TECTONICS - Plate boundary types

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  • Plate boundary types and their distribution
    • Divergent
      • Constructive
      • displayed at mid-ocean ridges.
        • The Mid Atlantic Ridge. Iceland Basaltic magma).
      • shallow focus and low magnitude earthquakes (submarine [under the sea]). These generally do not trigger tsunamis.
      • new dense oceanic crust  is created by rising magma through the plates boundaries.
    • Convergent
      • Destructive-plates moving together
      • active collision locations where plate material melts in the mantle, causing earthquakes and volcanoes.
      • become really dangerous when one more-dense (oceanic) plate subducts below the other less-dense (continental) plate, causing a subduction zone with high levels of stress and friction.
      • Earthquakes- Japan Tohoku tsunami 2011, and Aceh, Indonesia 2004.
        • Volcanoes- magma fed by melting of subducting plate. (surface volcanism occurs in oceans directly above the down thrust plates.
          • volcanoes associate with explosive events with a composite cone volcano.
      • Between two continental plates, mountain ranges such as the Himalayas are formed
    • Conservative
      • The relative movement here is horizontal (Sinstrel [L] or Dextrel [R]).
      • Oblique-slip, sliding or transform.
      • The San Andreas Fault - Pacific Plate (north) creates friction against North American Plate (north at different speed).
      • Lithosphere is neither created nor subducted and are the sites of extensive shallow focus earthquakes. No volcanic activity.
    • Hot spot volcanoes are found in the middle of tectonic plates (anomalous volcanism).
      • The Hawaiian Islands are an example of this occurring (pacific plate).
      • Heat rises as a hot thermal plume from deep in the earth. High heat and low pressure at the base of the lithosphere enable melting of the magma. this rises through cracks.
        • the hot spot stays static and as the plate moves away, forming sea mounts, atolls and islands. Volcanoes are rafted away and new ones form.
    • Nearly all earthquakes are situated along the 'Pacific Ring of Fire' (70%)
    • Volcanoes tend to be situated near plate boundaries
    • intra-plate earthquakes
      • Caused by man-induced activity such as fracking.
      • Also caused by a weakness in the plate, a thermal plume or along a fault line.
      • The Charleston earthquake, North Carolina, 1886.

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