Volcanoes Flashcards
1
Q
What is the Sendai framework
A
15 year plan for countries around the world to do something about the risk
2
Q
What is the four priorities of the Sendai framework
A
Understanding risk.
Strengthening disaster risk governance.
Investment in DRR.
Preparedness and building back better.
3
Q
What are the 7 targets of the Sendai framework
A
Substantially reduce global disaster mortality by 2030.
Reduce the number of people affected globally.
Reduce direct disaster economic loss in relation to GDP.
Reduce disaster damage to critical infrastructure and distribution of services (2020)
Increase number of countries with national and local DRR.
Increase availability and access to multi hazards early warning systems.
4
Q
What are volcanoes
A
Vents in the earths surface through which molten or near molten material is emitted. Come in lots of shapes and not all have craters or calderas.
5
Q
Example of a stratovolcano
A
Cotopaxi (Ecuador).
Has permanent glaciers bc it’s so high so ready supply of water
6
Q
What is the biggest volcano on earth
A
Mauna Loa (Hawaii) a shield volcano
7
Q
Examples of a supply of water for volcanoes
A
In Alaska with lakes in crater
Iceland
8
Q
What is a submarine volcano
A
Close to water or several km below, the peak was a volcanic sea mount which had an explosive eruption in 2009
9
Q
What is scoria cone
A
Made from bits of lava falling onto side of mountain, just a little feature on side of volcano e.g in Kilauea
10
Q
How long can eruptions last
A
From 1 day to over 2400 years
11
Q
Example of volcano that’s erupting for 2400 years
A
Stromboli
12
Q
What is the typically duration of an eruption
A
7 weeks - might have periods of dormancy but once it erupts it takes a while for activity to settle
13
Q
Commonly where do eruptions usually occur
A
The same centre for several millions of years as what’s feeding them is a supply of magma - something in the mantle is causing it to melt and it’s a long process
14
Q
How long is the time between eruptions
A
Hundreds of thousands of years
15
Q
Why are eruptions after long periods of dormancy violent
A
Because the magmas been building up
16
Q
What is the difference between a live and dead volcano
A
Live has the potential for future eruptions a dead one does not
17
Q
What are the signs of a live volcano
A
Known historical eruptions.
14C dated eruptions within the past few tens of thousands of years.
Fumeroles, hot springs and geysers.
Other thermal signs like warm crater lake.
Frequent local earthquakes.
Young looking volcanic rock.
18
Q
How far back do known historical records go
A
Thousands of years due to record of human history being recent
19
Q
What is a fumerole
A
Gas vents releasing sulphur dioxide during emissions
20
Q
What is a hot sprint
A
Diffusion of water at the surface
21
Q
What is a geyser
A
Gaseous source in water that causes the water to shoot up like old faithful in yellow stone
22
Q
How does uneroded volcanic rock help decide if a volcano is live
A
Can see the way magma is moving around, remote areas can be studied using satellites. Geomorphology causes the volcanoes to be classified as live without actually sampling them
23
Q
How does 14C (radiocarbon) dating work
A
Sampling charcoal from pyroclastuc flow. Charred remains of trees or living things at time of eruption. By sampling you get date of eruption as you can find out when an organism died. Useful for eating up to 50,000 years ago
24
Q
How many volcanoes erupt is a year
A
50-70
25
How many volcanoes have been observed erupting
550
26
How many volcanoes have erupted within the Holocene
1500
27
How many live volcanoes on earth
10,000
28
Where do volcanoes occur
Pacific ring of fire.
Rift Valley in Africa.
Mid Atlantic ridge (Iceland).
29
What is the thickness of lithosphere
70km for oceanic and 100-159 for continental
30
What is the lithosphere
Earths rigid outer layer - crust is part of it but is not exclusive
31
How does the lithosphere move
The asthenosphere is underneath and is close to melting point so the layer is quite plastic and can flow which makes the lithosphere move
32
What are the four groups of volcanoes due to their tectonic setting
Subduction zones.
Mid-ocean ridges.
Oceanic hot spots (intraplate).
Continental hot spots and rift zones.
33
How do subduction zone volcanoes form
Converging plates - oceanic (denser and thin) and continental. Subduction lithosphere is water rich and carries water into mantle, 10s of km deep it heats up and water is driven off and percolates upwards through overlying plate and the waters lowers the melting point of the overlying plate. Partial melting occurs. Few drops of magma percolates upwards and Poole into a chamber below the surface. Every now and then the magma depressurises and erupts.
