8. Volcanoes Flashcards
What is magma temperature? What role does it play in how volcanoes melt?
- the temperature of the magma
- informs how viscous the magma will be
- determined by the silica content
- basalt has higher temperature, intermediate moderate, felsic low temperature
What is Silica?
- compound in rocks and melts at molecular unit
- tetrahedral structure that polymerizes together to form stiff framework
- higher the amount of silica, more viscous/ stiff and lower the melting point
What is rhyolite?
- a felsic volcanic rock
- has >60% silica
- more viscous and stiff, lower temperature
- in calderas and composite/ stratavolcanoes
- chemical equivalent to granite
What is Andesite?
- an intermediate volcanic rock
- intermediate in temperature and viscosity
- porphyritic in texture- has large crystals with fine grained texture
What is basalt?
- a mafic volcanic rock
- 45-50% silica
- high melting point, low in viscosity
- found in ocanic crust and in shield volcanoes
What is advection?
The flow of heat by a liquid
What 4 types of volcanoes are there?
- Composite/ stratavolcanoes
- Shield volcanoes
- Calderas
- Flood volcanoes
Describe composite/ stratavolcanoes.
- intermediate and felsic
- low melting temperature, high in viscosity
- steep sides
- explode- felsic and intermediate have the tendency to stay at depths and build up pressure
Describe shield volcanoes and their lava.
- lava high in CO2, H20, SO2
- basalt (mafic), low viscosity and silica
- some explosions
- In Hawaii, areas that have rifted
Describe Flood Basalts.
- thick basalt lava flows
- forms columnar jointing
- fissure eruption- a line of volcanic eruption
Describe calderas.
- intermediate and felsic
- massive collapsed dome
- super volcano
- magma beneath crust collapsed and landed on top of it
What is a tephra?
when ash falls and it becomes rock
What are the two factors that contribute to the explosive nature of volcanoes?
- Magma composition- tell us eruptive power/ how viscous
2. Dissolved volatiles- cause magmas to explode on surface
What are the 3 types of magma composition? Match them with the volcanic rocks.
- Felsic– rhyolite
- Intermediate– andesite
- Mafic– basalt
Describe felsic volcanic rock.
- rhyolite
- high viscosity
- in composite and calderas volcanoes
- > 60% silica–> stiff, rise slowly and builds up pressure
- sometimes explodes
- have more volatiles
- melt at lower temperature
Describe intermediate rock.
- andesite
- intermediate viscosity and melting temperature
- in compsoite and calderas volcanoes
- 50-60% silica
Describe mafic rock.
- basalt
- low viscosity
- sometimes sprays- fire mountains of shield volcanoes, fissure eruption in flood basalts
- high melting point
- Hawaii
- flood basalts, shield volcanoes
what tectonic feature did all composite volcanoes have in common?
by subduction zones
