How does the process of ridge push cause the formation of new oceans? ridge push causes a rift valley; as the plates move apart, a new ocean basin forms, filling with water and eventually becoming a mature ocean. ridge push causes a convergent plate boundary; as the plates move together, new islands form, which “trap” water between them, causing an ocean to form. ridge push causes plates to move apart from one another, creating a deep trench that eventually widens enough to become a new ocean. ridge push causes the plates to subduct, causing a deep trench that eventually fills with water and becomes a new ocean.