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GEO LECTURE > Volcanoes > Flashcards

Volcanoes Flashcards

1
Q

Where are volcanoes found? percent

A

90% at plate boundaries
10% in plate interiors/hot spots

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2
Q

What plate boundaries are volcanoes found? percentage of the 90%

A

convergent (subduction): 7-13%
divergent (mid ocean spreading centers): 80%

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3
Q

Name 2 places under hot spot

A

hawaii
yellowstone

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4
Q

why does volcanism happen at divergent plate boundaries

A

separating crust thins, sparking upwelling of mantle and upwarping of asthenosphere due to decrease in pressure, magma rises and creates volcanoes

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5
Q

What is the seafloor made of

A

volcanic rock-basalt

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6
Q

Basalt
- silica content and other
- silicates
- color
- dominent minerals

percent at surface

A

low
high in fe, mg, ca
dark silicates
dark
pyroxene and plagioclase fledspar

80

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7
Q

rhyolite
- silica content and other
- silicates
- color
- dominent minerals

percent at surface

A

high, calcium
light silicates
light
quartz and potassium feldspar

10

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8
Q

Andesite
- silica content
- color

percent at surface

A

intermediate

10

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9
Q

what are the three compositions of magma

A

andesitic, basaltic, rhyolitic

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10
Q

how is magma generated?

A

partial melting of the asthenosphere

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11
Q

Where is basaltic magma coming from?

A

mid ocean spreading centers

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12
Q

describe the volcanism at mid ocean spreading centers
- volume
- eruption
- hazard
- where

A

voluminous
gentle
not dangerous
mostly underwater

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13
Q

extensive basaltic flows are products of

A

hot spot volcanism by mantle plumes

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14
Q

how does basaltic magma propangate andesitic or rhyolitic magma?

A

basaltic magma rises in continental areas, but ponds at mantle-crust boundary, bc it’s hotter than c.c melt. temp, the continental rocks melt to produce silica rich, less dense, andesitic or rhyloitic magma

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15
Q

where is andesitic or rhylotic magma found

A

subduction zones

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16
Q

volcanism at subduction zones
- volume
- hazard
- where
- eruption

A

less volumuous
deadly
continents or islands
explosive

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17
Q

what does basaltic magma produce

A

lava flows
lava fountains

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18
Q

what does rhyolitic magma produce

A

ash

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19
Q

what are 2 other words for non explosive eruptions

A

quiescent
effusive

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20
Q

2 factors that determine how magma erupts

A

viscosity & volitiles/gas content

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21
Q

Viscosity

what does it mean for something to have high viscocity vs low viscocity

A

resistance to flow

high: doesn’t flow, thicker; low: flows easily, thin

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22
Q

what are the factors affecting viscosity

A

temp, silica and oxygen, crystal

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23
Q

Silica and oxygen content for viscosity

why (talk abt structure of atoms)

A

high SiO: more viscous
low SiO: less viscous

siO have strong close bonds (gas atoms vs solid atoms)

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24
Q

what magma will have the greatest viscocity

why

A

rhyolitic bc high SiO, low eruptive temp

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25
Q

what magma will be the least viscous

why

A

basaltic: low in siO, high eruptive temp

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26
Q

relationship btw viscosity and gas content

A

high viscocity: high gas content
low viscocity: low gas content

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27
Q

what magma will have lots of gas? Least?

A

rhyolitic
basaltic

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28
Q

volatile

A

substance thst evaporates easily (turns to gas)

29
Q

what volatile makes up 90% of magmas? followed by

A

water vapor
co2
so2

30
Q

how was our oceans and atmosphere created?

A

volatiles trapped in earth and brought to surface by volcanism
which is why the volatiles in magma are the sam as the aatmosphere

31
Q

how do the volatiles (dissolved gases) in the magma stay dissolved?

A

confining pressure of overlyign rock and cool temp

32
Q

how do gas bubbles form?

A

confining pressure reduced or increase in temp causes volatiles to separate from magma

33
Q

what happens as the gas bubbles rise?

