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Geological natural hazards > Magma properties > Flashcards

Magma properties Flashcards

1
Q

What is a hazard?

A

The process that can cuse harm

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2
Q

What should considerations of natural hazards take into account?

A

Frequency
Future probability
Onset speed
Magnitude
Duration
Extent

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3
Q

What does risk consider for the human population?

A

the exposure, sensitivity and resilience of:
- populaiton
- Economy
- Land use
- Infrastructure
- Culture
- natural resources

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4
Q

What is risk?

A

the interaction between hazards and human populations depending on vulnerability/ exposure

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5
Q

What is volcanism?

A

The manifestation at a planetary surface of internal thermal processes through the emission of solid, liquid or gaseous products

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6
Q

WHat are some examples of volcanic hazards that are not direclty related to magmatic eruptions?

A

Gas emissions
Pheartic activity
Volcanic landslides

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7
Q

What does volcanism originate from?

A

Melting of earths mantle

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8
Q

What specific conditions are needed for the melting of earths mantle?

A

Relativley high elevated temperatures and reduced pressure in parts of the mantle
Adding fluids to the mantle to reduce melting temp

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9
Q

What is produced when the conditions needed to melt earths mantle are met?

A

partial melt will occur if this ascends towards and reaches the surface volcanism occurs

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10
Q

WHat are the different settings for volcanism?

A

Subduction zones (volcanic arcs)
Rift
Intraplate

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11
Q

How many of earths volcanoes form as a result of subduction?

A

90%

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12
Q

What are the general differnecs between the volcanis settings?

A

In hazard terms fairly comparable but Arc volcanoes span a wider composition range and stsle and thus hazard

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13
Q

What are some examples of subduction zones/ volcanic arcs?

A

Andean volcanic zones
Japan
Indonesia
Lesser Antilles
Tonga

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14
Q

What type of melting occurs at subduction zones?

A

flux melting (addition of water/ volatiles)

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15
Q

How does crustal evolution affect subduction zones?

A

wide composiitonal range commonly evolved, volatile rich magmas Andesites and rhyolites)

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16
Q

What type of plate boundary is rift setting volcanics?

A

divergent

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17
Q

What is an example of a rift setting volcano?

A

Laki (Iceland)

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18
Q

What type of magma is present at the laki ruption?

A

basaltic

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19
Q

What are the eruptions in iceland augmented by?

A

mantle plume

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20
Q

WHat type of melting occurs at roft settings?

A

Decompression melting

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21
Q

What is decompression melting?

A

weight of mantle above creates high pressure raising meltin point when the rock moves to a lower pressure area the melting point is lowered

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22
Q

What does mantle genreation have its origin from?

A

Partial melting of mantle perioditite

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23
Q

What are the original magma melts generally like compositionally?

A

Basaltic in composition (~50wt%SiO2)

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24
Q

What happens to the original melts/ magmas as they ascend through the lithosphere?

A

evolve and accumulate

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25
What sort of processes occur as the magmas rise through the lithosphere?
Mixing Assimilation Fractional crystalisation
26
What catergories do the majority of volcanic rock compositions fall into?
Basalts Rhyolites
27
WHat are basalts like?
Primitive Mafic (basic)
28
What are rhyolites like?
Evolved Felsic (acid)
29
What types of volcanic rock does more than 50% of volcnic rock fall into?
Basalt Basaltic andesite Andesite Rhyolite
30
How long are sites of volcanic acitivity acitve for?
Hundreds of thousands to millions of years
31
What is polygenetic volcanism?
The build up of large volcanic landforms through a very large number of eruptions Linked to long lived focused crustal magma storage
32
What is monogenetic volcanism?
when the vents might have greater ditribution forming volcanic fields with several small volcanic constructions
33
What is the typical condition of most volcanic sites?
Not to be in eruption
34
The properties of magma affect how it reaches the surface and the hazards produced. What are these properties?
Volatile content Chemical composition Viscosity Temperature Crystallinity
35
Unlike in other areas of life what typically makes volcanoic impacts greater?
Size (it does matter in some cases)
36
What is another name for a polygenetic volcano?
Stratovolcanoes
37
# Lifetime Volume Output example What are the characteristics of a typical stratovolcano?
Lifetime - over 100 kyr Volume - over 100 km*3 Output flux - 0.1 to 1 km*3 magma per year Example - popocatepetl (mexico)
38
What might be closely similar between monogenetic volcanic fields and polygenetic volcanoes?
Overall output rate
39
What are the characteristic of a monogenetic volcanic field? (Chichinautzin volcanic field, mexico city)
Active for over 100 kyr Hundreds of vents active in single eruption and form monogentic cones
40
What controls how the products of an eruption are distributed?
eruption style
41
What will deposits be like for a powerful explosive eruption?
widely dispersed
42
What will deposits be like for a small explosive eruption?
Localised Layered cones from pulsatory
43
What will lava flows be like from low-viscosity lava?
sheet like or linear thin lava flows
44
WHat will lava flows be like for high viscosity lava?
Thick piles of lava (lava domes)
45
What does it mean saying many eruptions have changing behaviour?
explosive phase follwed by an effusive phase
46
What is an example of a volcanic eruption changing behaviour?
Chaiten chile 2008 POwerful explosive in may 08 followed by effusive eruption of lava dome
47
What leads to varying volcanic landforms and sizes?
Different eruption styles along with the dominant style at a long lived volcano
48
How is size of volcanic eruption indicated?
VEI (Volcanic Explosivity Index)
49
On the global scale what are more common small or large eruptions?
Small
50
Why is looking at eruption patterns important?
For assesing risk and monitoring and mitigation stratergies
51
Why is understanding the hazrads from a long lived volcano eruption challenging?
Due to the many different eruption styles, size, magma composition
52
What is a silicate melt?
polymerised mixture of silicon and oxygen atoms with varible proportions
53
What are the varied cations and volatiles in silicate melt?
Cations - Ca, Na, K, Fe, Mg, Al etc Volatiles - water, co2, halogens etc
54
What happens in the magma as it ascends?
The magma cools as pressure reduces allowing volatiles to exsolve intto gas bubbles and crystals begin to form
55
What is magma usuaully like in the upper crust?
polyphase mixture of liquid, solid and gas
56
What might mean the proportions of gas bubbles in polyphase mixtures in the upper crust varies?
The bubbles are only present above volatile saturation conditions (pressure depedent)
57
What causes over pressure to occur in crustal magma bodies?
Due to no open link to the surface, continued input of fresh, deeper magma, and exsolution of magma
58
What happens if overpressure exceeds the strength of the surrounding rock?
Propagating fracture will form allowing magma to ascend
59
60
What is the name for the magma filled fracture produced by over pressure?
A dyke
61
What is the silica content difference between basalt and rhyolite?
B = 50% R = 70%
62
What is the liquidus temp difference between basalt and rhyolite?
B - 1200c R - 900c
63
What is the melt density difference between basalt and rhyolite? (Annhydrous)
B - 2600kg/m*3 R - 2300kg/m*3
64
How does increasing the silica content of magma affect viscosity?
MOre silica = more viscous magma
65
What does a large increase in vicosity also promote?
crystallisation
66
What out of hazards, exposure and vulnerability can be chnaged to reduce risk?
exposure and vulnerability
67
What is exposure in relation to hazards?
something for the hazard to interact with
68
How many active/ erupting volcanoes are there each year?
~50
69
How many volcanoes have erupted in the holocene (10,000yrs)?
~1500
70
What does the presence of more volatiles do to explosivity do?
increase it
71
What causes fluids to be released from the subducting plate?
metamorphism

Geological natural hazards (21 decks)

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