Igneous Rocks and Volcanoes

1
Igneous Rocks and Volcanoes
2
View From Space - Klyuchevskaya, Russia
3
Cleveland Volcano, Alaska
4
Mount Etna From Space
5
Mount Etna From Space
6
Mount Etna From Space
7
Mount Etna
8
Shiveluch, Russia
9
Magma molten rock beneath the surfaceLava
molten rock on the surface
10
Igneous Rocks Cool from the Molten State

• Volcanic -- Erupted on Surface
• Plutonic -- Solidify Within Earth
• Large Grain Size ---gt Slow Cooling
• Volcanic Rocks -- Fine Grained
• Plutonic Rocks -- Coarse Grained
• Porphyritic TextureLarge Crystals in
  Fine-grained Setting

11
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 SeriesNaAlSi3O8......CaAl2Si2O8
• What Other Minerals Are Present? (Account for Fe,
  Mg)

12
Feldspars

• K - Feldspar KAlSi3O8
• Several Slightly Different Forms
• Microcline
• Orthoclase
• Plagioclase (Solid Solution)
• Albite NaAlSi3O8
• Anorthite CaAl2Si2O8
• Any Mixture of the Two Is Possible

13
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.

14
Bowen's Reaction Series
No igneous rock ever displays the whole sequence,
just a slice across the sequence.
15
Bowen's Series and Igneous Rocks
16
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
  

17
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

18
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

19
Some Igneous Rocks Are Named on Textural Criteria

• Pumice - Porous
• Obsidian - Glass
• Tuff - Cemented Ash
• Breccia - Cemented Fragments
• Porphyry - Fine Matrix, Large Crystals

20
Types of Volcanoes
21
A Cinder ConeWizard Island, Crater Lake, Oregon
22
Anatomy of a Cinder Cone, Hawaii
23
Tuff Ring Diamond Head, Hawaii
24
Tuff Ring Diamond Head, Hawaii
25
Shield Volcano Haleakala, Hawaii
26
Stratovolcano Mount Shasta, California
27
Shastina and Landslide Deposit
28
Lava Dome, California
29
Products of Eruptions

• Gases
• Steam
• Carbon Dioxide
• H2S
• SO2
• HCl
• HF

• Lava Flows
• Pyroclastic Debris
• Bombs
• Lapilli
• Ash
• Mudflows
• Landslides

30
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)

31
Pyroclastic Flow or Nuee Ardente (French Fiery
Cloud)
32
How Calderas Form
33
Crater Lake, Oregon
34
Jemez Caldera, New Mexico
35
Collapsing Volcanoes Mount Rainier
36
Collapsing Volcanoes - Hawaii
37
Evolution of Volcanoes

• An active volcanic landscape

38
Evolution of Volcanoes

• A volcanic landscape after a million years or so