Major and minor forms of extrusive activity

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  • Created by: Lilly
  • Created on: 28-02-14 12:29

Major forms

Volcanoes are major forms of extrusive activity

Involves 2 forms of lava:

         -- Balsaltic- low silica- runny

        -- Andestitic- high silica, viscous, gases


Fissure, Basic/ shield, Acid/dome, Ash and cinder cones, composite, calderas

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1- Fissure volcano (fissure vent/volcanic fissure)

  • Constructive margin
  • Produces basaltic lava
  • Long, linear vent- can be a few metres wide and several Kms long
  • Fairly flat- low viscosity of lava, flows long disatances

EG- Laki fissure system

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2- Basic/ Sheild volcano

  • Constructive marings/ hotsports
  • Produces basaltic lava
  • Gently sloping sides- low viscosity of lava= flows long distances, cover a large area

EG- Mauna Loa, Hawaii

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3- Acid/ Dome volcano

  • Destructive margins
  • Rhyolitic/ andesitic lava
  • Steep sided- high viscosity of lava from destructive margin- lava does not flow very long distances
  • Convex cones

EG- Puy De Dome, France

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4- Ash & Cinder Cones

  • Formed from ash, cinder and volcanic bombs ejected from crater
  • Steep sided, symmetrical

EG- Paricutin, Mexico

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5- Composite volcano

  • Classic pyrmaid shaoe
  • Layers of ash/ lava- andesitic lava

EG- Mt Etna, Sicily

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6- Calderas

  • Destructive margin
  • Andesitic/ Rhyolitic lava
  • Central part of the volcano has collapsed as magma chamber is empted ( build up of gases become extreme and hufe explosion removes summit)
  • Very wide, circular crater
  • Can be flooded by sea

EG- Krakatoa, Indonesia

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Minor forms of extrusive activity

1. Solfatara

2. Geysers

3. Hot Springs

4. Boiling Mud

5. Fumeroles

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A- Solfatara

  • A fumerole that contains sulfur
  • EG- Lake Nyos, Bay of Napes, Italy.
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B- Geysers

  • Type of hot spring where hot water and steam are ejected from surface in a fountain.
  • In areas of intsense volcanic activity

1- Groundwater is heated to above boiling point by magma deep in the crust

2- Water becomes pressurised, forces its way to the sruface along cracks

3- Hot water and steam spray out from vent

  • Erupt periodically- only erupt when pressure ahs built up enough to force water up and out

EG- Old Faithful, Yellowstone National Park USA.

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C- Hot Springs

  • Groundwater source flows close to area of recent intense volcanic activity, water is heated and becomes a hot spring
  • Temp varies between 20c- 90c+
  • Often have high mineral content- hot water dissolves a lot of solids.

EG- Rio Hondo, Argentina

North Island, New Zealand

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D- Boiling Mud

  • Type of hot spring
  • Form in areas of very fine-grained soil- volcanic ash or clay
  • Water and mud= mud pool
  • Can contain brightly coloured mud- minerals (iron and sulfur- can produce purple, organe and yellow mud)
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E- Fumeroles

  • Low pressure outlets of steam and gas
  • Associated with active and dormant volcanoes
  • Mainly steam adn carbon dioxide, can include CO, hydrochloric acid and sulfur gases
  • When they contain sulfur they become a SOLFATARA.
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