Geography - Hazards - Volcanic Hazards Flashcards
what do volcanic eruptions produce
Lava, Gases, Pyroclastic and Ash fallout, Pyroclastic flows, Lahars and Tephra
Lava
magma/molten rock above the surface. Moves as fast as 10km/h and bury or set things alight in its path
Gases
sulphur dioxide and carbon dioxide. sulphur can form acid rain. Carbon can harm humans and animals
Pyroclastic and Ash fallout
any material that has been ejected from a volcano and has travelled through the air and fallen to the ice. Tiny fragments, can block the sun
Pyroclastic Flows
currents of hot ash, lava and gas that can move downhill at speeds of up to 500km/h during an eruption
Lahars
mudflows. high to low viscosity. Fast moving flows of volcanic material and water. Destroy buildings and vegetation in their path
Tephra
eruptions produce tephra, rock fragments which are ejected from the eruption. Can be small or large and can be ejected at high speeds can travel as far as 80km away.
Destructive Plate Margins
- when the dense oceanic plate is forced under the lighter continental plate
- subduction
- pressure and heat causes the oceanic plate to melt creating magma
- friction causes cracks (vents)
- volcanoes are formed
- highly explosive
- produce a lot of gas and lava
Constructive Plate Margins
- plates move apart
- diverge
- where two oceanic plates move apart
- shield volcanoes are formed
Divergent Plate Margins
- convection currents in the mantle diverge (move apart) and cause a gap between plates
- magma rises up through the gaps
- lava runs over a large area as it has a low viscosity as it has a low silica content
- volcanoes created here can be very large
Collision Zones
form when two continental plates collide
- neither is forces under the other so both are forced up
- form fold mountains
Conservative Plate Boundary
- occurs when plates collide past each other in opposite directions or in the same direction but at different speeds
- friction causes the plates to slip past in a sudden movement
- shockwaves are created and produce an earthquake
Hotspots
- there is a hot mass of rising heat under a weakness in a plate
- magma rises to the surface through this weakness
- shield volcanoes form here
seismic waves
- can be monitored to see changes in activity
- increased seismic waves are a sign a volcano could be about to erupt
- earthquakes are a sign of a nearby volcanic eruption
Ways to Predict Volcanic Hazards
seismic waves, thermal images, gas emissions, volcanic swelling
