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Geography- Hazards > Volcanic Hazards > Flashcards

Volcanic Hazards Flashcards

1
Q

Shield volcano boundary

A

Constructive (and hotspots)

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2
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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3
Q

Shield volcano example

A

Eyjafjallajokull, Iceland

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4
Q

Shield volcano characteristics

A

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

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5
Q

Shield volcano explosivity

A

Low, as magma under little pressure

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6
Q

Composite volcano boundary

A

Destructive

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7
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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8
Q

Composite volcano example

A

Montserrat

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9
Q

Composite volcano characteristics

A

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

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10
Q

Composite volcano explosivity

A

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

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11
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
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12
Q

Volcanoes at hotspots formation

A

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

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13
Q

Why do extinct volcanoes subside at hotspots?

A

As they have put so much pressure on the crust

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14
Q

VEI

A

Volcanic Explosivity Index

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15
Q

VEI meaning

A 
Logarithmic scale (0-8) 
Measures height of eruption column and volume of tephra erupted
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16
Q

Disadvantages of VEI

A

Doesn’t consider climate impact

Ash, lava and lava bombs all treated alike

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17
Q

Icelandic Eruption

A

Basaltic lava flows gently from fissures

18
Q

Highest and Lowest Categories on VEI?

A 
Icelandic = lowest
Plinian = highest
19
Q

Plinian Eruption

A

Highly explosive and violent, with tephra and pyroclastic fall out

20
Q

Tephra Meaning

A

Solid material (ash-bombs) ejected into the atmosphere

21
Q

Pyroclastic Flow / Nuees Ardentes Meaning

A

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

22
Q

What are the secondary effects of pyroclastic flows?

A

Snow melt

Damming streams

23
Q

What are the secondary effects of tephra?

A

Grounding air traffic
Destroy vegetation- famine
Improve soil fertility

24
Q

What 4 factors affect the distance tephra travels?

A

Height of eruption column
Temperature of air
Wind speed
Wind direction

25
What 4 things are lava flows affected by?
Land steepness Extrusion rate Silica content Flow temperature
26
What temperatures are lava flows between?
550°c - 1400°c
27
Why are lava flows not a big hazard?
Because of their slow speeds
28
Mudflow / Lahar Meaning
Volcanic material + water (rainfall or ice melt)
29
What's the difference between mudflows and lahars?
Lahars set like concrete
30
Name some of the gases released by a volcano
Water vapour Carbon dioxide Sulphur dioxide- acid rain
31
Where does CO2 seep through the volcano and kill plants?
Mammoth Mountain
32
Why are tiltmeters and GPS used to monitor volcanoes?
Measure slope angles | Indicates expanding magma chamber
33
Why are seismometers and seismographs used to monitor volcanoes?
Microquakes | Rising magma fractures overlying rock
34
Why are magnetometers used to monitor volcanoes?
Changing magnetism indicates rising iron-rich magma
35
Protection- Land Use Planning
Build houses away from high risk areas
36
Preparation- Why should there be good communication systems?
To alert and update people
37
Preparation- There should be suitable ____ put aside to deal with an emergency
Funds
38
Preparation- Residents in high risk areas...
Need evacuating
39
Preparation- What should an emergency supply kit contain? Where should it be placed?
``` Tinned food Battery radio Torch Cash Breathing mask IN A CAR ```
40
Preparation- What should be included in a family emergency plan?
How to contact eachother How to meet What you will do in an emergency
41
East African Rift Valley
African plate Splitting into Somali and Nubian Created Kilimanjaro

Geography- Hazards (13 decks)

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