Seafloor spreading is an oceanic process involving the formation of new oceanic crust through the solidification of basaltic magma at mid-ocean ridges. This process is a partial explanation for the process of Continental Drift.
The magma that forms these new plates emerges when oceanic plates part from one another due to climatic or geological stresses. Convection currents in the relatively weak and flexible upper mantle of Earth's crust are the driving cause of these stresses.
Rifts have the following features:
- Most rift systems are triple-armed, meaning three fissures form.
- Rifts begin as domes created by rising heat and pressure in the Earth's mantle.
- Three-armed rifts spread until one arm dies and the remaining two extend to the extent of the crust's plasticity.
Full developed rifts can split continental masses from one another and eventually develop into new oceanic basins which will in time form oceans. Arabia and Africa are in the process of splitting due to the formation of just such a rift, but they will not complete this process for millions of years.
Existing rifts on the ocean floor map out the progress of continental masses and sea floor during the millennia of Earth's existence. Africa's Western coast is home to just such a concluded rift. The Earth is constantly being reshaped by this process.