Potholes are holes in the roadway that vary in size and shape. They are caused by the expansion and contraction of water after the it has entered into the ground under the pavement. When water freezes, it expands. Just like when ice cubes are made. A tray full of water is put into the freezer, and when the tray is removed from the freezer, the water has expanded. This same effect happens when water gets 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. When ice melts, the pavement contracts and leaves gaps or voids in the surface under the pavement, where water can get in and be trapped. If 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.
What happens when salt is brought into the picture? Water freezes at 32 degrees Fahrenheit. When salt is applied during the winter, it lowers the temperature that water will freeze. Thus creating an artificial freeze-thaw cycle that permits more occurrences of the damaging cycle to occur. This happens more often in the spring because of the melting that takes place and because the temperatures fluctuating above and below the freezing point very frequently.