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Volcanoes, Lavas, Minerals

Volcanoes, Lavas, Minerals. Allan Treiman LPI Heat Within , 2009. Plan of Talk. Breaking the Tyranny of Three Three types of volcanoes Three types of lavas Volcanoes explained simply Lava Properties Eruption Style Eruption Environments Lava Properties in terms of Atoms

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Volcanoes, Lavas, Minerals

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  1. Volcanoes, Lavas, Minerals Allan Treiman LPI Heat Within, 2009

  2. Plan of Talk • Breaking the Tyranny of Three • Three types of volcanoes • Three types of lavas • Volcanoes explained simply • Lava Properties • Eruption Style • Eruption Environments • Lava Properties in terms of Atoms • Igneous Rocks and Minerals

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

  4. At real scale. • Like comparing a brick to a brick building

  5. So Many More Kinds of Volcanoes • Caldera Complex ‘Super-Volcano’ • Lava Plateau • Dome • Single Flow • Tuff Ring • And …

  6. What Controls the Shape of a Volcano? • Properties of lava • Viscosity (runny or stiff) • Dissolved Gas - Explosive or Effusive • % Solid grains in lava • Volume and Rate of each eruption • Number of individualeruptions • Environment around eruption

  7. What is Lava? What is lava? • Molten material at a planet’s surface • Solidifies at surface conditions • Many sorts of ‘lava’ • Most common is silicate - abundant SiO44- • Molten sulfur, carbonate, iron oxide • Mud is not lava, really (but “mud volcanos”) • Water is not lava on Earth (but is elsewhere) • What is magma? • More general - not necessarily erupts

  8. Silicate lavas - molecular! • Si - O bonds much stronger than others • Silica tetrahedra, SiO44-, polymerize • In lava, single silica tetrahedra flowpast each other easily, like cous-cous • In lava, large silicate polymers tangle together, like spaghetti, and flow poorly

  9. More Silica (SiO2) = bigger, more connected polymers • Low Silica (SiO2 < 52%) is basalt • Runny as motor oil, or corn syrup • Intermediate Silica • Andesite: 52 - 63% SiO2 • Dacite: 63 - 68 % SiO2 • Stiffer than taffy • High Silica, > 68 % SiO2gives 3-D polymers • Rhyolite/Granite - flows like window glass

  10. Why does Vapor Matter? • Force for explosive eruptions • Water & CO2 vapor bubbles out as magma nears surface • No vapor, no explosion! • Stiff water-rich magma makes foam (pumice) & shards of glassy ash - huge eruptions • Pumice + ash and water vapor can flow together as a ‘slurry’ = an ash flow

  11. Volcanic Ash!

  12. Ash flow = pyroclastic flow Video at http://www.geo.mtu.edu/volcanoes/west.indies/soufriere/govt/images/051296/

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

  14. Crystals in Lava • Solid crystals make lava more viscous • What kinds of crystals? • Olivine (Mg,Fe)2SiO4 - olive 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. • Stop to look at minerals & rocks …

  15. Single Eruption or Flow • Paricutin Cinder Cone - 1.4 km3 lava (typical) • 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?

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

  17. Environment of Eruption • Into Air • Typical • Into Water • Maar Crater • Tuff Ring • Pillow Lava • Into Ice • Tuya Buttes • Into Vacuum ?

  18. The End.

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