Aim:Aim: What are the different types of plate boundaries and what are the geologic activities associated with these boundaries?

I. Plate BoundaryPlate Boundary – where two or more lithospheric plates meet.

A. Types of Plate Boundaries1. Divergent BoundariesDivergent Boundaries – when two plates move away from each other

a. As plates move apart, the asthenosphere rises up and fills in the open space. It hardens and forms new oceanic crust.

b. Most divergent boundaries are found on the ocean floor. Mid-ocean ridges are found at these boundaries.

c. Rift valleyRift valley – narrow valley in the center of a mid-ocean ridge formed as the plates separate.

2. Convergent BoundariesConvergent Boundaries – the direct collision of one plate with another plate.

a. Subduction ZoneSubduction Zone – when a plate with oceanic crust at its leading edge collides with a plate with continental crust at its edge.

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•Because the ocean crust is denser, it is subducted (forced under) the less dense continental crust.

•As a result of this, deep ocean trenches are formed and volcanic mountains are formed.

b. Continental Crust collides with Continental Crust

•The colliding edges are crumpled and uplifted, producing large mountain ranges.

c. Oceanic crust colliding with oceanic crust

•One plate subducts beneath the other creating trenches

•Island arcIsland arc – chain of volcanic islands created from this type of collision.

3. Transform BoundaryTransform Boundary – forms where two plates are grinding past each other.

•These areas are usually associated with earthquake activity. Ex: San Andreas Fault in California

http://www.geo.wvu.edu/~donovan/geol101/animations/02.swf

Convergent Plate Boundary

http://www.geo.wvu.edu/~donovan/geol101/animations/04.swf

Divergent Plate Boundary

http://www.geo.wvu.edu/~donovan/geol101/animations/01.swf

Plate Boundary Animations