GCSE geography - natural hazards (chapters 1, 2, 3, 4)

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natural hazard

a natural event which has the potential to threaten both life and property

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natural disaster

a natural hazard that has actually happened

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what are 7 examples of natural hazards?

earthquakes, volcanic eruptions, tsunamis, floods, droughts, landslides, storms

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what are 3 types of storms?

tornado, snow, lightning

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what are 3 examples of tropical storms?

hurricanes, cyclones, typhoons

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how are natural disasters categorised?

are they geological (tectonic + geomorphological) or meteorological?

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what is a meteorological natural disaster?

caused by weather conditions. this can be either over a short or long period of time. can affect a small or large area.

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what is a tectonic natural disaster?

caused by the movement of the earth’s tectonic plates

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what is a geomorphological natural disaster?

to do with the movement on top of the earth’s surface

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hazard risk

the chance or probability of being affected by a natural disaster

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what are the 8 main hazard risk factors?

education, frequency, geographical location, level of development/wealth, magnitude, natural factors, population density and distribution, time

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why is education a hazard risk factor?

won’t stop a natural disaster from occurring but may reduce impacts and allow more people to survive

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why is frequency a hazard risk factor?

how often a natural disaster occurs

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why is geographical location a hazard risk factor?

the position of a country or region in the world

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why is level of development/wealth a hazard risk factor?

allows richer countries (MEDCs) to respond quickly and effectively to natural disasters faster then in poorer countries (LEDCs)

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why is magnitude a hazard risk factor?

the size of the event

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why are natural factors hazard risk factors?

elements such as geology, topography and relief can affect the risk and severity of natural disasters

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why is population density and distribution a hazard risk factor?

the number of people living in a place and the spread of people in an area or country

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why is time a hazard risk factor?

very influential e.g. if its day or night

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what are some more hazard risk factors?

distance from epicentre, depth of epicentre, location of fault lines

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what are the four layers of the earth?

crust, mantle, outer core, inner core

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what is the continental drift theory?

the theory that all the continents on the earth were once joined, forming one large continent called Pangea. This theory was developed by Alfred Wegener in 1912.

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continental drift theory explanation

over 180 million years ago, Pangea separated and broke into separate continents.

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continental drift theory evidence (2)

  • the different continent borders and coastlines all fit together (e.g. east coast of south america and west coast of africa)

  • ores on the matching coastlines are the same

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what is the earth’s crust divided into?

slabs called tectonic plates

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what are these plates made of?

two types of crust- continental and oceanic

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how thick is oceanic crust?

5-10km thick

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how old is oceanic crust?

180 million years old

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does oceanic crust sink?


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what is oceanic crust made up of?


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is new crust formed with oceanic crust?

yes, at constructive plate margin

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is crust destroyed with oceanic crust?

yes, at destructive plate margin

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how thick is continental crust?

25-100km thick

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how old is continental crust?

3.4 billion years old

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is oceanic or continental crust more dense?

oceanic, so will result in subduction

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does continental crust sink?


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what is continental crust made up of?


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is new continental crust formed?


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is continental crust destroyed?


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<p>what is this?</p>

what is this?

destructive/convergent plate margin

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what will destructive/convergent plate margins result in?

earthquake / volcanic eruption

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<p>what is this?</p>

what is this?

constructive/divergent plate margin

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what will constructive/divergent plate margin result in?

earthquake / volcanic eruption

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<p>what is this?</p>

what is this?

conservative/transform plate margin

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what will conservative/transform plate margin result in?


