Igneous Rocks, Minerals, and Volcanos Allan Treiman LPI

Plan of Talk  Tyrrany of Three –Three types of volcanos –Three types of lavas  Volcanos in terms of Lava Properties and Environments  Lava Properties in terms of Atoms  Igneous Rocks and Minerals

Three Types of Volcanos  Shield  Composite / Stratovolcano  Cinder Cone

But So Many More …  Caldera Complex ‘Super- Volcano’  Lava Plateau  Dome  Single Flow  Tuff Ring  And …

What Controls the Shape of a Volcano?  Properties of lava –Viscosity of lava (runny or stiff) –Dissolved Gas - Explosive or Effusive –Solid grains in lava.  Volume of lava erupted  Single or Multiple eruptions  Environment around eruption

Lava Properties: Viscosity  Different sorts of lavas are stiffer or runnier  What is lava? –Molten material in the Earth –Solidifies at surface conditions  Many sorts of ‘lava’ –Most common is silicate - abundant SiO 4 4- –Molten sulfur, carbonate, iron oxide –Mud is not lava on Earth (but “mud volcanos”) –Water is not lava on Earth (but is elsewhere)

Silicate Lavas  Large Range of Viscosity –Basalt - as runny as motor oil –Andesite - stiffer than taffy –Rhyolite/Granite - like window glass  Depends on silica - SiO 2 –Basalt: < 52% SiO 2 in chemical analysis –Andesite: % SiO 2 –Dacite: % SiO 2 –Rhyolite: > 68 % SiO 2

Why does silica matter?  Si - O bonds much stronger than others  Silica tetrahedra, SiO 4 4- polymerize  In lava, single silica tetrahedra flow easily, like little balls  In lava, large silicate polymers flow poorly, like noodles

Why does Water Matter?  Force for explosive eruptions –Water vapor bubbles out as magma nears surface –No vapor, no explosion!  Stiff water-rich magma makes foam (pumice)& shards of glassy ash  Pumice + ash and water vapor can flow together as a ‘slurry’ = an ash flow

Ash flow = pyroclastic flow = ‘nuee ardent’

Caldera Complex “Super-Volcanos”  Valles Grandes, NM  Caldera is 22 km across  Rhyolite ash flows & domes  Slope outside caldera ~2° Yellowstone

An Invisible Caldera Complex “Super- Volcano”: Harney Basin  A shallow basin, slightly east of our field trip path.  Multiple Ash Flows –Devine Canyon: 9 mybp –Prater Creek: 8.4 mybp –Rattlesnake: 6.4 mybp  Nearly invisible under later basalts, and erosion  Typical of later cenozoic geology of Basin & Range!

Crystals in Lava  Solid crystals make lava more viscous  What kinds of crystals? –Olivine (Mg,Fe) 2 SiO 4 - green, glassy –Pyroxene (Ca,Mg,Fe)SiO 3 - black/green, breaks on flat surfaces (cleavage) –Feldspar - plagioclase (Ca, Na)(Al,Si)Si 2 O 8 - clear-white-greenish, glassy, breaks on flat surfaces. –Quartz - SiO 2 - clear, glassy, curved fractures.

Single Eruption  Paricutin Cinder Cone km 3 lava  Columbia River, Grande Ronde - to 750 km long, 2000 km 3 lava  Yellowstone - Lava Creek Tuff (like at Valles Caldera) - ~1000 km 3 ash  How much is a cubic kilometer?

Many Eruptions  Mauna Loa Shield - ~75,000 km 3 lava  Columbia River Basalts ~170,000 km 3 lava  Olympus Mons (Mars) - ~500,000 km 3 volume  Ontong-Java Plateau - ?6,000,000 km 3 lava

Environment of Eruption  Into Air –Typical  Into Water –Maar Explosion –Tuff Ring –Pillow Lava  Into Ice –Tuya Buttes

What Controls the Shape of a Volcano?  Properties of lava –Viscosity of lava (runny or stiff) –Dissolved Gas - Explosive or Effusive –Solid grains in lava.  Volume of lava erupted  Single or Multiple eruptions  Environment around eruption

Cinder Cone  Paricutin, Mexico –