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volcanoes (natural hazards) - Coggle Diagram
volcanoes (natural hazards)
why do people live close to volcanoes?
economic reasons: natural resources from the volcano provide jobs for those in desperate need
farming: ash from the volcano is good for the crops
tourism
inability to move
Mt Sinabung
23 dead
higher alert systems
food and masks were provided to the public
Indonesian government had warning due to Japanese technology
Mt Ontake
phreatic eruption: where ground water comes into contact with magma the water turns into steam expanding causing the eruption
why was there a high death toll ?
no warnings, no magma moved, no gas emissions, rated 1 the lowest possible risk
location close to tokyo
time was 11:53 the middle of the day
in the middle of hiking season
difficult to evacuate and rescue
effects
area was closed for 4 years
ash was nutrient rich good for the soil
63 people died
no hospitals or schools were damaged
hydrogen sulfide slowed rescue attemps
location: japan
hazards produced by a volcano
lava flows
pyroclastic flows
tsunami
gases: carbon monoxide which causes suffocation, sulphur dioxide, carbon dioxide
ridge push: rising magma pushes up the crust and gravity pulls it apart
slab pull: dense plate sinking pulls the plate apart
hotspots
occur away from plate boundaries
The heated magma expands and becomes less dense than the surrounding magma, so it rises to the surface in a magma plume
plate boundaries
convergent oceanic + oceanic
most dense plate is subducted, plate gets forced underneath, temperature 800, island arcs are formed/ hotspots
convergent continental + oceanic
most dense plate is subducted, weakness in the rock makes a volcano form
convergent continental + continental
fold mountains are produced, old oceanic plate is subducted but stops at continental
divergent oceanic + oceanic
rising magma forces the plates apart, any magma that reaches the surface cools
divergent continental + continental
volcanos form through weaknesses in the rock
conservative
no rising magma, plates move past each other causing earthquakes
evidence of plate tectonics
the continents fit together in a perfect jigsaw like fit
fossils found in locations thousands of kilometers from each others
mountain ranges on different sides of the ocean
evidence for the theory of sea floor spreading
palaeomagnetism
rising magma at an ocean ridge hits sea water and cools rapidly
in the magma are iron crystals that are a kind of kite shape
the earths magnetic field causes iron crystals to turn to point north