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<p>explain why volcanoes occur at destructive plate boundaries (6 marks)</p>

explain why volcanoes occur at destructive plate boundaries (6 marks)

  1. an oceanic plate (Nazca) is pushing towards a continental plate (south american)

  2. oceanic plate is subducted beneath continental plate because it’s denser

  3. the plate is destroyed in the mantle due to increased heat

  4. continuous movement causes a build-up of friction and pressure

  5. lava is forced into molten rock due to pressure, through the weakest point of the earth’s crust

  6. this is repeated until lava cools and solidifies to become a composite cone volcano

  7. if there is a volcanic eruption, it will be highly explosive, but they erupt less frequently than other volcanoes

  8. it will be highly explosive due to a build up of carbon from the seabed, and a build up of pressure and friction

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<p>what volcano is this</p>

what volcano is this

shield volcano

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<p>what volcano is this</p>

what volcano is this

cone volcano

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<p>what is a convergent collision/how are fold mountains formed?</p>

what is a convergent collision/how are fold mountains formed?

where two continental plates push into each other, or collide (where they are the same density), and create fold mountains

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what is an example of a convergent collision?

the Indoaustralian and euarasian plate = the himalayas

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what happens at a constructive/divergent plate boundary? (4 points)

  1. the tectonic plates are moving apart from eachother due to convection currents in the mantle

  2. a gap is formed and immediately filled by magma rising from the mantle

  3. this magma cools and solidifies to form rock or new volcanic crust

  4. this repeats until many layers of magma build up to form wide, low volcanoes called shield volcanoes

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how are fault lines formed on constructive/divergent plate boundaries?

  1. the plates can get stuck as they move apart, building stress

  2. this can cause big cracks (faults) to be created on the moving plates

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what is an example of a constructive/ divergent plate boundary which has formed a shield volcano?

north american and eurasian plates = Mid Atlantic Ridge

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what happens at conservative/ transform plate boundaries? (4 points)

  1. tectonic plates (in a slip fault) slide against each other either moving in the same or opposite direction (as a result of convection currents)

  2. this creates friction which builds up in the focus spot

  3. this friction is released in the form of seismic waves into the earth’s crust after a sudden slip

  4. these seismic waves trigger earthquakes

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when will the magnitude of the earthquake increase/decrease?

they will decrease as they cover more distance, so the further down in the earth the focus point is, the smaller the magnitude

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how are conservative/tranform plates different from constructive and destructive plates? (2 points)

  1. no volcanoes are involved

  2. no crust is destroyed or created

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where are composite volcanoes found and why?

destructive plate boundaries, because when the plates collide, the denser plate is subducted, magma replaces it etc …

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where are shield volcanoes found and why?

constructive plate boundaries, because the plates diverge, new crust emerges etc …

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do composite or shield volcanoes erupt more frequently?

shield volcano

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do composite or shield volcanoes have more ‘vicious’ eruptions?

composite volcano

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why do composite volcanoes erupt less frequently?

high viscosity lava traps bubbles of lava, so it’s more eruptive, and pressure needs to build up for this

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composite volcano lava type? (3)

  • volcanic gases rarely emerge

  • flows for short distances

  • viscous (thick + sticky lava)

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shield volcano lava type? (3)

  • volcanic gases stay in lava

  • flows for long distances

  • not viscous (hot + runny lava)

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examples of composite volcanoes? (2)

  • Krakatoa (Indonesia)

  • Mount St Helens (USA)

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examples of shield volcanoes? (2)

  • Mauna Lao (Hawaii)

  • Heimay (Iceland)

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what are 5 primary hazards caused by volcanic eruptions?

  1. Ash falls

  2. Gas clouds

  3. lava flows

  4. pyroclastic flows

  5. volcanic bombs

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what are ash falls?

small erupted material which can travel long distances

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what are gas clouds?

toxic clouds which can suffocate people e.g. CO2, hydrogen sulfide, sulphur dioxide

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what are lava flows?

streams of molten rock which slow as they cool

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what are pyroclastic flows?

very hot flows of gas and ash, up to speeds of 700km/h

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what are volcanic bombs?

solid lumps of lava which fly through the air (can be as big as a house)

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what are 5 secondary hazards of volcanic eruptions?

