LOCATING KARST FEATURES IN THE ONONDAGA FORMATION, WESTERN NY

An analysis of surface depressions, fracture trace features, and aerial photography in conjunction with field surveys was used to map areas that are sensitive to groundwater contamination. The study was conducted on the Onondaga FM in western New York State, an area which has suffered contamination events that have been attributed to fertilizer application on thinly-soiled karst. The methodology consisted of identifying closed sinks in a digital elevation model and using aerial photography and fracture trace maps to identify sites of concern. The results suggest many scales of closed depressions exist in the Onondaga FM. These features resulted from a complex history of karst and glacial processes as well as anthropogenic activities such as quarrying and landscape alteration. Fracture traces contained systems of sinkholes. Based on previous research and the results of 41 field surveys the features were classified into six types. These include solution sinkholes, pattern ground sinkholes, scoured bedrock zones, glacially enhanced sinkholes, glacial depressions and anthropogenic depressions. Solution sinkholes are steeply-walled collapse features that contain blocks of limestone at the bottom. Pattern ground sinkholes are broad areas of shallow depressions and ridges interpreted to be caused by immature sinkholes and popup ridges. Scoured bedrock zones are areas where fractured bedrock have been exposed by glacial meltwater and other erosion processes. Glacially enhanced sinkholes are depressions that are believed to be the surface expression of sinkholes buried by glacial sediments. Close inspection using aerial photography show that many of these features are hydrologically active in the early spring.