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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:

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

~ 2-10o

~ 10-30o

~ 30o

Plate Tect. Setting

Intraplate, Divergent

Convergent

Convergent

Examples

Hawaii, Iceland

Mount St. Helens

Wizard Island

 

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

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