubo’s Caldera
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U.S. Active Volcanoes
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