FIVE DECADES OF SINKHOLE MAPPING IN MN – A PUNCTUATED EVOLUTIONARY PROCESS

Over 15,000 sinkholes have been mapped in Minnesota and over 10,000 of the sinkholes are in Fillmore County. As SE MN was converted from prairie savanna to row crop agriculture in the 1850s and 1860s, the settlers were aware of sinkholes but viewed them as nuisances and/or convenient places to dispose of trash. The Fillmore County Soil Survey (Farnham, 1958), included many sinkholes in ag fields but did not map sinkholes in forested areas. In the 1970s systematic sinkhole mapping began in MN. The USGS 7.5’ topo sheets for SE MN, recorded some large, deep sinkholes and closed depressions, again mainly in ag fields. Cavers began to map and record sinkholes in the hope of finding caves. Environmental managers began to recognize that karst was a significant risk factor in ground water contamination and needed maps of the sinkhole locations for regulatory purposes. Karst mapping became part of the MGS’s County Atlas mapping program. Each sinkhole was visited. Locations were recorded in field books, air photos and topo sheets. In the 1980s the growing data set challenges required the rapid evolution in mapping processes. Serendipitously, the rapid growth of computer capability, data programs and GIS software technology permitted that evolution to proceed.

That rapid evolution has been “punctuated” by four major technological advances. 1: The maturation of GIS software in the 1980s and 1990s provided the ability to manipulate and analyze a wide variety of georeferenced sinkhole information with other relevant geologic and geographic data. 2: In 2000 high resolution GPS technology became available to field mappers enabling the location of each visited sinkhole, in all kinds of terrain, to a few meters. 3: In 2002 Yongli Gao developed of an integrated Karst Features Data Base providing a practical tool to record and analyze the growing volume of karst information with other geographic, hydrogeologic and land use information. 4: The advent of LiDAR mapping, which was systematically flown in SE MN in 2008. LiDAR provided a uniform technology for mapping sinkholes across the entire landscape. For the first time it was practical to map sinkholes in the wooded areas, for example. Whole clusters of previously unrecognized sinkholes were found. There is no reason to believe that evolution has ended.