Earth Hazards

Everything needed for OCR Geography Earth Hazards, combined from a number of text books, notes and revision guides.


Causes of mass movements

Slope failure is caused by:

  • a reduction in the internal resistence or shear strength of the slope, and/or
  • an increase in shear stress that is the forces attempting to pull a mass down slope

Mass movements are more common during periods of heavy precipitation which leads to increased levels of saturation in soils, or after cold conditions (solifluction) which leads to increased freeze-thaw activity and more rock falls

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Factors contributing to increased shear stress

Shear stress= the force acting on a body that causes movement of the body down slope

Factors increasing shear stress:

  • Climate- wet, lots of weathering, extremes of temperature
  • Slope angle- steepness of slope
  • Drainage- wet areas are lubricated
  • Rock type- geology e.g. clay, structure, beds, porosity and tilt of rocks
  • Vegetation- type and percentage cover
  • Animals- burrowing animals, walking on slopes
  • Removal of underlying support- undercutting by rivers or waves
  • Lateral pressure- water in cracks; swelling, pressure release
  • Short term stresses- earthquakes, movement of trees in wind
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Factors contributing to reduced shear strength

=The internal resistance of a body to movement

Factors contributing to reduced shear strength:

  • Weathering effects e.g. disintegration of rocks; hydration of clay minerals; solution of minerals in rock or soil 
  • Changes in soil or ground water pressure- saturation; softening of material
  • Changes in structure- creation of fissures in clay; remoulding of sands and clays
  • Biological effects- Burrowing of animals, growth and decay of roots
  • Adding weight to slopes e.g. building, walking
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Factors holding slopes in place

  • Friction and weight of particles
  • Cohesive forces e.g clay
  • Vegetation roots bind the soil
  • Human structures e.g. nets
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Ways of classifying of mass movements

  • By speed or rate of movement - fast versus slow
  • By type of movement - flows, slides, slumps
  • By type of material
  • By water content

A range of slope processes occur which vary in terms of magnitude, frequency and scales

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Types of mass movement

  • Creep/Heaves - slow and low water content results in terracettes therefore pose little threat
    • About 75% of the soil creep movement is induced by moisture changes
  • Avalanche-Rapid and can be wet or dry
  • Flow- rapid highly fluid, saturated soil so are therefore more mobile
    • continuous
  • Slide-sliding material retains shape and cohesion, clearly defined slide plane
    • e.g. Southern Leyte landslide in the Philippines in 2006 which killed 1126 people
  • Slips - on a slide plane, medium water content
  • Slump - usually rotates along a slip plane, medium water content
    • e.g. Holbeck Hall Hotel, Scarborough
  • Falls - occur on steep slopes, especially bare rock faces where joints are exposed

Mass movements become hazardous when they have a damaging effect on eoconomy and society. If damage to property and/or loss of life is particularly high, a hazard becomes a disaster

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Physical and human factors triggering mass movemen

  • Mass movements occur on slopes where the driving force is gravity
  • Two sets of forces operate on slopes: downslope forces and upslope forces
    • Gravity is main downslope force and increases with slope angle
    • Upslope forces resist mass movement- includes shear strength of slope materials, the frictional resistance between slope materials, binding effects of vegetation

Usually related to an external trigger that may be physical or human:

  • Steepening of slopes by erosion or human activity
  • Increased loading on slopes due to heavy and prolonged rainfall, building, tipping of waste materials
  • Undercutting the foot of a slope
  • Heavy rainfall that lubricates slope materials and reduces frictional resistance
  • Heavy rainfall that increases pore water pressure and reduces the coherence of slope materials
  • Deforestation that reduces the binding effect or tree roots and increases the amount of water absorbed by slope materials
  • Earthquakes or the vibrations caused by heavy lorry traffic or explosions
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Human factors contributing to mass movements

  • Deforestation either by overgrazing or by deliberate logging for timber/fuelwood or new farmland, disrupts the balance of forces on slopes
  • Torrential rainfall can then trigger mass movements
  • The mass movement disasters in Honduras (1998), Northern Venezuela (1999) and Guinsaugon (Philippines 2006) were all related to deforestation of steep slopes and extreme rainfall events
  • Mass movements caused by torrential rainfall from Hurricane Mitch, killed thousands of people in Nicaragua in 1998
  • Some mass movement hazards are caused entirely by natural processes
    • In 1985, the eruption of Nevado del Ruiz in Columbia produced mudflows that killed 23,000 people
    • Similar mudflows occured around Mount Pinatubo in the Philippines
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Impacts of mass movements

Environmental impacts:

  • Relief - reduces slope angles, fills in valleys/hollows, adds steps or bulges to slopes
  • Drainage - may dam or divert rivers, wetter at foot of slope
  • Vegetation- trees lean or fall
  • Soil- collects at base of slope (catena effect)
  • Rock Strata- may bend the ends of beds (cambering)

Social impacts- Buildings/walls - collapse, lean or have soil collect up side of slow- Disasters e.g. Aberfan 1966, 147 killed

Economic Impacts

  • Transport- road and rail distorted or broken, leading to disruption and cost of repair
  • Poles lean or fall leading to disruption in services/supply
  • Loss of farmland, damage to structures e.g. bridges, buildings, pipes
  • Quarrying and mining disasters
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Relative importance of factors causing mass moveme

  • Unlike earthquake and volcanic hazards, human activities can be a causal factor 
    • They contribute to mass movements by destabilising slopes
  • Taiwan is highly susceptible to severe mass movement hazards
    • Due to combination of physical and human factors
    • Physical factors include high rates of tectonic uplift, steep slopes, weake rocks, earthquakes and extreme rainfall events
    • In August 2009, Typhoon Morakot dumped 2,000mm of rainfall in just 3 days causing landslides and debris flows that killed hundreds
    • Susceptibility to mass movements is also high because of development in the mountains- road construction, the building of hotels and hot spring resorts, HEP schemes and fruit farming have degraded the environment and increased the risk from mass movement hazards
  • Some mass movement hazards, show no causal connection to human activities
    • The Sichuan earthquake in central china (2008) and the Sumatran quake (2009) were extreme events that triggered hundreds of landslides, which destroyed property and killed thousands of people
    • These mass movement hazards were not directly related to human activity
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Ways of reducing mass movement hazards

  • Reduce pressure on the top of the slope e.g. limit building
  • Control slope face processes, using drains, sheet piles or steel nets
  • Reduce slope foot processes e.g. gabions, revetments
  • Reduce moisture content of slope e.g. drains
  • Change the angle of the slope - regrade it as a gentler slope
  • Plant trees and bushes - helps bind the slope and dries it out
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Exposure and vulnerability to mass movements

