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Volcanoes Flashcards

1
Q

What is the Sendai framework

A

15 year plan for countries around the world to do something about the risk

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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.

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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.

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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.

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5
Q

Example of a stratovolcano

A

Cotopaxi (Ecuador).

Has permanent glaciers bc it’s so high so ready supply of water

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6
Q

What is the biggest volcano on earth

A

Mauna Loa (Hawaii) a shield volcano

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7
Q

Examples of a supply of water for volcanoes

A

In Alaska with lakes in crater

Iceland

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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

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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

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10
Q

How long can eruptions last

A

From 1 day to over 2400 years

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11
Q

Example of volcano that’s erupting for 2400 years

A

Stromboli

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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

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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

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14
Q

How long is the time between eruptions

A

Hundreds of thousands of years

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15
Q

Why are eruptions after long periods of dormancy violent

A

Because the magmas been building up

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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

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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.

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18
Q

How far back do known historical records go

A

Thousands of years due to record of human history being recent

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19
Q

What is a fumerole

A

Gas vents releasing sulphur dioxide during emissions

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20
Q

What is a hot sprint

A

Diffusion of water at the surface

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21
Q

What is a geyser

A

Gaseous source in water that causes the water to shoot up like old faithful in yellow stone

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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

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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

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24
Q

How many volcanoes erupt is a year

A

50-70

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25
Q

How many volcanoes have been observed erupting

A

550

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26
Q

How many volcanoes have erupted within the Holocene

A

1500

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27
Q

How many live volcanoes on earth

A

10,000

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28
Q

Where do volcanoes occur

A

Pacific ring of fire.
Rift Valley in Africa.
Mid Atlantic ridge (Iceland).

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29
Q

What is the thickness of lithosphere

A

70km for oceanic and 100-159 for continental

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30
Q

What is the lithosphere

A

Earths rigid outer layer - crust is part of it but is not exclusive

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31
Q

How does the lithosphere move

A

The asthenosphere is underneath and is close to melting point so the layer is quite plastic and can flow which makes the lithosphere move

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32
Q

What are the four groups of volcanoes due to their tectonic setting

A

Subduction zones.
Mid-ocean ridges.
Oceanic hot spots (intraplate).
Continental hot spots and rift zones.

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33
Q

How do subduction zone volcanoes form

A

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.

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34
Q

Why is it only partial melting in subducting zones

A

Because it’s basalt lava as only a few specific minerals melt. Peridotite partially melts a few percent.

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35
Q

Where are subduction volcanoes found

A

Parallel to the subduction zone on the overriding plate

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36
Q

When does an island arc form

A

If the overriding plate is oceanic, a curved chain of volcanic islands form

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37
Q

Example of an island arc

A

The lesser Antilles in the Caribbean

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38
Q

When does an active continental margin firm

A

If the overriding plate is continental, a chain of volcanoes form along the coastline

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39
Q

Example of an active continental margin

A

The Andes in South America

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40
Q

How do mid ocean ridges form volcanoes

A

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

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41
Q

What magma is there in mid ocean ridges

A

Basalt

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42
Q

Most MOR volcanoes are submarine, what’s the exception

A

Iceland

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43
Q

How do oceanic hot spot volcanoes form

A

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

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44
Q

What is a mantle plume

A

Solid rock that is warmer than average and only starts to melt when near the surface

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45
Q

Example of oceanic hot spot volcanoes

A

Hawaiian volcanoes in the central Pacific

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46
Q

How do continental hot spots and rift zones cause volcanoes

A

Some isolated volcanoes on continents have hot spots. Continental rifting produces groups of volcanoes and the hot spots often produce unusual magma compositions

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47
Q

Example of continental rifting producing volcanoes

A

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

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48
Q

Why do continental hot spots and rift zone produce unusual magma composition

A

Have thick layers of lithosphere to get through and the journey through the mantle changes the composition

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49
Q

What are the most hazardous volcanoes

A

Explosive ones

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50
Q

Why do most explosive eruptions occur at subduction zones

A

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.

