Volcanoes 2

Question 1

What is the most important factor that determines igneous texture (___)?

Answer 1

Cooling rate
(grain size)

Question 2

Extrusive or volcanic rocks cool ___ and are ___ grained

Answer 2

fast (days-months)
fine

Question 3

Intrusive or plutonic rocks cool ____ and are ____

Answer 3

slow (100+ years)
coarser

Question 4

Example of extrusive rock

Answer 4

• Basalt, lots of gas bubbles
• rhyolite
• andesite
• dacite

Question 5

Example of intrusive rock

Answer 5

granite

Question 6

Felsic rocks examples and colour

Answer 6

light color
ex/ granite, rhyolite

Question 7

Mafic rocks examples and colour

Answer 7

dark color
ex/ basalt, gabbro

Question 8

rhyolite is an ___ ___ rock

Answer 8

extrusive felsic

Question 9

basalt is an ____ ___ rock

Answer 9

extrusive mafic

Question 10

granite is an ___ ___ rock

Answer 10

intrusive felsic

Question 11

what is obsidian?

Answer 11

volcanic glass

Question 12

define glass

Answer 12

a non-crystalline or amorphous solid formed by quenching a melt
-> cools so fast that regular crystal lattice cannot form

Question 13

Temperature of mafic vs felsic rocks

Answer 13

mafic hot (1200-1400˚C)
felsic cool (600-900˚C)

Question 14

Water content of mafic vs felsic rocks

Answer 14

mafic low
felsic high

Question 15

viscosity of mafic vs felsic rocks

Answer 15

mafic low (runny)
felsic high (sticky)

Question 16

Explosivity of mafic vs felsic rocks

Answer 16

mafic non explosive (lava)
felsic explosive (pyroclastic)

Question 17

Silica content of mafic vs felsic rocks

Answer 17

mafic less (~50%)
felsic more (~70%)

Question 18

Example of intermediate rocks (between mafic and felsic)

Answer 18

andesite
dacite

Question 19

what are the two critical magma properties

Answer 19

density and viscosity

Question 20

Magma density

Answer 20

== buoyancy

2.5 - 3.3 g/cm^3

Question 21

Magma melt travels up because

Answer 21

they are less dense

Question 22

define viscosity

Answer 22

resistance to flow
controls flow, deformation, eruption

Question 23

Viscosity is strongly dependent on ____

Answer 23

temperature

Question 24

magma viscosity depends on ____

Answer 24

• temperature
• gas content
• crystal content

Question 25

What composition affects viscosity the most?

Answer 25

H2O :D

Question 26

in a magma chamber containing rhyolite on top of basalt, which erupts first?

Answer 26

rhyolite erupts first, then basalt then the basalt moves faster and overruns rhyolite (break thru)

Question 27

high viscosity basalt lavas are called

Answer 27

A'a (blocky)

Question 28

Cooling ___ melt viscosity, which increases ____

Answer 28

increases crystallization

Question 29

Lowest viscosity basalt lavas are called

Answer 29

pahoehoe (flows)

Question 30

A crystal rich lava will have ___ viscosity and ___ temperature than crystal poor lava of the same composition

Answer 30

higher viscosity lower temperature

Question 31

the loss of dissolved volatiles ____ viscosity

Answer 31

increases volatiles include dissolved gasses, and when magma rises -> lower P -> less solubility -> bubbles!

Question 32

Where do volcanoes occur?

Answer 32

plate boundaries hot spots

Question 33

Example of a famous area of volcanism

Answer 33

pacific ring of fire also Hawaii is a hot spot

Question 34

At which plate boundaries do volcanoes occur?

Answer 34

convergent and divergent

Question 35

Continental volcanic arcs happen as a result of what type of volcanoes?

Answer 35

subduction volcanoes

Question 36

Describe how continental volcanic arcs form

Answer 36

volatiles and partial melt from subducted ocean plate = mafic magma felsic magma as it is stored in continental crust felsic/intermediate as it is contaminated by stuff

Question 37

plates involved in our local continental volcanic arc

Answer 37

Cascadia subduction zone Juan de fuca plate subducting under North American plate

Question 38

Describe how oceanic volcanic arcs form

Answer 38

volatiles and melt rising from subducted ocean plate = mafic magma mafic/intermediate magmas and lavas

Question 39

The most voluminous volcanism on earth are from

Answer 39

mid ocean ridges - not exposed at surface except in Iceland

Question 40

Mafic magma from a plume of hot mantle: mantle plumes are ____ & ____

Answer 40

stationary and pulsatory

Question 41

Volcanic settings: Divergent boundaries

Answer 41

continental crust : East African Rift Zone btwn oceanic plates: Mid-Atlantic Ridge

Question 42

Volcanic Settings: Convergent boundaries

Answer 42

Oceanic-continental: Cascades Oceanic-oceanic: Aleutian islands

Question 43

Volcanic Settings: Hot spots

Answer 43

under continental crust: Yellowstone under oceanic crust: Hawaii

Question 44

Melting mechanisms: Divergent Boundaries

Answer 44

mantle stuff rises in a dike, pressure decrease - mafic magma may melt overlying crust

Question 45

Melting mechanisms: Convergent Boundaries

Answer 45

hydration of mantle by subjecting plate - mafic magma melts overlying crust

Question 46

Melting mechanisms: Hot Spots

Answer 46

mantle stuff rises in cylindrical plume, pressure decrease - mafic magma melts overlying crust

Question 47

Type of magma associated with oceanic plates/crust

Answer 47

mafic

Question 48

Type of magma associated with continental crust

Answer 48

mafic-int-felsic (mostly felsic)