  • Exposure refers to the magnitude and frequency of the natural event and the number of people living in the areas of risk
    • In mountainous regions like Kashmir and Taiwan, with steep slopes, large populations and frequent earthquakes, exposure to mass movement hazards is high
  • Vulnerability is the prepardness of a population in relation to a particular hazard and its ability to respond and mitigate the effect
  • Vulnerability to mass movements is lessened by programmes of reafforestation/forest conservation on steep slopes, hazard mapping of areas of greatest risk, emergency disaster planning etc
  • The Northern Venezuala debris flow of 1999 killed an estimated 30,000 people because the area suffered both high exposure and high vulnearbility
    • Disaster amplified by the vulnerability of the population as their was a lack of prepardness, with no strategy for managing a major natural disaster.
    • No attempt was made to remove impromptu slums built on steep slopes near the coast and no action was taken to clear sediments and debris which clogged river channels
    • Widespread deforestation accelerated run-off increasing the risk
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Mitigating the impact of mass movements

  • Means making people and society less vulnerable to the events
  • There are two approaches
    • Reduce the risks of mass movement occuring in the first place
    • Respond to the actual mass movement events to limit loss of life, injury and damage
  • In mountainous regions, reafforestation can reduce risk- conservation management
    • Local farmers in the Annapurra region of Nepal given an incentive to conserve forests and woodlands by recieving a proportion of income generated by ecotourism
    • Terracing is common throughout rice-growing areas of Asia especially in Indonesia
  • Artificial slope drainage reduces the risk of mass movement by lowering pore water pressure, increasing frictional resistance and reducing loading
  • Publication of hazard maps, showing areas of risk can minimise the hazard
  • Once the disaster is a reality, planning can get vital emergency aid to survivors, airlift the injured to hospital and organise search and rescue teams
  • Long-term development plans are needed to reconstruct housing, infrastructure and local economies
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Aberfan flow case study

  • 21st October 1966
  • Landslide involved over 100,000 cubic metres of colliery waste travelling at speeds of up to 30km/h
  •  2 million tonnes of mass was moved


  • Waste coal tip at a steep angle
  •  Prolonged heavy rain
  • Tip built on a spring
  •  Little vegetation to bind the waste
  • No management of the tip
  • The National Coal Board assumed any slide would be slow
  • It was a foggy day in the village so visibility was poor
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Aberfan flow case study


  •  144 people killed- 116 were schoolchildren from the Pantglas Junior School
  • 20 houses and a farm buried
  • Huge psychological impact
  • Loss of a generation
  • Cost of clean up

Responses- Short term

  • Emergancy rescue services
  • Hundreds of people from nearby villages drove to Aberfan with shovels to help with the rescue however these untrained rescuers just got in the way
    •  Nobody was rescued alive after 11am on the day of the disaster and it was nearly a week before all the bodies were recovered
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Aberfan case study

Responses- Long term

  •  Other tips checked and slope angles reduced
  • 1969 Mines and Quarry Act passed to control siting of tips
  • Over £20 million (2007 equivalent) in donations
  • Very expensive clean-up (£2 million)
  • No prosecutions

Mitigating the impact:

  • Before: the spoil tip could have been removed, stolen telephone cables could have been replaced
  • During: school could have been evacuated
  • After: More trained rescue teams could have been used and the untrained people not allowed near the site.
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Costa Rica Mass movement 2010

Where: San Antonio De Escazu

Impacts and Causes

  • At least 20 people killed
  • Landslide in the suburb San Antonio followed 2 days of heavy rains that flooded a river near the town and sent 1,500 people to shelters across Costa Rica
  • The San Antonio area received 6.3 inches of rain in just two hours
  •  There were boulders of 3m high
  • Many roads were flooded or blocked by landslides across Costa Rica, Schools were closed
  • At least 200 homes were underwater in Parrita which received more than 13 inches of rain and a bridge leading to the town was destroyed
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Costa Rica Mass movement 2010

Responses- Short term

  • The government declared the country in red alert
  • Shelters were set up for the people who were flooded out of their homes
  • Dozens of rescuers, some using dogs were searching for survivors as an undetermined number of people missing
  •  Relatives arrived with shovels to help but most were turned away because of the risk of another landslide

Responses- Long term

  • The president said the government has 7 billion colones ($14 million) available for relief efforts
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Holbeck Hall flow/landslide 1993

Facts and Figures

  • 6th June 1993
  • Landslip along the upper sections of the boulder clay at the 60m cliffs at Start Bay, Scarborough

Impacts- Destruction of Holbeck Hall Hotel which was constructed in 1883


  •  The coastline between Scarborough and Easington (Spurn Head) is among the most rapidly retreating areas in Britain and would cost millions of pounds to protect
  • The Ministry of Agriculture blamed a succession of droughts making the area unstable
  • The boulder clay had become dry and cracked in previous years and then saturated by the rains in spring and early summe so it became unstable and slumped along a slip plan causing an earth flow


  • Little can be done other to let the slip stabilise itself when it reaches an angle of  about 25'
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Floods and landslides in Brazil 2011

  •  12th January 2011, 900 people were killed by huge debris flows
  • Cuiaba River in Petropolis Muncipality was the main area affected
    •  Area has steep slopes, shallow soils and heavy thunderstorms in summer
    • Lack of urban planning has added to the risk
  •  Traditionally an area associated with rural activity the emphasis is now more on leisure, including small hotels, condominiums and second homes


  • Highly restricted distribution of rainfall in both space and time
  • There was a huge amount of precipitation within a well defined line
  • There are no rain gauges in Cuiaba valley recorded about 180mm in less than 24 hours
  • Atmospheric convergence played an important role- huge convective system on 10th January which was pushed upwards by a frontal system approaching the south causing the formation of large cumulonimbus clouds, up to 12km high
  • High altitudes, steep slopes and deep river valleys means that rainfall quickly enters valley bottoms
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flooding and landslides in Brazil 2011

  • Mass movements are common in the area since uncontrolled urban growth began
    • Some settlements are very close to the river bank
    • Others are built on steep slopes
  • Poor urban drainage, low vegetation cover and unplanned settlement leads to floods most years
  • No major efforts have been put into the reduction of floods due to the huge investment needed
  • The mountain range has been modified by human activity since the early 18th century, when it was almost completely deforested for agriculture and cattle grazing
  • Fire has helped transform the once rich high-altitude fields and forests into degraded vegetation which still undergoes annual burning
    • This progressive degradation has made the slopes more vulnerable to natural erosion and mass movement events
  • The slides brought down well-preserved forests, and this contributed to the destructive power of the stream
  • When the debris flow reached the low Santo Antonio River, the flow had turned into a typical flood, but was still very destructive
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Floods and landslides in Brazil 2011


  • Heavy thunderstorms caused an immense part of the high mountain basin of Cuiaba River to collapse starting a complex debris flow which included mud, boulders and tree trunks
  • The debris flow killed 71 people who lived along the riverside
  • Almost nothing remained of the popular tourist area in the Cuiaba valley after the flow
  • There were over 900 fatalities (436 in Nova Friburgo, 381 in Teresopolis, 71 in Petropolis, 21 in sumidouro, 4 in Sao Jose de Rio Preto and 1 in Bom Jardim)
  • 400 more people are still missing
  • Damage extended from the north to the northeast of the mountain range of Rio de Janeiro
  • Fieldwork immediately after the event was difficult as roads were closed for a considerable time
  • All buildings in the torrent were destroyed irrespective of constructive quality
  •  A wall of water then came down the valley with intense force bringing tree trunks, construction debris and even cars
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Causes of river and coastal floods

