Volcanos

Question 1

How much of the crust is volcanic?

Answer 1

90% of the top 16 km

Question 2

What makes volcanoes good things to live near?

Answer 2

geothermal energy, form fertile soils

Question 3

How do volcanos form fertile soils?

Answer 3

they bring nutrients from earth’s interior to the surface; add material to the surface that weathers easily, making fertile soil

Question 4

When and where was the last major eruption?

Answer 4

1815; Tambora

Question 5

What is magma?

Answer 5

molten rock

Question 6

What is lava?

Answer 6

magma on the earth’s surface

Question 7

What does plutonic mean?

Answer 7

intrusive - from the interior of the crust

Question 8

What are the 3 components of magma?

Answer 8

solid, liquid, dissolved gases

Question 9

What does volcanic mean?

Answer 9

extrusive - on the exterior of the crust

Question 10

What types of material are erupted from a volcano?

Answer 10

lava (liquid), pyroclastics (solid), and volcanic gas

Question 11

How does lava behave?

Answer 11

as a liquid

Question 12

In what direction does lava flow?

Answer 12

downhill (usually in stream courses)

Question 13

How thick are lava flows?

Answer 13

1 to 400 m (average ~ a few metres)

Question 14

How long can lava flows be?

Answer 14

> 100 km

Question 15

What can have a volume of 12.5 cubic km?

Answer 15

lava flows

Question 16

At what velocities can lava flow?

Answer 16

2 to 45+ km/h

Question 17

What factors control the size and shape of a lava flow?

Answer 17

viscosity, yield stress, topography, source geometry

Question 18

What controls viscosity of a lava flow?

Answer 18

compositoin

Question 19

What does viscosity of a lava flow control?

Answer 19

speed

Question 20

How does yield stress relate to lava flows?

Answer 20

lava flow stops when eruption stops - need to be adding lava for it to keep moving

Question 21

What are 2 types of lava flow sources?

Answer 21

point sources and line sources (fissure)

Question 22

What are pyroclastics?

Answer 22

solid debris erupted by a volcano

Question 23

What happens to pyroclastics upon eruption?

Answer 23

transported and deposited by wind and water

Question 24

What are the 5 types of pyroclastic particles, from smallest to largest?

Answer 24

dust, ash, lapilli, bomb, block

Question 25

What sort of size are ash particles?

Answer 25

sand-sized

Question 26

How big are lapilli?

Answer 26

pebble-sized

Question 27

How big are bombs?

Answer 27

head-sized

Question 28

How does the size of pyroclastic particles affect their transportation?

Answer 28

they sort by size, even in stratosphere - currents transport small particles farther than large ones

Question 29

Why is it dangerous to inhale volcanic ash?

Answer 29

it has sharp edges that can damage lungs

Question 30

How do volcanoes create their own weather?

Answer 30

water clumps around particles ejected into the atmosphere and the condensed water vapours form rain/clouds

Question 31

What does the cloud of pyroclastic material from an explosive volcano look like?

Answer 31

tall column above vent; lapilli falling close to the vent; ash falling from higher up; haze of dust spread away by wind; collaspsing column forming a pyroclastic flow down the slopes

Question 32

What is another term for a nuee ardente?

Answer 32

pyroclastic flow

Question 33

What is a pyroclastic flow?

Answer 33

density current (gravity flow) of pyroclastic particles and hot gas

Question 34

What usually causes a pyroclastic flow?

Answer 34

ac olumn collapse

Question 35

How does a pyroclastic flow move down the slopes of a volcano?

Answer 35

hottest particles at the bottom of the flow gives flow buyancy and heats the soil, giving a cushion of gas for it to flow over

Question 36

How does a pyroclastic flow behave?

Answer 36

like liquid - flows downhill

Question 37

What is an ignimbrite?

Answer 37

sheet of tuff (ash/lapilli) left from a pyroclastic flow

Question 38

What is a lahar?

Answer 38

mudflow of pyroclastic particles and water

Question 39

How does a lahar travel?

Answer 39

flows in channels down slopes

Question 40

What gases make up most volcanic gases?

Answer 40

water, CO2, nitrogen, SO2

Question 41

What gives volcanoes their "rotten egg" smell?

Answer 41

sulfur gases (SO2, SO3, S2)

Question 42

Why are sulfur gases so dangerous?

Answer 42

they're toxic and heavy (so they settle near the ground)

Question 43

What is viscosity?

Answer 43

resistance to stirring/flow

Question 44

What does viscosity depend on?

Answer 44

composition, temperature, and polymerization of SiO4

Question 45

How does polymerization of SiO4 relate to temperature?

Answer 45

it increases as temperature drops

Question 46

What magma is usually at ~1000 deg C?

