A cycle has begun and in time, a waterfall is born. Geologically, the life cycle of a waterfall is short. The very power that creates them also destroys them. As the softer rock below is eroded, the streambed is undercut creating an overhang. But then the overhang breaks off and the falls move upstream where the process begins again.
Powerful falls can almost run upstream.
Niagara Falls has moved seven miles from where it was first formed and is currently moving at an average rate of nearly four feet a year. Eventually the erosion comes to the end of the hard rock layer and the falls erodes itself away. From a geologic standpoint, the water crashing down the face of a cliff is like sand pouring through an hourglass. It is time measured. All great beauty is fleeting.