Volcanic Hazards Flashcards
Shield volcano boundary
Constructive (and hotspots)
Formation of shield volcanoes
Plates move apart Magma rises to surface, cools = new crust Sea floor spreading Layers built by eruptions Sea floor spreading = plates move apart
Shield volcano example
Eyjafjallajokull, Iceland
Shield volcano characteristics
Gentle sloping sides
Wide base
Low viscosity lava - BASALTIC
Frequent, basic lava eruptions
Shield volcano explosivity
Low, as magma under little pressure
Composite volcano boundary
Destructive
Formation of composite volcanoes
Plates move towards eachother Oceanic, denser, subducts Beinoff Zone Less dense molten material rises Layers of ash and lava build
Composite volcano example
Montserrat
Composite volcano characteristics
Steep sided
Layers of ash, dust, lava
Viscous lava - RHYOLITIC
Long dormant periods
Composite volcano explosivity
High, as magma rises in plumes through fissures in buckled continental plate- high pressure
Volcanoes in rift valleys formation
Rising magma Brittle continental crust buckles and fractures = Fault lines Plates move further apart Crust between parallel faults drops down = Rift Valley Thin crust Magma forces its' way to the surface
Volcanoes at hotspots formation
Concentration of radioactive elements below crust
Plume of magma rises
Breaks through surface
Why do extinct volcanoes subside at hotspots?
As they have put so much pressure on the crust
VEI
Volcanic Explosivity Index
VEI meaning
Logarithmic scale (0-8) Measures height of eruption column and volume of tephra erupted
Disadvantages of VEI
Doesn’t consider climate impact
Ash, lava and lava bombs all treated alike
Icelandic Eruption
Basaltic lava flows gently from fissures
Highest and Lowest Categories on VEI?
Icelandic = lowest Plinian = highest
Plinian Eruption
Highly explosive and violent, with tephra and pyroclastic fall out
Tephra Meaning
Solid material (ash-bombs) ejected into the atmosphere
Pyroclastic Flow / Nuees Ardentes Meaning
Fast moving current of hot gas and tephra
Up to 1000°c
Little warning = death and destruction
What are the secondary effects of pyroclastic flows?
Snow melt
Damming streams
What are the secondary effects of tephra?
Grounding air traffic
Destroy vegetation- famine
Improve soil fertility
What 4 factors affect the distance tephra travels?
Height of eruption column
Temperature of air
Wind speed
Wind direction
What 4 things are lava flows affected by?
Land steepness
Extrusion rate
Silica content
Flow temperature
What temperatures are lava flows between?
550°c - 1400°c
Why are lava flows not a big hazard?
Because of their slow speeds
Mudflow / Lahar Meaning
Volcanic material + water (rainfall or ice melt)
What’s the difference between mudflows and lahars?
Lahars set like concrete
Name some of the gases released by a volcano
Water vapour
Carbon dioxide
Sulphur dioxide- acid rain
Where does CO2 seep through the volcano and kill plants?
Mammoth Mountain
Why are tiltmeters and GPS used to monitor volcanoes?
Measure slope angles
Indicates expanding magma chamber
Why are seismometers and seismographs used to monitor volcanoes?
Microquakes
Rising magma fractures overlying rock
Why are magnetometers used to monitor volcanoes?
Changing magnetism indicates rising iron-rich magma
Protection- Land Use Planning
Build houses away from high risk areas
Preparation- Why should there be good communication systems?
To alert and update people
Preparation- There should be suitable ____ put aside to deal with an emergency
Funds
Preparation- Residents in high risk areas…
Need evacuating
Preparation- What should an emergency supply kit contain? Where should it be placed?
Tinned food Battery radio Torch Cash Breathing mask IN A CAR
Preparation- What should be included in a family emergency plan?
How to contact eachother
How to meet
What you will do in an emergency
East African Rift Valley
African plate
Splitting into Somali and Nubian
Created Kilimanjaro
