What is the main method of measuring volcanic hazards?
Volcanic explosivity index - VEI
What is the VEI?
A way of measuring the explosivity of a volcanic hazard, on a logorithmic scale from 0-8.
What are some criticisms of the VEI?
Does not take into account:
- Gas emissions
- Climatic impacts of eruptions
How the the frequency of eruption of any volcano be determined?
What are primary effects of volcanic hazards?
Effects brought about from the eruption itself/ the ejection of material:
- Pyroclastic flows / nuées ardentes
- Lava flows
What is tephra?
Solid material of varying grain size ranging from volcanic bombs to ash, all ejected into the atmosphere.
What are pyroclastic flows / nuées ardentes?
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.
What are the hazards associated with pyroclastic flows?
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.
What are hazards associated with lava flows?
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.
Give examples of volcanic gases:
- Carbon dioxide
- Carbon monoxide
- Hydrogen sulphide
- Sulphur dioxide
What are issues associated with volcanic gases?
- Sulphur dioxide - can cause respiratory issues, acid rain.
- Carbon dioxide - greenhouse gas that promotes global warming.
What lava is found at constructive margins?
What are the properties of basaltic lava?
- 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.
What lavas are found at destructive margins?
Andesitic and rhyolitic
What are properties of andesitic and rhyolitic lava?
- More viscous, so flow less easilt.
- Usually erupt intermittently and eruptions are short lived.
- Violent eruptions
Why are eruptions of andesitic and rhyolitic lava more violent?
- 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.
What lava is mostly found at hotspots?
What are the hazards associated with tephra?
- 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.
List secondary hazards of volcanic eruptions:
- Lahars (volcanic mud flows)
- Volcanic landslides
- Acid rain
- Climatic change
What are lahars?
What are the hazards?
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.
How is acid rain formed?
What are the hazards?
- 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.
How does climatic change occur following an eruption?
- Ejection of huge amounts of volcanic debris into atmosphere can reduce global temperatures.
How are volcanologists trying to accurately predict eruptions?