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Volcanism

Terms to learn:

viscosity            basaltic magma           silicic magma        pahoehoe
Aa                    pyroclastics-tephra       shield volcano       composite volcano
cindercone        volcanic dome          caldera                 crater
flood basalts      pillow basalts               lahar                    nuee ardente

Topic outline:

Factors affecting nature of volcanic eruption –viscosity
1. Amount of dissolved gases
2. Temperature
3. Silica content
Materials extruded during volcanic eruptions
1. Lava types
2. Gases
3. Pyroclastic material (tephra)
Types of Volcanoes

Property	Shield	Composite (strato)	Cinder Cone
Composition	Basaltic	Andesitic	Basaltic-Andesitic
Temperature	Hottest	Intermediate	Intermediate
Silica content	Least	Intermediate	Intermediate
Viscosity	Lowest (very fluid)	Intermediate	Intermediate
Products	Mostly flows	Flows and tephra	Tephra
Hazards	Lava flows	Lahars, tephra, nuees ardentes	Upward eruption of cinders
Slope	~ 2-10^o	~ 10-30^o	~ 30^o
Plate Tect. Setting	Intraplate, Divergent	Convergent	Convergent
Examples	Hawaii, Iceland	Mount St. Helens	Wizard Island

Other volcanic occurrences
1. volcanic domes
2. Caldera vs. craters
3. Flood Basalts
  1. columnar jointing
4. Submarine eruptions – pillow basalts
Volcanism and Plate Tectonics
1. Distribution of volcanic activity
2. 1. spreading centers
  2. subduction zones
  3. intraplate
Volcanic hazards and benefits
1. primary and secondary hazards
2. benefits

Interesting places to visit:

Great interactive page: http://www.learner.org/exhibits/volcanoes/

Lots of great info: http://www.cotf.edu/ete/modules/volcanoes/volcano.html

Volcanoes links page: http://www.volcanoes.com/webdocs/websitelinks.html

When you are finished with this topic, you should be able to answer these questions:

1. What three factors determine the nature of a volcanic eruption?

2. What do pillow lavas indicate about the environment of volcanism?

3. Why are extrusive rocks fine-grained?

4. Why do shield volcanoes have such low slopes?

5. What accounts for the differences between pahoehoe and aa lava flows?

6. Why do composite volcanoes occur near convergent plate boundaries?

7. Explain how Crater Lake formed.

Housing

Volcanism