Hazards: Volcanic hazards Flashcards
What are 3 features of a shield volcano?
Constructive plate boundary and hotspots.
Gentle slopes and wide base.
Eruptions frequent, not explosive.
Formed with layers of runny lava but no ash.
What are 3 features of a composite volcano?
Destructive plate margins
Steep slopes and narrow base
Eruptions infrequent but violent
Formed with layers of ash and rock
What can a composite volcano also be know as?
stratovolcano
Silica content: Basaltic
45%-55%
Silica content:Andestic
55%-65%
Silica content:Rhyoltic
65%-75%
Temperature of eruption:Basaltic
1050-1200C
Temperature of eruption:Andestic
800-1000C
Temperature of eruption:Rhyolitic
650-800C
ViscosityBasaltic
low
ViscosityAndestic
medium
ViscosityRhyolitic
High
Gas contentBasaltic
Low
Gas content Andestic
Medium
Gas content Rhyolitic
High
Type of volcanoBasaltic
Shield
Type of volcanoAndestic
Composite
Type of volcanoRhyolitic
Composite
Distribution (plate boundary)Basaltic
Constructive & hotspot
Distribution (plate boundary)Andestic
Destructive
Distribution (plate boundary)Rhyolitic
Destructive
Type of eruption Basaltic
Gentle, effusive (Hawaiin)
Type of eruption Andestic
Explosive, infrequent, short lived. Ash, rocks, gases and lava ejected.
Type of eruption Rhyolitic
Explosive, infrequent, short lived. Ash, rocks, gases and lava ejected.
What is the VEI?
Volcanic Explosivity Index
What three things does the VEI measure?
Volume of ejecta
Height of the eruption column Qualitative observations (including duration)
Give three criticisms of the VEI.
Gas emissions
Atmospheric/ climatic impacts of eruptions
All types of tephra considered alike despite differences in densities and impact
Give five ways volcanic eruptions vary.
Magnitude Frequency Randomness vs regularity Predictability Duration
What is a super volcano?
An unusually large volcano having the potential to produce an eruption with major effects on the global climate and ecosystem.
Describe Tephra ( Primary hazard)
Solid material of varying grain size ranging from volcanic bombs to ash all ejected into the atmosphere (either blasted by volcanic explosions or carried upwards by hot gases in eruption columns or lava fountains) during a volcanic eruption that then falls back to the ground.
Describe Pyroclastic flows (primary hazard)
Pyroclastic flows (nuees ardentes): Very hot (over 800C) gas charged high velocity flows made up of a mixture of super-heated gas and tephra (ash and volcanic rock) - hence high density mixture that flow downwards. These usually hug the ground and flow down the sides of the volcano with speeds of up to 700km per hour but typically > 80kmh often flowing a long distance from the volcano (10-15km).
Describe lava flows
molten rock (magma when under the surface), flows from a volcanic vent. The speed of the flow and distance travelled by the lava depends on the temperature and viscosity of the lava as well as the steepness of the slope. Low viscosity (runny) lava can flow up to 10kmh on a steep slope and travel tens of meters.
Describe Volcanic gases(primary hazard)
these include carbon dioxide, sulphur dioxide, hydrogen sulphide, carbon monoxide and chlorine.
Describe Lahars (secondary hazard)
Melted snow and ice as a result of the eruption or heavy rainfall following an eruption combines with volcanic ash and forms mud flows.
Describe Tsunamis(secondary hazards)
Sea waves generated by violent volcanic eruptions underwater or pyroclastic flows/lahars/landslides displacing water which often result in much more widespread impacts than the volcano itself.
Describe Acid rain(secondary hazards)
Volcanoes emit gases which include sulphur, this then combines with atmospheric moisture and results in acid rain.
Describe climate change in terms of hazards (secondary hazard)
The ejection of huge amounts of volcanic debris into the atmosphere can reduce global temperatures. Additionally sulphur dioxide emitted from volcanoes when combining with water vapour creates droplets of sulphuric acid which reflect sunlight.
How can volcanic activity be detected?
Sulphur/radon gases
Ground deformation
Energy release
Surface temperature changes
What is used to detect sulphur/radon gases?
spider robots; gas trapping bottles.
What is used to detect ground deformation?
tiltmeters; gravity changes
What is used to detect energy release?
infrasound; seismometers
What is used to detect Surface temperature changes
Thermal heat sensors
Give three methods of preparedness to reduce the risk of volcanic hazards.
Have emergency kits prepared
Installing monitoring systems to predict when an eruption might occur
Set up search and rescue teams or fire response units to tackle the impacts of an eruption
Give three methods of diverting lava flows?
Digging/using explosives to create earth trenches and use concrete: Mt Etna SicilyBombing lava tubes Use of ice water/cooling lava: 1973 Heimaey Iceland
How might people adapt to the risk of volcanic eruptions?
Strengthen buildings to reduce the chance of collapse from ash on roofs
Capitalize on the opportunities of living near volcanoes e.g. farming fertile soils or working in the tourism industry.
Give three primary impacts of volcanic events
People are killed and buildings are destroyed by pyroclastic flows
Ash causes damage to agricultural land
Death due to volcanic gasses (e.g. asphyxiation by carbon dioxide).
Give three secondary impacts of volcanic events
Acid rain acidifies aquatic ecosystems killing some plants/animals
Volcanic debris reflects sunlight resulting in crop destruction due to colder winters
Flash floods due to glacial melts
Tsunamis due to volcanic landslides
