Hazards

• How personality impacts peoples perception of hazards


  Some people fear hazards and others may find them exciting.
• How past experience impacts peoples perception of hazards


  If they have had a bad experience previously they may perceive the risk to be larger and have a greater understanding of the full effects of a hazard. However, there are also studies suggesting that people who have experienced hazards are likely to have an ​optimistic ​and ​unrealistic outlook.
• How mobility impacts peoples perception of hazards


  Those that live in a ​secluded location​, or if they have a disability or ​illness​ that may prevent them from easily leaving an area quickly, may feel more at risk.
• How religion impacts peoples perception of hazards


  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. 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.
• Fatalism (a passive response to a hazard)


  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.
• Prediction (an active response to a hazard)


  Using ​scientific research ​and ​past events in order to know when a hazard will take place, so that ​warnings ​may be ​delivered and ​impacts of the hazard can be reduced​.
• Adaptation (an active response to a hazard)


  For places which experience regular hazards a response is often to adapt or adjust their behaviour to be able to cope with future events better.
• Mitigation (an active response to a hazard)


  Any action taken to reduce or eliminate the long-term risk to human life and property.
• Risk Sharing (an active response to a hazard)


  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​ (e.g. buying insurance)
• Management (an active response to a hazard)


  This involves coordinated strategies to reduce a hazard's effects.
• Hazard Risk Equation


  Risk = hazard (H) x vulnerability (V) /capacity to cope (C)
• Define the Hazard Management Cycle (a.k.a disaster life cycle)


  The hazard management cycle or the disaster life cycle consists of the steps that emergency managers take in planning for, and responding to, disasters.

  
• Four steps in the Hazard Management Cycle (a.k.a disaster life cycle)


  1. Response (e.g. search and rescue)

  2. Recovery (e.g. Rebuilding services)

  3. Mitigation (e.g. hazard proof buildings)

  4. Preparedness (e.g. education, public awareness)
• Benefits of the Hazard Management Cycle


  1. It is a cycle so identifies that hazards need constant management.

  2. Addresses each stage of the hazard from pre to post hazard.

  3. Cheaper in the long term if mitigation is put in place.

  4. Clear model so all stakeholders (e.g. government and NGO's) have a coordinated relief efforts.
• Problems of the Hazard Management Cycle


  1. It is very generic (might vary depending on the hazard).

  2. Might not be suitable for under resourced communities (e.g mitigation is expensive).

  3. There is no clear distinct point at which the phases change throughout the cycle.

  4. It doesn't take into account responses if more than one area is hit.
• Define the Park Model (a.k.a disaster response curve)


  It describes a sequence of phases following such an event. It refers to the strategies and approaches taken to get 'back to normal' after a disaster.

  
• Five stages of the Park Model (a.k.a disaster response curve)


  1. Pre disaster- quality of life at its normal level

  2. Disruption- Loss of life/ amount of damage

  3. Relief- Rescue efforts

  4. Rehabilitation- Restoring infrastructure/ services

  2. Reconstruction- Rebuilding (often involving mitigation)
• Factors impacting the steepness of the curve on the Park Model


  Depends on the nature of the hazard e.g. earthquakes have immediate disruption whereas volcanoes might give weeks of warning.
• Factors impacting the depth of the curve on the Park Model


  Depends on the scale of the disaster and nature of the locality e.g. the greater the disruption, the deeper the curve.
• Benefits of the Park Model


  1. Shows that hazards are inconsistent (each hazard requires different responses)

  2. Takes into account different levels of development.

  3. In hazard events that affect multiple countries, each country has its own curve.

  4. It helps to visualise the impact the hazard and therefore makes it easier to compare and contrast with other events to understand what factors worsen the impact of the hazard.
• Problems of the Park Model


  1. It is important to take into account what was done in the run up to the disaster. The Park Model lacks information of the techniques used to help mitigate before the hazard hit.

  2. It doesn't take into account spatial variation meaning that it assumes that all areas of a country recover at the same rate.

  3. It is not good at showing quantitative data making the comparison problematic as it does not show number of deaths, homes destroyed etc.

  4. Doesn't take into account timescales and that some countries will take much longer to reach different stages.
• Lithosphere


  Just below the crust, where the the mantle is more brittle. It is where we find the tectonic plates. It moves over the weaker, plastic (ductile) asthenosphere.
• Theory of Continental Drift


  Wegener (1912) believed that the Earth used to be one huge supercontinent, Pangea, but that the continents gradually began to drift apart around 300 million years ago But had no explanation as to why the continents moved.

  
• Evidence of Continental Drift


  Mesosaurus fossil remains found in South America and Africa.

  It would have been impossible for it to swim between the continents.

  
• Theory of Convection Currents


  Holmes (1929) discovered that the earth's mantle is hottest closest to the core, so lower parts of the asthenosphere heat up, become less dense and slowly rise. As they move towards the top of the asthenosphere they cool down, become more dense and sink. These circular movements create a drag on the base of the tectonic plates, causing them to move.

