opt D- geophysical hazards

• Hazard event


  The occurrence of a hazard, the effects of which change demographic, economic and or environmental conditions
• Disaster

  A major hazard event that causes widespread disruption to a community or region, with significant demographic, economic and or environmental loses, and which affected community is unable to deal with adequately without outside help
• Risk


  The probability of a hazard event causing harmful consequences (deaths, injuries, property damage, economy, and environmental damage
• Vulnerability


  Geographical conditions that increase the susceptibility of a community to a hazard or to the impacts of a hazard event
• Hazard perception


  The degree to which a hazard is considered a threat by different people
• Hazard event


  The occurrence of a hazard, the effects of which change demographic, economic and or environmental conditions
• Disaster


  A major hazard event that causes widespread disruption to a community or region, with significant demographic, economic and or environmental loses, and which affected community is unable to deal with adequately without outside help
• Risk


  The probability of a hazard event causing harmful consequences (deaths, injuries, property damage, economy, and environmental damage
• Vulnerability


  Geographical conditions that increase the susceptibility of a community to a hazard or to the impacts of a hazard event
• Hazard perception


  The degree to which a hazard is considered a threat by different people
• Secondary hazard


  Indirect effects or secondary effects of a natural hazard occurring after the initial primary hazard
• Hazard


  A threat whether natural or human that has the potential to cause loss of life, injury, property damage, socio-economic disruption, or environmental degradation
• Resilience


  The ability to protect lives, livelihoods, and infrastructure from destruction, and to the ability to recover after a hazard has occurred
• Adaption


  Ways in which human activities/ actions are altered to consider the increasing risk of hazards
• Mechanism of plate movement

  1. The earth is made up of several layers

  2. Two main sources of flow of heat inside the earth's interior: radiogenic and primordial heat

  3. Earth heat transport occurs by convection, conduction, and volcanic advection

  4. Most of the earth's internal heat flow is due to mantle convection

  5. Remaining heat mainly comes from the Earth's crust

  6. Only 1% is due to volcanic activity
• Subduction


  1. Plunging of one plate beneath another

  2. Subduction zones form where an oceanic lithospheric plate collides with another plate

  3. The density of the oceanic plate is like that of the aesthenosphere, easily pushed down into upper mantle

  4. Subducted oceanic crust remains cooler and denser than the surrounding mantle
• Plume


  1. Small area of unusually high heat flow

  2. Can cause movement

  3. The outward flow of viscous rock from the centre may create a drag force on the plates and cause them to move

  4. Most are found near plate margins

  5. They are responsible for the original rifting of the crust
• Rift valleys


  1. Consist of rock that is hotter and less dense than the older, colder plate

  2. Hot material wells up beneath the ridges to fill the gaps created by the spreading plates

  3. This occurs at constructive plate boundaries
• Intra-plate volcanism


  Volcanoes occur away from plate boundaries - hot spots

  
• Hot spot


  1. Magma rises to the surface through cracks in the crust

  2. As tectonic plate moves slowly over the magma plume, a line of islands may form

  
• Volcano


  • Formed when magma erupts onto the Earth's surface as lava through a vent in Earth's crust
  • Magnitude is measured on the volcanic explosivity index (VEI) - scale open ended - highest recorded 8

  
• Features of an eruption

  • Lava
  • Ash
  • Earthquakes
  • Volcanic bombs

  
• Composite volcanoes (strato-volcanoes)

  • Steep-sided
  • Sticky lava
  • More explosive eruptions
  • Formed from altering layers of ash & lava
  • Tend to form on convergent (destructive) plate boundaries

  
• Shield volcanoes

  • Gently sloping sides
  • Runny/thin lava
  • Less explosive - gentle eruptions
  • Tend to form on divergent plate boundaries or hot spots
  • Frequent eruptions

  
• Cinder volcanoes

  • Circular & cone shaped
  • Usually less than 1000 feet high
  • Composed of hardened ash, tephra and lava
  • Lava us forcefully ejected from the volcano & cools whilst in the air, falling as cinder fragments

  
• Lava eruptions


  1. The amount of silica in a lava eruption is what makes the difference between the volcanoes

  2. Lava released where the oceans meet the continents absorbs silica-rich sediments, becoming more viscous and blocking the vents - pressure build up and breaks them open

  3. Icelandic lava eruptions: persistent fissure eruption/ large quantities of basaltic lava build up in horizontal plains

  4. Hawaiian eruptions: involve a central vent/ runny basaltic lava flows down the sides of the volcano and gases escape easily

