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 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 KAlSi 3 O 8 Plagioclase Series NaAlSi 3 O CaAl 2 Si 2 O 8 What Other Minerals Are Present? (Account for Fe, Mg)

Feldspars K - Feldspar: KAlSi 3 O 8 Several Slightly Different Forms: Microcline Orthoclase Plagioclase (Solid Solution) Albite: NaAlSi 3 O 8 Anorthite: CaAl 2 Si 2 O 8 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

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

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

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 2 S SO 2 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