Chapter Four
Volcanoes and Volcanism
VOLCANOES AND VOLCANISMS
Classification of volcanoes
Lava tube formation
Causes for Volcanism
Types of Lava
Basaltic lava flow
Basaltic pillow lavas
Basaltic pillow lavas-contd.
Basaltic pillow lavas-contd.
Tephra Layers
Pyroclastic Flows
Lahars
Gas emissions
Volcanic Landforms
Determined by the composition of Lava
• Shield volcanoes…gentle slope, effusive eruptionnon-explosive
Crater and Caldera
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Volcanic Domes
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Composite (Stratovolcanoe)
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Pyroclastic Cones (Cinder Cones)
Produce great amount of solid volcanic fragments
Alternating layers of pyroclast and solid lava
Loose pyroclastic materials around a vent
Lava-plateau formation
The Gorda ridge
Submarine volcano, infiltration
Submarine volcano, eruption
Muddy meltwater
Volcanic domes, gas escape
Volcanic domes, explosion
Mount Mazama
Mount Mazama-contd
Mount Mazama-contd.
Mount Mazama-contd.
Mount Mazama-contd.
PYROCLASTIC MATERIAL
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TEPHRA:
– CLASSIFIED BY SIZE
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• SMALL: VOLCANIC DUST & ASH- 1 MICRON
• MEDIUM: CINDERS OR LAPILLI (>1-62 MICRON)
• LARGE: VOLCANIC BOMBS (>64 MICRON)
RECORDERS IN LAKES
VOLCANIC MUDFLOWS-LAHAR
SECONDARY VOLCANIC EFFECTS:
• ACIDIC PRECIPITATION
• GLOBAL CLIMATIC CHANGES–
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REDUCED SUNLIGHT
REDUCED TEMPERATURE
PRODUCTS OF VOLCANISM
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OCCURRENCE:
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MAFIC LAVA (BASALT)-MOST COMMON
ANDESITIC LAVA – INTERMEDIATE
FELSIC LAVA – LEAST COMMON
ERUPTIVE STYLES
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ERUPTIVE STYLES:
– EFFUSIVE ERUPTION: NONEXPLOSIVE, BASALTIC
• CENTRAL VENT ERUPTIONS
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PRODUCE SHIELD VOLCANOES
PRODUCE CALDERAS AND FLANK ERUPTIONS
– FISSURE ERUPTIONS ON LAND PRODUCE LAVA PLATEAUS OR FLOOD BASALTS
– SUBAQUEOUS ERUPTIONS (MAINLY OCEAN)
– SUBGLACIAL ERUPTIONS (MAINLY UNDER GLACIERS)
Volcanic Hazards
Ash flow eruption
Ash flow -contd
Chapter Summary - 4
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Benefits of Volcanic Eruption/Environmental Effects
Active, Dormant, and Extinct Volcano
Pyroclastic Volcanoes
Definition of Viscosity
Relationship between Viscosity, Temperature, Si content in magma
Basaltic, Andesitic, Rhyolitic Lava – Most volcanic eruptions occur in what type of lava
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Classification of Tephra
Definition of Lahar
Contents of Volcanoes
Volcanoes, Pyroclastic occurrence
Effective means of dealing with volcanic hazards