Topic 4 Plate Tectonics

2. liquid magma that reaches the surface
4. a break in earth's crust along which rocks move
8. boundary a plate boundary where to plates move toward each other
10. a type of stress that stretches rock so that it becomes thinner in the middle
13. a type of stress that pushes masses of rock in opposite dir4ections, in a sideways movement
16. a giant wave usually causes by an earthquake beneath the ocean floor
18. a type of stress that squeezes rock until it folds or breaks
20. term used to describe a volcano that is not currently active but able to become active in the future
21. a molten mixture of rock-forming substances, gases, and water from the mantle

1. boundary a plate boundary where two plates move away from each other
3. process by which oceanic crust sinks beneath a deep-ocean trench and back into the mantle at a convergent plate boundary
5. term used to describe a volcano that is no longer active and unlikely to erupt again
6. the shaking that results from the movement of rock beneath earth's surface
7. spreading the process by which molten material adds new oceanic crust to the ocean floor
9. a force that acts on rock to change its shape or volume
11. trench an undersea valley that represents one of the deepest parts of the ocean
12. the measurement of an earthquake's strength based on seismic waves and movement along faults
14. spot an area where magma from deep within the mantle melts through the crust above it
15. a weak spot in the crust where magma has come to the surface
17. ridge an undersea mountain chain where new ocean floor is produced; a divergent plate boundary under the ocean
19. boundary a plate boundary where two plates move past each other in opposite directions