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VISCOSITY

VISCOSITY. The resistance of material to flow the higher the viscosity, the less easily something (magma/lava) can flow Motor oil: Flagstaff vs. Phoenix hotter temps = lower viscosity oil lower temps = higher viscosity oil. Cinder cones/maars. Basalt Short lived (<10 years?)

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VISCOSITY

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  1. VISCOSITY • The resistance of material to flow • the higher the viscosity, the less easily something (magma/lava) can flow • Motor oil: Flagstaff vs. Phoenix • hotter temps = lower viscosity oil • lower temps = higher viscosity oil

  2. Cinder cones/maars Basalt Short lived (<10 years?) Cinder/scoria, lava flows (out the bottom) Most any tectonic environment Tephra, tephra, tephra ~1 km wide, 300 m tall

  3. Shield volcanoes • Very wide, tall • Centuries to a few million years • Basalt • Often have a caldera at the rim • Very low angle slopes • Highly fluid flows VERY low viscosity • Subduction zones and hotspots (larger volcanoes = hotspots) • Cool picture is here: http://mars.jpl.nasa.gov/mep/science/oly-az.jpg

  4. Domes • Relatively small (few hundred m on a side) • (usually) dacite to andesite to rhyolite • Convergent/subduction margins • Pyroclastic flows often due to collapse of the dome • Can be several thousand years, but really variable – a few years to several thousand • Toothpaste • http://a.abcnews.com/images/US/volcanoe_112004_east_ssh.jpg

  5. Stratovolcanoes (also called composite volcanoes) • Erupts everything (pyroclastic, lava, mudflows (lahars)) • Intermediate (basalt to dacite) • Hundreds of thousands years lifespan • Big! 4000’ high from base (so Cascade volcanoes often 12,000’ or more) • Subduction zone/convergence • High viscosity, often explode • polygenetic

  6. Calderas • Largest volcanoes on earth – 15 x 30 km • Largest eruptions 2-1000 km3 • Magma rising to earth’s surface swells the surface, erupts pyroclastic material, magma chamber collapses. Shallow magma chamber. • RHYOLITE!! (also dacite) • All types of tectonic settings • Lifespan to several million years • Tuff is the most common erupted material, both as flows and as material falling from the air: pyroclastics rule • Vents along margins of caldera (lava domes), earthquakes common

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