Divergent BoundariesDivergent Boundaries

• Plates move away from each other

• Marine– Ocean basins open & seafloor created

• Continental– Rift zones & new ocean basins created

Rift ZoneRift Zone

• East African Rift Valley

• Kilimanjaro and Mount Kenya

• Graben

Divergent BoundariesDivergent Boundaries

Transform BoundariesTransform Boundaries

• Plates slide past one another

• Neither created nor destroyed

Convergent BoundariesConvergent Boundaries

• Plates move toward each other

• Marine– Trenches, destruction of sea floor & closing of

ocean basins

• Continental– Creation of mountain ranges

Convergent BoundariesConvergent Boundaries

• Three types:

1. Ocean-Continent Convergence

2. Ocean-Ocean Convergence

3. Continent-Continent Convergence

Ocean-Continent ConvergenceOcean-Continent Convergence

Mount St. HelensMount St. Helens

Ocean-Ocean ConvergenceOcean-Ocean Convergence

Continent-Continent ConvergenceContinent-Continent Convergence

HimalayasHimalayas

Continental MarginsContinental Margins

• Two types:

1. Passive– Closest to the divergent

plate boundary

2. Active– Closest to the

convergent plate boundary

Mechanisms of MotionMechanisms of Motion

• Convection cells??

• Ridge push force

• Slab pull force

Rates of MotionRates of Motion

• 1 – 20 cm per year

• Average rate of 5 cm/yr

• Slow spreading rates– Steep slopes

• Fast spreading rates– Gentle slopes

IcelandIceland

Hawaiian IslandsHawaiian Islands

Hydrothermal VentsHydrothermal Vents