1. Volcanism and Extrusive Rocks Physical Geology

2. Volcanism and Earth’s Systems
Atmosphere originally created from gases released by magmas
Hydrosphere produced by condensation of volcanic water vapor
Biosphere both positively and negatively influenced by volcanism
Lava flows and ash weather to produce fertile soils
Violent eruptions can destroy nearly all life in their paths
Large amounts of ash and volcanic gases in atmosphere can trigger rapid climate changes and contribute to mass extinctions

3. Volcanic Eruptions Lava is produced when magma reaches Earth’s surface
Explosive eruptions can produce rapidly cooled rock fragments called pyroclasts
Size range from dust (ash) to boulders (blocks and volcanic bombs)
Calm oozing of magma out of the ground produces lava flows
Pyroclastics and lava flows form extrusive igneous rocks
Lava flows and pyroclasts pile up to form volcanoes

4. Living with Volcanoes Mythology, religion and volcanoes Hawaii - Pele
Iceland - Loki
Growth of volcanic islands (Hawaii)
Geothermal energy
Natural steam harnessed as clean
energy resource
Climatic effects
Very large eruptions can result in measurable global cooling
Resulting crop failures and famines
Volcanic catastrophes
Mt. St. Helens, Pompeii, Krakatoa,
Tambora, Crater Lake

5. Crater Lake, Oregon

6. Eruptive Violence and Physical Characteristics of Lava
Violence of eruptions controlled by:
Amount of Dissolved gases in the magma
Water vapor, carbon dioxide, sulfur dioxide, etc.
The more dissolved gases, the more fluid the lava
Ease/difficulty of gases escaping to atmosphere
Viscosity- a fluid’s resistance to flow
Silica content
Higher silica contents produce higher viscosities
Lava temperature
Cooler lavas have higher viscosities

7. Extrusive Rocks and Gases
Scientific Investigation of Volcanism
Rocks, gases and events from observed eruptions compared to similar lavas elsewhere to infer the nature of past activity
Rock Composition
Rhyolite - high silica; light color
Basalt - low silica; dark color
Andesite - intermediate silica and color

8. Extrusive Textures
Texture - appearance of a rock with respect to size, shape and arrangement of its grains
Texture terms:
Glassy - glass without mineral crystals
ex: Obsidian
Fine-grained - most crystals < 1 mm
ex: Basalt
Porphyritic - larger crystals in a matrix of much finer crystals or glass
ex: Andesite

9. Extrusive Textures Vesicular/Frothy - trapped gas bubbles
Vesicular basalt
Pumice
Fragmental - particles blasted apart by explosive eruptions
Dust and ash (<2 mm)
Cinders (2-64 mm)
Blocks and bombs (>64 mm)

10. Volcanic Landforms Vent - opening through which lava erupts
Crater - basin-like depression over the vent at the summit of the volcano
Caldera - volcanic depression much larger than the original crater, having a diameter of at least 1 km

11. Types of Volcanoes Shield volcanoes Cinder cones Broad Gently sloping
Composed of solidified lava flows
Flows often contain lava tubes
Cinder cones
Small
Steeply sloping
Composed of a pile of loose cinders

12. Types of Volcanoes Composite volcanoes Volcanic domes
Also called stratovolcanoes
Moderately to steeply sloping
Constructed of alternating layers of pyroclastic debris and solidified lava flows
Composed primarily of intermediate composition volcanic rocks (i.e., andesite)
Most common type of volcano at convergent plate boundaries (e.g., Pacific Ring of Fire) ex: Cascade volcanos
Volcanic domes
Extremely high viscosity, degassed, felsic lavas (often glassy, e.g., obsidian)

14. Other Eruption Types Flood eruptions Submarine eruptions
Very fluid (basalts)
Extremely large in volume
Create extensive lava plateaus
Eruption times correspond with largest mass extinction events
Submarine eruptions
Nearly always basaltic
Mid-ocean ridge eruptions
Pillow basalts
Columbia river flood basalts
Pillow basalts

16. Volcanism on Other Planets
Shield volcanoes
Venus, Mars, Io
Lava domes
Venus, Moon
Flood eruptions
Very fluid (basalts)
Extremely large in volume
Extensive flat lava plains (Moon, Mars, Venus, Mercury?)
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Olympus Mons on Mars
Volcanic eruption on Io
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Lava domes on Venus
Lava channel in volcanic
plains on Moon