How does water cause a pothole?

Maybe you have seen a clean, round hole cut deep into a hard and solid bed of rock. This would most likely be a pothole. We are told that water wears the stones but we wonder why and how water can wear away shapes like the pothole.

Actually, the water needs a helper to make a pothole. It needs the assistance of a hard round stone. Sometime such a stone gets trapped in a whirlpool or swift flowing stream. Back and forth it is bashed by the eddying water. Its bashing soon begins to chap off bits of the hard river bed and it soon wears itself a dent.

There is now no way for it to escape. More bashing only deepens the hole, rounder and rounder. Sooner or later the river may dry up or change its course and the stone and its hole are left high and dry. Maybe the stone too is lost or rolls away; all that is left is a mysterious round hole deep in the hard rock.