A

expand bc it’s decreasing in temp, and creates new bubbles until its moslty a gas jet with some globs of magma

34
Q

lava fountains
- from what magma
- viscocity of that magma
- why it’s able

A

basaltic
- low viscocity (less thick)
- gases can rise and escape easily

35
Q

what does it mean for a lava to be fluid?

what is it triggerede by>

A

low viscocity (can flow)

new molten rock remobilizes semi-liquid lava

inflation of the summit creates fissures for the fluid lava to rise through

36
Q

why is rhyolitic magma explosive

A

the gas bubbles remain dissolved bc it can’t escape (very viscous magma)

37
Q

more volatiles equals

A

more energetic eruptions

38
Q

what happens when the gas bubbles in rhyolitic magma rises?

pressure exceeds

A

expand

the confining pressure of the overlying rock, creating fractures

39
Q

what happens as it moves through fractures?
(rhyolitic)

A

more bubbles are created bc of drop in confining pressure (collapse of flank reduces pressure)

40
Q

what happens when rhyolitic magam reaches surface

are these eruptions a one time thing

describe lava flow

A

blown into pumice and ash creating an eruption column (cloud of gas and ash)

series

viscous so it piles up and its slow

41
Q

what propels lava fountains

what comes first lava flow or lava fountain

A

escaping gas pushes lava up

lava fountain

42
Q

pahoehoe

A

basaltic lava flow
ropy
fluid, more volatiles

43
Q

aa

aa and pahoehoe relationship

A

basaltic lava flow
blocky and rough texture
less fluid, less volatile

pahoehoe>aa but not vice versa f/ temp decrease and gas bubble formation

44
Q

lavatube

A

crust of solidified lava surrounding lava flow so it can travel farther

45
Q

pillow basalts

A

toothpaste, lava solidifies but interior lava breaks through and repeats steps

46
Q

what is pyroclastic material

aka

A

pyro-fire
clastic-fragments
fragments of magma from explosive eruptions

tephra

47
Q

4 pyroclastic materials in order of small to large particles

A

ash
cinders
blocks and bombs

48
Q

what’s the difference btw blocks and bombs

what do they hold in common

A

blocks: solid when airborne
bombs: liquid when airborne

size and close to vent

49
Q

scoria vs pumice magma

A

scoria: basaltic
pumice: rhyolitic

50
Q

Describe the cycle of pyroclastic material

A

magma rises and gases expand which creates a frothy melt, explosively ejected as tiny glass (ash) in a pyroclastic plume, which rains down ash and cinders which falls and creates tuff

51
Q

airfall depostis

A

layered and sorted by grain size

52
Q

pyroclastic flows

aka

A

eruption column collapses and ssssends cloud down volcano
not sorted by grain size and not layered, thick

ash flow deposits

53
Q

welded tuff vs regular tuff

A

welded: magma hot enough for ash to fuse
harder, denser

54
Q

shield volcanoes are made of
- shape
- how does viscosity affect shape
- other characteristics
- end of growth

ex

A

fluid basaltic lava
- broad with gentle slopes
- basaltic lava is less viscous, so it easily flows fast & far
- lava tubes
- calderas (depressions in summit)
- eject pyroclastic material which is more visocus so it will be short and thick, cinder cones

mauna loa

55
Q

what are cinder cones?
- rock made of
- what can it produce
- shape
- viscocity and volatiles
- life span

A

piles of basaltic pyroclastic debris around central vent
- scora
- lava flows
- deep craters, con shape ,s teep slope,
- medium viscosity and medium volatile
- erupt once and done, produced in one eruptive event

56
Q

shield volcanoes in height

A

tallest from seafloor up

57
Q

example of cinder cones

A

paricutin

58
Q

Composite volcanoes aka

A

stratovolcanoes

59
Q

where are most stratovolccanoes/composite volcanoes

thee are associated with what type of plate boundary

A

ring of fire continental volcanoes

subduction (convergent)

60
Q

describe the things composite volcanoes are built on

A

alternating layers of pyroclastic debris and andesitic to ryholitic lava flows (cake)

61
Q

how do composite cones get their shape from viscosity

A

medoum to high viscosity (andesitic to rhyolitic)
silica rich equals magma doesn’t move as far before hardeneing=steep slopes and
summit steep bc ocarse material accumulaate near sourse but finer sediment flatten the flank of cone
shorter flows armour summit area

62
Q

how do cinder cones get theri shape

A

low wvisscosity, when cinder cone volcanoes erupt, the lava spews high into the air and then falls back right on the volcano.

63
Q

are composite volcanoes explosive of effusive?

A

eexplosive (pyroclastic)

64
Q

stratovolcano eexample

A

mt fuji
mt vesivous

65
Q

what type of material covered the cities close to vesuvoius
lava flow comp

A

pumice
Rhyolotic

66
Q

what is the vei scale

A

relative measure of the explosiveness of volcanic eruptions.

67
Q

things that are basaltic

A

scoria, lava flow, tube, fountain, pahoehoe, aa, lava bombs, pillow basalts

68
Q

things that are rhylolitic

A

tuff
welded tuff
oumice
pyroclastic material
obsidian

69
Q

What kind of magma produces shield? Cone? Composite?

A

Basaltic
Andesitic

GEO LECTURE (19 decks)

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