A combination of pavement fatigue, poor soil and moisture combine to cause potholes. They form most often in the spring during repeated cycles of freezing and thawing. Water enters through cracks in the pavement and from the sides of the road, and is trapped. When the water freezes, it expands, and after it thaws, it leaves a void where the water was once before. Continuous freezing and thawing causes the pavement to break into pieces and when traffic loosens the pieces, a pothole results.