Volcanic Hazards Flashcards
How are volcanoes formed at destructive boundaries?
- Denser O plate is subducted and material melts
- Molten material is less dense and rises in the mantle and erupts at the surface
How are volcanoes formed at constructive boundaries?
- Plate diverge leaving a gap in the crust
- Magma rises due to low pressure and erupts
What are volcanoes at destructive boundaries like?
- Eruption of andesitic lava (high viscosity)
- Eruption of tephra
- Explosive eruptions (gas doesn’t escape as easily from the lava)
What are volcanoes at constructive boundaries like?
- Eruption of basaltic lava (low viscosity)
- Lava flows longs distances
- Effusive eruptions (gas escapes easily from the lava)
What are the primary hazards of a volcanic eruption?
- Tephra
- Pyroclastic flow
- Lava flow
- Volcanic gases
What is tephra?
Large fragments of ash and rock (volcanic bombs) ejected into the atmosphere
What is pyroclastic flow?
Gas and tephra collapses down the slopes of a volcano at up to 700 km/h
What are lava flows?
Lava pours from an erupting vent at constructive boundaries
What are volcanic gases?
Gases such as CO2, CO and SO2 escape during an eruption
What are the secondary hazards of a volcanic eruption?
- Lahars (mudflows)
- Flooding (jokulhlaup)
- Acid rain
What are lahars?
Volcanic material is mobilised by melting ice and snow and moves at up to 60 km/h
What is a jokulhlaup?
Serious flooding when an eruption takes place beneath glaciers and ice caps
What is acid rain?
SO2 combined with atmospheric moisture to produce acidic precipitation
What is the distribution of volcanoes?
- Plate boundaries and hotspots
- The Pacific Ring of Fire (high volcanic and seismic activity)
How can eruptions be defined?
- Explosive (high VEI)
- Effusive (low VEI)
How is eruption magnitude measured?
VEI - Volcanic Explosivity Index (logarithmic scale from 0-8)
What is VEI determined by?
Volume of ejected material (tephra)
How is eruption frequency determined?
- Volcanoes are classified as active, dormant or extinct
- Effusive eruptions are more frequent than explosive ones
Are volcanic eruptions regular?
Mostly when on the same plate boundary - can be irregular though
How can volcanoes be monitored?
- Gas emissions
- Seismic activity
- Ground deformation
- Thermal monitoring
How can gas emissions predict an eruption?
- SO2 release
- Gas levels drop rapidly just before an eruption
How can ground deformation predict an eruption?
- Magma movement in the lithosphere can deform the ground above
- Volcanoes swell prior to an eruption as magma gathers
How can seismic activity predict an eruption?
- Increased frequency and intensity of seismic activity can signal an eruption
- Harmonic tremors (magma pushes against rock and creates a humming effect)
What are the social impacts of volcanic events?
- Loss of life
- Homelessness
- Trauma/PTSD
- Fires break out
What are the economic impacts of volcanic events?
- Travel disruption
- Businesses destroyed
- Impact on tourism
- Loss of jobs
What are the environmental impacts of volcanic events?
- Habitat destruction
- Acid rain
- Release of greenhouse gases
- Wildlife killed
What are the political impacts of volcanic events?
- Government buildings destroyed
- Conflict over food security and insurance payouts
What are the short-term responses to a volcanic event?
- Call for international aid
- Evacuations/exclusion zones
- Food and water distribution
- Temporary infrastructure such as shelters for the homeless
What are the long-term responses to a volcanic event?
- Improvements to the local economy
- Relocation
- Resilience education
- Rebuilding infrastructure
How can volcanic hazards be prevented?
They cannot - risk can be prevented by not allowing building near volcanoes
How can volcanic hazards be mitigated?
- Construct lava flow diversion channels
- Strengthen existing buildings
- Drain lakes in craters to reduce risk of lahars
How can society adapt to volcanic hazards?
- Move away from high risk areas
- Capitalise on tourism opportunities
What do volcanoes at destructive boundaries look like?
Steep-sided/composite volcanoes
What do volcanoes at constructive boundaries look like?
Gentle-sloped/shield volcanoes
