Hess reasoned that if the Hess reasoned that if the ocean floor was moving away ocean floor was moving away from either side of the from either side of the mid-mid-ocean ridge. Then it must be ocean ridge. Then it must be

colliding somewhere else, such colliding somewhere else, such as the edge of a continent.as the edge of a continent.

The area where the plates The area where the plates meet is called a meet is called a Plate Plate

BoundaryBoundary. There are 3 types . There are 3 types of plate boundaries.of plate boundaries.

1. Divergent Boundaries: This is where two plates are

moving away from one another and new oceanic crust

is forming.

Underwater mountain Underwater mountain ranges are formed at the ranges are formed at the

divergent boundary.divergent boundary.

2. Convergent Boundaries: As seafloor spreading moves plates apart at one boundary,

those plates push into neighboring plates. Causing a

collision of plates.

Collisions between Collisions between oceanic crust and oceanic crust and

continental crust, will continental crust, will cause the oceanic crust cause the oceanic crust to subduct, under the to subduct, under the

continental crust.continental crust.

This type of plate This type of plate collision forms a collision forms a

trench & Continental trench & Continental Volcanoes.Volcanoes.

Neither plate is subducted. Instead the colliding edges are crumpled and uplifted, producing large mountain

ranges.

One side will subduct, causing a very deep trench. The plate that is subducted melts and the molten rock rises to the

surface along the trench which causes a long chain of

volcanic islands.

This is when two plates grind past each other horizontally. When

enough friction builds up an earthquake will

occur.