Definitions

• accretion wedge

  The accumulation of material at the point of subduction
• aseismic buildings

  buildings designed to withstand or minimise destruction during an earthquake
• ash

  fine particles and dust ejected during an eruption, which can remain airborne as clouds or accumulate on the ground
• continental crust

  crust that forms the continents of the lithosphere, on average 35km thick
• continental drift

  the movement of tectonic plates, due to varying weights of crust. It was originally thought that convection currents caused the movement of the plates, but now Slab Pull is thought of as the primary driving force
• convection currents

  the circulation of magma within the mantle (asthenosphere). Magma is heated by radioactive processes in the core and cools at the surface, and so circulates between the two places
• epicentre

  the point on the surface, directly above the earthquake's origin
• focus

  the place in the crust where the pressure/seismic energy is released
• hot spot volcano

  volcanoes found away from the plate boundary, due to a magma plume closer to the surface eg Hawaii
• 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
• oceanic crust

  crust, usually thinner than continental crust, that forms the sea floor. It is on average 7km thick
• partial melting

  elements within the lithosphere have different melting points, and so rock is partially melted, partially solid
• pyroclastic flow

  a mixture of gases and rock fragments, at high temperatures travelling at rapid speeds
• seismic waves

  the energy released during an earthquake, in the form of Primary, Secondary, Love and Rayleigh Waves
• tsunami

  initial vertical water displacement (often from a submarine earthquake) creates waves, with large destructive power
• volcanic island arc

  a series of volcanoes (often in the shape of an arc) that are formed consecutively, as a tectonic plate moves across a magma plume
• seismic hazards

  Generated when rock within 700km of the surface breaks under stress
• magma plume

  an area under the crust, the magma melts the crust causing it to come through
• Degg’s model

  this model shows that a hazard becomes a disaster if it affects a vulnerable population

  
• hazard mitigation cycle

  the sequence of governance of a natural hazard: prevention & mitigation, preparation, response and recovery

  
• park’s model

  a model describing the decline and recovery of a country over time, following a natural disaster

  
• the pressure and release model (PAR)

  The model suggests that disasters are the result of two factors: pressures and vulnerabilities. Pressures are the underlying root causes of disasters eg poverty and inequality. Vulnerabilities are the conditions or factors that make people and communities susceptible to disasters like weak infrastructure, lack of preparedness, and limited access to resources.

  
• asthenosphere

  the upper mantle layer of the earth. it is semi-molten and approximately 440km thick

  
• lithosphere

  • outermost layer of earth (crust and some of upper mantle) around 100km
  • it moves very slowly all the time and is broken into tectonic plates

  
• love waves

  a surface earthquake wave with horizontal displacement

  
• primary waves

  an earthquake wave causing compression within the body of rock

  
• rayleigh waves

  a surface earthquake wave causing both horizontal and vertical displacement

  
• secondary waves

  an earthquake wave causing vertical displacement within the body of rock

  
• slab pull

  the force contributing to the movement of tectonic plates. slab pull is due to the weight of the plate

  
• paleomagnetism

  the alternating polarisation of new land created. As magma cools, the magnetic elements within will align with the earths magnetic field, which can alternate over thousands of years

  
• mid-ocean ridge

  parting oceanic plates at a constructive plate boundary create a ridge, with new land at the base of the oceanic valley

  
• richter scale

  a logarithmic measure of earthquakes intensity

  
• subduction

  oceanic plate is forced below continental plate, due to the oceanic plate being more dense than the continental plate

  
• volcanic explosivity index (VEI)

  a measure of the magnitude of volcano eruptions

  
• wadati-benioff zone

  a region of the subducting plate, most affected by pressure and friction, where most destructive margin earthquakes originate

  
• moment magnitude scale

  a measure of an earthquake’s energy released, considered the most accurate measure

  
• sea floor spreading

  molten magma is forced up from the asthenosphere and hardens, forms new oceanic crust, the old crust pushed apart

  
• Plate tectonics

  A theory that explains large scale movement of the lithosphere (based off evidence from sea floor spreading and paleomagnetism )