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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
what magma will be the least viscous | why
basaltic: low in siO, high eruptive temp
26
relationship btw viscosity and gas content
high viscocity: high gas content low viscocity: low gas content
27
what magma will have lots of gas? Least?
rhyolitic basaltic
28
volatile
substance thst evaporates easily (turns to gas)
29
what volatile makes up 90% of magmas? followed by
water vapor co2 so2
30
how was our oceans and atmosphere created?
volatiles trapped in earth and brought to surface by volcanism which is why the volatiles in magma are the sam as the aatmosphere
31
how do the volatiles (dissolved gases) in the magma stay dissolved?
confining pressure of overlyign rock and cool temp
32
how do gas bubbles form?
confining pressure reduced or increase in temp causes volatiles to separate from magma
33
what happens as the gas bubbles rise?
expand bc it's decreasing in temp, and creates new bubbles until its moslty a gas jet with some globs of magma
34
lava fountains - from what magma - viscocity of that magma - why it's able
basaltic - low viscocity (less thick) - gases can rise and escape easily
35
what does it mean for a lava to be fluid? | what is it triggerede by>
low viscocity (can flow) | new molten rock remobilizes semi-liquid lava ## Footnote inflation of the summit creates fissures for the fluid lava to rise through
36
why is rhyolitic magma explosive
the gas bubbles remain dissolved bc it can't escape (very viscous magma)
37
more volatiles equals
more energetic eruptions
38
what happens when the gas bubbles in rhyolitic magma rises? | pressure exceeds
expand | the confining pressure of the overlying rock, creating fractures
39
what happens as it moves through fractures? (rhyolitic)
more bubbles are created bc of drop in confining pressure (collapse of flank reduces pressure)
40
what happens when rhyolitic magam reaches surface | are these eruptions a one time thing ## Footnote describe lava flow
blown into pumice and ash creating an eruption column (cloud of gas and ash) | series ## Footnote viscous so it piles up and its slow
41
what propels lava fountains | what comes first lava flow or lava fountain
escaping gas pushes lava up | lava fountain
42
pahoehoe
basaltic lava flow ropy fluid, more volatiles
43
aa | aa and pahoehoe relationship
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
lavatube
crust of solidified lava surrounding lava flow so it can travel farther
45
pillow basalts
toothpaste, lava solidifies but interior lava breaks through and repeats steps
46
what is pyroclastic material | aka
pyro-fire clastic-fragments fragments of magma from explosive eruptions | tephra
47
4 pyroclastic materials in order of small to large particles
ash cinders blocks and bombs
48
what's the difference btw blocks and bombs | what do they hold in common
blocks: solid when airborne bombs: liquid when airborne | size and close to vent
49
scoria vs pumice magma
scoria: basaltic pumice: rhyolitic
50
Describe the cycle of pyroclastic material
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
airfall depostis
layered and sorted by grain size
52
pyroclastic flows | aka
eruption column collapses and ssssends cloud down volcano not sorted by grain size and not layered, thick | ash flow deposits
53
welded tuff vs regular tuff
welded: magma hot enough for ash to fuse harder, denser
54
shield volcanoes are made of - shape - how does viscosity affect shape - other characteristics - end of growth | ex
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
what are cinder cones? - rock made of - what can it produce - shape - viscocity and volatiles - life span
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
shield volcanoes in height
tallest from seafloor up
57
example of cinder cones
paricutin
58
Composite volcanoes aka
stratovolcanoes
59
where are most stratovolccanoes/composite volcanoes | thee are associated with what type of plate boundary
ring of fire continental volcanoes | subduction (convergent)
60
describe the things composite volcanoes are built on
alternating layers of pyroclastic debris and andesitic to ryholitic lava flows (cake)
61
how do composite cones get their shape from viscosity
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
how do cinder cones get theri shape
low wvisscosity, when cinder cone volcanoes erupt, the lava spews high into the air and then falls back right on the volcano.
63
are composite volcanoes explosive of effusive?
eexplosive (pyroclastic)
64
stratovolcano eexample
mt fuji mt vesivous
65
what type of material covered the cities close to vesuvoius lava flow comp
pumice Rhyolotic
66
what is the vei scale
relative measure of the explosiveness of volcanic eruptions.
67
things that are basaltic
scoria, lava flow, tube, fountain, pahoehoe, aa, lava bombs, pillow basalts
68
things that are rhylolitic
tuff welded tuff oumice pyroclastic material obsidian
69
What kind of magma produces shield? Cone? Composite?
Basaltic Andesitic

GEO LECTURE (19 decks)

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