The weight of vehicles causes depressions in the asphalt where cracks can start to form. These cracks allow moisture to get into the earth below the asphalt.
When that water freezes, it expands, pushing the pavement up. This raised surface gets more impact from the vehicles on it.
When the temperature rises, the pavement stays where it is but the earth returns to normal as the water evaporates, creating a cavity that has no support underneath it.
The pavement crumbles under the weight of the vehicles on it, revealing the space below and creating a pothole.