3. Plate Boundaries (H)

Plate Boundaries

Types of Plate Boundaries:

• Divergent: Plates move apart, creating new crust (mid-ocean ridges, rift valleys).

• Convergent: Plates move towards each other. Types:

  • Oceanic-Continental: Oceanic subducts, forming ocean trenches and volcanic arcs.

  • Oceanic-Oceanic: Older oceanic plate subducts, leading to ocean trenches and volcanic island arcs.

  • Continental-Continental: No subduction, creating mountain ranges (e.g., Himalayas).

• Transform: Plates slide past each other, causing earthquakes without crust creation or destruction.

Key Processes Driving Plate Movement:

• Slab Pull: Subducting plate's weight pulls trailing slab.

• Ridge Push: Elevated mid-ocean ridges push plates away due to gravity.

Common Locations:

• Active Margins: Tectonically active with earthquakes and volcanism (e.g., West Coast USA).

• Passive Margins: Stable with low tectonic activity (e.g., East Coast USA).

Examples of Features:

• Convergent: Aleutian & Mariana islands (O-O), Himalayas & Alps (C-C), Andes (O-C).

• Divergent: Mid-Atlantic Ridge, East African Rift.

• Transform: San Andreas Fault, Alpine Fault.

Summary: Oceanic crust subducts at convergent boundaries; volcanic activity occurs at oceanic-continental boundaries but not at continental-continental boundaries.