Plate tectonics

1. what is the oceanic crust made of
3. a hypothesis, first proposed in the 1960s by harry hess
4. what moves the crust
6. plates are moving up and down each other
12. has a greater density than continental crust
14. has a less density than oceanic crust
15. mountains formed in part igneous activity associated with the subduction of oceanic lithosphere beneath a continent
16. made the hypothesis of the sea floor spreading
18. they are made by earthquakes
19. what does a convergent plates make
20. a narrow elongated depression of the sea floor

2. elevated areas of the sea floor characterized by high heat flow and volcanism
5. of irregular topography on the deep ocean floor
7. occurs when two tectonic plates move away from each other.
8. older,denser portions of oceanic lithosphere descends
9. the primary source of the movement of plates
10. a continues elevated zone on the floor of all the major ocean basins
11. a chain of volcanic islands generally located a few hundred km from trench
13. plates are moving towards one another.
17. two oceanic plates converge