Physical causes:

  • Usually by altering the balance of stores, imputs and outputs in the system
  • Climate- snowmelt, heavy rain (thunderstorms) low evaporation, storm surges
  • Previous weather conditions, e.g. a long period of wet weather
  • Relief- very flat, low-lying area
  • Drainage- density, regime, hydrograph, drainage pattern and density, channel type
  • Vegetation- grass versus trees
  • Rock type- permeability, porosity, water table
  • Soil conditions- wet versus dry, baked imperable by drought
  • Natural disaster- earthquake, landslide
  • Subsidence- area is sinking (isostatic, removal of groundwater)
  • Rising sea levels - global warming melting ice sheets
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Causes of river and coastal floods

Human causes of floods

  • usually by putting human activities in areas at risk and interfering with the natural cycle/hydrology
  • Construction of impermeable surfaces e.g. towns, roads
  • Removal of vegetation cover- deforestation, removal of coastal marshes/mangroves, farming
  • Soil erosion, leading to silting of channels and storage lakes
  • Drainage- ditches, waste disposal, drains, excessive irrigation
  • Changing rivers- dams, diversions, embankments, removing or adding deposits
  • Constricting channels e.g. bridges, levees
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Physical factors influencing flooding

Rivers flood when they overtop their banks and inundate the adjacent valley floor

  • Most obvious cause is intense and/or prolonged rainfall
    • Heavy convectional rainfall associated with thunderstorm cells causes flash floods
    • Slow floods occur after days/weeks of prolonged rain or snowmelt- less hazardous
  • Many rivers, particularly in the tropics and sub-tropics have an uneven flow pattern during the year.
    • In tropical Africa and monsoon Asia, rivers flood annually during the wet season
  • Relief and geology also influence flooding
    • Upland areas intensify rainfall events (orographic effects) but their steep slopes also cause rapid run off increasing peak flows (e.g. Cumbria floods, 2009)
    • Where catchment geology consists of impermeable rocks, natural storage of water following rainfall events is minimal- large proportion of rain becomes runoff
  • Vegetation has a direct effect on the amount of water reaching stream and river channels by intercepting rainfall and absorbing water from the soil through root systems
    • Where catchments are sparsely vegetated, levels of interception and transpiration are low and rivers have a greater propensity to flood
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Human factors influencing flooding

  • Flood hazards are increased by urbanisation, farming, deforestation and land drainage
  • Urbanisation modifies the local hydrological cycle
    • Towns and cities are dominated by impermeable materials such as concrete, tarmac, brick and tiles and these materials have little capacity to store water
    • Urban areas have efficient drainage systems promoting rapid runoff
    • Streams and rivers draining urban areas have short lag times and high peak flows
    • Urban growth often extends onto floodplains increasing risk
  • Some farming practices also increase the risk of flooding
    • In mid-latitudes, replacing pasture with arable crops leaves fields with little plant cover for half the year reducing interception and transpiration, increasing run off
    • Unsustainable farming practices may lead to soil erosion and the siltation of rivers- the build up of silt in rivers reduces channel capacity and again increases flood risk
  • Deforestation alters the movement of water in drainage basins
    • On steep hillsides, deforestation is likely to result in soil erosion
    • Rivers that drain catchments that have suffered widespread deforestation (e.g. Brahmaputra in South Asia) invariably show an increased frequency of flooding
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Human factors influencing coastal flooding

  • Less significant as causal agents in coastal floods than in river floods
  • At the global scale, many lowland coasts are experiencing a heightened flood risk due to rising sea levels linked to global warming
    • Most scientists agree that global warming is anthropogenic
    • Large parts of bangladesh are already under serious threat from rising sea levels and may have to be abandoned within the next 2 or 3 decades
  • Global warming is also responsible for climate change and the increased frequency and power of storms
    • Settlements in lowland coastal areas such as the Gulf of Mexico and the Bay of Bengal face an uncertain future as powerful storms like hurricane katrina become more common
  • In the Mississippi Delta natural gas extraction has caused widespread land subsidence, which has increased the flood risk to New Orleans
  • The drainage of salt marshes has a similar effect
  • Flood hazards arise because millions of people live in coastal regions
  • Rapid population growth in coastal communities on the Gulf of Mexico has increased levels of exposure to storm surges
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Impacts of flooding

Primary impacts- immediate effects (first few days)

  • Deaths (humans, pets and livestock), evacuation, destruction of buildings/possessions, pollution (sewage, oil, etc), disease from polluted water, stress (loss of security)

Secondary impacts- subsequent to primary impacts (months to years)

  • Transport links broken (bridges, roads, rail), cost of clean up and replacement, loss of jobs, crops ruined (animals may starve), rehousing costs
  • May take over a year to dry out buildings

Tertiary impacts- long-term impacts (many years)

  • Flood-prone areas decline as property values decrease, difficult for owners to get insurance or sell property
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Impacts of floods

  • In July 2009 floodwaters on the floodplain of the River Wear near Durham carved a huge gulley in a field of barley, removing 12,000m3 of soil and gravel
  • In July 2007 in the Severn Valley in Gloucestershire also caused significant environmental damage
    • Thousands of small mammals drowned and large numbers of fish were left stranded
  • Environmental damage also has an adverse economic and social effect
    • The storm surge generated by Cyclone Sidr which hit Bangladesh in 2007 damaged large areas of coastal mangrove which would take 40 years to recover
    • Coastal floods of Bangladesh in 2009 led to the salinisation of farmland, which will remain uncultivable for years
  • Major floods cause death and injury
    • the 1931 river floods in China killed an estimated 2-4 million people
    • Coastal flooding in the wake of Cyclone Nargis killed 140,000 people in Myanmar
    • Storm surge following hurricane katrina caused 1,400 deaths
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Impacts of floods

  • The principal economic effect of floods are damage to property and infrastructure
  • Tends to be higher in developed than in developing countries because:
    • greater fixed investments
    • assets such as land, housing and commercial buildings with higher value
  • In developed countries most assets are protected by insurance that makes good the losses following a flood disaster
  • The economic cost of hurricane katrina - over US$90 billion - was the costliest natural disaster in US history
  • The total insured loss from the July 2007 floods in Gloucestershire was £1-1.5billion
    • losses covered damage to property and motor vehicles, as well as the disruption to businesses and the expense of providing temporary accommodation for people forced to leave their homes
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Responses to flooding

Preventative planning

  • Planning- avoid flood plains and green sectors e.g. parks
  • Planned retreat- leave certain areas to flood e.g. Somerset levels
  • Reduce surface flow, e.g. afforestation, contour ploughing

Structural planning

  • Channel modification e.g. overflows, storage areas, dams, widen channels
  • Embankments- raise them, reinforce them, put up flood gates
  • Flood relief channels
  • Flood barrages e.g. on the River Thames
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Responses to flooding


