NATIONAL-SCALE KARST MAPPING IN THE UNITED STATES: PAST, PRESENT AND FUTURE

The earliest known version of a karst map of the entire USA was published by Stringfield and LeGrand (Journal of Hydrology, 1969), based on the compilation work of William Davies. Various versions of essentially the same map have been published since (e.g., Davies et al., 1984; Veni, 2000; Tobin and Weary, 2004). Here, we present a new digital map and database depicting the extent of karst, potential karst and pseudokarst areas of the United States of America including Puerto Rico and the Virgin Islands. These data were compiled from multiple sources at various spatial resolutions, mostly as digital data supplied by state geological surveys, and refined by the authors. Our database includes polygons of 1) carbonate rocks, 2) evaporite rocks, 3) volcanic rocks with potential pseudokarst, 4) major subsurface evaporite basins, and, 5) non-soluble sedimentary units with potential pseudokarst. Each polygon has attributes for rock type, formation names, unit descriptions, lithologic age, thickness of surficial cover (where data are available), and Level III Ecoregions. These attributes are intended to facilitate classification of karst regions. Approximately 17.5% of the surface of the 50 United States is underlain by soluble bedrock. In the eastern United States the extent of outcrop of soluble rocks provides a good first-approximation of the distribution of karst and potential karst areas. In the arid western states, the extent of soluble rock outcrop tends to overestimate the extent of regions that might be considered as karst under current climatic conditions, but encompasses those regions nonetheless. Data necessary for further refinement of the map units include the distribution and density of caves, sinkholes, and other karst features. Issues complicating the compilation and classification process include: 1) a lack of coherence in spatial precision and lithologic classification among the various geologic maps; 2) lack of easily obtainable statewide and region-wide karst feature data; and, 3) recognition and quantification of non-lithologic factors affecting the development and distribution of karst features. Ongoing and future work includes delineating areas of pseudokarst in sedimentary strata, and improving delineation and classification of principal karstic aquifers.