Igneous Rocks and Volcanoes

View From Space - Klyuchevskaya, 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 ClassificationHow 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)

FeldsparsK - 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 RocksDunite  Gabbro   Diorite                   GraniteFluid               Lava Is...                 ViscousMild                Eruptions                 Violent

Type of VolcanoShield Volcano     Stratovolcano    Plug Dome

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

• H2S

• 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 VolcanoesAn active volcanic landscape

Evolution of VolcanoesA volcanic landscape after a million years or so