Hazards

• What is a hazard

  A ​hazard is a potential threat to ​human life ​and ​property caused by an event. Hazards can be human caused or occur naturally (natural hazards). An event will only become a ​hazard when it is a threat to ​people​.
• Dregg's Model


  Dregg's model states that there are two factors, size of the hazard and the vulnerability of the population.

  
  

  Risk: Exposure of people to a hazardous event which may present a potential threat to people or their possessions, including buildings and structures.

  
  

  Vulnerability: The degree which you are susceptible to a hazard.

  
• Geophysical hazards


  Hazards caused by earths processes. They can be caused by internal earth processes of tectonic activity, or by external processes of geomorphic origin including mass movement.

  
• Hydrological hazards


  Caused by the occurrence, movement and distribution of surface and underground water. eg. floods

  
• Atmospheric hazards


  hazards caused by atmospheric processes and the conditions created because of these, such as weather systems eg. hurricanes.

  
• Hazard perception


  People have different ​viewpoints of how ​dangerous hazards are and what ​risk ​they pose. These perceptions are dependent on ​lifestyle factors which include ​economic ​and ​cultural ​elements. Note that these are the economic and cultural factors of ​individual people rather than an entire population's views. How they perceive it determines how they will respond to it.
• HP (Wealth)


  The financial situation of a person will affect how they ​perceive hazards. Wealthier people may perceive a hazard to be ​smaller ​as they are less ​vulnerable (e.g. they have the ability to evacuate with transport access, build stronger houses etc.) However, wealthier people may also view a risk as ​greater ​as there is more risk of ​property damage ​and ​financial loss ​than someone less wealthy.
• HP(Experience)


  Someone who has ​experienced more hazards ​may be more likely to understand the ​full effects ​of a hazard. There are also studies suggesting that people who have experienced hazards are likely to have an ​optimistic ​and ​unrealistic outlook on future hazards
• HP (religion and beliefs)


  Some may view hazards as put there by ​God ​for a reason, or being part of the ​natural cycle of life etc. so may not perceive them to be negative. In contrast, those who believe strongly in ​environmental conservation ​may perceive hazards to be a huge risk to the natural environment, especially hazards that are becoming more frequent due to global warming.
• HP (Education)


  A person who is more educated about hazards may understand their full ​effects ​on people and how ​devastating they can be and have been in the past. Those who are less educated may not understand the full extent of a hazard and may not evacuate etc.
• Factors affecting risk of a hazard

  - Magnitude of the event - the larger the event the more people at risk.

  - Frequency - If people are used to it, the risk is less

  - Climate change - more regular, more severe storms in tropical areas. More rain = more flooding. Drought in the areas due to less rain.

  - Urbanisation
• Human Responses to Hazards

  1) Fatalism - a passive response - The viewpoint that hazards are ​uncontrollable natural events, and any losses should be ​accepted​ as there is nothing that can be done to stop them.

  2) Adaptation - Attempting to live with hazards by adjusting ​lifestyle choices so that vulnerability to the hazard is lessened (e.g. earthquake proof houses).

  3) Risk sharing - A form of ​community preparedness​, whereby the community ​shares the risk ​posed by a natural hazard and ​invests collectively to mitigate the impacts of ​future hazards​.
• Fear


  When the fear of the hazard becomes too great, people move away.
• Why people choose to live in hazardous areas

  1) Hazard events are unpredictable - frequency, magnitude, location, duration.

  2) Lack of alternatives - Growing population, marginal areas, urban growth, levels of wealth

  3) The benefits may outweigh the costs - fertile soil/flat land eg. floodplains, location /jobs eg. California
• Aspects of Hazards and How They Affect Human Responses (Incidence)


  - ​Frequency of a hazard. This is not affected by the strength of a hazard, it is just how often a hazard occurs.

  - Low incidence hazards ​may be ​harder to predict ​and have less ​management strategies put in place, meaning the hazard could be more catastrophic when it does eventually occur.
• Aspects of Hazards and How They Affect Human Responses (Distribution)


  - Where hazards ​occur ​geographically.

  - Areas of high hazard distribution are likely to have a lot of management strategies, and those living there will be ​adapted to the hazardous landscape because it dominates the area more so than in places with low hazard distribution.
• Aspects of Hazards and How They Affect Human Responses (Intensity)


  - ​The​ power​ of a hazard i.e. how strong it is and how damaging the effects are
• Aspects of Hazards and How They Affect Human Responses (Magnitude)

  - The size of the hazard

  - High magnitude​, high intensity ​hazards will have ​worse effects​, meaning they will require more management​, e.g. more mitigation strategies will be needed to lessen the effects and ensure a relatively normal life can be carried out after the hazard.
• The park model


  - The park model shows the different phases of response to a hazard:

  1) Pre disaster - before the event, the situation is normal.

  2) Disruption - During and directly after the hazard event occurs, there is destruction of property, loss of life etc. before people begin to respond.

  3) Relief - In the aftermath of the event, rescue efforts focus on saving people and preventing further damage.

  4) Rehabilitation - Once the immediate impacts are under control, people start to resolve longer - term problems, eg. providing temporary shelter and aid for those affected.

  5) Reconstruction - This involves rebuilding permanent houses, infrastructure etc. This results in one of two outcomes:

  - If buildings are built to the same standard as before, the area returns to normal.

  - If buildings are built to a higher standard than before, the area improves so vulnerability decreases.

  
• Why is the park model useful?

