Pothole formation comes down to basic physics. Water gets into the subsurface below the pavement, often through cracks, and expands as it freezes.
If everything freezes in a consistent way, it's not as much of a problem, Berry said. But often water distributes itself unevenly through the subsurface, meaning some areas expand more than others.
Then, when the ice melts, the pavement contracts and weakens. Add the weight of heavy vehicles to the mix, and the weak spot can become a hole.
That hole, in turn, can grow as car and truck tires chip away at the damaged asphalt.
Actually, there is also another factor to this. I often see potholes a couple of days after a snow storm. Why? All those freezing and thawing tends to loosen clumps of asphalt and concrete, especially those that were used to patch up a street. When a snow plow comes along to plow away the snow, these loose patches also tend to get caught in the plow and voila! You have a pothole. So while the weather certainly plays a factor in creating potholes, snow plowing simply accelerates such creations.
Didn't think you'd read about potholes in a physics blog, did you? :)