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Dangerous World Lecture Slides > Lecture 9: Volcanic Hazards > Flashcards

Lecture 9: Volcanic Hazards Flashcards

1
Q

How many active volcanoes in the world?

A

596

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2
Q

Since 1950 there have been how many eruptions from how many volcanoes?

A

2208 eruptions from 347 volcanoes

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3
Q

Average number of eruptions per year since 1950 is

A

63

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4
Q

Volcanic eruptions can cause

A

loss of life and livelihoods in exposed communities, damage critical infrastructure, displace populations, disrupt business and add stress to already fragile environments.

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5
Q

Currently, an estimated…live within 100 km of a volcano that has the potential to erupt.

A

800 million people

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6
Q

Single events have the potential for

A

devastating mass casualties in a single event

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7
Q

Divergent boundaries

A

new crust is generated as the plates pull away from each other.

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8
Q

Convergent boundaries

A

crust is destroyed as one plate dives under another.

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9
Q

Transform boundaries

A

crust is neither produced nor destroyed as the plates slide horizontally past each other.

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10
Q

Hotspots

A

areas of volcanic activity away from plate boundaries.

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11
Q

Spreading ridge volcanism

A

Volcanism related to plate divergence

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12
Q

Composite or stratovolcano

A

Volcanism at an ocean-continent boundary (similar processes take place at ocean-ocean boundaries)

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13
Q

Shield volcano

A

Volcanism related to a mantle plume

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14
Q

Volcanic rocks, lava and ash are classified by the amount of silica they contain

A

Increased Si = Increased Pressure = More Explosive Volcanism

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15
Q

Shield volcanoes are almost exclusively

A

basalt, a type oflavathat is very fluid when erupted.

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16
Q

Shield volcanoes are most likely to produce

A

smaller geographically constrained eruptions – only explosive if water enter the vent

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17
Q

90% of the volcano is

A

lava rather than pyroclastic material

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18
Q

Largest percentage of the Earth’s individual volcanoes (~60%)

A

Stratovolcano

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19
Q

Stratovolcanoes

Most are characterised by eruptions of…

A

andesite and dacite lava that are more viscous than basalt – allows gas pressure to build explosive eruptions
Usually 50% lava and 50% pyroclastic material

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20
Q

Calderas and Caldera Complexes

A

Caldera complexes are the most explosive volcanoes – when they erupt they collapse in on themselves

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21
Q

Common eruptions types are:

A 
Hawaiian
Strombolian
Vulcanian
Plinian
Phreatomagmatic
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22
Q

Hawaiian Eruptions

Type of magma

A

Basic, low viscosity

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23
Q

Strombolian eruptions

Type of magma

A

Moderate viscosity

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24
Q

Vulcanian Eruptions

Type of magma

A

Acid, viscous

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25
Q

Plinian Eruptions

Type of magma

A

Acid, viscous

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26
Q

Hawaiian Eruptions

Nature Of Effusive Activity

A

Thin, extensive flows from central vent

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27
Q

Strombolian eruptions

Nature Of Effusive Activity

A

Flows often absent

28
Q

Vulcanian Eruptions

Nature Of Effusive Activity

A

Flows often absent

29
Q

Plinian Eruptions

Nature Of Effusive Activity

A

Absent

30
Q

Hawaiian Eruptions

Nature Of Explosive Activity

A

Very weak

31
Q

Strombolian eruptions

Nature Of Explosive Activity

A

Weak to violent

32
Q

Vulcanian Eruptions

Nature Of Explosive Activity

A

Moderate to violent

33
Q

Plinian Eruptions

Nature Of Explosive Activity

A

Cataclysmic

34
Q

Hawaiian Eruptions

Structures Formed Around The Vent

A

Broad lava domes and shields

35
Q

Strombolian eruptions

Structures Formed Around The Vent

A

Cinder cones and lava flows

36
Q

Vulcanian Eruptions

Structures Formed Around The Vent

A

Ash cones, explosion craters

37
Q

Plinian Eruptions

Structures Formed Around The Vent

A

Large explosion calderas

38
Q

Phreatomagmatic eruptions

A

Volcanic eruption resulting from the interaction between magma and water

39
Q

Phreatomagmatic eruptions

Surtseyan

A

volcanic eruption caused by shallow-water interactions between water and lava

40
Q

Phreatomagmatic eruptions

Subglacial

A

volcanic eruption characterized by interactions between lava and ice, often under aglacier

41
Q

Volcanic Explosivity Index (VEI)

A

A relative measure of the explosiveness ofvolcanic eruptions.
Volume of products, eruption cloud height, and qualitative observations are used to determine the explosivity value.
The scale is logarithmic, with each interval on the scale representing a tenfold increase in observed ejecta criteria.

