Plates are constantly in motion and are all moving at unique speeds. The African plate, for example, is moving at approximately 2.15 cm/year (about an inch/year), while the South American plate is moving at approximately 1.45 cm/year (about half an inch/year). Plates are constantly interacting at their boundaries. Scientists have identified three distinct kinds of plate boundaries, each of which interacts differently. These plate boundaries include divergent boundaries, convergent boundaries, and transform fault boundaries.
A divergent boundary is formed when two plates move apart. New mid-oceanic ridges start as a rift valley.
Divergent Boundaries
A divergent boundary represents an area where two plates are moving apart, or are diverging from one another. New magma from the mantle flows up to fill the space opened up by the plates moving apart. A narrow valley known as a rift valley usually forms in the space between the two plates as they pull apart. Since new crust is being created as a result of the plate motions, divergent boundaries are also known as constructive margins.
Divergent boundaries are usually found underwater as two plates of oceanic crust pull apart resulting in mid-oceanic ridges, but they can also be seen on land with two sections plates of continental crust moving apart.
The Red Sea was formed as a result of the African plate diverging from the Arabian plate.
What Do You Think?
The Formation of the Atlantic Ocean
It took over 100 million years for the Atlantic Ocean to assume its current shape.
- Click on each date in order to see the shape of the Atlantic Ocean at that time.
- How has the size of the Atlantic Ocean changed over the last 100 million years? The Atlantic Ocean has steadily increased in size over the last 100 million years.
- What kind of tectonic plate motion must have been responsible for this change in the size of the Atlantic? What do you think? The increase in size of the Atlantic Ocean could only have been caused by plates moving apart (i.e. divergent plates).
- Click here to add in the plate names.
- Click here to zoom in on the North Atlantic Ocean.
- What divergent plates are responsible for the formation of the North Atlantic Ocean? The North Atlantic Ocean was formed as a result of the divergence of three plates; the North American Plate, the Eurasian Plate, and the African Plate.
- Rotate the globe and zoom in on the South Atlantic Ocean.
- What divergent plates are responsible for the formation of the South Atlantic Ocean? The South Atlantic Ocean was formed as the result of the divergence of two plates; the South American Plate, and the African Plate.