  
• Evidence of Convection Currents


  This theory helped to explain why features such as volcanoes and fold mountains were concentrated where plate boundaries meet e.g. where convection currents drag two plates apart, magma can escape to form volcanoes.
• Theory of Seafloor Spreading


  Hess (1962) discovered this at mid-ocean ridges (constructive margin) where two plates move away from each other and gradually magma rises up to fill the gap. This will then, over time, move away from the ridge, causing the seafloor to spread.

  
• Evidence of Seafloor Spreading

  Hess dated the rocks of the Atlantic sea bed from the Mid-Atlantic Ridge outwards to the coast of North America. He discovered that the newest rocks were at the centre near Iceland, and the oldest at the coast. This is because when basaltic lava cools on the sea floor, individual minerals separate and these minerals then align themselves on the sea floor in the direction of the magnetic pole (the Earth's magnetic field- palaeomagnetism- reverses periodically, about every 400,000 years).

  
• Theory of Ridge Push


  Hales (1969) found that at constructive plate margins magma rises to the surface and forms new crust, which is very hot. It heats the surrounding rock, which expand and rise above the surface creating a higher elevation and forming a slope.

  The new crust cools and becomes denser. Gravity causes the denser rock to move downslope, away from the plate margin. This puts pressure on the tectonic plates, causing them to move apart.

  
• Theory of Slab Pull


  Hales (1969) found that at destructive plate margins the movement is driven by the weight of cold, older, dense plate material sinking into the mantle at deep ocean trenches and pulling the rest of the plate with it as gravity causes them to slide downwards.

  
• Formation of Composite Volcanoes


  1. Continental plate meets oceanic plate (at a destructive margin)

  2. Oceanic plate subducts because it is denser

  3. Plate melts as it descends due to friction

  4. Magma rises through the crust

  4. Trapped seawater gets hot and can erupt as steam to make extremely explosive volcanoes.
• Earthquakes at Conservative Margins


  1. Two plates move at slightly different speeds/ directions.

  2. They become stuck due to friction as they do not move smoothly and pressure builds.

  3. Eventually one plate overcomes the friction and the pressure is released as seismic waves.

  4. Forms shallow focus earthquakes.

  
• Magma plumes or hot spots


  If radioactive decay is concentrated, hot spots will form around the core. These hot spots heat the lower mantle creating thermal currents where magma plumes rise vertically. These plumes occasionally rise within the centre of plates and then 'burn' through the lithosphere to create volcanic activity on the surface.

  
• Formation of Fold Mountains (e.g. Himalayas)


  1. Where an area of sea separates two continental plates, sediments(transferred from rivers) settle on the sea floor in depressions. These sediments gradually become compressed into sedimentary rock.

  2. When the two plates move towards each other at a collision destructive boundary, the layers of sedimentary rock on the sea floor become crumpled and folded.

  3. Eventually the sedimentary rock appears above sea level as a range of fold mountains.

  
• Formation of Rift Valleys (e.g. East African Rift Valley)


  1. When two plates move apart at a constructive margin, rising magma causes the continental crust to bulge and fracture, forming fault lines (cracks).

  2. As the plates keep moving apart, the crust between parallel faults thins and eventually drops down to form a rift valley.

  3. The thinner crust also allows gas and steam eruptions to occur.

  
• Formation of Ocean Ridges (e.g. Mid Atlantic Ridge)


  1. Where a constructive boundary can be found underwater, an ocean ridge forms, due to seafloor spreading.

  2. As the tectonic plates pull apart, magma, comes up from below to fill in the gaps, forming a raised area and forcing the more solid rock above to crack apart.

  3. Where there are weaker areas in the crust along the mid-ocean ridges, the ridge can divide into segments, called fracture zones.

  
• Formation of Deep Ocean Trenches (e.g. Mariana Trench)


  1. Where continental and oceanic plates move towards each other at a destructive boundary, the more dense oceanic crust is forced under the less dense continental crust.

  2. The friction and pressure created by the movement of these plates can cause the leading edge of the subducting plate to be pushed down into the mantle, creating a trench-like depression on the ocean floor.

  
• Formation of Island Arcs (e.g. The Lesser Antilles Island Chain)


  1. Where two plates meet at a destructive boundary, the denser oceanic plate subducts.

  2. Hot, melted material from the subducting plate rises and forces its way through the crust, forming a series of volcanoes.

  3. The curved shape of island arcs is a result of the bending and deformation of the subducting plate as it descends into the mantle.

  
• Formation of Shield Volcanoes


  1. At a constructive plate boundary, two plates move apart.

  2. As the two plates move apart, magma rises up to fill the gap through cracks called fissures.

  3. Layers build, forming shield volcanoes.

  4. However, since the magma can escape easily at the surface the volcanoes do not erupt with much force.

  
• Characteristics of Composite Volcanoes


  1. Erupt infrequently

  2. Viscous lava

  3. Made up of rhyolitic (high silica content of 65 to 75%) or andesitic magma (intermediate silica content of 55 to 65%)

  4. Explosive eruptions

  5. Explosive nature leads to layers of lava- ash

  6. Lava flows slowly due to its high viscosity creating steep slopes.