Grotzinger • Jordan
Understanding Earth
Sixth Edition
Chapter 12:
VOLCANOES
© 2011 by W. H. Freeman and Company
Chapter 12
Volcanoes
About Volcanoes
• Volcanoes are windows through which
we can see the interior of the Earth.
• Volcanoes help us understand the plate
tectonic process and mantle convection.
• Volcanoes are also connected to Earth’s
atmosphere and hydrosphere.
Lecture Outline
1. Volcanoes as geosystems
2. Lavas and other volcanic deposits
3. Eruptive styles and landforms
4. Interactions of volcanoes with other
geosystems
5. The global pattern of volcanism
Lecture Outline
6. Volcanism and human affairs
1. Volcanoes as Geosystems
● Parts of the volcano
● hill or mountain made of:
● lavas
● other erupted materials
1. Volcanoes as Geosystems
● Parts of the geosystem
● rocks
● magmas and lavas
● processes of melting and
eruption
Pipe
Central vent
Lava flows
Side vent
Magma
chamber
Lithosphere
Volcanic
geosystem
Pipe
Central vent
Volcanic
geosystem
Lava flows
Side vent
Magma
chamber
Lithosphere
Magma, which
originates in the
asthenosphere...
Pipe
Central vent
Lava flows
Side vent
Magma
chamber
Lithosphere
Volcanic
geosystem
...rises through the
lithosphere to form
a crustal magma
chamber.
Magma, which
originates in the
asthenosphere...
Pipe
Central vent
Volcanic
geosystem
Lava flows
Side vent
Lavas erupt through
a central vent and
side vents,...
Magma
chamber
Lithosphere
...rises through the
lithosphere to form
a crustal magma
chamber.
Magma, which
originates in the
asthenosphere...
Pipe
Central vent
Lava flows
Side vent
Volcanic
geosystem
...accumulating on
the surface to form
a volcano.
Lavas erupt through
a central vent and
side vents,...
Magma
chamber
Lithosphere
...rises through the
lithosphere to form
a crustal magma
chamber.
Magma, which
originates in the
asthenosphere...
1. Volcanoes as Geosystems
● Functions of the geosystem
● volcanic plumbing systems
● volcanoes as chemical
factories
Thought questions for this chapter
Give a few examples of what geologists have learned
about Earth’s interior by studying volcanoes and volcanic
rocks.
2. Lavas and Other Volcanic Deposits
● Types of lava
● basaltic lavas (10001200ºC)
● aa
● pahoehoe
● pillow lavas
Pillow lavas on the sea floor
2. Lavas and Other Volcanic Deposits
● Types of lava (continued)
● andesitic lavas (<1000ºC)
● rhyolitic lavas (600800ºC)
Mt. St. Helens’ andesitic cone
2. Lavas and Other Volcanic Deposits
● Texture of volcanic rocks
● reflect conditions under which
they crystallized or formed
● vesicles (bubble holes)
● glassy texture (no crystals)
● pyroclasts (broken pieces)
Vesicles in basalt
2. Lavas and Other Volcanic Deposits
● Texture of volcanic rocks
● pyroclastic deposits
● volcanic ejecta (ash, bombs)
● pyroclastic flows (volcanic
tuffs and breccias)
Arenal, Costa Rica:
pyroclastic eruption
Volcanic ejecta bomb
Volcanic tuff
Volcanic breccia
Mt. Uzen, Japan:
pyroclastic ash flow
2. Lavas and Other Volcanic Deposits
● Eruptive styles and landforms
● central eruptions
● shield volcanoes
● volcanic domes
● cinder cones
● stratovolcanoes
● volcanic craters
● calderas
● diatremes
Eruptive styles
Eruptive
styles
Crater Lake,
Oregon
Ship Rock,
New Mexico
Diatreme
Diatreme (Ship Rock)
2. Lavas and Other Volcanic Deposits
● Eruptive styles and landforms
● eruptions from linear cracks
● fissure eruptions
● flood basalts
● ash-flow deposits
Fissure eruption:
Laki fissure,
Iceland
Sequence
of events:
formation
of a
fissure
eruption
Flood basalts:
Columbia
Plateau,
Washington
Thought questions for this chapter
Why are eruptions of stratovolcanoes generally more
explosive than those of shield volcanoes?
While on a field trip, you come across a volcanic
formation that resembles a field of sandbags. The
individual ellipsoid forms have a smooth, glassy surface
texture. What type of lava is this, and what information
does this give you about its history?
3. Interactions of Volcanoes
with Other Geosystems
● Volcanism and the hydrosphere
● fumaroles and geysers
● Volcanism and the atmosphere
● aerosols and ash
Fumarole:
Merapi volcano,
Indonesia
Old Faithful
geyser:
Yellowstone
National Park
4. Global Pattern of Volcanism
4. Global Pattern of Volcanism
● Basalt-producing spreading centers
● mantle source for lava
(decompression melting)
● axial volcanoes of mid-ocean
ridge
4. Global Pattern of Volcanism
4. Global Pattern of Volcanism
● Volcanism in subduction zones
● chains of volcanoes
● island arcs
● formation of new continental
crust
4. Global Pattern of Volcanism
● Intraplate volcanism: the mantle
plume hypothesis
● hot spots and mantle plumes
● sea mounts and island chains
● large igneous provinces
4. Global Pattern of Volcanism
4. Global Pattern of Volcanism:
Hawaiian Island Chain /
Emperor Seamounts
4. Global Pattern of Volcanism:
Yellowstone Volcanic Tracks
4. Global Pattern of Volcanism:
Large Igneous Provinces
4. Global Pattern of Volcanism:
Large Igneous Provinces
Thought questions for this chapter
Why are the volcanoes on the northwest side of the
Hawaiian Islands dormant whereas those on the southeast
side are more active?
5. Volcanism and Human Affairs
● Volcanic hazards
● lahars
● flank collapse
● caldera collapse
● eruption clouds
5. Volcanism and Human Affairs
● Mantle-plume hypothesis
● predicting eruptions
● controlling eruptions
5. Volcanism and Human Affairs
● Natural resources
● volcanic soils
● industrial materials
● ore formation
● heat energy
5. Volcanism and Human Affairs
5. Volcanism and Human Affairs: Potentially
Hazardous Volcanoes
5. Volcanism and Human Affairs:
Geothermal Energy
Thought questions for this chapter
What might be the effects on civilization of a Yellowstonetype caldera eruption, such as the one described at the
beginning of this chapter?
How do interactions between volcanic geosystems and
the climate system increase volcanic hazards?
Key terms and concepts
Andesitic lava
Ash-flow deposit
Basaltic lava
Caldera
Crater
Diatreme
Fissure eruption
Flood basalt
Geothermal energy
Hot spot
Hydrothermal activity
Lahar
Large igneous province
Mantle plume
Pyroclastic flow
Key terms and concepts
Rhyolitic lava
Shield volcano
Stratovolcano
Tuff
Volcanic geosystem
Volcano