natural hazards - tectonics Flashcards

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1
Q

what is a natural hazard

A

natural event that has a huge social impact

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2
Q

different types of natural hazards

A

volcanic eruptions
earthquakes
storms
tsunami
landslides
floods

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3
Q

what is hazard risk

A

probability of being affected by natural event

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4
Q

what factors affect hazard risk? (urbanisation, climate change, farming, poverty)

A

urbanisation - some of world’s most densely populate areas are most at risk of natural risks
climate change - leads to more intense storms and hurricanes
farming - farmland at risk of flooding
poverty - may have to live in areas of risk - unstable slopes prone to landslides

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5
Q

development of plate tectonic theory

A

continents used to be joined together (pangaea), continents parted due to continental drift
sonar used to find underwater mountain ranges similar to above water

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6
Q

oceanic plate

A

relatively recently formed, thin and dense - basalt (black lava flow)

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7
Q

continental plate

A

older, thicker, less dense - granite

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8
Q

constructive plate margin

A

two plates move apart from each other, magma forces to surface, causes rock to fracture and crack, leads to earthquakes
magma escapes as lava, very hot, flows long distances before cooling, flat and broad volcanoes (shield), eruptions fiery, non-explosive
(mid-atlantic ridge through atlantic ocean)

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9
Q

destructive plate margin

A
  1. two continental plates move towards one another, collide, crumpling, uplifting crust, leads to formation of fold mountain ranges, powerful earthquakes, no volcanoes, no magma (himalayas from indo-australian and eurasian)
  2. dense oceanic plate subducts under less dense continental plate, heated, melts to form magma, friction triggers earthquakes, magma viscous to composite volcanoes conical shaped, violent eruptions - ash clouds, pyroclastic flows (nazca plate beneath south american plate)
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10
Q

conservative plate margin

A

plates slide alongside each other, stresses built up by friction suddenly released creates earthquakes, no volcanic activity cuz no magma

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11
Q

convection currents

A

currents of heat, rising magma at constructive plate margins when plates move apart

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12
Q

gravitational sliding

A

ridge push - constructive, fresh magma rises, forces plates apart
slab pull - destructive plate margin, gravity acts on denser plate pulls it under

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13
Q

distribution of earthquakes

A

majority form belts along plate margins
some are narrow, sparsely distributed (constructive margins)
denser broader zone on edge of pacific ocean ‘ring of fire’, 80% occur there (destructive margins)
some occur away from plate margins due to human activity (mining, oil extraction)

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14
Q

distribution of volcanoes

A

coincide with constructive and destructive margins
high concentration at ‘pacific ring of fire’
none at conservative, no source of magma
in hawaiian islands crust is thin so magma can break through

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15
Q

japan earthquake

A

march 2011, 9.0 magnitude 100km east of sendai on japanese island of honshu
destructive margin between north american and pacific plate
earth shifted on axis, 3-5 minutes of ground shaking and then tsunami wave took 30 minutes to hit, defences overtopped

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16
Q

nepal earthquake

A

25 april 2015, 7.9 magnitude, 80km north wesr of kathmandu, destructive margin between indo-australian and eurasian plate, 15km below surface, severe ground shaking, landslides, avalanches, caused damages in india, tibet pakistan

17
Q

primary effects of tokoku, japan earthquake

A

ground shaking causes injuries, deaths, homes, roads, rails destroyed electricity, water and sewage systems disrupted - 4 mil without electricity, 1.5 mil without water

18
Q

secondary effects of tohoku, japan earthquake

A

10m tsunami - 18000 deaths, 500000 homeless, destroyed port facilities, infrastructure, homes
many without electricity, sanitation, water
explosions at fukushima nuclear plant - fear of radioactive leaks

19
Q

primary effects of nepal earthquake

A

9000 people died, 20000 injured
3 million homeless
electricity, water supplies, sanitation, communications affected
7000 schools destroyed

20
Q

secondary effects of nepal earthquake

A

landslides, avalanches - 19 people killed on everest, blocked roads, blocked kali gandaki river, people evacuated at risk of flooding

21
Q

japan: immediate responses

A

search and rescue teams, people evacuated before tsunami, emergency shelter food and water, roads restored within a few days, power soon restored

22
Q

japan: long-term responses

A

most debris cleared by early 2015, 2020 - nearly 30000 units of public housing completed (replacing temporary housing), upgraded tsunami warning system launched, sea walls and embankments constructed to protect cities

23
Q

nepal: immediate responses

A

international search and rescue teams, emergency food kits and shelter material, helicopter rescues, field hospitals from red cross etc.

24
Q

nepal: long-term responses

A

new national disaster risk reduction policy, most roads repaired by end 2015 UNESCO working with government to restore 700 damaged temples, palaces and museums

25
Q

why do people live in hazardous areas?

A

cheaper, hazards dont happen often, people may not be aware, volcanoes can bring fertile soil, rocks for building, hot water

26
Q

life near natural hazards in iceland

A

volcanic rocks used in construction for roads and buildings, hot water from crust provides heat and hot water, eruption of volcano in iceland in 2010 led to surge in tourism

27
Q

monitoring volcanoes

A

magma rising through a volcano gives warning signs - monitored with seismographs to detect and record quakes, tiltometers for ground deformation, instruments monitoring gas emissions and changes in water chemistry, warnings sent out if eruption seems likely

28
Q

monitoring earthquakes

A

network of seismometers in japan, warnings issues to public - immediate shelter, trains slow, factories halt - 15 seconds warning in sendai, 2011
buoys detect early tsunami waves

29
Q

predicting volcanoes

A

scientifically monitoring earthquake activity beneath surface - quite accurate

30
Q

predicting earthquakes

A

impossible to be accurate - no clear warning signs, study historical records to identify areas at most risk

31
Q

protection from volcanoes

A

attempts to divert lava flows, buildings designed to withstand collapsing from volcanic ash, tilted roofs prevent build up, window shutters prevent entry

32
Q

protection from earthquakes

A

infrastructure designed to withstand ground shaking, 400km sea wall built up to 12.5m high to protect cities etc.

33
Q

planning for volcanoes

A

hazard maps used to help protect 500 million people from eruptions - based on evidence from previous eruptions
predicts likelihood of ash falls, pyroclastic flows, lahars
maps used to control evacuation routes

34
Q

planning for earthquakes

A

shakemaps show impact of of ground shaking, used to locate high-value developments away from high-risk areas