  
• Pyroclastic eruptions

  1. Strombolian eruptions: produce pyroclastic rock / white cloud of steam emitted from the crater/ gas explosions blast quantities of runny lava into the air - when settle & cool they form cone

  2. Vulcanian eruptions: violent & occur when the pressure of trapped gases in viscous magma become sufficient to blow off the overlying crust of solidified lava/ clears a blocked vent & spews large quantities of volcanic ash into the atmosphere

  3. Vesuvian eruptions: very powerful blasts of gas that push ash clouds high into the sky/ lava flows occur/ ash falls to cover surrounding area

  4. Plinian eruptions: extremely violent eruptions characterized by huge clouds pf pulverized rock & ash that are kilometres thick / sticky lava & blasts ash & fragments into the sky in huge explosions/ gas cloud & lava rush down slopes / part of volcano may be blasted away during eruption

  
• Secondary hazards of volcanoes

  • Acid rain
  • Pyroclastic flow
  • Lahars
  • Landslides

  
• Earthquake characteristics

  • Sudden, violent shaking of the ground
  • Earthquake are result of pressure building when tectonic plates move
  • Violent shaking of the ground is the release of this pressure as energy travelling through the crust
  • The epicentre: point on the Earth's surface directly above the focus
  • Focus: point at which the earthquake starts below the Earth's surface - energy released by the earthquake travels out from the focus
  • Magnitude: amount of energy released by earthquakes is measured on the Moment Magnitude Scale, which replace the Richter scale
  • Damage caused by earthquakes is measured on the Mercalli Scale
• Type of seismic wave

  • Primary - P-wave
  • Secondary - S-wave
  • Love-L-waves (Q waves)
• Characteristics of seismic waves

  • P-waves: Body wave / fastest/ reach the surface first / travel through liquids and solids / cause backwards and forwards shaking / least damaging

  1. waves: Body waves/ slower than P waves / only travel through solids/ cause a sideways motion / more damaging

  Love-L-waves: Surface waves / slowest / cause a side-to-side motion/ larger & energy is focussed on the surface / most damaging
• Causes of an earthquake

  1. Can occur anywhere but mostly occur at or near a plate boundaries

  2. Happen at all plate boundaries

  3. Plate movement leads to the build-up and then release of pressure

  Constructive plate boundary: Earthquakes are weaker as the plates are moving apart

  Destructive plate boundary: Collision & conservative plate boundaries, earthquakes are stronger

  At destructive boundaries, the narrow area where earthquakes tend to occur in the subduction zone is known as the Benioff Zone

  Collision plate boundaries: Plates of similar density move towards each other, land is forced upwards forming fold mountains

  Conservative plate boundary: Plates move passed each other
• Human triggers of earthquakes

  Dam building: Building of dams lead to the formation of a reservoir, added weight of the water in the reservoir adds stress to fault lines, causing them to fracture

  Resource extraction: Injection of water at high pressure is used to crack rock formation in hydraulic fracturing or fracking, allows gas to be extracted
• Secondary hazards of earthquakes

  • Tsunami
  • Liquefaction
• Tsunami

  When an earthquake is beneath the sea bed this can lead to a tsunami - as sea bed jolts due to the release of pressure, water is displaced and forced upwards - create a wave

  As wave approaches the land it slows, and the wavelength becomes compressed - increase wave height

  As water reaches shore - vacuum is created and the water recedes rapidly out to sea - leaving seabed exposed

  Other causes of tsunami include: Landslides, Underwater volcanic eruptions, Rarely - caused by a meteor strike
• Liquefaction

  Occurs when the shaking causes particles in the ground to move further apart - causing it to act like a liquid rather than a solid

  Process occurs when saturated, unconsolidated soil is affected by the s-waves in an earthquake

  Causes the water-filled pore spaces to collapse, increases the water pressure and the soil particles can move more freely

  This causes the soil to behave like a liquid and buildings to collapse
• Mass movement

  • The downhill movement of material under the influence of gravity

  Throughflow and runoff caused by heavy rain can also make slopes more unstable and increase the likelihood of mass movement

  Mass movement includes landslides, slumping and rockfalls

  Types of movement is influenced by: Angle of slope, Nature of weathered material, Amount and type of vegetation, Water, Type & structure of rock, Human activity, Climate

  
• Types of mass movement

  • Soil creep
  • Flow
  • Slide
• Soil creep

  Speed is below 1cm per year / common in humid climates / soil expands - individual particles lifted up / soil expands when it freezes / when soil shrinks gain - particles fall straight back down / takes long time
• Flow

  Occur at slopes 5-15º / usually after soil has become saturated with a flow of water across the surface/ vegetation flattened & carried away with soil / speed = 1-15km per year