  • Early warnings- better weather and river level forecasts, communications
  • Flood insurance
  • Public relief funds
  • Accept the risk and live accordingly
  • Ignore the risk ('head in the sand' approach)

Emergency rescue

  • Rescue people and animals
  • Save property and possessions
  • Use sandbags, erect flood barriers, pump out property 
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Storm surges

  • =Changes in sea level resulting from variations in atmospheric pressure and associated winds
  • Generated by tropical and extra tropical storms
    • The low air pressure and wind direction combine to produce large, temporary rises in sea level that have the capacity to cause extensive flooding
  • Usually associated with strong winds and large onshore waves
  • Largest surges are produced by hurricane landfalls
  • Occur on top of normal tides and when surges are added to high tides they can cause extremely high water levels and flooding
  • Magnitude is controlled by the intensity and track of the storm and partly by the configuration of the coastline and seabed
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Physical factors influencing coastal flooding

  • Flooding occurs along lowland coasts due to exceptionally high tides or storm surges
  • Exceptional high tides, known as spring tides occur twice a month and the highest tides of the year happen around the equinox
  • Storm surges caused by gale force winds and low pressure raise sea levels
    • Floods in New Orleans in 2005 in the wake of Hurricane Katrina were caused by an 8m storm surge
  • Climate also has an effect on coastal flooding
    • Coastlines in the sub-tropics that experience hurricanes and tropical storms face high risks from flooding
  • Deltas, estuaries and reclaimed fens and marshlands are most susceptible to flooding
    • In the UK, lowland coasts such as the Broads in East Anglia and the Somerset Levels are at greatest risk
  • Vegetation can lessen the threat of coastal floods
    • In the tropics, mangroves encourage sedimentation and reduce wave power
    • Salt marshes have the same effect in higher latitudes
    • Bangladesh faces increasing risks of flooding partly because of destruction of mangrove forests
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Responding to storm surges

Approaches to hazard reduction basd on purposeful adjustment Choose change

  • change location of settlement 
  • Reduce losses
  • Prevent effects of natural hazards- flood protection
  • Modify natural hazard event- flood warning

Accept losses

  • Share loss of natural hazards- insurance
  • Bear loss of natural hazards- exploiting reserves
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Short term responses to flood disasters

  • Focus on evacuation and emergency aid
  • Early warnings of floods allow time for evacuation to safe areas
    • In the Brahmaputra-Ganges delta in Bangladesh the death toll from storm surges since 1991 has been greatly reduced thanks to the construction of elevated cyclone shelters and the implementation of effective early warning
  • Major flood disasters such as Cyclone Nargis require immediate short-term aid
    • Flood victims need food, fresh water, temporary shelter, sanitation and medicines
    • Often the only way to reach victims is by helicopter
  • Most developing countries lack the resources to respond effectively to major flood disasters and rely on the international community
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Long term responses to flood hazards

  • Fall into two categories: structural and non-structural
  • Structural rely on hard engineering to confine river floodwaters to river channels and protect coastal areas
    • Dams and reserviors store floodwaters which are released gradually
    • Sluice gates and flood basins operate in a similar way
    • Flood embankments or levees raise the height of river banks increasing channel capacity
    • Channel straightening works by increasing flow velocities and bankfull discharge
    • Artificial channels (flood relief channels) divert a part of a river's flow reducing discharge in the main channel- often built to protect certain settlements
    • Seawalls are designed to prevent overtopping and flooding by spring tides and storm surges- expensive to construct so only built to protect large settlements
    • On rural stretches of coast, flood embankments replace sea walls
    • In some estuaries, where the tidal range is amplified, flood barriers (e.g. Thames barrier) protect major centres of population
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Long term responses to flood hazards

  • Non-structural approaches to flooding:
    • Flood abatement aims to prevent floods developing in the first place
    • Affirestation of catchment headwater increases lag times, reduces peak flows and is effective in limiting the size of river floods
    • In coastal regions the conservation of mangroves in the tropics, and salt marshes and mudflats in middle and high latitudes does this
    • Controlling development in areas of highest risk is increasingly favoured
      • Climate change and forecasts of more frequent floods makes this approach sustainable
    • Production of detailed hazard maps shows areas most at risk
  • Flood warnings issued by national agencies help to mitigate the impact of floods
    • Bangladesh is monitored by the National Warning Forecasting Centre in Dhaka, an agency which issues warnings 24 hours in advance
  • In developed countries the impact of flooding on businesses and individual households is mitigated by flood insurance
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Flood and storm surge Cornwall 2004

  • A more frequent type of coastal flooding occurs when storm waves overtop sea defences such as sea walls and flood embankments
  •  The flooding usually lasts for 1 to 3 hours around high tide
  •  Damage caused is often fairly localised
  • 27th and 28th October 2004
  •  A deep depression hit the coast of Southern Cornwall
  •  Winds gusting to 90kmh-1 whipped up huge waves
  •  The storm coincided with spring tide
  •  Waves topped and damaged the sea wall at Penzance causing extensive flooding to properties along the promenade
  • Flooded homes had to be evacuated, roads were closed and rail services suspended
  • In Looe, 30 homes and business were flooded
  • Flooding was also reported in Porthleven and Flushing near Falmouth
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Flooding in Pakistan- September 2012

10th September

 Khyber Pakhtunkhwa province and Pakistani-administered Kashmir are the worst hit regions

Causes- Heavy monsoon rain


  • 78 people have died
  • 1,600 houses destroyed
  • 5,000 houses damaged


  • Hundreds of tents were sent as part of the relief effort
  •  State of emergency was declared in the Dera Ghazi Khan and Rajanpur districts of Punjab province
  • Questions were asked to the disaster management authorities about what they have done in the past 12 months to prevent flooding
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Flooding in Pakistan- September 2012

25th September


  • Tens of thousands of people made homeless
  •  120,000 homes destroyed
  •  Flooding in Balochistan affected 80% of the population
  • People lived in the open without shelter on whatever dry patch of ground they could find
  • Balochistan is Pakistan’s largest province in size but ranks lowest in terms of infrastructure and services
  • Food, tents and medicine in short supply- people surviving on one meal a day


  •  Tens of thousands of tents distributed
  • Medical centres set up to treat gastric problems, malaria and other illness among 500,000 people who were made homeless
  • The army called in to help with the rescue operation
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Flooding in Pakistan- September 2012

28th September


  •  Floods began in early September because of heavy monsoon rains


  • More than 400 people killed
  • Tens of thousands homeless- 890,000 affected in Punjab province, 700,000 affected in Balochristan


  • European Union announced additional funding of £11.7million
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India floods, September 2012

Causes - Heavy monsoon rains


  •  1.5 million people in the north-eastern state of Assam were forced to leave their homes
  • 11 people died in separate drowning incidents
  • 2,000 villagers had been inundated by water overflowing from the main Brahmaputra river
  •  The Kaziranga national park, home to 2/3 of the world’s remaining 1-horned rhinos had been flooded
    • The July floods killed at least 559 animals including 14 one-horned rhinos