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51
Q

What percentage of the magma mass in subduction volcanoes is water

A

5-6%

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52
Q

Why does a high silica content mean the eruption is likely to be explosive

A

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

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53
Q

Chemical name of silica

A

SiO2

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54
Q

What is viscosity

A

Resistance to flow

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55
Q

When does viscosity increases

A

With increasing silica and decreasing temperature making the magma thick

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56
Q

How much silica in basalt lava

A

Less than 52% so runny

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57
Q

How much silica in andesite lava

A

52-64%

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58
Q

How much silica in dacite

A

64+% so it’s sticky

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59
Q

How does basalt form

A

The original partially melting

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60
Q

How does dacite form

A

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

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61
Q

What are volatiles

A

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.

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62
Q

What are the types of explosive eruptions

A

Phreatic.
Phreato-magmatic.
Auto-explosive.

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63
Q

What is phreatic eruption

A

External water and hot rock - not magma but rock that’s been heated by magma or magma that’s partially cooled to solidification

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64
Q

What is phreato-magmatic eruption

A

External water and magma

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65
Q

What is auto-explosive eruption

A

Volatile rich magmas and no external water - tend to be only in subduction so magma has high water content anyway

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66
Q

Example of big city on the flanks of a volcano

A

Naples with 3 million

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67
Q

Gloabblly how many people live within 100km it a potentially active volcano

A

1 in 9

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68
Q

What is hazard level

A

Probability of a hazard occurring within a specified time scale

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69
Q

What is vulnerability

A

Exposure to the hazard (people, property etc)

70
Q

How many cities are close to one or more potentially active volcanoes

A

67 critics with populations over 100,000

71
Q

Which cities are at risk of volcanoes

A 
Tokyo
Mexico City
Manila (Philippine) 
Naples
Bandung (Indonesia) 
Seattle

Docmore for exams - 2nd volcano

72
Q

What are the six steps to reducing vulnerability

A 
Risk assessment.
Appropriate land use.
Hazard defences.
Advance emergency planning.
Monitor volcanic activity -> forecast eruptions.
Fight or flight.
73
Q

Components of the risk assessment

A

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
Q

Why are bridges important

A

For an evacuation route

75
Q

What can computer models be used to

A

Stimulate flows

76
Q

Land use policies that can be determined by a hazard map

A 
Exclusion zones.
Population density limits.
Relocation of residents to safer areas.
Special building regulations.
Evacuation routes.
Hazard defences if appropriate.
77
Q

Example of special building regulation

A

Slopes roofs to allow ash to fall off so it doesn’t collapse

78
Q

Examples of hazard defences

A

Crater lake drainage.
Gas pump system.
Strong shelters.
Dykes, diversionary ditches and sabo dams.
Barriers or other interventions to divert small lava flows.

79
Q

Why is crater lake drainage a good hazard defence

A

Would be a spruce of water so drain it to keep it from interacting with magma

80
Q

Example of crater lake drainage

A

Kelut, Indonesia

81
Q

Example of gas pump systems

A

Lake Nyos, Cameroon

82
Q

Why are strong shelters needed

A

To protect against heavy ash fall, blacks and bombs and lightening like in Sakurijima in Japan

83
Q

Why are dykes, diversionary ditches and sabo dams used

A

To protect against small Lahars like the dykes at Mt Mayon, Philippines or the sabo dams at Sakurajima, Japan

84
Q

Example of barriers diverting lava

A

Krafla, Iceland. Sicilily walls helped limit mt etnas flow

85
Q

What do sabo dams do

A

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
Q

How many explosions does Sakurijima have a year

A

300

87
Q

How many overs does debris flow affect near Sakurijima

A

10

88
Q

What can nothing protect against

A 
Pyroclastic flows.
Sector collapse.
Directed blasts.
But lahar.
Big lava flows.
89
Q

Why is advanced emergency planning needed

A

To help people understand how they work and how to evacuate

90
Q

What is involved in advanced emergency planning

A

Volcanic hazards education and training.
Plan evacuation routes, transport, temporary accommodation, emergency aid.
Warning systems.

