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Igneous Rocks, Minerals, and Volcanos

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

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Igneous Rocks, Minerals, and Volcanos

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  1. Igneous Rocks, Minerals, and Volcanos Allan Treiman LPI

  2. 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

  3. Three Types of Volcanos • Shield • Composite / Stratovolcano • Cinder Cone

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

  5. 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

  6. 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 SiO44- • Molten sulfur, carbonate, iron oxide • Mud is not lava on Earth (but “mud volcanos”) • Water is not lava on Earth (but is elsewhere)

  7. Silicate Lavas • Large Range of Viscosity • Basalt - as runny as motor oil • Andesite - stiffer than taffy • Rhyolite/Granite - like window glass • Depends on silica - SiO2 • Basalt: < 52% SiO2 in chemical analysis • Andesite: 52 - 63% SiO2 • Dacite: 63 - 68 % SiO2 • Rhyolite: > 68 % SiO2

  8. Why does silica matter? • Si - O bonds much stronger than others • Silica tetrahedra, SiO44- polymerize • In lava, single silica tetrahedra flow easily, like little balls • In lava, large silicate polymers flow poorly, like noodles

  9. 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

  10. Ash flow = pyroclasticflow = ‘nuee ardent’

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

  12. 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!

  13. Crystals in Lava • Solid crystals make lava more viscous • What kinds of crystals? • Olivine (Mg,Fe)2SiO4 - green, glassy • Pyroxene (Ca,Mg,Fe)SiO3 - black/green, breaks on flat surfaces (cleavage) • Feldspar - plagioclase (Ca, Na)(Al,Si)Si2O8 - clear-white-greenish, glassy, breaks on flat surfaces. • Quartz - SiO2 - clear, glassy, curved fractures.

  14. Single Eruption • Paricutin Cinder Cone - 1.4 km3 lava • Columbia River, Grande Ronde - to 750 km long, 2000 km3 lava • Yellowstone - Lava Creek Tuff (like at Valles Caldera) - ~1000 km3 ash • How much is a cubic kilometer?

  15. Many Eruptions • Mauna Loa Shield - ~75,000 km3 lava • Columbia River Basalts ~170,000 km3 lava • Olympus Mons (Mars) - ~500,000 km3 volume • Ontong-Java Plateau - ?6,000,000 km3 lava

  16. Environment of Eruption • Into Air • Typical • Into Water • Maar Explosion • Tuff Ring • Pillow Lava • Into Ice • Tuya Buttes

  17. 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

  18. Cinder Cone • Paricutin, Mexico • 1943 - 1952

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