  • Maximum health alert declared in the affected areas to prevent outbreaks of disease like diarrhoea and typhoid
  •  Doctors and paramedics sent to places were victims of flooding were taking shelter
  • 166 relief camps had been set up for affected people
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Tectonic processes

The tectonic plates that make up the Earth's crust move about on convection currents in the mantle. At their edges they may:


  • Destrictive margin (collision) = deep earthquakes, explosive eruptions
  • Destructive margins (subduction) = deep earthquakes, trench


  • Conservative margin= shallow quakes, lava flows and shield volcanoes, rift valleys

Slide past:

  • Conservative margin = shallow quakes, hot springs, few eruptions
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Hazards of earthquakes

Hazards have the potential to cause loss of life and/or damage to property (so people need to be present)

  • Primary hazards - ground shaking, landslides, faulting at the surface
  • Secondary hazards - liquefaction, ground failure, rock falls, mud flows, tsunamis
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Causes of Earthquakes

  • Caused by sudden movements of the Earth's crust and lithosphere
  • Result in primary hazards such as ground shaking, liquefaction, landslides and tsunamis
  • Due to stresses in the crust and lithosphere in the form of compression, tension and shearing
    • Compression occurs at convergent plate margins where subduction takes place- compressive forcecs give rise to low-angled thrust faults producing high magnitude quakes such as the Sumatran quake in 2004
    • Tensional forces are associated with divergent plate margins or mid-ocean ridges, where stretching leads to faulting and rifting of the crust and lithosphere
    • Earthquakes at conservative plate margins are due to horizontal or shearing movements as two plates slide past each other producing violent earthquakes e.g. california
  • Many large earthquakes occur a long way from tectonic plate margins e.g. Sichuan quake in 2008. These are intra-plate quakes aand also result from compressional and tensional forces  
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Impacts of earthquakes

Impacts are what actually happens. There is a contrast between the immediate disaster and the long-term impacts; the scale of the impact is crucial.

Primary impacts

  • destruction, casualties, landslides, fires, loss of services/utilities and communications, shock and traumatic stress, violence (looting)

Secondary impacts

  • disease (sewage and water pipes broken), loss of infrastructure, housing, jobs, food and water shortages, floods

Tertiary impacts

  • cost of recovery, loss of crops, damage to mines/industries, trade, long-term depression, out-migration
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Impacts of earthquakes over time and location

The extent of earthquake damage is influenced by the following factors:

  • The strength of earthquake and number aftershocks
    • the stronger the earthquake the more damage it will do- Richter scale 6.0 is 100 times more powerful than one of 4.0
    • The more aftershocks there are the greater the damage
  • Population density
    • more damage if high population density e.g. Tokyo, Japan than an area of low population and building density like the Mid-Atlantic Ridge at Thingvellir, Iceland
  • The types of buildings
    • MEDCs generally have better quality buildings with insurance cover than those in LEDCs - California have different impacts and responses to India
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Impacts of earthquakes over time and location

  • The time of day
    • An earthquake during a busy time of day such as rush hour may cause more deaths
    • Industrial and commercial areas have fewer people in them on Sundays
    • Homes have more people in them at night
  • The distance from the epicentre of the earthquake
    • the closer a place is to the centre of the earthquake the greater the damage
  • The type of rocks and sediment
    • Loose materials may act like liquid when shaken
    • Solid rock is much safer and building ideally should be built on flat areas of solid rock
  • Secondary hazards
    • mudslides and tsunami, fires, contaminated water, disease, hunger and hypothermia
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Environmental impacts of earthquakes

  • Often trigger mass movements (especially landslides) in mountainous regions
    • such as Kashmir and Sichuan, destroying settlements and farmland and blocking roads and railways
    • The Sichuan quake in 2008 led to landslides that dammed rivers and created dozens of temporary barrier lakes
    • Pollution of lakes by domestic waste threatened health of local populations
    • The Sumatran tsunami caused severe damage to mangroves and coral reefs in Indonesia and Malaysia
    • Farmland, contaminated by salt water, had to be abandoned and salt water also polluted freshwater aquifers
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Social impacts of earthquakes

  • Major earthquakes cause large-scale mortality, especially in poorer countries
    • 87,000 people died in the Kashmir quake (2005)
    • The 2004 tsunami killed an estimated 250,000 people in 11 countries
  • Large numbers of injuries also result from earthquake events, mainly due to falling masonry and collapsed buildings
    • The Sichuan quake, made 5.4 million people homeless
  • Millions of people are displaced increasing the threat from disease e.g. from continated drinking water
  • There is often an acute shortage of medicines, doctors and hospitals to treat survivors
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Economic impact of earthquakes

  • Economic impact is greatest in the world's richest countries
  • The Northridge quake in southern California in 1994 killed just 57 people, but cost US$20billion
    • The quake brought down freeway intersections, ruptured pipelines and damaged buildings
    • Many steel-framed buildings suffered damage and houses were destroyed by landslides
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Responses to Earthquakes

Emergency aid- rescue, tents, medicine, food, water, often involving the military and charities

Short-term aid- rehousing people, rebuilding hospitals, repairing infrastructure

Long-term aid- moving population, improving warning systems, emergency planning

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Short term responses to earthquakes

  • The immediate response to earthquake disasters is to provide emergency rescue and relief to surviors
    • In major earthquakes such as Gujarat 1999 and Kashmir 2005 international relief was needed with contributions from NGOs and foreign governments
  • Immediate priority is to rescue people trapped beneath collapsed buildings
  • The focus then shifts to providing food, water, shelter, heating, medicines and sanitation for survivors
  • Main threat to survivors is disease caused by inadequate sanitation and contaminated water
  • The nature of emergency relief depends on the location and timing of the disaster
    • In remote regions like Kashmir, helicopters were essential to reach isolated communities in the mountains
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Long term responses to earthquake disasters

  • Reconstruction of the devestated areas
  • Homes, schools, hospitals, business, roads, bridges and other essential infrastructure needs to be rebuilt and jobs have to be provided
    • Slow process which may take decades and cost billions of dollars
    • E.g. Reconstruction bill for Sichuan earthquake exceeds US$150billion, Kobe cost US$120 billion
  • The reconstruction plan for the Sichuan quake shows the enormous scale of the task
    • 169 new hospitals
    • 4,500 new primary schools
    • 3 milion homeless rural families will get new houses and 860,000 city apartments will be built
    • In developing countries, reconstruction on this scale requires aid from foreign governmental and multilateral agencies
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Exposure to earthquakes

Exposure combines the magnitude of the quake with the number of people at risk in the affected area

  • Exposure is high in tectonically active regions such as Japan, Southern California and eastern China, which are densely populated and large quakes occur frequently
  • The social and economic impact of earthquakes in regions with similar exposure is highly variable
  • Wealthy countries like the USA and Japan have relatively low death tolls but high economic cost
    • 1994 Northridge quake in California killed 57 but cost US$20billion
  • In poor countries the number of fatalities and scale of homelessness are usually much higher but the economic costs are often lower
    • Kashmir quake killed 87,000 pople but only cost US$5billion
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Vulnerability to earthquakes

