EOSC 114 Study Guide - Final Guide: Continental Crust, Magma Chamber, Volcanic Arc

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Published on 15 Apr 2013
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Volcanoes Slide Notes 26/02/2013 13:24:00
-Slide 1-
Plinean Eruption
Named after Pliny the younger
Pliny wrote a letter describing the eruption and death of his
uncle, who was saving people
Risk
Risk= Vulnerability X Hazard / Mitigation
Hazard = size, frequency, type of damage
Vulnerability = what is impacted and value
Mitigation = $ invested t reduce vulnerability or to control hazard
Magma
Melted rock in the earth, below earth surface
Melt + crystal + bubbles
Created by the melting of pre-existing rock in earth’s interior
(mantle & crust)
It reaches the surface through fractures an erupts as lava or as
pyroclastic material
Lava
Melted rock exposed at the earth’s surface
Melt + crystal + bubbles
Volcanic system
From bottom to top
o Source region
In the mantle, 1000°C
Mantle (peridotite) into magma (basaltic -> granitic)
Magma is less dense
o Transport region
Magma channels, moving along cracks in the earth’s
crust
Forming dikes and sills
Dikes- vertical intrusion of magma
Sills horizontal intrusion of magma
o Storage region
Magma chamber
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Magma ponds below the surface in large chambers
Intrusive rock
Magma freezes in crust, is not erupted
Large crystals from magma cooling down
slowly
Eruptive Region
Ingeous rocks
Cooled at the surface
o Extrusive/volcanic
o Basalt, andesite, dacite, rhyolite (hot to cool, less to more
silica, non explosive (lava) to explosive (pyroclastic))
o Small crystals/fine grained
Cooled below surface
o Intrusive/plutonic
o Large crystals/course grained
o Slow cooling
Silica Content (SiO^2)
Felsic rocks: 65-75% SiO
o Light color
o Rich in K, Na, Al, Si
o High viscosity (sticky)
o Eg. Granite, rhyolite
Mafic rocks: 45-55%
o Dark color
o Rich in Mg, Fe
o Low viscosity (runny)
o Eg. Basalt, Gabbro
-Slide 2-
Glass formation
Glass is a non-crystalline or amorphous, metastable solid formed
by quenching a melt
Cools so fast that a regular crystal lattice cannot form
Rising magma
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Causes
o Crystallization
o Exsolve volatiles
Volatiles (gases)
Dissolved >> exsolved
Physical properties of magmas
Melt density: g cm^-3 or kg m^-3
o Decreases: basal -> rhyolite, rising temperature
o Increases: cooling, pressure
o Controls: ascent, eruption
Viscosity: Pa s
o Resistance to flow
o Controls: flow, deformation, eruption
o High viscosity (sticky): cooler, felsic, high silica
o Low viscosity (runny): hot, mafic, lower silica
- Slide 3 -
Volcanic eruptions two main styles
Effusive: outpouring of molten magma from the vent; lavas
o Passive eruption of magma
Lava flows (mafic-intermediate)
Lava domes (felsic-intermediate)
Gravitational collapse of lava flows/domes (blocks
and ash flows)
o Lava flows downslope, ponds in topographic lows
o Outer crust cools and solidifies insulating the molten
interior
Explosive gas driven violent eruptions -> pyroclastic deposits
o Active eruption of magma
Buoyant eruption column of ash
Pyroclastic airfall
Pyroclastic flows
Ballistics proximal to vent
o Pyroclastic fall
Eruption colums: 10’s o km’s
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Document Summary

Pliny wrote a letter describing the eruption and death of his uncle, who was saving people. Hazard = size, frequency, type of damage. Vulnerability = what is impacted and value. Mitigation = $ invested t reduce vulnerability or to control hazard. Melted rock in the earth, below earth surface. Created by the melting of pre-existing rock in earth"s interior (mantle & crust) It reaches the surface through fractures an erupts as lava or as pyroclastic material. Melted rock exposed at the earth"s surface. From bottom to top: source region. Mantle (peridotite) into magma (basaltic -> granitic) Magma is less dense: transport region. Magma channels, moving along cracks in the earth"s crust. Sills horizontal intrusion of magma: storage region. Magma ponds below the surface in large chambers. Magma freezes in crust, is not erupted. Large crystals from magma cooling down slowly.

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