1. 9.3 – Actions at Plate Boundaries – Part I

2. Do Now
What is seafloor spreading?

3. Do Now What is seafloor spreading?
The process by which plate tectonics produces new oceanic lithosphere.

4. Key Words
Segment

5. Vocab Words
Oceanic Ridge
Rift Valley
Seafloor Spreading

6. Divergent Boundaries
Most divergent boundaries are located along the crests of oceanic ridges.
Divergent boundaries is where new oceanic lithosphere is created.
When the plates move away from each other, fractures are created, and hot molten magma wells up from the hot mantle below, cools and forms new seafloor.

7. Oceanic Ridges
Along well-developed divergent plate boundaries, the seafloor is elevated, forming the oceanic ridge.
The system of oceanic ridges is the longest physical feature on Earth’s surface, stretching more than 70,000 kilometers in length.
Deep faulted structures called rift valleys are found along the axes of some segments.

8. Seafloor Spreading
Seafloor spreading is the process by which plate tectonics produces new oceanic lithosphere.
Typical spreading rates = 5 cm/year
Slow on a human time scale
But this is still fast in terms of geologic time.
All of the current ocean basins could have been generated within the last 200 million years; none of the ocean floor has been dated older than 180 million years old.

9. Seafloor Spreading

10. Continental Rifts
When the spreading centers develop within a continent, the landmass may split into two or more smaller segments.
EX: East African Rift Valley
May represent the beginning stages of the break up of the African continent.
Rift valleys show us the what possibly happened with the continental breakup idea.

11. Group Activity
On page 259, Figure 9; copy the picture and label all the parts, put them in your folder when you complete it.