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17. Convergent Plate Boundaries

Expedition Menu

1. Introduction

2. Theory

3. Formation

4. Evidence

5. Earth's Interior

6. Magnetic Field

7. Heat Engine

8. Mid-ocean Ridge

9. On the Ridge

10. Seafloor Spreading

11. Magnetic History

12. Magnetic Patterns

13. The Plates

14. More on Plates

15. Boundaries

16. Divergent

17. Convergent

18. Transform

Contact Don Reed
Dept. of Geology
San Josˇ State University

Here you see one type of convergent plate boundary where oceanic lithosphere in brown and tan (which includes the crust in brownish gray) sinks under continental lithosphere (and crust).  Notice how continental lithosphere is thicker than oceanic lithosphere (remember the lithosphere includes both the crust and uppermost mantle). Continental lithosphere is also less dense, which accounts for sinking of oceanic lithosphere (and not the continental lithosphere).

Convergent plate boundaries have the following characteristics:

1. plate motion is toward plate boundary,
2. oceanic lithosphere sinks back into Earth and is recycled,
3. the volcanic arc is region of highly explosive volcanoes, like Mt. St. Helens and Mt. Rainer in Washington,
4. The plate boundary is marked on the seafloor by a deep-sea trench, or just trench, the deepest areas of the ocean,
5. These types of plate boundaries have the strongest earthquakes!

 

Listen to the Lessons of Mount St. Helens -- a volcano located in the volcanic arc along northern California, Oregon and Washington associated with convergent plate in the offshore region in this area.

And great earthquakes and tragic tsunamis!

©Copyright 1999
Last Updated on June 21, 1999

Let's examine the third and final type of plate boundary...transform plate boundaries