Chapter: Formation of Mountain Ranges

b. Divergent Boundaries on Land

Divergent plate boundaries on land form as follows.

First a convection cell forms underneath a continent. Then slowly a rift/trench forms like this:
Through the convection cell pressure is applied to the rocks of the continental crust, until they give in and cracks appear. These cracks keep becoming wider until whole blocks start to lower themselves. This process continues till a trench has formed. In this phase volcanism develops.

This occurrence can be found in today's Africa, where we have the Great Rift Valley. Maybe you even know that there exist volcanoes in Africa. They are by the majority located near the rift valley. When the rift has lowered itself far enough, it will form a connection to an existing ocean and fill with sea water; a new estuary has formed.

Now a MOR will form in the estuary and new oceanic crust will be produced. So, if the Great Rift Valley in Africa continues to develop, the Red Sea will flow through Africa in the near future - geologically spoken - and Africa will be split in two halfs. This phase can be found at the moment in the Red Sea.

If you look at a world map, you will find it between Arabia and Egypt. A long time ago, these countries lay side by side. Then a rift formed, which filled with sea water. Since then the Red Sea continues to grow, as oceanic crust is formed at a MOR.

After that we arrive at the final stage, the finished ocean, like the Atlantic. But even he won't exist anymore one day.

To the Convergent Boundaries