Farm ponds are particularly abundant in the southern half of Iowa where the rolling topography favors their construction, and the lack of abundant groundwater resources makes these impoundments a valuable water supply. Photo by Roger A. Hill. The site has yielded a year-round water supply for wildlife, livestock, and people for at least 100 years. Upwelling of groundwater can occur where a water source, confined under pressure by overlying impermeable rock, finds a natural opening to the land surface or is tapped by a drilled well. Photo by Lynette Seigley .
Springs occur where groundwater flows from rock or soil material to the land surface.
This spring tumbles from crevice openings in limestone near the entrance to Spook Cave in Clayton County. Photo by Carol Thompson. Caverns form as groundwater moves through subterranean crevices in limestone over long periods of geologic time. Groundwater continues to flow by gravity along the cavern floor and down through other openings in the limestone formation. Cold Water Cave, Winneshiek County.