Types of Hazard

A hazard is something that's a potential threat to human life or property

A natural hazard is caused by natural processes

Types of natural hazards:

  • geophysical hazards - caused by land processes e.g. earthquakes, volcanic eruptions, landslides + tsunamis
  • atmospheric hazards - caused by climatic processes e.g. tropical cyclones, storms, droughts, + wildfires
  • hydrological hazards - caused by water movement e.g. floods + avalanches

Disaster - when a hazards seriously affects humans

Risk - the likelihood humans will be seriously affected by a hazard

Vulnerability - how susceptible a population is to the damage caused by a hazard

1 of 36

Concepts of Hazard


  • ability to give warnings so that action can be taken to reduce the impact of hazard events
  • improved monitoring, information + communications technology have meant predicting hazards + issuing warnings have become more important in recent years


  • attempts by people or communities to live with hazard events
  • by adjusting their living conditions, people are able to reduce their levels of vulnerability

Magnitude - the assessment of the size of the impact of a hazard event

Distribution - spatial coverage of the hazard + area where hazard likely to occur

Frequency - distribution of hazard through time

2 of 36

Factors Affecting Perception of Hazards

Wealth - richer people may be able to afford to move to areas less prone to hazards or build houses to withstand hazards so may percieve as having a smaller risk

Religion - some people view hazards as act of god sent to punish people

Education - people with more education may have better understanding of risks associated with hazards so can mitigate these impacts

Past experiences - people who live in hazard-prone areas may affect perception of future hazards

Personality - some people are more fearful of hazards but some may find exciting

3 of 36

Hazard Responses


  • people can try to either prevent a hazards or reduce it's magnitude
  • this is only possible for certain hazards e.g. floods using flood defences
  • not all hazards can be prevented e.g. volcanic eruptions


  • reducing the impacts of a hazard
  • prediction - working out when + where a hazard is likely to occur
  • adaptation - making changes to deal with the impact of hazards e.g. adding earthquake resistant features to buildings

Governments coordinate responses to manage hazards effectively

Fatalism - people believe hazards can't be avoided so accept the impacts

Risk sharing - sharing the costs of a hazard e.g. insurance schemes

Success of management depends on - hazard incidence, magnitude/intensity + distribution

4 of 36

Park Response Model


5 of 36

Hazard Management Cycle

Mitigation - minimise the impacts of future disasters e.g. building flood defences or adding fire-resistant roofs to buildings in areas prone to volcanic eruptions

Preparedness - planning how to respond to a hazard e.g. making sure warning systems are in place or educating people

Response - how people react when a disaster occurs e.g. emegency services rescuing people who've been trapped or evacuating people

Recovery - getting the affected area back to normal e.g. reparing or rebuilding

Constant cycle

6 of 36

Structure of Earth

7 of 36

Structure of Earth 2


  • inner core - solid ball containing lots of iron + nickel
  • outer core - semi-molten containing lots of iron + nickel
  • very hot (6000°) + earth main source of internal energy


  • mostly made of silicate rocks
  • rigid nearest core
  • asthenosphere - semi-molten layer above
  • rigid top of mantle


  • outer layer of earth
  • rigid top of mantle + crust called lithosphere
  • continental crust - thicker (30-70 km) + less dense
  • oceanic crust - thinner (6-10 km) + more dense
8 of 36

Alfred Wegener Theory

In 1912 Alfred Wegener realised that the east coast of South America + the west coast of Africa appeared to fit together

First proposed that the earth once had one continent called pangaea

Felt that continents beegan to drift apart around 300 million years ago known as continental drift

Found fossil evidence to support this

Proposed spin of the earth had split the continents but this later dismissed

9 of 36

Plate Movement Theories

Lithosphere is divided into plates with 3 theories as to how these move

Convection currents:

  • the mantle is hottest close to the core so lower parts of the asthenosphere heat up, become less dense + rise
  • provide an internal energy source
  • as they move towards the top of the asthenosphere they cool down, become denser + sink
  • these circular movements of semi-molten rock (convection currents) create drag on base of plates + cause them to move

Slab pull:

  • at destructive plate margins denser crust is forced under less dense crust
  • the sinking of the plate edge pulls the rest of the plate towards the boundary

Ridge push/gravitational sliding:

