Plate Boundary Notes

3 Forces that Move the Plates Convection currents in the asthenosphere create 3 forces that move the lithospheric plates around. Tension Compression Shearing

Tension – pulls plates away from each other. Divergent Boundary – when 2 plates are pulled apart. Causes rift valleys & mid-ocean ridges.

Compression –pushes plates towards each other. Convergent Boundary – when 2 plates are pushed together.

Oceanic-Continental Convergence When oceanic crust & continental crust converge, the oceanic plate subducts under the continental plate & melts, creating a trench & a volcanic arc. Ex: the Andes

Subduction - When 1 plate is pushed under another plate & back into the mantle, forming trenches & volcanoes.

Trench Oceanic Crust Continental Crust

Oceanic-Oceanic Convergence When both edges of two plates that are converging are made of oceanic crust, the older, denser plate subducts under the younger oceanic plate, forming a trench & a volcanic island arc. Ex: The Marianas Trench & Mariana Islands

Trench Oceanic Crust Oceanic Crust

Volcanoes

Continental-Continental Convergence When 2 continents meet head-on, the crust buckles & is pushed upward. Ex: The Himalayan mountain range

Continental Crust Continental Crust

Shearing –pushes plates past each other in opposite directions. Transform Boundary – when 2 plates are pushed past each other in opposite directions. Produces earthquakes (San Andreas Fault).

Earthquakes

Hot Spots A large, stationary plume of super hot magma that breaks through the tectonic plate moving over it, causing continual volcanic activity.