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Earth Science > Volcanic hazards > Flashcards

Volcanic hazards Flashcards

1
Q

What is a volcano?

A

A vent in the Earth’s crust where molten rock, gas and heat can escape a magma chamber

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2
Q

Lava

A

Molten rock above or on the Earth’s surface, forms extrusive igneous rocks

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3
Q

Magma

A

Molten rock below the Earth’s surface, forms intrusive ingneous rock

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4
Q

Magma types

A

Mafic
Ultramafic
Intermediate
Felsic

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5
Q

Mafic magma

A

Rich in Fe and Mg
Dark colour
Basalt (fine), Dolerite (intermediate) or Gabbo (coarse)

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6
Q

Intermediate magma

A

Grey colour

Andesite (fine), Microdolerite (intermediate), Diorite (coarse)

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7
Q

Felsic magma

A

Rich in silica
White/pink colour
Rhyolite (fine), Microgranite (intermediate), Granite (coarse)

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8
Q

Sill

A

Part of sub volcanic plumbing system that follows sedimentary units and bedding planes

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9
Q

Dyke

A

Part of sub volcanic plumbing system that cuts across sedimentary units and bedding planes

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10
Q

Batholith

A

Part of sub volcanic plumbing system, crystallised magma chamber

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11
Q

Volcanic neck

A

Part of sub volcanic plumbing system that connects magma chamber to surface of the Earth

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12
Q

Intrusive igneous rocks

A

Cooled slowly, therefore, deeper in the Earth and more insulated
Produces coarser crystals

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13
Q

Extrusive igneous rocks

A

Cool quickly

Produce fine crystals or glass

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14
Q

Volcanic Explosivity index, VEI

A
  • Measures how explosive a volcanic eruption is
  • Based on volume of explosive products erupyed and height of eruption cloud
  • Logarithmic scale of 0-8
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15
Q

Lake Toba

A

Crater lake in Indonesia

  • VEI of 8
  • Dust and sulphurous gases in the atmosphere cooled the Earth
  • Humans almost wiped out
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16
Q

Super-volcano affects

A 
Severe burning and death
Ash collapsing house roofs
Suffocation
Crop failure
Volcanic winter
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17
Q

Vesuvius

A
  • VEI of 5
  • Deadliest in European history
  • Petrified the city
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18
Q

Mt Tambora - Year without a summer

A
  • VEI of 7
  • Global temperature dropped by almost 1 degree
  • Caused major food shortages and famine
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19
Q

Krakatau

A
  • VEI of 6
  • Volcano tore itself and the island apart
  • Landslide exposed magma chamber and water mixed w/ it and generated a huge explosion
  • Produced massive pyroclastic density currents
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20
Q

Living near a volcano - benefits

A

Energy (e.g. geothermal)
Tourism
Nutrient rich soil
Mineral resources

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21
Q

Geothermal energy process

A
  1. Pump cold water down
  2. Heat from magma warms the water and produces steam
  3. Steam turns turbine to generate electricity
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22
Q

How do volcanoes assist in fertilising soil?

A
  1. Volcanic ash and lava weather away and erode

2. Products of erosion introduced key nutrients for plants into the soil (k, Fe, P)

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23
Q

Mineral resources provided by volcanoes

A
  • Diamond
  • Copper
  • Nickle
  • Aluminium
  • Gold
  • Lead
  • Zinc
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24
Q

Fissure volcanoes

A
  • Long linear vent
  • Effusive eruption producing basaltic lavas
  • Fed by dykes that connect the magma chamber to the surface
  • Found in rift zones and spreading centres
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25
Q

Shield volcanoes

A
  • V. shallow slopes
  • Basaltic magma w/ low gas content
  • Made of lava flows from effusive eruptions
  • Lava is v. hot and runny and so spreads over large distances
  • Found at spreading centre and intraplate hotspots
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26
Q

Dome volcanoes

A
  • Formed by relatively small bulbous masses of lava
  • Viscous basaltic-rhyolite lava that cant travel far from vent as it is cooler
  • Grows by slow expansion
  • Found on convergent plates
  • Mostly effusive but some explosive eruptions
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27
Q

Ash-Cinder volcanoes

A
  • Small, grows v. quickly and steep
  • Often near or attached to larger volcano
  • Gas rich magma
  • Made of unconsolidated ash, pyroclastic material, scoria and ejected rock fragments
  • Cone-shaped, circular base and crater with a vent
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28
Q

Composite (stratavolcano) volcanoes

A
  • Consists of altering layers of lava and pyroclastic material
  • Felsic-intermediate magma composition
  • Explosive type eruptions
  • Steep, cone-shaped and w/ crater
  • Lava flows from craters or from fissures
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29
Q

Caldera volcanoes

A
  • Large volcanic eruptions that empty their magma chamber
  • Ground above then falls into empty magma chamber to form a caldera
  • Steep basin shaped depression
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30
Q