  • at constructive plate margins magma rises to the surface + forms new crust which is very hot
  • this heats the surrounding rock which expands + rises above surface of surrounding crust - forming a slope
  • the new crust cools + becomes denser with gravity causing the denser rock to move down the slope
  • this puts pressure on tectonic plates + causes them to move apart
10 of 36

Sea-Floor Spreading

1) As tectonic plates diverge (move apart) magma rises up to fill gap created then cools to form new crust

2) Over time new crust is dragged apart + new crust is formed between it

3) When this occurs at a plate margin under the sea the sea floor gets wider

4) this creates mid-ocean ridges - ridges of higher terrain on either side of margin

11 of 36

Constructive Plate Margins

Occurs when two plates are moving apart (diverging)

The mantle is under pressure from plates above + when they move apart, pressure released at margin - causing the mantle to melt + produce magma

Magma less dense than above plate so magma can rise to form volcano

Parts of the plates can move at different speeds which causes pressure to build up as cracks are created (fault line) which causes an earthquake

Ocean ridge - when diverging plates are underwater mid-ocean ridges are formed e.g mid-atlantic ridge + underwater volcanoes can erupt along these ridges e.g iceland formed on these eruptions

Rift valley:

  • when plates diverge beneath land rising magma causes continental crust to bulge + fracture to form fault lines
  • as plates keep moving apart the crust between parallel faults drops down to form a rift valley e.g. East African Rift System where Nubian + Somalian plates are diverging - creating volcanoes such as Mount Kilimanjaro
12 of 36

Destructive Plate Margins

When two plates are moving towards each other (converging)


  • the denser oceanic crust is forced under the less dense continental crust (subducted) to form deep sea trench e.g. Peru-Chile trench in Pacific Ocean
  • fold mountains form where plates meet made up of sediment that's accumulated on the continental crust which is folded upwards
  • the oceanic crust is heated by friction + contact with upper mantle - melting it into magma
  • the magma is less dense than the continental crust above + will rise back to the surface to form volcanoes
  • as one plate moves under the other they get stuck + cause pressure to built up until they jerk past each other + release pressure in form of earthquake

Oceanic-oceanic - same processes occur when plates are moving towards each other but the denser of the two will be subducted + underwater eruptions create island arcs which are clusters of islands sitting in curved lines e.g. Mariana Islands

Continental-continental - neither plate is subducted so volcanoes aren't created but the pressure built up between them cause earthquakes + creates fold mountains e.g. Himalayas

13 of 36

Conservative Plate Margins

Occurs when two plates are moving past each other

The two plates get locked together + causes pressure to build up

When plates jerk past each other energy is released as earthquake

Volcanoes can't be created

Pacific plate is moving past North American plate resulting in earthquakes occuring e.g. on San Andreas fault

14 of 36

Young Fold Mountains

Plates forming continental crust have a much lower density than the underlying layers so not much subduction when they meet

As such plates move towards each other, their edges + sediments between them are forced up into fold mountains

As there is little subduction, there there is no volcanic activity

Material forced downwards to form deep mountain roots

e.g. Andes where Nazca plate subducted beneath South American plate

15 of 36

Magma Plumes

Can form volcanoes away form plate margins in areas of intense volcanic activity

1) A magma plume is vertical column of extra-hot magma that rises up from the mantle

2) Volcanoes form above mantle plumes

3) The magma plume remains stationary over time but the crust moves above it

4) Volcanic activity in the part of the crust that was above the magma plume decreases as it moves away

5) New volcanoes form in the part of the crust that is now above the magma plume

6) As the crust continues to move, a chain of volcanoes is formed

7) Magma cools to form island arcs

Hawaii is made up of several islands that are formed by mantle plumes

16 of 36

Volcanic Hazards at Margins

Constructive Margins:

  • basaltic lava is formed which is very hot with low viscocity so flows easily + quickly
  • eruptions of basaltic lava are frequent and last a long time but aren't violent
  • if margin is underwater magma rises to fill space left by plates moving apart - forming ocean ridges
  • if margin on land + plates pull apart, the rift valleys formed become thinner + magma able to break through surface

Destructive Margins:

  • andesitic + rhyolitic lavas are formed here which are cooler and more viscous than basaltic lava so don't flow as easily
  • eruptions are occasional + short lived
  • at subduction zones, the viscocity of rising magma causes blockages + pressure builds until cleared by violent eruptions
17 of 36

