Geology Test 3

Front 1

chemical characteristics of mantle

Back 1

low SiO2, Na2O, K2O
high FeO, MgO

Front 2

under normal conditions, mantle...

Back 2

does NOT melt

Front 3

mantle melting requires

Back 3

something special

Front 4

to make mantle melt...

Back 4

increase temperature, decrease pressure, start with substance that is solid and hot and add another substance (most likely H2O)

Front 5

melting of mantle generates..

Back 5

basaltic (low SiO2) magma

Front 6

through fractional crystallization low SiO2 magmas generate...

Back 6

intermediate and high SiO2 magmas

Front 7

when magma crystallizes it forms crystals with

Back 7

a different chemical composition than the magma

Front 8

in fractional crystallization the composition of the liquid portion of the magma

Back 8

must change

Front 9

gravitational settling of crystals...
that magma is equal to the liquid so it...

Back 9

removes them from the magma. -
must change chemical composition

Front 10

in a natural magma, fractional crystallization leads to...

Back 10

increase in SiO2, Na2O, K2O, and H2O
decrease in FeO, MgO, CaO

Front 11

viscosity

Back 11

a measure of the degree of "stiffness" of a fluid

Front 12

viscosity of natural magma increases with...

Back 12

SiO2 content

Front 13

Low SiO2 magmas= ___ viscosity

Back 13

low (very fluid)

Front 14

Intermediate SiO2 magmas= ___ viscosity

Back 14

intermediate

Front 15

High SiO2 magmas= ___ viscosity

Back 15

high

Front 16

viscosity of natural magma increase with

Back 16

decreasing temperature

Front 17

natural magmas consist of

Back 17

SiO4 (4 molecules that form chains or polymerize)

Front 18

chains "interact" with one another. Longer chains= ___

Back 18

more interaction, high viscosity

Front 19

The more Si that a magma contains...

Back 19

the greater the number and the longer the chains

Front 20

___ breaks chains apart which leads to ___

Back 20

increasing temperature, higher viscosity

Front 21

2 most important controlling parameters of eruption style

Back 21

viscosity and H2O content

Front 22

shield volcano

Back 22

low viscosity, low H2O, thin laterally extensive lava flows

Front 23

composite/ stratovolcano

Back 23

intermediate viscosity, intermediate H2O, thick lava flows and/or air fall and ashflow tuffs

Front 24

caldera

Back 24

high viscosity, high H2O- explosive eruptions

Front 25

cinder cone

Back 25

low viscosity, high H2O- eruption of scoria

Front 26

lava dome

Back 26

high viscosity, low H2O, effusive eruption

Front 27

characteristics of mid ocean ridge magmatism

Back 27

low SiO2 magma/large, overlapping shield volcanoes/ largely underwater, exotic features, weird biological communities(tube worms), black smokers

Front 28

origin of mid ocean ridge magmatism

Back 28

decompression melting of upwelling convection cells in the mantle

Front 29

characteristics of subduction zone magmatism

Back 29

low SiO2 to high SiO2 magmas, large impressive stratovolcanoes

Front 30

origin of subduction zone magmatism

Back 30

-dewatering of suducted oceanic crust adds water to mantle
-mantle melts to produce basaltic magmas that have a lot of H2O
- basaltic magmas can lose buoyancy and "pond" in the crust to create a magma chamber
-fractional crystallization in the magma chamber generates intermediate to high SiO2 magmas

Front 31

characteristics hot spot magmatism

Back 31

occurs in the middle of tectonic plates, low SiO2 magmas, large shield volcanoes

Front 32

origin of hot spot magmatism

Back 32

-poorly understood hot spot in core heats up mantle
- hot mantle becomes buoyant and rises towards the surface
-undergoes decompression melting to produce low SiO2, basaltic magmas

Front 33

why do magmas erupt

Back 33

bubbling of H2O creates pressure in the magma and causes it to erupt onto the surface

Front 34

what does bubbling of H2O take place

Back 34

as pressure decreases, H2O is no longer soluble in a magma and it starts to bubble off

Front 35

types of eruptions

Back 35

fountain, explosive, spattering, effusive

Front 36

fountain eruption

Back 36

low viscosity, low H2O content- produces a lava flow

Front 37

explosive eruption

Back 37

high viscosity, high H2O content- produces pyroclastic material- material blasted high in the air but collapses back on itself

Front 38

spattering eruption

Back 38

low viscosity, high H2O content- produces scoria

Front 39

effusive eruption

Back 39

high viscosity, low H2O content- produces a lava dome

Front 40

correlation between magma type and eruption style

Back 40

most low SiO2 magmas have low H2O, most high SiO2 magmas have high H2O, most intermediate magmas have intermediate H2O

Front 41

volcano secondary effects

Back 41

airfall, volcanic mudflow (lahar)