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Atoms to volcanoes - 33739 > Extrusive processes > Flashcards

Extrusive processes Flashcards

1
Q

What is the volcanic spectrum?

A

Effusive to explosive

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2
Q

What is the eruptive process controlled by?

A

Amount of dissolved gasses in magma
Viscosity

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3
Q

What are some examples of dissolved gasses which can be trapped in magma?

A

Water
CO2
SO2

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4
Q

What is viscosity?

A

fluids resistance to flow & ability to degas

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5
Q

What is viscosity of lava related to?

A

Silica content
Lava temperature

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6
Q

What does a higher silica content mean?

A

higher viscosity

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7
Q

What will the viscosity of a cooler lava be?

A

higher

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8
Q

How do volcanic systems form at convergent boundaries?

A

Partial melting oceanic crust
Melt rises and collect in magma chamber (pressure builds)
Erupts on surface forming volcanic cone
Post eruption- magma solidify and plug vent
Magma continually accumulates and cools

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9
Q

What will eruptions at convergent boundaries/ subduction zones be like?

A

Most violent eruptions

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10
Q

What will magma be like at convergent boundaries?

A

High viscosity of intermediate to felsic magma
high volatile content (water dehydration melting)

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11
Q

What type of colour rock will be produced from felsic magma?

A

lighter coloured rock (rhyolite)

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12
Q

What will felsic magma be enriched by?

A

lighter elements (silicon, oxygen, aluminium, sodium, potassium)

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13
Q

What is the viscosity of felsic magma like?

A

high viscosity- sticky doesn’t flow easy

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14
Q

What does having high viscosity magma mean for the explosivity at convergent coundaries?

A

pressure can build making eruption more explosive

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15
Q

What type of volcanoes is most associated with convergent boundaries?

A

stratovolcanoes

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16
Q

What is an example of a stratovolcanoes?

A

Mt St Helens

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17
Q

What are stratovolcanoes also known as?

A

composite volcanoes

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18
Q

Why are stratovolcanoes known as composite volcanoes?

A

comprised of interbedded (andesitic) lava flows and pyroclastic debris

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19
Q

What do the layers on composite volcanoes reflect?

A

gradual calm and then more violent phases of volcanic development

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20
Q

What leads to a well formed cone shape for composite volcanoes?

A

Moderate to high viscosity
High angle of repose for pyroclastic debris

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21
Q

What happens to the neck and vent of a volcano post eruption?

A

plugged with fragments of pyroclastic debris and lava

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22
Q

What will begin to form over time below the plugged section of the neck and vent?

A

pressure increases and build a lava dome

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23
Q

What happens when magma and expanding gases being to move in the volcano when it is plugged?

A

plug can rupture leading to eruption

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24
Q

What happens to material around the vent when an eruption occurs?