Types of Volcanic Hazards

Primary hazards:

  • lava flows - lava can flow from volcanic vent down the side of a volcano with varying speed + distances depending on steepness of slope + viscocity but generally very slow so people can evacuate despite being very destructive
  • volcanic gases - lava contains gases such as carbon dioxide + sulfur dioxide which get released into atmosphere when volcano erupts + some of these can be harmful to humans
  • pyroclastic flows (nuees ardentes) - mixture of super-heated gas, ash + volcanic rock that flows down the side of a volcano at high speeds (80km/h) for long distances (10-15 km) which cause widespread death as so fast with little warning
  • tephra - solid material of varying size ejected into atmosphere

Secondary hazards:

  • pyroclastic + ash fallout - material ejected from volcano + lands on ground thousands of kilometres away with smallest materials travelling furthest away + tephra can damage buildings + kill people + ash harmful if breathed in
  • mudflows (lahars) - occur when volcanic material mixes with water from rainfall or melted ice which travels at over 80 km/h for tens of kilometres which can bury or destroy natural habitats
  • acid rain - volcanic gases react with water vapour in atmosphere to create acid rain e.g. sulfur dioxide reacts with water to form weak sulfuric acid which damages ecosystems
  • tsunamis - sea waves generated by violent eruption e.g. 1883 Krakatoa killed 36,000 people
18 of 36

Magnitude + Frequency of Volcanic Hazards


  • volcanic events range from small, slow lava flows to huge eruptions of lava, ash + gas
  • Volcanic Explosivity Index - grades volcanoes on scale of 0-8 based on amount of material ejected + how high material blasted


  • some active volcanes erupt only once every 100,000 years whereas others erupt every few months
  • less frequent eruptions larger in magnitude and more damaging

Randomness vs regularity - some volcanoes erupt at regular intervals whearas others may be dormant for hundreds of years and then erupt several times in quick succession


  • regularity with which a colcano erupts helps scientists predict when it may erupt
  • monitor tiny earthquakes and changes in shape of volcano which suggest eruption imminent
19 of 36

Impacts of Volcanic Events


  • people killed + buildings + infrastructure destroyed by pyroclastic flows + fallout
  • mudflows + flooding from ice melts can cause further damage + deaths


  • ecosystems damaged or destroyed by flows + fallout of volcanic material
  • acid rain causes acidification of aquatic ecosystems, killing some plants + animals + removing nutrients form soil
  • volcanic gases contribute to enhanced greenhouse effect + add to global warming
  • clouds of ash + volcanic debris reduce amount of sunlight reaching earth, increasing temperatures over alrge areas


  • eruptions can destroy businesses, + ash clouds prevent airplanes flying + damage crops which may damage economy
  • damage to buildings + infrastructure expensive to repair
  • eruptions + scenery created can attract tourists + boost economy

Damage to agricultural land can cause food shortages, leading to conflict + political unrest + governments may have to pay to repair damage which will slow development

20 of 36

Responses to Volcanic Hazards

Hazard mitigation - anything done to reduce severity or impacts of hazard

Short term responses - occur immediately before, during + after hazard begins

Long term responses - designed to reduce impacts of future eruptions by managing risk

Prevention - not possible to prevent volcanic eruption but can prevent risk e.g. preventing land around volcanoes being developed


  • what happens before eruption to minimise risk + vulnerability
  • install monitoring systems to predict when eruption may occur + then make evacuation plans
  • stop people entering area around volcano if eruption imminent
  • individuals make sure they're prepared e.g. find out where nearest emergency shelter is + prepare emergency kit
  • communities set up search + rescue teams or fire response units


  • how people change behaviour or surroundings to minimise risks + maximise benefits of living near volcano
  • building strengthened to reduce chance of collapse if layer of ash lands on top
  • people capitalise on opportunities living near volcano e.g. farming (volcanic ash makes soil fertile) or tourism
21 of 36


Caused by tension that builds up at all three types of plate margin

When plates jerk past each other it sends shockwaves

The shockwaves spread from the focus with closest waves stronger + causing more damage

Epicentre - the point on the earths surface where the earthquake is felt first + is straight above the focus

Cause the ground to shake + sometimes rupture (split along the fault)

Measured by:

