Volcanic hazards Flashcards
Vulcanicity at destructive plate margins
- Subduction at destructive plate margins result in volcanic activity
- Once oceanic crust dips below the continental crust, temperature rise due to increased depth and melting occurs
- The resulting magma moves slowly to the surface where It erupts through volcanoes and fissures as vicious, thick andesitic lava and tephra
- Viscous magma traps steam and other gases, creating violent explosions and eruptions
Vulcancity at constructive plate margins
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- Two plates seperating causes Tension in the crust and litosphere reduces pressure and allows magma to flow to the surface
- Lava, tephra and hot gases erupt through volcanoes and fissures
- Most eruptions are on the ocean floor as constructive plate margins are found at mid-ocean ridges
- Lava is basalt and eruptions are less violent (effusive) because gases escape easily from the basalt
Hazards associated with volcanoes
- Lava flows - lava can flow quickly or slowly depending on its viscosity. Silica makes lava viscous and slow, which is common in explosive eruptions.
- Lahars (mudflows) - caused by a number of reasons, usually by melting ice at high latitudes
- Glacial floods = when temperatures are high from magma, glaciers or ice sheets at high temperatures quickly melt and a large amount of water is discharged
- Tephra - any type of rock that is ejected by a volcano -
- Toxic gases - released during some eruptions, even CO₂ can be toxic as it can replace oxygen as it is heavier
- Acid rain - caused when gases such as sulfur dioxide are released into the atmosphere
- Nuées ardentes/pyroclastic flows - clouds of burning hot ash and gas that collapses down a volcano at high speeds. Average speeds of around 60 mph but can reach 430 mph
Spatial distrubution of volcanoes
- The Ring of Fire is an area of high volcanic and earthquake activity located in the Pacific, and the majority of large volcanoes occur within this 25,000 mile belt
Magnitude of volcanoes
- Vulcanicity is measured using the Volcanic Explosivity Index(VEI)
. - Multiple features are considered when calculating the VEI, including how much tephra erupts, how long it lasts, how high the tephra is ejected etc
. - Intense high magnitude eruptions are explosive whereas calmer, lower magnitude eruptions are effusive.
Frequency of volcanoes
- Frequency of eruptions varies per volcano
. - Volcanoes are classed as either active, dormant or extinct.
- An estimated 50-60 volcanoes erupt each month
- Usually, a higher frequency eruption means the eruptions are effusive whereas low frequency means the eruptions are explosive.
Regularity of volcanoes
- Volcanic eruptions are regular in that the eruptions on each type of boundary are similar
- Sometimes eruptions may be irregular and not fit patterns.
Predictability of volcanoes
- can help estimate when eruptions will take place
- Seismic activity, gases releasing, elevation etc. can all indicate an imminent eruption, but there is no definite predictions to a volcanic eruption.
- monitor level of magma
- measure seismic waves
Primary impacts of volcanic hazard
- Ecosystems damaged through various volcanic hazards
- Wildlife killed
- Businesses and industries destroyed or disrupted
- People killed
- Homes destroyed from lava/pyroclastic flows
- Government buildings and other important areas destroy
Secondary impacts of volcanic hazards
- Water acidified by acid rain
- Volcanic gases contribute to greenhouse effect (global warming)
- Jobs lost
- Profit from tourism industry
- Fires can start which puts lives at risk
- Mudflows or floods
- Trauma
- Homelessness
- Conflicts concerning government response, food shortages, insurance etc.
Response and risk management to volcanic hazards = Prevention
- Volcanic eruptions cannot be prevented
- Only the risk to people can be prevented by not allowing people near volcanic hazards
Response and risk management to volcanic hazards = Preparedness
- Monitoring increases the notice of volcanic eruptions, so warnings can be given out
- Education on volcanoes in areas of risk so people know what to do
- Evacuation procedures planned
- Training response teams
Response and risk management to volcanic hazards = Mitigation
- Direct intervention to the volcano
- Strengthening buildings that are at the risk of mudflows or ash pileup
- Evacuation and exclusion zones
- Mitigating effects on health by having emergency aid and rescue
Response and risk management to volcanic hazards = Adaption
- Move away from area at risk
- Capitalise on opportunities, such as encouraging tourism
- Changing profession so it is less likely to be affected by volcanic hazards