42
Q

Hazards and Impacts

A 
Volcanic ash and tephra
Pyroclastic flows, surges and blasts
Lahars and Floods
Debris Avalanches and Landslides
Lava Flows
Volcanic gases
43
Q

Tephra and Volcanic Ash

A

Anything that comes out of a volcano during an eruption
Blocks (>64mm)
Lapilli (64 – 2mm)
Ash (2mm

44
Q

Pyroclastic flows, surges and blasts

A

Pyroclastic flows contain a high-density mix of hot lava,blocks, pumice,ashand volcanic gas.
They move at very high speed down volcanic slopes, typically following valleys - up to 200 m/s

45
Q

Pyroclastic flows, surges and blasts

Hazards

A

Most lethal volcanic hazard – 1/3 of all fatalities
Destroy nearly everything in their path
Severe damage to infrastructure, vegetation and agricultural land
Extreme temperatures can ignite fires and melt snow and ice
On the margins of pyroclastic flows, death and serious injury to people and animals may result from burns and inhalation of hotashand gases.
Can lead to secondary hazards such as flooding and lahars

46
Q

Lahars and Floods

A

Lahars are fast moving mixtures of volcanic debris and water
Commonly occur when intense rain moves loose volcanic rock during an eruption
Also caused by volcanic activity melting ice caps and glaciers
Can threaten an area for years after an eruption

47
Q

Lahars and Floods

Hazards

A

Largelaharscan crush, abrade, bury, or carry away almost anything in their paths.
Buildings and valuable land may be partially or completely buried.
By destroying bridges and roads, lahars can also trap people in areas vulnerable to other hazardous volcanic activity
Confined to valleys and areas close to volcano so can identify vulnerable areas.

48
Q

Debris Avalanches and Landslides

A

Landslides are large masses of wet or dry rock and soil that fall, slide, or flow very rapidly under the force of gravity.
Landslides are common on volcanic cones because they are tall, steep, weakened by the rise and eruption of molten rock and constructed from poorly consolidated deposits.
Can lead to lateral volcanic blasts as highly pressurized volcanic interior is exposed
Can also cause tsunamis if material enters the sea

49
Q

Several conditions can trigger landslides:

A

Explosive eruptions
Largeearthquakedirectly beneath a volcano or nearby
Heavy or long-lived rainfall that saturates the ground.

50
Q

Debris Avalanches and Landslides

Hazards

A

Typically destroy everything in their path
Can cause additional hazards
Dam lakes leading to lahars
Change pressure of magma chamber triggering further eruptions

51
Q

Lava Flows

A

Streams of molten rock that pour or ooze from an eruption vent

52
Q

Lava Flows

Hazards

A

Destroys everything in its path
Deaths are uncommon because it moves slowly
Can bury homes and agricultural land under tens of meters of hardened black rock
People are rarely able to use land buried bylavaflows or sell it for more than a small fraction of its previous worth.

53
Q

The speed at whichlava moves across the ground depends on several factors

A

Type of lava erupted and its viscosity
Steepness of the ground over which it travels
Whether the lava flows as a broad sheet, through a confined channel, or down alava tube
Rate of lava production at the vent.

54
Q

Volcanic Gases

A

Magma contains dissolved gases which escape during reduction in pressure as the magma moves towards the surface.
Main gas is water vapour (60-99%) which is harmless
Other gases include
Carbon Dioxide – up to 10%
Sulphur dioxide and other sulphur gases – up to 15%
Halogens, including chlorine – up to 5%

55
Q

Volcanic Gases

Hazards

A

Fatalities and health impacts
Damage eyes and respiratory system
CO2 asphyxiation
Damage to vegetation, livestock, infrastructure and property
Impact varies widely and depends on the amount and type of gas emitted.
Environmental hazards
Cooling of the Earth and Acid rain

56
Q

Volcano Monitoring

A

Volcanic eruptions are typically preceded by days to months of precursory activity, unlike other natural hazards like earthquakes.
Volcano observatories play a key role in monitoring and early warning due to the localised character and individuality of volcanoes around the world
Set up on all active volcanoes that threaten the human population
Designed to monitor and potentially predict the eruptive behaviour

57
Q

Volcano Monitoring Methods

A 
Seismic activity
Increase in local earth quake activity
Audible rumblings
Ground deformation
Upwelling near volcanic vent
Changes in ground slope
Hydrothermal phenomena
Increased discharge or temperature from hot springs or fumaroles
Rise in temperature in crater lakes
Melting of ice and snow on the volcano
Withering of vegetation of volcano slopes
Chemical changes
Changes in chemical composition of gas from vents
58
Q

Hazard Mitigation

A

The process for mitigating risk differs from country to country.
Communities need to understand their risk and take action to mitigate risk.

59
Q

Hazard Mitigation

Pyroclastic flows

A

Prior evacuation of threatened areas (identified by hazard mapping) can reduce loss of life. Effects of pyroclastic flows could be mitigated via long-term urban planning (subways, strong buildings)

60
Q

Hazard Mitigation

Lava flows

A

Hazard maps can be developed for areas of at risk of flow-related damage

61
Q

Hazard Mitigation

Lahars and Floods

A

Hazard mapping to identify high risk areas (valleys). Warning systems that permit evacuation could reduce the lethal effect of lahars.
Engineering measures, such construction of sediment dams, can reduce flow mass and resulting destruction. Long-term urban planning can also reduce risk by avoidance of dense population concentrations in valleys and deltas.

62
Q

Hazard Mitigation

Tephra

A

In the developing world, tephra accumulation on roofs of poorly constructed buildings often results in collapse; campaigns to promote ash removal can reduce fatalities and damage from tephra-induced roof collapse. Humanitarian assistance can reduce potential long-term impacts of resulting crop loss, livestock deaths, and economic disruption.

63
Q

Hazard Mitigation

Debris avalanches

A

Prior evacuation the only measure for preventing loss of life.

64
Q

Hazard Mitigation

Gas

A

Identification and ongoing monitoring of hazardous lakes, resettlement, pre-evacuation, and establishing guidelines relative to areas of refuge.

65
Q

USGS employs a nationwide volcano alert-level system.

A

Ranked terms to inform people on the ground about a volcano’s status
Ranked colors to inform the aviation sector about airborneash hazards.

Dangerous World Lecture Slides (20 decks)

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