  • Richter scale - measures the magnitude (power) of an earthquake + logarithmic + no upper limit
  • Moment Magnitude scale - total amount of energy released by earthquake + logarithmic + no upper limit
  • Mercalli scale - measures impacts using observations of event on scale of 1-12 (1 only detected by intruments + 12 causing total destruction)
22 of 36

Other Siesmic Hazards


  • large waves caused by displacement of large volumes of water
  • triggered by underwater; earthquakes, volcanic eruptions or landslides
  • cause seabed to move + displace water with waves radiating from the epicentre
  • more powerful if starts close to coast as otherwise lose energy
  • travel very fast in deep water so give little warning

Landslides + avalanches - shaking of ground displaces rock, soil or snow which travels quickly downslope

Soil liquefaction - when soil saturated with water, vibrations of an earthquake cause it to act like a liquid so more likely to subside, especially if heavy weight on top such as a building

23 of 36

Factors Affecting Seismic Hazards

Margin type:

  • the biggest earthquakes occur at destructive plate margins due to large pressure being built up at subduction zone
  • earthquakes at constructive plate margins have the lowest magnitude

Depth of focus - deep focus earthquakes have higher magnitude but do less damage as shock waves have further to travel

Rate of movement - tectonic plates move in relation to each other at different rates (1-15 cm per year) + no clear relationship between rate of movement + earthquake magnitiude

24 of 36

Magnitude + Frequency of Seismic Hazards

Magnitude + frequency - low magnitude earthquakes happen frequently but high magnitude earthquakes are more rare

Randomness vs regularity - no clear trend so largely random

Predictability - scientists monitor movement of tectonic plates to predict which areas are at risk however it is impossible to tell when an earthquake will strike a particular place and what magnitude it will be

25 of 36

Seismic Hazards Impacts


  • can cause buildings to collapse, killing + injuring people + leaving people homeless
  • earthquakes + liquefaction cause gas lines + power lines to break which can cause fires
  • broken water pipes can cause flooding + lack of clean water causes disease to spread
  • tsunamis can flood large areas, killing people + damaging property


  • power plants can be damaged + cause leaks of chemicals or radioactive material that damage environment
  • fires started by damaged gas + electricity lines destroy ecosystems
  • tsunamis flood freshwater ecosystems which kills plants + animals + salinises water + soil


  • liquefaction + earthquakes destroys businesses + damages economy
  • damage to industry may mean country has to rely on expensive imports of goods + energy
  • damage to buildings expensive to repair

Political - shortages of food, water + energy causes conflict + political unrest + may have to go into debt to pay for damage

26 of 36

Seismic Hazards Responses

Short term response - occur immediately before, during or immediately after hazard event

Long term responses - designed to mitigate impacts of future hazards by managing risks

Prevention - not possible to prevent but prevent risks e.g. by preventing land prone to liquefaction being built on + building giant sea walls to prevent tsunamis


  • earthquake warning systems detect weaker seismic waves that may signal more powerful waves to come + send out warnings e.g. through TV + SMS
  • individuals + businesses have plans for how people should respond e.g. finding door frame to shelter or staying away from buildings
  • tsunami warning systems developed + make sure evacuation routes well signposted
  • communities set up search + rescue teams + fire response units


  • buildings designed to withstand earthquakes e.g. flexible materials + energy absorbing foundations
  • buildings designed to reduce tsunami vulnerability e.g. tall strong buildings allow people to escape tsunami quickly 
27 of 36

Tropical Storms

Huge spinning storms with strong winds + torrential rain

Conditions required for formation:

  • disturbance near sea-surface e.g. area of low pressure
  • warm sea water - above 27˚C to at least 50m below surface so lots of water will evaporate
  • convergence of air in lower atmosphere causing air to rise
  • location of at least 5˚ from equator otherwise Coriolis effect doesn't make spin

Called hurricanes in Caribbean sea, cyclones in Bay of Bengal, typhoons in China Sea + willie willies in Australia

Lose strength when move over land because supply of warm, moist air cut off

Initially move westward due to easterly winds of tropics + away from equator due to Coriolis effect


  • circular in shape + hundreds of km wide
  • centre of storm is area of low pressure - eye
  • rising air spirals around the eye in the eyewall cause strong winds
  • outflow of moisture-laden air near top so clouds cover above eye for long distances
28 of 36

