plate margins

• types of plate margins

  • conservative
  • destructive - OCEANIC PLATES CONVERGE
  • destructive - CONTINENTAL MEETS OCEANIC
  • destructive - CONTINENTAL MEETS CONTINENTAL
  • constructive
• seismicity and vulvanicity at conservative plate margins

  • no volcanoes found here due to lack of material being destroyed
  • as they move past each other , friction builds and energy is released = earthquake
  • shallow focus earthquakes due to lack of subduction
  • deadly , high magnitude earthquakes - friction released close to surface
• conservative : landforms

  earthquakes occur along this fault - e.g San Andreas Fault in California
• conservative : named examples

  Haiti - Caribbean and Northern American Plate
• destructive - oceanic plates converge : seismicity and vulcancity

  • volcanoes explosive - resulting magma from subduction is silica-rich andesitic magma with high levels of gas (explosive)
  • earthquakes tend to be intermediate and deep focus
• destructive - oceanic plates converge : characteristic landforms

  • deep sea trench - triggering earthquakes and volcanic eruptions
  • underwater volcanic eruptions create island arcs - clusters of islands that sit in a curved line e.g Mariana Islands
• oceanic plates converge : named examples

  Japan and Aleutian Islands ; both curved lines of volcanoes
• destructive : continental meets oceanic - seismicity and vulcanicity

  • oceanic plate gets subducted
  • oceanic plate melts in Beinhoff Zone
  • very explosive volcanoes - composite
  • earthquakes - high magnitude due to pressure built up between the two plates
• continental meets oceanic - landforms

  • deep sea trench
  • fold mountains
  • volcanoes
• continental meets oceanic - named examples

  Iceland - North American and South American Plats diverging
• destructive - continental meets continental : seismicity and vulcancity

  • neither plate can be subducted due to plates having similar density - collision zone
  • plates collide and form upwards to form fold mountains
  • no volcanic activity
  • earthquakes = violent due to constant friction , shallow focus
• continental meets continental - landforms

  Fold Mountains

  • Nepal Earthquake - 7.9 magnitude
• continental meets continental - named examples

  Himyalas - Indo-Australian plate meets with the Eurasian plate
• constructive plate - seismicity and vulcancity

  • lack of pressure causes lava from these volcanoes to have low viscosity and low silica content (shield volcanoes)
  • earthquakes - high frequency + low magnitude
• constructive plates - landforms

  ocean ridges and rift valley
• constructive plate - examples

  Rift Valley - East African rift system - 4000km
• what is a magma plume?

  a vertical colun of extra-hot magma that rises up from the mantle
• magma plumes remains stationary over time but crust moves above it

  • volcanic activity in the part of the crust that is now above the magma plume
  • as crust continues to move , a chain of volcanoes is formed
• named example of magma plume

  Hawaii