34
Why is it only partial melting in subducting zones
Because it’s basalt lava as only a few specific minerals melt. Peridotite partially melts a few percent.
35
Where are subduction volcanoes found
Parallel to the subduction zone on the overriding plate
36
When does an island arc form
If the overriding plate is oceanic, a curved chain of volcanic islands form
37
Example of an island arc
The lesser Antilles in the Caribbean
38
When does an active continental margin firm
If the overriding plate is continental, a chain of volcanoes form along the coastline
39
Example of an active continental margin
The Andes in South America
40
How do mid ocean ridges form volcanoes
Plates move apart, earths solid mantle rises as less pressure is on the plates due to the separating, it decompressed and partially melts to produce magma. Magma erupts onto the sea floor forming new oceanic lithosphere when it cools. Underwater volcanoes form
41
What magma is there in mid ocean ridges
Basalt
42
Most MOR volcanoes are submarine, what’s the exception
Iceland
43
How do oceanic hot spot volcanoes form
Volcanic islands far from plate boundaries caused by these. They are partially formed by subduction cooling down other parts of the mantle so when there’s been little subduction the mantle is warmer and is buoyant so rises, higher temperatures and decrease in pressure causing the melting. Basaltic magma
44
What is a mantle plume
Solid rock that is warmer than average and only starts to melt when near the surface
45
Example of oceanic hot spot volcanoes
Hawaiian volcanoes in the central Pacific
46
How do continental hot spots and rift zones cause volcanoes
Some isolated volcanoes on continents have hot spots. Continental rifting produces groups of volcanoes and the hot spots often produce unusual magma compositions
47
Example of continental rifting producing volcanoes
East African rift zone - triple junction between 3 plates (Arabian, Nubian, Somalian) all moving apart. Nubian and Somalian are causing a mid ocean ridge. East Africa the volcanoes aren’t oceanic but lots of rifting suggests the eastern part of Africa will move into ocean
48
Why do continental hot spots and rift zone produce unusual magma composition
Have thick layers of lithosphere to get through and the journey through the mantle changes the composition
49
What are the most hazardous volcanoes
Explosive ones
50
Why do most explosive eruptions occur at subduction zones
Magmas contain a greater proportion of volatiles - high water content as formed in water rich environment.
High silica contents which makes them viscous.
Lots of bubbles which can’t escape - explosive.
51
What percentage of the magma mass in subduction volcanoes is water
5-6%
52
Why does a high silica content mean the eruption is likely to be explosive
Because it causes the magma to be viscous which means when it decompressed some of the water that was dissolved in solution comes up in bubbles, pressure reduces and bubbles expand. If it’s viscous they can’t escape and pressure increases on them causing an explosive effect
53
Chemical name of silica
SiO2
54
What is viscosity
Resistance to flow
55
When does viscosity increases
With increasing silica and decreasing temperature making the magma thick
56
How much silica in basalt lava
Less than 52% so runny
57
How much silica in andesite lava
52-64%
58
How much silica in dacite
64+% so it’s sticky
59
How does basalt form
The original partially melting
60
How does dacite form
If the magma has been around for ages it evolves to be silica rich as the less silica rich minerals crystallise and sink leaving the dacite
61
What are volatiles
Gases which are dissolved in magma at high oresssures (deep underground) and come out of solution as they rise due to decreasing pressure exsolving them forming bubbles.
62
What are the types of explosive eruptions
Phreatic.
Phreato-magmatic.
Auto-explosive.
63
What is phreatic eruption
External water and hot rock - not magma but rock that’s been heated by magma or magma that’s partially cooled to solidification
64
What is phreato-magmatic eruption
External water and magma
65
What is auto-explosive eruption
Volatile rich magmas and no external water - tend to be only in subduction so magma has high water content anyway
66
Example of big city on the flanks of a volcano
Naples with 3 million
67
Gloabblly how many people live within 100km it a potentially active volcano
1 in 9
68
What is hazard level
Probability of a hazard occurring within a specified time scale
69
What is vulnerability
Exposure to the hazard (people, property etc)
70
How many cities are close to one or more potentially active volcanoes
67 critics with populations over 100,000
71
Which cities are at risk of volcanoes
```
Tokyo
Mexico City
Manila (Philippine)
Naples
Bandung (Indonesia)
Seattle
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Docmore for exams - 2nd volcano
72
What are the six steps to reducing vulnerability
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Risk assessment.