Vulnerability describes how resistant a society is to earthquake hazards, strongly influenced by levels of prepardness and the ability to mitigate earthquake impacts

  • Geographical variations in vulnerability explain differences in the impact of earthquakes
  • Rich countries can afford to build earthquake-resistant societies
    • Earthquake-proof and fire-proof buildings, trained emergency services, educated population, local government disaster plans and management strategies
    • Overall effect of these measures is to lower vulnerability in areas of high exposure and reduce the number of deaths and injuries
    • Economic losses will also be reduced, but given the scale of investment and the value of the built environment in developed countries, they will generally be much higher than in developing countries
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Reducing the impact of earthquake hazards

Earthquakes cannot be predicted, however their impacts can be reduced

  • Measures largely confined to rich countries
  • Buildings in earthquake zones can be strengthened using solid steel frames, reinforced concrete and steel braces
  • High-rise buildings are vulnerable to ground shaking and liquefaction and may have flexible structures, massive concrete pillars, counterweights and deep foundations
  • Construction of earthquake proof buildings isn't useful unless mandatory building codes are enforced
    • Huge loss of life in Sichuan earthquake partly due to inadequate enforcement of building codes, shoddy workmanship and poor-quality building materials
  • Disaster planning is vital
    • Tokyo's disaster plan involves individuals and the government
    • Identifies buildings that need upgrading, roads, expressways, bridges and utilities are strengthened
    • Refuge sites are designated in public parks and other open spaces.
    • Sets priorities and target for recovery and reconstuction
    • An educational programme raising public awareness has been established
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Bhuj, India earthquake 2001

 7.9 on Richter scale,  26th January 2001 Tremors lasted one minute


  •  Estimated between 30,000 and 100,000 people died
  •  Many of the buildings were poorly constructed so collapsed easily crushing people
  • Hospitals, fire stations and civil administration buildings were all destroyed
  • There were very limited medical facilities
  •  No power or communications in many parts of Gujarat
  • 500,000 people were made homeless


  •  Aftershocks were felt for up to five days, and the rescue operation was unable to start in some areas for nearly 3 days
  • Poor sanitation and lack of drinking water led to the spread of disease such as cholera
  • Hypothermia set in
  • There was much psychological trauma
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Haiti after the 2010 earthquake

  • The earthquake of 12th January 2010 brought catastrophic damage to Haiti
    • Increased by widespread poverty
    • Inadequate public infrastructure
    • The country’s ever present food insecurity
  • 2.3 million of population were displaced
  • 500,000 deaths and injuries, 230,000 killed
  • Earthquake magnitude 7

Impacts after quake

  •  International donors pledged US$5.8billion of relief to be delivered by September 2011
    • Less than half of this was released, most of it was used for debt relief rather than assistance on the ground
  • Haitians need a legitimate government to deal with the political issues of rebuilding, such as land tenure, property rights and spending priorities
  • Port-au-Prince, Haiti’s capital was the area worst hit
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Haiti after the 2010 earthquake

  • Small businesses were important to the economy before the earthquake but many people lost everything
  • 100,000 damaged buildings that are useable but the majority of people are unemployed and cannot afford the rent
  • A million or so people were still in dangerous tented camps a year later
  •  Another million live in the slums of Port-au-Prince
  • People lack incentives to move out from camps and 87% of the homeless are still there
  •  Increase in sexual violence- dozens of rapes are committed every day
  •  Cholera has become an epidemic
  •  20 million m3 of rubble was created and less than 5% has been cleared
  • The governments housing strategy is to move people in bulk out of Port-au-Prince
  • The international community has not done enough to support good governance and effective leadership in Haiti
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Japan earthquake March 2011

  • The landmass lies on two continental plates and to the east of Japan lies 2 oceanic plates
  •  Four major tectonic plates converge
  •  Ocean trenches such as the Japan trench mark plate boundaries where subduction occurs
  • Exposure is high due to the large population densities especially o the coasts

The nuclear disaster in 2011

  •  The Fukushima reactors to shut down automatically when their motion sensors felt tremors
  •  The multiple cooling systems required to remove residual heat from the core failed
  • Radiation escaped into the atmosphere through hydrogen explosions in two reactors which increased radiation levels close to the plant to 400 millisieverts (mSv) an hour
  • Some of the 300 engineers who tried to regain control of the plant were treated for radiation exposure
  •  A 20km exclusion zone was imposed resulting the forced migration of 70,000 people
  •  Radioactive dust caused local food sources, including milk and spinach to show radiation levels seven times higher than the legal limits
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Japan earthquake March 2011

March 2011

  • 9.0 on Richter scale
  • Its epicentre was about 130km off the town of Sendai
  • Tsunami devastated several fishing villages, killing over 20,000 people
  • Earthquake caused by the Pacific plate subducting under the North American plate
  •  Earthquake produced a 4.4m horizontal shift

Vulnerability of Japanese cities

  • Kobe earthquake in January 1995 destroyed Japan’s myth of safe cities- Caused 6400 deaths, Destroyed 200,000 homes

Earthquake risk in Tokyo

  • The 1923 Great Kanto quake killed over 140,000 people and injured a further 140,000
  • Massive interplate earthquakes in Tokyo have a recurrence interval of 100-200 years and their focus is directly under Tokyo
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Earthquake management in Tokoyo

  • Rapid urbanisation and urban growth has increased exposure
  • Planning involves the Tokyo Metropolitan Government (TMG), individual and community
  • A disaster plan which is due to be completed in 2017 was revised- Aims to make a disaster resistant city
    • Priority is given to making as many buildings as possible earthquake resistant
    • High-density wooden housing are being fire-proofed to reduce risk
    • Roads, express ways, bridges, coastlines and essential infrastructure are being strengthened
    • Important buildings such as government offices, police stations, fire service offices and hospitals are being strengthened
    • Plan identifies hundreds of open spaces where people can assemble for refuge sites which will be provided with emergency supplies
    • People will also be accommodated in 3000 public shelters (e.g. schools) with a planned capacity of 4.27 million
    • Rapid recovery and long-term reconstruction will be vital after the earthquake so the plan includes reconstruction plans, restrictions on building rights and the formation of recovery organisations
    • The TMG plan plans to build a ‘strong society’ against earthquakes by raising public awareness of earthquake hazards.
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=waves set off by submarine earthquakes, landslides into water, slumps and volcanic explosions under water

Most tsunamis consist of a series of waves generated by the rapid movement of the seabed. They differ from wind generated waves in a number of ways:

  • Wavelength is very long- commonly 150-250km but can by up to 1000km
  • Velocities may reach 700-800km per hour
  • They have a low amplitude: 0.5-5.0 metres
  • They have a long wave period: 15-60+ minutes
  • The wave height is shallow in relation to the wavelength, so tsunamis are often undetectable in open oceans

As a tsunami approaches the coastline, its speed and wavelength decrease rapidly, but the time between waves remains the same, thus wave height increases

