- Convection currents in the asthenosphere cause continental crust to dome upwards.
- The upward pressure causes the crust to crack leaving an unsupported middle section.
- The unsupported section collapses forming a rift valley with steep stacks.
- If the convection currents are strong enough a line of volcanoes will form at the bottom
- of a rift valley, producing a basaltic rock which will eventually form an ocean floor.
- The largest of these features is in the African Rift valley which extends 4,000km from Mozambique to the Red Sea.
