Volcanoes 1 and 2 Flashcards by Monique Yuan

How are sedimentary rocks formed? metamorphic? igneous?

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

where they solidified
temperature
melting conditions (water, pressure)
geologic setting

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

underground = magma
surface of planet = lava

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

underground: plutonic or intrusive
above ground: volcanic or extrusive

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How does cooling time affect crystal size in igneous rocks?

slower cooling (longer cooling time) = bigger crystals

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

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

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

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

FALSE: 99% of magma cools underground

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Where did the purcell sills rocks cool?

underground

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What is a pyroclastic rock?

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

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What is tephra?

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

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what is a mafic igneous rock made of? felsic?

mafic = magnesium and ferric
felsic = feldspar and silica

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What percent composition of SiO2 would be considered ultramafic?

<45%

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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

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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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

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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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

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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How can you tell that a rock could be granite?

pink crystals (K-rich feldspars)

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

felsic

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What are 3 plutonic rock types? Volcanic rock types?

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

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How do you melt rock/make magma?

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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Does melt rise or sink? Why?

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

What is magma differentiation? What are the 3 steps?

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

What determines the type of volcano that forms?

the type of magma that makes it to the surface

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

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

What determines how much the first melt will differentiate?

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

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

- 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

TRUE or FALSE: Iceland mid-ocean ridge forms basalt

FALSE: forms mix b/c thick crust note: iceland is an exception

What is a volcano?

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

what are the volcano shapes? Provide examples

- 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)

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

- 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

TRUE or FALSE: viscosity decreases as SiO2 decreases

TRUE

TRUE or FALSE: increasing SiO2 leads to decreasing explosivity

FALSE: increasing SiO2 --> increasing viscosity --> increasing explosivity

which type of lava results in quiet eruptions?

mafic lava (basalt)

What kind of volcanoes are composed of the largest mountains?

shield volcanoes

How do shield volcanoes form? What are some examples?

- fluid basalt lava flows layer upon layer on a low angle - Muana Kea, Skjaldbreidur (Iceland)

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

- 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

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

- form from mafic lava NOT coming form a central vent - flank of Kilauea and Fagradalsfjall (Iceland)

How do kimberlites (ultra-mafic volcanoes) form?

- very powerful eruptions that originate in the mantle; where diamonds come from; never witnessed

which type of lava results in explosive eruptions?

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

which volcanoes/eruptions result from mafic lava?

- shield volcanoes - cinder cones- fissure eruptions - kimberlites

How are stratovolcanoes formed? what are some examples?

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

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

- 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

How do calderas form? What are some examples?

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

What are the 7 volcanic hazards?

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

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

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

What is a lahar?

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

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

Mt. Rainier

Why is Mt. Rainier very dangerous?

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

Which eruptions caused massive tsunamis?

Krakatau and Unzen

Which eruptions caused one of the largest landslides?

mount meager

LeWhat kind of gases can be found in an eruption?

- water vapour - CO2 - HCl - HF - H2S (and sulfur)