Hazards

• Hazard


  An event which threatens human life or property
• Disaster


  An event that causes significant loss or impact to life or economy
• Natural phenomena can be exacerbated or produced by human's actions such as the increased frequency of storm surges
• Categories of natural events


  • Geophysical
  • Hydrological
  • Atmospheric
• Geophysical events


  Caused by geological or geomorphological processes in lithosphere, earthquakes, volcanos, landslides, tsunamis
• Hydrological events


  Caused by the water process, flash floods, storm surges and flooding, avalanches
• Atmospheric events


  Caused by the atmospheric process, tornados, bush fires, tropical storms and droughts
• Perceptions of hazards


  • Acceptance/Fatalism
  • Fear
  • Adaptation
• Acceptance/Fatalism


  The perception that hazard events are inevitable and part of life, events are random and humanity can only respond
• Fear


  People believe they are vulnerable to natural events, they perceive locations as dangerous because of the impacts and they may choose to avoid locations such as hotspots
• Adaptation


  People and emergency planners recognise that through using models such as the hazard management cycle and data they can reduce impact of hazards making locations safer
• Degg model


  Shows how a hazard impacts a vulnerable population and how this can be categorised as a disaster
• Significant loss categorises a natural hazard as a disaster, the definitions any vary but usually losses mean 10+ deaths and over hundred affected and one million in economic loss
• Some communities have a higher capacity to cope with hazardous events due to high resilience and low vulnerability such as having emergency plans
• Vulnerability


  Describes the risk exposure to hazards combined with the inability to cope
• Risk


  Probability of socio-economic impacts
• Park model


  Used to demonstrate the impact of hazards, and the impact that they have to an area's quality of life. It shows how a typical and effective human response to natural events, it can be used by emergency planners and services to plan for a response such as relief stages the emergency services may need to provide emergency care and afterwards it takes time to rehabilitate
• Hazard management cycle


  The risk management cycles are used before and after a natural hazard, its aim is to minimise the damage and prevent a disaster. There is four stages two pre and two post. A hazard occurs before a response, and the model is used by governments and emergency planners to reduce the socio-economic impacts by responding.
• Planning


  Ensuring that the public and emergency services have prepared responses and reactions, such as doing drills, training emergency services also offering education into impacts of hazards to alter perceptions
• Response


  Immediately after search and rescue efforts occur, it also focuses on the immediate needs of a population such as providing provisions of food and having a medical response. Response may also include evacuating areas
• Recovery


  Once the event has occurred there needs to be long term responses to recover. Such as clean ups and rebuilding
• Mitigation


  Pre-event stage 3 after a place has recovered it is important to plan and do more than recover but adapt to reduce the impacts of another hazard, examples may be building to a better quality using better materials, architecture or engineering. Looking back at the previous hazard and reacting to reduce future impacts
• Wegner's continental drift theory


  Produced by scientist Wegner in the 1912s, claimed that at one point in history there was no separate continents and there was the prehistoric supercontinent Pangaea which over million years had drifted apart to form the seven continents
• Wegner's theory was controversial and was only confirmed by his discovery of fossils of animals such as the Mesosaurus which wouldn't have been able to swim in modern oceans
• Wegner's evidence also includes rock and mountain correlation and also the obvious similarities and fit of the coastlines
• Mid Atlantic ridge


  An ocean ridge, a form of mountains covering most of the ocean floor, the rocks found in the mid Atlantic ridge are relatively new, volcanic showing that oceanic crust is being produced
• Palaeomagnetism


  The theory suggests that the earth's magnetic poles switch and when this occurs basalt, minerals but mainly iron would split causing magnetic stripping, this has been found at the mid-Atlantic ridge and provides evidence that the continents are drifting
• Hess - Sea floor spreading

  The sea floor is spreading at an estimated 5 cm annually which is confirmed by palaeomagnetism. Hess found that at the oldest rocks would be found closest the USA and the newest rock would be formed at the mid Atlantic ridge, oceanic crust is being formed continuously
• The three theories (Mid Atlantic ridge, Palaeomagnetism, Hess - Sea floor spreading) are interlinked and provide evidence for the existence of Wegner's theory – leading to the plate tectonic theory
• Types of plate boundaries

  • Convergent destructive (oceanic and oceanic, oceanic and continental, continental and continental)
  • Conservative (just earthquakes)
  • Divergent (constructive)
• Convergent destructive - oceanic and oceanic

  The denser plate is subducted, pressure causes earthquakes and highly explosive underwater volcanos, can lead to the formation of volcanic island arcs
• Convergent destructive - oceanic and continental

  The oceanic plate is subducted below the continental, producing a deep ocean trench, the oceanic plate melts in the Benioff zone forming explosive and high-pressure composite cone volcanic eruptions, fold mountains also occur
• Convergent destructive - continental and continental

  Neither plate is subducted, pressure builds up in the collision zone leading to uplifting and forming fold mountains, no volcanic activity but shallow focused earthquakes occur
• Conservative plate boundaries


  Plates move alongside each other at different speeds or in different directions, no plates are destroyed so no volcanic activity or formation of new crust or landforms, intense pressure builds up due to frictional stresses resulting in deadly high magnitude shallow focused earthquakes
• Divergent plate boundaries

  Ridge push occurs as oceanic lithosphere is formed due to magma cooling into crust, as it cools it is pushed away from the ridge causing slab pull, this causes divergent oceanic plate boundaries to form and sea floor spreading, can form mid-oceanic ridges and shield volcanoes
• Continental divergence


  As continental plates diverge the lithosphere stretches and eventually collapses into deep valleys, forming rift valleys such as the Great African Rift Valley
• Hotspots/Magma plumes


  Stationary isolated slender long columns that originate deep in the mantle due to radioactive decay becoming concentrated, cause magma to rise vertically, form islands such as Hawaii or the Canaries as plate motion causes the hotspot to move away
• Hotspots provide evidence against the plate tectonic theory but show the existence of convection currents, however most of the earth's tectonic activity occurs on boundaries in linear patterns such as the Pacific Ring of Fire