1. Plate Tectonics
Part II: Plate Boundaries

2. Three Types of Plate Boundaries

3. DIVERGENT: Move Apart  Oceanic - Oceanic
• Oceanic ridges – elevated areas where new seafloor forms (seafloor spreading.)
• Rift valleys are deep faulted structures

4. East African Rift Valley
Continental – Continental
Continental Rifts
• rift valley on land
landmass may split into two, forming a rift.
East African Rift Valley

5. CONVERGENT: Move together
2 plates collide. Different things happen depending on the type of crust involved.
Oceanic – dense – basaltic
Continental – less dense – granitic

6.  Oceanic-Continental
• subduction zone occurs when the oceanic plate is forced below the continental plate. Trenches form.
• Continental volcanic arcs form when the subduction of oceanic lithosphere beneath a continent melts and rises.
• Examples include the Andes, Cascades, and the Sierra Nevadas.

7.  Oceanic-Oceanic
• Two oceanic slabs converge and one descends beneath the other.
• Volcanic island arcs form as volcanoes emerge from the sea.
• Examples include the Aleutian, Mariana, and Tonga islands.

8.  Continental-Continental
• Two continents collide and the land buckles upwards
• This kind of boundary can produce new mountain ranges, such as the Himalayas.

9. Transform: Slide past each other
 At a transform fault boundary, plates grind past each other without destroying the lithosphere.
• Most join two segments of a mid-ocean ridge.

10. San Andreas Fault

11. HOT SPOT Some volcanoes form from hot spots
Hot mantle plumes reach the surface, forming a volcano far away from plate boundaries