What Is one way a rift can form

Under the pressure and force from the Mantle layer on the Crust layer the continental plates move, when in situation where they move away from each other a rift is starting to form on their ever growing separating like and thus make the rift bigger and bigger. When this happens there's also earthquakes because of the cracks in the Crust layer and they often cause speeding up of the growing of the rift's size.

When plates move away from each other it can cause rift valleys to form.