pothole, in geology, cylindrical pit formed in the rocky channel of a turbulent stream. It is formed and enlarged by the abrading action of pebbles and cobbles that are carried by eddies, or circular water currents that move against the main current of a stream. Potholes are most commonly found at the bottoms of eddies in rivers and in plunge pools below cataracts; sometimes potholes in a rock outcrop indicate the former site of a rapid or cataract. Potholes are often found in formerly glaciated regions where whirling columns of glacial meltwater sank well-like holes, or moulins, through the ice. Notable potholes are found in Ausable Chasm, N.Y., and Shelburne Falls, Mass. Potholes also refer to holes formed in human-made materials found in roads that are effected by natural freeze-thaw cycles or moisture (see weathering).

Prairie Pothole Region, large geographic area of central North America consisting of grass-covered wetlands. Stretching northwest from N Iowa through SW Minnesota, E South Dakota, E and N North Dakota, SW Manitoba, and S Saskatchewan to SE and E central Alberta (and including bordering areas of N Montana), the region is covered with thousands of shallow, sometimes seasonal ponds known as potholes or sloughs, which were created when continental glaciers retreated more than 10,000 years ago. The area is the summer home and breeding grounds of some 45 million mallard, pintail, gadwall, and teal ducks as well as many other shore-, song-, and gamebirds, and is popular with hunters and birdwatchers. Located in an important agricultural region, the ponds were routinely drained by farmers to plant wheat and other crops prior to 1985, and the bird and wildlife population had fallen precipitously. The 1985 U.S. federal farm bill, however, provided for conservation subsidies and, in a "swampbusters" provision, withdrew agricultural subsidies from farmers who drained wetlands. As a result, grass replaced wheat in many parts of the region, providing habitat for birds and other animals and leading to an increase in their populations. The program also aided the efforts of family farmers to keep their land by providing funds that counteracted economic losses resulting from low grain prices.