EOSC 114 Exam 1 Questions with Correct
Answers
What are the types of eruptions?
Hawaiian, Strombolian, Vulcanian, Plinian
Describe Hawaiian eruptions?
More effusive
Basaltic magma
Associated with Shield Volcanoes
Low explosivity & low viscosity
Lava fountaining, lava flows, lava lakes
Describe Strombolian eruptions?
Basaltic/andesitic magma
Mildly explosive
Associated with Cinder Cones
Lava fountaining, volcanic bombs, lava flows
Describe Vulcanian eruptions?
Viscous andesitic/rhyolitic magma
Very explosive
Sustained explosions of ash
Associated with Stratovolcanoes
,Ash plume, lapilli, volcanic ash rain, volcanic bomb
Describe Plinian eruptions?
Andesitic/rhyolitic ash
Violently explosive
Sustained column of ash
Pyroclastic flows
Associated with Stratovolcanoes
Ash plume, volcanic ash rain
What is the Volcanic Explosivity Index (VEI)?
Describes the size of an explosive volcanic eruption
1. Volume of ash produced
2. Height of eruption cloud above the vent
3. Duration of eruption
0-8, each interval represents an increase by a factor of ten
ex. a VEI 4 is 10x larger than 3, and 100x more than a 2
ex. VEI 1 = Hawaiian, VEI 3 = Vulcanian, VEI 5 = Plinian, VEI 6 = Ultra-Plinian
What are the ways magma is erupted?
Quietly as lava or violently as pyroclastics
Describe lava flows?
Mafic & low viscosity
,Slow - usually not dangerous
Easy to predict flow path based on topography (Lava flows downslope, ponds in
topographic lows)
Rarely causes fatalities, primarily economic damage to buildings and livelihoods.
When lava interacts with infrastructure, as it cannot be easily removed -- economic sunk cost
-- cannot be rebuilt, only relocated
What is the least and most useful way to protect people from lava flows?
Least useful: building barriers and dams
Most useful: not building towns/villages in valleys
Describe fire fountaining?
If basaltic lava is gas-rich
Small explosive eruptions form fire fountains
As some of the liquid drops fall back to the ground, they may coalesce to form a lava flow.
Incredibly localised, only a hazard if feet away
Describe Spindle/Lava bombs?
Made of basaltic magma; very dense.
In an eruption, there is much molten lava ejected that partly solidifies during flight - when
enough magma particles form together, a spindle bomb is formed
Describe pyroclastic falls (ash falls)?
The most wide-reaching volcanic product, when the ash hits the stratosphere, it moves
laterally and travels very far (impeding air traffic)
, When rain mixes with ash, fertile land is produced.
Hazards to people: breathing in ash (can be deadly), total darkness, and roofs
collapsing (most dangerous, as most fatalities are people trying to shelter)
Hazards to aircraft: Engines suck in ash and fail, windshields are scratched and break, and
turbulence
Describe pyroclastic flows?
An avalanche of pyroclastic material (air, and gas) driven by gravity.
Velocity: 40-400 km/h - very fast moving
Usually stays in valleys, but if big enough, can flow over ridges and even water
Dome collapse is usually followed by pyroclastic flows, which have a dense core of
boulders hidden by billows of ash
What are the origins of pyroclastic flows?
Most common: collapse of a volcanic column (e.g. Mt. St. Helens & Vesuvius)
- sustained fountaining in a Plinian column
- quasi-steady current
OR
explosive collapse of lava dome (e.g. Mt Unzen & Montserrat)
- single-pulse dome collapse and avalianche
- unsteady current
- silica-rich magma, highly viscous, steep-sided domes
Answers
What are the types of eruptions?
Hawaiian, Strombolian, Vulcanian, Plinian
Describe Hawaiian eruptions?
More effusive
Basaltic magma
Associated with Shield Volcanoes
Low explosivity & low viscosity
Lava fountaining, lava flows, lava lakes
Describe Strombolian eruptions?
Basaltic/andesitic magma
Mildly explosive
Associated with Cinder Cones
Lava fountaining, volcanic bombs, lava flows
Describe Vulcanian eruptions?
Viscous andesitic/rhyolitic magma
Very explosive
Sustained explosions of ash
Associated with Stratovolcanoes
,Ash plume, lapilli, volcanic ash rain, volcanic bomb
Describe Plinian eruptions?
Andesitic/rhyolitic ash
Violently explosive
Sustained column of ash
Pyroclastic flows
Associated with Stratovolcanoes
Ash plume, volcanic ash rain
What is the Volcanic Explosivity Index (VEI)?
Describes the size of an explosive volcanic eruption
1. Volume of ash produced
2. Height of eruption cloud above the vent
3. Duration of eruption
0-8, each interval represents an increase by a factor of ten
ex. a VEI 4 is 10x larger than 3, and 100x more than a 2
ex. VEI 1 = Hawaiian, VEI 3 = Vulcanian, VEI 5 = Plinian, VEI 6 = Ultra-Plinian
What are the ways magma is erupted?
Quietly as lava or violently as pyroclastics
Describe lava flows?
Mafic & low viscosity
,Slow - usually not dangerous
Easy to predict flow path based on topography (Lava flows downslope, ponds in
topographic lows)
Rarely causes fatalities, primarily economic damage to buildings and livelihoods.
When lava interacts with infrastructure, as it cannot be easily removed -- economic sunk cost
-- cannot be rebuilt, only relocated
What is the least and most useful way to protect people from lava flows?
Least useful: building barriers and dams
Most useful: not building towns/villages in valleys
Describe fire fountaining?
If basaltic lava is gas-rich
Small explosive eruptions form fire fountains
As some of the liquid drops fall back to the ground, they may coalesce to form a lava flow.
Incredibly localised, only a hazard if feet away
Describe Spindle/Lava bombs?
Made of basaltic magma; very dense.
In an eruption, there is much molten lava ejected that partly solidifies during flight - when
enough magma particles form together, a spindle bomb is formed
Describe pyroclastic falls (ash falls)?
The most wide-reaching volcanic product, when the ash hits the stratosphere, it moves
laterally and travels very far (impeding air traffic)
, When rain mixes with ash, fertile land is produced.
Hazards to people: breathing in ash (can be deadly), total darkness, and roofs
collapsing (most dangerous, as most fatalities are people trying to shelter)
Hazards to aircraft: Engines suck in ash and fail, windshields are scratched and break, and
turbulence
Describe pyroclastic flows?
An avalanche of pyroclastic material (air, and gas) driven by gravity.
Velocity: 40-400 km/h - very fast moving
Usually stays in valleys, but if big enough, can flow over ridges and even water
Dome collapse is usually followed by pyroclastic flows, which have a dense core of
boulders hidden by billows of ash
What are the origins of pyroclastic flows?
Most common: collapse of a volcanic column (e.g. Mt. St. Helens & Vesuvius)
- sustained fountaining in a Plinian column
- quasi-steady current
OR
explosive collapse of lava dome (e.g. Mt Unzen & Montserrat)
- single-pulse dome collapse and avalianche
- unsteady current
- silica-rich magma, highly viscous, steep-sided domes
