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