plate boundaries

• types of plate margins

  divergent ( constructive )

  convergent ( destructive)

  conservative ( transform faults )
• oceanic meets continental plate - destructive 


  oceanic plate is denser so it slides beneath the continental plate into the mantle and melts.

  this causes fold mountains.

  the friction causes deep earthquakes in the benioff zone

  volcanic eruptions are generated as magma pushes up through the continental plate.
• continental plate meets continental plate - destructive 


  a collision margin occurs. This is because both plates have the same density + are less dense than the asthenosphere so neither plates are subducted.

  although they collide + sediments are crumpled and forced upwards forming fold mountains.

  no volcanoes + shallow focus earthquakes
• oceanic plate meets oceanic plate - destructive 


  1 plate is subducted beneath the other. deep ocean trenches form and the subducted plate melts creating magma which rises up the benioff zone forming underwater volcanoes.

  this forms island arcs
• island arcs


  volcanoes rise above sea level and form seperate island volcanos.
• constructive plate margin 


  2 plates are diverging apart leading to a new crust forming oceanic ridges (if in ocean) or rift valleys ( if on land).

  breaks in mid-ocean ridges are called transform vaults. regular volcanic eruptions also create submarine volcanoes.
• rift valleys 


  the crust stretches + breaks into sets of parallel faults. this land then collapses forming rift valleys.
• conservative plate 


  2 plates slide past eachother resulting in a break in the crust between them as they move. this is a fault or a transform fault on a larger scale.

  tectonically active

  the 2 plates may stick when moving past eachother building pressure causing an earthquake ( shallow focus)
• convection currents 


  movements of a fluid caused by a temp or density difference in a material.
• continental crusts 


  outermost layer of lithosphere making up continents + continental shells.
• oceanic crust 


  denser layer (crustal) which makes up portions of tectonic plates in deep oceans.
• lithosphere 


  rocky rigid outer layer
• mid oceanic ridge


  the area where 2 oceanic plates diverge at the point where rising convention currents within the mantle spread sideways forcing plates apart making a rift.
• rift valley 


  lowland regin which forms where tectonic plates move apart / rift
• sea floor spreading 


  occurs at mid ocean ridge. new oceanic crust is formed through volcanic activity + then slowly moves away from the ridge
• slab pull 


  a force from denser oceanic plates sinking beneth less dense continental plates along convergent boundaries + subduction zones.
• subduction 


  process by which one edge of the lithosphere is forced bellow the edge of another
• subduction zone 


  1 plate slides underneath another at a converging plate boundary
• mantle convection 


  heat produced by decay of radio active elements in the earths core heats the lower mantle creating convection currents. it moves in circles in the athenosphere so the plates move.
• the lithosphere is broken up into several major + several minor parts (tectonic plates)
• tectonic plate 


  large, irregularly shaped slabs of solid rock which move slowly. the study of these plates is called the tectonic theory.
• structure of the earth

  1. crust : oceanic and contineted
  2. listosphere
  3. mantle : asthenosphere
  4. outer core
  5. inner core
• inner core 


  solid due to pressure from other layers (compacted molecules). made of iron + nickel.
• outer core


  less pressure so is liquid. There is shrinking due to cooling.
• mantle

  3000-1000’. cooler closer to crust. the mantle near the outer core is the mesosphere which is compressed. the part closer to the crust is the athenosphere.
• the listophere is divided into the oceanic and continental crust. the continental crust is less dense. when the oceanic crust forms sea floor spreading occurs. this is when the oceanic crust pushes the tectonic plates apart.
• hazard profile

  physical characteristic of an event
• hazard risk equation

  risk = hazard x vulnerability

  _______________

  capacity to cope