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