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  Igneous Rocks and Minerals

Three Types of Volcanoes ?  Shield  Composite / Stratovolcano  Cinder Cone

At real scale.  Like comparing a brick to a brick building

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?  Properties of lava –Viscosity (runny or stiff) –Dissolved Gas - Explosive or Effusive –% Solid grains in lava  Volume and Rate of each eruption  Number of individual eruptions  Environment around eruption

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 SiO 4 4- –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!  Si - O bonds much stronger than others  Silica tetrahedra, SiO 4 4-, polymerize  In lava, single silica tetrahedra flow past 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  Low Silica (SiO 2 < 52%) is basalt –Runny as motor oil, or corn syrup  Intermediate Silica –Andesite: % SiO 2 –Dacite: % SiO 2 –Stiffer than taffy  High Silica, > 68 % SiO 2 gives 3-D polymers –Rhyolite/Granite - flows like window glass

Why does Vapor Matter?  Force for explosive eruptions –Water & CO 2 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

Volcanic Ash!

Ash flow = pyroclastic flow Video at

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

Crystals in Lava  Solid crystals make lava more viscous  What kinds of crystals? –Olivine (Mg,Fe) 2 SiO 4 - olive 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.  Stop to look at minerals & rocks …

Single Eruption or Flow  Paricutin Cinder Cone km 3 lava (typical)  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 lava  Ontong-Java Plateau - ?6,000,000 km 3 lava

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

The End.