Volcanic Eruptions - MAGMAS

Question 1

Volcanoes are mostly found along

Answer 1

convergent boundaries

Question 2

Much magmas are expelled along

Answer 2

divergent boundaries

Question 3

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

Answer 3

magma ; eruption ; tectonic setting

Question 4

what are the three types of magma

Answer 4

basaltic, andesitic, rhyolitic

Question 5

what is a magma

Answer 5

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

Question 6

what is the solid part of the magma

Answer 6

crystals

Question 7

what are the gaseous part of the magma

Answer 7

H2O, CO2, SO2

Question 8

what is the liquid part of the magma

Answer 8

molten rock

Question 9

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

Answer 9

basaltic or andesitic magma

Question 10

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

Answer 10

andesitic or rhyolitic

Question 11

what type of magma is found in oceanic hotspot

Answer 11

basaltic magma

Question 12

what type of magma is found in continental hot spot

Answer 12

rhyolitic magma

Question 13

how does continental hotspot produce rhyolitic magma?

Answer 13

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

Question 14

silica content of basaltic magma

Answer 14

48-52%

Question 15

silica content of andesite/dacite magma

Answer 15

52-68%

Question 16

silica content of rhyolite magma

Answer 16

68-77% or >66%

Question 17

silica content of ultramafic magma

Answer 17

<45%

Question 18

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

Answer 18

T

Question 19

t or f: high temperature magma have high viscosity

Answer 19

F (low viscosity)

Question 20

the viscosity of magma increases with ____ SiO2 and ______ tempeature

Answer 20

increasing ; decreasing

Question 21

they are the least viscous type of magma

Answer 21

basaltic magma

Question 22

why are basaltic magmas least viscous?

Answer 22

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

Question 23

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

Answer 23

T

Question 24

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

Answer 24

T

Question 25

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

Answer 25

F (vary in composition)

Question 26

depicts the sequence in which minerals crystallize to form magmas

Answer 26

Bowen's Reaction Series

Question 27

draw the bowen's reaction series

Question 28

mechanisms that allow evolution of magma

Answer 28

magmatic differentiation crystal settling assimilation magma mixing partial melting

Question 29

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

Answer 29

crystal settling

Question 30

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 _____

Answer 30

a rock with mineralogy much different from the parent magma

Question 31

what are the early-forming minerals?

Answer 31

olivine, pyroxene, ca-plag

Question 32

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

Answer 32

silica

Question 33

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

Answer 33

remaining melt

Question 34

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

Answer 34

magmatic differentiation

Question 35

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

Answer 35

depletion ; enrichment

Question 36

t or f: crystal settling is part of magmatic differentiation

Answer 36

T

Question 37

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

Answer 37

Palisades Sill

Question 38

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

Answer 38

80 km long ; monzonite

Question 39

what are the layers of palisades sill?

Answer 39

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

Question 40

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

Answer 40

T

Question 41

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

Answer 41

assimilation

Question 42

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

Answer 42

upward stress ; fracture

Question 43

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

Answer 43

magma mixing

Question 44

in partial melting minerals with _____ are the first to melt

Answer 44

lowest melting temperature

Question 45

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

Answer 45

Partial melting

Question 46

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

Answer 46

volatiles

Question 47

how does volatile trigger partial melting?

Answer 47

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

Question 48

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

Answer 48

basaltic

Question 49

basaltic magma has a temperature of

Answer 49

1000 to 1250 degrees celsius

Question 50

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

Answer 50

high-pressure ; partial melting ; peridotite

Question 51

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

Answer 51

primary or primitive magmas

Question 52

partial melting caused by a reduction in the confining pressure

Answer 52

decompression melting

Question 53

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

Answer 53

subduction zones ; subducting slab ; oceanic crust

Question 54

one way andesitic magma can be formed:

Answer 54

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

Question 55

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

Answer 55

andesitic composition

Question 56

evolved (changed) magmas are termed:

Answer 56

secondary magmas

Question 57

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

Answer 57

assimilate

Question 58

granitic magmas are mostly generated by _____

Answer 58

partial melting of continental crust

Question 59

magmas also contain various types of gas molecules that form when

Answer 59

minerals within a rock body begin to melt

Question 60

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

Answer 60

near the surface ; decreased pressure

Question 61

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

Answer 61

T

Question 62

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

Answer 62

670 cubic meters

Question 63

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

Answer 63

True