Classroom presentations
to accompany
Understanding Earth, 3rd edition
prepared by
Peter Copeland and William Dupré
University of Houston
Chapter 5
Volcanism
Plumbing System of a Volcano
Fig. 5.1
May 1990 Eruption of Kilauea, Hawaii
James Cachero/Sygma
Volcanic rocks
Major difference between
plutonic
and volcanic rocks is texture, a
reflection of cooling rate.
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.
Types of Lava
aa
pahoehoe
Aa Lava
Pahoehoe
Lava
Kim Heacox/DRX
Fig. 5.3
Columbia Plateau Flow Basalts
Martin G. Miller
Fig. 5.2
Tephra
• Pyroclastic flow
• Air-fall
• Mudflow (lahar)
Pyroclastic flow
(nueé ardente)
Mixture of hot gases, ash, and
rocks
forming a super-heated and dense
current capable of moving 150
km/hr.
Pyroclastic Flow from the 1998
Eruption on Montserrat
R.S.J. Sparks
Escaping a
Pyroclastic
Flow at Mount
Unzen, Japan,
1991
AP/Wide World Photos
Fig. 5.9
Volcanic Bomb
Science Source/Photo Researchers
Fig. 5.7
Volcanic Breccia
Doug Sokell/Visuals Unlimited
Fig. 5.8
Submarine eruptions
• Pillow basalt
• Phreatic explosions
Pillow Lava
Woods Hole Oceanographic Institute
Fig. 5.4
Phreatic
Explosion
in the
Pacific
Maritime Safety Agency, Japan
Fig. 5.18
Vesicular Basalt
Glen Oliver/Visuals Unlimited
Fig. 5.5
Pyroclasic
Eruption at
Arenal
Volcano,
Costa Rica
Gregory G. Dimijian/Photo Researchers
Fig. 5.6
Eruptive styles and landforms
• Shield volcanoes
• Stratovolcanoes (composite)
• Domes and cones
• Fissure eruptions (flood basalts)
• Submarine eruptions
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
Shield Volcano
Fig. 5.10
Olympus Mons
Shield Volcano
NASA, Viking Orbiter 1
Cinder cones
•
•
•
•
Formed of pyroclastics only
Steep sides — ~30 degrees
Relatively small
Short duration of activity
Cinder Cone
Fig. 5.12
Cerro Negro
Cinder Cone,
near
Managua,
Nicaragua
in 1968
Mark Hurd Aerial Surveys
Fig. 5.13
Volcanic domes
• Forms above a volcanic vent
• Viscous lava — usually silicarich (or cooler magma)
• Associated with violent
eruptions
Fig. 5.11
Inyo Obsidian Domes-California
P. L. Kresan
Lava
Dome
Lyn Topinka/USGS
Fig.
5.11
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
Composite Volcano
Fig. 5.14
Mt Fujiyama, Japan
Raga/The Stock Market
Fig. 5.15
Before May, 1980
Emil Muench/Photo Researchers
After May, 1980
David Weintraub/Photo Researchers
Caldera
• Depression at top of volcano
produced during an eruption
• May have younger domes within it
Fig. 5.16
Crater Lake, Oregon
Greg Vaughn/Tom Stack
Fig. 5.17
Shiprock, New Mexico
an exposed volcanic pipe
(diatreme)
Fred Padula
Fig. 5.19
Fissure eruptions
When low-viscosity lava is
issued from cracks in the
Earth
tens of kilometers long.
1971 Fissure Eruption, Kilauea, Hawaii
Fissure Eruptions Form Lava Plateaus
Fig. 5.20
Laki fissure
(Iceland) erupted
in 1783
extruding the
largest lava flow
in human history.
Tony Waltham
Fig. 5.21
Lava floods
• Mafic lava — solidifies to basalt
• Fissure flows
–Plateau basalts
• Columnar structure or jointing
Fig. 5.22
Columbia Plateau Flow Basalts
Martin G. Miller
Fig. 5.2
Welded Tuff: California
Gerals and Buff Corsi/Visuals Unlimited
1 foot
Fig. 5.23
Ash-flow Sheets Draping
Topography, Japan
S. Aramaki
Fig. 5.24
Caution: Volcanologist at Work
Maurice Krafft/Photo Researchers
Fig. 5.25
Volcanic Mudflow (lahar):
A mixture of water and
pyroclastic
material in a concrete-like slurry
capable of moving up to 100
km/hour!
23,000 killed in 1985 by volcanic
mudflows, Nevada del Ruiz
Barbara and Robert Decker
Other material ejected from volcanoes
Volatile material
• Steam (H2O)
• Carbon dioxide (CO2 )
• Hydrogen sulfide (H2S)
• Many other constituents
Sulfur-encrusted fumerole:
Galapagos Islands
Christian Grzimek/Photo Researchers
Fig. 5.26
Stokkur
geyser in
Iceland
Simon Fraser/Photo Researchers
Fig. 5.27
Tectonic setting of volcanoes
• Convergent plate boundaries
• Divergent plate boundaries
• Within plate “hotspots”
The World’s Active Volcanoes
Fig. 5.28
Cross Section of the East Pacific Rise
Fig. 5.29
Volcanism Associated with
Plate Tectonics
Fig. 5.30
Effects of volcanoes on
humans
•
•
•
•
Growth of Hawaii
Geothermal energy
Effect on climate
Volcanic catastrophes
»Mt. St. Helens
»Vesuvius
»Krakatoa
»Mt. Pelée
»Montserrat
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
San Juan, Mexico,
Buried by Paricutin Lava Flows
E. Tad Nichols
Scientists Investigate Mt. Pinatubo’s Caldera
Roger Ressmeyer/Corbis
Fig. 5.31
U.S. Active
Volcanoes