Tropical Storm Measurement + Prediction

Saffir-Simpson scale used to classify storms based on wind speed with category 5 strongest + category 1 weakest

Around 100 occur a year but some never reach land

Many factors determine where + when a tropical storm occurs so no clear pattern

Satellites can tell when a tropical storm is forming so scientists can predict where + when it will hit land

29 of 36

Tropical Storm Hazards

High winds - wind speeds can reach over 300km/h so can destroy buildings, uproot trees + carry debris

Storm surges - large rise in sea level caused by high winds pushing water towards the coast + low pressure of storm

Heavy rain - as warm, moist air rises it cools + condenses which causes torrential rain

River flooding - heavy downpours cause river discharge to increase suddenly so they burst their banks + flood surrounding area

Coastal flooding - rain reaches up to 500mm/day in coastal areas of high relief

Landslides - water infiltrates rocks, making them less stable + increasing risk of landslides

30 of 36

Tropical Storm Impacts


  • people may drown, be injured or killed by debris
  • houses destroyed so people homeless
  • electricity cables damaged so supplies cut off
  • flooding casues sewage overflows + therefore water contamination so lack of clean water
  • damage to agricultural land causes food shortages

Political - authorities blamed for shortages and have to repair damage

Economic - expensive repairs to buidlings, businesses and agricultural land


  • beaches eroded + coastal habitats damaged
  • environments polluted from damaged factories
  • landslides can block watercourses
31 of 36

Responses to Storm Hazards

Short term responses normally occur immediately before, during or after a hazard e.g. evacuating people from areas at risk

Long term responses designed to mitigate impacts of future storms:

  • prevention - storms cannot be prevented but can be studied to help scientists which areas most likely to be affected
  • preparedness - people + authorities can make sure they're prepared for storm e.g. emergency services train + prepare + educate people
  • adaptation - buildings designed to withstand tropical storms e.g. reinforced concrete or by fixing roofs securely + flood defences built
32 of 36


Uncontrolled fires that destroy forests, grassland + other vegitation areas

Usually occur in rural areas


  • ground fire - where ground itself (peat + tree roots) burn a slow, smouldering fire with no flame + little smoke
  • surface fire - where leafs + low-lying vegitation burn
  • crown fire - where fire moves rapidly through canopy - likely to be intense + fast moving

Conditions for wildfires:

  • vegetation type - thick undergrowth or closely spaced trees allow fire to travel easily with some trees such as eucalyptus burning very easily
  • fuel characteristics - fine + dry material such as thin twigs dry more easily
  • climate + recent weather - rainfall must be sufficent for vegitation to grow for fuel + dry season causes vegitation to dry up + become more flammable
  • fire behaviour - creeping fires move across the grounds surface slowly but running fires spread more rapidly
33 of 36

Causes of Wildfires

Natural causes:

  • lightning likely to start a fire if it occurs with little rain
  • volcanic eruptions can produce very hot lava, ash or gas which will start fires

Human causes:

  • most fires started by people
  • dropping cigarettes
  • allowing campfires or barbecues to get out of control
  • fireworks or sparks land in vulnerable areas
  • started on purpose in arson
34 of 36

Wildfire Impacts


  • people killed or injured if dont evacuate in time
  • homes destroyed so people homeless
  • wildfires can destroy power lines + damage reservoirs
  • cause health problems e.g. inhaling smoke

Political - governments face criticism + have to change forest management practices


  • wildfires destroy businesses so loss of jobs + income
  • high cost + insurance premiums increase dramatically
  • may discourage tourists


  • habitats destroyed + species may not return to area
  • soils damaged as fire removes organic matter
  • smoke casues air pollution + water sources contaminated with ash
  • some ecosystems rely on wildfires to clear dead vegitation
35 of 36

Wildfire Responses

Short term responses occur immediately after hazard e.g. putting fire out, diverting away from settlements, evacuating from areas of risk + spraying water on roofs to prevent embers setting them alight

Long term responses:

  • prevention - public education regarding risks of using campfires + barbecues + using fire beaters to put small fires out
  • preparedness - households have emergency plans, emergency supplies + emergency shelters
  • adaptations - using non-flammable building materials + creating fire breaks (gaps in trees) around settlements to stop fire spreading 
36 of 36


No comments have yet been made

Similar Geography resources:

See all Geography resources »See all Natural hazards resources »