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Geohazard > Volcanic Eruptions - MAGMAS > Flashcards

Volcanic Eruptions - MAGMAS Flashcards

1
Q

Volcanoes are mostly found along

A

convergent boundaries

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2
Q

Much magmas are expelled along

A

divergent boundaries

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3
Q

the type of ____and consequent type of _____ of a volcano depends on the _____ it is formed

A

magma ; eruption ; tectonic setting

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4
Q

what are the three types of magma

A

basaltic, andesitic, rhyolitic

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5
Q

what is a magma

A

a magma is an extremely hot mixture of solid, gas, and liquid, located under Earth’s surface

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6
Q

what is the solid part of the magma

A

crystals

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7
Q

what are the gaseous part of the magma

A

H2O, CO2, SO2

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8
Q

what is the liquid part of the magma

A

molten rock

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9
Q

what type of magma are formed in an oceanic-oceanic subduction zone

A

basaltic or andesitic magma

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10
Q

what type of magma are formed in an oceanic-continental subduction

A

andesitic or rhyolitic

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11
Q

what type of magma is found in oceanic hotspot

A

basaltic magma

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12
Q

what type of magma is found in continental hot spot

A

rhyolitic magma

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13
Q

how does continental hotspot produce rhyolitic magma?

A

silica-poor basalt still rises toward the surface; as the magma rises, it melts its way trough thick, silica-rich continental crust forming shallow silica-rich (rhyolitic) magma chambers

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14
Q

silica content of basaltic magma

A

48-52%

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15
Q

silica content of andesite/dacite magma

A

52-68%

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16
Q

silica content of rhyolite magma

A

68-77% or >66%

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17
Q

silica content of ultramafic magma

A

<45%

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18
Q

t or f: as silica content increases, the silica structure of the magma becomes more 3D

A

T

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19
Q

t or f: high temperature magma have high viscosity

A

F (low viscosity)

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20
Q

the viscosity of magma increases with ____ SiO2 and ______ tempeature

A

increasing ; decreasing

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21
Q

they are the least viscous type of magma

A

basaltic magma

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22
Q

why are basaltic magmas least viscous?

A

they form in the upper mantle where the temperature is high and the SiO2 content is low

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23
Q

t or f: basaltic magmas are formed in the deep and hot upper mantle while andesite and rhyolitic magmas form at much shallower and cooler depths

A

T

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24
Q

t of f: magmas evolve in different ways, one process can’t explain the entirety of its evolution

A

T

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25
Q

t or f: overtime, a volcano may extrude lavas that are uniform in composition

A

F (vary in composition)

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26
Q

depicts the sequence in which minerals crystallize to form magmas

A

Bowen’s Reaction Series

27
Q

draw the bowen’s reaction series

A
28
Q

mechanisms that allow evolution of magma

A

magmatic differentiation
crystal settling
assimilation
magma mixing
partial melting

29
Q

it is the process where the early-formed minerals are denser than the liquid and sink toward the magma chamber

A

crystal settling

30
Q

in crystal settling, when the remaining melt solidifies either in place or in another location, if it migrates into fractures in the surrounding rocks, it will form _____

A

a rock with mineralogy much different from the parent magma

31
Q

what are the early-forming minerals?

A

olivine, pyroxene, ca-plag

32
Q

in crystal settling, the remaining melt will become more enriched in ____

A

silica

33
Q

crystal settling results in a change in the composition of the ______

A

remaining melt

34
Q

it is the formation of one or more secondary magmas from a single parent magma

A

magmatic differentiation

35
Q

magmatic differentiation results in _____ of ferromagnesian minerals and ______ of silica-rich minerals

A

depletion ; enrichment

36
Q

t or f: crystal settling is part of magmatic differentiation

A

T

37
Q

it is an intrusion extending from New York to New Jersey that was formed through magmatic differentiation

A

Palisades Sill

38
Q

how long was the Palisades Sill intrusion and composed of what rock?

A

80 km long ; monzonite

39
Q

what are the layers of palisades sill?

A

Sandstone
Basalt
Na-rich plag
Ca-rich plag, pyroxene
Olivine
Basalt
Sandstone

40
Q

t or f: magmatic differentiation by itself cannot account for the entire compositional spectrum of igneous rocks

A

T

41
Q

some of the surrounding rock (country rock) may be incorporated into the upwelling magma

A

assimilation

42
Q

in assimilation, rising magma creates an _____ applied to overlying layer causing the country rock to ______

A

upward stress ; fracture

43
Q

occurs during the ascent of two chemically distinct magma bodies as the more buoyant mass overtakes the more slowly rising body

A

magma mixing

44
Q

in partial melting minerals with _____ are the first to melt

A

lowest melting temperature

45
Q

is the process that generates a magma that is nearer the felsic (granitic) end of the compositional spectrum than the parent rock from which it was derived, because silica rich minerals are first to melt

A

Partial melting

46
Q

partial melting can be triggered by addition of ____ to the overlying rock layer

A

volatiles

47
Q

how does volatile trigger partial melting?

A

as volatiles gets squeezed out from the subducting slab, it reacts with overlying rock, decreasing its melting temperature thus, low-temp rocks melt first

48
Q

most magma that erupts on the earth’s surface is _____ in composition

A

basaltic

49
Q

basaltic magma has a temperature of

A

1000 to 1250 degrees celsius

50
Q

experiments show that under the ______ conditions calculated for the upper mantle, _____ of the ultramafic rock ____ will yield a magma of basaltic composition

A

high-pressure ;
partial melting ;
peridotite

51
Q

basaltic (mafic) magmas that originate from partial melting of mantle rocks are called _____ or _____ because they have not yet evolved

A

primary or primitive magmas

52
Q

partial melting caused by a reduction in the confining pressure

A

decompression melting

53
Q

basaltic magmas are also generated at ______, where water driven from the ______ of _____ promotes partial melting of the rocks that lie above

A

subduction zones ; subducting slab ; oceanic crust

54
Q

one way andesitic magma can be formed:

A

when rising mantle-derived basaltic magma undergoes magmatic differentiation thru crystal settling as it slowly makes it way through the continental crust

55
Q

if iron-rich components are separated from the liquid by crystal settling, the remaining melt will have an _____

A

andesitic composition

56
Q

evolved (changed) magmas are termed:

A

secondary magmas

57
Q

andesitic magmas can also form when rising basaltic magmas _______ crustal rocks that tend to be silica-rich

A

assimilate

58
Q

granitic magmas are mostly generated by _____

A

partial melting of continental crust

59
Q

magmas also contain various types of gas molecules that form when

A

minerals within a rock body begin to melt

60
Q

gaseous molecules in magmas remain dissolve until the magma gets _____, where the ______ allows the gases to escape

A

near the surface ; decreased pressure

61
Q

t or f: higher content of dissolved gases within a magma will result to a more explosive volcanic eruption

A

T

62
Q

one cubic meter of magma with 5% of dissolved water will expand to:

A

670 cubic meters

63
Q

t or f: andesitic magmas contain more water molecules than basaltic magma

A

True

Geohazard (25 decks)

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