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EOSC 114 > Volcanoes 2 > Flashcards

Volcanoes 2 Flashcards

1
Q

What is the most important factor that determines igneous texture (___)?

A

Cooling rate
(grain size)

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2
Q

Extrusive or volcanic rocks cool ___ and are ___ grained

A

fast (days-months)
fine

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3
Q

Intrusive or plutonic rocks cool ____ and are ____

A

slow (100+ years)
coarser

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4
Q

Example of extrusive rock

A
  • Basalt, lots of gas bubbles
  • rhyolite
  • andesite
  • dacite
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5
Q

Example of intrusive rock

A

granite

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6
Q

Felsic rocks examples and colour

A

light color
ex/ granite, rhyolite

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7
Q

Mafic rocks examples and colour

A

dark color
ex/ basalt, gabbro

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8
Q

rhyolite is an ___ ___ rock

A

extrusive felsic

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9
Q

basalt is an ____ ___ rock

A

extrusive mafic

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10
Q

granite is an ___ ___ rock

A

intrusive felsic

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11
Q

what is obsidian?

A

volcanic glass

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12
Q

define glass

A

a non-crystalline or amorphous solid formed by quenching a melt
-> cools so fast that regular crystal lattice cannot form

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13
Q

Temperature of mafic vs felsic rocks

A

mafic hot (1200-1400˚C)
felsic cool (600-900˚C)

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14
Q

Water content of mafic vs felsic rocks

A

mafic low
felsic high

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15
Q

viscosity of mafic vs felsic rocks

A

mafic low (runny)
felsic high (sticky)

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16
Q

Explosivity of mafic vs felsic rocks

A

mafic non explosive (lava)
felsic explosive (pyroclastic)

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17
Q

Silica content of mafic vs felsic rocks

A

mafic less (~50%)
felsic more (~70%)

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18
Q

Example of intermediate rocks (between mafic and felsic)

A

andesite
dacite

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19
Q

what are the two critical magma properties

A

density and viscosity

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20
Q

Magma density

A

== buoyancy

2.5 - 3.3 g/cm^3

21
Q

Magma melt travels up because

A

they are less dense

22
Q

define viscosity

A

resistance to flow
controls flow, deformation, eruption

23
Q

Viscosity is strongly dependent on ____

A

temperature

24
Q

magma viscosity depends on ____

A
  • temperature
  • gas content
  • crystal content
25
Q

What composition affects viscosity the most?

26
Q

in a magma chamber containing rhyolite on top of basalt, which erupts first?

A

rhyolite erupts first, then basalt

then the basalt moves faster and overruns rhyolite (break thru)

27
Q

high viscosity basalt lavas are called

A

A’a
(blocky)

28
Q

Cooling ___ melt viscosity, which increases ____

A

increases
crystallization

29
Q

Lowest viscosity basalt lavas are called

A

pahoehoe
(flows)

30
Q

A crystal rich lava will have ___ viscosity and ___ temperature than crystal poor lava of the same composition

A

higher viscosity
lower temperature

31
Q

the loss of dissolved volatiles ____ viscosity

A

increases

volatiles include dissolved gasses, and when
magma rises -> lower P -> less solubility -> bubbles!

32
Q

Where do volcanoes occur?

A

plate boundaries
hot spots

33
Q

Example of a famous area of volcanism

A

pacific ring of fire
also Hawaii is a hot spot

34
Q

At which plate boundaries do volcanoes occur?

A

convergent and divergent

35
Q

Continental volcanic arcs happen as a result of what type of volcanoes?

A

subduction volcanoes

36
Q

Describe how continental volcanic arcs form

A

volatiles and partial melt from subducted ocean plate = mafic magma

felsic magma as it is stored in continental crust

felsic/intermediate as it is contaminated by stuff

37
Q

plates involved in our local continental volcanic arc

A

Cascadia subduction zone
Juan de fuca plate subducting under North American plate

38
Q

Describe how oceanic volcanic arcs form

A

volatiles and melt rising from subducted ocean plate = mafic magma

mafic/intermediate magmas and lavas

39
Q

The most voluminous volcanism on earth are from

A

mid ocean ridges
- not exposed at surface except in Iceland

40
Q

Mafic magma from a plume of hot mantle:
mantle plumes are ____ & ____

A

stationary and pulsatory

41
Q

Volcanic settings: Divergent boundaries

A

continental crust : East African Rift Zone
btwn oceanic plates: Mid-Atlantic Ridge

42
Q

Volcanic Settings: Convergent boundaries

A

Oceanic-continental: Cascades
Oceanic-oceanic: Aleutian islands

43
Q

Volcanic Settings: Hot spots

A

under continental crust: Yellowstone
under oceanic crust: Hawaii

44
Q

Melting mechanisms: Divergent Boundaries

A

mantle stuff rises in a dike, pressure decrease
- mafic magma may melt overlying crust

45
Q

Melting mechanisms: Convergent Boundaries

A

hydration of mantle by subjecting plate
- mafic magma melts overlying crust

46
Q

Melting mechanisms: Hot Spots

A

mantle stuff rises in cylindrical plume, pressure decrease
- mafic magma melts overlying crust

47
Q

Type of magma associated with oceanic plates/crust

48
Q

Type of magma associated with continental crust

A

mafic-int-felsic
(mostly felsic)

EOSC 114 (30 decks)

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