Download 3. Type of lava

V. Volcanoes and Volcanism
A. Mafic Volcanism and Volcanic Rocks
B. Felsic Volcanism and Volcanic Rocks
Mafic Volcanism
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6. Characteristics of formations
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5. Types of Rocks
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4. Types of eruptions which controls
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3. Type of lava which controls
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2. Source of lava which controls
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1. Plate tectonics 
1. 2 . Source of Lava
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Partial melting of mantle
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Partial melting of dry mantle
At mantle plumes or
Divergent plate boundaries
3. Types of Lava
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Types of lava Basaltic
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Hot (>1000oC)
Non-Viscous (runny, flows easily)
“Dry” (no H2O or C02)
4. Types of Eruptions
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Non-explosive
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Lava flows,
streams, ponds, floods
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Fountains
Spatter cones
Pyroclastic eruptions
5. Types of Rocks
Composition and Texture
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Basalt
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‘A’a
Pahoehoe
Vesicular Basalt
Pillow Basalt
Columnar Jointing
Obsidian
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Volcanic Glass
Figs. 4.9, 4.11, 4.17, 4.18
6. Characteristic Formations
Fissures Through Crust
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Flood basalts and
basalt plateaus
Shield volcanoes
Cinder cones
Calderas atop of
Kilauea Shield
Hawaii Cinder Cone
Columnar Jointing in basalt floods
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As lava floods cool and
solidify
The basalt contracts and
Splits into hexagonal
columns
Devil’s Post Pile, California
Columnar
Jointing
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Columnar jointing
may occur in
volcanic stocks
(large cylindrical
core of volcanoes)
Devils Tower, Wyoming
Pillow Basalts
Evidence of
submarine eruptions
Volcanic Hazards
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Map out rift
zones
Use topography
to determine
flow direction
Rift Zones and Lava Flows
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Kilauea, Hawaii
Hawaii Hazards
B. Felsic Volcanism
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6. Characteristics of volcanoes
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5. Types of Rocks
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4. Types of eruptions
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3. Type of lava
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2. Source of lava
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1. Plate tectonics 
1, 2. Plate tectonics and
Sources of Lava
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Partial melting at
Subduction Zone
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Partial melting of
continental crust
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Convergent plate
boundaries
Fig. 3.24
3. Types of Lava
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Felsic
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Cool (<800oC)
Viscous
Gaseous (H2O, CO2)
4. Types of Eruptions
Fig. 4.1
Mt. St. Helen’s
Cascade Range
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Explosive
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Pyroclastic Flows
and surges
Lahars (saturated
pyroclastics)
Fig. 4.20
5. Types of Rocks
Composition and Texture
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Andesite (and Rhyolite)
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Pumice (quenched glass froth)
Porphyritic Texture (partial
crystallization and extrusion)
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Welded Tuffs (welded
pyroclastics)
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Breccias (welded, coarse,
angular pyroclatics)
1mm
6. Characteristics of Volcanism
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Lava Domes
Composite Volcanoes
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Layers of Pyroclastics
(or tephra), ash and
Lava flows
Pyroclastic
Layers
Mt. St. Helen’s Before and After
1 mile
Vocanic Hazards
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Volcanic Earthquakes
Directed Blast
Tephra
Volcanic Gases
Lava Flows
Pyroclastic Flows and
Surges
Lahars
Debris Avalanches,
Landslides, and Tsunamis
Locating Volcanoes and Volcanism
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Convergent Plate Boundaries Composite Volcanoes of Andesite
Mid-Ocean Ridges Pillow basalts forming new oceanic crust
Hot spots in oceans  Forming shield volcanoes
Hot spots and divergent boundaries on continents  Forming flood
basalts, shield volcanoes (maybe some composite volcanoes)