HAZARDS : Volcanic hazards

Question 1

What is the main method of measuring volcanic hazards?

Answer 1

Volcanic explosivity index - VEI

Question 2

What is the VEI?

Answer 2

A way of measuring the explosivity of a volcanic hazard, on a logorithmic scale from 0-8.

Question 3

What are some criticisms of the VEI?

Answer 3

Does not take into account:

• Gas emissions
• Climatic impacts of eruptions

Question 4

How the the frequency of eruption of any volcano be determined?

Question 5

What are primary effects of volcanic hazards?

List examples.

Answer 5

Effects brought about from the eruption itself/ the ejection of material:

• Tephra
• Pyroclastic flows / nuées ardentes
• Lava flows
  *

Question 6

What is tephra?

Answer 6

Solid material of varying grain size ranging from volcanic bombs to ash, all ejected into the atmosphere.

Question 7

What are pyroclastic flows / nuées ardentes?

Answer 7

Very hot, gas charged, high-velocity flows made up of a mixture of gas and tephra.

Ususally hug the ground and flow down sides of volcano with speeds of up to 700km per hour.

Question 8

What are the hazards associated with pyroclastic flows?

Answer 8

They can travel fast and can happen with relatively little warning, so cause widespread death and destruction, through for example burning and burial under debris.

Happened at Pompeii.

Question 9

What are hazards associated with lava flows?

Answer 9

Most flows are relatively slow, so people often have time to evacuate.

BUT lava flows destroy everything in their path, including buildings and vegetation, by burning, burial and knocking things down.

Question 10

Give examples of volcanic gases:

Answer 10

• Carbon dioxide
• Carbon monoxide
• Hydrogen sulphide
• Sulphur dioxide
• Chlorine

Question 11

What are issues associated with volcanic gases?

Answer 11

• Sulphur dioxide - can cause respiratory issues, acid rain.
• Carbon dioxide - greenhouse gas that promotes global warming.

Question 12

What lava is found at constructive margins?

Answer 12

Basaltic

Question 13

What are the properties of basaltic lava?

Answer 13

• Very hot
• Low viscosity (runny), so flows easily and quickly.
• Eruptions are frequent and go on for a long period, but are not very violent.

Question 14

What lavas are found at destructive margins?

Answer 14

Andesitic and rhyolitic

Question 15

What are properties of andesitic and rhyolitic lava?

Answer 15

• Cooler
• More viscous, so flow less easilt.
• Usually erupt intermittently and eruptions are short lived.
• Violent eruptions

Question 16

Why are eruptions of andesitic and rhyolitic lava more violent?

Answer 16

• One plate pulled under another at subduction zone.
• Causes melting of plate forming magma, rising to surface as volcanoes.
• Because lava is viscous, it forms blockages in vents, causing pressure to build.
• Can only be cleared by violent eruption.

Question 17

What lava is mostly found at hotspots?

Answer 17

Basaltic lava

Question 18

What are the hazards associated with tephra?

Answer 18

• Large pieces can damage buildings and kill/injure people.
• Finer material can form layer up to serveral metres in thickness, which can kill vegetation, hinder road and rail transport and cause buildings to collapse.
• Respiratory issues from inhaling ash.

Question 19

List secondary hazards of volcanic eruptions:

Answer 19

• Lahars (volcanic mud flows)
• Flooding
• Volcanic landslides
• Tsunamis
• Acid rain
• Climatic change

Question 20

What are lahars?

What are the hazards?

Answer 20

Melted snow and ice as a result of the eruption combined with volcanic as forms mud flows that can move down the course of river valleys at high speeds.

Can bury or destroy natural habitats, settlements and infrastructure.

Question 21

How is acid rain formed?

What are the hazards?

Answer 21

• Volcanoes emit gases including sulphur.
• When this combines with atmospheric moisture, it forms acid rain.

Damages ecosystems, and can cause stone and metal to corrode.

Question 22

How does climatic change occur following an eruption?

Answer 22

• Ejection of huge amounts of volcanic debris into atmosphere can reduce global temperatures.

Question 23

How are volcanologists trying to accurately predict eruptions?

Answer 23

• Monitoring land swelling.
• Monitoring changes in groundwater levels.
• Monitoring chemical composition of groundwater and gas emissions.
• Monitoring seismic activity looking for shock waves that result in magma moving towards the surface.