Volcanicity
- Created by: Austen Poole
- Created on: 13-03-17 09:22
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- Volcanicity
- Rock types
- Intrusive
- Igneous
- Formed by the crystallization of magma below the surface of the earth
- Extrusive
- Igneous
- Formed by crystallization above the earth
- As the lava gets cooler it becomes more viscous
- Intrusive
- Types of volcano
- The type of cone is dependent on:
- Nature of the eruptions
- The type of lava
- The plate margin type
- Shield volcanoes
- Found in mid-ocean ridges, hot spots, rift valleys
- Repeated, relatively frequent eruptions
- Runny lava
- Runny lava
- Gently sloping cone
- Basaltic
- Eruptions gentle and predictable
- e.g. Mauna Loa
- Layers of solidified lava
- Composite volcanoes
- Found on land at destructive margins
- Formed from layers of ash, tephra and lava
- Relatively steep slopes
- May have a secondary cone
- Rock type is andestic
- Explosions are explosive and unpredictable
- e.g. Mt. Vesuvius
- Very viscous lava
- Lava erupted at very low temperatures
- Lava has a high silica content
- High volatile content - very explosive
- Pyroclastic flows are common
- Acid dome volcanoes
- Found on continental crust at destructive margins
- Lava is viscous and cannot flow far
- Very steep convex sloped cones
- Lava is viscous and cannot flow far
- The rock type is rhyolitic
- Eruptions are extremely explosive and unpredictable
- e.g. Mt Pelee, Martinique
- The type of cone is dependent on:
- Magma types
- Variations in magma include
- Silica content - varies from 45% to 75%
- Volatiles - gas content - h2o vapour, co2, so2, h2s
- Temperature - from 1200 degrees c to 800 degrees c
- Hawaiian Lava
- Low viscosity
- Erupted at a high temperature
- Low silica content
- High volatile content
- Dark lava flows are the youngest
- Light lava flows are the oldest
- Variations in magma include
- Volcanic landforms
- Calderas
- Found at destructive margins
- The rock type is andestic
- Explosions are unpredictable and violent
- Gases build up below a blocked vent
- This results in an eruption that destroys the top of the volcano
- This leaves a massive crater that is often filled by a lake
- This results in an eruption that destroys the top of the volcano
- e.g. Lake Taupo, New Zealand
- Fissure eruptions
- Found at constructive margins and rift valleys
- Essentially long, thin cracks in the crust that allow lava to spill out
- Rock type is basaltic
- Eruptions are gentle and persistent
- e.g. heimaey, iceland
- Lava plateaux are formed where the basalt layers pour out from cracks in the earths surface
- the lava is runny so flows a long way from the crack
- It takes a long time to cool too
- These structures are layered
- Geysers
- These require three elements
- A water supply
- A heat source
- A proper underground water circulation suplly
- e.g. Pohutu Geyser, NZ
- These require three elements
- Hot springs
- Produced by the emergence of geothermally heated groundwater
- e.g. Yellowstone NP
- Fumaroles
- Formed when superheated water turns to steam as the pressure drops
- When the steam mixes with sulphur gases it becomes a solfatara
- e.g. Craters of the moon, NZ
- Formed when superheated water turns to steam as the pressure drops
- Boiling mud pools
- These form in high-temperature geothermal areas
- The thickness of the mud changes with the seasons and the water table
- The mud is very viscous, like slurry
- Sometimes the mud is squirted out of the brim and creates a tiny mud volcano
- Rotorua, NZ
- Dykes
- Forms when magma solidifies in a vertical crack or fissure in the rock
- Normally they comprise of resistant material and form a wall like feature often in swarms
- Occasionally the lava is the weaker material and is eroded leaving a ditch
- Sills
- A horizontal or gently inclined layer of solidified magma
- Batholiths
- These are large scale features which the other features may emanate from before it solidifies
- Calderas
- Rock types
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