Igneous Rocks and Volcanoes
View From Space - Klyuchevskaya, Russia
Cleveland Volcano, Alaska
Mount Etna From Space
Mount Etna From Space
Mount Etna From Space
Mount Etna
Shiveluch, Russia
Magma – molten rock beneath
the surface
Lava – molten rock on the
surface
Igneous Rocks Cool from the
Molten State
• Volcanic -- Erupted on Surface
• Plutonic -- Solidify Within Earth
Large Grain Size ---> Slow Cooling
• Volcanic Rocks -- Fine Grained
• Plutonic Rocks -- Coarse Grained
Porphyritic Texture:
Large Crystals in Fine-grained Setting
Igneous Rock Classification
How Much Silica? (account for Si)
• Excess - Rock Has Quartz
• Just Enough to Form Other Silicates
• Deficient - Silica-Poor Minerals (Like Olivine)
What Feldspars? (Account for Al, Ca, K, Na )
• Potash Feldspar KAlSi3O8
• Plagioclase Series
NaAlSi3O8......CaAl2Si2O8
What Other Minerals Are Present? (Account for
Fe, Mg)
Feldspars
K - Feldspar: KAlSi3O8
• Several Slightly Different Forms:
• Microcline
• Orthoclase
Plagioclase (Solid Solution)
• Albite:
NaAlSi3O8
• Anorthite:
CaAl2Si2O8
• Any Mixture of the Two Is Possible
Bowen's Reaction Series
• The geologist N.L. Bowen found that
minerals tend to form in specific sequences
in igneous rocks
• These sequences could be assembled into a
composite sequence.
Bowen's Reaction Series
No igneous rock ever displays the whole sequence, just a slice
across the sequence.
Bowen's Series and Igneous Rocks
Bowen's Series and Igneous
Rocks
Volcanic Rocks
(Rare) Basalt Andesite
Rhyolite
Plutonic Rocks
Dunite Gabbro Diorite
Granite
1200 C
Melting Point
700 C
Mg, Fe
Rich In...
Si, Na, K
Rapid
Weathering
Slow
Usually Dark
Color
Often Light
Bowen's Series and Volcanoes
Volcanic Rocks
(Rare) Basalt Andesite
Rhyolite
Plutonic Rocks
Dunite Gabbro Diorite
Granite
Fluid
Lava Is...
Viscous
Mild
Eruptions
Violent
Type of Volcano
Shield Volcano Stratovolcano Plug Dome
Basalt and Andesite
• Hard to tell apart by eye
• Distinction is mostly chemical
• Why it Matters:
– Basalt = Planetary Raw Material
– Andesite = Basalt reacting with silica rich crust
Some Igneous Rocks Are
Named on Textural Criteria
•
•
•
•
•
Pumice - Porous
Obsidian - Glass
Tuff - Cemented Ash
Breccia - Cemented Fragments
Porphyry - Fine Matrix, Large Crystals
Types of Volcanoes
A Cinder
Cone:
Wizard
Island, Crater
Lake, Oregon
Anatomy of a Cinder Cone, Hawaii
Tuff Ring: Diamond Head, Hawaii
Tuff Ring: Diamond Head, Hawaii
Shield Volcano: Haleakala,
Hawaii
Stratovolcano: Mount Shasta,
California
Shastina and Landslide Deposit
Lava Dome, California
Products of Eruptions
Lava Flows
Pyroclastic Debris
• Bombs
• Lapilli
• Ash
Mudflows
Landslides
Gases
• Steam
• Carbon Dioxide
• H 2S
• SO2
• HCl
• HF
Environmental Hazards of
Volcanoes
Pollution
• SO2, HCl in
Water
Lava Flows
Falling Ejecta
Ash Falls
• Building Collapse
• Crop Destruction
Mudflows
• Direct Damage
(Colombia, 1985)
• Floods (Several Types)
Blast (Mt. St. Helens, 1980)
Pyroclastic Flow (St. Pierre,
1902)
Gas (Lake Nyos,
Cameroon, 1986)
Pyroclastic Flow or Nuee
Ardente (French: Fiery Cloud)
How Calderas Form
Crater Lake, Oregon
Jemez Caldera, New Mexico
Collapsing Volcanoes – Mount Rainier
Collapsing Volcanoes - Hawaii
Evolution of Volcanoes
An active volcanic landscape
Evolution of Volcanoes
A volcanic landscape after a million years or so