Volcanic Hazards

Question 1

Shield volcano boundary

Answer 1

Constructive (and hotspots)

Question 2

Formation of shield volcanoes

Answer 2

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

Question 3

Shield volcano example

Answer 3

Eyjafjallajokull, Iceland

Question 4

Shield volcano characteristics

Answer 4

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

Question 5

Shield volcano explosivity

Answer 5

Low, as magma under little pressure

Question 6

Composite volcano boundary

Answer 6

Destructive

Question 7

Formation of composite volcanoes

Answer 7

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

Question 8

Composite volcano example

Answer 8

Montserrat

Question 9

Composite volcano characteristics

Answer 9

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

Question 10

Composite volcano explosivity

Answer 10

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

Question 11

Volcanoes in rift valleys formation

Answer 11

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

Question 12

Volcanoes at hotspots formation

Answer 12

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

Question 13

Why do extinct volcanoes subside at hotspots?

Answer 13

As they have put so much pressure on the crust

Question 14

VEI

Answer 14

Volcanic Explosivity Index

Question 15

VEI meaning

Answer 15

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

Question 16

Disadvantages of VEI

Answer 16

Doesn’t consider climate impact

Ash, lava and lava bombs all treated alike

Question 17

Icelandic Eruption

Answer 17

Basaltic lava flows gently from fissures

Question 18

Highest and Lowest Categories on VEI?

Answer 18

Icelandic = lowest
Plinian = highest

Question 19

Plinian Eruption

Answer 19

Highly explosive and violent, with tephra and pyroclastic fall out

Question 20

Tephra Meaning

Answer 20

Solid material (ash-bombs) ejected into the atmosphere

Question 21

Pyroclastic Flow / Nuees Ardentes Meaning

Answer 21

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

Question 22

What are the secondary effects of pyroclastic flows?

Answer 22

Snow melt

Damming streams

Question 23

What are the secondary effects of tephra?

Answer 23

Grounding air traffic
Destroy vegetation- famine
Improve soil fertility

Question 24

What 4 factors affect the distance tephra travels?

Answer 24

Height of eruption column
Temperature of air
Wind speed
Wind direction

Question 25

What 4 things are lava flows affected by?

Answer 25

Land steepness Extrusion rate Silica content Flow temperature

Question 26

What temperatures are lava flows between?

Answer 26

550°c - 1400°c

Question 27

Why are lava flows not a big hazard?

Answer 27

Because of their slow speeds

Question 28

Mudflow / Lahar Meaning

Answer 28

Volcanic material + water (rainfall or ice melt)

Question 29

What's the difference between mudflows and lahars?

Answer 29

Lahars set like concrete

Question 30

Name some of the gases released by a volcano

Answer 30

Water vapour Carbon dioxide Sulphur dioxide- acid rain

Question 31

Where does CO2 seep through the volcano and kill plants?

Answer 31

Mammoth Mountain

Question 32

Why are tiltmeters and GPS used to monitor volcanoes?

Answer 32

Measure slope angles | Indicates expanding magma chamber

Question 33

Why are seismometers and seismographs used to monitor volcanoes?

Answer 33

Microquakes | Rising magma fractures overlying rock

Question 34

Why are magnetometers used to monitor volcanoes?

Answer 34

Changing magnetism indicates rising iron-rich magma

Question 35

Protection- Land Use Planning

Answer 35

Build houses away from high risk areas

Question 36

Preparation- Why should there be good communication systems?

Answer 36

To alert and update people

Question 37

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

Answer 37

Funds

Question 38

Preparation- Residents in high risk areas...

Answer 38

Need evacuating

Question 39

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

Answer 39

``` Tinned food Battery radio Torch Cash Breathing mask IN A CAR ```

Question 40

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

Answer 40

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

Question 41

East African Rift Valley

Answer 41

African plate Splitting into Somali and Nubian Created Kilimanjaro