Major and minor forms of extrusive activity

Volcanoes are major forms of extrusive activity

Involves 2 forms of lava:

         -- Balsaltic- low silica- runny

        -- Andestitic- high silica, viscous, gases

TYPES OF VOLCANOES:

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

• 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

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

EG- Mauna Loa, Hawaii

• 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

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

EG- Paricutin, Mexico

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

EG- Mt Etna, Sicily

• 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

1. Solfatara

2. Geysers

3. Hot Springs

4. Boiling Mud

5. Fumeroles

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

• 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.

• 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

• 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)

• 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.