Karst in the United States: A Digital Map Compilation and Database

Abstract

This report describes new digital maps delineating areas of the United States, including Puerto Rico and the U.S. Virgin Islands, having karst or the potential for development of karst and pseudokarst. These maps show areas underlain by soluble rocks and also by volcanic rocks, sedimentary deposits, and permafrost that have potential for karst or pseudokarst development. All 50 States contain rocks with potential for karst development, and about 18 percent of their area is underlain by soluble rocks having karst or the potential for development of karst features. The areas of soluble rocks shown are based primarily on selection from State geologic maps of rock units containing significant amounts of carbonate or evaporite minerals. Areas underlain by soluble rocks are further classified by general climate setting, degree of induration, and degree of exposure. Areas having potential for volcanic pseudokarst are those underlain chiefly by basaltic-flow rocks no older than Miocene in age. Areas with potential for pseudokarst features in sedimentary rocks are in relatively unconsolidated rocks from which pseudokarst features, such as piping caves, have been reported. Areas having potential for development of thermokarst features, mapped exclusively in Alaska, contain permafrost in relatively thick surficial deposits containing ground ice. This report includes a GIS database with links from the map unit polygons to online geologic unit descriptions.

The maps in this report do not indicate degrees of karst hazards within the areas depicted, such as susceptibility for sinkhole collapse or flooding. Rather, these maps depict areas containing rock types that, under a very broad definition, have developed or have the potential for developing karst features. Ground collapse potential within these areas varies greatly, and areas having significant karst hazards are only a small subset of the areas delineated here. These maps provide first approximations for delineating areas of interest within which further, focused studies of karst or karst-related issues, such as collapse hazards, karst aquifer vulnerability, and biological diversity, may take place.

First posted August 7, 2014