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Hazards of volcanoes


  • Landslides, fire, mudflows, rock bombs, lava flows, gas, heat, ash, pyroclastic flows


  • tsunamis, crop failure, famine, disease
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Causes of volcanic activity

Found at three types of location, convergent margins, divergent margins and hot spots

  • Subduction occurs at convergent margins as one tectonic plate underthrusts the other and descends into the upper mantle. Volcanoes associated with subduction zones are andesitic, explosive and extremely hazardous
    • E.g. the North American plate subducting beneath the Caribbean plate forming volcanoes like Soufriere Hills on Montserrat.
  • At divergent margins along mid-ocean ridges and continental locals like east Africa's Great Rift Valley. Tension stretches the crust and creates a series of parallel faults causing rifting and this reduction in pressure allows molten rock to flow to the surface
  • Eruptions generally non-explosive or effusive and comprise basalt lava
    • E.g. formation of volcanic islands like Iceland
  • Effusive eruptions also take place at hot spots like Hawaii, where rising plumes of hot magma have punched a hole through the crust
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Impacts of volcanoes

The scale of the impact is crucial


  • destruction, casualties, landslides, fires


  • disease, loss of infrastructure, housing and jobs, food and water shortages


  • cost of recovery, loss of crops, damage to mines/industries, trade
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Impacts of volcanic eruptions

The primary hazards of volcanic eruptions are lava flows, ashfalls, pyroclastic flows, lahars and poisonous gases

Lava flows

  • Streams of molten and semi molten magma erupted from a volcano
  • Fairly localised, rarely a threat to life but destroys everything in its path
  • Lava flows that are non-viscous and not confined in valleys can spread out to form vast lava fields. E.g. loss of villages in Hawaii

Volcanic ash

  • More widespread- localised ashfalls and accumulations of Scoria can cause buildings to collapse, farmland can be buried under several metres of ash
  • Ash from major volcanic eruptions is pumped high into the atmosphere and within a few weeks completely encircles the planet and can even lower averal global temperatures
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Impacts of volcanic eruptions

Pyroclastic flows

  • Ground hugging avalanches of hot ash, pumice, rock fragments and gas
  • Temperature within pyroclastic flows may exceed 500'C and can travel at over 100kmh
  • They destroy everything in their path and can even move across sea and lake surfaces


  • Fast-moving mudflows caused by run-off from heavy rain and/or snow transporting large volumes of loose volcanic ash
  • Follow a well defined path along river valleys and because of their spped (up to 50kmh) are particularly deadly
  • In 1985, lahars killed 23,000 people in the eruption of Nevado del Ruiz in Colombia

Toxic gas

  • Emissions highly dangerous and threaten human health, livestock, crops and forests
  • Acidify rivers and lakes
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Factors affecting the impact of a volcano

  • The properties of the lava
    • Runny basalric lava eruptions such as Mauna Loa, Hawaii, result in more continuous, less violent eruptions and generally less loss of life
    • Explosive eruptions such as Mount St Helens result in greater destruction of the environment, local economy and potential loss of life
  • Population density
    • greater impact in areas of high population density
    • e.g. impact of an eruption of Vesuvius is much creted than that of Mount St Helens
  • The size of the eruption
    • Eruption of Krakatoa in 1883 was heard thousands of miles away whereas the small-scale eruptions and lave flows of Etna 2000 did not result in any loss of life
    • The potential impact of 'supervolcano' located under Yellowstone National Park in the USA is unknown but likely to be considerable
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Factors affecting the impact of a volcano

  • Frequency of eruptions
    • eruptions that occur frequently like in Hawaii reduce pressure within the magma chamber so an explosive eruption is unlikely
    • Where there is a big build-up of pressure such as Mount St Helens the likelihood of an explosive eruption increases
  • Monitoring and prediction
    • The Nyiragongo volcano in the Demoncratic Republic of Congo was not predicted whereas the eruption of Mount St Helens
    • The ongoing monitoring of the Soufriere volcano means that future loss of life is low
  • Some people are more at risk
    • Some are more at risk to the main secondary hazards of volcanoes
  • Attempts to manage the hazards
    • Eldfell volcano impact was reduced by spraying the advancing lava flows with sea water
    • Etna, diversion channels have been dug to divert lava flows form settlements
    • Monitoring and prediction may suggest an imminent eruption
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Emergency aid

  • rescue, tents, medicines, food, water, often involving the military and charities

Short-term aid

  • rehousing people, rebuilding hospitals, repairing infrastructure

Long-term aid

  • moving population, improving warning systems, emergency planning
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Short term responses to volcanic disasters

  • Most volcanic eruptions can be predicted days or even weeks in advance
  • Immediate response is to evacuate the population
    • in 2008, the Chaiten volcano in southern Chile erupted and the entire population (c4,000) was evacuated by sea within 24 hours
    • Following the eruption of the Soufriere Hills Volcano in Montserrat in 1995, the southern part of the island was declared an exclusion zone and the population evacuated to safe areas in the north
  • Following the Nyriagongo eruption in 2002, thousands of refugees were housed in temporary camps
    • Poor sanitation and overcrowding polluted drinking water from Lake Kivu and threatened a cholera outbreak
    • Swift action taken by NGOs to provide chlorinated drinking water contained the disease
    • Aid agencies also provided immunisation and distributed emergency food rations
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Long term response to volcanic disasters

  • Attention and resources focus on normalising the economic and social systems by restoring infrastructure, services and employment
  • The volcanic eruptions that devestated Montserrat between 1995 and 1997 were followed by a period of reconstruction
    • Emergency shelters were replaced by low-cost permenant housing and many islanders were resettled
    • The construction of a new airport helped to rebuild the island's tourism industry
    • In future, a new observatory staffed by foreign scientists will monitor the Soufriere Hills volcano
    • Several NGOs have been involved in the long-term reconstruction of Montserrat's economy and infrastructure, and the UK and EU have invested around £200 million on regeneration projects
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Reducing the impact of volcanic hazards

  • Observation of volcanoes and monitoring their behaviour can give early warning of impending eruptoiona
  • Seismic activity increases before an eruption as magma forces its way to the surface and fractures rocks inside the volcano. Monitored by networks of seismometers
  • Gravity increases as the magma chamber fills and this change is monitored
  • Gases emitted by fumaroles are also sampled
    • increased levels of sulphur dioxide and hydrogen chloride often signal an imminent eruption
  • Ground deformation (inflation) is measured
  • Diverting lava flows has been successful e.g. At Heimacy in Iceland in 1973 the lava flow was halted by spraying it with sea water
  • Hazard mapping is useful for predicting the flow paths and mudflows. Sediments deposited by previous lahars can be mapped to show the areas of greatest risk
  • Hazard warnings are broadcast to local populations and evacuation is ordered
  • Lahar detection systems around Mount Rainier in Washington state trugger automatic alerts and managers implement emergency evacuation for communities up to 100km from the volcano
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Exposure to volcanic hazards

