Divergent Boundary: This is when two plates tectonics are moving away from each other. When this occurs in continental crust, a rift is produced which produces a rift valley. When this occurs in the oceanic crust , it produces a mid-ocean ridge. Divergent boundaries also can produce volcanic islands because when they separate they leave a gap and magma rises through there and cools down.
Rift Valleys: This is a valley that develop along a rift and it is produced by a divergent boundary. It is when the continental crust is spreading apart.