Appropriate land use.
Hazard defences.
Advance emergency planning.
Monitor volcanic activity -> forecast eruptions.
Fight or flight.
```
73
Components of the risk assessment
Identity live volcanoes.
Assess hazard level and potential types of hazard.
Produce a hazard map showing land area, rivers, population and infrastructure that could be affected by an eruption.
74
Why are bridges important
For an evacuation route
75
What can computer models be used to
Stimulate flows
76
Land use policies that can be determined by a hazard map
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Exclusion zones.
Population density limits.
Relocation of residents to safer areas.
Special building regulations.
Evacuation routes.
Hazard defences if appropriate.
```
77
Example of special building regulation
Slopes roofs to allow ash to fall off so it doesn’t collapse
78
Examples of hazard defences
Crater lake drainage.
Gas pump system.
Strong shelters.
Dykes, diversionary ditches and sabo dams.
Barriers or other interventions to divert small lava flows.
79
Why is crater lake drainage a good hazard defence
Would be a spruce of water so drain it to keep it from interacting with magma
80
Example of crater lake drainage
Kelut, Indonesia
81
Example of gas pump systems
Lake Nyos, Cameroon
82
Why are strong shelters needed
To protect against heavy ash fall, blacks and bombs and lightening like in Sakurijima in Japan
83
Why are dykes, diversionary ditches and sabo dams used
To protect against small Lahars like the dykes at Mt Mayon, Philippines or the sabo dams at Sakurajima, Japan
84
Example of barriers diverting lava
Krafla, Iceland. Sicilily walls helped limit mt etnas flow
85
What do sabo dams do
Aims to filter out the debris from a lahar luke boulders and tree trunks to stop it reaching big settlements. Expensive and ppl have to remove the debris
86
How many explosions does Sakurijima have a year
300
87
How many overs does debris flow affect near Sakurijima
10
88
What can nothing protect against
```
Pyroclastic flows.
Sector collapse.
Directed blasts.
But lahar.
Big lava flows.
```
89
Why is advanced emergency planning needed
To help people understand how they work and how to evacuate
90
What is involved in advanced emergency planning
Volcanic hazards education and training.
Plan evacuation routes, transport, temporary accommodation, emergency aid.
Warning systems.
91
Who must advanced emergency planning involve
```
Volcanologists.
Emergency and medical services.
Local authorities.
Teachers.
Community leaders.
Local residents.
```
92
Example of a volcano alert system
USGS system - green is normal, yellow is advisory, orange is watch, red is warning.
93
How does monitoring and forecasting work
Combination of methods used to detect movement of magma within a volcano.
Important to do baseline monitoring so that changes can be detected.
Monitoring intensifies and emergency plans activated.
94
What are the physical monitoring methods
```
Seismic methods.
Ground deformation.
Thermal signal
Gravity measurements.
Electromagnetic measurements.
Infrasonic.
```
95
What are the seismic methods of monitoring
Instal a network of seismometers to detect location, frequency and magnitude of earthquakes and other sources of ground vibrations.
Different sources distinguished by amplitude, frequency and duration of vibrations.
96
What are high frequency (HF) earthquake swarms caused by and how long do they last
Magma movement and 5 days
97
How to work out ground deformation
Satellite based Global Positioning System (GPS).
Satellite radar interferometry (InSAR).
Ground based electronic distance measurements (EDM).
Ground based tiltmeters.
98
What is ground deformation
Changes in the ground e.g tilt and height
99
What does InSAR Do
Radio waves down to surface and measuring how long it takes for them to reflect back to satellite. If volcano is inflating you see a change in the time it takes to bounce back. Stripes represent how far the ground has moved and circles for where the inflating is center.
100
How does EDM work
Use laser emitter and reflector to detect horizontal distance changes.
101
What is the thermal signs
Remote sensing (infrared)
Temperature of hot springs and crater lakes.
Snow melts
102
What is gravity measurements
Changes in gravity due to differences of mass underground as magma moves.
