Hazards - Content

• Outline the process of liquefaction [4 marks]

  • Liquefaction occurs when compacted sediments loses strength and stiffness in response to an applied stress such as shaking during an earthquake (1).
  • Material that is ordinarily a solid behaves like a liquid (1)(d).
  • Liquefaction requires a degree of soil saturation to occur (1) (d).
  • Liquefaction can cause buildings and infrastructure to collapse as well as a significant risk to life as it acts like quick sand (1).
• Outline the concept of the Hazard Management Cycle. [4 marks]

  • The hazard management cycle is continuous loop which explains an approach to managing a known hazard (1).
  • Preparedness is concerned with using evidence and data from previous events to plan for hazards associated with the event. (1)
  • Good preparation is the key to minimising impact upon the population (1)(d).
  • Response is concerned with deploying services and resources to save people and property from harm (1).
• Outline factors which lead to the formation of mudflows, a volcanic hazard. [4 marks]

  • Mudflows (or lahars) are associated with the rapid melting of ice and snow following a volcanic eruption (and associated geothermal activity)(1).
  • These only occur where there is a substantial amount of snow or ice, typically at high altitude (1) (d).
  • Lahars can also be triggered in some locations by tropical storms following an eruption (1) (d).
  • The debris itself is comprised of water, volcanic ash, rocks and pyroclastic slurry (1).
• Accretion Wedge:

  • The accumulation of material at the point of subduction
• Aseismic Buildings:

  • Buildings designed to withstand or minimise destruction during an earthquake
• Asthenosphere:

  • The upper mantle layer of the Earth
  • Semi-molten and approximately 2000 km wide
• Ash:

  • Fine particles and dust ejected during an eruption
  • Can remain airborne as clouds or accumulate on the ground
• Continental Crust:

  • Crust that forms the continents of the lithosphere
  • On average 35 km thick
• Continental Drift:

  • The movement of tectonic plates due to varying weights of crust
  • Originally thought to be caused by convection currents, but now Slab Pull is considered the primary driving force
• Controlled Burning:

  • Intentionally burning vegetation to reduce fuel available for a wildfire and disrupt the fire’s path
• Convection Currents:

  • The circulation of magma within the mantle (asthenosphere)
  • Magma is heated by radioactive processes in the core and cools at the surface, circulating between the two places
• Coriolis Effect:

  • The Earth’s spin affects the movement of air masses and winds, depending on a location’s latitude
• Crown Fires:

  • Wildfires that burn the entirety of a tree from top to bottom
  • Often the most destructive and dangerous type of wildfire
• Degg’s Model:

  • A model showing that a hazard becomes a disaster if it affects a vulnerable population
• Epicentre:

  • The point on the surface directly above the earthquake's origin
• Fatalism:

  • The belief that hazards are uncontrollable, so any losses should be accepted and mitigation is unnecessary
• Fire Breaks:

  • The felling of trees and clearing vegetation to create a gap to disrupt a wildfire’s path
• Focus:

  • The place in the crust where the pressure/seismic energy is released
• Ground Fires:

  • Wildfires that burn through the peat and vegetation beneath the surface
  • Slow but difficult to extinguish
• Hazard Management Cycle:

  • The sequence of governance of a natural hazard: preparedness, response, recovery, and mitigation
• Hot Spot:

  • Volcanoes found away from the plate boundary due to a magma plume closer to the surface
• Jokulhaup:

  • A sudden glacial flood caused by a glacier on top of or near a volcano melting due to the heat from the eruption
• Lahar:

  • A flow of mud and debris
• Lithosphere:

  • The upper crust of the Earth with an average thickness of 100km
• Love Waves:

  • A surface earthquake wave with horizontal displacement
• Mid-Ocean Ridge:

  • Parting oceanic plates at a constructive plate boundary creates a ridge with new land at the base of the oceanic valley
• Moment Magnitude Scale:

  • A measure of an earthquake's energy released, considered the most accurate measure
• Oceanic Crust:

  • Crust that forms the sea floor, usually thinner than continental crust
  • On average 7km thick
• Paleomagnetism:

  • The alternating polarisation of new land created
  • Magma cools, magnetic elements align with the Earth’s magnetic field, which can alternate over thousands of years
• Park’s Model:

  • A model describing the decline and recovery of a country over time following a natural disaster
• Partial Melting:

  • Elements within the lithosphere have different melting points, so rock is partially melted and partially solid
• Primary Waves:

  • An earthquake wave causing compressions within the body of rock
• Pyroclastic Flow:

  • A mixture of gases and rock fragments at high temperatures travelling at rapid speeds
• Rayleigh Waves:

  • A surface earthquake wave causing both horizontal and vertical displacement
• Richter Scale:

  • A logarithmic measure of an earthquake’s intensity
• Secondary Waves:

  • An earthquake wave causing vertical displacement within the body of rock
• Seismic Waves:

  • The energy released during an earthquake in the form of Primary, Secondary, Love, and Rayleigh Waves
• Slab Pull:

  • The force contributing to the movement of tectonic plates
  • Due to the weight of the plate
• Subduction:

  • Oceanic plate is forced below continental plate due to the oceanic plate being more dense
• Surface Fires:

  • Wildfires that only burn the leaf litter and are the easiest kind to extinguish