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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

Volcanoes, Lavas, Minerals

Allan Treiman

LPI

Heat Within, 2009

plan of talk
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
three types of volcanoes
Three Types of Volcanoes ?
  • Shield
  • Composite / Stratovolcano
  • Cinder Cone
at real scale
At real scale.
  • Like comparing a brick to a brick building
so many more kinds of volcanoes
So Many More Kinds of Volcanoes
  • Caldera Complex ‘Super-Volcano’
  • Lava Plateau
  • Dome
  • Single Flow
  • Tuff Ring
  • And …
what controls the shape of a volcano
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
what is lava
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
silicate lavas molecular
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
more silica sio 2 bigger more connected polymers
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
why does vapor matter
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
ash flow pyroclastic flow
Ash flow = pyroclastic flow

Video at

http://www.geo.mtu.edu/volcanoes/west.indies/soufriere/govt/images/051296/

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

Yellowstone

crystals in lava
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 …
single eruption or flow
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?
many eruptions
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
environment of eruption
Environment of Eruption
  • Into Air
    • Typical
  • Into Water
    • Maar Crater
    • Tuff Ring
    • Pillow Lava
  • Into Ice
    • Tuya Buttes
  • Into Vacuum ?
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