Features of Plate Margins

Constructive (Divergent) margins
When plates move apart in oceanic areas produce mid-oceanic ridges.
Rift valleys are formed when they move apart in continental crust.
The space between diverging plate is filled with basaltic lava upwelling from below.

Oceanic Ridges:
Longest ocntinous uplifted features on the surface of the planet
Rise 3,000m above ocean floor

Rate of formation
Slow Rate (10-15mm per year)
      Mid-Alantic Ridge
      Wide Ridge Axis (30-50km
      Deep 3,000m ceneteral rift vallet with inward facing fault scarps

Intermediate Rate (50-90mm per year)
     Galapagos Ridge (Pacific)
     Less well-marked rift (50-200m deep) - smooth outline

Rapid Rate (>90mm per year)
    East Pacific rise
    Smooth crest and no rift

Submarine Volcanoes- Island Volcanoes
Volcanic activity occurs along the ridge, forming submarine volcanoes
These sometime rise above sea level
E.g Surtsey (Iceland)
Volcanoes have failry gentle sides
Low viscosity of basaltic lava
Eruptions frequent but fairly gentle (effusive)
As new crust forms and spreads, trandform faults ocur at right angles to the plate boundary.
Parts of the spreading plates on either side of there faults may move at…