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EAS 205 > Volcanoes 1 and 2 > Flashcards

Volcanoes 1 and 2 Flashcards

1
Q

How are sedimentary rocks formed? metamorphic? igneous?

A

sedimentary: weathering, erosion, transportation, sedimentation, deposition, lithification, precipitation, diagenesis
metamorphic: increased pressure and temperature leading to re-crystallization and deformation
igneous: melting, crystallization of magma

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2
Q

What are the various compositions and textures of igneous rocks controlled by?

A
  • where they solidified
  • temperature
  • melting conditions (water, pressure)
  • geologic setting
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3
Q

What is the term for molten rock underground? molten rock on surface of planet?

A

underground = magma
surface of planet = lava

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4
Q

What is the classification for an igneous rock that solidified underground? above ground?

A

underground: plutonic or intrusive
above ground: volcanic or extrusive

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5
Q

How does cooling time affect crystal size in igneous rocks?

A

slower cooling (longer cooling time) = bigger crystals

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6
Q

What do the crystals/grains of a plutonic rock look like? volcanic rock? why?

A

plutonic rock = coarser (large) grained crystals, visible to eye –> b/c cool slower
volcanic rock = finer-grained or no crystals (glass) –> b/c cool faster

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7
Q

What is the term for a plutonic rock based on its crystal size? volcanic rock?

A

plutonic = PHANERITIC (large crystals)
volcanic = APHANTIC (small crystals)

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8
Q

TRUE or FALSE: most magma reaches the surface of the Earth

A

FALSE: 99% of magma cools underground

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9
Q

Where did the purcell sills rocks cool?

A

underground

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10
Q

What is a pyroclastic rock?

A

extrusive volcanic rocks/deposits formed by the eruption of a volcano

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11
Q

What is tephra?

A

material that was ejected into the air during an eruption (e.g. ash or pumice)

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12
Q

what is a mafic igneous rock made of? felsic?

A

mafic = magnesium and ferric
felsic = feldspar and silica

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13
Q

What percent composition of SiO2 would be considered ultramafic?

A

<45%

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14
Q

Describe the following about mafic igneous rocks:
- percent composition of SiO2
- viscosity
- temperature at which it melts/forms
- colour
- amount of ferromagnesian (abundant or fewer)
- type of feldspar
- extrusive rock example
- intrusive rock example
- main setting where they form

A
  • percent composition of SiO2: 45-50%
  • viscosity: low/runny
  • melting temp: 1200 degrees celcius
  • colour: dark
  • amt of ferromagnesian: abundant
  • feldspar type: Ca-rich (plagioclase)
  • extrusive: BASALT
  • intrusive: GABBRO
  • main setting where they form: mid-ocean ridges, hotspots under ocean crust
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15
Q

Describe the following about intermediate igneous rocks:
- percent composition of SiO2
- viscosity
- temperature at which it melts/forms
- colour
- extrusive rock example
- intrusive rock example
- main setting where they form

A
  • percent composition of SiO2: 50-70%
  • viscosity: moderate
  • melting temp: intermediate temperatures
  • colour: purple/greenish/grey
  • extrusive: ANDESITE and DACITE
  • intrusive: DIORITE (GRANDIORITE)
  • formation setting: stratovolcanoes that form over subduction zones
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16
Q

Describe the following about felsic igneous rocks:
- percent composition of SiO2
- viscosity
- temperature at which it melts/forms
- colour
- amount of ferromagnesian (abundant or fewer)
- type of feldspar
- extrusive rock example
- intrusive rock example
- main setting where they form

A
  • SiO2: >70%
  • viscosity: high/very thick
  • melting temp: low, 800 degrees celcius
  • colour: pale…tan, white, pinkish
  • ferromagnesian: fewer
  • feldspar type: K-rich
  • extrusive: RHYOLITE
  • intrusive: GRANITE
  • main setting where they form: hot spots under continental crust, and subduction zones
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17
Q

How can you tell that a rock could be granite?

A

pink crystals (K-rich feldspars)

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18
Q

Which type of igneous rock (mafic, intermediate, felsic) takes the longest time and thicker continental crust to form?

A

felsic

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19
Q

What are 3 plutonic rock types? Volcanic rock types?

A

plutonic: gabbro, diorite, granite
volcanic: basalt, andesite, rhyolite

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20
Q

How do you melt rock/make magma?

A

1) decrease overlying pressure (decompression melting; spreading zone)
2) raise the temperature (mantle plume/hot spot; subducting plate)
3) and/or add water (subducting plate)

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21
Q

Does melt rise or sink? Why?

A

rises (if it can find a way) b/c less dense than the surrounding rock

22
Q

What is magma differentiation? What are the 3 steps?

A
  • used to describe change from one melt composition to another, usually from mafic to felsic
  • steps: 1) country rock partial melt, 2) fractional crystallization, 3) partial melt/recharge
23
Q

What determines the type of volcano that forms?

A

the type of magma that makes it to the surface

24
Q

What is the first melt produced in magma differentiation? Why?

A

first melt = basaltic (mafic) because it happens deep in the lithosphere or upper mantle

25
Q

What determines how much the first melt will differentiate?