Effusive eruptions

A
  • Produces lava flows that ooze out of vent
  • Magma has low viscosity
  • Typically Fe-Mg rich
  • Low water/gas content
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31
Q

Explosive eruptions

A
  • Produces tephra
  • Magma has high viscosity
  • Typically Si rich
  • High water/gas content
  • Gas expands rapidly generating an explosion
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32
Q

Hydrothermal eruptive material

A
  • Just hot water, no magma
  • Explosive pulverized rock producing ash
  • Generally v. small and short
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33
Q

Phreatic eruption

A
  • Heat from old magma interacts with water
  • No new magma
  • Explosive, producing ash
34
Q

Phreatomagmatic

A
  • New magma and water

- V. explosive

35
Q

Icelandic (fissure) eruptions

A
  • Effusive eruption
  • Flows out of long parallel fissures
  • Basaltic lava
  • Builds large plateaus of lava
36
Q

Characteristic of basaltic lava

A

Hot
Gas poor
Low viscosity

37
Q

Hawaiian eruptions

A
  • Effusive eruption
  • Lava flows out of central vent and radial fissures
  • Basaltic lava
  • Builds a shield volcano
38
Q

Strombolian eruption

A
  • Explosive, mild sized, regular eruptions
  • Magma is more viscous
  • Basaltic or andesitic magma
  • Caused by bursting slugs in volcanic conduit
  • Produces ash and pyroclastic density currents
39
Q

What is a slug?

A

Large bubble of gas

40
Q

Vulcanian eruption

A
  • Explosive eruption
  • Short, violent and small explosion of viscous magma
  • Andesite or rhyolite magma
  • Caused by fragmentation of plug in volcanic conduit
  • Ejection of cinders and lava bombs
  • Produces cinder cones
41
Q

Pelean eruption

A
  • Viscous magma produces lava domes that then collapse
  • Adesitic or rhyolite magma
  • Produces many pyroclastic density currents
42
Q

Plinian eruption

A
  • Largest and most explosive
  • Fragmentation of gassy and v. viscous magma
  • Rhyolitic magma
  • Produce large columns of ash and pyroclastic density currents
  • Magma chamber completely emptied
43
Q

Characteristics of flood basalt eruption

A
  • Large scale effusive, short and silent
  • HUGE lava volume
  • Produces thick lava flows that cover huge areas
  • Basaltic magma is v. hot and runny causing the lava to flood
  • Create lava plateaus and mountain ranges
44
Q

Formation of flood basalt eruptions

A

Large mantle plumes produce them by

  • Hot materials from core-mantle boundary rising
  • Plume hits base of the crust and raises the temp.
  • Huge amount of melting occurs
45
Q

Central Atlantic magmatic province

A

Flood basalt eruption 200 million yrs ago
Covered 10 million km2 of the Earth’s surface
Split the super continent of Pangea

46
Q

Flood basalts on the moon

A

Marias:

The dark patches on the lunar surface, these are evidence for huge basalt eruptions

47
Q

Deccan traps, India

A
  • Successive layers of thick basalt rock from lava flow
  • Caused by a deep mantle plume in the reunion island hotspot
  • Produced a rift valley
48
Q

Deccan traps and the dinosaurs

A
  • Release of large volumes of volcanic gases, like sulphur dioxide, caused an intense climate change
  • Global temp. dropped by 2 degrees
  • V. toxic world was produced
49
Q

Siberian traps, Russia

A
  • 250 million yrs ago

- Most likely caused by large magma plume

50
Q

The great dying, Permian-Triassic mass extinction

A

Most devastating mass extinction, caused by the volcanic gases, emitted by Siberian traps, causing severe climate change

51
Q

Hot water springs and what can they help predict?

A
  • When H2O comes into contact w/ hot rocks heated by magma underground
  • Can change temp. or chemistry quickly, CAN signify an impending eruption
52
Q

New thermal areas and what do they indicate?

A
  • New areas of hot spring activity or reactivation of old hot springs
  • indicate movement of magma
53
Q

Geysers

A
  • Underground plumbing systems where a cavity of H2O is heated by magma and hot rock
  • This vaporises the H2O and generating a pocket of steam

Steam rapidly rises to surface, displacing H2O on the surface above

54
Q

Geysers and predicting eruptions

A

Geysers can be regular and therefore not a clear sign of an eruption. However, change in geyser behaviuos can be.

55
Q

Acidified H2O before an eruption

A
  • Lakes and seas near volcanoes become saturated w/ CO2 and SO2, producing sulphuric and carbonic acid
  • pH 0.1 can be reached, causing severe burns and death
  • Lake ecology is killed
  • Rapid change CAN signify an eruption
56
Q

Drying up of springs/wells before an eruption

A

Movement of magma produces cracks, causing H2O to drain away

57
Q

Fumaroles and relation to an eruption

A
  • Heavy and toxic gases released in large amounts from vents
  • Sink to ground forming a toxic pocket of gas that travels downhill to into valleys/depressions
  • Can be regular, but a change in behaviour could signify an eruption
58
Q

Effects of fumaroles

A

Humans and animals - asphyxiation, respiratory diseases and skin burns

Famine due do crop and vegetation death

59
Q

Lake Nyos: Consequences

A
  • Many people and livestock died
  • Thousands made ill w/ respiratory diseases, lesions and paralysis
  • Lake dropped 1m, turned red and knocked down bank trees
60
Q

Lake Nyos: What happened?

