Mount Pelee 1902

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Mount Pelee 1902
St. Pierre
Mount Pelee
28,000 killed 1 survivor
17 ships in the harbor destroyed
Ash cloud swept through town at 125MPH
Event lasted 5 minutes
Masonry walls 3 feet thick blown apart
Temperatures over 10000F
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Magma
Magma Molten material consisting of liquid, gas,
and a crystals. 1) Basaltic magma 50 SiO2 ,
1-2 gas temperature _at_ 900-12000C Ca-rich
plagioclase feldspar pyroxene minerals dark - gt
40 dark minerals tends to be highly fluid, low
viscosity 2) Granitic magma 65-77 SiO2 ,
10-15 gas lt8000C temperature quartz, orthoclase
feldspar, Na-rich plagioclase minerals light
colored - lt 15 dark minerals highly viscous -
silica tetrahedrons link together to resist flow
Magma which reaches the surface and erupts from
a volcano is termed extrusive, such as lavas and
ash clouds. That which crystallizes underground
is called intrusive or plutonic.
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Bowens
Crystallization order of minerals in a basaltic
magma
Mg, Fe rich Dark, dense
Ionic Substitution
1st to melt
Na, K, Al, Si rich
Light-colored, less dense minerals
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Igneous Rocks
Intrusive (slow cooling)
Extrusive (fast cooling)
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Interlocking Grains
Phaneritic texture
Quartz
Biotite
Feldspar
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Thin section
Biotite
Feldspar
Quartz
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Aphanitic Texture
Phenocryst
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Glass
An amorphous solid--no internal crystalline
structure
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Magma Generation
Partial melting of down-going slab Si, Al, Na,
Ca, K
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Crystallization
Early-forming minerals, such as olivine
pyroxene and sulfide minerals
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Plutonic Rock Features
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Intrusive
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Intrusive Igneous Rocks
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Devils Tower
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Sill
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Dike, Neck
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Batholith
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Sierra Nevada
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West Coast Batholiths
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Basaltic Volcanism
Generally non-explosive
Basaltic magma Only 50 SiO2, very fluid
Generally results in lava flows, little ash
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Mid-Oceanic Ridge
80 of worlds volcanism
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Flood Basalts
Over 1km thick
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Basaltic Lava Flow
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Columbia River Basalts
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Hawaii
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Shield Volcano
Builds up over time, lava flow on top of lava flow
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Pahoehoe Lava
Outer crust cools quickly, hardens
Very fluid, thin, and ropy
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Aa Lava
Thick and chunky Slow moving
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Lava Tube
Window
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Kilauea, Hawaii
Caldera
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Ocean
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Kalapana, Hawaii
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Fountain
Fountain
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Scoria
Vesicular Fe Mg rich Ejected as liquid
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Cone
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Cinder Cone
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Mauna Kea