Answer 46

mafic

Question 47

What magma is usually at ~700 deg C?

Answer 47

felsic

Question 48

What is the range of viscosities for natural silicate liquids?

Answer 48

olive oil to cold honey

Question 49

What makes felsic magma so viscous?

Answer 49

large silicate composition; lower temperature; silicate liquid near freezing point - so starts crystallizing to SiO4 tetrahedra and polymerizing while still a liquid

Question 50

What is the viscosity of mafic magma and how does it relate to its velocity?

Answer 50

low viscosity, allowing it to flow quickly

Question 51

What magma forms basalt?

Answer 51

mafic

Question 52

What are the properties of a basaltic flow?

Answer 52

fluid, hot (1000 deg C), long thin flows

Question 53

What is the composition of a basaltic flow?

Answer 53

silica poor; Fe and Mg rich

Question 54

What are the properties of an andesitic flow?

Answer 54

viscous, cool (800 deg C), short thich flows, explosive

Question 55

Why is an andesitic flow so explosive?

Answer 55

it's viscous, making it difficult for dissolved gases to get out; gases expand in bubbles and explode out

Question 56

What is the composition of an andesitic flow?

Answer 56

silica rich; Al, K, Na rich

Question 57

How much of a mafic magma is silicate?

Answer 57

50%

Question 58

What makes up mafic magma?

Answer 58

SiO2, Mg, Fe, Ca, Al, calcium feldspar, olivine, pyroxene

Question 59

What rock is the volcanic rock of the oceans?

Answer 59

basalt

Question 60

Why is felsic lava rare?

Answer 60

it's very viscous, so it takes a while to flow up to the crust's surface

Question 61

How much silicate makes up felsic magma?

Answer 61

>65%

Question 62

What makes up felsic mgma?

Answer 62

SiO2, Na, I, Al, K-feldspar, Na-feldspar, quartz

Question 63

What type of magma forms basalt?

Answer 63

mafic

Question 64

What type of magma forms rhyolite?

Answer 64

felsic

Question 65

How much silicate makes up intermediate magma?

Answer 65

50-65%

Question 66

What type of rock does intermediate magma form?

Answer 66

andesite

Question 67

What are two common volcano styles?

Answer 67

shield volcanoes and composite volcanoes

Question 68

How are shield volcanoes constructed?

Answer 68

non-viscous mafic lava flows spreading out and building up over time (but little ash)

Question 69

What type of volcano is massive and has gentle slopes?

Answer 69

shield volcanoes

Question 70

What type of magma forms shield volcanoes?

Answer 70

basalt (mafic magma)

Question 71

What is another term for composite volcanoes?

Answer 71

stratovolcanoes

Question 72

What are the 2 main components of composite volcanoes and the ratio between the?

Answer 72

pyroclastic deposites and lava flows; 50:50

Question 73

What type of magma forms stratovolcanoes?

Answer 73

andesite (intermediate magma)

Question 74

How does the structure of composite volcanoes differ from that of shield volcanoes?

Answer 74

steeper slopes and smaller cross-sectional areas

Question 75

Which type of volcanoe is usually more explosive?

Answer 75

composite

Question 76

What are plateau basalts?

Answer 76

thick accumulations of long fluid flows

Question 77

What type of source geometry would be needed for a plateau basalt?

Answer 77

fissure eruption?

Question 78

What type of volcano style has never been experienced in known history?

Answer 78

plateau basalts

Question 79

What are ignimbrite sheets?

Answer 79

pyroclastic deposits at a similar scale to that of plateau basalts

Question 80

What is the scale of a plateau basalt?

Answer 80

400 km x 400 km x 4 km

Question 81

What is caused by the collapse of a composite volcano?

Answer 81

caldera

Question 82

How does a caldera form?

Answer 82

magma withdrawal from chamber leaves empty space; volcano collapses into chamber after eruption (especially explosive ones)

Question 83

How large are calderas?

Answer 83

2-30 km in diameter

Question 84

Where are 3 places volcanoes are often found?

Answer 84

ocean islands, mid-ocean ridges, continental fringe

Question 85

What is the difference between island chains and island arcs?

Answer 85

island chains only have active volcanoes at one end; arcs have active volcanoes throughout arc

Question 86

Where are most volcanoes found?

Answer 86

ocean islands

Question 87

What are mantle xenoliths?

Answer 87

inclusions of material magma brought up from beneath crust

Question 88

Why are mantle xenoliths important?

Answer 88

gives us knowledge of the mantle

Question 89

What are some hazards from eruptions?

Answer 89

lava flows, falling ash/lapilli, explosion, landslides, earthquakes, tsunamis, lahars

Question 90

How are earthquakes caused by volcanic eruptions?

Answer 90

movement of magma breaks rocks underground