91
Q

Who must advanced emergency planning involve

A 
Volcanologists.
Emergency and medical services.
Local authorities.
Teachers.
Community leaders.
Local residents.
92
Q

Example of a volcano alert system

A

USGS system - green is normal, yellow is advisory, orange is watch, red is warning.

93
Q

How does monitoring and forecasting work

A

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
Q

What are the physical monitoring methods

A 
Seismic methods.
Ground deformation.
Thermal signal
Gravity measurements.
Electromagnetic measurements.
Infrasonic.
95
Q

What are the seismic methods of monitoring

A

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
Q

What are high frequency (HF) earthquake swarms caused by and how long do they last

A

Magma movement and 5 days

97
Q

How to work out ground deformation

A

Satellite based Global Positioning System (GPS).
Satellite radar interferometry (InSAR).
Ground based electronic distance measurements (EDM).
Ground based tiltmeters.

98
Q

What is ground deformation

A

Changes in the ground e.g tilt and height

99
Q

What does InSAR Do

A

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
Q

How does EDM work

A

Use laser emitter and reflector to detect horizontal distance changes.

101
Q

What is the thermal signs

A

Remote sensing (infrared)
Temperature of hot springs and crater lakes.
Snow melts

102
Q

What is gravity measurements

A

Changes in gravity due to differences of mass underground as magma moves.

103
Q

What is electromagnetic measurements

A

Conductivity of rock

104
Q

What are infrasonics

A

Seismic waves through the air (sound). low frequency sound produced by explosive eruption in an area that’s not being monitored closely

105
Q

What is the chemical monitoring methods

A

Acidity of hot springs and crater lakes.

Composition of volcanic gases.

106
Q

How are Sulphur Dioxide (SO2) concentrations measured

A

By Correlation Spectrometer (COSPEC) or by satellites

107
Q

What does gas solubility depend on

A

Pressure

108
Q

Where do you measure chemicals

A

In fumeroles but it’s dangerous so use drones or long hand held items

109
Q

What does the possibility of predicting an eruption depend on

A

Likely eruption location/size/type/hazards

110
Q

Time frame of usually predicting an eruption

A

Within a few days/ weeks

111
Q

What is it difficult to balance in fight or flight

A

Risks of evacuating too early vs too late

112
Q

What are the factors affecting success of warnings and evacuation

A

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
Q

Case study for volcanoes

A

Pinatubo (1991)

114
Q

History of pinatubo

A

It was not known to be a potentially dangerous volcano until a few weeks before its cataclysmic eruption

115
Q

What promoted the USGS crash team to respond to pinatubo

A

Increased seismic and fumeroles activity and steam explosions

116
Q

What did USGS do in Pinatubo

A

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
Q

Hazards in pinatubo eruption

A

Massive blankets of ash, volcano mobilised by typhoon to create lahars

118
Q

How were so many lives saved in Pinutubo

A

Good monitoring, communications, timely warnings and evacuation of 60,000 people

119
Q

How many people died in the pinatubo eruption

A

350

120
Q

Why did many people die in Pinatubo

A

Because of collapsing roofs from ash fall

121
Q

Where are volcanoes

A 
Pacific ring of fire
In Andes and Central America
Indonesia
East Africa rift zone
Mediterranean
122
Q

What are volcanoes more explosive in subduction zones

A

Because higher silica as thicker crust (continental) and water content

123
Q

What is sector collapse

A

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
Q

How many times has sector collapse occurs

A

Twice in the past - v dangerous tho

125
Q

When are volcanic blast most dangerous

A

When directed laterally

126
Q

Example of sector collapse

A

Mt St. Helens 1980

127
Q

What happened in Mt St. Helens 1980

A

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
Q

Facts about blacks and bombs

A

Can travel up to 10km, kill upon impact, damage buildings and roads

129
Q

What are blocks and bombs

A

Large fragments ejected and falls back to ground but small fragments are lobbed away. Cm-m in Disney

130
Q

What are blocks

A

Solid rock - volcanic material that’s cooled

131
Q

What is bombs

A

Partially molten that lands and cools like bread crust bombs

132
Q

Where donblocks and bombs generally affect

A

Areas close to the vent due to size but sometimes destroys buildings e.g in Japan and Mt Etna

133
Q

What is air fall tephra

A

Small, tiny fragments of ash and rock that’s broken into small mm pieces. Carried in atmospheric currents.