103
What is electromagnetic measurements
Conductivity of rock
104
What are infrasonics
Seismic waves through the air (sound). low frequency sound produced by explosive eruption in an area that’s not being monitored closely
105
What is the chemical monitoring methods
Acidity of hot springs and crater lakes.
| Composition of volcanic gases.
106
How are Sulphur Dioxide (SO2) concentrations measured
By Correlation Spectrometer (COSPEC) or by satellites
107
What does gas solubility depend on
Pressure
108
Where do you measure chemicals
In fumeroles but it’s dangerous so use drones or long hand held items
109
What does the possibility of predicting an eruption depend on
Likely eruption location/size/type/hazards
110
Time frame of usually predicting an eruption
Within a few days/ weeks
111
What is it difficult to balance in fight or flight
Risks of evacuating too early vs too late
112
What are the factors affecting success of warnings and evacuation
Deciding a primary community system.
Have in place ways of helping people to move.
Lots of planning before a successful evacuation.
Need evacuation practice runs to identity weakness.
Wearing a dust mask if you decide to stay.
Stay aware of volcanic gases as they are irritant.
Shovel ash off low roof.
113
Case study for volcanoes
Pinatubo (1991)
114
History of pinatubo
It was not known to be a potentially dangerous volcano until a few weeks before its cataclysmic eruption
115
What promoted the USGS crash team to respond to pinatubo
Increased seismic and fumeroles activity and steam explosions
116
What did USGS do in Pinatubo
Rapidly map/date deposits to find reminents of large pyroclastic flows. They created a hazard map and after a few weeks evacuated people as it was much bigger than they thought it would be.
117
Hazards in pinatubo eruption
Massive blankets of ash, volcano mobilised by typhoon to create lahars
118
How were so many lives saved in Pinutubo
Good monitoring, communications, timely warnings and evacuation of 60,000 people
119
How many people died in the pinatubo eruption
350
120
Why did many people die in Pinatubo
Because of collapsing roofs from ash fall
121
Where are volcanoes
```
Pacific ring of fire
In Andes and Central America
Indonesia
East Africa rift zone
Mediterranean
```
122
What are volcanoes more explosive in subduction zones
Because higher silica as thicker crust (continental) and water content
123
What is sector collapse
Intruding magma causes a bulge which in turns create a huge avalanche As it becomes gravitationally unstable where a while side f the volcano slides away decompressing the Manama chamber. Explosive eruption. Lateral blast.
124
How many times has sector collapse occurs
Twice in the past - v dangerous tho
125
When are volcanic blast most dangerous
When directed laterally
126
Example of sector collapse
Mt St. Helens 1980
127
What happened in Mt St. Helens 1980
Inflating by 1m a day and there wasn’t great awareness due to Russia.
Different topography after eruption and ash blankets countryside.
Two blasts - one up and one sidewises (63). Mostly in logging c didn’t evacuate properly.
128
Facts about blacks and bombs
Can travel up to 10km, kill upon impact, damage buildings and roads
129
What are blocks and bombs
Large fragments ejected and falls back to ground but small fragments are lobbed away. Cm-m in Disney
130
What are blocks
Solid rock - volcanic material that’s cooled
131
What is bombs
Partially molten that lands and cools like bread crust bombs
132
Where donblocks and bombs generally affect
Areas close to the vent due to size but sometimes destroys buildings e.g in Japan and Mt Etna
133
What is air fall tephra
Small, tiny fragments of ash and rock that’s broken into small mm pieces. Carried in atmospheric currents.
134
How far can air fall tephra travel
1000s of Km in direction of wind
135
What are the effects of air fall tephra
Bury and collapse of buildings - several m thick.
Destroy crops and kill animals -> famine.
Choke lungs and engines.
136
What are pyroclastic flows
Hot and fast flowing mixture of gas, ash and rocks. 800*C
137
How far do pyroclastic flows travel
Tens of km
138
What percentage of pyroclastic flows can be gas
99% allowing it to be mobile
139
How far can pyroclastic flows trace
200km
140
Why are pyroclastic flows dangers
Burns, chokes and flattered
141
How are pyroclastic flows generated
```
Dome collapse (explosive)
Column collapse
```
142
What is dome collapse
Extruded lava piles up around vent; it’s hot but biscuits and becomes unstable so collpasrez. Typographically channeled as it follows line it easiest descent
143
What is column collapse
Explosive eruption produces ash plume that can be 10-15km up high into atmosphere. Once initial eruption has played out the material sinks back down sides of volcano
144
Example of pyroclastic flow
Repeated growth and collapse of lava dimes at Soufruere Hille volcano in Montserrat.
