Potholes result from a combination of traffic and water.
Roadways are constructed in layers. The top layer is water resistant and curved to drain water off the road and onto the shoulder.
A road surface develops cracks due to the stresses caused by traffic and because of the heating and cooling of the surface. During the day, the sun warms the roadway causing it to expand a small amount, while nighttime cooling causes the road to contract.
Even small cracks in the surface allow water to seep below the surface into the underlying materials. During the cold nights the water freezes and expands.
During a clear sky day, the sun warms the road which melts the underlying ice. The melted water can flow to a different section of the roadway.
When the ice melts, the pavement contracts and leaves gaps in the surface under the pavement, where again water can get in and be trapped.
Stresses on the roadway from traffic can widen existing cracks, allowing more water to seep in and freeze during the night. This freeze-thaw cycle will weaken the surface.
Traffic over the weak spot in the road causes the roadway material to break down, and when that broken-down material is removed by constant traffic, it creates a pothole.
We see many potholes develop in the early spring as that is when we get nighttime temperatures below freezing and daytime temperatures above freezing due to the longer daylight hours.
This temperature cycle results in several freeze-thaw cycles that cause potholes. Early spring can be considered pothole season.
Repairing potholes is a challenge as one has to not only fill the hole but also seal it to keep water from getting into any cracks.