A

pulverised

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25
What is the charging element of pyroclastic debris?
gas
26
What is pyroclastic debris?
airborne volcanic fragments
27
What speed can pyroclastic debris reach?
200km/h
28
What allows pyroclastic debris to reach such high speeds?
minimal drag and frictional resistance
29
What can fast moving pyroclastic debris be called?
pyroclastic flow or glowing avalanches
30
What happens when water mixes with loose ash in the atmosphere?
lahars- destructive mudflows are created
31
How long might it take for fine ash to come down from the atmosphere?
depends on ejection height but can range from months to years
32
When did Mt St Helens erupt?
1980
33
What was different about the pyroclastic flow for the Mt St Helens eruption?
occurred on the north flank with a lateral eruption. Created largest mass movement as whole north face collapsed
34
How could geoscientists tell an eruption was imminent at Mt St Helens?
Shallow earthquakes sign of magma moving combined with bulging and deformation of volcano
35
What path will magma take when moving through a volcano?
the weakest point in the structure
36
How much of the surrounding area was devastated by the 1980 Mt St Helens eruption?
150 miles*2
37
How long was Mt St Helens dormant before the 1980 eruption?
120 years
38
What are cinder cone volcanoes like?
small volcanic cones generally developed on flank of large volcano (found in clusters)
39
What are cinder cones mainly composed of?
pyroclastic cinders (pea sized blobs of lava) cooled mid air
40
What will there rarely be evidence of with with cinder cones?
lava flows
41
What are the typical dimensions of cinder cones?
rarely over 250m in height or 500m in diameter
42
What happens when a caldera erupts due to be so explosive?
the top of he volcano collapses in
43
What are huge amounts of pyroclastic debris and gases released from in calderas?
ring fractures
44
What is a caldera?
the crater left after eruption when the volcano collapses in because of the mass ejection of magma
45
What is an example of a past caldera?
Crater lake (oregon) last Mt Mazama eruption 7000yrs ago
46
What was the scale of crater lake caldera?
Relatively small with 10km diameter
47
What is the last eruption of Mt Mazama associated with?
ash deposition across western US and Canada
48
How many super volcanoes are there?
20
49
When was the last super volcano eruption?
27,000 years ago Taupo New Zealand
50
What are tuffs description?
fragments 2mm in diameter look sedimentary but lithified volcanic ash Welded
51
What does welded mean with volcanic deposits?
material was still hot enough that they partially recrystallised when emplaced and consolidated
52
What are Breccias?
rock formed from angular gravel and boulder-sized clasts cemented together in a matrix
53
What is the structure of breccias like?
rock formed from angular gravel and boulder-sized clasts cemented together in a matrix
54
How does pumice form?
when lavas have a lot of water and other volatiles
55
What is pumice like?
Glassy texture Light (mostly air many void spaces) Frothy appearance
56
What are cinders? (volcanic deposits)
pebble sized particles
57
What are volcanic bombs?
baseball to car sized chunks (due to cooling in air will have head and tail shape)
58
What are mantle plumes?
stationary plumes of heat in the mantle that dome the lithosphere and produce magma by decompression
59
What does the magma plume process lead to on land and in oceans?
Rift formation within continental plates Volcanic island chain on oceanic plates
60
What will usually happen first from a mantle plume before hotspot volcanoes?
Flood eruptions
61
What happens with flood eruptions?
very fluid basaltic lava creates a extensive lava plateau
62
What are some examples of flood eruptions?
Deccan traps- India in cretaceous Siberian traps- Permian, Triassic boundary
63
What are the general characteristics of mafic magma?
Usually darker rock produced Low silica Fe and Mg rich Less viscous - less sticky
64
What type of eruption will you get with mafic lava?
effusive as lava flows
65
What is created with hotspot activity under continental crust?
rift systems
66
What is the characteristic geometry of rift systems?
"triple junction"
67
What is triple junction geometry?
where three lithospheric plates meet
68
How does continental crust cause assimilation of magma to share similar characteristics with subduction volcanoes?
Under continent more rock to get through for magma to get to surface so more time for assimilation of material
69
Where is the greatest volume of volcanic rock produced?
along oceanic ridges at divergent boundaries
70
What type of basalt is extruded underwater at divergent plate boundaries?
pillow basalt
71
How does pillow basalt shape form?
rapid exterior quenching of lava bodies
72
What are eruptions like at mid ocean ridges?
gentle due to low viscosity and low volatile content
73
What type of magma will form shield volcanoes?
mantle derived mafic lava hot non-viscous (runny) dry (limited volatiles)
74
How do shield volcanoes form?
Basaltic lava builds up in flat layers creating a large volcano with gentle slopes
75
What is an example of a shield volcano?
Typical of Hawaii (Mauna Kea)
76
What type of lava is mafic lava?
Block lava
77
What are the characteristics of block lava?
less mobile more viscous Rough irregular surface
78
What happens when block lava cools?
goes to angular chunky texture causes lava to thicken and break apart as flow continues downslope
79
What are vesicles in block lava?
few and irregular in shape
80
What is the texture of blocky lava referred to as?
a-a (sound you make when walking on a flow)
81
What is another name for ropey lava? (mafic lava)
pahoehoe
82
What is ropey lava like?
more mobile less viscous wrinkled but smooth and shiny
83
What are vesicles like in ropey lava?
more abundant small spherical shape

Atoms to volcanoes - 33739 (16 decks)

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