1. Types of Volcanoes
Chapter 11
Section 2

2. Types of Eruptions: Quiet Explosive Determined by:
Amount of water vapor/trapped gases in the magma.
Amount of silica (silicon and oxygen) in the magma.

3. Quiet Eruptions Contain basaltic magmas
Low in silica
Flows very easily
Contain gases that are easily released due to the high viscosity (ability to flow) of the magma.

4. Quiet Eruptions Pahoehoe Aa Pillow lava
Lava cooled in a rope-like structure Aa
Forms at lower temperatures than pahoehoe
Pillow lava
Igneous rock structures shaped like baloons, tubes, or pillows.

5. Quiet Eruptions
Examples:
Hawaii
Rift zones (Iceland)

6. Explosive Eruptions Contain granitic magma
High in silica
Thick
Low in viscosity (ability to flow)
Contains many trapped gases
May also contain andesitic magma
Intermediate silica content

7. Explosive Eruptions
Examples
Convergent boundaries

9. Forms of Volcanoes Dependent upon type of magma and type of eruption.
3 basic forms:
Shield volcanoes
Cinder cone volcanoes
Composite volcanoes

10. Shield Volcano Broad volcano with gently sloping sides.
Result of basaltic magma and quiet eruptions.
Example: Hawaii

12. Flood Basalts
Occur when basaltic magma flows onto the surface of the earth through large cracks called fissures.
When the magma cools, it covers large areas with thick igneous rock.
Accounts for largest volume of erupted volcainc material on Earth.
Examples:
Columbia Plateau
New ocean floor

14. Cinder Cone Volcano
Form when tephra fall to the ground and form a loosely-packed steep-sided structure.
Tephra consist of bits of rock or solidified lava drpped from the air.
Includes volcanic ash, cinders, and larger rocks called bombs and blocks
Example:
Paricutin – Feb 20th, 1943

16. Types of Tephra Volcanic Ash Volcanic Dust Lapilli
Tephra particles less than 2 mm in diameter.
Volcanic Dust
Particles less than 0.25 mm in diameter.
Lapilli
Larger tephra particles, less than 64 mm in diameter.
Generally fall near the vent.

17. Types of Tephra Volcanic Bombs Volcanic Blocks
Tephra particles with round or spindle shape.
Volcanic Blocks
Solid rocks blasted from a fissure.

18. Composite Volcano
Formed from alternating quiet and explosive eruptions, depending on the amount of trapped gases and silica content at the time of eruption.
Result is alternating layers of tephra and lava.
Examples:
Convergent boundaries – Mount St. Helen’s, Mount Raineer

20. Krakatau Island in the Sunda Straits near Indonesia.
Erupted in August of 1883, causing the “island” to collapse into the empty magma chamber (caldera-forming).
More than 36,000 people were killed (mainly by a tsunami)
Global temps dropped as much as 1.8 degrees Celsius for five years.

22. Effects of Eruptions Lava flows Collapse of buildings from ash fall
Air pollution (lung disease/stress)
Acid rain
Pyroclastic flows
Huge, hot, fast rush of ash and debris down the mountain (can result in fires)
Permanent/Temporary Evacuation