Column followers at Mayon volcano in Philippines.
145
What are mud flows (Lahars)
Ash and water from rain, river, crater lake, melted air mobilise very destructively
146
When can Mud flows occur
Months or years after eruption
147
Example of worst mud flow
Nevado del Ruiz, Columbia 1985.
In Andra the strata volcano linked to subduction under South America plate. Small eruption with ice cap. Mobilised the ash and flew towards a town. Could have been warned but something wrong with communication and bad planning. 22,000 killed.
148
How can eruptions be hazards to aircrafts
Can damage engines through ashfall tephra. Near misses as satelittrles senseint to track plumes in atmosphere to steer away
149
Example of hazards to aircraft
Eyjafjalljokull eruption in Iceland 2010. Prevailing wind south-east so over to eurpople and grounded planes for a week or two
150
Why is lightening generated by ash clouds
Don’t full understand but ash gains positive and negative charges and separates Into layers having charges between them
151
How can tsunamis be a risk
Can be generated by submarine explosive eruptions or volcanic avalanches into the sea
152
Example of tsunami generated
Krakatau eruption 1883, 15m high, 36,000 people killed along coast of Java and Sumatra
153
What are the none explosive hazards
Lava flows.
Jokulhlaups.
Gas emissions.
154
How does lava flows move
Usually slow as they are cooking
155
What is lava flow a threat to
Land and buildings rather than to people as it’s difficult to divert
156
What is the fastest lava
Low viscosity e.g in Nyiragongo
157
When did flood basalts occur
In the past but none in the last 14 Ma as it would be catastrophic
158
What is Jokulhlaups
Suddenly floods of meltwater causes by subglaxual eruptions - topples over craters and floods downhill
159
When can gas emissions be emitted
During eruptions or between
160
How is carbon dioxide w threat
It’s colorless, Odourless and hugs the ground.
Highly soluble in water - dense co2 lakes at bottom of crater lakes.
If stratification is disturbed the co2 exaolves rising bubbles and emitting has.
161
Example of co2 causing a hazard
Lakes Nyos Cameroon 1986.
stratification disturbed and the water overturned and mixed, layer depressurised and dissolved gas cane out. Bubbles expanded and floated to surface. Hugging ground and flowed down hill
162
How does S, Cl and F cause hazards
Can create acids - sulfuric acid, hydrochloric acid, carbonic acid. Hazardous precipitation, poisoning from F and Cl.
Acid rain.
163
Example of acid rain
Lake Fissure eruption in Iceland produced low lying haze or acid aerosols across eurpope and destroyed crops causing famine. 1/3 of people in Iceland died
164
What are aerosols
Acid droplets and tiny ash particles
165
What is aerosol effect
Big explosive eruptions can inject so2 and ash into the stratosphere where it remains for ages (10km high). Above level of weather. The aerosols scatter solar radiation from earth causing global cooling
166
What do climatic impacts of volcanic eruptions vary with
Latitude, season, magma composition, explosivity, duration or eruption, feedback effects
167
What have climatic effects of major historical eruptions been
Small (0.2-0.5), short term, difficult to pick out from normal temp
168
Example of recent climactic effect
Global mean temp decreased by 0.5 in 1992 after pinatubo eruption with high S.
Cooolint of 5-10 followed Toba eruption 80 ka ago. Biggest known explosive eruption. 2000km^3 pyrcoclataic flow.
169
What do lpresent day rates of volcanic co2 outgassing have an effect on climate change
Neglible. 350 times smaller co2 emissions than humans. In history there was big eruptionsxausing climate change
170
What kind of eruptions in history triggered global warming
Flood basalt
171
Example of flood basalt eruptions causing global warming
+0.5 with Deccan Traps eruption (India 65 Ma ago) warmed for millions of years - dinosaur?
+3-8 with mid-Cretaceous superplume (120-80 Ma ago) enough to melt all ice caps and sea levels higher. Continet sunder water at this time. 40 million years of extra C in atmosphere