A
  • Volcanic gasses became trapped at lake bottom
  • Earthquake or landslide released the heavy gases into atmosphere
  • Gases hugged the ground and travelled dowm=n valleys and smothered villages
61
Q

Lake Nyos: Precautions now takes

A
  • Degassing station penetrates lake bed and releases any trapped gases
  • Prevents gas build-up
62
Q

Plant dieback in relation to an eruption

A
  • Affect of toxic gases/liquids released from volcano
  • Trees/plants yellow and die as a result of increased CO2 in the soil
  • New areas of dying plantlife CAN be a sign of an eruption
63
Q

Landslides in relation to an eruption

A

Volcanoes are weak structures and so landslides near summit, w/ no other explanatory cause, could be due to movement of magma FRACTURING EARTH SURFACE or GAS RELEASE

64
Q

Soil temp. in relation to an eruption

A
  • Ground near volcanic systems can be v. hot

- Soil heating up/cooling down indicates activity below surface

65
Q

Ground uplift in relation to an eruption

A
  • Ground level rising/falling

- Can indicate magma, H2O and gas is building up underground causing an uplift

66
Q

Volcanic earthquakes in relation to an eruption:

VOLCANIC TECTONIC EARTHQUAKES

A

Caused by regional tectonic forces OR injection of new magma

Good indicators of an eruption

67
Q

Volcanic earthquakes in relation to an eruption:

LONG PERIOD EARTHQUAKES

A

Caused by vibrations from movement of magma/fluid OR pressure build-up causing rocks to break

Good indicators of an eruption

68
Q

Harmonic tremors in relation to an eruption:

A
  • Specific type of long-lasting rhythmic seismic signal
  • Caused by magma moving through fractures in rock
  • V. good indicator of an imminent eruption
69
Q

Changes in wildlife in relation to an eruption:

A

ANECDOTAL

Reported that animals behave strangely prior to an eruption and migrate away from volcanic area

70
Q

What is ash fall

A
  • Rain of volcanic ash
  • Small abrasive particles of glass
  • Travels v. far
  • Severity depends on layer thickness & grain size
71
Q

Ash effects on humans

A
  • Can be irritating or deadly
  • Small particles, < 4 micrometres, can be breathed into the lungs alveoli
  • Mixes w/ H2O to form a type of concrete in the lungs, resulting in a respiratory disease
72
Q

Ash effects on plants

A
  • Ash cloud can block out sun for days-years
  • Layer of ash covers leaves
  • Plants die
73
Q

Ash effects on buildings

A
  • Layers of ash can become v. heavy
  • Ash is twice as heavy when wet
  • This can cause roofs to collapse
74
Q

Ash effects on electrical systems

A
  • Wet volcanic ash is conductive

- Shorts out electrical systems and damages power lines

75
Q

Ash effects on air travel

A
  • Scratches windows obscuring visibility
  • Shuts engines down by fusing w/ turbines
  • St Elmos fire
76
Q

What is a St Elmos fire

A
  • Type of lightening
  • Electrical field is caused by static build-up in a volcanic ash cloud
  • Lightening caused by ionisation of the air around sharp objects in the electrical field
  • N and O in atmosphere cause blue fluorescence
77
Q

Ash effects: Lahar’s

A
  • Volcanic mudflow w/ consistency similar to wet concrete
  • Consists of H2O, ash, pyroclastic material and rock
  • Solidifies once it stops moving
  • Fast moving, can travel up to 10s of m/s
78
Q

Lahar causes

A
  • Melting snow/glaciers come in contact w/ lava or pyroclastic material
  • Rainfall or ash deposit after eruption
  • Breakout of a crater lake
  • Landslides
  • Can form during/after an eruption
79
Q

Volcanic explosion aftermath: Sulphurous gases

A
  • Air had eggy smell
  • Leaves/fruit fell from trees
  • Persistent fog
  • Respiratory problems, struggling to breath and death
80
Q

Volcanic winter

A
  • When enough SO2 and ash is released into upper atmosphere and the albedo of the planet increases
  • Reflects sunlight back to space
  • Cools the planet down (climate change)
81
Q

Volcanic explosion aftermath: Erosion of the volcano

A
  • Volcanic structures are not particularly strong, the shape is maintained by volcanic activity
  • Once volcanism has ceased, the volcano begins to rapidly erode
  • Eventually, only the plug remains

Earth Science (3 decks)

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