Download EXTRUSIVE IGNEOUS ROCKS Magma and Lava

EXTRUSIVE IGNEOUS
ROCKS
Volcanoes and Volcanic Rocks
Igneous Rock Names
and Compositions
• Composition • Intrusive
Rock Name
Name
•
•
•
•
Ultramafic
Mafic
Intermediate
Silicic (felsic)
•
•
•
•
Peridotite
Gabbro
Diorite
Granite
• Volcanic
Rock Name
•
•
•
•
(Komatiite)
Basalt
Andesite
Rhyolite
Magma and Lava
• Magma is the term for any molten
silicate material, whether below
the surface or on top.
• Volcanic rocks are erupted on the
surface.
– Volcanic rocks are fine-grained (<1
mm)
• Lava is the term for a magma on
the surface.
1
Most Volcanoes are at Plate Boundaries
Geologic Settings
2
Basaltic Eruptions
• Low Viscosity
• High Temperature (1000 - 1200ºC)
• Normally Quiescent Lava Flows
– Aa - early, low temperature, blocky
flow
– Pahoehoe - later high temperature
ropy flow
– Pillow Lavas - underwater flow
• Edifice
– Shields
– Cinder cones
Pahoehoe, Hawaii (Basalt)
Aa, Hawaii (Basalt)
3
Pillow Lava, Kauai (Basalt)
Nyiragongo, Congo (Zaire)
4
Goma, Congo (Zaire)
Skjaldbreidur Shield, (Basalt)
Cinder
Cone,
Pu’uo’o,
Hawaii
(Basalt)
5
Cinder Cone + Caldera, (Basalt)
Basaltic Eruptions
• Low Viscosity
• High Temperature (1000 - 1200ºC)
• Normally Quiescent Lava Flows
– Aa - early, low temperature, blocky
flow
– Pahoehoe - later high temperature
ropy flow
– Pillow Lavas - underwater flow
• Edifice
– Shields
– Cinder cones
Most Volcanoes are at Plate Boundaries
6
Andesite Eruptions
•
•
•
•
•
Higher viscosity (higher polymerization )
Lower temperature
More water, more explosive
Subduction zone volcanism
Flows
– Viscous lava flows
– Pyroclastic flows
• Edifice
– Composite Cones
Geologic Settings
Andesite Flow, Mt Shasta
7
Composite Cone, Mt. Fuji
Composite Cone, Mt. Daisen
Composite Cone, Mt. St Helens
8
9
Andesite Eruptions
•
•
•
•
•
Higher viscosity (higher polymerization )
Lower temperature
More water, more explosive
Subduction zone volcanism
Flows
– Viscous lava flows
– Pyroclastic flows
• Edifice
– Composite Cones
10
Rhyolite Eruptions
• Very high viscosity
• Low temperature (600 - 800ºC)
• Massive Pyroclastic eruptions
– Air fall (pumice)
– Ash Flow (Nuée Ardente) Tuff
– Obsidian Flows
• Edifice
– Caldera (5 - 25 km)
– Resurgent dome
Rhyolite Eruptions
• Associated Phenomena
– Hot Springs
– Geysers
– Fumaroles
• Geologic Setting
– Continental Margins and Interiors
– Subduction Zones
Geologic Settings
11
Pumice = Glass foam
Ash-Flow
Tuff
with AirFall Units
Ash-Flow Tuff Unit
Non-Welded Top
Welded Core
Vitrophyre
Non-welded base
12
Silicic Tuff Units (Jemez, NM)
Obsidian Flow
Non-welded
Air-Fall Units
Sulfur Fumarole, Nysseros
Caldera with Cinder Cone
Crater Lake, OR
13
Geyser
Old Faithful
(Yellowstone)
Rhyolite Eruptions
• Very high viscosity
• Low temperature (600 - 800ºC)
• Massive Pyroclastic eruptions
– Air fall (pumice)
– Ash Flow (Nuée Ardente) Tuff
– Obsidian Flows
• Edifice
– Caldera (5 - 25 km)
– Resurgent dome
14
Andesite Eruptions
•
•
•
•
•
Higher viscosity (higher polymerization )
Lower temperature
More water, more explosive
Subduction zone volcanism
Flows
– Viscous lava flows
– Pyroclastic flows
• Edifice
– Composite Cones
Basaltic Eruptions
• Low Viscosity
• High Temperature (1000 - 1200ºC)
• Normally Quiescent Lava Flows
– Aa - early, low temperature, blocky
flow
– Pahoehoe - later high temperature
ropy flow
– Pillow Lavas - underwater flow
• Edifice
– Shields
– Cinder cones
Geologic Settings
15
Most Volcanoes are at Plate Boundaries
16