A

thicker crust –> takes longer to reach the surface –> tends to evolve more (mafic –> intermediate –> felsic)
(i.e. thicker crust = more differentiation)

26
Q

What types of igneous rocks can be found in the following tectonic settings? Explain why, based on magma differentiation.
- subduction zones
- hot spot under ocean crust
- mid-ocean ridges
- continental rifts
- hot spot under (continental) crust

A
  • subduction zones: intermediate rocks –> moderate crustal thickness, moderate residence time
  • hot spot under ocean crust: basalt –> directly from mantle
  • mid-ocean ridges: basalt –> directly from mantle
  • continental rifts: mix –> continents are thick but thinned at rifts
  • hot spot under crust: rhyolite –> lots of crust to travel through, long residence time
27
Q

TRUE or FALSE: Iceland mid-ocean ridge forms basalt

A

FALSE: forms mix b/c thick crust

note: iceland is an exception

28
Q

What is a volcano?

A

central vent or fissure where molten rock, gas, and rock fragments are ejected during an eruption

29
Q

what are the volcano shapes? Provide examples

A
  • broad domes (Mauna Kea)
  • deep depressions (Yellowstone/Santorini)
  • long fissures (Kilauea east rift eruption)
  • prefect cones ( mount Cleveland)
  • rugged or towering not-so-perfect cones (Rainier)
30
Q

What types of volcanoes can be found in the following tectonic settings?
- subduction zones
- hot spot under ocean crust
- mid-ocean ridges
- continental rifts
- hot spot under (continental) crust

A
  • subduction zones: stratovolcanoes
  • hot spot under ocean crust: shield volcanoes, fissures
  • mid ocean ridges: fissures
  • continental rifts: mix
  • hot spot under crust: calderas, flood basalts
31
Q

TRUE or FALSE: viscosity decreases as SiO2 decreases

A

TRUE

32
Q

TRUE or FALSE: increasing SiO2 leads to decreasing explosivity

A

FALSE: increasing SiO2 –> increasing viscosity –> increasing explosivity

33
Q

which type of lava results in quiet eruptions?

A

mafic lava (basalt)

34
Q

What kind of volcanoes are composed of the largest mountains?

A

shield volcanoes

35
Q

How do shield volcanoes form? What are some examples?

A
  • fluid basalt lava flows layer upon layer on a low angle
  • Muana Kea, Skjaldbreidur (Iceland)
36
Q

How do cinder cones (volcanoes) form? What are some examples?

A
  • form when extremely gas-charged mafic lava ejects from a single vent; lava is blown into the air, breaks into smaller fragments as it solidifies, forming cinders, which fall around the vent forming a cone
  • Eva Cone
37
Q

How do fissure eruptions (volcanoes) form? What are some examples?

A
  • form from mafic lava NOT coming form a central vent
  • flank of Kilauea and Fagradalsfjall (Iceland)
38
Q

How do kimberlites (ultra-mafic volcanoes) form?

A
  • very powerful eruptions that originate in the mantle; where diamonds come from; never witnessed
39
Q

which type of lava results in explosive eruptions?

A

felsic and intermediate (b/c high viscosity, gases cannot escape magma)

40
Q

which volcanoes/eruptions result from mafic lava?

A
  • shield volcanoes
  • cinder cones- fissure eruptions
  • kimberlites
41
Q

How are stratovolcanoes formed? what are some examples?

A
  • alternating layers of lava, tephra, pyroclastic flow deposits –> classic cone-like volcano shape
  • Mount Fuji and Mount St. Helens
42
Q

How do lava domes form? Where are they commonly found? What are some examples?

A
  • erupting lava too thick to flow –> piles up to form steep-sided dome –> push up and out as it grows
  • common in stratovolcanoes –> rebuild volcano after destructive eruption
  • Caliente dome, Mount St Helens
43
Q

How do calderas form? What are some examples?

A
  • very large craters or giant depressions that form when ground collapses after magma chamber beneath the erupting volcano is drained
  • Crater Lake, Yellowstone
44
Q

What are the 7 volcanic hazards?

A

1) lava flows
2) tephra (ash) fall
3) pyroclastic flows
4) mudflows (lahars)
5) tsunamis/landslides
6) gas emissions
7) climate change

45
Q

What is a pyroclastic flow? When does it most commonly occur?

A
  • fluidized masses of rock fragments and gases that move rapidly in response to gravity
  • explosive (felsic/intermediate) eruptions, or lava dome collapses
46
Q

What is a lahar?

A

debris flow composed of a slurry of pyroclastic material, rocky debris, and WATER

47
Q

Which volcano is ranked #16 in most dangerous volcanoes in the world?

A

Mt. Rainier

48
Q

Why is Mt. Rainier very dangerous?

A

covered in glaciers and made up of weak volcanic rock –> just warming up will lead to lahar (doesn’t need to erupt)

49
Q

Which eruptions caused massive tsunamis?

A

Krakatau and Unzen

50
Q

Which eruptions caused one of the largest landslides?

A

mount meager

51
Q

LeWhat kind of gases can be found in an eruption?

A
  • water vapour
  • CO2
  • HCl
  • HF
  • H2S (and sulfur)

EAS 205 (16 decks)

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