Hazards: Volcanic hazards

Question 1

What are 3 features of a shield volcano?

Answer 1

Constructive plate boundary and hotspots.
Gentle slopes and wide base.
Eruptions frequent, not explosive.
Formed with layers of runny lava but no ash.

Question 2

What are 3 features of a composite volcano?

Answer 2

Destructive plate margins
Steep slopes and narrow base
Eruptions infrequent but violent
Formed with layers of ash and rock

Question 3

What can a composite volcano also be know as?

Answer 3

stratovolcano

Question 4

Silica content: Basaltic

Answer 4

45%-55%

Question 5

Silica content:Andestic

Answer 5

55%-65%

Question 6

Silica content:Rhyoltic

Answer 6

65%-75%

Question 7

Temperature of eruption:Basaltic

Answer 7

1050-1200C

Question 8

Temperature of eruption:Andestic

Answer 8

800-1000C

Question 9

Temperature of eruption:Rhyolitic

Answer 9

650-800C

Question 10

ViscosityBasaltic

Answer 10

low

Question 11

ViscosityAndestic

Answer 11

medium

Question 12

ViscosityRhyolitic

Answer 12

High

Question 13

Gas contentBasaltic

Answer 13

Low

Question 14

Gas content Andestic

Answer 14

Medium

Question 15

Gas content Rhyolitic

Answer 15

High

Question 16

Type of volcanoBasaltic

Answer 16

Shield

Question 17

Type of volcanoAndestic

Answer 17

Composite

Question 18

Type of volcanoRhyolitic

Answer 18

Composite

Question 19

Distribution (plate boundary)Basaltic

Answer 19

Constructive & hotspot

Question 20

Distribution (plate boundary)Andestic

Answer 20

Destructive

Question 21

Distribution (plate boundary)Rhyolitic

Answer 21

Destructive

Question 22

Type of eruption Basaltic

Answer 22

Gentle, effusive (Hawaiin)

Question 23

Type of eruption Andestic

Answer 23

Explosive, infrequent, short lived. Ash, rocks, gases and lava ejected.

Question 24

Type of eruption Rhyolitic

Answer 24

Explosive, infrequent, short lived. Ash, rocks, gases and lava ejected.

Question 25

What is the VEI?

Answer 25

Volcanic Explosivity Index

Question 26

What three things does the VEI measure?

Answer 26

Volume of ejecta | Height of the eruption column Qualitative observations (including duration)

Question 27

Give three criticisms of the VEI.

Answer 27

Gas emissions Atmospheric/ climatic impacts of eruptions All types of tephra considered alike despite differences in densities and impact

Question 28

Give five ways volcanic eruptions vary.

Answer 28

``` Magnitude Frequency Randomness vs regularity Predictability Duration ```

Question 29

What is a super volcano?

Answer 29

An unusually large volcano having the potential to produce an eruption with major effects on the global climate and ecosystem.

Question 30

Describe Tephra ( Primary hazard)

Answer 30

Solid material of varying grain size ranging from volcanic bombs to ash all ejected into the atmosphere (either blasted by volcanic explosions or carried upwards by hot gases in eruption columns or lava fountains) during a volcanic eruption that then falls back to the ground.

Question 31

Describe Pyroclastic flows (primary hazard)

Answer 31

Pyroclastic flows (nuees ardentes): Very hot (over 800C) gas charged high velocity flows made up of a mixture of super-heated gas and tephra (ash and volcanic rock) - hence high density mixture that flow downwards. These usually hug the ground and flow down the sides of the volcano with speeds of up to 700km per hour but typically > 80kmh often flowing a long distance from the volcano (10-15km).

Question 32

Describe lava flows

Answer 32

molten rock (magma when under the surface), flows from a volcanic vent. The speed of the flow and distance travelled by the lava depends on the temperature and viscosity of the lava as well as the steepness of the slope. Low viscosity (runny) lava can flow up to 10kmh on a steep slope and travel tens of meters.

Question 33

Describe Volcanic gases(primary hazard)

Answer 33

these include carbon dioxide, sulphur dioxide, hydrogen sulphide, carbon monoxide and chlorine.

Question 34

Describe Lahars (secondary hazard)

Answer 34

Melted snow and ice as a result of the eruption or heavy rainfall following an eruption combines with volcanic ash and forms mud flows.

Question 35

Describe Tsunamis(secondary hazards)

Answer 35

Sea waves generated by violent volcanic eruptions underwater or pyroclastic flows/lahars/landslides displacing water which often result in much more widespread impacts than the volcano itself.

Question 36

Describe Acid rain(secondary hazards)

Answer 36

Volcanoes emit gases which include sulphur, this then combines with atmospheric moisture and results in acid rain.

Question 37

Describe climate change in terms of hazards (secondary hazard)

Answer 37

The ejection of huge amounts of volcanic debris into the atmosphere can reduce global temperatures. Additionally sulphur dioxide emitted from volcanoes when combining with water vapour creates droplets of sulphuric acid which reflect sunlight.

Question 38

How can volcanic activity be detected?

Answer 38

Sulphur/radon gases Ground deformation Energy release Surface temperature changes

Question 39

What is used to detect sulphur/radon gases?

Answer 39

spider robots; gas trapping bottles.

Question 40

What is used to detect ground deformation?

Answer 40

tiltmeters; gravity changes

Question 41

What is used to detect energy release?

Answer 41

infrasound; seismometers

Question 42

What is used to detect Surface temperature changes

Answer 42

Thermal heat sensors

Question 43

Give three methods of preparedness to reduce the risk of volcanic hazards.

Answer 43

Have emergency kits prepared Installing monitoring systems to predict when an eruption might occur Set up search and rescue teams or fire response units to tackle the impacts of an eruption

Question 44

Give three methods of diverting lava flows?

Answer 44

Digging/using explosives to create earth trenches and use concrete: Mt Etna SicilyBombing lava tubes Use of ice water/cooling lava: 1973 Heimaey Iceland

Question 45

How might people adapt to the risk of volcanic eruptions?

Answer 45

Strengthen buildings to reduce the chance of collapse from ash on roofs Capitalize on the opportunities of living near volcanoes e.g. farming fertile soils or working in the tourism industry.

Question 46

Give three primary impacts of volcanic events

Answer 46

People are killed and buildings are destroyed by pyroclastic flows Ash causes damage to agricultural land Death due to volcanic gasses (e.g. asphyxiation by carbon dioxide).

Question 47

Give three secondary impacts of volcanic events

Answer 47

Acid rain acidifies aquatic ecosystems killing some plants/animals Volcanic debris reflects sunlight resulting in crop destruction due to colder winters Flash floods due to glacial melts Tsunamis due to volcanic landslides