  1. lahars

  2. tsunamis

  3. climate change

  4. landslides

  5. glacier bursts

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what are lahars/ how are they caused by volcanic eruptions?

volcanic mud flows which travel along river valleys

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what are tsunamis/ how are they caused by volcanic eruptions?

giant sea waves generated by underwater volcanoes

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what is climate change/ how is it caused by volcanic eruptions?

volcanoes send ash into the atmosphere, reflecting radiation from the sun back into space, causing heating

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what are landslides/ how are they caused by volcanic eruptions?

rock and earth which tumble down a slope, triggered by tectonic activity

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what are glacier bursts/ how are they caused by volcanic eruptions?

large floods caused by the melting of ice beneath a glacier

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what are 3 primary/ immediate effects and impacts of volcanic eruptions?

  1. many people killed/injured

  2. farmland + buildings destroyed

  3. communications damaged/disrupted (e.g. transport, water, electricity)

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what are 5 secondary/ long term effects of volcanic eruptions?

  1. spread of disease due to no clean water/ broken sewers

  2. hospitals are overwhelmed

  3. shortage of necessities (e.g food, water, shelter, medicine)

  4. local businesses have reduced income + food production

  5. economic impact from cost of rebuilding + air travel disruption

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how can we react to volcanic eruptions? (3 points)

  1. set up exclusion (safe) zones

  2. build volcano observatories

  3. rebuild buildings + economy

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how can we measure earthquakes? (2)

  1. richter scale (measures magnitude/energy of earthquakes)

  2. mercalli scale (measures intensity/damage caused by earthquakes, 1-12 levels)

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what is the richter scale?

a logarithmic scale (each 1.0 is 10x bigger, e.g 6.0 is 10x bigger than 5.0)

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is the richter or mercalli scale more accurate?

richter, because with mercalli, the results can change, and it’s subjective

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why do some people continue to live in areas at risk from tectonic hazards? (4)

  1. well developed settlements would struggle to relocate

  2. jobs/families in endangered areas

  3. tourism creates jobs and opportunities in endangered areas (e.g. Blue Lagoon in Iceland)

  4. land is fertile so opportunity for farmers

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what is a LIC tectonic hazard?

Nepal (Ghorka) Earthquake

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basic facts about the Ghorka earthquake? (4)

  • 7.8 magnitude

  • 8km deep focus point

  • on a convergent collision plate boundary

  • in April 2015

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primary impacts of ghorka earthquake (4)

  • 9000 dead (approx)

  • 19000 injured

  • hundreds of thousands homeless

  • triggered an avalanche on the himalayas(20 dead)

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secondary impacts of ghorka earthquake (3)

  • tourism rates dropped, $7 billion loss, main source of income

  • 600,000 buildings destroyed

  • crops damaged, loss that harvest season

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immediate responses to ghorka earthquake (2)

  • $1 million+ aid pledged from India + China

  • 100+ search + rescue teams provided by the UK

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long term responses to ghorka earthquake (1)

  • aid donated by many countries

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what is a HIC earthquake case study?

New Zealand

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basic facts about new zealand earthquake (4)

  • february 2011

  • 12.51pm

  • 5km deep focus point

  • 6.3 magnitude

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primary impacts of new zealand earthquake? (3)

  • 185 dead

  • approx 2000 injured

  • 10,000 houses needed to be rebuilt

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secondary impacts of new zealand earthquake? (2)

  • liquefaction occurred, land cannot be rebuilt on

  • infrastructure severely damaged (roads, bridges etc)

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immediate responses to new zealand earthquake (3)

  • search + rescue teams came globally

  • temporary housing provided

  • pop up hospitals

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long term responses to new zealand earthquake (2)

  • unstable buildings were demolished

  • infrastructure was rebuilt

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what is liquefaction?

when the ground shakes and causes water + mud to rise to the surface

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what part of the earth is the sun concentrated at?

the equator

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what part of the earth is the suns rays more spread out?

the polar regions

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cold air …


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