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Tectonics pt3 (Volcanoes) - Coggle Diagram
Tectonics pt3 (Volcanoes)
Key terms
Active
-- this is a volcano that has erupted in the last 10,000 years.
Dormant
-- this is a volcano that could erput, but hasn't done so in the last 10,000 years.
Extinct
-- this is a volcano that can't erupt because its magma supply has dried up.
Tephra
-- this is a term that is used to describe the material that is thrown up by a volcano.
Caldera
-- this is a crater created by a volcanic explosion that either blows the top of the mountian off the volcano or leads to the top of the mountian collapsing into the magma chamber.
VEI
This is the Volcanic Explosivity Index.
It is a logorithmic scale from 0-8.
0 = lava flows gently and the eruption is not dangerous.
8 = These are extinction level events like the one that killed the dinasours.
Types of eruptions
Explosive and effusive
Explosive
Occur on convergent plate boundaries.
Rhyolite (more acidic) and andersite (less acidic lava).
Lava has a high viscoisty with relativly low tempretures and a high silica content (making it more acidic).
Eruptions are voilents as bubbles of gas in the magma rush to the top. This voilence shatters the top of the volcano.
These euptions release:
Gas
Dust
Tephra
Ash
Lava bombs
These are low frequency eruptions.
They form steep sided strat volcanos with calderas.
Effusive
Occur on divergent plate boundaries.
Basalt lava.
Lava has a low viscosity, reletavily high tempreture and a low silica content (less acidic).
Eruptions are not voilent as gas bubbles expand freely in the magma chamber creating very little explosive force.
These eruptions release:
Gas
Lava flows
These are higher frequency and can last for a few months.
Sheild volcano with gentle sloping sides and some can have lava plateaus formed from multiple fisures.
Types of volcanoes
Icelandic lava eruptions
These occur when their is a constant flow of lava, usally at divergent plate boundries.
They form large horrizontal plains/plateaus.
Hawaaiin eruptions
These are calm, effusive eruptions with very viscous lava.
Strombolian eruptions
These have frequent gas explosions that blast running lava into the air.
These are explosive with large amounts of pyroclastic rock thrown out.
Vulcanian eruptions
Voilent gas explosions blast out plugs of sticky or cooled lava.
Large amounts of ash are usally released as they usally clear blocked vents.
Vesuvian eruptions
Powerful gas expolsions push ash clouds high into the sky (these are more violent then vulcanian eruptions).
Plinian eruptions
Gas rushes through sticky lava and blasts ash and tephra into the sky.
Creates clouds of ash, gas and volcanic debris several km thick.
Can create a cladera.
Why do volcanoes erupt
Magma collects in magma chamber.
As more magma is added presure increases (more gases = more pressure).
Magma is less dense then sourounding rock and thus rises.
Magma erupts onto the surface as lava, ash and gas.