  • Exposure refers to the scale and violence of an eruption and to the density of population living near the volcano
  • Andestitic volcanoes like Mount St Helens are explosive presenting much greater threat than effusive eruptions from volcanoes like Kilauea (Hawaii)
    • When Mount Pelee, an andesitic volcano on the island of Martinique erupted in 1902, pyroclastic flows killed 30,000 in the capital, Saint Pierre
    • In contrast, the explosive eruption of Mount St Helens in Washington state in 1980 killed just 57 people
    • The difference is due to population distribution- region around Mount St Helens is mainly forested and sparsely populated so hazard exposure was much lower than near Mount Pelee
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Vulnerability to volcanic hazards

  • Impacts are mitigated in rich countries such as Italy, Japan and Iceland, where volcanoes can be monitored, evacuation organised and resources for emergency relief and reconstruction programmes mobilised
  • This level of preparedness is notably absent in most developing countries resulting in higher death and injury tolls
  • In the post-disaster period there is also greater threats from disease, polluted water supplies and inadequate medical care in developing countries
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Impacts on human activities vary over time according to:

  • Level of development/technology
  • Recurrence interval and frequency of event
  • Time of day, season and year
  • Build-up of events - warning interval
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Impacts on human activities vary with location according to:

  • Distance from plate margin, river, slope etc
  • Ability to predict or forecast (level of technology)
  • Population density, distribution, level of perception and education
  • Level of communications - warning systems
  • Mobility of population
  • Highland versus lowland
  • Level of development- building type, ability to warn/evacuate
  • Remoteness
  • Type and size (magnitude) of hazard or mix of hazards
  • Geology and rock structure - weak rock is more vulnerable
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Differences between floods, earthquakes and volcan


  • Possible to predict? Quite possible e.g. by checking rainfall level
  • Known hazard? usually a history of flooding
  • Warning- usually some warning - up to a few days
  • Scale? vary from local to regional
  • Duration? a few days
  • Impacts? variable- depends on size of river
  • Area of impacts- from local to regional
  • Short term- deaths, destruction, disruption
  • Long term- Few long-term problems as floods recede and can rebuild, Long-term gain as floods leave fertile soil
  • Relative impact in deaths per million from 1990-1999:
    • Asia: 14
    • Africa: 10
    • North America: 1
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Differences between floods, earthquakes and volcan


  • Possible to predict? Virtually impossible- seismic gap idea
  • Known Hazard? not always and not always located
  • Warning? often no warning
  • Scale? Regional
  • Duration? Seconds
  • Impacts? Severe but depends on strength and depth of quake
  • Area of impacts- from local to regional
  • Short term- Deaths, destruction, disruption
  • Long term- lot of medium term problems (reconstruction) but few long-term problems
  • Relative impact in deaths per million from 1990-1999:
    • Asia: 23
    • Africa: 2
    • North America: 1
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Differences between floods, earthquakes and volcan

  • Possible to predict? fairly good if monitoring equipment in place
  • Known hazard? Usually obvious, cone-shaped mountain etc
  • Warning? Usually precursor events e.g. swelling, earthquakes etc
  • Scale? Local to regional
  • Duration? Days to years
  • Impacts? Variable- depends on scale of eruption and type of volcanic material
  • Area of impacts- Local to global (ash cloud)
  • Short term- Few, as can usually evacuate people, Destruction
  • Long term- Problems for years as landscape is changed, but eventually nature and economy recover
  • Relative impact in deaths per million from 1990 to 1999:
    • Asia: 0.00005
    • Africa: 0.000003
    • North America: 0.000002
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Hazard management and risk assessment

Ways of managing the consequences

  • Modifying the hazard event, through building design, building location and emergency procedures
  • Improved forecasting and warning 
  • Sharing the cost of loss, through insurance or disaster relief

Risk assessment involves consideration of:

  • The likely size and range of natural processes involved
  • The extent of the impacts
  • Ways in which the impacts can be reduced

Most risk assessment involves a statistical likelihood of the size and impact of the event

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Stages in reducing impacts- management strategies

  • Prediction - based on past events (hazard mapping), monitoring of gas/pressure etc, tiltmeters, chemical sensors, ultrasound
  • Risk assessment- calculate size and extent of risk, inform population, building design, location of vital buildings/facilities, e.g. power stations
  • Prior prevention- lubricate fault lines, afforest slopes, raise and strengthen levees, move vulnerable population and livestock, establish exclusion zones
  • Planning- individual, local authority, state or central
  • Preparation- education, contingency plans
  • Warnings- use of media, communications level of threat, planned evacuations
  • During prevention- dam or divert lava flows, flood volcanic vents, stabilise slopes, divert rivers
  • Response- search and rescue, emergency aid, insurance, state or international aid for rescue, relocation
  • Recovery- clearance of debris, state aid for reconstruction, tax relief
  • Redevelopment- long-term plans
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The hazard management cycle

Pre-disaster planning:

  • Prevention: action to reduce severity of the impact
  • Mitigation: action to reduce property damage and minimise economic impacts
  • Prepardness: action to increase speed and efficiency of response

Post-disaster responses

  • Response: effectiveness depends on education, training and experience of emergency response teams
  • Recovery: action to assist communities to return to pre-disaster conditions
  • Redevelopment: action to manage economic losses; there should be a long-term link between natural hazard and national economic activities
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Physical adjustments to reduce hazards

  • Altering characteristics of hazards e.g. in Iceland, Heimaey lava flow halted by spraying with seawater
  • Building to withstand hazards e.g. earthquake-proof structures in California
  • Constructing diversions, barriers etc, e.g. on Mount Etna in 2001 to divert lava
  • Moving people to less vulnerable locations e.g. evacuating them from Mount Pinatubo
  • Preventing where and when a hazard might occur
  • Identifying (mapping) and avoiding sites where hazards are likely to occur
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Social adjustments to reduce hazards

  • Public awareness via education, media etc e.g. Japan's annual earthquake day
  • Evacuation plans and preparations e.g. California's household regulations, in case of an earthquake
  • Greater community involvement to reduce vulnerability e.g. following kashmir earthquake
  • Issuing early warnings of imminent hazards
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Political adjustments to reduce hazards

  • Evacuation plans, services and emergency centres e.g. these were increased in the Indian Ocean following the 2004 tsunami
  • Land use zoning and restrictions e.g. along the River Avon in the West Midlands to reduce flood risk
  • Issuing early warnings and co-ordinnating emergency services e.g. in the 2007 Tewskesbury floods
  • Spreading economic loss through insurance, grants, etc e.g. UK government following Montserrat eruption
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Managing earth hazards

Managing earth hazards effectively depends upon:

  • The nature of the hazard - its severity, scale, frequency, any build-up signs etc
  • The level of preparation and awareness of risks
  • The nature of the area- its structure, geology, relief, climate, etc
  • The level of development- research, technology available, communications, warnings etc
  • Political organisation- co-ordination, priority, existence of emergency plans, etc
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Mr A Gibson


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Megan Stewart


I love all you're geography revision cards for AS and now A2!:-D amazing!

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