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AQA A-Level Physical Geography > 🌋3.1.5.3 - Volcanic Hazards > Flashcards

🌋3.1.5.3 - Volcanic Hazards Flashcards

1
Q

What type of lava is rich in silica?

A

Slow flowing, viscous lava

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2
Q

What is generally erupted from volcanoes at destructive margins?

A

Lava bombs, ash, dust

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3
Q

What are lava flows?

A

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

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4
Q

What are the two types of lava?

A

Pahoehoe and A’a

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5
Q

What are the characteristics of pahoehoe lava?

A

Smooth, billowy surface, relatively thin

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6
Q

What are the characteristics of A’a lava?

A

Rough, jagged surface and thick lava

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7
Q

When lava solidifies, what does it form?

A

Igneous rock

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8
Q

What are the main gases that lead to acid rain?

A

Carbon Dioxide and Sulphur Dioxide

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9
Q

How can acid raid impact the environment?

A

Polluting waterways and soil, killing plants and trees, dissolving rock

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10
Q

What is ash made up of?

A

Fragments of pulverised rock, minerals and volcanic glass

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11
Q

How is ash formed?

A

When dissolved gases in magma expand and escape violently into the atmosphere in explosive eruptions

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12
Q

How fast can pyroclastic flows move?

A

700km/h

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13
Q

How do pyroclastic flows form?

A

Form collapse of an eruption column, colapse of lava domes, or ‘boiling over’

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14
Q

What are lahars triggered by?

A

Heavy rain or large amounts of ground water flowing through rocks as it causes the top layer of soil to be removed

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15
Q

How can tephra lead to a pyroclastic flow?

A

If the rock fragments are hot enough to fuse together

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16
Q

How can tephra cause a temperature drop?

A

If they reflect light and heat from the sun while in the atmosphere

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17
Q

What can form part of a nuees ardentes?

A

Pyroclastic flow

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18
Q

What attempted control was used on Mauna Loa in 1935?

A

Bombing lava tubes

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19
Q

How was Eldfell’s lava controlled on Heimay in 1973?

A

It was blasted with freezing sea water to cool it rapidly

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20
Q

How was Mount Etna controlled in 1983?

A

Barriers of rock and ash were constructed to divert the lava

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21
Q

How can volcanoes be monitored using geological observations?

A

A tiltmeter can be used to measure slope angle and bulges, and GPS to measure horizontal movements caused by expansion before an eruption

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22
Q

How can volcanoes be monitored using seismic activity?

A

Seismographs measure earthquakes around a volcano as it prepares to erupt

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23
Q

How can gas emissions be used to monitor volcanic activity?

A

As magma nears the surface and pressure decreases, gases escape. Sulphur dioxide is released as large amounts reach the surface, and concentrations can be measured

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24
Q

What is the main disadvantage of monitoring volcanoes using seismic activity?

A

Most volcanoes are on plate boundaries, so it can be difficult to distinguish between volcanic earthquakes and routine tremors

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25
Q

Formation of shield volcanoes

A

Plates move apart
Magma rises to surface, cools = new crust
Sea floor spreading
Layers built by eruptions
Sea floor spreading = plates move apart

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26
Q

Shield volcano example

A

Eyjafjallajokull, Iceland

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27
Q

Shield volcano characteristics

A

Gentle sloping sides
Wide base
Low viscosity lava - BASALTIC
Frequent, basic lava eruptions

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28
Q

Shield volcano explosivity

A

Low, as magma under little pressure

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29
Q

Composite volcano boundary

A

Destructive

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30
Q

Formation of composite volcanoes

A

Plates move towards eachother
Oceanic, denser, subducts
Beinoff Zone
Less dense molten material rises
Layers of ash and lava build

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31
Q

Composite volcano example

A

Montserrat

32
Q

Composite volcano characteristics

A

Steep sided
Layers of ash, dust, lava
Viscous lava - RHYOLITIC
Long dormant periods

33
Q

Composite volcano explosivity

A

High, as magma rises in plumes through fissures in buckled continental plate- high pressure

34
Q

Volcanoes in rift valleys formation

A

Rising magma
Brittle continental crust buckles and fractures
= Fault lines
Plates move further apart
Crust between parallel faults drops down
= Rift Valley
Thin crust
Magma forces its’ way to the surface

35
Q

Volcanoes at hotspots formation

A

Concentration of radioactive elements below crust
Plume of magma rises
Breaks through surface

36
Q

Why do extinct volcanoes subside at hotspots?

A

As they have put so much pressure on the crust

37
Q

Volcanic Explosivity Index

A

Volcanic Explosivity Index

38
Q

VEI meaning

A

Logarithmic scale (0-8)
Measures height of eruption column and volume of tephra erupted

39
Q

Disadvantages of VEI

A

Doesn’t consider climate impact
Ash, lava and lava bombs all treated alike

40
Q

Icelandic Eruption

A

Basaltic lava flows gently from fissures

41
Q

Highest and Lowest Categories on VEI?

