Geology and Sinkhole Development in the Hagerstown Valley, MD: Phase 1.

摘要

Areas underlain by carbonate rocks such as limestone, marble, and dolomite are prone to dissolution by groundwater. Such solution of bedrock produces distinctive topographic features that characterize what is known as karst terrane. While karst terranes are present to some degree in all areas underlain by carbonate rocks, they develop at varying levels based on changes in the chemical makeup and geologic structure of the bedrock. Thus, there is no such thing as a typical karst terrane. The application of modern detailed geologic and karst mapping and data analysis allows characterization of various areas within a karst terrane by utilizing a karst susceptibility index (KSI). The KSI was developed and used in a previous study of the Frederick Valley karst terrane by the Maryland Geological Study, in cooperation with the Maryland State Highway Administration. When area data obtained from detailed GIS-based geologic maps were merged with karst feature data, the empirical KSI gave a primary picture of sinkhole potential allowing engineers, developers, and planners to gain a better understanding of sinkhole susceptibility in the area. The methods used in the Frederick Valley study were used in this study which evaluates Maryland's largest karst terrane, the Hagerstown Valley. This phase evaluated five of the ten 7.5 minute quadrangles that make up the eastern half of the Valley. The area was mapped in detail to determine the distribution of geologic units. During bedrock geologic mapping, more than 1,500 karst features were identified and located utilizing a global positioning system.