Volcanoes Pt. I

Question 1

what are the three main rock types?

Answer 1

-igneous
-sedimentary
-metamorphic

Question 2

what is the source of igneous rocks and how are they formed?

Answer 2

-melting of rocks in crust and upper mantle
-crystallization of molten rock (magma/lava)

Question 3

what is the source of sedimentary rocks and how are they formed?

Answer 3

-weathering and erosion of surface rocks
-transportation, depositions, sedimentation, precipitation

Question 4

what is the source of metamorphic rocks and how are they formed?

Answer 4

-rocks under under pressure and temp in crust and upper mantle
-recrystallization/deformation of rocks in new state

Question 5

what is magma?

Answer 5

molten rock underground

Question 6

what is lava?

Answer 6

molten rock at the surface

Question 7

what are the conditions that control igneous rock composition?

Answer 7

-where solidification happens
-temperature
-melting conditions
-physical setting

Question 8

what are the two ways that igneous rocks are classified?

Answer 8

• where they solidified (above/below ground)
• silicia content

Question 9

what is the name and characteristics of igneous rocks that solidify underground?

Answer 9

-plutonic/intrusive
-coarse grained crystals that are visible to the eye

Question 10

what is the name and characteristics of igneous rocks that solidify above ground?

Answer 10

-volcanic/extrusive
-fine-grained or no crystals (glassy)

Question 11

what crystal size in igneous rocks indicate?

Answer 11

the time that the rocks had to cool (bigger crystals - slower cooling time -> likely underground/plutonic/intrusive)

Question 12

what is the volcanic pipe?

Answer 12

where magma passes to reach surface

Question 13

what is a dike? what is sill? what is laccolith? what is batholith? what is xenolith? what is stock?

Answer 13

volcanic pipe of older volcanoes
-flat intrusion of igneous rock (same layer)
-dome-like intrusion (connected to dike)
-large intrusive igenous rocks (cooled deep in crust)
-rock embedded in magma while the magma was cooling
-a remnant of the vent of a volcano

Question 14

what is pyroclastic rock?

Answer 14

deposits and rocks formed by eruption of volcano (extrusive)

Question 15

what is tephra?

Answer 15

material ejected during eruption like ash/pumice

Question 16

igneous rocks can be mafic, felsic, or intermediate. what are the main characteristic of this classification?

Answer 16

-mafic: high in magnesium and iron
-felsic: high in silica and feldspar
intermediate: intermediate

Question 17

mafic rocks silica content?

Answer 17

45-50% (less 45% is ultramafic)

Question 18

what are the characteristics of mafic igneous rocks?

Answer 18

-low viscosity (runny)
-melts around 1200C
-dark colour (high Fe/Mg)
- has ferromagneisian minerals like pyroxene
- has Ca-rich feldspar (plagioclase)

Question 19

what is the extrusive mafic rock?

Answer 19

basalt

Question 20

what is intrusive mafic rock?

Answer 20

gabbro (has no quartz)

Question 21

what are the characteristics of intermediate igneous rocks?

Answer 21

-50-70% silicia
-intermediate viscosity
-melts around moderate temp
-purple/green/grey colour
- has ferromagneisian minerals like amphibole
- has Ca-rich feldspar (plagioclase)

Question 22

what is the extrusive intermediate rock?

Answer 22

andesite (dacite)

Question 23

what is the intrusive intermediate rock?

Answer 23

diorite (granodiorite), more plagioclase visible than gabbro

Question 24

what are the characteristics of felsic igneous rocks?

Answer 24

->70% silicia
-high viscosity
-melts around low temp (800 C)
-pale/pinkish/tan/white colour
- has fewer ferromagneisian minerals
- has K-rich feldspar (orthoclase/sanidine), Na-rich, quartz

Question 25

what is the extrusive felsic rock?

Answer 25

rhyolite

Question 26

what is the intrusive felsic rock?

Answer 26

granite (pink crystals = orthoclase)

Question 27

To melt rock, you need to do what three things? (magma= partial melt)

Answer 27

-decrease overlying pressure -raise temp -add water

Question 28

magma composition depends on type of rock & conditions because of what?

Answer 28

rocks are made of different minerals that melt under different conditions

Question 29

what is magma differentiaition?

Answer 29

change from one melt composition to another

Question 30

partial melting and fractional crystallization often cause magma to do what? what change occurs?

Answer 30

-change composition (generally going from mafic to felsic)

Question 31

the type of volcano that forms is often determine by what characteristic?

Answer 31

type of magma

Question 32

why is the first melt often basaltic?

Answer 32

melt happens in deep crust where rocks are ultramfaic

Question 33

the longer that it takes for melt to reach surface, the more melt evolves. in what way?

Answer 33

evolve from mafic to intermediate to felsic

Question 34

what is volcano?

Answer 34

-central vent/fissure where molten rock, gas, rock fragments are ejected during eruption; conduit for magma

Question 35

main types of volcanoes

Answer 35

-fissure -shield -lava dome -cinder -composite/stratovolcano -caldera`

Question 36

what are the four typical volcanic settings?

Answer 36

-hot spots -divergent boundaries -young spreading zones -subduction/collisions zones (literally anywhere magma is made and path exists to surface)

Question 37

subduction zones - magma type

Answer 37

intermediate (moderate crust thickness)

Question 38

hot spot under ocean crust - magma type

Answer 38

basalt (more direct from mantle)

Question 39

mid ocean ridges - magma type

Answer 39

basalt (more direct from mantle); not iceland

Question 40

continental rifts - magma type

Answer 40

varied cause crust is thinned at rifts

Question 41

hot spot under continental crust - magma type

Answer 41

rhyolite (high silica cause thick crust)

Question 42

where do most eruptions happen?

Answer 42

mid-ocean ridges (70%)