As soon as the first vehicle crosses it, damage begins accumulating in a pavement. This damage typically starts as a single crack where the wheels run on the pavement. Once this type of cracking occurs, if the pavement is not promptly repaired, the structural integrity of the pavement is lost and traffic will start knocking the pavement chunks loose. At this point, a pothole is born. Water seeping into the pavement through the cracks can accelerate this process by softening the soil under the pavement.
Water expanding and contracting due to freezing can make things even worse.
However, potholes can form in any unmaintained pavement, even in dry, hot places like Arizona. Argonne National Laboratory, Division of Educational Programs, Harold Myron, Ph.D., Division Director.