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 KAlSi 3 O 8 • Plagioclase Series NaAlSi 3 O 8 ......CaAl

2 Si 2 O 8

What Other Minerals Are Present?

Fe, Mg) (Account for

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

Bowen's Series and Igneous Rocks

Volcanic Rocks

(Rare) Basalt Andesite

Plutonic Rocks

Dunite Gabbro Diorite 1200 C

Melting Point

Mg, Fe Rapid Usually Dark

Rich In...

Weathering Color

Rhyolite Granite 700 C Si, Na, K Slow Often Light

Bowen's Series and Volcanoes

Volcanic Rocks

(Rare) Basalt Andesite

Plutonic Rocks

Dunite Gabbro Diorite Fluid Mild

Lava Is...

Eruptions Type of Volcano

Shield Volcano Stratovolcano Rhyolite Granite Viscous Violent 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 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