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DISP Earth Science > Volcanos > Flashcards

Volcanos Flashcards

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1
Q

How much of the crust is volcanic?

A

90% of the top 16 km

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2
Q

What makes volcanoes good things to live near?

A

geothermal energy, form fertile soils

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3
Q

How do volcanos form fertile soils?

A

they bring nutrients from earth’s interior to the surface; add material to the surface that weathers easily, making fertile soil

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4
Q

When and where was the last major eruption?

A

1815; Tambora

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5
Q

What is magma?

A

molten rock

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6
Q

What is lava?

A

magma on the earth’s surface

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7
Q

What does plutonic mean?

A

intrusive - from the interior of the crust

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8
Q

What are the 3 components of magma?

A

solid, liquid, dissolved gases

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9
Q

What does volcanic mean?

A

extrusive - on the exterior of the crust

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10
Q

What types of material are erupted from a volcano?

A

lava (liquid), pyroclastics (solid), and volcanic gas

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11
Q

How does lava behave?

A

as a liquid

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12
Q

In what direction does lava flow?

A

downhill (usually in stream courses)

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13
Q

How thick are lava flows?

A

1 to 400 m (average ~ a few metres)

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14
Q

How long can lava flows be?

A

> 100 km

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15
Q

What can have a volume of 12.5 cubic km?

A

lava flows

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16
Q

At what velocities can lava flow?

A

2 to 45+ km/h

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17
Q

What factors control the size and shape of a lava flow?

A

viscosity, yield stress, topography, source geometry

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18
Q

What controls viscosity of a lava flow?

A

compositoin

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19
Q

What does viscosity of a lava flow control?

A

speed

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20
Q

How does yield stress relate to lava flows?

A

lava flow stops when eruption stops - need to be adding lava for it to keep moving

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21
Q

What are 2 types of lava flow sources?

A

point sources and line sources (fissure)

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22
Q

What are pyroclastics?

A

solid debris erupted by a volcano

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23
Q

What happens to pyroclastics upon eruption?

A

transported and deposited by wind and water

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24
Q

What are the 5 types of pyroclastic particles, from smallest to largest?

A

dust, ash, lapilli, bomb, block

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25
Q

What sort of size are ash particles?

A

sand-sized

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26
Q

How big are lapilli?

A

pebble-sized

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27
Q

How big are bombs?

A

head-sized

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28
Q

How does the size of pyroclastic particles affect their transportation?

A

they sort by size, even in stratosphere - currents transport small particles farther than large ones

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29
Q

Why is it dangerous to inhale volcanic ash?

A

it has sharp edges that can damage lungs

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30
Q

How do volcanoes create their own weather?

A

water clumps around particles ejected into the atmosphere and the condensed water vapours form rain/clouds

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31
Q

What does the cloud of pyroclastic material from an explosive volcano look like?

A

tall column above vent; lapilli falling close to the vent; ash falling from higher up; haze of dust spread away by wind; collaspsing column forming a pyroclastic flow down the slopes

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32
Q

What is another term for a nuee ardente?

A

pyroclastic flow

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33
Q

What is a pyroclastic flow?

A

density current (gravity flow) of pyroclastic particles and hot gas

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34
Q

What usually causes a pyroclastic flow?

A

ac olumn collapse

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35
Q

How does a pyroclastic flow move down the slopes of a volcano?

A

hottest particles at the bottom of the flow gives flow buyancy and heats the soil, giving a cushion of gas for it to flow over

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36
Q

How does a pyroclastic flow behave?

A

like liquid - flows downhill

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37
Q

What is an ignimbrite?

A

sheet of tuff (ash/lapilli) left from a pyroclastic flow

38
Q

What is a lahar?

A

mudflow of pyroclastic particles and water

39
Q

How does a lahar travel?

A

flows in channels down slopes

40
Q

What gases make up most volcanic gases?

A

water, CO2, nitrogen, SO2

41
Q

What gives volcanoes their “rotten egg” smell?

A

sulfur gases (SO2, SO3, S2)

42
Q

Why are sulfur gases so dangerous?

A

they’re toxic and heavy (so they settle near the ground)

43
Q

What is viscosity?

A

resistance to stirring/flow

44
Q

What does viscosity depend on?

A

composition, temperature, and polymerization of SiO4

45
Q

How does polymerization of SiO4 relate to temperature?

A

it increases as temperature drops

46
Q

What magma is usually at ~1000 deg C?

