1. Magma from the Earth's mantle rises: Hot, molten rock (magma) from deep within the Earth's mantle rises up through the ocean floor.

2. New crust is created: The magma erupts along a crack in the ocean floor, called a rift valley. As the magma cools and solidifies, it creates new oceanic crust.

3. Plates move apart: The new crust pushes older crust away from the rift valley, causing the plates to move apart. This process is known as divergent plate movement.

4. Ridge formation: As the plates move apart, the process of magma rising and creating new crust continues, forming a long, elevated underwater mountain range called a mid-ocean ridge.

In essence, mid-ocean ridges are the "seams" where new oceanic crust is constantly being generated.