134
Q

How far can air fall tephra travel

A

1000s of Km in direction of wind

135
Q

What are the effects of air fall tephra

A

Bury and collapse of buildings - several m thick.
Destroy crops and kill animals -> famine.
Choke lungs and engines.

136
Q

What are pyroclastic flows

A

Hot and fast flowing mixture of gas, ash and rocks. 800*C

137
Q

How far do pyroclastic flows travel

A

Tens of km

138
Q

What percentage of pyroclastic flows can be gas

A

99% allowing it to be mobile

139
Q

How far can pyroclastic flows trace

A

200km

140
Q

Why are pyroclastic flows dangers

A

Burns, chokes and flattered

141
Q

How are pyroclastic flows generated

A 
Dome collapse (explosive)
Column collapse
142
Q

What is dome collapse

A

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
Q

What is column collapse

A

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
Q

Example of pyroclastic flow

A

Repeated growth and collapse of lava dimes at Soufruere Hille volcano in Montserrat.
Column followers at Mayon volcano in Philippines.

145
Q

What are mud flows (Lahars)

A

Ash and water from rain, river, crater lake, melted air mobilise very destructively

146
Q

When can Mud flows occur

A

Months or years after eruption

147
Q

Example of worst mud flow

A

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
Q

How can eruptions be hazards to aircrafts

A

Can damage engines through ashfall tephra. Near misses as satelittrles senseint to track plumes in atmosphere to steer away

149
Q

Example of hazards to aircraft

A

Eyjafjalljokull eruption in Iceland 2010. Prevailing wind south-east so over to eurpople and grounded planes for a week or two

150
Q

Why is lightening generated by ash clouds

A

Don’t full understand but ash gains positive and negative charges and separates Into layers having charges between them

151
Q

How can tsunamis be a risk

A

Can be generated by submarine explosive eruptions or volcanic avalanches into the sea

152
Q

Example of tsunami generated

A

Krakatau eruption 1883, 15m high, 36,000 people killed along coast of Java and Sumatra

153
Q

What are the none explosive hazards

A

Lava flows.
Jokulhlaups.
Gas emissions.

154
Q

How does lava flows move

A

Usually slow as they are cooking

155
Q

What is lava flow a threat to

A

Land and buildings rather than to people as it’s difficult to divert

156
Q

What is the fastest lava

A

Low viscosity e.g in Nyiragongo

157
Q

When did flood basalts occur

A

In the past but none in the last 14 Ma as it would be catastrophic

158
Q

What is Jokulhlaups

A

Suddenly floods of meltwater causes by subglaxual eruptions - topples over craters and floods downhill

159
Q

When can gas emissions be emitted

A

During eruptions or between

160
Q

How is carbon dioxide w threat

A

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
Q

Example of co2 causing a hazard

A

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
Q

How does S, Cl and F cause hazards

A

Can create acids - sulfuric acid, hydrochloric acid, carbonic acid. Hazardous precipitation, poisoning from F and Cl.
Acid rain.

163
Q

Example of acid rain

A

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
Q

What are aerosols

A

Acid droplets and tiny ash particles

165
Q

What is aerosol effect

A

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
Q

What do climatic impacts of volcanic eruptions vary with

A

Latitude, season, magma composition, explosivity, duration or eruption, feedback effects

167
Q

What have climatic effects of major historical eruptions been

A

Small (0.2-0.5), short term, difficult to pick out from normal temp

168
Q

Example of recent climactic effect

A

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
Q

What do lpresent day rates of volcanic co2 outgassing have an effect on climate change

A

Neglible. 350 times smaller co2 emissions than humans. In history there was big eruptionsxausing climate change

170
Q

What kind of eruptions in history triggered global warming

A

Flood basalt

171
Q

Example of flood basalt eruptions causing global warming

A

+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

Natural Hazards (7 decks)

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