Spring in Wisconsin means longer days, blooming bulbs, baseball...and potholes.
Potholes are caused by the same science that makes a can of soda explode in your freezer - the expansion and contraction of water. Ground water gets under the pavement, expands when frozen, and contracts when it melts. The expansion bends and weakens the asphalt, and the contraction leaves gaps behind where the pavement can collapse and create a hole. This is why potholes multiply in spring as the ground thaws.