Volcanoes Flashcards
Where do volcanoes occur?
On divergent and destructive boundaries
What happens at a divergent boundary?
Plates move apart
Magma rises through crust
Magma cools and forms new crust
Repeats
What happens at a destructive boundary?
Oceanic crust is subducted
Pressure builds in continental, folds then cracks
Magma rises through cracks
What volcano forms at a divergent boundary?
Shield
Normally underwater
What volcano forms at a destructive boundary?
Strato
What are the primary effects?
Lava flows
Pyroclastic flows
Tephra/ash falls
Gas eruptions
What are the secondary effects?
Jokulhlaup
Lahars
What are lava flows?
Sheets of liquid rock expelled from an erupting volcano
What are pyroclastic flows?
Gas and lava that flow down the side of the volcano
What are tephra/ash falls?
Volcanoes project ash and it covers the ground
What are gas eruptions?
Water vapour, CO2, sulphur dioxide and sulphur trioxide are released
What are jokulhlaup?
Water/ice melted from glaciers leading to mud flows
What are lahars?
Volcanic mud flows, ash mixed with snow and ice
What are the features of a shield volcano?
Wide base- 180km
Slopping sides
Solidified layers of lava
What are the features of a strato volcano?
Narrower base- 18km
Steep sides
Solidified layers of ash and pyroclastic materials
How is volcanic eruption measured?
Volcanic explosivity index- 1-8
Composition of basaltic lava
1000-2000 degrees- hottest
Low silica content- 50%
Low gas content- 0.5-2.0%
Low viscosity
How is basaltic lava formed?
Melting of the mantle
What is the eruption energy like of basaltic lava?
Effusive
Where is basaltic lava found?
Ocean hotspots
Mid-ocean ridges
Shield volcanoes
What is an example of a volcano with basaltic lava?
Mauna Loa, Hawaii
Composition of andesitic lava
800- 1000 degrees- middle
Intermediate silica content- 60%
Medium gas content- 3-4%
Intermediate viscosity
How is andesitic lava formed?
Subduction of oceanic plate
Where is andesitic lava found?
Subduction zones + strato volcanoes