A

mafic

47
Q

What magma is usually at ~700 deg C?

A

felsic

48
Q

What is the range of viscosities for natural silicate liquids?

A

olive oil to cold honey

49
Q

What makes felsic magma so viscous?

A

large silicate composition; lower temperature; silicate liquid near freezing point - so starts crystallizing to SiO4 tetrahedra and polymerizing while still a liquid

50
Q

What is the viscosity of mafic magma and how does it relate to its velocity?

A

low viscosity, allowing it to flow quickly

51
Q

What magma forms basalt?

A

mafic

52
Q

What are the properties of a basaltic flow?

A

fluid, hot (1000 deg C), long thin flows

53
Q

What is the composition of a basaltic flow?

A

silica poor; Fe and Mg rich

54
Q

What are the properties of an andesitic flow?

A

viscous, cool (800 deg C), short thich flows, explosive

55
Q

Why is an andesitic flow so explosive?

A

it’s viscous, making it difficult for dissolved gases to get out; gases expand in bubbles and explode out

56
Q

What is the composition of an andesitic flow?

A

silica rich; Al, K, Na rich

57
Q

How much of a mafic magma is silicate?

A

50%

58
Q

What makes up mafic magma?

A

SiO2, Mg, Fe, Ca, Al, calcium feldspar, olivine, pyroxene

59
Q

What rock is the volcanic rock of the oceans?

A

basalt

60
Q

Why is felsic lava rare?

A

it’s very viscous, so it takes a while to flow up to the crust’s surface

61
Q

How much silicate makes up felsic magma?

A

> 65%

62
Q

What makes up felsic mgma?

A

SiO2, Na, I, Al, K-feldspar, Na-feldspar, quartz

63
Q

What type of magma forms basalt?

A

mafic

64
Q

What type of magma forms rhyolite?

A

felsic

65
Q

How much silicate makes up intermediate magma?

A

50-65%

66
Q

What type of rock does intermediate magma form?

A

andesite

67
Q

What are two common volcano styles?

A

shield volcanoes and composite volcanoes

68
Q

How are shield volcanoes constructed?

A

non-viscous mafic lava flows spreading out and building up over time (but little ash)

69
Q

What type of volcano is massive and has gentle slopes?

A

shield volcanoes

70
Q

What type of magma forms shield volcanoes?

A

basalt (mafic magma)

71
Q

What is another term for composite volcanoes?

A

stratovolcanoes

72
Q

What are the 2 main components of composite volcanoes and the ratio between the?

A

pyroclastic deposites and lava flows; 50:50

73
Q

What type of magma forms stratovolcanoes?

A

andesite (intermediate magma)

74
Q

How does the structure of composite volcanoes differ from that of shield volcanoes?

A

steeper slopes and smaller cross-sectional areas

75
Q

Which type of volcanoe is usually more explosive?

A

composite

76
Q

What are plateau basalts?

A

thick accumulations of long fluid flows

77
Q

What type of source geometry would be needed for a plateau basalt?

A

fissure eruption?

78
Q

What type of volcano style has never been experienced in known history?

A

plateau basalts

79
Q

What are ignimbrite sheets?

A

pyroclastic deposits at a similar scale to that of plateau basalts

80
Q

What is the scale of a plateau basalt?

A

400 km x 400 km x 4 km

81
Q

What is caused by the collapse of a composite volcano?

A

caldera

82
Q

How does a caldera form?

A

magma withdrawal from chamber leaves empty space; volcano collapses into chamber after eruption (especially explosive ones)

83
Q

How large are calderas?

A

2-30 km in diameter

84
Q

Where are 3 places volcanoes are often found?

A

ocean islands, mid-ocean ridges, continental fringe

85
Q

What is the difference between island chains and island arcs?

A

island chains only have active volcanoes at one end; arcs have active volcanoes throughout arc

86
Q

Where are most volcanoes found?

A

ocean islands

87
Q

What are mantle xenoliths?

A

inclusions of material magma brought up from beneath crust

88
Q

Why are mantle xenoliths important?

A

gives us knowledge of the mantle

89
Q

What are some hazards from eruptions?

A

lava flows, falling ash/lapilli, explosion, landslides, earthquakes, tsunamis, lahars

90
Q

How are earthquakes caused by volcanic eruptions?

A

movement of magma breaks rocks underground

DISP Earth Science (7 decks)

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