A

Icelandic = lowest
Plinian = highest

42
Q

Plinian Eruption

A

Highly explosive and violent, with tephra and pyroclastic fall out

43
Q

Tephra Meaning

A

Solid material (ash-bombs) ejected into the atmosphere

44
Q

Pyroclastic Flow / Nuees Ardentes Meaning

A

Fast moving current of hot gas and tephra
Up to 1000°c
Little warning = death and destruction

45
Q

What are the secondary effects of pyroclastic flows?

A

Snow melt
Damming streams

46
Q

What are the secondary effects of tephra?

A

Grounding air traffic
Destroy vegetation- famine
Improve soil fertility

47
Q

What 4 factors affect the distance tephra travels?

A

Height of eruption column
Temperature of air
Wind speed
Wind direction

48
Q

What 4 things are lava flows affected by?

A

Land steepness
Extrusion rate
Silica content
Flow temperature

49
Q

What temperatures are lava flows between?

A

550°c - 1400°c

50
Q

Why are lava flows not a big hazard?

A

Because of their slow speed

51
Q

Mudflow / Lahar Meaning

A

Volcanic material + water (rainfall or ice melt)

52
Q

What’s the difference between mudflows and lahars?

A

Lahars set like concrete

53
Q

Name some of the gases released by a volcano

A

Water vapour
Carbon dioxide
Sulphur dioxide- acid rain

54
Q

Where does CO2 seep through the volcano and kill plants?

A

Mammoth Mountain

55
Q

Why are tiltmeters and GPS used to monitor volcanoes?

A

Measure slope angles
Indicates expanding magma chamber

56
Q

Why are seismometers and seismographs used to monitor volcanoes?

A

Microquakes
Rising magma fractures overlying rock

57
Q

Why are magnetometers used to monitor volcanoes?

A

Changing magnetism indicates rising iron-rich magma

58
Q

Protection- Land Use Planning

A

Build houses away from high risk areas

59
Q

Preparation- Why should there be good communication systems?

A

To alert and update people

60
Q

Preparation- There should be suitable ____ put aside to deal with an emergency

A

Funds

61
Q

Preparation- Residents in high risk areas…

A

Need evacuating

62
Q

Preparation- What should an emergency supply kit contain? Where should it be placed?

A

Tinned food
Battery radio
Torch
Cash
Breathing mask
IN A CAR

63
Q

Preparation- What should be included in a family emergency plan?

A

How to contact eachother
How to meet
What you will do in an emergency

64
Q

East African Rift Valley

A

African plate
Splitting into Somali and Nubian
Created Kilimanjaro

65
Q

3 ps

A

Prediction, protection and preparation

66
Q

Bombing lava tubes

A

. In theory, bombs would destroy the lava tubes, ruining transport channel + exposing lava to air cooling it
. But in practice, while bombs created craters in parts of the tubes, they were soon filled again by the lava

67
Q

What are lava tubes

A

Cooled and hardened outer crusts of lava which provide insulation for the faster-flowing, molten rock inside

68
Q

Lava control: water

A

. Lava stoped in the 1970s on Haimey (Iceland)
. For five months in 1973, sea water was blasted through cannons towards the lava
. As water hit the superheated rock, it turned into steam, allowing the lava’s heat to dissipate
. But conditions were right and lava was slow moving

69
Q

Lava control: build a barrier

A

. Mount Etna, in March 1983
. Barriers of rock and ash were constructed to divert the lava
. One of the first barriers, 18m high and 10m wide, was overrun, but a second barrier blocked lava from moving further west

70
Q

Lahars

A

. Mixture of hot or cold water and rock fragmented which flow down the steep side of a volcano
. Grow as they travel picking up material

71
Q

Eruption styles: Icelandic

A

. Low viscosity and highly effusive
. May have water therefore phreatic
. Lava flows gently from fissures
. Basaltic lava

72
Q

Eruption styles: Hawaiian

A

. Effusive, minor explosivity, with fire fountain and low viscosity lava flow
. Lava flows gently from a central vent
. Basaltic lava

73
Q

Eruption styles: Strombolian

A

. Eruption with gas bubbles so eject tephra
. Frequent explosions of tephra and steam
. Occasional, short lava flows
. Thicker basaltic magma

74
Q

Eruption styles: Vulcanian

A

. Higher gas build up than Strombolian highly viscous lava
. A series of short lived explosions, with tephra including bombs, ash and gases
. Thicker basaltic, andestic and rhyolitic magma

75
Q

Eruption styles: Pelean

A

. Explosive eruptions with range of tephra with nuee ardent (glowing cloud) pyroclastic flows
. Andesitic and rhyolitic magma

76
Q

Eruption styles: Plinian

A

. Highly explosive, large eruption column (up to 45km) range of tephra and pyroclastic fallout, including flows
. Torrential rainstorms cause Lahars
. Rhyolitic magma

AQA A-Level Physical Geography (28 decks)

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