VISCOSITY

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 (lt10 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_eas
  t_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 earths 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