Volcanic Hazards

Question 1

How are volcanoes formed at destructive boundaries?

Answer 1

• Denser O plate is subducted and material melts
• Molten material is less dense and rises in the mantle and erupts at the surface

Question 2

How are volcanoes formed at constructive boundaries?

Answer 2

• Plate diverge leaving a gap in the crust
• Magma rises due to low pressure and erupts

Question 3

What are volcanoes at destructive boundaries like?

Answer 3

• Eruption of andesitic lava (high viscosity)
• Eruption of tephra
• Explosive eruptions (gas doesn’t escape as easily from the lava)

Question 4

What are volcanoes at constructive boundaries like?

Answer 4

• Eruption of basaltic lava (low viscosity)
• Lava flows longs distances
• Effusive eruptions (gas escapes easily from the lava)

Question 5

What are the primary hazards of a volcanic eruption?

Answer 5

• Tephra
• Pyroclastic flow
• Lava flow
• Volcanic gases

Question 6

What is tephra?

Answer 6

Large fragments of ash and rock (volcanic bombs) ejected into the atmosphere

Question 7

What is pyroclastic flow?

Answer 7

Gas and tephra collapses down the slopes of a volcano at up to 700 km/h

Question 8

What are lava flows?

Answer 8

Lava pours from an erupting vent at constructive boundaries

Question 9

What are volcanic gases?

Answer 9

Gases such as CO2, CO and SO2 escape during an eruption

Question 10

What are the secondary hazards of a volcanic eruption?

Answer 10

• Lahars (mudflows)
• Flooding (jokulhlaup)
• Acid rain

Question 11

What are lahars?

Answer 11

Volcanic material is mobilised by melting ice and snow and moves at up to 60 km/h

Question 12

What is a jokulhlaup?

Answer 12

Serious flooding when an eruption takes place beneath glaciers and ice caps

Question 13

What is acid rain?

Answer 13

SO2 combined with atmospheric moisture to produce acidic precipitation

Question 14

What is the distribution of volcanoes?

Answer 14

• Plate boundaries and hotspots
• The Pacific Ring of Fire (high volcanic and seismic activity)

Question 15

How can eruptions be defined?

Answer 15

• Explosive (high VEI)
• Effusive (low VEI)

Question 16

How is eruption magnitude measured?

Answer 16

VEI - Volcanic Explosivity Index (logarithmic scale from 0-8)

Question 17

What is VEI determined by?

Answer 17

Volume of ejected material (tephra)

Question 18

How is eruption frequency determined?

Answer 18

• Volcanoes are classified as active, dormant or extinct
• Effusive eruptions are more frequent than explosive ones

Question 19

Are volcanic eruptions regular?

Answer 19

Mostly when on the same plate boundary - can be irregular though

Question 20

How can volcanoes be monitored?

Answer 20

• Gas emissions
• Seismic activity
• Ground deformation
• Thermal monitoring

Question 21

How can gas emissions predict an eruption?

Answer 21

• SO2 release
• Gas levels drop rapidly just before an eruption

Question 22

How can ground deformation predict an eruption?

Answer 22

• Magma movement in the lithosphere can deform the ground above
• Volcanoes swell prior to an eruption as magma gathers

Question 23

How can seismic activity predict an eruption?

Answer 23

• Increased frequency and intensity of seismic activity can signal an eruption
• Harmonic tremors (magma pushes against rock and creates a humming effect)

Question 24

What are the social impacts of volcanic events?

Answer 24

• Loss of life
• Homelessness
• Trauma/PTSD
• Fires break out

Question 25

What are the economic impacts of volcanic events?

Answer 25

- Travel disruption - Businesses destroyed - Impact on tourism - Loss of jobs

Question 26

What are the environmental impacts of volcanic events?

Answer 26

- Habitat destruction - Acid rain - Release of greenhouse gases - Wildlife killed

Question 27

What are the political impacts of volcanic events?

Answer 27

- Government buildings destroyed - Conflict over food security and insurance payouts

Question 28

What are the short-term responses to a volcanic event?

Answer 28

- Call for international aid - Evacuations/exclusion zones - Food and water distribution - Temporary infrastructure such as shelters for the homeless

Question 29

What are the long-term responses to a volcanic event?

Answer 29

- Improvements to the local economy - Relocation - Resilience education - Rebuilding infrastructure

Question 30

How can volcanic hazards be prevented?

Answer 30

They cannot - risk can be prevented by not allowing building near volcanoes

Question 31

How can volcanic hazards be mitigated?

Answer 31

- Construct lava flow diversion channels - Strengthen existing buildings - Drain lakes in craters to reduce risk of lahars

Question 32

How can society adapt to volcanic hazards?

Answer 32

- Move away from high risk areas - Capitalise on tourism opportunities

Question 33

What do volcanoes at destructive boundaries look like?

Answer 33

Steep-sided/composite volcanoes

Question 33

What do volcanoes at constructive boundaries look like?

Answer 33

Gentle-sloped/shield volcanoes