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Types of Volcanoes

Types of Volcanoes. Chapter 11 Section 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. Quiet Eruptions. Contain basaltic magmas Low in silica Flows very easily

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Types of Volcanoes

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  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 • 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

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

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

  10. 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

  11. 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

  12. Types of Tephra • Volcanic Ash • 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.

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

  14. 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

  15. 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.

  16. 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

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