  - It shows how responses progress during a disaster, which may help planners predict which resources will be needed at each stage. The model can also help planners to prepare for future hazard events. For example, the reconstruction phase of the model shows that conditions can be improved after a disaster (eg.installing warning systems / designing hazard resistant buildings) which will help to mitigate the impacts of future hazard events.
• Hazard management cycle


  1) Mitigation - Aims to minimise the impacts of future disasters. eg. building flood defences or adding fire resistant roofs to buildings in areas prone to volcanic eruptions. Mitigation can happen before a hazard occurs or afterwards. when an area is recovering.

  
  

  2) Preparedness - Planning how to respond to a hazard eg. making sure there are warning systems in place or educating people about how to evacuate safely.

  
  

  3) Response - How people react when a disaster occurs, eg. emergency services rescuing trapped people or evacuating people from the danger zone.

  
  

  4) Recovery - This is about getting the affected area back to normal eg. repairing or rebuilding houses and restoring services such as medical care and electricity.

  
• Structure of the earth

  Inner core, outer core, mantle, athenosphere, lithosphere, crust

  
• Inner core


  - Solid ball of iron/nickel

  - Very hot due to ​pressure​ ​and radioactive decay​ ​(

  - This heat is responsible for Earth's internal energy​, and it spreads throughout

  
• Outer core


  - Semi - molten and contains lots of iron and Nickel.
• The mantle


  - Widest section of the earth - it is 2900km thick.

  - The part of the mantle that is nearest to the core is quite rigid.

  - The layer above this, called the asthenosphere, is semi - molten.

  - And the very top part is very rigid.
• The lithosphere


  Together, the crust and the upper mantle are known as the lithosphere. It is the zone that the tectonic plates are formed.

  
• Crust:


  - The outermost layer.

  - There are 2 types continental and oceanic
• Continental crust


  - Thickness of 30-70km

  - Over 1500 million years old

  - Less dense

  - Mainly granite, silicon, aluminium and oxygen.

  
• Oceanic crust


  - Thickness of 6-10km

  - Less than 200 million Years old

  - More dense
• tHE THEORY of plate tectonics

  - It was developed by Wegner in the 1960s, who gathered evidence to suggest that just one giant continent (Pangea) existed about 300 million years ago.

  
  

  - He believed that is later split into 2 smaller continents (Laurasia and Gondwanaland)

  
  

  - Today's continents were then formed from further splitting of these 2 masses. Wegner called his ideas the theory of continental drift.
• Convection currents


  1) The earths mantle is closest to the core, so lower parts of the asthenosphere heat up, become less dense and slowly rise.

  
  

  2) As they move towards the top of the asthenosphere they cool down, become more dense and slowly sink.

  
  

  3) These circular movements of semi - molten rock are called convection currents.

  
  

  4) They create drag on the base of the tectonic plates, causing them to move.

  
• Ridge pull


  1) At constructive plate margins, magman rises to the surface and forms new crust, which is very hot. It heats the surrounding rocks, which expand and rise above the surface of the surrounding crust, forming a slope.

  
  

  2) The new crust cools and becomes denser. Gravity causes the denser rock to move downslope, away from the plate margin.

  
  

  3) This puts pressure on the tectonic plates, causing them to move apart.

  
• Slab pull


  1) At destructive plate margins, the denser crust is forced under less dense crust.

  
  

  2) The sinking of the plate edge pulls the rest of the plate towards the boundary.

  
• Sea floor spreading


  New land​ forming on the ocean floor by lava filling the gaps is known as​ ​sea floor spreading​ ​(as the floor spreads and gets wider).

  
• Constructive plate margins


  1) Where 2 plates are moving apart (diverging)

  2) The mantle is under pressure from the plates above. When they move apart, the pressure is released at the margin.

  3) The release of pressure causes the mantle to melt producing magma.

  4) The magma is less dense than the plate above, so it rises and can erupt to form a volcano.

  5) The plates don't move in a uniform way - some parts move faster than others. This causes pressure to build up. When the pressure becomes too much the plates crack, making a fault line and causing an earthquake.

  
• Constructive plate margins (Ocean ridge)


  1) Where diverging plates are underwater, an ocean ridge forms. eg. The mid - Atlantic ridge, where the eurasian plate and North American plate are moving apart.

  2) Underwater volcanoes erupt along mid - ocean ridges and they can build - up to be above sea level. eg Iceland.

  
• Constructive plate margins (Rift valleys)

  1) When plates diverge beneath land, rising magma causes the continental crust to bulge and fracture, forming fault lines.

  2) As the plates keep moving apart, the crust between parallel faults drop down to form a Rift Valley. eg. East African rift system is a series of rift valleys that stretches from Mozambique to the Red Sea about 4000km.

  
  

  3) Volcanoes are found around rift valleys. eg. Mount Kenya

  
• Destructive plate boundaries (oceanic and continental)

  1) Denser oceanic plate ​subducts ​below the continental. The plate subducting leaves a deep ocean trench​.

  2) Fold mountains ​occur when sediment is pushed upwards during subduction.

  3) The oceanic crust is melted as it subducts into the asthenosphere.

  4) The magma is less dense than the continental crust above and will rise back to the surface to form volcanoes.

  5) as one plate moves under another they can get stuck. This causes pressure to build. When the pressure becomes too much the plates jerk past each other and cause an earthquake.

  
• Destructive plate boundaries (oceanic and oceanic)


  1) Most of the same processes occur where 2 plates of oceanic crust are moving towards each other - and the denser of the two will be subjected, forming a deep sea trench and triggering earthquakes and volcanic eruptions.

  2) Volcanic eruptions that take place underwater create island arcs.

  
• Destructive plate boundaries (Continental and continental)

  1) Neither are subducted so there aren't any volcanoes - but the pressure that builds up between them can cause earthquakes.

  2) Fold mountains eg. Himalayans