At divergent plate boundaries, plates move away from each other, creating a low-pressure area between them. This causes mantle material to rise up through the crust, creating a long crack or rift valley. Magma, or molten rock, also rises from the mantle and erupts to form new crust on the lithosphere. Most divergent plate boundaries are underwater and form submarine mountain ranges called oceanic spreading ridges. The process of forming these mountain ranges is volcanic, but volcanoes and earthquakes along oceanic spreading ridges are not as violent as they are at convergent plate boundaries.

In summary, the geologic process that takes place in divergent plate boundaries is the formation of new crust through volcanic activity and the creation of submarine mountain ranges called oceanic spreading ridges.