Hazards: Seismic events (earthquakes), volcanic activity and tropical storms
A natural hazard = perceived event that threatens both life and property
- Often result in disasters + cause some loss of life/damage to the built environment
Risks = increased as humans build shanty towns on unstable slopes, urbanise volcanic areas etc
- Exacerbated by failing to recognise a potential hazard and not act accordingly
Natural hazards often have similar characteristics:
1. Origins are clear and the effects they produce are distinctive
2. Most only allow a short warning before the event
3. Exposure to the risk is involuntary
4. Most losses to life and damage to property occur shortly after the event although other
effects can be felt in communities long after that
5. The scale and intensity require emergency response
Risk and Vulnerability:
Vulnerability: The potential for loss –vary geographically/over time + among different social groups
- A hazard can have widely varying impacts in different parts of the community (similar sized
hazards can have different impacts depending where they are in the world)
- Richer people/countries can protect themselves better by building sea defences, earthquake
resistant buildings etc
The perception of natural hazards:
Perception: This is the way in which an individual/group views the threat of a hazard event –
determining the course of action taken
Perception is influenced by many factors including:
- Socio-economic factors
- Level of education
- Religion/ethnic/cultural background
- Family/marital status
- Past experience
- Values/personality/expectations
Difference in perception - between people of differing levels of economic development
- Wealthier areas sense that = better prepared = better at withstanding
- Helplessness sense in deprived areas
Hazards are perceived in the following ways:
Fatalism (acceptance): Hazards are natural events which come with living in an area – action is direct
and concerned with safety – losses are inevitable, and people remain where they are
Adaptation: People prepare for and therefore survive the hazard by
prediction/prevention/protection
Fear: The perception of a hazard is such that people feel vulnerable to an event that they are no
longer able to face living in the area and move away to regions that are unaffected
,Management of natural hazards:
Key Terms:
Risk sharing/community preparedness: Involves prearranged measures that aim to reduce the loss
of life and property damage through public education and awareness programmes etc
Frequency: The distribution of a hazard through time
Integrated risk management: The process of considering the social, economic and political factors
involved in risk analysis
Magnitude: The assessment of the size of the impact of a hazard event
Prediction: The ability to give warnings so that action can be taken to reduce the impact of hazard
events
Primary effects: The effects of a hazard event that result directly from the event
Resilience: The sustained ability of individuals or communities to be able to utilise available
resources to respond to, withstand and recover from the effects of a natural hazard
Secondary effects: Effects that result from the primary ones (e.g an earthquake secondary effects
are tsunamis and fires)
- Community resilience = sustained ability to utilise available resources to respond to,
withstand and recover from the effects of natural hazards
- Hazards are best combated with the use of an integrated risk management
People and organisations try and manage natural hazards in the following ways:
Prediction: It may be possible to give warnings to enable action – improved monitoring can be used
to predict and give warnings – National Hurricane Centre
Prevention: For natural hazards this is generally unrealistic
Protection: Aim to protect people, their possessions and the built environment from the impact of
the event – usually involves modifications such as earthquake resistant buildings or sea walls
- Community preparedness – prearranged measures that reduce the loss of life and property
damage by education programmes, shelters and provision of emergency supplies
All this can be shown through the
disaster/risk management cycle
- Appropriate actions at all
points of the cycle lead to
greater preparedness, better
warnings and reduced
vulnerability
- One of the main goals is the
promotion of sustainable
livelihoods – this gives
people greater capacity to
deal with disasters and their
recovery is quicker
,The Disaster/response curve: To show hazards can have varying impacts over time,
Relief: Medical, rescue services and
overall care delivered – from this
quality of life slowly increases – few
hours to days
Rehab: People try to return to normal,
providing food, water and shelter to
those effected – few days to weeks
Reconstruction: Infrastructure
property are reconstructed - people
learn how to respond to the next
event better
Events can have different impacts – the differences in the impact depends on the type of hazard,
degree of readiness, speed of relief effort and nature of recovery and rebuilding
Distribution, frequency and magnitude:
Distribution: The spatial coverage–area affected by a single event:
localised/regional/national/international
- Earthquakes/volcanic eruptions associated with tectonic boundaries whereas tropical
cyclones occur between 5 and 25 north/south of equator
Frequency: The distribution of the hazard through time
Magnitude: Assesses the size of the impact
The theory of plate tectonics:
- Core: Dense rocks – iron nickel – solid inner and molten outer – temp over 5000 degrees
- Mantle: Molten + semi molten rocks containing lighter elements oxygen and silicon
- Crust: Even lighter - oxygen silicon aluminium potassium and sodium - varies thickness –
under oceans 6-10km under continents 30-40km under mountain ranges = 70km
- Lithosphere: Core + rigid upper mantle - 80-90km thick –divided into plates
- Asthenosphere: Lies beneath this layer and is semi-molten which plates move/float on
- Focus: Point at which the pressure is released
- Epicentre: Point immediately above the focus on the Earth’s surface
Difference between continental and oceanic plates:
Continental Oceanic
Thickness 30-70km 6-10km
Age Over 1500 million Less than 200mil
Density 2.6 - lighter 3.0
Composition Granite, silicon, aluminium, Basalt, silicon, magnesium,
oxygen oxygen
Landforms associated with plate movements:
, Ocean ridges: Formed when plates move apart in oceanic areas – space between the plates is filled
with basaltic lava – volcanic activity occurs - Surtsey in Iceland
Rift valleys: Plates moving apart - continental areas – brittle crust fractures as sections move apart –
areas of crust drop - parallel faults forming the valley – area between two valleys forms an
upstanding block (horst)
Deep sea trenches: Oceanic v continental meet – oceanic subducts – forms deep part of the ocean–
Nazca plate subducted under South American plate forming the Peru- Chile trench
Island arcs: During subduction descending plate encounters hotter surroundings + friction heat –
plate begins to melt – material less dense than asthenosphere begins to rise towards surface as
plutons of magma – when they reach surface form composite volcanoes – known as island arcs
Plate Margins:
The crust of the plate margin composed of hot rocks, rise and become less dense – ocean floor is
highest + closest to the ocean surface at plate margins
- Crust spreads away from margin - cools and subsides – ocean becomes deeper the further
away from the margin
Constructive plate boundaries - plates moving away - above rising convection currents.
- Rising current pushes up - bottom of lithosphere, lifting it - flowing laterally beneath it
- Lateral flow causes plate material above to be dragged along in direction of flow - crest of
the uplift - overlying plate is stretched thin, breaks + pulls apart
- Continental features such as the East African Rift Valley
Effects - divergent boundary - oceanic plates: a submarine mountain range such as the Mid-Atlantic
Ridge; volcanic activity in the form of fissure eruptions; shallow earthquake activity; creation of new
seafloor and a widening ocean basin.
- When they move apart the
basaltic lava erupts from
parallel fissures to from ridges
Convergent plate boundaries:
Lithospheric plates moving towards - plate collisions produce earthquakes, volcanic activity, and
crustal deformation
Continental + oceanic plates collide, the thinner/more dense oceanic plate overridden by the thicker
and less dense continental plate.
- oceanic plate forced down into the mantle in a process known as "subduction." - oceanic
plate descends, forced into higher temperature environments - 160 km, materials in the
subducting plate begin to approach their melting temperatures and a process of partial
melting begins.
Partial melting produces magma chambers above the subducting oceanic plate.
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