1. The Theory of Plate Tectonics

2. Today, the theory of continental drift and the process of sea-floor spreading have been combined into the study of plate tectonics.
Plate tectonics is the theory that the lithosphere is divided into tectonic plates that move around on top of the asthenosphere.

3. As tectonic plates move, they can collide, slide past each other, or move apart.
There are three types of plate boundaries: divergent, convergent, and transform.
Divergent boundaries move away from each other creating new lithospheric plate between them.

4. The mid-Atlantic ridge is a divergent boundary.
Ridge, rift and rise are all features associated with divergent boundaries.
Click on the picture for a video.

5. Divergent boundaries are not always on the ocean floor
Divergent boundaries are not always on the ocean floor. A divergent boundary can be on a continent and create a new ocean or sea.

6. The East African Rift which is located on the African continent and is a divergent boundary. Eventually Africa will be split by a new ocean.

7. A second type of plate boundary is a transform boundary
A second type of plate boundary is a transform boundary. Transform boundaries occur when plates slide past each other.
Click for video

8. There is a transform boundary between the Pacific plate and the North American plate that runs along California.
This transform boundary has produced many faults. One major fault is the San Andreas Fault.
Since Los Angeles is on the Pacific plate and moving north and San Francisco is on the North American plate and moving south, the two cities will eventually meet.

9. The third type of plate boundary is a convergent boundary.
Convergent boundaries occur when plate boundaries come together.
Convergent boundaries tend to create mountains, volcanoes, faults, and trenches when they converge.

10. There are three types of convergent boundary collisions: oceanic/continental collisions, oceanic/oceanic collisions, and continental/continental collisions.
Oceanic / continental
Oceanic / oceanic
Click for video
Continental / continental

11. The Mariana Trench is formed when the Philippine oceanic plate collides with the Pacific oceanic plate.
The Mariana Trench is the deepest place on Earth. At the Challenger Deep point of the trench it is almost 7 miles deep.
This is a convergent, oceanic-oceanic collision.

12. When two continental plates converge, they push up mountains.
Where the Indian plate collides with the Eurasian plate, the Himalayan Mountains are being formed. Since the collision is still occurring, the Himalayan Mountains are increasing in size by over one centimeter each year. Mount Everest is in these mountains (29,035 ft).
This is a covergent, continental-continental collision.

13. Each plate has multiple types of boundaries
Each plate has multiple types of boundaries. For instance, the Pacific Plate has divergent, convergent, and transform area.

14. There are seven major plates: North American, South American, African, Eurasian, Australian, Antarctic, and Pacific.
There are 8 minor plates: Juan de Fuca, Caribbean, Cocos, Nazca, Scotia, Arabian, Indian, and Philippines.

15. The largest tectonic plate is the Pacific Plate
The largest tectonic plate is the Pacific Plate. It is also the only plate that is primarily oceanic crust.

16. The boundary of the Pacific Plate has been named the “Ring of Fire” because of the large number of volcanoes and earthquakes that happen in this active tectonic area.

17. In many locations the hot molten magma from deep within the Earth rises up through the crust to reach the surface. This sometimes happens in the middle of plates. When a hot spot forms in the middle of a plate, it remains constant, as the plate continues to move over it.
The result is that a trail of volcanoes is left behind, with older volcanoes moving away from the hot spot, and newer ones forming over top of the hot spot.

18. There are many hot spots that are found on the earth
There are many hot spots that are found on the earth. Examples include the Hawaiian Islands, Yellowstone, Iceland, the Azores and the Galapagos Islands.

19. One of the most famous hot spots on Earth is the Hawaiian Islands
One of the most famous hot spots on Earth is the Hawaiian Islands. The oldest islands found in the Hawaiian Island chain consist of mostly dead volcanoes. These volcanoes were active millions of years ago, but the moving crust of the ocean floor has carried them away the hot spot that feed the volcanoes.
The newest island is the big island, which today has two active volcanoes. These volcanoes are fed by the same hot spot that used to feed the dead volcanoes on older islands. Millions of years from now, it is likely that additional islands will form over the same hot spot, as the Earth’s crust carries the big island away from the hot spot it now sits on.