Potholes are holes in the roadway that vary in size and shape. They are caused by the expansion and contraction of ground water after the water has entered into the ground under the pavement. . If it has a chance to freeze, it will take up more space under the pavement, and the pavement will expand, bend, and crack, which weakens the pavement. Then when ice melts, the pavement contracts and leaves gaps in the surface under the pavement, where water can get in and be trapped. If the water freezes and thaws over and over, the pavement will weaken and continue cracking.
As the weight of cars and trucks pass over the weak spot in the road, pieces of the roadway material weaken, which will cause the material to be displaced or broken down from the weight, creating the pothole.
Why are potholes such a nuisance? A pothole can do a number of bad things to the wheels and tires on your car! This can be costly to fix or replace! So beware during the Spring time months for forming potholes along your drives!
Sources:
[1] http://www.summitengineer.net/resources/learning/52-potholes