Welcome to GLG101C Introduction to Geology Fall 2004 Professor James Tyburczy
Department of Geological Sciences
	Class Notes Chapter 6 - Volcanoes

Check out the Volcano World Web Site, the "premier source of volcano info on the web" (even if it does say so itself).

Mauna Loa Volcano in Hawaii has been showing signs recently of increased activity - check it out at http://hvo.wr.usgs.gov/maunaloa/

The US Geological Survey has a good volcano web site, which also has links to volcano observatories in Hawaii, Alaska, and Washington. Also, the Smithsonian Institution and the USGS have a Volcanic Activity Report site

The Electronic Volcano is another great site for volcanophiles.

Check out your textbook, too, for a bunch of other links and interesting exercises, too. Really!

Chapter 5. Volcanism and Extrusive Rocks - fine-grained, cool quickly

Why study volcanoes

• Volcanic Hazard
• Samples of Earth's interior
• Fundamental process in plate tectonics

Volcanic Products

• Lava Flows - effects of chemical composition, gas content, and temperature
• Obsidian, rhyolite, andesite, basalt. Pillow lavas
• Pyroclastic material - ash, bombs --> tuff, breccia. Ash fall versus pyroclastic flow
• Volcanic gases -> vesicles - pumice. The gasses are mostly H2O, but CO2, SO2, other gasses can be important
• Influence of lava viscosity and dissolved gas content on eruption type

Classification:

• Textures -> grain size (fine-grained, coarse-grained, mixed coarse and fine), vesicles (trapped gas bubbles), fragmental textures (tuff or breccia)
• Composition -> felsic, intermediate, mafic

Classification of chemical composition ranges of extrusive rocks

• Characteristic minerals, temperature, viscosity, and extrusive rock
• Names - basalt, andesite, rhyolite (obsidian is glass of rhyolite composition)

Types of volcanoes and volcanic land forms

• Shield volcanoes - ex. Hawaii
• Composite volcanoes (stratovolcanoes) - ex. Mt. St. Helens, San Francisco Peaks --> circum-Pacific "Ring of Fire" and Mediterranean volcanic belts - form above subduction zones
• Lava Domes - extrusion of very viscous, very thick lava - St. Helens
• Cinder cones - ex. Mojave desert, Sunset Crater
• Summit crater
• Calderas
• Fissure Eruptions
  1. Continental flood basalts - eastern Washington, India, ... flows up to 50-100 km long
  2. Submarine eruptions - mid-ocean ridges (Iceland) (pillow lavas)

Other eruptive products

• Lahars (mud flows) - water plus loose pyroclastic material. Can be very destructive
• Volcanic gases - mostly water vapor (H2O), also CO2, SO2. Volcanic aerosols (very fine droplets) can remain suspended for long periods (months), cool the earth

The Source of lavas - magma formed in outer 100 km or so of the Earth

Spatial distribution of volcanic activity - Plate tectonics

• Mid-ocean ridges - divergent plate boundary - basaltic lava (oceanic crust is basalt)
• Subduction zones (circum-Pacific 'Ring of Fire'): convergent plate boundaries.
1. Ocean-continent collision, composite volcanoes, mostly andesite, some basalt, some rhyolite.
2. Ocean-ocean collision - mostly basaltic, some andesitic volcanism
• Intraplate or 'Hotspot' Volcanoes (example- Hawaiian Islands, Emperor Seamounts, Columbia River basalts, Yellowstone) - Not on a plate margin
  1. Usually basalt when on an oceanic plate - can be rhyolitic if on continental plate (Yellowstone)
  2. Continental flood basalts
  3. mantle plumes

Volcanoes and Human Affairs

• Landforms, soils (and tourism)
• Geothermal energy Climate
• Samples of the Earth's interior
• Geologic hazard - volcanic eruptions as well as mud flows etc.
  1. Influence of lava viscosity and dissolved gas content on eruption type
  2. Prediction - seismic activity, gases emitted, ground swelling
  3. Other hazards - particulates in air - aviation